Post by: hamdani yusuf on 23/01/2023 14:30:59
Time dilation is not a function of acceleration and there's no mathematical formula expressing it in terms of acceleration.If acceleration has no effect on time dilation, then the observation of the accelerated twin should be equally valid as non-accelerated one.
Alternatively, there must be something else which makes their situations different, such as their relative motion against an external object, like CMB.
Post by: hamdani yusuf on 15/05/2023 23:23:52
Any thoughts about this?Here's another video responding to those in the op.
Quote
The REAL Reason You Don't Understand Relativity
Think Relativity is confusing? Well, it's not just you -- even the experts can't seem to agree on its meaning, and often get basic facts about the formalism completely wrong. Here, we critique one such renowned professional who, in claiming to be clarifying the standardized theory of relativity, turns out to actually be promoting a misguided personal interpretation. What is this expert's confusion exactly, and why are such misconceptions so prevalent amongst the physics community?
Indeed, be cautious of posturers, gaslighters, stigmatizers, and Giordano-Bruno-burners who want to convince you that your inability to understand Relativity stems from your own deficient reasoning -- because when even the experts can't agree, you know there is something up...
Contents:
00:00 - Intro
01:11 - The Many Interpretations of Relativity
04:55 - Examining Sabine's Interpretation, Pt. 1
08:30 - Examining Sabine's Interpretation, Pt. 2
10:58 - The Source of Confusion
12:12 - Are There Better Interpretations?
Post by: Janus on 23/05/2023 16:36:37
The observation of the accelerated twin is equally valid. It is just that his observations are effected by his acceleration while he is actively accelerating. This includes clocks in the direction of the acceleration running fast compared to his own by a factor determined by the magnitude of the acceleration and the distance to the clock.Time dilation is not a function of acceleration and there's no mathematical formula expressing it in terms of acceleration.If acceleration has no effect on time dilation, then the observation of the accelerated twin should be equally valid as non-accelerated one.
Alternatively, there must be something else which makes their situations different, such as their relative motion against an external object, like CMB.
An analogy would something along these lines:
Two men are back to back and then separate. According to each of them, the other is a given distance "behind" him. Man 1 them turns 180 degrees. By his perspective, Man 2 goes from being behind him to being in front of him. As far as Man 2 is concerned Man 1 is still behind him, and this did not change when Man 1 turned around. The observations of each is equally valid.
With Relativity, time is also involved, And "front" and "back" are replaced with temporal measurements. Acceleration involves a reorientation in space-time for the accelerated observer.
Post by: hamdani yusuf on 16/06/2023 12:59:20
Here is a link that Fermilab put out,Imagine we can put 5 giant clocks synchronized to each other, after being placed close to the trajectory of the space ship. They are all stationary in earth frame. First clock is on earth, second clock is 1 light years away, and so on, and the fifth clock is near the destination star.
. At 12:00, it explains that the reason for the time dilation of the twin is because of the change in direction and not acceleration (although he does say that acceleration plays a small part).
At the beginning of the journey, earth observers see the fifth clock using a powerful telescope, and see year 0. At the same time, fourth clock shows year 1, third clock shows year 2, second clock shows year 3, first clock on earth shows year 4.
What will the travelling twin see when he is passing those clocks?
Post by: Origin on 16/06/2023 13:10:31
What will the travelling twin see when he is passing those clocks?I suppose it would depend how fast he was going.
Post by: hamdani yusuf on 16/06/2023 13:22:08
The video at 2:45 timestamp says 99.9% of light speed.What will the travelling twin see when he is passing those clocks?I suppose it would depend how fast he was going.
Post by: Origin on 16/06/2023 13:36:32
At the beginning of the journey, earth observers see the fifth clock using a powerful telescope, and see year 0. At the same time, fourth clock shows year 1, third clock shows year 2, second clock shows year 3, first clock on earth shows year 4.So at 0.999c we can approximate the speed at c. The first clock of course would read 4, the next would read 5, the next would read 6, the next would read 7 and the last would read 8.
What will the travelling twin see when he is passing those clocks?
Post by: hamdani yusuf on 16/06/2023 14:06:33
So at 0.999c we can approximate the speed at c. The first clock of course would read 4, the next would read 5, the next would read 6, the next would read 7 and the last would read 8.Continuing your reasoning, on the return trip, he will read 9, 10, 11, and finally 12 when he gets back to earth.
Is it really this simple? Do you think the paradox is solved this way?
If the travelling twin brings a smaller clock which is synchronized to the earth clock at the beginning of the trip, what does it read when he's passing the giant clocks?
Post by: Origin on 16/06/2023 14:19:16
Continuing your reasoning, on the return trip, he will read 9, 10, 11, and finally 12 when he gets back to earth.Let's not jump forward until you respond to my assessment of the scenario you presented.
It is my contention that if there is a clock 1 ly away from the earth and a ship moves at ~c from the earth to the clock then the clock will show that 1 year has elapsed. Do you disagree?
Post by: hamdani yusuf on 16/06/2023 14:19:46
Quote
The twin paradox is a thought experiment in special relativity involving identical twins, one of whom makes a journey into space in a high-speed rocket and returns home to find that the twin who remained on Earth has aged more.
The paradox arises because, according to special relativity, moving clocks run slower than stationary clocks. So, if the traveling twin is moving at a high speed relative to the Earth-bound twin, then their clock should run slower. However, the traveling twin could also argue that they are stationary and the Earth-bound twin is moving, in which case the Earth-bound twin's clock should run slower.
The resolution to the paradox is that the twins' situations are not symmetrical. The traveling twin undergoes acceleration during the journey, while the Earth-bound twin does not. Acceleration breaks the symmetry of the situation and allows for a difference in aging between the two twins.
The amount of time dilation that occurs depends on the speed and duration of the journey. For example, if the traveling twin travels at 99% the speed of light for 10 years, they will return to Earth 20 years younger than the Earth-bound twin.
The twin paradox is a fascinating example of the strange effects of special relativity. It highlights the importance of acceleration in determining how time passes.
Here are some additional details about the twin paradox:
The paradox was first proposed by Hermann Minkowski in 1909.
The first experimental test of the twin paradox was conducted in 1971 by the Gravity Probe A team.
The twin paradox has been used to explain a number of other phenomena, such as the aging of astronauts in space.
The twin paradox is a reminder that our intuition about time is not always correct.
Post by: hamdani yusuf on 16/06/2023 14:23:00
Agree, the clock should read 1/0.999 ≈ 1,001 year when he is passing the second clock.Continuing your reasoning, on the return trip, he will read 9, 10, 11, and finally 12 when he gets back to earth.Let's not jump forward until you respond to my assessment of the scenario you presented.
It is my contention that if there is a clock 1 ly away from the earth and a ship moves at ~c from the earth to the clock then the clock will show that 1 year has elapsed. Do you disagree?
Post by: Origin on 16/06/2023 14:32:04
Agree, the clock should read 1/0.999 ≈ 1,001 year when he is passing the second clock.OK.
Post by: hamdani yusuf on 16/06/2023 14:49:35
I asked Google Bard, what's the best explanation to the twin paradox?Interestingly, it also suggest "Search related topics"
what's the best explanation to the twin paradox?
which brings to the link
https://www.wondriumdaily.com/is-the-twin-paradox-of-special-relativity-really-a-paradox/#:~:text=The%20twin%20paradox%20assumes%20that,sister%20who%20stayed%20on%20Earth.
and shows this diagram
(https://www.wondriumdaily.com/wp-content/uploads/2020/08/Twin_Paradox_Minkowski_Diagram_thumbnail.svg_.png)
Quote
The Mistaken Theory on AccelerationIt seems that Bard doesn't learn from the article that it suggests as one of the best explanation.
The common response to this paradox, even from physicists who don?t work with relativity would be that the two twins are different as one of them experiences acceleration. According to this theory, Gabby experiences acceleration to catch up the speed, decelerates to turn around, and then again decelerates to land on Earth.
So, if acceleration is the answer, it means that while the spaceship is freewheeling between the stars, both twins age equally and when the acceleration turns on, there is instant aging. However, there is only one problem, this theory is incorrect.
Post by: hamdani yusuf on 16/06/2023 14:57:44
Don Lincoln posted another follow up video, which seems to undercut the response video from Dialect above.Any thoughts about this?Here's another video responding to those in the op.QuoteThe REAL Reason You Don't Understand Relativity
Think Relativity is confusing? Well, it's not just you -- even the experts can't seem to agree on its meaning, and often get basic facts about the formalism completely wrong. Here, we critique one such renowned professional who, in claiming to be clarifying the standardized theory of relativity, turns out to actually be promoting a misguided personal interpretation. What is this expert's confusion exactly, and why are such misconceptions so prevalent amongst the physics community?
Indeed, be cautious of posturers, gaslighters, stigmatizers, and Giordano-Bruno-burners who want to convince you that your inability to understand Relativity stems from your own deficient reasoning -- because when even the experts can't agree, you know there is something up...
Contents:
00:00 - Intro
01:11 - The Many Interpretations of Relativity
04:55 - Examining Sabine's Interpretation, Pt. 1
08:30 - Examining Sabine's Interpretation, Pt. 2
10:58 - The Source of Confusion
12:12 - Are There Better Interpretations?
Does acceleration solve the twin paradox?
Quote
Special relativity is known to make mind-blowing predictions, perhaps most notably the Twin Paradox, in which two individuals claim that the other person?s clock is doing something funny. There have been many explanations, including two videos, one here on the Fermilab channel and one by fellow YouTuber Sabine Hossenfelder. These two videos seem to contradict each other, but they really don?t. In this video, Fermilab?s Dr. Don Lincoln explains how the two videos can be reconciled.
Post by: Origin on 16/06/2023 15:00:08
Post by: Halc on 16/06/2023 15:07:05
I asked Google Bard, what's the best explanation to the twin paradox?Which is a good reason not to ask a chatbot for correct answers. It gave a terrible one. The bits about the history and the scenario are correct, as is the bit about the asymmetry, but asymmetry isn't the cause since two objects can take asymmetrical paths but still find their respective ages the same upon reuniting.
A good answer would be one that can be generalized, that isn't specific to this one particular case. It didn't give that.
The site you linked seems only relevant to instant-acceleration cases (discontinuous velocity), but to be honest I didn't read it. The diagram is accurate.
Please don't go to Sabine on this one. I've show that hers not only fails to generalize, but it is actually wrong. I find that horribly disappointing. She apparently doesn't peer review her videos before releasing them.
Origin's answers are spot on.
If the travelling twin brings a smaller clock which is synchronized to the earth clock at the beginning of the trip, what does it read when he's passing the giant clocks?He ages ~130 days through the whole thing. That gets divided into 8 equal portions as the 8 clocks are 'passed'. From his point of view, it is the clocks that pass him, one every 16.3 days, not the other way around.
Post by: hamdani yusuf on 16/06/2023 15:10:17
Google bard is just a chatbot and not going to be very good for science other than just general info.I think it will, eventually. And that won't be long, considering the exponential progress in AI. Even if Bard turns out to be a failure, its competitor will take its place. BTW, here's a message when I opened a new chat with Bard.
Quote
Bard is still in its experimental phase. Chatting with it and rating its responses will help improve the experience.
Post by: hamdani yusuf on 16/06/2023 15:19:38
The site you linked seems only relevant to instant-acceleration cases (discontinuous velocity), but to be honest I didn't read it. The diagram is accurate.The diagram is similar to the explanation by Minutephysics.
Complete Solution To The Twins Paradox
Quote
This video is about the famous ?Twins paradox? of special relativity, how time can appear to be faster for two different observers at the same time, and which twin really is older (or younger) ? the one who stays on earth or the one who flies in a rocket ship to the stars?
REFERENCES
Muon lifetime and time dilation/relativity: http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/muon.html#c2
Paper on twin paradox under constant acceleration: https://arxiv.org/pdf/physics/0604025v3.pdf
Taking Cesium atomic clocks aboard airplanes: https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment
Post by: hamdani yusuf on 16/06/2023 15:24:09
So he sees the giant clocks tick faster than his onboard clock, both on going and return trips.If the travelling twin brings a smaller clock which is synchronized to the earth clock at the beginning of the trip, what does it read when he's passing the giant clocks?He ages ~130 days through the whole thing. That gets divided into 8 equal portions as the 8 clocks are 'passed'. From his point of view, it is the clocks that pass him, one every 16.3 days, not the other way around.
But that's not what the explanation shown by MinutePhysics' video.
Post by: Origin on 16/06/2023 16:17:46
But that's not what the explanation shown by MinutePhysics' video.I come to the forum for discussions so I don't watch video recommendations. If the video says that a clock (stationary relative to spaceship) located 1 ly from a spaceship traveling towards it at 0.999c would have an elapsed time other than 0.999 years when it passes the clock, then the video is wrong. I doubt that is what the video says, but it could be a bad video.
Post by: hamdani yusuf on 17/06/2023 00:41:41
The twins scenario illustrates time differential, which is an objective (frame independent) fact. Time dilation is a coordinate effect and is entirely frame dependent. Just pointing this part out so hopefully the terms get used more correctly.Most of sources I've seen on special relativity don't distinguish them, and only use time dilation term, such as the case with muons.
Post by: hamdani yusuf on 17/06/2023 01:02:06
Let me rephrase my statement you quoted.So he sees the giant clocks tick faster than his onboard clock, both on going and return trips.It only appears to run fast if it is approaching you, which is true only half the time. I didn't offer an explanation. You asked what the rocket guy would see on the clocks as they passed by, and I answered that.
More details: Suppose he always watches the Earth clock. For 65 days it is receding and during those 2+ months it appears to advance about 4 minutes, 22500x slower. On the 2nd leg, Earth is approaching and it appears to run about 45 times faster, so it appears to gain about 8 years in those 65 days.
The Earth observer sees the same thing if he watches the ship clock. 22500x slower when outbound and 45x faster when it is returning, but in his case, the vast majority of the time (over 8 years) is spent watching it recede, and the return leg appears to take only a day and a half.
His onboarding clock ticks slower on average than the giant clocks.
Traveling twin sees the giant clock the he is passing by showing the time according to Origin's calculation.
Earth clock ~ 4
Second clock ~ 5
Third clock ~ 6
Fourth clock ~ 7
Star clock ~ 8, then return.
Fourth clock ~ 9
Third clock ~ 10
Second clock ~ 11
Earth clock ~ 12
According to the diagram, his own clock ticks 22.4 times faster during first leg as well as second leg of the journey. But somehow at the turning point, the clock changes its reading to compensate for the difference, hence in the end, traveling clock shows smaller value than earth clock.
Lorentzian relativity says that traveling clock ticks slower than giant clocks in both legs, and in the end both twins agree what their clocks would read when they reunite, as well as in each milestones. The asymmetry is caused by relative motion through aether. But special relativity tells a different story.
Post by: Halc on 17/06/2023 03:36:32
So he sees the giant clocks tick faster than his onboard clock, both on going and return trips.It only appears to run fast if it is approaching you, which is true only half the time. I didn't offer an explanation. You asked what the rocket guy would see on the clocks as they passed by, and I answered that.
More details: Suppose he always watches the Earth clock. For 65 days it is receding and during those 2+ months it appears to advance about 4 minutes, 22500x slower. On the 2nd leg, Earth is approaching and it appears to run about 45 times faster, so it appears to gain about 8 years in those 65 days.
The Earth observer sees the same thing if he watches the ship clock. 22500x slower when outbound and 45x faster when it is returning, but in his case, the vast majority of the time (over 8 years) is spent watching it recede, and the return leg appears to take only a day and a half.
Quote
But that's not what the explanation shown by MinutePhysics' video.The video is a pretty good one and I have no objections to it. It doesn't in any way describe what either observer sees when looking at distant clocks or when passing moving clocks. They're different questions. The video is trying to explain the time differential (them being different ages upon meeting later on). It isn't about appearances at all.
The twins scenario illustrates time differential, which is an objective (frame independent) fact. Time dilation is a coordinate effect and is entirely frame dependent. Just pointing this part out so hopefully the terms get used more correctly.
Let me rephrase my statement you quoted.Which clock ticks faster is a frame dependent thing, and no frame was specified, so no, this isn't correct.
His onboarding clock ticks slower on average than the giant clocks.
Relative to Earth, the ship clock ticks slower. Relative to some inertial frame in which the ship is stationary, the Earth clock and all the giant clocks tick slower.
Quote
Traveling twin sees the giant clock the he is passing by showing the time according to Origin's calculation.Yes. This is consistent with the numbers in my prior post.
Earth clock ~ 4
Second clock ~ 5
Third clock ~ 6
Fourth clock ~ 7
Star clock ~ 8, then return.
Fourth clock ~ 9
Third clock ~ 10
Second clock ~ 11
Earth clock ~ 12
For instance, from the ship PoV, at the start, the 2nd clock appears to read 3 (just like you said in post 36). 16.3 days later when the 2nd clock passes by, it reads 5, which means it appears to run ~45x as fast because it is approaching, exactly the rate that I posted.
Post by: hamdani yusuf on 17/06/2023 10:37:40
Which clock ticks faster is a frame dependent thing, and no frame was specified, so no, this isn't correct.According to traveling twin, his own clock ticks faster than the giant clocks, which is moving relative to him. I think this is the consensus among modern physicists.
For instance, from the ship PoV, at the start, the 2nd clock appears to read 3 (just like you said in post 36). 16.3 days later when the 2nd clock passes by, it reads 5, which means it appears to run ~45x as fast because it is approaching, exactly the rate that I posted.
Post by: hamdani yusuf on 17/06/2023 12:20:45
What's the rocket clock showing when it's passing the second giant clock, as seen by the CCTV on it?
What's the rocket clock showing when it's passing the giant clock at the turning point, as seen by the CCTV on it?
Post by: Origin on 17/06/2023 13:27:56
Imagine we have CCTV in every giant clock.Why? What would be the point?
Post by: hamdani yusuf on 17/06/2023 13:49:46
So we can get the observations from both frames of reference locally, where the events take place, ie, when the spaceship is passing a giant clock. So we can compare them in order to determine which side of the paradox is invalid.Imagine we have CCTV in every giant clock.Why? What would be the point?
Post by: Origin on 17/06/2023 14:07:31
So we can get the observations from both frames of reference locally, where the events take place, ie, when the spaceship is passing a giant clock.I don't understand.
Post by: hamdani yusuf on 17/06/2023 15:59:19
Earth twin represents non-changing frame of reference. Traveling twin represents changing frame of reference. Unless when they are meeting on earth in the beginning and end of the journey, the earth twin only observes the key events remotely, especially at the turning point.
Spaceship clock is in two different inertial frame of reference, one during outgoing trip, and the other during return trip.
All giant clocks are in the same inertial frame of reference, despite being in vastly different positions. They allow the traveling twin to trace the events locally from his own position, without having to observe distant events like the reading of earth clock.
The CCTV s allow the earth twin to trace the events locally in his own frame of reference, and compare the reading of spaceship clock and giant clocks as they are passing by.
Post by: Origin on 17/06/2023 17:06:00
The CCTV s allow the earth twin to trace the events locally in his own frame of reference, and compare the reading of spaceship clock and giant clocks as they are passing by.I don't see how that would be possible. If the transmitter of the CCTV is 2 ly away the person on earth won't receive the transmission for 2 years, so what's the point?
Post by: hamdani yusuf on 17/06/2023 23:27:00
The point is to capture the events locally, which will be investigated later on. They're for matching up between traveling clock and giant clock as they are passing by. That becomes necessary since the video mentions that the clock reading can be affected by observer's motion and position when done remotely.The CCTV s allow the earth twin to trace the events locally in his own frame of reference, and compare the reading of spaceship clock and giant clocks as they are passing by.I don't see how that would be possible. If the transmitter of the CCTV is 2 ly away the person on earth won't receive the transmission for 2 years, so what's the point?
The CCTV can be replaced by independent observers which will communicate the results. When the information arrive isn't important, but what they tell is what's important.
Post by: Origin on 18/06/2023 01:09:36
The CCTV can be replaced by independent observers which will communicate the results.I see, there is no point to having a CCTV.
Actually there is no point in running this impossible experiment anyway since we already know what the results will be.
Post by: hamdani yusuf on 18/06/2023 03:01:49
We've agreed what the giant clocks show when the traveling twin is passing them. What would the traveling clock show in each event, when observed at the same time and position?The CCTV can be replaced by independent observers which will communicate the results.I see, there is no point to having a CCTV.
Actually there is no point in running this impossible experiment anyway since we already know what the results will be.
Post by: hamdani yusuf on 18/06/2023 03:22:44
The importance of local observers is made clear by Janus' post that's also pointed out by Halc.The point is to capture the events locally, which will be investigated later on. They're for matching up between traveling clock and giant clock as they are passing by. That becomes necessary since the video mentions that the clock reading can be affected by observer's motion and position when done remotely.The CCTV s allow the earth twin to trace the events locally in his own frame of reference, and compare the reading of spaceship clock and giant clocks as they are passing by.I don't see how that would be possible. If the transmitter of the CCTV is 2 ly away the person on earth won't receive the transmission for 2 years, so what's the point?
The CCTV can be replaced by independent observers which will communicate the results. When the information arrive isn't important, but what they tell is what's important.
The observation of the accelerated twin is equally valid. It is just that his observations are effected by his acceleration while he is actively accelerating. This includes clocks in the direction of the acceleration running fast compared to his own by a factor determined by the magnitude of the acceleration and the distance to the clock.
Post by: Origin on 18/06/2023 13:36:01
Thought experiments are only useful to examine consistency among many assumptions taken to build a model. It can't check if the model accurately represent physical reality. That would take physical experiments.We are talking about a thought experiment.
Post by: Origin on 18/06/2023 13:51:37
We've agreed what the giant clocks show when the traveling twin is passing them. What would the traveling clock show in each event, when observed at the same time and position?Halc has given you those numbers twice.
The importance of local observers is made clear by Janus' post that's also pointed out by Halc.Nobody has said otherwise. Your idea about the CCTV is an unnecessary complication, you should just drop it.
Post by: hamdani yusuf on 18/06/2023 22:49:06
Let's pair the values of the giant clocks with travelling clock.Let me rephrase my statement you quoted.Which clock ticks faster is a frame dependent thing, and no frame was specified, so no, this isn't correct.
His onboarding clock ticks slower on average than the giant clocks.
Relative to Earth, the ship clock ticks slower. Relative to some inertial frame in which the ship is stationary, the Earth clock and all the giant clocks tick slower.
QuoteTraveling twin sees the giant clock the he is passing by showing the time according to Origin's calculation.Yes. This is consistent with the numbers in my prior post.
Earth clock ~ 4
Second clock ~ 5
Third clock ~ 6
Fourth clock ~ 7
Star clock ~ 8, then return.
Fourth clock ~ 9
Third clock ~ 10
Second clock ~ 11
Earth clock ~ 12
For instance, from the ship PoV, at the start, the 2nd clock appears to read 3 (just like you said in post 36). 16.3 days later when the 2nd clock passes by, it reads 5, which means it appears to run ~45x as fast because it is approaching, exactly the rate that I posted.
Earth clock ~ 4Y --- 0 d
Second clock ~ 5Y --- 16.3 d
Third clock ~ 6Y --- 32.6 d
Fourth clock ~ 7Y --- 49 d
Star clock ~ 8Y --- 65.3 d, then return.
Fourth clock ~ 9Y --- 81.6 d
Third clock ~ 10Y --- 97.9 d
Second clock ~ 11Y --- 114.2 d
Earth clock ~ 12Y --- 130.6 d
Observers on giant clocks and travelling clock should agree with these values.
Post by: hamdani yusuf on 20/06/2023 05:35:00
The CCTV are necessary to pinpoint where and when the asymmetry appears. Minutephysics video seems to conclude that it appears at the turning point, when the spaceship reverses its direction.We've agreed what the giant clocks show when the traveling twin is passing them. What would the traveling clock show in each event, when observed at the same time and position?Halc has given you those numbers twice.The importance of local observers is made clear by Janus' post that's also pointed out by Halc.Nobody has said otherwise. Your idea about the CCTV is an unnecessary complication, you should just drop it.
Post by: Origin on 20/06/2023 17:22:05
The CCTV are necessary to pinpoint where and when the asymmetry appears. Minutephysics video seems to conclude that it appears at the turning point, when the spaceship reverses its direction.That CCTV sure seems important to you. It's just a thought experiment so don't sweat it.
Post by: hamdani yusuf on 24/06/2023 12:17:59
The asymmetry was known once the itinerary was made. Everybody from anywhere can see it. I have no idea why you think a CCTV present at the star-clock would show anything not already visible to everybody else, including the ship which happens to actually be there.Imagine that the CCTV on the turning point is also equipped with a powerful telescope which can observe the giant clocks as well as the clock on the space ship. What would it see during the experiment?
When the twin started the flight, the earth clock has already shown 4 y, while traveling clock is still 0, which will be seen by the distant CCTV 4 years later. When the signals arrive at the turning point, it's own clock would already show 8 y.
When the space ship arrives at the turning point, the giant clock there shows 4 + 4/0.999 = 8.004 y. The traveling clock shows 4/0.999/22.4 = 0.18 y
Post by: Origin on 24/06/2023 15:26:51
Imagine that the CCTV on the turning pointImagine you were able to stop talking about CCTVs. One has to wonder how Einstein ever develop his theories without CCTVs! ::)
Post by: Janus on 24/06/2023 16:40:16
What any observer would visually see in a telescope is not the same thing as what they would determine the present reading is on the clock they are observing. For example, a planet 4 ly from us, at this moment would be seeing events that occured on Earth in 2019. But they would determine that, it is presently 2023 on Earth, because they know it took 4 years for the light they are presently seeing to reach them.The asymmetry was known once the itinerary was made. Everybody from anywhere can see it. I have no idea why you think a CCTV present at the star-clock would show anything not already visible to everybody else, including the ship which happens to actually be there.Imagine that the CCTV on the turning point is also equipped with a powerful telescope which can observe the giant clocks as well as the clock on the space ship. What would it see during the experiment?
When the twin started the flight, the earth clock has already shown 4 y, while traveling clock is still 0, which will be seen by the distant CCTV 4 years later. When the signals arrive at the turning point, it's own clock would already show 8 y.
When the space ship arrives at the turning point, the giant clock there shows 4 + 4/0.999 = 8.004 y. The traveling clock shows 4/0.999/22.4 = 0.18 y
An observer traveling at 0.8 c relative to both Earth and the planet would, as he passed the planet see exactly the same thing, Earth in 2019. But he'd come to a different conclusion as to what year is was on Earth as that moment. Unlike the planet, which maintained a constant distance to Earth for the entire time, the distance between this observer and the Earth has been changing, and the distance between them was not 4 ly when the light left Earth. And for the observer on the ship, it was the distance between Earth and himself when the light left Earth that determines how long it took the light to reach him at c. If he had been traveling from Earth to the planet, he would have been less than 4 ly from Earth when the light left Earth, and it would have taken less than 4 years for the light to reach him. Thus, when he sees 2019 on Earth as he passes the planet he cannot conclude that it is 2023 on Earth at that moment but an earlier year.
Adding CCTVs only means that you now have to take light propagation delays into account, on top of the Relativistic effects.
Post by: Eternal Student on 24/06/2023 18:16:55
I'm a bit surprised this thread is still going - but it's an interesting topic and can be examined from many angles.
Some of the older posts have lost their special symbols and especially any equations but there's a diagram that survives.
Post #45 had this diagram which is a great diagram:
(https://www.wondriumdaily.com/wp-content/uploads/2020/08/Twin_Paradox_Minkowski_Diagram_thumbnail.svg_.png)
I would say a diagram like that explains most of what people want to know. I'd just like to colour all the events that happen at Earth between the highest blue line and the lowest red line . Here is that diagram:
Twins-green.jpg (41.62 kB . 511x421 - viewed 1419 times)Looking at the blue lines of simultaneity we can label those lines (from bottom to top) t'=1 unit, t'=2 and t'=3 (where t' is the time elapsed for the travelling twin). We see that the events in the green area are still in the future for the travelling twin on their outbound journey. For example, assume the twin had NOT turned around at t'=3 (at spatial location = Alpha Centauri ) but instead had just continued on in uniform motion. Here's the diagram for that:
Twins2.jpg (25.32 kB . 511x421 - viewed 1519 times)We see that events in the green area (which are spatial located at Earth) fall along a blue line of simultaneity with t' > 3 (that is later than t'=3, when the twin reached Alpha Centauri and should have turned around).
However the travelling twin does turn around at t'=3. Which immediately changes the slope of the lines of simultaneity, we have the red lines of simultaneity. We can start labelling those from bottom to top as t'=3, t'=4 and t'=5. Note the lowest red line is t'=3 exactly as for the latest blue line of simultaneity when the travelling twin reached Alpha Centauri - we assume the turn-around took negligible time for the twin.
So on the return portion of the travelling twins journey all the green events are effectively in what they would consider as the past - e.g. the green events would lie along the red lines of simultaneity for t' < 3.
Here's the diagram for that:
Twins4.jpg (25.48 kB . 511x421 - viewed 1182 times)Anyway, that hopefully explains, with diagrams, what was discussed in earlier posts. When the travelling twin changes their direction of motion at Alpha Centauri, they change rest frames. This has the consequence of making all the green events that were located at Earth, no longer be events that the travelling twin would consider as being in their future (t' > 3). When the travelling twin changed direction, the green events immediately change into events that the travelling twin would consider as being in their past (t' <3).
Some events (located on earth) were in the travelling twins future (in the old rest frame) but they abruptly changed to being events that were in their past (in the new rest frame), they were never in their present or "now" , they were skipped over entirely.or, as Janus wrote:
An analogy would something along these lines:
Two men are back to back and then separate. According to each of them, the other is a given distance "behind" him. Man 1 then turns 180 degrees. By his perspective, Man 2 goes from being behind him to being in front of him.
- - - - - - - - - - -
Anyway, I quite like the diagram approach and just seeing where the "green events" will map to on the outward journey compared to the return journey. It reduces the Twins paradox to a situation that is almost identical to "the Andromeda paradox" (where an invasion fleet has or has not yet been launched from Andromeda depending on which direction you are moving in). It is all seen to be a consequence of the idea that spacetime is like a loaf of bread and there is no preferred or correct way to cut it into time slices. We can foliate it (slice it) at different angles to obtain very different "now" slices: Boost to another frame of reference and we change the angle at which we slice through that bread, so that events that were at some spatial distance from us can sometimes be moved into what we would consider as the past, the future or "now" just by changing your motion.
So you (Hamdani and/or Dimensional who started the thread) can have that as another explanation of the "exact cause" of different aging of the twins if you want it: It's a consequence of our ability to foliate spacetime in different ways just by changing the motion of one twin together with there being some physical distance between them when that change of motion occurred. So you can recover all the criteria that has previously discussed: For example, the distance between earth and Alpha Centauri is important because you're going to pivot around Alpha Centauri and hence sweep out a greater amount of what has been drawn as green events on Earth. Similarly the speed of travel for the travelling twin is important because that determines the angle at which you will be foliating spacetime (if the travelling twin has high speed relative to the Earth twin the blue and red lines of simultaneity are severely angled from the horizontal on the diagram). The acceleration of the travelling twin at Alpha Centauri is important but not numerically important: The traveling twin HAD to change the direction of their motion at Alpha Centauri but exactly how that was done didn't matter much, for convenience it was assumed to be almost instantaneous. If the acceleration had been done over 0.1 s instead of 1 s then the size of the acceleration would have been ten times larger but it doesn't matter and doesn't affect the age of either twin much. All that matters is the total angle swept through when you foliate spacetime for the outbound journey compared to the return journey (the angle between the blue line of simultaneity vs. the red line at t'=3 when you pivot around spatial location= Alpha Centauri).
Already too long.... I'll hide the next bit. It may only add confusion anyway. If you're happy with events being moved from the future to the past then that's fine, leave it there.
Spoiler: show
Best Wishes.
Post by: hamdani yusuf on 26/06/2023 02:08:56
I would say a diagram like that explains most of what people want to know. I'd just like to colour all the events that happen at Earth between the highest blue line and the lowest red line . Here is that diagram:According to the observer at the turning point, the green events happen during the beginning and finishing of the trip. Although it is in the same frame of reference as the earth twin.
(https://www.thenakedscientists.com/forum/index.php?action=dlattach;topic=86033.0;attach=33942;image)
Post by: hamdani yusuf on 26/06/2023 03:19:05
You can replace the CCTV with other kind of observers.Imagine that the CCTV on the turning pointImagine you were able to stop talking about CCTVs. One has to wonder how Einstein ever develop his theories without CCTVs! ::)
Post by: hamdani yusuf on 26/06/2023 08:42:40
Adding CCTVs only means that you now have to take light propagation delays into account, on top of the Relativistic effects.The simultaneity planes shown in the diagram are basically taking the propagation delays into account.
(https://www.wondriumdaily.com/wp-content/uploads/2020/08/Twin_Paradox_Minkowski_Diagram_thumbnail.svg_.png)
We can find many different explanations trying to solve the twin paradox, as shown by problem statement in wikipedia.
Quote
In physics, the twin paradox is a thought experiment in special relativity involving identical twins, one of whom makes a journey into space in a high-speed rocket and returns home to find that the twin who remained on Earth has aged more. This result appears puzzling because each twin sees the other twin as moving, and so, as a consequence of an incorrect[1][2] and naive[3][4] application of time dilation and the principle of relativity, each should paradoxically find the other to have aged less. However, this scenario can be resolved within the standard framework of special relativity: the travelling twin's trajectory involves two different inertial frames, one for the outbound journey and one for the inbound journey.[5] Another way of looking at it is to realize the travelling twin is undergoing acceleration, which makes him a non-inertial observer. In both views there is no symmetry between the spacetime paths of the twins. Therefore, the twin paradox is not actually a paradox in the sense of a logical contradiction.I want to see which explanation is more consistent with different observers in the same frame of reference as the earth observer. Is the asymmetry appears during the acceleration only, or it's when there's relative velocity instead.
Starting with Paul Langevin in 1911, there have been various explanations of this paradox. These explanations "can be grouped into those that focus on the effect of different standards of simultaneity in different frames, and those that designate the acceleration [experienced by the travelling twin] as the main reason".[6] Max von Laue argued in 1913 that since the traveling twin must be in two separate inertial frames, one on the way out and another on the way back, this frame switch is the reason for the aging difference.[7] Explanations put forth by Albert Einstein and Max Born invoked gravitational time dilation to explain the aging as a direct effect of acceleration.[8] However, it has been proven that neither general relativity,[9][10][11][12][13] nor even acceleration, are necessary to explain the effect, as the effect still applies if two astronauts pass each other at the turnaround point and synchronize their clocks at that point. Such observer can be thought of as a pair of observers, one travelling away from the starting point and another travelling toward it, passing by each other where the turnaround point would be. At this moment, the clock reading in the first observer is transferred to the second one, both maintaining constant speed, with both trip times being added at the end of their journey.[14]
https://en.wikipedia.org/wiki/Twin_paradox
Note that in this case, there are five observers instead of two like in standard twin paradox problem. They are two travelling twins, from earth and AC. The other three are stationary relative to each other: stay on earth twin, twin who stays on AC, and the CCTV at midway.
How to use transformation formula to convert observations from one observer to the others, given the relative motions between them?
Post by: hamdani yusuf on 10/08/2023 16:53:10
Supposed that there are also twins living on Alpha Centauri. One of them going through a journey just like the travelling twin from earth. To synchronize, the travelling twins were waiting for a signal transmitted by midway giant clock at t=-2 year. Thus travelling twin from earth and travelling twin from Alpha Centauri start simultaneously at t=0.
What the midway clock will see when the twins from earth and Alpha Centauri pass by at t=2 year?
By symmetry, it should see both travelling twins' clocks show the same value, whatever it is. But what the travelling twin from earth see of the clock carried by the travelling twin from Alpha CentauriCentauri, and vice versa?
Post by: hamdani yusuf on 11/08/2023 12:24:29
In physics discussions, particularly when addressing concepts like time dilation and relativistic effects, precision in language is crucial to avoid confusion. If you believe that Don Lincoln's explanations have led to misunderstandings or misrepresented certain aspects of the topic, it's valid to provide additional context or clarification, especially if you have a strong background in the subject matter.I'm open to anyone who wants to explain the problem I posted above. Which part of the thought experiment with symmetrical travelling twins isn't clear yet?
Post by: Janus on 13/08/2023 16:19:38
Since we are looking for the cause of asymmetry, we better start with a system that is perfectly symmetrical. After all the implications have been settled, we can change one parameter at a time, and see what happens, when the symmetry starts to break.Twin leaving Earth: During his acceleration phase to AC, he will determine that the coordinate time for clocks at AC and the other traveling twin will have sped up compared to his own. Once he ends his acceleration, Both the the other twin's clock will run slow. But, that other twin will also be further along their trip to the center point than he himself is, and will have ticked off more time. By the time they meet at the midpoint, the other twin's clock will read the same as his own. In other words, the other ship's clock runs fast, then slow, and ends up reading the same as his which ran at a constant rate the whole time when they meet.
Supposed that there are also twins living on Alpha Centauri. One of them going through a journey just like the travelling twin from earth. To synchronize, the travelling twins were waiting for a signal transmitted by midway giant clock at t=-2 year. Thus travelling twin from earth and travelling twin from Alpha Centauri start simultaneously at t=0.
What the midway clock will see when the twins from earth and Alpha Centauri pass by at t=2 year?
By symmetry, it should see both travelling twins' clocks show the same value, whatever it is. But what the travelling twin from earth see of the clock carried by the travelling twin from Alpha CentauriCentauri, and vice versa?
It all goes back the relativity of simultaneity. As each twin transitions from being at rest in one inertial frame to another his notion of what events are simultaneous also changes.
The AC twin determines the same happening to the Earth traveling twin.
Post by: hamdani yusuf on 14/08/2023 08:35:19
Twin leaving Earth: During his acceleration phase to AC, he will determine that the coordinate time for clocks at AC and the other traveling twin will have sped up compared to his own. Once he ends his acceleration, Both the the other twin's clock will run slow. But, that other twin will also be further along their trip to the center point than he himself is, and will have ticked off more time. By the time they meet at the midpoint, the other twin's clock will read the same as his own. In other words, the other ship's clock runs fast, then slow, and ends up reading the same as his which ran at a constant rate the whole time when they meet.Can you give quantitative values? Assume that the acceleration can be nearly instantaneous, or, if you think it's impossible, put the maximum acceleration you think is permitted by physical law.
It all goes back the relativity of simultaneity. As each twin transitions from being at rest in one inertial frame to another his notion of what events are simultaneous also changes.
The AC twin determines the same happening to the Earth traveling twin.
Post by: Janus on 17/08/2023 17:17:38
Okay, simplest case of near instantaneous acceleration, with an assumption of 0.8c velocity for both ships.Twin leaving Earth: During his acceleration phase to AC, he will determine that the coordinate time for clocks at AC and the other traveling twin will have sped up compared to his own. Once he ends his acceleration, Both the the other twin's clock will run slow. But, that other twin will also be further along their trip to the center point than he himself is, and will have ticked off more time. By the time they meet at the midpoint, the other twin's clock will read the same as his own. In other words, the other ship's clock runs fast, then slow, and ends up reading the same as his which ran at a constant rate the whole time when they meet.Can you give quantitative values? Assume that the acceleration can be nearly instantaneous, or, if you think it's impossible, put the maximum acceleration you think is permitted by physical law.
It all goes back the relativity of simultaneity. As each twin transitions from being at rest in one inertial frame to another his notion of what events are simultaneous also changes.
The AC twin determines the same happening to the Earth traveling twin.
E = Earth
ES = Earth ship
AC = Alpha Centauri
ACS = Alpha Centauri Ship
Events according to E, starting from the moment it reaches 0.8c relative to Earth
E time =0
AC time = 3.44 yr (relativity of simultaneity)
ACS time = ~1.26 yr
Distance of ACS to midpoint = ~0.283 ly
Relative velocity of ACS to ES = ~0.976c (addition of velocities)
Time dilation factor for ACS according to ES = ~0.22
closing speed between ACS and midpoint = ~0.176c (0.976c-0.8c)
Distance to midpoint for ES = ~1.29 ly (length contraction)
Time for ES to reach midpoint = ~1.61 yr
time for ACS to reach midpoint = ~1.61 yr (0.28 ly/.176c)*
Time accumulated for ACS while ES travels to midpoint = ~0.354 yr (1.61*0.22)
Time on ACS upon arrival to midpoint ~1.61 yr (1.26yr+0.354 yr)
Now what ES would visually see:
At moment of reaching 0.8c:
AC time = -4.3 yr (ES is basically seeing same light that E is, and E is seeing a 4.3 yr old image
ACS time = -4.3 (still waiting in port for departure)
When it first sees ACS leave AC:
Time on ES = 1.43 yr
Doppler shift factor for AC = 3
Time ES sees on ACS was it leaves AC = 0 ( -4.3+1.43*3)
Doppler shift factor for ACS once it is on its way = 9
Length of time ES see ACS Doppler shifted by above factor =~0.18 yr (1.61-1.43)
Amount of time accrued on ACs clock during this period ~1.61 yr (9*0.18 yr)
If we change to the ACS frame we get the same results. Just swap E for AC and ES for ACS
* the values used in this example have been rounded off, so you are not going to get exact agreement between some answers.
Post by: hamdani yusuf on 18/08/2023 04:22:55
The key events are :
1. Travelling twins start the journey. From midway perspective, they should be simultaneous due to symmetry.
2. Travelling twins arrive at midway. Again, from midway perspective, they should be simultaneous due to symmetry.
3. Travelling twins arrive at the destination and start the return journey.
4. Travelling twins arrive at midway in their return journey.
5. Travelling twins get back home.
In each events, the midway observer writes down the clocks that they observe:
1. The clock stays on earth.
2. The clock stays on midway.
3. The clock stays on Alpha Centauri.
4. The clock carried by travelling earth twin.
5. The clock carried by travelling AC twin.
The result would be a 5x5 matrix. This is before we transform to other observers.
Post by: hamdani yusuf on 18/08/2023 13:41:48
Here are the observations of those 5 key events as recorded by midway observer.
1. The journey starts on earth at t=0 local time. The light signal takes 2 years to the midway observer, thus he will see the event when his clock shows t=2 years. Journey from Alpha Centauri is the same due to symmetry.
2. The travelling twins take 2 ly / 0.999c = 2.002... year to get to the midway. Thus the observer will see his clock showing t=2.002... years.
3. The journeys take 4 ly / 0.999c = 4.004... year to get to the turning point in on going leg. But it takes additional 2 years for light signal to the midway observer, thus he will see the event when his clock shows t=6.004... years.
4. The travelling twins take 6 ly / 0.999c = 6.006... years to get to the midway in return leg. Thus the observer will see his clock showing t=6.006... years.
5. The total journeys take 8 ly / 0.999c = 8.008... years to get home in return leg. But it takes additional 2 years for light signal to the midway observer, thus he will see the event when his clock shows t=10.008... years.
Post by: Janus on 18/08/2023 16:53:15
To be consistent, let's use the speed used in Don Lincoln's video, which is 0.999c.During which time the midpoint observer will see the traveling twins' clock Doppler shifted by a factor of 44.710, and accumulating 44.710 * .002 = 0.089 yr, thus having their clocks each reading 0.089 yr upon reaching the midpoint.
Here are the observations of those 5 key events as recorded by midway observer.
1. The journey starts on earth at t=0 local time. The light signal takes 2 years to the midway observer, thus he will see the event when his clock shows t=2 years. Journey from Alpha Centauri is the same due to symmetry.
2. The travelling twins take 2 ly / 0.999c = 2.002... year to get to the midway. Thus the observer will see his clock showing t=2.002... years.
Quote
3. The journeys take 4 ly / 0.999c = 4.004... year to get to the turning point in on going leg. But it takes additional 2 years for light signal to the midway observer, thus he will see the event when his clock shows t=6.004... years.After each twin passes the midpoint, and are receding from it, the Midpoint observer will seeing them Doppler shifted by a factor of 0.0224, with each accumulating 4.004 * .0224 = 0.89 yr on their clocks to read 0.178 yr upon arrival at their destinations. (while the clocks at the destinations will read 6.004-2= 4,004 yrs)
Quote
4. The travelling twins take 6 ly / 0.999c = 6.006... years to get to the midway in return leg. Thus the observer will see his clock showing t=6.006... years.
5. The total journeys take 8 ly / 0.999c = 8.008... years to get home in return leg. But it takes additional 2 years for light signal to the midway observer, thus he will see the event when his clock shows t=10.008... years.
The return legs are just mirrored versions of the outbound legs, and give the same results, with an additional 1.79 yrs added to each twin's clock and 4.004 yrs added to the planets' clocks as seen by the midpoint observer.
Post by: hamdani yusuf on 18/08/2023 22:27:29
During which time the midpoint observer will see the traveling twins' clock Doppler shifted by a factor of 44.710, and accumulating 44.710 * .002 = 0.089 yr, thus having their clocks each reading 0.089 yr upon reaching the midpoint.Why the Doppler shift matters in clock reading? Isn't Lorentz' time dilation enough?
Post by: hamdani yusuf on 19/08/2023 23:06:15
At starting event, all clocks are stationary according to midway observer. While at meeting event at midway, traveling clocks are right in front of the midway observer. They are neither approaching nor receding.During which time the midpoint observer will see the traveling twins' clock Doppler shifted by a factor of 44.710, and accumulating 44.710 * .002 = 0.089 yr, thus having their clocks each reading 0.089 yr upon reaching the midpoint.Why the Doppler shift matters in clock reading? Isn't Lorentz' time dilation enough?
Post by: Janus on 20/08/2023 15:00:58
The Lorentz time time dilation factor is what the observer determines is occurring at the other clock at a given moment.During which time the midpoint observer will see the traveling twins' clock Doppler shifted by a factor of 44.710, and accumulating 44.710 * .002 = 0.089 yr, thus having their clocks each reading 0.089 yr upon reaching the midpoint.Why the Doppler shift matters in clock reading? Isn't Lorentz' time dilation enough?
Doppler shift is what he directly see and measures.
With a two clocks stationary with respect to each other and 1 light hour apart, if each sees the other clock as being 1 hr behind theirs, they still determine that the clocks are simultaneous once they account for the light propagation delay.
Likewise, Doppler shift is what you see, and time dilation is what remains after you account for the constantly changing light propagation delay. ( when the object is approaching you, the delay gets shorter and shorter, and when it is receding, it gets longer and longer.)
Of co
Post by: Janus on 20/08/2023 15:14:19
But to get from starting point to midpoint they have to approach the midpoint, and to get to the end point from the midpoint, they have to recede from the midpoint. It's during these periods that the "interesting stuff" takes place. It's also the bit you need to grasp to have any hope of understanding what is going on.At starting event, all clocks are stationary according to midway observer. While at meeting event at midway, traveling clocks are right in front of the midway observer. They are neither approaching nor receding.During which time the midpoint observer will see the traveling twins' clock Doppler shifted by a factor of 44.710, and accumulating 44.710 * .002 = 0.089 yr, thus having their clocks each reading 0.089 yr upon reaching the midpoint.Why the Doppler shift matters in clock reading? Isn't Lorentz' time dilation enough?
Post by: hamdani yusuf on 20/08/2023 15:35:36
when the object is approaching you, the delay gets shorter and shorter, and when it is receding, it gets longer and longerWhen the object isn't approaching nor receding, the delay isn't changing.
Let's assume that the space ship doesn't hit the midway observer. He is 1 km away from the trajectory of the ship. The distance between the ship and observer can be plotted as such.
https://www.wolframalpha.com/input?i=plot+sqrt%281%2Bx%5E2%29+from+-10+to+10
This infinitesimaly short moment is what defines the second event.
Post by: Janus on 21/08/2023 03:04:49
The difference between the ship passing an infinitesimal distance from the observer and missing by a kilometer is negligible( it wouldn't even show up at the number of significant decimal places we are dealing with in this problem).when the object is approaching you, the delay gets shorter and shorter, and when it is receding, it gets longer and longerWhen the object isn't approaching nor receding, the delay isn't changing.
Let's assume that the space ship doesn't hit the midway observer. He is 1 km away from the trajectory of the ship. The distance between the ship and observer can be plotted as such.
https://www.wolframalpha.com/input?i=plot+sqrt%281%2Bx%5E2%29+from+-10+to+10
This infinitesimaly short moment is what defines the second event.
Why are you obsessed with one "infinitesimaly short moment" when it takes an understanding of the whole of the problem to grasp what's occuring?
It's seems to me that you are trying as hard as possible to Not understand Relativity.
Post by: hamdani yusuf on 21/08/2023 12:20:34
It's seems to me that you are trying as hard as possible to Not understand Relativity.It seems like that to you because you've been misunderstanding it without you realized.
What's the reading of the travelling clock by midway observer, one day before passing the mid point, and one day after passing it?
Post by: Janus on 21/08/2023 17:48:17
Outbound trip:It's seems to me that you are trying as hard as possible to Not understand Relativity.It seems like that to you because you've been misunderstanding it without you realized.
What's the reading of the travelling clock by midway observer, one day before passing the mid point, and one day after passing it?
0ne day prior to ship arriving( by Midpoint's clock):
Actual time on ship clock: 32 days, 15 hrs, 34 min and 13.5718217858 sec.
What the Midpoint observer visually sees: The ship sitting at its planet of origin, waiting to depart.
One day after ship passes midpoint:
Actual time on ship: 32 days, 17 hrs, 42 min, and 59.490547741 sec
What the observer visually sees: 32 days, 17 hrs, 10 min, 48.9770892 sec
During return leg:
One day before:
Actual time: 98 days 0 hr, 51 min, 26.63419131 sec
What is visually seen: The ship not quite having reached the turn around point, and a bit short of reading 65 days 9hr, 17 min, and 13.06236952 sec
One day after:
Actual time: 98 days 3 hrs, 0 min, 12.55291726 sec
What is visually seen: 98 days 2 hr, 28 min, and 12.5529176 sec.
Post by: paul cotter on 21/08/2023 21:44:11
Post by: hamdani yusuf on 22/08/2023 06:05:34
I appreciate your effort to do the calculations. Now we can narrow down the observation around the passing event at mid point.Outbound trip:It's seems to me that you are trying as hard as possible to Not understand Relativity.It seems like that to you because you've been misunderstanding it without you realized.
What's the reading of the travelling clock by midway observer, one day before passing the mid point, and one day after passing it?
0ne day prior to ship arriving( by Midpoint's clock):
Actual time on ship clock: 32 days, 15 hrs, 34 min and 13.5718217858 sec.
What the Midpoint observer visually sees: The ship sitting at its planet of origin, waiting to depart.
One day after ship passes midpoint:
Actual time on ship: 32 days, 17 hrs, 42 min, and 59.490547741 sec
What the observer visually sees: 32 days, 17 hrs, 10 min, 48.9770892 sec
During return leg:
One day before:
Actual time: 98 days 0 hr, 51 min, 26.63419131 sec
What is visually seen: The ship not quite having reached the turn around point, and a bit short of reading 65 days 9hr, 17 min, and 13.06236952 sec
One day after:
Actual time: 98 days 3 hrs, 0 min, 12.55291726 sec
What is visually seen: 98 days 2 hr, 28 min, and 12.5529176 sec.
What's the reading of the travelling clock by midway observer, one second before passing the mid point, and one second after passing it?
At least in principle, we should be able to narrow down further to microsecond or picosecond, to approach the reading exactly at the passing event.
Post by: hamdani yusuf on 22/08/2023 06:40:26
Hamdani, here is an analogy: suppose we have a coil and we want to produce a magnetic field with it, then what is required? We need to put a certain level of current through it, how do we do that? We apply a voltage. Now which produces the magnetic field, the voltage or the current? We know the current was responsible but we needed a voltage to do that. Similarly the acceleration is needed to produce the speed necessary for the relativistic effects but the speed is what determines the outcome, not the acceleration.We are trying to find the symmetry breaker in the twin paradox case. In the original case, one twin accelerates, while the other doesn't. That difference is thought to be the reason to disqualify the travelling twin from applying simple Lorentz transform and observe time dilation experienced by staying twin. Otherwise, both twins will see the other's clock to be slower than their own, which is a contradiction.
Where's the symmetry breaker in your analogy?
Post by: paul cotter on 22/08/2023 10:01:41
Post by: Janus on 22/08/2023 16:30:10
The difference is in what happens according to the Twin that undergoes the acceleration while under they are under acceleration.Hamdani, here is an analogy: suppose we have a coil and we want to produce a magnetic field with it, then what is required? We need to put a certain level of current through it, how do we do that? We apply a voltage. Now which produces the magnetic field, the voltage or the current? We know the current was responsible but we needed a voltage to do that. Similarly the acceleration is needed to produce the speed necessary for the relativistic effects but the speed is what determines the outcome, not the acceleration.We are trying to find the symmetry breaker in the twin paradox case. In the original case, one twin accelerates, while the other doesn't. That difference is thought to be the reason to disqualify the travelling twin from applying simple Lorentz transform and observe time dilation experienced by staying twin. Otherwise, both twins will see the other's clock to be slower than their own, which is a contradiction.
Where's the symmetry breaker in your analogy?
When the two have a constant velocity with respect to each other, they both are able to simply apply the time dilation formula to the other's clock.
In fact, the non-traveling twin, since he never experiences any acceleration, can always do such. For Him, the only thing that happens to the other twin during the acceleration is that the time dilation rate changes as the relative velocity changes.
It's different for the Twin actually undergoing the acceleration. On top of the time dilation due to changing velocity, there are other factors affecting his measurements. Clocks in the direction of the his acceleration will run faster, and one in the opposite direction will run slower, according to him. This even includes clocks within his own ship that are not moving relative to him by his measure. A clock in the nose of the ship run faster than one in the middle, which runs faster than one in the tail.*
The difference in tick rate this creates by his determination is proportional not only to the magnitude of the acceleration, but also the distance separating the clocks. This is what leads to him agreeing at the end of the trip that he has aged less than his stay at home twin, even though fro the majority of the trip he would have said that it was the stay at home twin that was aging slower. For him, his brother aged slow, then aged really fast, then aged slow again, with it all adding up at the end with his twin having aged more in total.
Again, this is what each twin determines after factoring out light propagation delays.
As to what they actually see:
Stay and home twin:
1. Sees traveler receding and ticking slow by the Doppler shift factor. He will see this for the amount of time needed fro the ship to reach the destination plus the time it take for light to travel from there to him. (with a 4 light year trip and traveling at 0.999 c, it will be 8.004 yrs, ticking at a rate of 0.0224, accumulating ~0.179 yrs.
Then, for 0.004 yrs ( total trip time minus the above) it sees a Doppler effect rate of 44.71, seeing the ship accumulate another ~.179 yrs. this gives 0.358 yrs total for the ship and 8.008 for Earth.
For the traveling twin, the 4 ly distance as measured from Earth is only ~.01788 ly due to length contraction by his measure, which takes 0.179 yrs to cross at 0.999 c. During which time he sees the Earth age ~0.004 yrs due to Doppler shift. Now, since he is the one doing the acceleration, and thus making the change of velocity, he doesn't have to wait any time to see the effect this has on the Doppler shift, but will see an immediate change to the ~44.71 rate, which he then sees for the ~0.179 yrs needed to return to the Earth, adding 8.004 yrs to the 0.004 yrs for a total of 8.008 yrs for Earth upon return, to his 0.358 yrs.
*Our non- accelerating observer will also note a difference in these clocks, but for a different reason. In his frame, The ship, as a whole, is changing velocity with respect to him, thus its length contraction is also changing. This, in turn, means that the ends of the ship cannot be traveling at equal velocities relative to him, and the clocks at the ends have different time dilation rates and not tick in sync.
Post by: hamdani yusuf on 22/08/2023 22:41:52
For him, his brother aged slow, then aged really fast, then aged slow again,Why in return trip the travelling twin observes slow age of staying on earth twin, when they are moving closer?
Post by: hamdani yusuf on 22/08/2023 22:49:40
You can put your formulas in a spreadsheet, so that you can change the time of interest to any value and immediately get the results.I appreciate your effort to do the calculations. Now we can narrow down the observation around the passing event at mid point.Outbound trip:It's seems to me that you are trying as hard as possible to Not understand Relativity.It seems like that to you because you've been misunderstanding it without you realized.
What's the reading of the travelling clock by midway observer, one day before passing the mid point, and one day after passing it?
0ne day prior to ship arriving( by Midpoint's clock):
Actual time on ship clock: 32 days, 15 hrs, 34 min and 13.5718217858 sec.
What the Midpoint observer visually sees: The ship sitting at its planet of origin, waiting to depart.
One day after ship passes midpoint:
Actual time on ship: 32 days, 17 hrs, 42 min, and 59.490547741 sec
What the observer visually sees: 32 days, 17 hrs, 10 min, 48.9770892 sec
During return leg:
One day before:
Actual time: 98 days 0 hr, 51 min, 26.63419131 sec
What is visually seen: The ship not quite having reached the turn around point, and a bit short of reading 65 days 9hr, 17 min, and 13.06236952 sec
One day after:
Actual time: 98 days 3 hrs, 0 min, 12.55291726 sec
What is visually seen: 98 days 2 hr, 28 min, and 12.5529176 sec.
What's the reading of the travelling clock by midway observer, one second before passing the mid point, and one second after passing it?
At least in principle, we should be able to narrow down further to microsecond or picosecond, to approach the reading exactly at the passing event.
Post by: hamdani yusuf on 22/08/2023 22:52:01
Di they have the same age at meeting point?
Post by: Janus on 23/08/2023 16:15:38
What will travelling earth twin see about travelling Alpha Centauri twin?I've already covered this in an earlier post. (while in that example I assume a 0.8 c rather than 0.999 c, the basic math still applies. )
Di they have the same age at meeting point?
When two or more clocks pass each other, everyone will agree as what they read as they do so. The fact that the traveling Earth twin, the traveling AC twin and the midpoint clock all agree as to what times each of them read as they pass is mundane and is to be expected( in fact, required for us to live in a consistent universe). You are really not going to learn anything about Relativity from this.
Post by: hamdani yusuf on 24/08/2023 05:50:01
I've already covered this in an earlier post. (while in that example I assume a 0.8 c rather than 0.999 c, the basic math still applies. )You haven't mentioned the observation of a travelling twin on the clock of the other travelling twin when they meet at mid point.
Post by: hamdani yusuf on 24/08/2023 05:59:03
When two or more clocks pass each other, everyone will agree as what they read as they do so. The fact that the traveling Earth twin, the traveling AC twin and the midpoint clock all agree as to what times each of them read as they pass is mundane and is to be expected( in fact, required for us to live in a consistent universe). You are really not going to learn anything about Relativity from this.There must be some reasons why after more than a century, there are still disputes even among experts and researchers on the cause of twin paradox. They seem to be convinced by the end results, but they disagree on how they get that same results. That's a problem with thought experiments.
Post by: Janus on 24/08/2023 16:17:40
In reply #88I've already covered this in an earlier post. (while in that example I assume a 0.8 c rather than 0.999 c, the basic math still applies. )You haven't mentioned the observation of a travelling twin on the clock of the other travelling twin when they meet at mid point.
ES is the Earth traveling twin
ACS is the Alpha Centauri traveling twin
Velocites of ES and ACS to the planets and midpoint: 0.8c (As already mentioned, the exact value really does not matter in the big picture)
Events according to ES, starting from the moment it reaches 0.8c relative to Earth
ACS time = ~1.26 yr
Distance of ACS to midpoint = ~0.283 ly
Relative velocity of ACS to ES = ~0.976c (addition of velocities)
Time dilation factor for ACS according to ES = ~0.22
closing speed between ACS and midpoint = ~0.176c (0.976c-0.8c)
Distance to midpoint for ES = ~1.29 ly (length contraction)
Time for ES to reach midpoint = ~1.61 yr
time for ACS to reach midpoint = ~1.61 yr (0.28 ly/.176c)*
Time accumulated for ACS while ES travels to midpoint = ~0.354 yr (1.61*0.22)
Time on ACS upon arrival to midpoint ~1.61 yr (1.26yr+0.354 yr)
Post by: Janus on 24/08/2023 16:36:34
Except there really is no real dispute. What you see as a disagreement by looking at a couple of YouTube videos, are merely different approaches at explaining it to a layman audience. And it really isn't that easy for these experts to do so.When two or more clocks pass each other, everyone will agree as what they read as they do so. The fact that the traveling Earth twin, the traveling AC twin and the midpoint clock all agree as to what times each of them read as they pass is mundane and is to be expected( in fact, required for us to live in a consistent universe). You are really not going to learn anything about Relativity from this.There must be some reasons why after more than a century, there are still disputes even among experts and researchers on the cause of twin paradox. They seem to be convinced by the end results, but they disagree on how they get that same results. That's a problem with thought experiments.
The big problem is that they are so familiar with the subject that they tend to see certain parts of it as obvious and don't go over it as clearly as they should, because they assume the audience will also see it as obvious. This can leave things open for the audience to misinterpret what is being said.
Post by: hamdani yusuf on 24/08/2023 16:54:10
AC time = 3.44 yr (relativity of simultaneity)Where do you get this number from?
Post by: Janus on 24/08/2023 20:20:04
As stated, it is due to the Relativity of Simultantaneity. It can be calculated by vx/c^2, whereAC time = 3.44 yr (relativity of simultaneity)Where do you get this number from?
v is the relative velocity between ES and AC,
x is the Earth AC distance measured in the Earth rest frame.
It gives you the difference between the Earth clock and the AC clock in the rest frame of ES, assuming that they read the same in the Earth/AC rest frame.
Earth clock reads 0 at that moment, So AC clock reads 0.8c x 4.3 ly/ c^2 = 3.44 yrs.
This is also consistent with the fact that it takes 3.225 years by the ES clock to reach AC. During which time the AC clock is ticking slow by a factor of 0.6 and accumulates 1.935 yrs according to ES. But it reads 5.375 yrs upon the arrival of ES. 5.375-1.935 = 3.44, So the AC clock had to already read 3.44 yrs as ES left Earth according to ES.
If you want to use a 4 ly distance and a velocity of 0.999c, then the AC clock reads 3.996 yrs when ES leaves Earth according to ES,
Post by: hamdani yusuf on 25/08/2023 04:10:08
Earth clock reads 0 at that moment, So AC clock reads 0.8c x 4.3 ly/ c^2 = 3.44 yrs.At that moment, what does the midway clock read?
What does the midway clock read in the case below?
If you want to use a 4 ly distance and a velocity of 0.999c, then the AC clock reads 3.996 yrs when ES leaves Earth according to ES,
Post by: hamdani yusuf on 25/08/2023 04:21:45
What's the reading of the travelling clock by midway observer, one second before passing the mid point, and one second after passing it?
Post by: alancalverd on 25/08/2023 08:08:46
Post by: hamdani yusuf on 25/08/2023 09:39:26
Whose second?In my early scenario, everything is measured by the midway observer, because it's where the symmetry is guaranteed.
Post by: hamdani yusuf on 25/08/2023 15:18:55
If you want to use a 4 ly distance and a velocity of 0.999c, then the AC clock reads 3.996 yrs when ES leaves Earth according to ES,Your statement seems to imply that earth travelling twin can see events on Alpha Centauri in the future which midway observer hasn't been able to observe yet. Cmiiw.
Post by: Janus on 25/08/2023 16:09:41
Pay attention. I already pointed out that what he would SEE would be the same thing as what someone on Earth would see at that moment: Events that occurred at AC 4.3 years ( by the AC time measure) prior to the AC ship leaving.If you want to use a 4 ly distance and a velocity of 0.999c, then the AC clock reads 3.996 yrs when ES leaves Earth according to ES,Your statement seems to imply that earth travelling twin can see events on Alpha Centauri in the future which midway observer hasn't been able to observe yet. Cmiiw.
The Earth observer sees this and uses it to work that the AC ship is also leaving at that moment in the Earth-AC rest. Hwe can do this either by being aware of the setup with the signal originating at the midpoint, or waiting 4.3 years until he sees the AC ship leave, and working backwards.
The Earth ship, moving at 0.8c relative to both the Earth and AC, and seeing that same light has to come to a different conclusion: That in order to be seeing this light from AC at this moment, the clock at AC has to already be reading 3.44 yr past when the AC ship left at that same moment.
Grasping the relativity of simultaneity is key to understanding SR. It really is the first thing you need to come to grips with before proceeding to anything else.
Post by: hamdani yusuf on 26/08/2023 05:58:35
Perhaps you can avoid confusion by using more consistent and succinct words.Pay attention. I already pointed out that what he would SEE would be the same thing as what someone on Earth would see at that moment: Events that occurred at AC 4.3 years ( by the AC time measure) prior to the AC ship leaving.If you want to use a 4 ly distance and a velocity of 0.999c, then the AC clock reads 3.996 yrs when ES leaves Earth according to ES,Your statement seems to imply that earth travelling twin can see events on Alpha Centauri in the future which midway observer hasn't been able to observe yet. Cmiiw.
The Earth observer sees this and uses it to work that the AC ship is also leaving at that moment in the Earth-AC rest. Hwe can do this either by being aware of the setup with the signal originating at the midpoint, or waiting 4.3 years until he sees the AC ship leave, and working backwards.
The Earth ship, moving at 0.8c relative to both the Earth and AC, and seeing that same light has to come to a different conclusion: That in order to be seeing this light from AC at this moment, the clock at AC has to already be reading 3.44 yr past when the AC ship left at that same moment.
Grasping the relativity of simultaneity is key to understanding SR. It really is the first thing you need to come to grips with before proceeding to anything else.
You can rewrite this statement,
the AC clock reads 3.996 yrs when ES leaves Earth according to ES,to
the AC clock reads 3.996 yrs when ES leaves Earth as calculated by ES,
to distinguish the interpretation that it were what's actually read/seen by ES.
Post by: hamdani yusuf on 26/08/2023 06:04:39
What's the reading of the travelling clock by midway observer, one second before passing the mid point, and one second after passing it?
Whose second?In my early scenario, everything is measured by the midway observer, because it's where the symmetry is guaranteed.
To be clear, I'm not trying to propose a new theory here. Just like the OP's question, I want to know what are actually described by currently most accepted/mainstream theory, and what their implications and consequences are.
Post by: Janus on 26/08/2023 16:12:20
Since by this point of the thread I had already mentioned at least twice that ES would, at that moment, see the same thing as Earth would, I don't think that my wording here is really at issue, as its meaning is quite clear when taken in context with what had been said earlier.Perhaps you can avoid confusion by using more consistent and succinct words.Pay attention. I already pointed out that what he would SEE would be the same thing as what someone on Earth would see at that moment: Events that occurred at AC 4.3 years ( by the AC time measure) prior to the AC ship leaving.If you want to use a 4 ly distance and a velocity of 0.999c, then the AC clock reads 3.996 yrs when ES leaves Earth according to ES,Your statement seems to imply that earth travelling twin can see events on Alpha Centauri in the future which midway observer hasn't been able to observe yet. Cmiiw.
The Earth observer sees this and uses it to work that the AC ship is also leaving at that moment in the Earth-AC rest. Hwe can do this either by being aware of the setup with the signal originating at the midpoint, or waiting 4.3 years until he sees the AC ship leave, and working backwards.
The Earth ship, moving at 0.8c relative to both the Earth and AC, and seeing that same light has to come to a different conclusion: That in order to be seeing this light from AC at this moment, the clock at AC has to already be reading 3.44 yr past when the AC ship left at that same moment.
Grasping the relativity of simultaneity is key to understanding SR. It really is the first thing you need to come to grips with before proceeding to anything else.
You can rewrite this statement,the AC clock reads 3.996 yrs when ES leaves Earth according to ES,to
the AC clock reads 3.996 yrs when ES leaves Earth as calculated by ES,
to distinguish the interpretation that it were what's actually read/seen by ES.
Post by: Origin on 26/08/2023 17:09:43
I don't think that my wording here is really at issue, as its meaning is quite clear when taken in context with what had been said earlier.For some reason Hamdani likes to go over the same ground again and again, he's done that in many of his marathon threads.
Post by: hamdani yusuf on 26/08/2023 23:27:49
Since by this point of the thread I had already mentioned at least twice that ES would, at that moment, see the same thing as Earth would, I don't think that my wording here is really at issue, as its meaning is quite clear when taken in context with what had been said earlier.They become different 1 second later. That's why the distinction becomes important.
Post by: hamdani yusuf on 26/08/2023 23:38:46
Maybe you can help him answer my question.I don't think that my wording here is really at issue, as its meaning is quite clear when taken in context with what had been said earlier.For some reason Hamdani likes to go over the same ground again and again, he's done that in many of his marathon threads.
Just in case you've missed to read this question.What's the reading of the travelling clock by midway observer, one second before passing the mid point, and one second after passing it?Whose second?In my early scenario, everything is measured by the midway observer, because it's where the symmetry is guaranteed.
Post by: hamdani yusuf on 01/09/2023 13:32:53
Maybe you can help him answer my question.https://www.doubtnut.com/question-answer-physics/a-stationary-observer-receives-a-sound-from-a-sound-of-freqeuency-v0-moving-with-a-constant-velocity-11393557
The formula shown there suggests that right at mid point, cos θ = 0, and the observer gets original frequency.
I think this can be a clue.
Post by: hamdani yusuf on 03/09/2023 02:32:19
If a formula has really been accepted to be the solution, then it should not be a problem to input different values of the variables in it, and get an answer. I'm curious why it isn't the case.Maybe you can help him answer my question.I don't think that my wording here is really at issue, as its meaning is quite clear when taken in context with what had been said earlier.For some reason Hamdani likes to go over the same ground again and again, he's done that in many of his marathon threads.Just in case you've missed to read this question.What's the reading of the travelling clock by midway observer, one second before passing the mid point, and one second after passing it?Whose second?In my early scenario, everything is measured by the midway observer, because it's where the symmetry is guaranteed.
Post by: Origin on 05/09/2023 18:32:23
Let's start with the simplest frame of reference first, which is the midway observer. What will he observe when he meet both travelling twins? At that moment, what's shown by his own clock, and the clocks brought by the travelling twins?Assuming the mid way point is exactly 2 ly and the twins acceleration was instantaneous:
Twins speed 0.999c. From the frame of the observer at the mid point the elapsed time on the clocks would be:
1. Mid point clock - 2.002 years
2. Earth twins clock - 0.0894 yrs
3. Alpha Centauri twin - 0.0894 yrs
Post by: hamdani yusuf on 06/09/2023 12:42:49
Thanks for giving quantitative answers.Let's start with the simplest frame of reference first, which is the midway observer. What will he observe when he meet both travelling twins? At that moment, what's shown by his own clock, and the clocks brought by the travelling twins?Assuming the mid way point is exactly 2 ly and the twins acceleration was instantaneous:
Twins speed 0.999c. From the frame of the observer at the mid point the elapsed time on the clocks would be:
1. Mid point clock - 2.002 years
2. Earth twins clock - 0.0894 yrs
3. Alpha Centauri twin - 0.0894 yrs
How did you get those numbers?
Did you involve Doppler effect?
Do you think these represent the mainstream view of science community?
Post by: Origin on 13/09/2023 15:57:08
Thanks for giving quantitative answers.Sorry, I didn't see your reply.
How did you get those numbers?
For the mid point observer's clock: 2 ly/.999 c
For the space ships: t' = sqrt{1 - ({v^2}/{c^2})
Did you involve Doppler effect?No, it is not involved in this case.
Do you think these represent the mainstream view of science community?Yes, I think I did the math correctly.
Post by: hamdani yusuf on 14/09/2023 14:45:29
Post by: Origin on 14/09/2023 14:59:36
It makes me curious where did Janus get his Doppler effect and accumulation of time difference from.Janus definitely knows what he is talking about, however I don't know which of the many different questions he was answering. I believe that I correctly answered your specific question.
Post by: hamdani yusuf on 15/09/2023 12:44:18
Let him explain himself when he has the time to spare.It makes me curious where did Janus get his Doppler effect and accumulation of time difference from.Janus definitely knows what he is talking about, however I don't know which of the many different questions he was answering. I believe that I correctly answered your specific question.
Meanwhile, what will be seen by the travelling twins during that meeting point? Will they see the clocks to have the same values as observed by midway observer?
Post by: hamdani yusuf on 24/12/2023 23:00:23
Quote
Since the discovery of the special theory of relativity in 1905 due to weird phenomena like time dilatation and length contraction, people started to find many possible paradoxes within the theory.In summary, it says that the difference is due to equivalence principle.
The most famous of them all is the Twin paradox which is still discussed today. In this video, we take a look at what is really weird and paradoxical about this scenario and why this happens, and whether it can be solved purely within the special relativity framework or we need something more (like general relativity).
Post by: Origin on 25/12/2023 14:53:05
In summary, it says that the difference is due to equivalence principle.I guess you will never be able to understand the twin 'paradox' with all the different explanations on Youtube.
Post by: Halc on 25/12/2023 14:56:39
The Twin Paradox: What is it Really All AboutWhat it is about has already been well explained. Most you-tube videos on the subject contain mistakes. The one you provide is blatantly wrong in several areas.
In summary, it says that the difference is due to equivalence principle.Which is blatantly wrong since the EP is about the local equivalence of acceleration and gravity, and the twins thing has nothing whatsoever to do with gravity, and it isn't local.
A minor mistake is made at about 5:10 where he says that both observers see the clock of the other running slow at all time. This is false. A directly receding clock is seen to run slow, and an approaching one is seen to run fast. This is one of the ways to explain the paradox. What he seems to mean here is that the other clock is computed to run slow. It takes a computation to account for the light travel time. One does not see the other clock run at half speed in either direction.
The bigger mistake comes when GR is invoked.at 9:10 and he says that there's no measurable difference between an accelerating rocket and a uniform gravitational field, and that there are no tidal forces for either. All this is very wrong. There are tidal forces in a continuously accelerating rocket, and the acceleration field is not uniform. There is no such thing as a uniform gravitational field under GR. Such a field would have a valid tensor, and there is no valid tensor with the properties described. Newtonian physics allows it (with an infinite 2D sheet of mass say), but GR does not.
Post by: alancalverd on 25/12/2023 23:00:44
The meaningful question is "what causes apparent simultaneity?"
Post by: Zer0 on 03/01/2024 16:55:25
If i am in a spacecraft moving at 1%
Speed of Light...
I'm at the Centre..
Which blinking light would i see first, the front or the back one?
Post by: hamdani yusuf on 04/01/2024 08:10:54
Eliminating paradox can be done by showing the mistakes in every contradicting explanation, except one.In summary, it says that the difference is due to equivalence principle.I guess you will never be able to understand the twin 'paradox' with all the different explanations on Youtube.
Post by: hamdani yusuf on 04/01/2024 08:15:15
What it is about has already been well explained. Most you-tube videos on the subject contain mistakes. The one you provide is blatantly wrong in several areas.Can you find a YouTube video on the subject that doesn't contain mistakes?
Post by: hamdani yusuf on 04/01/2024 08:19:27
As relativistic mechanics is now accepted as fundamental, with classical or newtonian mechanics being a special case where v<<c, the question is actually badly phrased.Is there any experimental evidence showing that traveling twin age less than staying twin, excluding every other effects but their speed?
The meaningful question is "what causes apparent simultaneity?"
Post by: hamdani yusuf on 04/01/2024 08:23:27
Hope the OP won't mind me Intruding.Theoretically, you will see them at the same time.
If i am in a spacecraft moving at 1%
Speed of Light...
I'm at the Centre..
Which blinking light would i see first, the front or the back one?
Practically, you'll see the one you are facing to, except you use some helping devices like a mirror.
Post by: alancalverd on 04/01/2024 14:46:05
Is there any experimental evidence showing that traveling twin age less than staying twin, excluding every other effects but their speed?It is not possible to do so directly. You need to synchronise your clocks, which requires that they are not moving with respect to one another, then accelerate one to the required speed.
You can however calculate and subtract all the effects of acceleration, gravitation etc from any practical observation.
Post by: Origin on 04/01/2024 15:53:27
Is there any experimental evidence showing that traveling twin age less than staying twin, excluding every other effects but their speed?You mean like humidity changes or something?
Post by: Halc on 04/01/2024 20:41:59
Eliminating paradox can be done by showing the mistakes in every contradicting explanation, except one.Even one explanation with a mistake contradicting the theory would still be a wrong one.
Try all the ones that don't contradict relativity. There are many different valid explanations of the twins scenario, and none of them contradict SR or each other. If one claims to be the "one correct" explanation, it is wrong.
Can you find a YouTube video on the subject that doesn't contain mistakes?The Minutephysics video you linked in post 17 seems reasonable. It isn't the simplest explanation, but it isn't wrong because of that.
Is there any experimental evidence showing that traveling twin age less than staying twin, excluding every other effects but their speed?It wasn't ever done with human twins, no. There is very much experimental evidence done with say crude clocks, and all done in a way that gravity plays no role, such as in a cyclotron.
If i am in a spacecraft moving at 1% Speed of Light...Relative to what? I mean, Earth is moving at 1% c relative to something. It is also moving at 95%c relative to something else.
Quote
I'm at the Centre.. Which blinking light would i see first, the front or the back one?If both lights blink simultaneously in the frame of the ship, then since light moves at c relative to that frame, the light will reach the center at the same event.
If the lights blink simultaneously relative to any frame in which the ship is moving, then they probably have different distances to travel in that alternate frame and will thus probably not arrive simultaneously at the detector.
Point is, you didn't say how the blinking lights in the ship are synced. You specified no frame in which they blink at the same time, or if they blink at the same time at all. Maybe they blink hours apart. You don't say.
The meaningful question is "what causes apparent simultaneity?"You give zero indication of what you think 'apparent simultaneity' means. It's not a known term. Simultaneity is a convention, an abstraction. There's nothing physical about it, and no empirical test for it. The phrase seems to imply that there's a way to measure it without first presuming an abstract coordinate system.
You need to synchronise your clocks, which requires that they are not moving with respect to one anotherClocks in each other's presence can be synced to the same value at that event, without any requirement of them being mutually stationary.
You need a citation to back this speculation.
Post by: hamdani yusuf on 05/01/2024 07:10:55
Yes. Also other effects like temperature, pressure, electromagnetic radiation, gravitational acceleration and potential.Is there any experimental evidence showing that traveling twin age less than staying twin, excluding every other effects but their speed?You mean like humidity changes or something?
Post by: hamdani yusuf on 05/01/2024 07:41:08
Even one explanation with a mistake contradicting the theory would still be a wrong one.Many Youtube videos trying to explain Twin Paradox point out what's wrong in explanations provided by other videos or books. Latter videos try to correct earlier ones while declaring that they still follow theory of relativity, either special or general one.
Try all the ones that don't contradict relativity. There are many different valid explanations of the twins scenario, and none of them contradict SR or each other. If one claims to be the "one correct" explanation, it is wrong.
Some say that special relativity is not adequate to explain the paradox, while the others say that it is adequate. They are contradicting each other.
Some say that Doppler effect must be taken into account, while the others say it's unnecessary.
Some even declare that there is no paradox even without analyzing the situation from the perspective of traveling twin.
Saying that they are equally valid is not a logically sound position.
Post by: alancalverd on 05/01/2024 07:41:35
Quotefrom: alancalverd on 25/12/2023 23:00:44You give zero indication of what you think 'apparent simultaneity' means. It's not a known term. Simultaneity is a convention, an abstraction. There's nothing physical about it, and no empirical test for it. The phrase seems to imply that there's a way to measure it without first presuming an abstract coordinate system.
The meaningful question is "what causes apparent simultaneity?"
That's the whole point: simultaneity is a convention. We perceive and describe two nearby events as simultaneous if we receive information from both of them coincidentally, but we know that if the sources are at different distances from us, or indeed travelling at different velocities relative to us, they would not appear simultaneous to an observer for whom the arrangement was symmetrical.
Synchronisation doesn't just mean showing the same number at a given instant. There is a presumption in "gentlemen, synchronise your watches" that they will all continue to tick at the same rate for long enough to effectively coordinate the invasion. But relativity tells us that as the army, navy and air force travel at different speeds, they won't be coordinated when they reach alpha centauri.Quotefrom: alancalverd on Yesterday at 14:46:05Clocks in each other's presence can be synced to the same value at that event, without any requirement of them being mutually stationary.
You need to synchronise your clocks, which requires that they are not moving with respect to one another
You need a citation to back this speculation.
Post by: Zer0 on 05/01/2024 18:07:38
Hope the OP won't mind me Intruding.Theoretically, you will see them at the same time.
If i am in a spacecraft moving at 1%
Speed of Light...
I'm at the Centre..
Which blinking light would i see first, the front or the back one?
Practically, you'll see the one you are facing to, except you use some helping devices like a mirror.
What if i was standing Sideways?
Or
Assume both Blinkers were Synchronised while spacecraft was at Speed 0.
Gradually 1%c is reached.
My left eye tracking Front blinker.
My right eye tracking Back blinker.
Let's say i am Not interested in the Theoretical part of it.
I just wanna know Which one i'd see blinking first/faster?
ps - is there any possible way U could avoid using SR/GR & give a Simplistic answer.
Post by: Origin on 05/01/2024 19:19:01
Let's say i am Not interested in the Theoretical part of it.If the lights were synchronized at zero m/s, then no matter how fast you were going they would stay synchronized. IOW the light from both sources would continue to hit you at exactly the same time.
I just wanna know Which one i'd see blinking first/faster?
Post by: Halc on 06/01/2024 00:41:07
Many Youtube videos trying to explain Twin Paradox point out what's wrong in explanations provided by other videos or books.Which means either that these videos are wrong, or they're correct about the mistakes being made by the other videos/books. If they say that their own explanation is the one correct one, then the former is true.
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Some say that special relativity is not adequate to explain the paradox, while the others say that it is adequate. They are contradicting each other.The latter case is correct here. The former claims indeed contradict that, and are wrong.
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Some say that Doppler effect must be taken into account, while the others say it's unnecessary.The latter would be the correct one here. Mind you, the twins thing can be explained by perspectives and appearances, and Doppler needs to be taking into account if you do it that way, but the valid video I mentioned above makes no mention of Doppler, illustrating that indeed not always necessary,.
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Some even declare that there is no paradox even without analyzing the situation from the perspective of traveling twin.That would be correct. There is not paradox no matter how you look at it. It only becomes paradoxical if one drags in biases from outside of relativity theory.
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Saying that they are equally valid is not a logically sound position.I didn't say all the 'explanations' mentioned above are equally valid, since several make incorrect assertions. So I agree with this statement, but nobody is claiming all these statements are valid.
Quote from: alancalverd link=topic=86033.msg719218#msg719218
simultaneity is a convention.Simultaneity at a distance is a convention. Simultaneity at one event is tautological physical fact.
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We perceive and describe two nearby events as simultaneous if we receive information from both of them coincidentally, but we know that if the sources are at different distances from us, or indeed travelling at different velocities relative to us, they would not appear simultaneous to an observer for whom the arrangement was symmetrical.All this is irrelevant to two clocks passing and syncing at some event at which both are present. The sources are zero distance away, and very much appear simultaneous to any observer, even those not present at the event of their meeting at speed. To suggest otherwise to imply that the light from the two respective objects travels at some speed other than c.
Synchronisation doesn't just mean showing the same number at a given instant.Yes it does. That's exactly what it means.
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There is a presumption in "gentlemen, synchronise your watches" that they will all continue to tick at the same rate for long enough to effectively coordinate the invasion.I never claimed the two passing clocks would stay in sync in any given frame. Which clock runs faster would be a frame dependent thing.
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But relativity tells us that as the army, navy and air force travel at different speeds, they won't be coordinated when they reach alpha centauri.Yes. That's pretty much the twins thingy, with everybody taking different worldlines between two mutually common events.
What if i was standing Sideways?Relativity theory isn't in any way about the limits of human physiology. A human can detect perhaps a 20th of a second difference in arrival of two pulses. Any less than that and they'll appear simultaneous to a human. Your train example will produce differences on the order of nanoseconds.
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Assume both Blinkers were Synchronised while spacecraft was at Speed 0.OK, that's a good frame reference. They are (or were at at least) synced relative to the frame in which the speed of 1%c is eventually measured.
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Gradually 1%c is reached.You'll see the one in front blink first if you were a high precision measuring device. As a human, you'd never be able to detect the nanosecond difference.
My left eye tracking Front blinker.
My right eye tracking Back blinker.
Let's say i am Not interested in the Theoretical part of it.
I just wanna know Which one i'd see blinking first/faster?
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ps - is there any possible way U could avoid using SR/GR & give a Simplistic answer.That seemed pretty simple to me. It even works in Newtonian mechanics, so I managed to answer without using SR/GR.
If the lights were synchronized at zero m/s, then no matter how fast you were going they would stay synchronized.Not true. Them being synced is a frame dependent thing, and after acceleration, they'd be synced in neither the train frame nor the original frame, although at 0.01c, they'd be really close to being in sync in the original frame.
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IOW the light from both sources would continue to hit you at exactly the same time.Sorry but no. The front one hits you first since you're moving toward it in the frame in which the two blinks are synced.
Post by: Origin on 06/01/2024 00:58:46
Not true.You are absolutely right, sorry for misleading anyone!
Post by: varsigma on 06/01/2024 09:29:53
Can you find a YouTube video on the subject that doesn't contain mistakes?Yes, you can.
Look for lectures on special relativity by people like Susskind, or any from the likes of MIT or UC. Google is your friend; just type in the right words.
Post by: hamdani yusuf on 06/01/2024 10:00:14
Which means either that these videos are wrong, or they're correct about the mistakes being made by the other videos/books. If they say that their own explanation is the one correct one, then the former is true.Anyone who put their efforts to make and upload videos on YouTube most likely think that they're correct, at least when they are being uploaded.
Post by: hamdani yusuf on 06/01/2024 11:55:15
If general theory of relativity isn't necessary to explain twin paradox, will using it anyway cause a double counting?QuoteSome say that special relativity is not adequate to explain the paradox, while the others say that it is adequate. They are contradicting each other.The latter case is correct here. The former claims indeed contradict that, and are wrong.
Post by: alancalverd on 06/01/2024 12:14:32
Post by: hamdani yusuf on 06/01/2024 12:19:07
We can make statements without further explanation. But they will remain as hypotheses. Our confidence in the validity of a statement depends on the quality of its explanations.QuoteSome even declare that there is no paradox even without analyzing the situation from the perspective of traveling twin.That would be correct. There is not paradox no matter how you look at it. It only becomes paradoxical if one drags in biases from outside of relativity theory.
Post by: hamdani yusuf on 06/01/2024 13:06:58
Do they use general theory of relativity framework? Or they strict to special theory of relativity instead?Can you find a YouTube video on the subject that doesn't contain mistakes?Yes, you can.
Look for lectures on special relativity by people like Susskind, or any from the likes of MIT or UC. Google is your friend; just type in the right words.
Do they take Doppler effect into account?
Post by: hamdani yusuf on 06/01/2024 13:15:56
ps - is there any possible way U could avoid using SR/GR & give a Simplistic answer.Do you prefer Galilean Relativity?
There are some theories in this framework. Ritzian or ballistic relativity says that light speed is constant relative to the source, based on observed star aberration.
Observations of binary stars were used to refute this theory.
Maxwellian relativity says that light speed is constant relative to the medium. In vacuum of space, the medium is called aether.
Null result of Michelson-Morley experiment is compatible with ballistic relativity but not with aether. That's why Lorentz proposed length contraction to make up for the discrepancy.
Post by: alancalverd on 06/01/2024 14:29:22
Post by: hamdani yusuf on 06/01/2024 14:54:37
I don't recall Maxwell mentioning relativity. He simply proposed a formula for the propagation of an electromagnetic wave.He thought that light speed is constant relative to aether. That's what motivated MMX in the first place.
Post by: hamdani yusuf on 06/01/2024 15:32:12
In zero's scenario, both blinking lights are standing still relative to each other. They are accelerated uniformly, which means nothing breaks the symmetry, and they should stay synchronized regardless of the final speed of the spacecraft.QuoteQuote from: Origin on Yesterday at 19:19:01
If the lights were synchronized at zero m/s, then no matter how fast you were going they would stay synchronized.
Not true. Them being synced is a frame dependent thing, and after acceleration, they'd be synced in neither the train frame nor the original frame, although at 0.01c, they'd be really close to being in sync in the original frame.
Post by: varsigma on 06/01/2024 15:58:02
Do they use general theory of relativity framework? Or they strict to special theory of relativity instead?My suggestion is that you type the following into your search bar: "special relativity lectures".
Do they take Doppler effect into account?
After hitting return, you'll get a lot of hits. Try some of the material from universities, they have to teach the "right stuff", 'cause they just do.
Post by: hamdani yusuf on 06/01/2024 16:03:12
It would provide absolute reference frame. You would know your absolute velocity without referring to external object. Which is in contradiction to the first postulate of special theory of relativity.QuoteQuoteSorry but no. The front one hits you first since you're moving toward it in the frame in which the two blinks are synced.
IOW the light from both sources would continue to hit you at exactly the same time.
Post by: hamdani yusuf on 06/01/2024 16:04:09
Have you watched them yourself?Do they use general theory of relativity framework? Or they strict to special theory of relativity instead?My suggestion is that you type the following into your search bar: "special relativity lectures".
Do they take Doppler effect into account?
After hitting return, you'll get a lot of hits. Try some of the material from universities, they have to teach the "right stuff", 'cause they just do.
Can you summarize what they say?
What makes them more trustworthy than the others?
Post by: varsigma on 06/01/2024 16:20:42
Have you watched them yourself?I have watched some of them. Different lecturers go over the same material in different ways. That's one of the take aways
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Can you summarize what they say?Probably. If I could be bothered.
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What makes them more trustworthy than the others?Well, there is the fact that they have a reputation to uphold. All those fee-paying students learning the wrong ideas would be quite the scandal, don't you think?
Post by: alancalverd on 06/01/2024 22:43:00
I have no idea what he thought. What he proved was that em radiation can propagate at a speed c = 1/√(εμ) where ε and μ are constants that can be measured at any frequency for any medium or no medium.I don't recall Maxwell mentioning relativity. He simply proposed a formula for the propagation of an electromagnetic wave.He thought that light speed is constant relative to aether. That's what motivated MMX in the first place.
In the case of propagation through a vacuum, it is obvious that they are not frequency-dependent (since there is no material present) so we have the remarkable result that you can calculate the speed of light in vacuo from experiments with direct current electricity in a laboratory.
Furthermore, there being no material present, ε0 and μ0 must be isotropic, so the speed of light is independent of direction in free space.
Post by: alancalverd on 06/01/2024 22:51:47
If the lights were synchronized at zero m/s, then no matter how fast you were going they would stay synchronized.Alas no. If you define 0 m/s as being the state at which they were synchronised, then in order to reach any other speed hey must have been accelerated. If they are accelerated along the axis of propagation, this is equivalent to placing them in a divergent gravitational field, and the Pound-Rebka experiment demonstrated the resulting asynchronicity.
Post by: hamdani yusuf on 06/01/2024 23:34:38
I have no idea what he thought.I can ask Google Bard.
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James Clerk Maxwell's view on the aether was complex and evolved throughout his career. Here's a summary:
Early Acceptance (1860s):
Initially, Maxwell embraced the aether concept, believing it necessary for explaining light propagation as transverse vibrations. His famous equations for electromagnetism were built upon the aether model.
He saw the aether as a stationary, elastic medium permeating all space, capable of transmitting electromagnetic waves without significant energy loss.
Post by: hamdani yusuf on 07/01/2024 00:12:22
If they are accelerated along the axis of propagation, this is equivalent to placing them in a divergent gravitational field,Acceleration isn't equivalent with a divergent gravitational field.
Post by: hamdani yusuf on 07/01/2024 03:33:36
In the travelling twin's frame, the giant clocks should tick slower than his own. Thus when he arrives at the star, it should have increased by a smaller amount than his own. Can anyone explain the discrepancy?Let's pair the values of the giant clocks with travelling clock.Let me rephrase my statement you quoted.Which clock ticks faster is a frame dependent thing, and no frame was specified, so no, this isn't correct.
His onboarding clock ticks slower on average than the giant clocks.
Relative to Earth, the ship clock ticks slower. Relative to some inertial frame in which the ship is stationary, the Earth clock and all the giant clocks tick slower.
QuoteTraveling twin sees the giant clock the he is passing by showing the time according to Origin's calculation.Yes. This is consistent with the numbers in my prior post.
Earth clock ~ 4
Second clock ~ 5
Third clock ~ 6
Fourth clock ~ 7
Star clock ~ 8, then return.
Fourth clock ~ 9
Third clock ~ 10
Second clock ~ 11
Earth clock ~ 12
For instance, from the ship PoV, at the start, the 2nd clock appears to read 3 (just like you said in post 36). 16.3 days later when the 2nd clock passes by, it reads 5, which means it appears to run ~45x as fast because it is approaching, exactly the rate that I posted.
Earth clock ~ 4Y --- 0 d
Second clock ~ 5Y --- 16.3 d
Third clock ~ 6Y --- 32.6 d
Fourth clock ~ 7Y --- 49 d
Star clock ~ 8Y --- 65.3 d, then return.
Fourth clock ~ 9Y --- 81.6 d
Third clock ~ 10Y --- 97.9 d
Second clock ~ 11Y --- 114.2 d
Earth clock ~ 12Y --- 130.6 d
Observers on giant clocks and travelling clock should agree with these values.
Post by: alancalverd on 07/01/2024 13:52:08
Post by: Eternal Student on 07/01/2024 18:56:28
There's a post here: https://www.thenakedscientists.com/forum/index.php?topic=86033.msg719317#msg719317
which was related to this forum thread. It was posted around the same time this forum thread was relocated, split into two or whatever happened. It's ended up staying with a different thread and that's OK - it's reasonable in that thread.
Best Wishes.
Post by: Zer0 on 08/01/2024 20:12:39
i am in my Spacecraft at Rest.
2 Blinkers, front & back, Synchronised.
Gradual Acceleration until 1%c attained.
I am standing facing Sideways, utilizing Peripheral vision.
Left eye tracking Front & Right eye tracking Back.
Because Craft is moving Forward...
Front blinking light has to cover less distance/space.
Back blinking light has to cover more distance/space.
Hence, i see Front Blinker flickering more Frequently than the Back Blinker.
Now...Please tell me...
How the Heck am i seeing the Front one faster/more?
Left side of my body is Ageing faster than Right side?
OR
My Left Brain & Right Brain have Unsynchronized with each other?
OR
i am just in a pub drunk out n totally wazted n those blinkerz are discoballz n the barmaid just offered me a shot of ayahuasca!
ps - The Speed of Light remains Constant...ALWAYS!
Post by: pzkpfw on 08/01/2024 22:19:07
... Because Craft is moving Forward ...
According to whom is the craft moving forward? You, at rest in it?
Post by: alancalverd on 08/01/2024 23:49:01
Because Craft is moving Forward...Why aren't you standing equidistant between them?
Front blinking light has to cover less distance/space.
Back blinking light has to cover more distance/space.
At which point Bondi's ghost says "how would you know you are equidistant?" and the argument becomes intriguingly circular.
Post by: Eternal Student on 09/01/2024 06:40:46
There was some some acceleration involved in your ( @Zer0 description). The spacecraft was accelerating w.r.t. some frame (probably an inertial reference frame with origin at the centre of planet earth) rather than having the spacecraft moving at a constant velocity.
Basically, if the spacecraft had a constant velocity (w.r.t. the centre of earth) then you do not see the front blinking light hit you faster or more frequently than the back blinking light. On the other hand, if the craft is actually accelerating toward the flash of light from the front then things can be different.
Now...Please tell me...Actually, yes, different parts of your body will age at different rates in this acceleration. Moving further to the front or back of the spacecraft changes the ratio (or rate) of local time passed compared to (let's say) the time co-ordinate for the centre of planet earth frame. The acceleration in the spacecraft is indistinguishable from being in a uniform gravitational field and gravitational time dilation results will apply.
How the Heck am i seeing the Front one faster/more?
Left side of my body is Ageing faster than Right side?
Your head really does age faster than your feet on planet earth purely as a consequence of gravitational time dilation. On your spacecraft the left side of you is further up the spacecraft than the right, so it will age faster than the right side. The difference in the amount of local time elapsed (per unit of local time at the middle of the craft) is most noticeable between the very front and very back of the craft. Indeed, at the end of your acceleration you may notice that the light at the
Late Editing: front <--> back, see @Halc's post later, thank you.
Best Wishes.
ps - The Speed of Light remains Constant...ALWAYS!A very reasonable statement and almost completely correct. In any inertial frame it's true and is the cornerstone of much of physics. In a non-inertial frame (often phrased as an "accelerated frame") a light flash can propogate in different ways at different speeds. The acceleration of your spacecraft is what made it interesting.
Post by: alancalverd on 09/01/2024 11:51:56
(a) no acceleration = no "paradox"
(b) acceleration or gravitational field = perceived change in clock rate
(c) as predicted by Einstein and observed by Heafle-Keating, Pound-Rebka and GPS systems everywhere.
(d) therefore no paradox.
Post by: Halc on 09/01/2024 13:46:25
Indeed, at the end of your acceleration you may notice that the light at the back has experienced more time than the light at the front and requires replacement while the front light is still good. The back light has been running for more hours and hence emitted more flashes of light for you to see in the middle of the craft.Nit: You got this part backwards. Everywhere else in the post you correctly say that the front light blinks quicker. Thanks for the thorough response.
In the ship accelerating frame, time simply passes faster at the front. At the end of acceleration, the clocks are out of sync, but at 0.01c, the difference might be somewhere between a microsecond and nanoseconds, depending on unspecified ship length.
In Earth frame, during acceleration of the ship, the front light is always moving slower than the back one, Therefore the front light logs more blinks than the back light. The rear of the ship stops accelerating first and later on the front goes inertial. In the end, both clocks are moving at the same speed and the front is a wee bit ahead due to it moving slower during acceleration. This difference might be between nanoseconds and picoseconds. They're much closer to being in sync in this original frame than they are in the ship frame.
There's a post here:Yes, you did that just as I split the thread. It didn't directly address any comment here, and it was a good general post. So I left it there.
How the Heck am i seeing the Front one faster/more?As ES points out, you only see the front blink more during acceleration. After that ceases, both lights blink at the same rate, just not in sync anymore.
First of all, there is no 'the travelling twin's frame' since in no inertial frame is the travelling twin always stationary. So you need to be more specific, such as in the outbound frame (S') where the travelling twin is stationary for 65.3 days.QuoteLet's pair the values of the giant clocks with travelling clock.In the travelling twin's frame, the giant clocks should tick slower than his own. Thus when he arrives at the star, it should have increased by a smaller amount than his own. Can anyone explain the discrepancy?
Earth clock ~ 4Y --- 0 d
Second clock ~ 5Y --- 16.3 d
Third clock ~ 6Y --- 32.6 d
Fourth clock ~ 7Y --- 49 d
Star clock ~ 8Y --- 65.3 d, then return.
Fourth clock ~ 9Y --- 81.6 d
Third clock ~ 10Y --- 97.9 d
Second clock ~ 11Y --- 114.2 d
Earth clock ~ 12Y --- 130.6 d
Observers on giant clocks and travelling clock should agree with these values.
In that frame 65.3 days pass for him, and during those 2+ months, nearly 3 days (2.92) pass for each of the giant clocks moving past him at 0.999c.
You could have figured out that very trivially yourself since the gamma of 22.4 has already been posted (by you no less, in post 39).
Likewise in the inbound frame, 65.3 more days pass for him, and during those 2+ months, nearly 3 days pass for each of the giant clocks moving past him at 0.999c in the other direction.
All the rest is simply relativity of simultaneity. The clocks are synced differently from one frame to the next.
No discrepancy has been identified. If you think there is one, you need to point it out.
Post by: varsigma on 09/01/2024 21:04:27
A good 'primitive' for a clock is a wave, as William Burke points out in his textbook. So clock synchronization has the same problems as wave synchronization.
I guess you could conclude that what's special about special relativity is the possibility of synchronous clocks, aside from the practicalities. In general clocks are not synchronized, as Einstein sorta points out.
Post by: Zer0 on 10/01/2024 20:07:17
... Because Craft is moving Forward ...
According to whom is the craft moving forward? You, at rest in it?
If One canNot contemplate the question, what then, are the Chances of answering it.
As it is Visibly clear, i have received Satisfactory answers from the Seniors.
Still, thanks for your input.
Better luck, next time, try Harder!
ps - anyways evaluating users neurological disorders & getting threads locked up is your only forte!
Post by: pzkpfw on 10/01/2024 20:11:56
... Because Craft is moving Forward ...
According to whom is the craft moving forward? You, at rest in it?
If One canNot contemplate the question, what then, are the Chances of answering it.
As it is Visibly clear, i have received Satisfactory answers from the Seniors.
Still, thanks for your input.
Better luck, next time, try Harder!
ps - anyways evaluating users neurological disorders & getting threads locked up is your only forte!
Yes, you've missed the point.
Post by: hamdani yusuf on 12/01/2024 10:28:30
Furthermore, there being no material present, ε0 and μ0 must be isotropic, so the speed of light is independent of direction in free space.Is the velocity of light also independent of direction in free space?
Post by: hamdani yusuf on 12/01/2024 10:52:34
My common sense says, an observer staying in the same inertial frame of reference as the ship before it started accelerating.... Because Craft is moving Forward ...
According to whom is the craft moving forward? You, at rest in it?
As zero said, the ship is steadily moving away from its initial position at 1%c during the experiment with the blinkers. It's no longer accelerating.
Let's not complicate things unnecessarily just to avoid giving a falsifiable scientific answer.
Post by: hamdani yusuf on 12/01/2024 11:20:23
(a) no acceleration = no "paradox"This video says otherwise.
How to intuitively solve the twin's paradox? (No acceleration)
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Chapters:
00:00 What is the twin's paradox?
00:48 Why acceleration doesn't solve twin's paradox
2:24 Twin's paradox without acceleration (Earth's frame)
4:42 The traveling frame
7:13 My new website - floatheadphysics (ad)
8:48 Earth's frame again - with the flag
11:38 Travelling frame again - with the flag
13:30 The resolution!
14:45 Relativity of simultaneity
17:02 Isn't the root cause the acceleration?
18:20 What do they 'see'?
In this video, we'll intuitively resolve the twin's paradox. This version of the twin's paradox involves no acceleration. And no, you don't need equivalence principle, and you don't need general relativity to solve it. Twin's paradox can be completely solved using special theory of relativity and the correct usage of relativity of simultaneity.
Post by: hamdani yusuf on 12/01/2024 12:23:11
Actually, yes, different parts of your body will age at different rates in this acceleration.In my understanding of zero's question, the acceleration has stopped when the speed is 1%c.
Post by: hamdani yusuf on 12/01/2024 13:27:54
So you need to be more specific, such as in the outbound frame (S') where the travelling twin is stationary for 65.3 days.So, when the star clock arrives at him, it shows around 8Y, but it only increased by 2.92d during the outbound trip.
In that frame 65.3 days pass for him, and during those 2+ months, nearly 3 days (2.92) pass for each of the giant clocks moving past him at 0.999c.
And when the earth clock arrives back at him, it will show around 12Y, while also only increased by 2.92d during the inbound trip.
Post by: Zer0 on 12/01/2024 18:25:11
... Because Craft is moving Forward ...
According to whom is the craft moving forward? You, at rest in it?
If One canNot contemplate the question, what then, are the Chances of answering it.
As it is Visibly clear, i have received Satisfactory answers from the Seniors.
Still, thanks for your input.
Better luck, next time, try Harder!
ps - anyways evaluating users neurological disorders & getting threads locked up is your only forte!
Yes, you've missed the point.
& You missed the Whole ps Line!
Goodbye & Tc.
@Halc
I am Sorry for Breaking the Rules.
i Apologize.
Being harsh n rude n judging layman enthusiasts & hinting they are schizoid or loony or cuckoo just coz they think differently & trying to learn difficult concepts is Totally Wrong!
ps - don't judge a book by it's cover, or a fish by it's ability to climb a wall.
(idk & idc who said it, but it matters)
Post by: hamdani yusuf on 13/01/2024 07:06:24
Bad idea to reference your common sense or intuitions when discussing relativity that you obviously don't understand.Here's what understanding means.
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Gregory Chaitin propounds a view that comprehension is a kind of data compression.[19] In his essay "The Limits of Reason", he argues that understanding something means being able to figure out a simple set of rules that explains it. For example, we understand why day and night exist because we have a simple model?the rotation of the earth?that explains a tremendous amount of data?changes in brightness, temperature, and atmospheric composition of the earth. We have compressed a large amount of information by using a simple model that predicts it. Similarly, we understand the number 0.33333... by thinking of it as one-third. The first way of representing the number requires five concepts ("0", "decimal point", "3", "infinity", "infinity of 3"); but the second way can produce all the data of the first representation, but uses only three concepts ("1", "division", "3"). Chaitin argues that comprehension is this ability to compress data. This perspective on comprehension forms the foundation of some models of intelligent agents, as in Nello Cristianini's book "The shortcut", where it is used to explain that machines can understand the world in fundamentally non-human ways.
https://en.wikipedia.org/wiki/Understanding#As_a_model
Post by: hamdani yusuf on 13/01/2024 07:23:07
For instance, there is not, and never way, a paradox in the twins scenario. There's no rule broken, so no paradox to resolve. It perhaps contradicts ones intuitions, but that't the problem with the intuitions/common sense rather than the theory.You can repeat saying that there's no paradox to resolve, and stop at it.
We can also say that 2≠1, and stop at it. But if someone comes saying that he can proof that 2=1, we might be interested to find out where the mistake was made.
Post by: hamdani yusuf on 13/01/2024 07:30:59
This question, as worded, makes no sense. If you are asking if light pulses travelling in different directions have the same velocity, of course not, by definition. If you're asking if a given pulse of light has the same velocity in one inertial frame as another, the answer there is also no.Yet, you can answer it. My question is a binary question, which only accept yes or no as answer, but perhaps still depends on other factors not mentioned in the question. It's similar to the question "is 2=1?". The answer is no, but the question is not meaningless.
Post by: hamdani yusuf on 13/01/2024 07:33:48
All participants are in all frames. It is not possible to exit a frame in SR. What you probably mean is 'an observer remaining stationary relative to the frame in which the ship was stationary before it started accelerating'.You think it isn't clear because you seem to ignore the word "inertial" there.
I'm just trying to stress clarity here. It doesn't help the discussion to make ambiguous statements.
Post by: hamdani yusuf on 13/01/2024 07:37:51
It does not anywhere state that the twins scenario is paradoxcal.
It does initially call it a paradox, because that's how it is typically named in pop literature, but it it was never actually a paradox, SR would be disproved by being self-inconsistent.
This is literally in the description of the video.
Quote
2:24 Twin's paradox without acceleration (Earth's frame)
Post by: alancalverd on 13/01/2024 09:45:08
2:24 Twin's paradox without acceleration (Earth's frame)This phrase does not make sense.
"Twins" means two identical clocks initially synchronised.
If they don't move relative to each other, they stay in sync, and we have to observe them for some time (at least one tick) to establish that fact.
To establish a relative velocity, we have to accelerate at least one of them.
The consequent loss of synchrony has been measured and corresponds precisely with the relativistic prediction.
Therefore no paradox.
Post by: hamdani yusuf on 13/01/2024 12:14:08
To establish a relative velocity, we have to accelerate at least one of them.What do you think would happen if they are both accelerated equally in magnitude, but in opposite direction?
They will have some relative velocity to each other. What would happen when they are brought back to initial position?
Will they still be synchronized?
Post by: alancalverd on 13/01/2024 16:07:12
Post by: Eternal Student on 13/01/2024 16:27:25
What do you think would happen if they are both accelerated equally in magnitude, but in opposite direction?I don't know. Where is the inertial frame? You need to provide more information.
I have to assume some things. I'll assume there is an inertial frame, F, with respect to which both people can be considered to have equal and opposite accelerations at all times, t, using the co-ordinates of frame F. The situation is then perfectly symmetric for the two people, there is no dependance on which direction the people went in. So the proper time elapsed for each person will be identical and if their clocks were synchronised at the start then they remain synchronised when they finally meet up again.
This is different to the usual Twin paradox situation where only one of the twins would would have experienced an acceleration. The usual twin paradox was clearly asymmetric (not symmetric).
The good news: There will always be a frame of reference where you can consider the people to have equal and opposite motions.
The bad news: However, that frame of reference may not be an inertial frame. If it isn't an inertial frame, then a different result will follow.
Example 1: The Hafele-Keating experiment discussed earlier / maybe in some vaguely related thread. The clocks on the aeroplane showed a positive/negative time difference compared to the clock that stayed on earth depending on whether the aeroplane flew eastward or westward. The frame in which the earth clock was at rest was not an inertial frame, if it had been then eastward or westward travel would have made no difference.
Example 2: In the conventional twins paradox situation, it is tempting to consider a frame of reference where the origin will always be half-way between the travelling and earth-bound twin. If the earth-bound twin considers the travelling twin to have velocity v then this "half-way frame" must have a velocity v/2 relative to the earth-bound twin. On the outward part of the journey the half-way frame was a Lorentz boost of the earth-bound frame by a velocity off-set parameter +v/2 but when the travelling twin turns around at Andromeda (or wherever the furthest point was), that frame has a velocity off-set parameter of -v/2 (it moves the other way). Assuming the earth-bound frame was an inertial frame (which is what we do in the usual Twin paradox) then the "half-way frame" cannot be. All inertial frames are just a consistent Lorentz boost of any other inertial frame and the half-way frame wasn't one consistent Lorentz boost throughout the whole journey. As illustrated in the Hafele-Keating experiment, we are not surprised that westward or easward travel with respect to a non-inertial frame can make a difference to the elapsed time recorded by the clocks.
This is another way in which you could resolve the so-called "paradox" of the twin paradox. The only reference frame in which the motion of both twins is genuinely symmetric (as regards displacement, velocity, acceleration and any other derived motion parameters like dn x(t) / dtn ) is a non-inertial frame. We know from the Hafele-Keating experiment that motion in different directions (eastward or westward) w.r.t. a non-inertial frame really can affect the elapsed times recorded by the clocks.
Best Wishes.
Post by: Halc on 13/01/2024 17:38:18
I'll assume there is an inertial frame, F, with respect to which both people can be considered to have equal and opposite accelerations at all times, t, using the co-ordinates of frame F. The situation is then perfectly symmetric for the two peopleThe situation is perfectly symmetric only if F is the inertial frame in which the two of them are initially stationary.
Quote
The good news: There will always be a frame of reference where you can consider the people to have equal and opposite motions.Only if the people are initially stationary in that frame. If not, then they won't.
Quote
Example 1: The Hafele-Keating experiment discussed earlier / maybe in some vaguely related thread. The clocks on the aeroplane showed a positive/negative time difference compared to the clock that stayed on earth depending on whether the aeroplane flew eastward or westward. The frame in which the earth clock was at rest was not an inertial frame, if it had been then eastward or westward travel would have made no difference.But HK is not an example of identical proper acceleration. OK, it could have been identical coordinate acceleration relative to the rotating frame. If we idealize it (use trains on a uniform-altitude track to eliminate gravitational effects), and use trains that take a day to circumnavigate the globe so the start/stop point is identical for the frames we're using, the Eastbound train will experience less proper acceleration all the way than does the westbound one. They will have identical coordinate acceleration (0 all the way except at beginning/end) relative to the rotating frame, but not identical coordinate acceleration relative to the inertial frame of Earth.
Post by: pzkpfw on 13/01/2024 21:08:10
In this badly drawn spacetime diagram (x) stays home, (y) and (z) fly off in rockets.
A: (y) and (z) apply identical accelerations to leave Earth.
B: (y) applies acceleration to reverse course and go back to Earth
C: later, (z) applies acceleration identical to what (y) used, to reverse and go back to Earth
D: (y) applies acceleration to stop at Earth
E: later, (z) applies acceleration identical to what (y) used, to stop at Earth
F: (x), (y), and (z) have three different ages.
Code: [Select]
.
F|xyz
E|xyZ
|xy z
|xy z
|xy z
D|xY z
C|x y Z
|x y z
B|x Yz
|x yz
|x yz
A|xYZ
--+------------
|At all times of inertial travel, the situation(s) are symmetrical.
All proper accelerations are identical (B=C, D=E).
... but the overall situation is not symmetrical, the three paths through spacetime are different.
Post by: hamdani yusuf on 14/01/2024 00:00:44
I don't know. Where is the inertial frame? You need to provide more information.Let's say the twins started from the earth.
Post by: hamdani yusuf on 14/01/2024 00:15:49
I have to assume some things. I'll assume there is an inertial frame, F, with respect to which both people can be considered to have equal and opposite accelerations at all times, t, using the co-ordinates of frame F. The situation is then perfectly symmetric for the two people, there is no dependance on which direction the people went in. So the proper time elapsed for each person will be identical and if their clocks were synchronised at the start then they remain synchronised when they finally meet up again.We can make any assertion we like to believe, but our confidence in its validity depends on the quality of its supporting explanation.
Halc and many science Youtubers have shown that traveling twin can also have valid observation, and eventually get the same conclusion as the staying twin. He only need to take relativity of simultaneity into account. We don't just say that his observation is invalid, whatever it is, only because he changes his frame of reference.
We can also change the speed of one twin to make the situation no longer perfectly symmetrical. They go to the opposite direction in the same amount of time, say 4 years, then go back home. If your previous explanation is valid, it should also give the correct results in the slightly different situations.
Post by: Eternal Student on 14/01/2024 04:22:45
The situation is perfectly symmetric only if F is the inertial frame in which the two of them are initially stationary.Not sure I agree - but I'll go half-way.
1. Relax the statement you ( @ Halc ) made slightly:
The two people didn't have to be stationary in the frame F initially. If the two people had initial velocities (in Frame F) that were equal in magnitude but opposite in direction then that would be just fine.
Work in the frame F unless told otherwise
Person 1 has initial velocity +vinitial, while person 2 has velocity -vinitial (I'll keep this 1 dimensional for simplicity and not make velocity into vectors). We also have that the accelerations of each person are equal in magnitude but opposite in direction,
a1 (t) = - a2 (t).
From which we obtain that v1 (t) = - v2 (t). [Eqn 0]
The velocities of both people are equal and opposite at all times (in the frame F).
Now we could just jump straight to the usual time-dilation formula for SR. Select two close events, A and B along the path of person 1. We'll choose to have Person 1 use their rest frame centred around themselves to describe co-ordinates of these events A and B. There'll be different co-ordinates for events A and B in frame F.
The small time difference, δt (in Frame F time co-ordinates) between event A and B is related the difference in time co-ordinates allocated by person 1, δT, by the following:
δT = γ δt where γ is the usual gamma factor. [Eqn 1]
(We had to use close events with only a small amount of time difference because the acceleration was of an unspecified nature, person 1 may be accelerating and we can only apply [Eqn 1] with the velocity appearing in the gamma factor equal to the instantaneous velocity).
Since person 1 was using their rest frame, this quantity δT is actually just the proper time elapsed for them between events A and B. Additionally, the instantaneous velocity v(t) that will appear in that gamma factor γ is precisely the velocity of person 1 as determined in Frame F.
We can integrate the expression [Eqn 1] to obtain a total time elapsed for person 1,
ΔT = ∫dT = ∫ γ(t) dt [Eqn 2]
where this is a definite integral performed between limits we'll call tearly and tlater as measured in the time co-ordinate of frame F. It doesn't have to be the start and end of the entire journey, just some times t (in Frame F time co-ordinates) corresponding to two events along the path taken through spacetime by person 1.
(We'll pause to take a minor note that the exact position in space that person 1 has at some time doesn't influence the total elapsed time they experience along any segment of their journey. The RHS of [Eqn 2] involves only the gamma factor and is therefore only infuenced by their velocity during that segment of the journey. So, for example, we could shift their initial position and it doesn't matter provided their motion remains the same).
An expression for the total time elapsed for person 2 can be obtained similarly (exactly the same as [Eqn 1] and [Eqn 2] but γ uses the velocity of person 2 in Frame F]. The γ(t) that appears in the RHS of [Eqn 2] is only dependant on v2 and not on the sign of the velocity, v. So, from [Eqn 0] we know that the RHS will be identical. So the total elapsed times recorded by either person will be identical when we progress from t=0 to t=now as measured in the Frame F.
Now we're all done. Just press the <Play> button in Frame F and watch the people take their paths through spacetime. They started at time t=0 in Frame F and somehow synchronized their stop watches. That's easy if they were in the same initial position but there's an agreed procedure for synchronizing even if they were spatially separated. The usual procedure is to have a light flash released half-way between them and have each person set their stop-watch going when the light flash reaches them. (we would have needed to set off the light flash just before t=0, so let's assume it was). Then they travel for a while and at some later time tlater they compare the elapsed times displayed by their stopwatches somehow. That's also easy if they are in the same place at time tlater but there can be an agreed procedure even if they are spatially separated. The time interval in Frame F was tlater - initial time = tlater - 0 (or just tlater to keep it simple). So we see from [Eqn 2] that both people have recorded the same elapsed time on their stopwatches.
We don't even need to be precise about whose time co-ordinate we are using. [Eqn 2] links the elapsed time for person 1 to the elapsed time in Frame F, one is a monotonic function of the other because γ(t) is always a positive number. The time shown on the stopwatch is the same for person 1 and person 2 at every instant (use any one of the time co-ordinates to declare an instant of time).
If we now inlcude the "minor note" made a little earlier (about our ability to shift the initial positions) then we have the following.... although it may be easier to show it in diagrams....
When we have an inertial Frame F, so that particle 1 takes a path like this:
path1.jpg (15.74 kB . 368x379 - viewed 417 times).... or whatever you want.
Then provided particle 2 takes a path like this:
path2.jpg (16.6 kB . 368x379 - viewed 419 times)... where the motion is equal in magnitude but opposite in direction.
Then the proper time elapsed for both paticles will be the same, at every instant of time through that motion.
We don't need the start and end positions of both particles to be the same, they can be wherever you want. Also we don't need the particles to have been at rest in Frame F initially - just moving in opposite directions with the same magnitude.
We can generalise the result even further if we wish: We only needed the gamma factors to be the same at all instants of time. Particle 1 and particle 2 can move at arbitrary angles to each other. If the motion of particle 1 is the same as particle 2 upto some rotation and/or reflection of the frame, then the result holds.
- - - - - - - - - - -
2. I'll stiffen my earlier statement to inlcude that requirement and re-word it is as follows:
I'll assume there is an inertial frame, F, with respect to which both people can be considered to have equal and oppositeWhere motion is understood appropriately: Identical (but directionally opposed) velocities initially along with identical but opposed accelerations at subsequent times.accelerationsmotion at all times, t, using the co-ordinates of frame F. The situation is then perfectly symmetric for the two people, there is no dependance on which direction the people went in.....
- - - - - -
This post is too long, I won't go through the minor details related to the rest of your post, it hardly matters and it isn't sensible to side-track the OP any further.
Best Wishes.
Post by: hamdani yusuf on 14/01/2024 07:43:29
traveling twin can also have valid observation, and eventually get the same conclusion as the staying twin. He only need to take relativity of simultaneity into account. We don't just say that his observation is invalid, whatever it is, only because he changes his frame of reference.We only need to explain how much his changes of reference frame affect his calculated age of the other twin.
So far, I haven't produced my own explanation for the twin paradox. I only cited various sources which I thought interesting or plausible, and then explored their implications, and found out how far they can be extrapolated until they break down and give nonsensical or clearly wrong results.
Post by: Origin on 14/01/2024 19:27:45
We only need to explain how much his changes of reference frame affect his calculated age of the other twin.Still not able to figure out why the twin paradox isn't actually a paradox?
So far, I haven't produced my own explanation for the twin paradox. I only cited various sources which I thought interesting or plausible, and then explored their implications, and found out how far they can be extrapolated until they break down and give nonsensical or clearly wrong results.
Post by: hamdani yusuf on 14/01/2024 21:47:55
If you think you can, please let us know. Let's start with this.We only need to explain how much his changes of reference frame affect his calculated age of the other twin.Still not able to figure out why the twin paradox isn't actually a paradox?
So far, I haven't produced my own explanation for the twin paradox. I only cited various sources which I thought interesting or plausible, and then explored their implications, and found out how far they can be extrapolated until they break down and give nonsensical or clearly wrong results.
We can also change the speed of one twin to make the situation no longer perfectly symmetrical. They go to the opposite direction in the same amount of time, say 4 years, then go back home. If your previous explanation is valid, it should also give the correct results in the slightly different situations.Let's make the staying twin in previous scenario move at 0.5c in the opposite direction of Alpha Centauri. To be consistent, the twin traveling to Alpha Centauri and back moves at 0.999c. How do you analyze the age of one twin from the perspective of the other twin?
Post by: Origin on 14/01/2024 22:30:19
If you think you can, please let us know. Let's start with this.It has already been discussed. The traveling twin accelerates to an inertial frame that is different than the at home twin and after the trip he then decelerates back to the at home twins inertial frame.
Post by: hamdani yusuf on 15/01/2024 16:26:12
Let's start with this.Let's make a simpler case. One twin stay on earth, while another one travels to Alpha Centauri 4 light years away and back at 0.999c, just like before. One more twin travels with the second one, but only up to midway, and then returns to earth, and then turns around again to midway, and then finally returns to earth. According to earth observer, both travelling twins always move at speed 0.999c during their 8 years plus journeys, which makes them younger by gamma factor around 22.4.
But according to the first travelling twin, the second travelling twin moves relative to him for half of the journey, which should produce time dilation. How should their calculations be reconciled?
Post by: alancalverd on 15/01/2024 17:04:18
both travelling twins always move at speed 0.999cNot true. The fundamental error of almost everyone who talks about a paradox is to forget that a change of velocity is an acceleration. Even if you could have instantaneous acceleration, "go there at c and come back at c" is two different velocities.
Post by: Origin on 15/01/2024 19:40:59
Let's make a simpler case.That isn't a simpler case. The most simple case is a one way trip to another star or point in space.
The scenario is not important anyway since you will never figure out what is going on, you never reach a conclusion, you just go round and round and get more confused as your thread goes on.
Post by: Eternal Student on 16/01/2024 00:35:54
But according to the first travelling twin, the second travelling twin moves relative to him for half of the journey, which should produce time dilation.It will - but that's not the only thing that influences the total time Emma would allocate to Fred. The number and location of Emma and Fred's changes in motion will also be important.
Exactly as you stated here....
...traveling twin(s) can also have valid observation, and eventually get the same conclusion as the staying twin. He only need to take relativity of simultaneity into account.And relativitity of simultaneity includes treating the changes that follow when a twin changes direction.
See post #42, https://www.thenakedscientists.com/forum/index.php?topic=86675.msg707537#msg707537
One of your twins (triplets? since there were 3 twins?), makes 3 changes in direction and sweeps out some events. Another makes only 1 change of direction. The earth twin made no changes. The locations of every other twin relative to a twin who was changing direction is a complicated mess - but you could spend the time to identify it all, if you want.
Anyway, you would see that the total time that Emma allocates to Fred's total journey depends on quite a few things, including the number of -, and the location of -, changes in direction of motion that Fred and Emma may have had.
according to the first travelling twin, the second travelling twin moves relative to him for half of the journey,Simply knowing that Fred had some motion relative to Emma for half the total journey is not enough information. Emma's allocation of time for Fred depends on a bunch of things.
- - - - - - -
Overall, it's easier to solve the problem a different way (avoid working in Emma's co-ordinates as much as possible).
(i) Draw a spacetime diagram that shows everyones journey through spacetime - use the co-ordinates of the earth frame for this because it's easier.
(ii) Measure space-time intervals between important events. We know that's an invariant in any other inertial reference frame. Along appropriate segments and for the appropriate twin these space-time intervals become purely time intervals in the rest frame of that twin. That's the proper time elapsed for that twin and recorded on their stopwatch. Add up the elapsed proper time for each twin along all the segments involved in their own journey to get their total elapsed time on their stopwatch. Compare the final results.
Best Wishes.
Post by: hamdani yusuf on 16/01/2024 02:07:37
It's numerically simpler, since there is only one speed of the journey relative to the earth observer.Let's make a simpler case.That isn't a simpler case. The most simple case is a one way trip to another star or point in space.
The scenario is not important anyway since you will never figure out what is going on, you never reach a conclusion, you just go round and round and get more confused as your thread goes on.
I'll let competing ideas compete, and let the best idea win. They don't have to be perfect, but I'll stick to the best one for the time being.
My criteria for best idea is effectiveness and efficiency, which in this case can be seen as generality and simplicity, respectively. The idea should be still applicable for some variations of the original thought experiment without giving clearly wrong or inconsistent results. When there are some ideas passing this first test, then apply Occam's razor to select the simplest one, which means that it uses least assumptions.
Post by: hamdani yusuf on 16/01/2024 02:13:00
It may sound unintuitive, but if you can recite a section of textbook verbatim, you don't necessarily understand it.Bad idea to reference your common sense or intuitions when discussing relativity that you obviously don't understand.Here's what understanding means.QuoteGregory Chaitin propounds a view that comprehension is a kind of data compression.[19] In his essay "The Limits of Reason", he argues that understanding something means being able to figure out a simple set of rules that explains it. For example, we understand why day and night exist because we have a simple model?the rotation of the earth?that explains a tremendous amount of data?changes in brightness, temperature, and atmospheric composition of the earth. We have compressed a large amount of information by using a simple model that predicts it. Similarly, we understand the number 0.33333... by thinking of it as one-third. The first way of representing the number requires five concepts ("0", "decimal point", "3", "infinity", "infinity of 3"); but the second way can produce all the data of the first representation, but uses only three concepts ("1", "division", "3"). Chaitin argues that comprehension is this ability to compress data. This perspective on comprehension forms the foundation of some models of intelligent agents, as in Nello Cristianini's book "The shortcut", where it is used to explain that machines can understand the world in fundamentally non-human ways.
https://en.wikipedia.org/wiki/Understanding#As_a_model
You need to compress the information so you can generalize it and apply the same idea in some different situations.
Post by: alancalverd on 16/01/2024 10:29:15
Similarly, we understand the number 0.33333... by thinking of it as one-third.So how do we "understand" 1.414213......, 3.141459..... 2.71828..... or any other irrational number?
Post by: hamdani yusuf on 16/01/2024 13:14:44
I mentioned speed instead of velocity.both travelling twins always move at speed 0.999cNot true. The fundamental error of almost everyone who talks about a paradox is to forget that a change of velocity is an acceleration. Even if you could have instantaneous acceleration, "go there at c and come back at c" is two different velocities.
Post by: hamdani yusuf on 16/01/2024 13:19:40
By memorizing mathematical operations like square root, exponentiation, integration, etc. Then apply them to some natural numbers to get those irrational number algorithmically.Similarly, we understand the number 0.33333... by thinking of it as one-third.So how do we "understand" 1.414213......, 3.141459..... 2.71828..... or any other irrational number?
Post by: Origin on 16/01/2024 13:24:58
I'll let competing ideas compete, and let the best idea win. They don't have to be perfect, but I'll stick to the best one for the time being.Great. What is the best one?
Post by: alancalverd on 16/01/2024 17:42:47
By memorizing mathematical operations like square root, exponentiation, integration, etc. Then apply them to some natural numbers to get those irrational number algorithmically.I said "understand", not "calculate".
Post by: alancalverd on 16/01/2024 17:47:17
I mentioned speed instead of velocity.And there's your misunderstanding. To go there at speed a and return at speed a, your velocity has changed by -2A
where A is a vector of magnitude a and direction "from here to there", so you have accelerated.
Post by: Eternal Student on 16/01/2024 20:29:56
Quote
Alancalverd said: how do we "understand" 1.414213......, 3.141459..... 2.71828..... or any other irrational number?
Hamdani replied: By memorizing mathematical operations like square root, exponentiation, integration, etc....
So just memorising some information is sometimes an acceptable way to understand?
Despite Gregory Chaitin's view of comprehension, you don't always have to introduce concepts and some model to compress the information?
It's hard to say what human understanding is.
If you can predict something and also use it to acheive results you wanted, perhaps that's a demonstration of understanding. So tennis players understand the motion of a ball. A physicist using Newton's law also has some understanding of the motion of a ball. However, the two ways of understanding probably weren't the same. It's unlikely you could identify neurological processes occuring in the tennis player that correspond to performing some numerical calculation.
There are other theories describing what understanding might, especially what "knowledge" might be. In the theory of social constructivism, knowledge is not located in one individual. Knowledge is located in society. Language is important and there can be a specific set of vocabulary, a Lexicon, that accesses knowledge in society. So you could trade an abstract object like irrational numbers for an object that, while equally abstract, society has made more tangible as a form of knowledge and understanding. Some of the vocabulary you've used like "exponentiation" and "integration" has been key. There's been a trade between some object you wished to understand (irrational numbers) and some knowledge and understanding of abstract objects that society has. Although "exponentiation" and "integration" may seem like only two things, there's really no way to count how many things, ideas or concepts were involved and synthesised together when society came to an understanding of integration and exponentiation.
You may have taken a single abstract object (irrational numbers) and replaced it with more concepts than if you had just not tried to understand it in this way. None the less, it seems more understood, it can be used etc. This is quite different to Chaitin's view of understanding where he implies that if less concepts are involved, the better the understanding is likely to be.
Best Wishes.
Post by: hamdani yusuf on 17/01/2024 09:57:46
The one which can give consistent answers for original twin paradox, the twins travelling in opposite direction, and also twin that changes frame of reference several times. It's yet to be demonstrated here.I'll let competing ideas compete, and let the best idea win. They don't have to be perfect, but I'll stick to the best one for the time being.Great. What is the best one?
Post by: hamdani yusuf on 17/01/2024 10:01:20
The triplet paradox!
Quote
We will finally resolve the twin's paradox with complete intuition!In the summary, he says that the key is the relativity of simultaneity.
Chapter:
00:00 Intro
00:45 Why you don't understand Twin's paradox
1:28 Einstein's clock synchronisation
2:30 What do the brothers see?
3:14 What does the sister see?
4:46 The first half of twin's paradox
5:30 The relativity of simultaneity
7:53 Relativity of simultaneity equation
10:47 Resolving the first half of twin's paradox
12:20 It's NOT the acceleration!
14:24 Who is accelerating?
16:38 Resolving twin's paradox (What the brothers see)
17:12 Resolving twin's paradox (What the sister sees)
19:31 Summary
Post by: hamdani yusuf on 17/01/2024 10:13:19
Understanding only needs you to know how to get the final result, without having to produce the exact final result. If you don't know ho to get it, it means you haven't understood it.By memorizing mathematical operations like square root, exponentiation, integration, etc. Then apply them to some natural numbers to get those irrational number algorithmically.I said "understand", not "calculate".
Post by: hamdani yusuf on 17/01/2024 10:15:36
Does time dilation depend on velocity?I mentioned speed instead of velocity.And there's your misunderstanding. To go there at speed a and return at speed a, your velocity has changed by -2A
where A is a vector of magnitude a and direction "from here to there", so you have accelerated.
Post by: hamdani yusuf on 17/01/2024 10:18:45
So just memorising some information is sometimes an acceptable way to understand?Without memory, you won't understand anything. It's necessary, but inadequate for understanding. You are missing the word "then" in my statement. That's why you sound surprised. I suppose it's unintentional.
Post by: hamdani yusuf on 17/01/2024 10:26:21
You may have taken a single abstract object (irrational numbers) and replaced it with more concepts than if you had just not tried to understand it in this way.You would need infinite amount of information bits to express the exact value of irrational numbers in decimal. On the other hand, you can express it in finite amount of information bits to express them if you understand how to relate them to more familiar concepts.
Post by: Halc on 17/01/2024 12:19:26
All the valid explanations/techniques do that.Great. What is the best one?The one which can give consistent answers for original twin paradox, the twins travelling in opposite direction, and also twin that changes frame of reference several times.
I mean, you're not going to find a you-tube video that gives the specific answer for the scenario you just made up, but using the methods as explained in the valid videos, you'll get the same answer in all cases.
It's yet to be demonstrated here.Many valid explanations have been posted, and they all give the same results. Your claim here is not substantiated. You need to show that the method posted yields inconsistent results, and you've not done that. You don't even try.
Apparently no explanation, however correct, will satisfy you. You will continue to not learn it, and post all these denialist claims.
This guy here thinks he has resolved the twin's paradox with complete intuition.I didn't see him use 'complete intuition' anywhere, but I didn't watch it all. He does leave out some critical frame references, especially when discussing the sync convention, so I find the video likely to confuse someone trying to learn.
If the video says that the key is relativity of simultaneity, that's often true, and is very much key in resolving the way he first describes the paradox. Almost all novices tend to discount RoS. On the other hand, neither of two of the explanations I gave (the interval one that works in the most general case, and the single-frame one that is simplest) needed to reference relativity of simultaneity.
Understanding only needs you to know how to get the final result, without having to produce the exact final result. If you don't know ho to get it, it means you haven't understood it.Agree. Apparently nothing we post can actually make you understand this simplest of relativity illustrations.
In SR, it depends on speed. You're correct here. It's about speed, not velocity.Does time dilation depend on velocity?I mentioned speed instead of velocity.And there's your misunderstanding. To go there at speed a and return at speed a, your velocity has changed by -2A where A is a vector of magnitude a and direction "from here to there", so you have accelerated.
So in your twin going out halfway and back, twice, both travelers have the same speed relative to Earth at all times and thus arrive together back at Earth the same age as each other. All the velocity changes don't matter. What matters is that the speed in that frame is constant.
Note that this is using the 'easy method' I mentioned above.
Post by: alancalverd on 17/01/2024 12:25:13
What matters is that the speed in that frame is constant.But it isn't. At some point you have to slow down, stop, turn round, and accelerate again.
Post by: Origin on 17/01/2024 13:04:22
The one which can give consistent answers for original twin paradox, the twins travelling in opposite direction, and also twin that changes frame of reference several times. It's yet to be demonstrated here.However I see Halc already did and I have to agree with his reply:
Many valid explanations have been posted, and they all give the same results. Your claim here is not substantiated. You need to show that the method posted yields inconsistent results, and you've not done that. You don't even try.Especially the bolded part - you never accept any answer, it is very frustrating trying to have a conversation with someone like that.
Apparently no explanation, however correct, will satisfy you. You will continue to not learn it, and post all these denialist claims.
Post by: hamdani yusuf on 17/01/2024 21:53:55
Many valid explanations have been posted, and they all give the same results. Your claim here is not substantiated. You need to show that the method posted yields inconsistent results, and you've not done that. You don't even try.What I said was a plain fact.
The one which can give consistent answers for original twin paradox, the twins travelling in opposite direction, and also twin that changes frame of reference several times. It's yet to be demonstrated here.
Post by: hamdani yusuf on 17/01/2024 21:54:46
Apparently no explanation, however correct, will satisfy you. You will continue to not learn it, and post all these denialist claims.How do you know? You haven't tried it yet.
Post by: hamdani yusuf on 17/01/2024 22:16:14
I didn't see him use 'complete intuition' anywhere, but I didn't watch it all. He does leave out some critical frame references, especially when discussing the sync convention, so I find the video likely to confuse someone trying to learn.IMO, the explanation in Mahesh' video there is the most general yet that I've seen. It explains the case for triple twin well. It takes into account the effects of acceleration on earth at the beginning and the end of the journey. It also breaks down the turning point into deceleration to stop and acceleration to move in the opposite direction.
If the video says that the key is relativity of simultaneity, that's often true, and is very much key in resolving the way he first describes the paradox. Almost all novices tend to discount RoS. On the other hand, neither of two of the explanations I gave (the interval one that works in the most general case, and the single-frame one that is simplest) needed to reference relativity of simultaneity.
But still, it hasn't explained the case where both twins changed their frame of reference. How their change of reference can cancel out the time difference?
Post by: hamdani yusuf on 17/01/2024 22:20:10
Agree. Apparently nothing we post can actually make you understand this simplest of relativity illustrations.Appearance can be deceiving.
If the video says that the key is relativity of simultaneity, that's often true, and is very much key in resolving the way he first describes the paradox. Almost all novices tend to discount RoS. On the other hand, neither of two of the explanations I gave (the interval one that works in the most general case, and the single-frame one that is simplest) needed to reference relativity of simultaneity.Maybe you are among those novices?
Some of the authors that you disagree with are professional physicists.
Post by: hamdani yusuf on 17/01/2024 22:37:00
In SR, it depends on speed. You're correct here. It's about speed, not velocity.The easy method doesn't even address the core problem in twin paradox, which is the same events seen from the perspective of the travelling twin. Unlike in Lorentz' relativity, the travelling twin is also an equally valid observer in special theory of relativity.
So in your twin going out halfway and back, twice, both travelers have the same speed relative to Earth at all times and thus arrive together back at Earth the same age as each other. All the velocity changes don't matter. What matters is that the speed in that frame is constant.
Note that this is using the 'easy method' I mentioned above.
It's not surprising if you don't find any problem there.
Post by: hamdani yusuf on 17/01/2024 22:45:38
How do they affect time dilation and the total time elapsed in both frame of references?What matters is that the speed in that frame is constant.But it isn't. At some point you have to slow down, stop, turn round, and accelerate again.
Post by: hamdani yusuf on 17/01/2024 22:49:17
However I see Halc already didCan you point out which post?
How do change of reference frame cancel out time difference accumulated from time dilation during the journey?
Post by: hamdani yusuf on 17/01/2024 22:53:44
Especially the bolded part - you never accept any answer, it is very frustrating trying to have a conversation with someone like that.It's the contrary. I accept every answer, including those which disagree with yours. I just want to go one step further, which is finding out the most effective and efficient one.
Post by: pzkpfw on 17/01/2024 23:12:56
Especially the bolded part - you never accept any answer, it is very frustrating trying to have a conversation with someone like that.It's the contrary. I accept every answer, including those which disagree with yours. I just want to go one step further, which is finding out the most effective and efficient one.
It's extremely easy to keep coming up with more and more convoluted scenarios, but a lot of work then for someone like halc to do all the calculations for you.
Why not research (from good sources like University papers, not pop sci youtube videos) how to do the calculations - and work through them yourself? Doing the work, then asking for review would be way more useful.
Post by: Origin on 17/01/2024 23:23:22
It's the contrary. I accept every answerThat is my point and that is the problem.
Post by: hamdani yusuf on 18/01/2024 13:45:27
It's extremely easy to keep coming up with more and more convoluted scenarios, but a lot of work then for someone like halc to do all the calculations for you.I don't think the calculation is especially hard. You can do it easily using a spreadsheet, as long as you know which formula to use in each part of the scenario.
Post by: hamdani yusuf on 18/01/2024 13:48:27
That becomes a problem because you don't follow through the next step, which is evaluating every answer that you have accepted previously to find the best answer in terms of generality and simplicity.It's the contrary. I accept every answerThat is my point and that is the problem.
Post by: Origin on 18/01/2024 15:28:43
which is evaluating every answer that you have accepted previously to find the best answer in terms of generality and simplicity.You never do this, you just have threads that never end, they just go round and round without ever reaching a conclusion.
Post by: hamdani yusuf on 18/01/2024 15:46:38
I'm giving other members the chance to use their best explanation to answer my questions. When the time is up and no one comes up with the best possible answer, I might have to answer them myself.which is evaluating every answer that you have accepted previously to find the best answer in terms of generality and simplicity.You never do this, you just have threads that never end, they just go round and round without ever reaching a conclusion.
Post by: hamdani yusuf on 04/02/2024 08:18:02
Quote
Chapters:Let's see if anyone has objection to the explanation given in this video, which is an improvement of previous video by the same authorauthor, Mahesh Shenoy from Floatheadphysics.
00:00 What is the twin's paradox?
00:48 Why acceleration doesn't solve twin's paradox
2:24 Twin's paradox without acceleration (Earth's frame)
4:42 The traveling frame
7:13 My new website - floatheadphysics (ad)
8:48 Earth's frame again - with the flag
11:38 Travelling frame again - with the flag
13:30 The resolution!
14:45 Relativity of simultaneity
17:02 Isn't the root cause the acceleration?
18:20 What do they 'see'?
In this video, we'll intuitively resolve the twin's paradox. This version of the twin's paradox involves no acceleration. And no, you don't need equivalence principle, and you don't need general relativity to solve it. Twin's paradox can be completely solved using special theory of relativity and the correct usage of relativity of simultaneity.
Post by: Eternal Student on 04/02/2024 16:45:36
Let's see if anyone has objection to the explanation given in this video,Comment #1: It's about half an hour, few people will watch it.
Comment #2: At a glance, it's not significantly different to some of the earlier explanations.
Best Wishes.
Post by: alancalverd on 04/02/2024 21:31:12
Post by: hamdani yusuf on 05/02/2024 05:13:07
Hi.It has been viewed 33 thousand times since it was uploaded 3 weeks ago. I don't think it's few, although it's relative.Let's see if anyone has objection to the explanation given in this video,Comment #1: It's about half an hour, few people will watch it.
Comment #2: At a glance, it's not significantly different to some of the earlier explanations.
Best Wishes.
This one shows some details which are omitted by many earlier videos on twin paradox. Those details let us evaluate the explanation when applied in some different variations of the twin paradox.
Post by: hamdani yusuf on 05/02/2024 05:19:09
Why would anyone want to watch a video about a paradox that doesn't exist? Better to spend a few minutes learning about relativity (where there's no paradox) and how it degenerates to classical mechanics at very low relative velocities.The fact that experts in physics have expressed their disagreements in solving the paradox may trigger curiosity in the mind of some people who still have some level of critical thinking. If you think it's too demanding to watch a 22 minutes video, perhaps this problem is really not for you.
Post by: alancalverd on 05/02/2024 09:52:56
Simultaneity and synchronism are only observed when vrel → 0.
Post by: hamdani yusuf on 06/02/2024 09:38:53
The problem lies with people who persist in calling something a paradox when the explanation has been obvious for almost 100 years.They can also be achieved when relative position=zero to the observer.
Simultaneity and synchronism are only observed when vrel → 0.
Post by: alancalverd on 06/02/2024 17:39:03
Post by: hamdani yusuf on 07/02/2024 02:38:59
No. If A is moving relative to B you can't establish synchronism because the next time the clock ticks, Δx ≠ 0!
When Δx ≠ 0, it doesn't qualify my previous statement.
They can also be achieved when relative position=zero to the observer.
Post by: alancalverd on 07/02/2024 18:15:17
Post by: pzkpfw on 07/02/2024 19:53:28
Post by: alancalverd on 07/02/2024 23:21:19
Post by: hamdani yusuf on 08/02/2024 14:50:08
You miss the point. Two identical clocks might agree at some time, but if they are moving relative to one another, they won't do so before or after that time. Synchronism means continuously agreeing, which is not possible.Are you suggesting that GPS won't work?
Post by: alancalverd on 08/02/2024 21:48:16
Post by: hamdani yusuf on 10/02/2024 14:20:24
Thanks to our understanding of relativity, it works very well.Which means they can be synchronized. It's not impossible.
Post by: hamdani yusuf on 15/02/2024 10:00:22
I have a clock and a watch, both radio-controlled. Immediately after the radio sync phase, if I'm standing still, they can remain mutually synchronised because Δx = 0.If I move, so Δx ≠ 0, I will have accelerated the wristwatch and imposed a relative velocity, so I can't expect them to remain synchronised.What if both accelerated equally in opposite direction?
Post by: alancalverd on 15/02/2024 21:25:29
Post by: alancalverd on 15/02/2024 21:28:57
Which means they can be synchronized. It's not impossible.Not at all. We know the relativistic offsets and can either adjust each clock so that the time signals received at a reference point on Earth appear synchronised, or apply the relativistic correction to the time stamp of each received signal.
Post by: hamdani yusuf on 16/02/2024 21:29:32
Which then makes them synchronized.Which means they can be synchronized. It's not impossible.Not at all. We know the relativistic offsets and can either adjust each clock so that the time signals received at a reference point on Earth appear synchronised, or apply the relativistic correction to the time stamp of each received signal.
Post by: pzkpfw on 16/02/2024 21:58:02
Which then makes them synchronized.Which means they can be synchronized. It's not impossible.Not at all. We know the relativistic offsets and can either adjust each clock so that the time signals received at a reference point on Earth appear synchronised, or apply the relativistic correction to the time stamp of each received signal.
What exactly do you think synchronised means with respect to two clocks?
Post by: hamdani yusuf on 16/02/2024 22:10:57
What exactly do you think synchronised means with respect to two clocks?When they can show the same value at one time, and still show the same value at later time.
Post by: pzkpfw on 16/02/2024 22:22:43
What exactly do you think synchronised means with respect to two clocks?When they can show the same value at one time, and still show the same value at later time.
(Ignoring for now who is deciding (and how) the times they are compared ...)
If the two clocks are in relative movement (the distance between them is changing), will they tick at the same rate (and according to whom)?
Post by: hamdani yusuf on 17/02/2024 08:47:23
If the two clocks are in relative movement (the distance between them is changing), will they tick at the same rate (and according to whom)?According to relativity principle, an observers who keep their position right between those clocks should see them synchronized, based on symmetry.
Post by: pzkpfw on 17/02/2024 18:13:17
If the two clocks are in relative movement (the distance between them is changing), will they tick at the same rate (and according to whom)?According to relativity principle, an observers who keep their position right between those clocks should see them synchronized, based on symmetry.
Between the clocks is one special case, yes. But does that really mean those two clocks were synchronised?
And this is not quite what you earlier said:
They can also be achieved when relative position=zero to the observer.
And ... how does this apply to GPS?
Post by: alancalverd on 18/02/2024 09:08:30
It resolves very simply if you compare observation with relativistic prediction (so far, no discrepancy) and accept that relativity applies for all values of vrel including zero.
Post by: hamdani yusuf on 18/02/2024 09:23:52
Between the clocks is one special case, yes. But does that really mean those two clocks were synchronised?Thinking otherwise would lead to contradiction.
Post by: hamdani yusuf on 18/02/2024 09:29:34
And ... how does this apply to GPS?Send a spacecraft to geostationarily float near the orbit of a GPS satellite. Set the clock the same as the satellite is passing by. Wait until the satellite return to the same spot. Compare the results. Make adjustments as needed.
Post by: alancalverd on 18/02/2024 15:20:10
The why would each clock appear to be running slow when viewed from the other? And wouldn't they both appear slow to the midpoint observer with an identical clock?Between the clocks is one special case, yes. But does that really mean those two clocks were synchronised?Thinking otherwise would lead to contradiction.
What your midpoint observer sees is two clocks, equally wrong.
Send a spacecraft to geostationarily float near the orbit of a GPS satellite.Bit of a problem there. GPS satellites orbit every 12 hours, at about 20,000 km altitude. Geostationary orbit doesn't move, at 36 ,000 km altitude.
But the Haefle-Keating experiment demonstrated the effect to most people's satisfaction, just using an aeroplane.
Post by: pzkpfw on 18/02/2024 19:49:09
Between the clocks is one special case, yes. But does that really mean those two clocks were synchronised?Thinking otherwise would lead to contradiction.
WHAT contradiction? (Are you a dentist?)
And, doesn't this basically mean any two clocks are synchronised? What's even the point then of specifying that clocks are synchronised or not?
Post by: hamdani yusuf on 20/02/2024 12:29:20
You seem to forget about the requirement that the observer keeps his position right between those two clocks.Between the clocks is one special case, yes. But does that really mean those two clocks were synchronised?Thinking otherwise would lead to contradiction.
WHAT contradiction? (Are you a dentist?)
And, doesn't this basically mean any two clocks are synchronised? What's even the point then of specifying that clocks are synchronised or not?
Post by: hamdani yusuf on 20/02/2024 12:31:14
wouldn't they both appear slow to the midpoint observer with an identical clock?Both slow down equally, thus they are still synchronized to each other.
Post by: pzkpfw on 20/02/2024 18:27:22
You seem to forget about the requirement that the observer keeps his position right between those two clocks.Between the clocks is one special case, yes. But does that really mean those two clocks were synchronised?Thinking otherwise would lead to contradiction.
WHAT contradiction? (Are you a dentist?)
And, doesn't this basically mean any two clocks are synchronised? What's even the point then of specifying that clocks are synchronised or not?
No, I am not forgetting the very thing I am responding to. You tend to throw out snippets that contradict your own previous snippets, or lead to consequences that don't make sense. This is one.
Take Alice and Bob passing each other in space, in inertial relative movement.
Alice can consider herself at rest, and Bob is passing at 100 kph.
Bob can consider himself at rest, and Alice is passing at 100 kph.
Alice has a clock that ticks at 1 second per second, but for her, Bob's clock is slow.
Bob has a clock that ticks at 1 second per second, but for him, Alice's clock is slow.
Thus, their clocks cannot be synchronised. This is basic relativity.
Well, yes, you can insert Carol who remains between Alice and Bob, for whom they are both doing 50 kph. For Carol, Alice and Bob's clocks tick at the same rate. (*1)
But does that mean Alice and Bob's clocks ARE in an absolute sense (or can be) synchronised?
Would Alice and Bob agree?
And, if that were true, doesn't that mean you could postulate a Carol for ANY two such clocks? (*2)
Do you think it matters to Alice and Bob if there is a Carol there or not?
Notes:
*1 For Carol, Alice and Bob's clocks will tick slower than hers of course, so you've also just moved the synchronisation issue one step deeper
*2 That's why I made my previous post
Post by: Halc on 20/02/2024 20:27:39
You seem to forget about the requirement that the observer keeps his position right between those two clocks.There is no such requirement. Clocks running in sync is a function of a reference frame, not of observation, location, or even coordinate system (*). 'Clocks being in sync' is meaningless without a frame reference. If two clocks are in sync relative to frame F, that means they read the same value in frame F at all times, which is true regardless of any observer's location or motion. It has nothing whatsoever to do with observation.
In particular, it doesn't mean that any given observer sees both clocks reading the same value.
I do acknowledge that the intended purpose of an observer is often to simply hang a name tag on a frame, so 'according to Carol' becomes shorthand for 'relative to the frame in which Carol is stationary', but 1) it matters not a hoot then where Carol is in that frame, and 2) a rock with 'Carol' painted on it serves the same purpose.
Take Alice and Bob passing each other in space, in inertial relative movement.Your scenario seems to have the clocks meet at a common event, but to generalize a bit, and to remove all unnecessary observers, consider flat spacetime containing two inertial clocks at arbitrary locations, moving at arbitrary velocities, and set to arbitrary times.
Alice can consider herself at rest, and Bob is passing at 100 kph.
Bob can consider himself at rest, and Alice is passing at 100 kph.
Alice has a clock that ticks at 1 second per second, but for her, Bob's clock is slow.
Bob has a clock that ticks at 1 second per second, but for him, Alice's clock is slow.
Thus, their clocks cannot be synchronised. This is basic relativity.
Well, yes, you can insert Carol who remains between Alice and Bob, for whom they are both doing 50 kph. For Carol, Alice and Bob's clocks tick at the same rate.
In exactly one frame C will those clocks be moving in equal and opposite velocities. There will be events EA and EB on the respective worldlines where each clock is closest in C to the other clock. If the spatial distance in C between those two events is less than the difference in time that each clock reads at those respective clocks, then there will be a set of inertial frames in which both clocks run in sync. If the time difference is not less than that limit, then in no frame will this be true.
* A coordinate system is a reference frame with the addition of specification of an origin and axis orientations, so I'm saying that the sync of clocks is not dependent on those selections, only a function of the frame selection.
Post by: alancalverd on 20/02/2024 21:05:11
Both slow down equally, thus they are still synchronized to each other.But each appears to be running slow from the point of view of the other, and neither is in sync with the midpoint observer's clock. So none is synchronised with any other. It just happens that, seen from the midpoint, both departing clocks are equally wrong.
Post by: pzkpfw on 20/02/2024 21:06:19
Take Alice and Bob passing each other in space, in inertial relative movement.
Alice can consider herself at rest, and Bob is passing at 100 kph.
Bob can consider himself at rest, and Alice is passing at 100 kph.
Alice has a clock that ticks at 1 second per second, but for her, Bob's clock is slow.
Bob has a clock that ticks at 1 second per second, but for him, Alice's clock is slow.
Thus, their clocks cannot be synchronised. This is basic relativity.
Well, yes, you can insert Carol who remains between Alice and Bob, for whom they are both doing 50 kph. For Carol, Alice and Bob's clocks tick at the same rate.
Your scenario seems to have the clocks meet at a common event, ...
No, I don't think it does.
... but to generalize a bit, and to remove all unnecessary observers, consider flat spacetime containing two inertial clocks at arbitrary locations, moving at arbitrary velocities, and set to arbitrary times.
In exactly one frame C will those clocks be moving in equal and opposite velocities. ...
Yes, the simple scenario implies this. Though I named two velocities to try to make it less abstract for the OP.
(Personally, I think the OP is diving off into Twins' Paradox etc, with ever increasing complexity, when they don't really grasp the significance of the basics of relativity. I think the explanations need to get simpler, not more complex.)
Post by: hamdani yusuf on 21/02/2024 03:00:28
I do acknowledge that the intended purpose of an observer is often to simply hang a name tag on a frame, so 'according to Carol' becomes shorthand for 'relative to the frame in which Carol is stationary', but 1) it matters not a hoot then where Carol is in that frame, and 2) a rock with 'Carol' painted on it serves the same purpose.That's good to know.
Post by: hamdani yusuf on 21/02/2024 03:02:38
No, I am not forgetting the very thing I am responding to. You tend to throw out snippets that contradict your own previous snippets, or lead to consequences that don't make sense. This is one.It looks like we're talking pass each other. Let's start with the basic common ground. How do you define synchronized clocks?
Take Alice and Bob passing each other in space, in inertial relative movement.
Alice can consider herself at rest, and Bob is passing at 100 kph.
Bob can consider himself at rest, and Alice is passing at 100 kph.
Alice has a clock that ticks at 1 second per second, but for her, Bob's clock is slow.
Bob has a clock that ticks at 1 second per second, but for him, Alice's clock is slow.
Thus, their clocks cannot be synchronised. This is basic relativity.
Well, yes, you can insert Carol who remains between Alice and Bob, for whom they are both doing 50 kph. For Carol, Alice and Bob's clocks tick at the same rate. (*1)
But does that mean Alice and Bob's clocks ARE in an absolute sense (or can be) synchronised?
Would Alice and Bob agree?
And, if that were true, doesn't that mean you could postulate a Carol for ANY two such clocks? (*2)
Do you think it matters to Alice and Bob if there is a Carol there or not?
Notes:
*1 For Carol, Alice and Bob's clocks will tick slower than hers of course, so you've also just moved the synchronisation issue one step deeper
*2 That's why I made my previous post
The same question for Alan.
Both slow down equally, thus they are still synchronized to each other.But each appears to be running slow from the point of view of the other, and neither is in sync with the midpoint observer's clock. So none is synchronised with any other. It just happens that, seen from the midpoint, both departing clocks are equally wrong.
Post by: hamdani yusuf on 21/02/2024 03:05:43
In exactly one frame C will those clocks be moving in equal and opposite velocities.That's only true if we were living in a one space dimension universe.
Post by: pzkpfw on 21/02/2024 05:04:50
It looks like we're talking pass each other. Let's start with the basic common ground. How do you define synchronized clocks?
First, they must tick at the same rate as each other.
Second, some process will have been used to set them to a known start time. (Though this can be relaxed as long as their time as at an agreed event is known; their offsets can be accounted for.)
Where we differ is your claim that a special observer (i.e. one between the two clocks, for whom the clocks tick at the same rate) can claim they are synchronised. But no, to claim the clocks ARE synchronised - it's the clocks themselves (or observers at rest with them) that need to agree they tick at the same rate. That means they must be at rest with respect to each other, i.e. not like my Alice and Bob, regardless of what Carol says.
Post by: alancalverd on 21/02/2024 09:10:22
Let's start with the basic common ground. How do you define synchronized clocks?Two clocks are synchronised if A knows what time B is showing, simply by looking at his own clock.
The same question for Alan.
If the clocks are identical, this can only be the case if there is no relative motion between them. Where there is relative motion, he must apply a relativistic correction and thus needs additional information to determine the time shown at B.
Remember, the whole point of "gentlemen, synchronise your watches" is to ensure that the army, navy and air force hit the target in the required sequence tomorrow, so there is an assumption of adequate identicality and negligible relative velocity between clocks. Nowadays we can guarantee a high degree of identicality by using atomic clocks, and measure the relativistic discrepancy at fairly small velocities. Hence no "paradox".
Post by: Halc on 21/02/2024 13:32:16
How do you define synchronized clocks?I notice I do not get asked. Am I considered so correct that there's no trolling my mistakes? I do assure you that I make mistakes.
The same question for Alan.
'Synchronized clocks' means that the clocks read the same value at any given time. Due to relativity of simultaneity,, the 'at the same time' part of that definition is ambiguous in the absence of a frame reference.
To be synced relative to a frame means that the two clocks read the same value at all times in that frame. This is why Einstein put out his sync convention, which is a way to get two clocks in sync relative to some frame, but that convention only works for clocks stationary in the referenced frame. There are other conventions that can be used for moving clocks, but clocks cannot be synced in any frame in which they 'tick at' different rates.
To be synced at an event means that both clocks read the same value (typically one being set to the time of the other, or both zeroed) at some event at which both clocks are present. This is an objective sync. It doesn't persist over time, and it is frame independent.
Two clocks are synchronised if A knows what time B is showing, simply by looking at his own clock.You give an epitemological definition, one I've never seen used. The definition as worded allows clocks to run at different rates.
Quote
If the clocks are identicalWhat do you mean identical? What if only one is pink? If they don't both measure proper time, then are they really clocks?
Quote
this can only be the case if there is no relative motion between them.One can only know the time the other clock says if it is relatively stationary? Have fun justifying that.
Quote
Where there is relative motion, he must apply a relativistic correction and thus needs additional information to determine the time shown at B.So if clock B is shot from a gun from Earth at time zero (on both clocks) at 0.866c, later on, the A (the Earth observer) looks at his clock and it says 2 hours, he knows that right now in his frame, B's clock reads 1 hour. Since he knows the time on the B clock, the clocks are in sync by your definition.
I am sure that Hamdani will hang on your words, similar to his attraction to hobbyist you-tubes. Clearly he already does, and this will totally reinforce that preference.
First, they must tick at the same rate as each other.Possibly a frame dependent requirement. They might tick at the same rate in one frame, but not another.
Quote
Second, some process will have been used to set them to a known start time.Not the same time? If not, then what's the purpose of Einstein's sync conventions? The clocks, being relatively stationary, already by definition tick at the same rate. The convention serves a different purpose than to get the clocks synced relative to that frame in which they are mutually stationary?
If you want me to shut up, I'm all for it. If I'm wrong about any of this, say where. I don't correct Hamdani because he has no desire to learn. I correct Alan because I disagree with almost everything he says on this subject.
You and I seem to differ on definitions. I say A & B are potentially synced in the Carol frame (both are running at the same rate, even if dilated. Your definition seems to require that they're synced in either the A or B frame. This is why I say the phrase 'clocks are in sync' is meaningless without a frame reference.
An assertion that is flat out wrong. If you disagree, then either come up with a 2D or 3D example of two clocks at different velocities and positions where there is no frame in which they have equal and opposite velocities, or an example where this is true in more than one inertial frame. If you can't do that, then your assertion is vacuous.In exactly one frame C will those clocks be moving in equal and opposite velocities.That's only true if we were living in a one space dimension universe.
I'm giving other members the chance to use their best explanation to answer my questions. When the time is upThat time has long since come and gone. Based on your other topics going on for years with zero conclusion, the time will never be up.
Post by: paul cotter on 21/02/2024 15:05:17
Post by: alancalverd on 21/02/2024 19:17:58
One can only know the time the other clock says if it is relatively stationary? Have fun justifying that.Not what I wrote. If you can only see clock A, you cannot know the time shown on B's clock (however "identical" they may be) unless you know their relative velocity.
Something to do with relativity. I won't bore you with the details as you set it out very neatly in your next paragraph!
Post by: hamdani yusuf on 22/02/2024 13:06:30
Let's put the context back to the discussion. If an observer see two clocks tick at the same rate, and both are moving at the same speed relative to him, regardless of the direction, he can say that those clocks are synchronized to each other. Assume no gravitational effect.If the two clocks are in relative movement (the distance between them is changing), will they tick at the same rate (and according to whom)?According to relativity principle, an observers who keep their position right between those clocks should see them synchronized, based on symmetry.
Between the clocks is one special case, yes. But does that really mean those two clocks were synchronised?
And this is not quite what you earlier said:They can also be achieved when relative position=zero to the observer.
And ... how does this apply to GPS?
Post by: hamdani yusuf on 22/02/2024 13:11:08
I am sure that Hamdani will hang on your words, similar to his attraction to hobbyist you-tubes. Clearly he already does, and this will totally reinforce that preference.How did you come up with that conclusion?
Post by: hamdani yusuf on 22/02/2024 13:11:54
I do assure you that I make mistakes.Which one?
Post by: hamdani yusuf on 22/02/2024 13:22:51
I don't correct Hamdani because he has no desire to learn. I correct Alan because I disagree with almost everything he says on this subject.How can you read my mind?
I analyzed different explanations for the twin paradox from various sources. So far, Mahesh' explanation is the most general, effective and efficient one, compared to the alternatives. It consistently includes the frame changes at the beginning and the end of the journey, unlike Minutephysics'.
If you think you have a better explanation, please describe it. What's wrong with Mahesh' explanation?
Post by: hamdani yusuf on 22/02/2024 13:28:23
That time has long since come and gone. Based on your other topics going on for years with zero conclusion, the time will never be up.I'm giving you the chance to give your best shot. Take your time, no need to hurry. Good things come to those who wait.
Some of my other threads already have best answer. Which means the number of conclusions are more than zero. I assume you know how to count.
Post by: hamdani yusuf on 22/02/2024 22:02:02
With enough data, patterns appear.Which data took your attention the most?
Post by: hamdani yusuf on 22/02/2024 22:15:16
I'm glad you found one you like. No video is tagged with that name, but I'm guessing the one in post 184.This one, I added his name in the post.
Why twin's paradox is NOT about acceleration?It should show my intention to learn, but somehow you can't see it.QuoteChapters:Let's see if anyone has objection to the explanation given in this video, which is an improvement of previous video by the same author, Mahesh Shenoy from Floatheadphysics.
00:00 What is the twin's paradox?
00:48 Why acceleration doesn't solve twin's paradox
2:24 Twin's paradox without acceleration (Earth's frame)
4:42 The traveling frame
7:13 My new website - floatheadphysics (ad)
8:48 Earth's frame again - with the flag
11:38 Travelling frame again - with the flag
13:30 The resolution!
14:45 Relativity of simultaneity
17:02 Isn't the root cause the acceleration?
18:20 What do they 'see'?
In this video, we'll intuitively resolve the twin's paradox. This version of the twin's paradox involves no acceleration. And no, you don't need equivalence principle, and you don't need general relativity to solve it. Twin's paradox can be completely solved using special theory of relativity and the correct usage of relativity of simultaneity.
On the other hand, if you are already convinced that your current explanation is the correct one, and the others are wrong, you won't be able to learn.
Post by: alancalverd on 22/02/2024 22:19:27
and both are moving at the same speed relative to himThere's the catch. He needs to know something more than just what the clocks are telling him.
Post by: Eternal Student on 23/02/2024 03:36:02
I'm giving you the chance to give your best shot.I think a lot of people have already made a lot of attempts to explain and more generally just to discuss the twins paradox.
The main issue isn't really about being able to predict something or explain something in one way that is somehow better than another way. The twins paradox is something all physicists will explore several times over in their career and they will see something slightly differently each time if they're lucky.
Perhaps it's just about being human and reconciling how Nature seems to be, or ought to be, compared to how it actually might be. I don't know. I suspect it's the investigation that is worth doing rather than coming up with a definitive "best answer" for some scenario. Whatever best video or explanation you ( @hamdani yusuf ) decide upon now, that will probably change in a few years, if you're lucky.
It also probably won't be the best explanation for someone else, we're all different. In the kindest possible way, I hope they do disgaree with your opinions and are lucky enough to have their own journey trying to understand the Twins paradox and deciding whose frame of reference is worthy of more attention than some other frame. Ater a while of worrying if everything works in everyones frame, you often come round to recognising that it was never all that important to assume that time is some important variable. Time isn't something you need to understand or deserves any special attention. In SR there is only a space-time interval that is important and will be invariant. Trying to worry about where different observers have their disagreements over the passage of time for Alice or Bob may be putting the emphasis in all the wrong places.
Best Wishes.
Post by: alancalverd on 23/02/2024 08:34:36
Perhaps it's just about being human and reconciling how Nature seems to be, or ought to be, compared to how it actually might be.One of the enduring problems of science!
From a human perspective, a flat earth, geocentric universe, static species and synchronous travelling clocks are "good enough" and Newtonian (but not Aristotelian) mechanics put a man on the moon, so it is obvious that Hipparchus, Copernicus, Darwin and Einstein were Sinning against God (a "good enough" explanation of the blindingly obvious) by suggesting that things might be otherwise.
Kruger-Dunning Syndrome affects us all to some extent, but once you have appreciated the Pound-Rebka and Haefle-Keating experiments (why do critical advances in psychology and physics have hyphens?) or used a GPS navigator, you have to set aside such childish things and realise that twins or clocks only remain synchronised if they don't move relative to one another, and "good enough" may not be universally true.
The paradox is why anyone thinks it is a paradox. And the answer is inertia and vanity.
Post by: hamdani yusuf on 23/02/2024 08:47:34
Yes, he needs to know the speeds of both clocks, which can be obtained from several methods.and both are moving at the same speed relative to himThere's the catch. He needs to know something more than just what the clocks are telling him.
Post by: alancalverd on 23/02/2024 10:34:11
I am unaware of any other useful definition.
The best way of A knowing their relative velocity is to assume that their clocks are identical and measure the redshift of B's clock signals. Except that he doesn't know the gravitational potential difference between them....so as ES implies, it's better to forget about time and twins altogether!
Post by: hamdani yusuf on 25/02/2024 09:24:58
The paradox is why anyone thinks it is a paradox. And the answer is inertia and vanity.Something is called a paradox if it seems like there's a contradiction, but a closer look can determine that there are errors in the line of thought leading to that contradiction.
On the other hand, if the contradiction is inherently within the described situation, and no error can be found in the reasoning, then the conclusion is to reject the proposition. It's called proof by contradiction.
Twin paradox is called paradox by those who accept STR. They think that it doesn't cause a real contradiction.
On the other hand, critics of STR think that twin paradox actually demonstrate a contradiction, instead of just a paradox. It causes them to reject STR.
Post by: alancalverd on 25/02/2024 14:46:21
Most human experience involves v << c, so we have a "good enough" and specific concept of "twins" that actually has no general validity.
What paradox?
Post by: alancalverd on 25/02/2024 21:00:57
the coordination of something like video and its soundtrackWe use the clapper board to mark the beginning of a sequence, then set the studio metronome to ensure that the music reaches its climactic discord when the hero dies, or whatever, 28.4 seconds later. If the studio clock doesn't count at the same rate as the video clock, you rather lose the dramatic effect. Or to put it another way, if your downbeat coincides with the clapper, you should be able to tell the number on the video timestamp by just looking at the studio clock at any time thereafter.
According to Einstein and experiment, it doesn't work if the video was recorded in orbit, even if the spacecraft carried the actual studio clock.
Studio band work is difficult enough when vrel = 0, thank you.
Post by: hamdani yusuf on 28/02/2024 12:52:04
That would be a seeming paradox, not an actual paradox.W. V. O. Quine (1962) distinguished between three classes of paradoxes.
https://en.m.wikipedia.org/wiki/Paradox
Post by: alancalverd on 28/02/2024 13:13:31
Any model is a mapping, and the characteristic of mapping is loss of dimension.
Now we have an apparently complete model of the behavior of clocks, twins, spectral lines or whatever, from relativity. If we map that behavior onto a model where vrel << c we can, for most practical purposes, ignore the loss of synchronism (using my definition of that word).
But in cases where vrel → c we cannot accurately construct the behavior of twins, clocks etc from observations made at vrel << c by assuming no loss of synchronism.
Post by: hamdani yusuf on 28/02/2024 13:14:33
My favorite are the articles claiming STR does not predict the Sagnac effect, and it's pretty trivial to spot the errors in these papers. Why does light travel west faster than it does east? Can you explain that in STR terms without violating its premise about the constancy of light speed?I asked Gemini. does light travel west faster than it does east?
Quote
No, the speed of light in a vacuum is constant regardless of the direction it travels, whether west, east, or any other direction. This is a fundamental principle of physics established by the theory of special relativity.
It's true that Earth rotates eastward, and objects on its surface, like airplanes, can travel faster eastward than westward due to this rotation. However, this doesn't affect the speed of light itself. Light travels independently of the motion of the source or observer.
There might be some confusion due to the Sagnac effect, which is a phenomenon observed in rotating reference frames. It predicts a minuscule difference in the travel time of light depending on its direction relative to the rotation. However, this effect is incredibly small and only significant in very precise measurements with extremely sensitive equipment.
For all practical purposes and everyday situations, the speed of light remains constant and independent of direction.
Post by: Halc on 28/02/2024 15:41:14
I asked Gemini. does light travel west faster than it does east?Always a good place to find wrong answers that sound authoritative.
Quote from: Gemini
No, the speed of light in a vacuum is constant regardless of the direction it travels, whether west, east, or any other direction. This is a fundamental principle of physics established by the theory of special relativity.This statement is wrong. The speed of light is posited to be constant only in an inertial frame in Minkowskian spacetime. In such a coordinate system, east is an undefined direction. If you disagree, then relative to the inertial frame of Earth, which direction is east? Why is no star labeled the east star?
'East' has meaning in a rotating reference frame, and Gemini eventually gets to that:
Quote from: Gemini
There might be some confusion due to the Sagnac effect, which is a phenomenon observed in rotating reference frames. It predicts a minuscule difference in the travel time of light depending on its direction relative to the rotation.Confirming my statement. In a rotating frame, light travels west faster than it does east, and only in said rotating frame is east and west defined as a valid direction.
Quote from: Gemini
However, this effect is incredibly small and only significant in very precise measurements with extremely sensitive equipment.With enough angular speed or large enough radius, the ratio of light travel speeds can be arbitrarily high.
Quote from: Gemini
For all practical purposes and everyday situations, the speed of light remains constant and independent of direction.So usage of the effect in airplanes doesn't constitute a practical purpose, according to Gemini.
Post by: hamdani yusuf on 01/03/2024 02:36:22
Quote from: Gemini
For all practical purposes and everyday situations, the speed of light remains constant and independent of direction.
So usage of the effect in airplanes doesn't constitute a practical purpose, according to Gemini.
Is there any example where airplanes usage changes the speed of light?
Post by: alancalverd on 01/03/2024 16:59:09
From Wikipedia:
Quote
Many tens of thousands of RLGs are operating in inertial navigation systems and have established high accuracy, with better than 0.01?/hour bias uncertainty, and mean time between failures in excess of 60,000 hours.
Post by: hamdani yusuf on 02/03/2024 11:03:41
Ring laser gyroscope.Does it confirm that speed of light isn't constant?
From Wikipedia:QuoteMany tens of thousands of RLGs are operating in inertial navigation systems and have established high accuracy, with better than 0.01?/hour bias uncertainty, and mean time between failures in excess of 60,000 hours.
Post by: alancalverd on 02/03/2024 11:39:39
But the important point here is that, as usual, a chatbot is promulgating a transparent untruth.
Post by: hamdani yusuf on 03/03/2024 04:49:42
Depends on what you mean by speed of light! The RLG works on the basis that the time taken for a photon to get from A back to A via a circular path depends on whether the path itself is rotating.So, in some definitions, speed of light is constant. While in some other definitions, it's not constant?
Post by: hamdani yusuf on 03/03/2024 04:53:27
But the important point here is that, as usual, a chatbot is promulgating a transparent untruth.What's usual now may no longer be usual later on.
Outputs of chatbots are determined by their training data. In this case, its mostly text books, and perhaps some encyclopedia.
Post by: alancalverd on 05/03/2024 10:35:54
There is no evidence of the gradual evolution of truth. Politics, religion, philosophy and every other evil known to Man rely on the growth of a convenient and locally profitable consensus that gradually smothers dissent and persuades people to ignore observation. Goebbels was right.Quotefrom: alancalverd on 02/03/2024 11:39:39What's usual now may no longer be usual later on.
But the important point here is that, as usual, a chatbot is promulgating a transparent untruth.
Post by: hamdani yusuf on 06/03/2024 10:33:48
In the example in the video, the gamma factor is 2, which means the speed is around 0.866c.I'm glad you found one you like. No video is tagged with that name, but I'm guessing the one in post 184.This one, I added his name in the post.Why twin's paradox is NOT about acceleration?It should show my intention to learn, but somehow you can't see it.QuoteChapters:Let's see if anyone has objection to the explanation given in this video, which is an improvement of previous video by the same author, Mahesh Shenoy from Floatheadphysics.
00:00 What is the twin's paradox?
00:48 Why acceleration doesn't solve twin's paradox
2:24 Twin's paradox without acceleration (Earth's frame)
4:42 The traveling frame
7:13 My new website - floatheadphysics (ad)
8:48 Earth's frame again - with the flag
11:38 Travelling frame again - with the flag
13:30 The resolution!
14:45 Relativity of simultaneity
17:02 Isn't the root cause the acceleration?
18:20 What do they 'see'?
In this video, we'll intuitively resolve the twin's paradox. This version of the twin's paradox involves no acceleration. And no, you don't need equivalence principle, and you don't need general relativity to solve it. Twin's paradox can be completely solved using special theory of relativity and the correct usage of relativity of simultaneity.
On the other hand, if you are already convinced that your current explanation is the correct one, and the others are wrong, you won't be able to learn.
In case of another twin travels with the same speed but opposite direction, the relative speed between them will be around 0.9897c, according to relativistic velocity addition. The gamma factor is around 7.
Post by: hamdani yusuf on 07/03/2024 03:31:47
Quote
What if there is another twin travel to the opposite direction with the same speed? And another one in perpendicular direction?Unfortunately no one has replied.
But there are some positive comments regarding the explanation in the video.
Quote
As a 60 year old physicist, I can say that this is the best demonstration of the twin's paradox I have seen, and I saw the first one when I was 15. I also love your enthusiasm. Bravo!
Quote
This is by far the best explanation for the twin paradox I?ve seen, and I have watched a lot of YouTube videos on this spanning close to a decade. This holds true for basically all of your videos. Thank you!!
Quote
Superb - I am a professor of geometry, and I never saw such a good explanation without drawing a space-time diagram.
Quote
Great video. Simultaneity in relativity is often overlooked. Nice explanation of why you can't ignore it. And it was great to highlight that what you measure using scientific apparatus, clocks, rulers etc is not the same thing as what you a see using your eyes or cameras. Nice.
Quote
That was such a good experience. I'm simultaneously Happy, impressed, dazzled, and awakened. I understand others comparing this to other explanations, but I want to say this is the first time it's ever really been explained. Your approach of having a conversation and asking all those questions is so incredibly effective. Thank you so much. Special relativity is itself an amazing leap of imagination. And then on top of that solving the paradoxes are a bunch of other giant leaps.
Post by: alancalverd on 07/03/2024 08:41:35
. And it was great to highlight that what you measure using scientific apparatus, clocks, rulers etc is not the same thing as what you a see using your eyes or cameras.Absurd. When did a camera cease being a scientific instrument? How do you read a clock or a ruler without your eyes?
Post by: alancalverd on 07/03/2024 08:44:55
What if there is another twin travel to the opposite direction with the same speed? And another one in perpendicular direction?Direction is irrelevant to time dilatation. What matters is relative velocity, i.e. the vector that describes their rate of separation.
Post by: hamdani yusuf on 07/03/2024 09:53:44
What do you think about my calculation below?What if there is another twin travel to the opposite direction with the same speed? And another one in perpendicular direction?Direction is irrelevant to time dilatation. What matters is relative velocity, i.e. the vector that describes their rate of separation.
In the example in the video, the gamma factor is 2, which means the speed is around 0.866c.
In case of another twin travels with the same speed but opposite direction, the relative speed between them will be around 0.9897c, according to relativistic velocity addition. The gamma factor is around 7.
Post by: hamdani yusuf on 07/03/2024 12:24:26
How do you read a clock or a ruler without your eyes?ask AI to read them out loud, or use direct brain interface.
Post by: hamdani yusuf on 08/03/2024 14:09:39
In the video, one of the twins travels 20 years to the right and then 20 years back with speed 0.866c, according to earth reference. At the end of the journey, earth clock shows 40 years, while the travelling clock shows only 20 years.What do you think about my calculation below?What if there is another twin travel to the opposite direction with the same speed? And another one in perpendicular direction?Direction is irrelevant to time dilatation. What matters is relative velocity, i.e. the vector that describes their rate of separation.In the example in the video, the gamma factor is 2, which means the speed is around 0.866c.
In case of another twin travels with the same speed but opposite direction, the relative speed between them will be around 0.9897c, according to relativistic velocity addition. The gamma factor is around 7.
I added a third twin, having similar journey with the first, but goes to the left from earth. Due to symmetry, his journey should end at the same time as the first twin, with his clock also shows 20 years.
But relative speed between the travelling twins produces gamma factor of 7. Thus during the constant velocity of 20 years in their own clock, they see the other travelling clock to increase by 20/7 years. Thus the remaining increase of the clock occurs during the frame jump, which amounts to 120/7, making the total of 140/7 years or 20 years.
Post by: hamdani yusuf on 08/03/2024 21:17:02
At the beginning, all clocks are 0.
During outbound journey, his own clock increases by 10 years. In his calculation, earth clock increases by 5 years. While the other travelling twin's clock increases by 10/7 years.
During short period of turn around, earth clock jump from 5 to 35 years. While the other travelling twin's clock jump from 10/7 to 130/7 years.
During return journey, his clock increases by 10 years. In his calculation, earth clock increases by 5 years. While the other travelling twin's clock increases by 10/7 years.
At the end of the journey, both travelling clocks show 20 years, while earth clock shows 40 years.
Post by: hamdani yusuf on 08/03/2024 21:46:36
During short period of turn around, earth clock jump from 5 to 35 years. While the other travelling twin's clock jump from 10/7 to 130/7 years.Earth clock jumps by 30 years, while the other travelling clock jumps by 120/7 years.
How are those numbers calculated?
They should depend on the distance and change of velocity. When the distance is zero, there's no time jump, just like at the start of the journey.
The other travelling clock is further than the earth clock during the turn around. But somehow it undergoes less time jump. Where did I miss?
Post by: alancalverd on 09/03/2024 00:44:16
change of velocity.Oh dear. That's called "acceleration", which some of our correspondents say is irrelevant.
Post by: hamdani yusuf on 09/03/2024 02:22:17
Those who said it's irrelevant argued that the observer who changes his velocity can be replaced by two observers with different velocities, one is the same as initial velocity, while the other is the same as final velocity. They meet at turn around point. Don and Mahesh used this argumentation.change of velocity.Oh dear. That's called "acceleration", which some of our correspondents say is irrelevant.
Post by: hamdani yusuf on 09/03/2024 10:10:49
What if there is another twin travel to the opposite direction with the same speed? And another one in perpendicular direction?The formula for perpendicular velocity addition is:
(https://wikimedia.org/api/rest_v1/media/math/render/svg/8db095d6c4d65e150aad0f4662d5b4376d88d23b)
https://en.wikipedia.org/wiki/Velocity-addition_formula
In our case, vx=vy=0.866c.
For convenience, I used spreadsheet to calculate.
putting the number to the left formula gives 0.247c
putting the number to the right formula gives 1.732c
Either result doesn't seem to be correct. It shouldn't be slower than the individual velocity. It shouldn't be higher than c either. Can someone show where the error is?
Post by: alancalverd on 09/03/2024 12:36:22
They meet at turn around point....and cannot synchronise their clocks because vrel >0.
Post by: hamdani yusuf on 10/03/2024 09:14:36
Why not?They meet at turn around point....and cannot synchronise their clocks because vrel >0.
The clocks were already synchronized before the experiment begun. They were identically manufactured at the meeting point. And then moved to their respective starting points for the experiment symmetrically.
Post by: hamdani yusuf on 10/03/2024 14:52:12
I want to make sure that this unexpected result is not caused by typo.During short period of turn around, earth clock jump from 5 to 35 years. While the other travelling twin's clock jump from 10/7 to 130/7 years.Earth clock jumps by 30 years, while the other travelling clock jumps by 120/7 years.
How are those numbers calculated?
They should depend on the distance and change of velocity. When the distance is zero, there's no time jump, just like at the start of the journey.
The other travelling clock is further than the earth clock during the turn around. But somehow it undergoes less time jump. Where did I miss?
In the original case, inertial earth observer didn't see time jump of travelling clock during the turn around. But the travelling twin did see time jump of earth clock during the turn around. It shows that time jump is determined by velocity change of the observer only.
Post by: alancalverd on 10/03/2024 17:19:09
Why not?Time dilatation.
If identical clocks are moving relative to one another, you can't tell the time shown at B simply by looking at clock A.
Post by: hamdani yusuf on 10/03/2024 21:05:22
Do you think that symmetry always break down? What determines the time difference?Why not?Time dilatation.
If identical clocks are moving relative to one another, you can't tell the time shown at B simply by looking at clock A.
Post by: hamdani yusuf on 10/03/2024 21:34:43
(Personally, I think the OP is diving off into Twins' Paradox etc, with ever increasing complexity, when they don't really grasp the significance of the basics of relativity. I think the explanations need to get simpler, not more complex.)Perhaps you can point out which basics of relativity I've missed out in my calculations with symmetrical twin travellings?
Post by: alancalverd on 11/03/2024 22:49:55
Do you think that symmetry always break down?It does, by theory and experiment. Nothing to do with what I think.
Post by: varsigma on 11/03/2024 23:07:40
In Te Reo, the sound at the end of a word is where you 'locate' the word. Words imply action or movement and aren't static descriptive things as in English. The meaning is fluid, and this isn't surprising given their ancestors were ocean explorers.
So in my country, a university is a Wananga, or Waananga. You take this apart, so the last sound (phonemic syllable), is 'nga', which translates variously as 'here', 'this way', etc. another word 'tenei' translates as 'this is', so you also get 'here is'--fluidity of meaning.
The rest of wananga is I believe a contraction of 'waha', meaning voice, or 'from the mouth', etc. and the 'a' connecting the two makes 'nga' into 'anga' meaning 'facing' (a direction), 'open', or 'unadorned, naked'.
So the whole word 'wananga' translates as 'voices facing (each other) here', i.e. a public forum. Polynesian languages are simpler than the one we use.
'The Maori language' -- 'Te Reo Maori', translates as 'the normal language'. Ironic just a little.
Post by: alancalverd on 11/03/2024 23:38:09
I live in a country that has two languages.Lucky man! Next best place to heaven - apart from the odd earthquake.
given their ancestors were ocean explorers.I gather that "canoe" can have umpteen meanings, dependent on context. Very economical! A bit like teenspeak, which seems to consist of "whatever" and up to two other words that change every week.
Post by: hamdani yusuf on 12/03/2024 04:52:43
The asymmetry can then be used to determine absolute frame of reference.Do you think that symmetry always break down?It does, by theory and experiment. Nothing to do with what I think.
Post by: alancalverd on 12/03/2024 10:17:45
Post by: hamdani yusuf on 12/03/2024 12:11:14
Or, to put it another way, relative velocity. There is no absolute frame of reference.In case of symmetrical motions, average relative velocity is zero. Thus no net difference in time dilation between the clocks. Which mean they can be synchronized while immediate relative velocity is not zero.
Post by: varsigma on 12/03/2024 20:52:46
I gather that "canoe" can have umpteen meanings, dependent on context. Very economical!That's my understanding of waka, where in Hawaiian it's vaka. Not surprising because Hawaii and NZ were the last places on the map, sort of.
So a waka or whaka means a canoe. But canoes carry people and people carry stories around. So a waka is a thing that moves people and stories--legends, myths such as a god, Maui, who fishes land out of the sea--from place to place.
Te reo uses pa for a place, repeat that and papa means places, but also movement. Hence one's ancestry is whakapapa;; carrying stories and people around.
p.s. an algebraicist might say that pasting these phonemes together is tensoring them to modify the meme. There is a linguistic order (grammar) imposed. Te Reo is a Maori treasure, all words are gifts you are supposed to "look after", because you give them back. That's a nice way to close things, Closure comes at the end, the terminals locate the meme.
Post by: varsigma on 12/03/2024 20:56:30
In case of symmetrical motions, average relative velocity is zero.?? I don't think you can just claim that separate motions are symmetrical. What do you mean symmetrical? What symmetry?
Post by: hamdani yusuf on 13/03/2024 03:52:53
Let two identical clocks stationary to each other. Accelerate both clocks at the same rate but opposite direction. They maintain the same distance to the original position at all time. After predetermined distance, they both return to the original position at the same speed.In case of symmetrical motions, average relative velocity is zero.?? I don't think you can just claim that separate motions are symmetrical. What do you mean symmetrical? What symmetry?
Both clocks experience symmetrical acceleration and speed at any time. They only differ in direction. Any difference in clock reading at the reunion can be attributed to difference of the original position to a preferred frame of reference, assuming that neither of clocks are defective.
Post by: hamdani yusuf on 16/03/2024 03:56:30
The asymmetry can then be used to determine absolute frame of reference.
Or, to put it another way, relative velocity. There is no absolute frame of reference.If that's the case, then there will be no asymmetry. And both clocks will still be synchronized when they reunite.
Post by: hamdani yusuf on 16/03/2024 04:01:28
I expected someone to come out using space time diagram to explain away the seemingly paradoxical symmetrically travelling twins thought experiment.(Personally, I think the OP is diving off into Twins' Paradox etc, with ever increasing complexity, when they don't really grasp the significance of the basics of relativity. I think the explanations need to get simpler, not more complex.)Perhaps you can point out which basics of relativity I've missed out in my calculations with symmetrical twin travellings?
Post by: alancalverd on 16/03/2024 16:37:35
Post by: hamdani yusuf on 17/03/2024 08:48:12
If two clocks have identical histories, you'd expect them to show the same time when they re-unite.Then relativity of simultaneity alone isn't adequate to explain the asymmetrical time dilation experienced by the twins in the original twin paradox.
Post by: alancalverd on 18/03/2024 11:04:16
As I have pointed out several times previously, time dilation is always asymmetric except in the case where vrel = 0, and now we might add "or the clock histories are symmetric and result in vrel = 0", but you'd have to qualify that statement too: if they accelerate equally in opposite directions and then stop, they would appear to an observer at the starting point to be synchronised to one another, but neither could tell the time on the other's clock (or the observer's) simply by looking at his own.
Post by: hamdani yusuf on 18/03/2024 12:57:18
if they accelerate equally in opposite directions and then stop, they would appear to an observer at the starting point to be synchronised to one another, but neither could tell the time on the other's clock (or the observer's) simply by looking at his own.Is there a formula to calculate the other's clock, when their relative position and motion are known?
If not, is it a random value? Is there a high or low limit for that random value?
Post by: hamdani yusuf on 02/05/2024 14:07:43
I searched and found this formula in quora.What if there is another twin travel to the opposite direction with the same speed? And another one in perpendicular direction?The formula for perpendicular velocity addition is:
(https://wikimedia.org/api/rest_v1/media/math/render/svg/8db095d6c4d65e150aad0f4662d5b4376d88d23b)
https://en.wikipedia.org/wiki/Velocity-addition_formula
In our case, vx=vy=0.866c.
For convenience, I used spreadsheet to calculate.
putting the number to the left formula gives 0.247c
putting the number to the right formula gives 1.732c
Either result doesn't seem to be correct. It shouldn't be slower than the individual velocity. It shouldn't be higher than c either. Can someone show where the error is?
Quote
...Plugging in the value, where vx=vy=0.866c, v is 0.968c.
This messy matrix is not a Lorentz boost. It is, in fact, a combination of a Lorentz boost (corresponding to some velocity in the x−y plane) and a spatial rotation (again in the x−y plane.)
However, at least we can get the magnitude of the resulting velocity from this matrix, as the upper left component of the matrix is not affected by the spatial rotation. It is determined purely by the Lorentz boost. A little bit of trivial algebra tells you the magnitude:
v=√(vx^2 + vy^2 - vx^2.vy^2/c^2)
The gamma factor is then around 3.98. For simplicity, I'll just round it up to 4.
Post by: hamdani yusuf on 02/05/2024 14:37:45
In chronological order, here's what a travelling twin's timeline.
At the beginning, all clocks are 0.
During outbound journey, his own clock increases by 10 years. In his calculation, earth clock increases by 5 years. While the other travelling twin's clock increases by 10/4 years.
During short period of turn around, earth clock jump from 5 to 35 years. While the other travelling twin's clock jump from 10/4 to 70/4 years.
During return journey, his clock increases by 10 years. In his calculation, earth clock increases by 5 years. While the other travelling twin's clock increases by 10/4 years.
At the end of the journey, both travelling clocks show 20 years, while earth clock shows 40 years.
Post by: hamdani yusuf on 02/05/2024 14:48:37
How are those numbers calculated?
They should depend on the distance and change of velocity. When the distance is zero, there's no time jump, just like at the start of the journey.
The other travelling clock is further than the earth clock during the turn around. But somehow it undergoes less time jump. Where did I miss?
Post by: Halc on 02/05/2024 17:05:36
How are those numbers calculated?The numbers come from integrating the interval of the remote worldline between the event where it is simultaneous with the acceleration event in the first frame, and the the event where it is simultaneous with the acceleration event in the second frame. This is pretty easy for an inertial object, but your traveling clock is not inertial, so it is best done in two pieces.
For an inertial object (like Earth) and an instantaneous frame change, t' = Lv
where t' is the inertial clock's time jump, v is the velocity component change towards the inertial thing as measured in the inertial object's frame, and L is the distance component between the two as measured by the inertial thing. Velocity component is negative if the accelerating thing accelerates away.
Things get more complicated (and require calculus) if the acceleration is smooth and not abrupt.
Quote
They should depend on the distance and change of velocity.Yes, Einstein called it 'moment of acceleration', kind of like moment of inertia which is zero for mass at the axis, and increases proportionally with the distance of the mass from the axis.
Quote
The other travelling clock is further than the earth clock during the turn around. But somehow it undergoes less time jump. Where did I miss?You missed the fact that the Earth clock is inertial between the two events of the 'jump' and the traveling clock is not, so its worldline is half the temporal length that it would have had had it been inertial between its two events.
Post by: hamdani yusuf on 03/05/2024 05:49:15
Your numbers in both posts are good except for that bit about 120/4 being 15.Not sure where 120/4 comes from. The 4 was from the perpendicular case, but the case being discussed was not the perpendicular one.15 years is the time jump required to compensate the time dilation on the other twin's clock to match with first twin's clock when they reunite. Where does the number come from? That's what I was asking.
As I mentioned when quoting answer from quora, 4 is the gamma factor for perpendicular case. For twins going on opposite direction, the gamma factor is 7,as I posted earlier.
Post by: hamdani yusuf on 03/05/2024 07:31:39
You missed the fact that the Earth clock is inertial between the two events of the 'jump' and the traveling clock is not, so its worldline is half the temporal length that it would have had had it been inertial between its two events.Where does the number "half" come from?
Post by: alancalverd on 03/05/2024 09:29:15
Is there a formula to calculate the other's clock, when their relative position and motion are known?Yes. Time dilatation formula. It's sufficiently accurate to allow GPS navigation.
Post by: hamdani yusuf on 03/05/2024 11:57:19
Then why you said this?Is there a formula to calculate the other's clock, when their relative position and motion are known?Yes. Time dilatation formula. It's sufficiently accurate to allow GPS navigation.
if they accelerate equally in opposite directions and then stop, they would appear to an observer at the starting point to be synchronised to one another, but neither could tell the time on the other's clock (or the observer's) simply by looking at his own.
Post by: alancalverd on 03/05/2024 17:57:22
Post by: hamdani yusuf on 04/05/2024 00:29:08
Because it's true. The difference between the two scenarios is "simply by looking at his own."Even when both twins accelerate equally in opposite directions and then stop?
Post by: alancalverd on 04/05/2024 11:03:26
Post by: hamdani yusuf on 08/05/2024 14:01:38
How does A know what has happened to B, simply by looking at his own clock?By calculating according to the Time dilatation formula., and assuming that B moves according to the planned sequence.
Post by: alancalverd on 08/05/2024 17:45:37
Post by: hamdani yusuf on 09/05/2024 10:35:41
Precisely my point. He can't tell B's time simply by looking at his own clock: he has to make a lot of assumptions. That's relativity.He can verify his assumptions by asking an external inertial observer, whether or not B moved according to the planned sequence.
Post by: hamdani yusuf on 09/05/2024 10:49:36
In the explanation by Henry's Minutephysics and Mahesh' Floatinghead Physics, acceleration of the observed clocks don't cause any time jump. Time jumps only occur when the observer is looking at far away clock while changing velocity.You missed the fact that the Earth clock is inertial between the two events of the 'jump' and the traveling clock is not, so its worldline is half the temporal length that it would have had had it been inertial between its two events.Where does the number "half" come from?
We know we are having a knowledge gap when we have a quantitative answer without knowing where it comes from.
Post by: alancalverd on 10/05/2024 20:31:52
He can verify his assumptions by asking an external inertial observer,Which is not "simply by looking at his own clock". Try reading the question before questioning the answer.
Post by: hamdani yusuf on 15/05/2024 16:31:03
Precisely my point. He can't tell B's time simply by looking at his own clock: he has to make a lot of assumptions. That's relativity.
How does it (looking only at his own clock) help solving the twin paradox, which is the main objective of this thread?He can verify his assumptions by asking an external inertial observer,Which is not "simply by looking at his own clock". Try reading the question before questioning the answer.
Post by: alancalverd on 16/05/2024 09:42:08
To repeat a mantra for the umpteenth time:
You can derive a nonrelativistic result from a relativistic model by putting v << c.
You can't derive a relativistic result from a nonrelativistic model.
Post by: hamdani yusuf on 16/05/2024 15:11:51
If A cannot tell the time on B's clock by looking at his own, he has no reason to assume that they are synchronised. Thus there is no paradox.So, what is the resolution of the paradox? Will they have different age at reunion? Which one is older?
To repeat a mantra for the umpteenth time:
You can derive a nonrelativistic result from a relativistic model by putting v << c.
You can't derive a relativistic result from a nonrelativistic model.
Post by: alancalverd on 16/05/2024 18:00:15
Post by: hamdani yusuf on 18/05/2024 01:18:14
There is no paradox, so no resolution is required. The time difference has been measured and consists with the calculated value.What's your calculation result?
Is the earth bound twin always the older?
Post by: alancalverd on 18/05/2024 12:39:02
Post by: hamdani yusuf on 18/05/2024 13:12:53
I recommend the Wikipedia entry for the Hafele-Keating experiment, which explains the corrections required for an earth-based observer.
Quote
The Hafele?Keating experiment was a test of the theory of relativity. In 1971,[1] Joseph C. Hafele, a physicist, and Richard E. Keating, an astronomer, took four caesium-beam atomic clocks aboard commercial airliners. They flew twice around the world, first eastward, then westward, and compared the clocks in motion to stationary clocks at the United States Naval Observatory. When reunited, the three sets of clocks were found to disagree with one another, and their differences were consistent with the predictions of special and general relativity.Do you think solution of twin paradox requires general relativity?
https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment
Is special relativity inadequate for this situation?
Post by: alancalverd on 19/05/2024 18:34:06
Relativity is the best description we have of how things work, and when v << c, relativistic mechanics simplifies to include such notions as simultaneity and synchronism, which are adequate for many everyday purposes but cannot be considered complete.
Post by: hamdani yusuf on 20/05/2024 03:20:56
There is no paradox.Which relativity?
Relativity is the best description we have of how things work, and when v << c, relativistic mechanics simplifies to include such notions as simultaneity and synchronism, which are adequate for many everyday purposes but cannot be considered complete.
Even the same theory can be interpreted differently.
Do you think solution of twin paradox requires general relativity?
Is special relativity inadequate for this situation?
Post by: alancalverd on 20/05/2024 17:16:31
Quote
Time dilation is the difference in elapsed time as measured by two clocks, either because of a relative velocity between them (special relativity), or a difference in gravitational potential between their locations (general relativity).
If there is no relative velocity or gravitational potential difference, the time dilation component degenerates to zero and we can assume synchronicity, i.e. the time measured by B's clock will be exactly the same as A's. This is the approximation that underlies classical (nonrelativistic) mechanics.
Where's the paradox?
Post by: hamdani yusuf on 21/05/2024 07:49:29
Where's the paradox?
Quote
In physics, the twin paradox is a thought experiment in special relativity involving identical twins, one of whom makes a journey into space in a high-speed rocket and returns home to find that the twin who remained on Earth has aged more. This result appears puzzling because each twin sees the other twin as moving, and so, as a consequence of an incorrect[1][2] and naive[3][4] application of time dilation and the principle of relativity, each should paradoxically find the other to have aged less. However, this scenario can be resolved within the standard framework of special relativity: the travelling twin's trajectory involves two different inertial frames, one for the outbound journey and one for the inbound journey.[5] Another way of looking at it is to realize the travelling twin is undergoing acceleration, which makes them a non-inertial observer. In both views there is no symmetry between the spacetime paths of the twins. Therefore, the twin paradox is not actually a paradox in the sense of a logical contradiction. There is still debate as to the resolution of the twin paradox.Should we take acceleration into the equation?
https://en.wikipedia.org/wiki/Twin_paradox
Post by: alancalverd on 21/05/2024 08:08:49
Thanks to relativistic time dilation, you can't assume clocks to be synchronised unless they are mutually stationary and close together (no gravitational potential difference).
Therefore at least one clock then needs to accelerate to produce v > 0.
Post by: hamdani yusuf on 21/05/2024 09:29:17
Why the symmetrically travelling twin's clock is only observed to time jump by half amount than earth's clock, from the perspective of the first travelling twin?In the explanation by Henry's Minutephysics and Mahesh' Floatinghead Physics, acceleration of the observed clocks don't cause any time jump. Time jumps only occur when the observer is looking at far away clock while changing velocity.You missed the fact that the Earth clock is inertial between the two events of the 'jump' and the traveling clock is not, so its worldline is half the temporal length that it would have had had it been inertial between its two events.Where does the number "half" come from?
We know we are having a knowledge gap when we have a quantitative answer without knowing where it comes from.
Post by: hamdani yusuf on 10/06/2024 05:47:45
Twin Paradox is NOT a Paradox: An Explanation that Makes Sense
Quote
Einstein's Theory of Special Relativity is confusing. It?s even harder to grasp when all the explanations disagree about how to interpret it. And to top it all off, the explanations all use a PARADOX.
I decided I needed to step in and give one more explanation to destroy the paradox once and for all. Did I succeed? Let me know in the comments what I should clarify in my next video.
Chapters:
00:00 - Intro
00:48 - The Story
03:03 - The Paradox
04:56 - The Problem
07:59 - Breaking the Symmetry
10:15 - Constructed Inertial Frames
12:27 - Video Evidence
15:21 - There is No Paradox
17:33 - Connecting the Dots
Post by: hamdani yusuf on 15/12/2024 09:51:19
Perhaps I can show an example to determine whether or not acceleration can explain the asymmetrical effects of time dilation in twin paradox. Instead of going back and forth on a single straight line, we make both twins to go through a rectangular route.
Imagine that the first twin takes the route of ABCDA, while the second twin takes the route of ADCDA.
By symmetry, both twins must arrive at C with the same age. But the second twin experiences higher acceleration to reverse direction. So in the journey between C and D they can already determine if they age differently because of their acceleration.
Post by: alancalverd on 15/12/2024 12:06:08
Post by: hamdani yusuf on 15/12/2024 12:31:23
No. Both twins experience one each of accelerations north-south, west-east, south-north, and east-west. Just in a different order.Do you think the acceleration in the trajectory of DCD has the same magnitude as in BCD?
Do they have equal amount of momentum change?
Post by: alancalverd on 15/12/2024 13:32:53
So ABC ≡ ADC, and on the journey CD or DA they should be in sync.
Post by: hamdani yusuf on 15/12/2024 13:42:58
Post by: hamdani yusuf on 16/12/2024 08:45:00
Twin Paradox 1 : Rectangular Route
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Investigating the exact cause of asymmetry in twin paradox thought experiment through a rectangular route. It allows us to see if difference in time dilation experienced by the twins can be fully attributed to difference in acceleration, and how they correlate to each other.
Post by: hamdani yusuf on 16/12/2024 14:41:17
Quote
Surprisingly few people are aware of Einstein's preferred solution to the Twin Paradox, which he detailed in a 1918 paper. We examine this solution, purported to take place within the framework of General Relativity, in hopes of finally finding an explanation to the twin paradox that can appease our empathic skepticism. Along the way we learn a thing or two about the nature of gravity, the distinctions between special and general relativity, and the philosophy of motion.
Post by: alancalverd on 16/12/2024 14:46:06
At point C, first twin changes his velocity by 90 degrees, while second twin changes his velocity by 180 degrees.But number one also changes through 90 degrees at B. Instead of a square, gradually shorten the BC and DA legs. Is there a singularity when the distance ABCD suddenly longer or shorter than ADCDA?
Instantaneous change of velocity implies infinite force, which will destroy a twin, so try radiusing the corners.
Post by: alancalverd on 16/12/2024 14:48:16
explanation to the twin paradox that can appease our empathic skepticism.Since it has been demonstrated, it is about 50 years too late for skepticism.
Post by: paul cotter on 16/12/2024 15:11:27
Post by: hamdani yusuf on 16/12/2024 15:14:45
This is a thought experiment, and we limit the parameters to be considered at minimum, just barely enough to distinguish one hypothesis from the others.At point C, first twin changes his velocity by 90 degrees, while second twin changes his velocity by 180 degrees.But number one also changes through 90 degrees at B. Instead of a square, gradually shorten the BC and DA legs. Is there a singularity when the distance ABCD suddenly longer or shorter than ADCDA?
Instantaneous change of velocity implies infinite force, which will destroy a twin, so try radiusing the corners.
Post by: hamdani yusuf on 16/12/2024 15:16:13
I reckon this discussion will be moving to the "new theories" zone fairly soon!Einstein's theory can't be new. He's already dead.
Post by: Halc on 16/12/2024 19:02:57
I reckon this discussion will be moving to the "new theories" zone fairly soon!Yet again, your instincts are good. Seemed silly to create a new topic when this one was already here.
Hamdani, you seem to have a talent for hunting down links to wrong answers to things. It seems very deliberate. Please stop posting explanations in the main sections of the forum. That section is for questions about established theory, not assertions about alternatives, especially ones that are obviously wrong. Ask questions there. Don't assert anything. Please!
I tire of moving so many of your posts down to the lighter side.
(https://upload.wikimedia.org/wikipedia/commons/b/b3/Geometrie_carre.png)It shows no such thing since your twins are never a different age when co-located.
Perhaps I can show an example to determine whether or not acceleration can explain the asymmetrical effects of time dilation in twin paradox. Instead of going back and forth on a single straight line, we make both twins to go through a rectangular route.
Quote
But the second twin experiences higher acceleration to reverse direction.This is wrong.
If you are positing them getting up to speed instantly, all accelerations are infinite (singular), and one cannot meaningfully say that one infinity is greater than another.
If you are positing that the acceleration is finite (100M g's say) but a very short duration, then everybody undergoes the exact same magnitude of acceleration at each corner since they must come to a stop, turn, and get going again.
If you round the corners, then the picture should show that. Indeed the acceleration magnitudes would be different since one ship takes point C at speed and the other stops, but only for a really short duration.
The solution to this is trivially solved by the method mentioned in reply 1 of the main topic. Speed of everybody is always identical in the frame where the letters don't move, so all clocks tick at the exact same rate all the time. No differential aging will be observed.
The post below was too much and prompted all this stuff being moved here.
Einstein, Gravity, and the Twin Paradox (Einstein's 1918 Solution)It references a letter written to somebody in 1918, not a peer reviewed paper. If the letter actually contains what the video shows, then it contains countless errors, some of which are pointed out in the video. One of the worst is the claim of a 'uniform gravitational field' which cannot exist except under Newtonian physics. There is no solution to the field equations which describe one. I would hope that Einstein would have known that by 1918, but who knows? Gravity is about curved spacetime, and there is no curved spacetime in the twins scenario, so invoking equations of gravity in a non-local scenario not involving curved spacetime is entirely wrong.QuoteSurprisingly few people are aware of Einstein's preferred solution to the Twin Paradox, which he detailed in a 1918 paper. We examine this solution, purported to take place within the framework of General Relativity, in hopes of finally finding an explanation to the twin paradox that can appease our empathic skepticism. Along the way we learn a thing or two about the nature of gravity, the distinctions between special and general relativity, and the philosophy of motion.
Post by: hamdani yusuf on 21/12/2024 10:44:55
Hamdani, you seem to have a talent for hunting down links to wrong answers to things. It seems very deliberate. Please stop posting explanations in the main sections of the forum. That section is for questions about established theory, not assertions about alternatives, especially ones that are obviously wrong. Ask questions there. Don't assert anything. Please!
What's considered established at some point, may no longer be the case a few decades or even years later. The videos in the OP also criticized what are considered as established explanations.
If what you are looking for is the most widely accepted explanation at present, then your best chance is by asking various AI chatbots, especially the newest versions, and compare the answers to their top competors. They are essentially statistics on steroids, as some AI researchers said. If your own explanation turns out to be different than theirs, it may be because you are believing a non-established science instead.
Post by: hamdani yusuf on 21/12/2024 11:07:00
It shows no such thing since your twins are never a different age when co-located.What does it show when they are not co-located? How is the situation of one twin from the perspective the other?
Post by: hamdani yusuf on 21/12/2024 11:36:32
If you are positing them getting up to speed instantly, all accelerations are infinite (singular), and one cannot meaningfully say that one infinity is greater than another.If the acceleration is done in circular manner, say 1 light second in circumference, while the twins travel at c/2, then to turn the direction by 90 degrees takes half second, while turning the direction by 180 degrees takes one second by maintaining their speed. Alternatively, if the second twin is only given half second to turn, he must turn around with smaller circle, thus higher centripetal acceleration.
If you are positing that the acceleration is finite (100M g's say) but a very short duration, then everybody undergoes the exact same magnitude of acceleration at each corner since they must come to a stop, turn, and get going again.
If you round the corners, then the picture should show that. Indeed the acceleration magnitudes would be different since one ship takes point C at speed and the other stops, but only for a really short duration.
Post by: Halc on 21/12/2024 14:26:36
What's considered established at some point, may no longer be the case a few decades or even years later.All the trolls say this. If you don't want to be branded a troll, it probably isn't a good idea to quote their handbook.
Turns out that nobody ever overturned established theory (however wrong) by not first understanding the established theory. I defy you to find a single exception to that.
Nobody overturned established theory by entering "Einstein wrong" as their search criteria, which is one way to find denialist videos.
Chatbots are also known to be consistently wrong when it comes to questions with so much misinformation in the training materials.
What does it show when they are not co-located?Differential aging is inapplicable to clocks that are not co-located. This is basic relativity of simultaneity, something you seem not to understand if you ask a question like that.
If the acceleration is done in circular manner, say 1 light second in circumference, while the twins travel at c/2, then to turn the direction by 90 degrees takes half second, while turning the direction by 180 degrees takes one second by maintaining their speed. Alternatively, if the second twin is only given half second to turn, he must turn around with smaller circle, thus higher centripetal acceleration.Cool. I take it these distances and speeds are as measured in the Earth frame. Speed maintained throughout, but one takes half a second longer to get to the new course heading. A couple fine details are missing, but assuming these turns are executed at exactly 90 or 180 degrees, there will indeed be differential aging when they meet at the end. Can you compute it? It's fairly trivial. Which will be older, and by how much? Most importantly, what do you think the example demonstrates?
If you can't compute this most basic thing, then what was the point of bringing it all up?
Post by: hamdani yusuf on 21/12/2024 16:56:02
All the trolls say this. If you don't want to be branded a troll, it probably isn't a good idea to quote their handbook.It doesn't matter who said that. What's important is whether it's true or not.
Post by: hamdani yusuf on 21/12/2024 16:58:58
Nobody overturned established theory by entering "Einstein wrong" as their search criteria, which is one way to find denialist videos.My search query was twin paradox. And the video agrees with Einstein.
Post by: hamdani yusuf on 21/12/2024 17:01:47
Chatbots are also known to be consistently wrong when it comes to questions with so much misinformation in the training materials.If that's what happens, top scientists will point it out and the developers will have to correct the answers. Otherwise they will lose market share to their competitors.
Post by: hamdani yusuf on 21/12/2024 17:03:45
It's fairly trivialWhat's more important is whether the equations accurately represent physical reality.
Post by: hamdani yusuf on 21/12/2024 17:11:36
what was the point of bringing it all up?To determine if acceleration has any effect on the symmetry breaking in twin paradox, which is the currently most taught explanation. Also to see if the travelling twin can be a valid observer, and how he views the time dilation experienced by the other twin.
Post by: alancalverd on 21/12/2024 23:32:47
the developers will have to correct the answers.Not possible. The whole point of a chatbot is that it scours cyberspace for anything that looks like information, without human intervention. The quantity of crap increases exponentially as (a) crap begets more crap and (b) crap is not subject to experimental verification and retraction and (c) some crap is compiled by other bots and posted as "research", so the consensus becomes incoherent or just plain wrong.
Post by: hamdani yusuf on 22/12/2024 01:47:17
Why not? ChatGPT now can correctly count the number of letter R in the word strawberry. As long as the topic gets public attention, there's economic incentive to improve.the developers will have to correct the answers.Not possible. The whole point of a chatbot is that it scours cyberspace for anything that looks like information, without human intervention. The quantity of crap increases exponentially as (a) crap begets more crap and (b) crap is not subject to experimental verification and retraction and (c) some crap is compiled by other bots and posted as "research", so the consensus becomes incoherent or just plain wrong.
Post by: alancalverd on 22/12/2024 22:33:15
ChatGPT now can correctly count the number of letter R in the word strawberry.And my dog, about the same age as ChatGPT, can catch rabbits and lick her own arse, without being taught either skill. This obviously qualifies her as a reliable source on all matters, so I asked her opinion on the "square trajectory" question and she agrees with me.
Post by: Halc on 22/12/2024 22:49:19
What's more important is whether the equations accurately represent physical reality.How are you going to know either?
1) you seem to have no knowledge of how to apply the equations
2) You seem to be working in complete absence of empirical evidence, the part that represents physical reality.
If you want to deny a theory, first requirement is evidence. I take that back. Evidence is second. First one is knowledge of the theory you're denying, without which you have no idea how the theory explains what the evidence shows.
How is bringing up this funny example going to do that when you don't know what really happens, and you don't know what the theory (the one you're denying) predicts.what was the point of bringing it all up?To determine if acceleration has any effect on the symmetry breaking in twin paradox, which is the currently most taught explanation.
Now you seem to be claiming that the most common explanation of asymmetrical paths is asymmetrical acceleration. That may be a true thing, but I've never seen a video bothering to point it out. The task was not to explain why the paths were asymmetrical, but what causes the differential aging. If a video claims that asymmetry in paths causes differential aging, then it is wrong since several examples were given where paths were very asymmetrical (or acceleration magnitudes or durations were different) and yet no differential aging occurs.
If this wrong explanation of differential aging is the most common one, then it is no wonder that all the chatbots also get it wrong since they gravitate toward the most prevalent crap instead of what's actually correct. No extra weight is given to peer reviewed textbooks over say social media posts, and your personal education material seems to come only from the latter source, and from the chatbots that regurgitate that content.
Quote
Also to see if the travelling twin can be a valid observerDifferential aging is an invariant: physical fact, not in any way dependent on coordinate choice or observation. Quantum mechanics has some obscure interpretations where talk about observers being valid or not is actually a question. Under relativity, none of it is dependent on observation. It's not a theory of idealism.
Quote
how he views the time dilation experienced by the other twin.Time dilation isn't something anybody experiences, per the first postulate of SR.
Post by: hamdani yusuf on 23/12/2024 06:39:39
What does she say?ChatGPT now can correctly count the number of letter R in the word strawberry.And my dog, about the same age as ChatGPT, can catch rabbits and lick her own arse, without being taught either skill. This obviously qualifies her as a reliable source on all matters, so I asked her opinion on the "square trajectory" question and she agrees with me.
Post by: hamdani yusuf on 23/12/2024 06:47:52
How are you going to know either?By comparing experimental results with the prediction from each theories.
Post by: hamdani yusuf on 23/12/2024 06:49:30
1) you seem to have no knowledge of how to apply the equationsYou seem to think that you know better than professional scientists working in this field, including Einstein.
2) You seem to be working in complete absence of empirical evidence, the part that represents physical reality.
Quote
Einstein reportedly said that he "didn't recognize" his theory of special relativity anymore because of how its interpretations and applications evolved far beyond his original formulation. When he developed the theory in 1905, his focus was on solving specific physical problems, such as reconciling Maxwell's equations of electromagnetism with the principle of relativity.
However, as the theory gained widespread acceptance, it became a foundational framework for theoretical physics and was interpreted in ways Einstein had not anticipated, especially in the hands of other physicists. For instance:
1. Mathematical Formalism: Mathematicians and physicists like Hermann Minkowski reformulated special relativity in a four-dimensional spacetime framework. While this interpretation became standard, Einstein initially resisted Minkowski's geometrical approach, as it was different from his more intuitive understanding of the theory.
2. Quantum Mechanics: Special relativity was later merged with quantum mechanics to form quantum field theory. Einstein, who was skeptical of some aspects of quantum mechanics, may have found this integration to be a departure from his original conception.
3. General Adoption and Popularization: The theory became widely accepted and interpreted by the broader scientific community in contexts Einstein hadn't focused on, leading to ideas and discussions he might not have entirely agreed with.
Einstein?s statement reflects the natural evolution of scientific theories: once introduced, they often take on lives of their own, shaped by new discoveries, interpretations, and applications.
ChatGPT
Post by: hamdani yusuf on 23/12/2024 06:52:17
Now you seem to be claiming that the most common explanation of asymmetrical paths is asymmetrical acceleration. That may be a true thing, but I've never seen a video bothering to point it out.Don Lincoln's first video mentioned it, and tried to refute it. While Sabine Hossenfelder's video defended it.
Post by: hamdani yusuf on 23/12/2024 07:14:46
No extra weight is given to peer reviewed textbooks over say social media postsHow do you know that?
Post by: hamdani yusuf on 23/12/2024 07:32:47
Time dilation isn't something anybody experiences, per the first postulate of SR.How do you reconcile this with your previous statement?
Differential aging is an invariant: physical fact, not in any way dependent on coordinate choice or observation.
Post by: alancalverd on 23/12/2024 11:49:36
What does she say?"You are right, Alan". (my translation)
Post by: alancalverd on 23/12/2024 11:52:39
How do you know that?The most peer-reviewed and authoritative textbook is the Bible, but I don't think ChatGPT thinks the planet is only 6000 years old.
Post by: paul cotter on 23/12/2024 20:43:30
Post by: hamdani yusuf on 23/12/2024 22:03:03
Because many other sources contradict it.How do you know that?The most peer-reviewed and authoritative textbook is the Bible, but I don't think ChatGPT thinks the planet is only 6000 years old.
Post by: hamdani yusuf on 23/12/2024 22:11:32
#369: time dilation is a coordinate phenomenon, differential ageing is a real world effect.
This diagram from Wikipedia is supposed to be the established explanation for twin paradox. It predicts apparent time jump in the observation by traveling twin, but no time jump observed by stationary twin. Without this time jump, the time dilation effect is symmetrical, hence caused a paradox.
(https://upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Twin_Paradox_Minkowski_Diagram.svg/1280px-Twin_Paradox_Minkowski_Diagram.svg.png)
This apparent time jump is basically like fast forward in record player, as shown when the acceleration during turn around is finite. In this case, the direction of the acceleration of the travelling twin is toward the stationary twin.
If we are willing to accept this explanation, we are forced to also accept reverse time jump or rewind when the direction of the acceleration is away from the observed twin.
Post by: hamdani yusuf on 24/12/2024 02:02:23
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One of the most famous paradoxes of all of physics ? who's older? Who's younger? and WHY?This is the screenshot of the video at 2:00 time stamp.
This video is about the famous ?Twins paradox? of special relativity, how time can appear to be faster for two different observers at the same time, and which twin really is older (or younger) ? the one who stays on earth or the one who flies in a rocket ship to the stars?
(https://www.thenakedscientists.com/forum/index.php?action=dlattach;topic=86675.0;attach=34534)
Look at the lines of simultaneity. The video only shows one side of them, i.e. the side where they leave gaps. The other side is where they overlap. This is where the reverse time jump appears in the analysis. I'm preparing my next video to describe this situation.
Post by: Eternal Student on 24/12/2024 17:15:46
If we are willing to accept this explanation, we are forced to also accept reverse time jump or rewind when the direction of the acceleration is away from the observed twin."Reverse Time Jump" ---> It sounds like you're describing something amazing, maybe time travel into the past. Of course, that's a feature that SR does not exhibit. So it either isn't that or else it will (probably) be wrong. Quite a few people have looked for ways to travel back into the past and SR doesn't seem to offer that ability. However, you're welcome to try again and it's certainly quite educational to give it a go.
Looking at the next post I can now see what this thing you're describing will end up being.
Look at the lines of simultaneity. The video only shows one side of them, i.e. the side where they leave gaps. The other side is where they overlap. This is where the reverse time jump appears in the analysis.Although it may sound like you'd be looking at something new, I suspect it's just going to be some re-wording of the Andromeda paradox that you're going to end up with.
Best Wishes.
Post by: hamdani yusuf on 25/12/2024 02:17:24
Although it may sound like you'd be looking at something new, I suspect it's just going to be some re-wording of the Andromeda paradox that you're going to end up with.I think it has similarity with Andromeda paradox. The difference is, the Andromeda paradox is caused by relative velocity, while in my case, it's caused by adequately high acceleration away from the observed object. My analysis shows that it is necessary for two travelling twins with almost completely constant speed at opposite direction to have symmetrical time dilation, and end up with the same age at the end of their journey.
Post by: hamdani yusuf on 25/12/2024 22:57:42
Twin Paradox 2: Reverse Time Jump
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Apparent forward time jump during the turn around has been used to explain the discrepancy in age observation between stationary twin and travelling twin.
Now we show the opposite effect when the observing twin is accelerating away. Although they come from the same mechanism, the reverse time jump is less mentioned in the literature.
Post by: hamdani yusuf on 26/12/2024 01:50:56
"Reverse Time Jump" ---> It sounds like you're describing something amazing, maybe time travel into the past. Of course, that's a feature that SR does not exhibit. So it either isn't that or else it will (probably) be wrong. Quite a few people have looked for ways to travel back into the past and SR doesn't seem to offer that ability. However, you're welcome to try again and it's certainly quite educational to give it a go.Original SR didn't exhibit forward time jump either, nor even the twin paradox in the first place. They appeared as the consequences of further analysis based on the initial assumptions.
Forward and reverse time jump only appear to the accelerating observer when the observed object is not co-located. The observed object itself isn't affected by the acceleration of the observer.
Post by: hamdani yusuf on 26/12/2024 12:36:24
Forward and reverse time jump only appear to the accelerating observer when the observed object is not co-located. The observed object itself isn't affected by the acceleration of the observer.If the acceleration is less extreme, the forward time jump becomes time sprint. While the reverse time jump can turn into time rewind. At the focal point of the simultaneity lines, the accelerating twin observes a time stop. With low acceleration away, he observes a time crawl.
Post by: Halc on 26/12/2024 22:28:30
What's considered established at some point, may no longer be the case a few decades or even years later.
It doesn't matter who said that. What's important is whether it's true or not.I completely disagree. It being true is a fairly trivial thing, but the fact that the new established theory has, without exception, only been made by those who first understood the previous established theory, means that no troll (somebody proposing anything with said understanding) has ever contributed to progress, and that was the point of the comment. Not saying that you're a troll, but I am noticing that you use arguments that seem only used by trolls, notably the first quote above.
What's more important is whether the equations accurately represent physical reality.The twins scenario is not representative of physical reality. The exercise is a simplified exercise in Minkowskian spacetime, and real spacetime is Minkowskian only locally. The twins scenario is not a local scenario.
This means that you need to use GR to represent non-local physical reality. The SR exercise (especially your funny diamond one) is inapplicable since the answers it gives are trivial differences compared to the differences GR would produce.
You seem to think that you know better than professional scientists working in this field, including Einstein.The average professional scientist knows next to nothing about relativity, but their field of expertise is elsewhere. No, I never claimed to know relativity better than any student that say took a graduate level course in it. I know it well enough for my purposes, which doesn't involve actually getting a rocket to go where I want it to.
This is a fairly accurate response by chatgpt. I didn't keep the entire quote. Minkowski reinterpreted his 1905 theory as spacetime geometry, not the way Einstein interpreted it in his paper. Without this new interpretation, he'd not have been abble to finish the theory (GR). Yes, he didn't recognize it at first, but he needed to recognize it to make progress. Minkowski (his mentor) did him an extreme favor by doing this. Minkowski was given too little credit for relativity theory. Einstein published it first, but did not do it on his own. He had to learn a lot of mathematics along the way.Quote from: chatgptEinstein reportedly said that he "didn't recognize" his theory of special relativity anymore because of how its interpretations and applications evolved far beyond his original formulation. When he developed the theory in 1905, his focus was on solving specific physical problems, such as reconciling Maxwell's equations of electromagnetism with the principle of relativity.
However, as the theory gained widespread acceptance, it became a foundational framework for theoretical physics and was interpreted in ways Einstein had not anticipated, especially in the hands of other physicists. For instance:
1. Mathematical Formalism: Mathematicians and physicists like Hermann Minkowski reformulated special relativity in a four-dimensional spacetime framework. While this interpretation became standard, Einstein initially resisted Minkowski's geometrical approach, as it was different from his more intuitive understanding of the theory.
#369: time dilation is a coordinate phenomenon, differential ageing is a real world effect.This is a super important distinction. A physical fact cannot be explained as a function of mental abstractions. Time dilation is a coordinate effect. Coordinate systems are mental abstractions, and no amount of mental imaginations are going to change what physically goes on.
This diagram from Wikipedia is supposed to be the established explanation for twin paradox.The wiki article mentions perhaps half a dozen ways to explain the twins thing, many of which are abstract.
The wiki article is a very good resource, but most of its text concerns coordinate effect (things that are true in one frame and not in others). This includes any mention of simultaneity, distances, durations, and any numbers (coordinates) assigned to points.
Physical facts include Differential aging and any event, and also spacetime intervals. These things are frame invariant and observer independent and are not abstractions. The twins scenario is about physical differential aging, and saying any physical fact is caused by human mental abstraction, is idealism at best, similar to saying the apple ceases to exist when not being perceived.. As I said, the wiki article is very good, and it never asserts anything like that.
The picture you reference is one of the abstractions. It shows lines of simultaneity, and simultaneity is completely abstract, having no physical meaning. That doesn't make the picture wrong, but it isn't a physical explanation.
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It predicts apparent time jump in the observation by traveling twinNo it doesn't. In fact, it doesn't mention observation at all since there are no light lines in the picture. If the twin looks at Earth when turning around, he sees the same thing just before and just after the acceleration. The observation only changes in redshift, but no time jump is observed. What is observed would be physical fact, and nobody regardless of where they are could contest it.
Point is, learn what the diagram actually shows. It shows an abstraction, something any person anywhere at any time could compute. All one needs to observe is an itinerary. No other observation need be made at all by anybody. Nobody observes a time jump. The jump is just a result of a change in arbitrary selection of inertial frame, and the Lorentz transformation details such changes. The Lorentz transform is once again purely an abstraction.
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to also accept reverse time jump or rewind when the direction of the acceleration is away from the observed twin.Yes, but again, this 'jump' is an abstraction, not anything that physically happens. One is always free to jump back and forth between two different reference frames. Acceleration isn't required at all to do it, and doing so makes zero physical difference to the universe.
"Reverse Time Jump" ---> It sounds like you're describing something amazing, maybe time travel into the past.Yes, it sounds kind of amazing when a coordinate effect is presented as a physical one, and this is indeed the gist of the Andromeda scenario. It's just an abstraction with no physical effect, no actual acceleration required, and no observation of any time 'jump' in either direction.
Post by: hamdani yusuf on 27/12/2024 02:11:01
No it doesn't. In fact, it doesn't mention observation at all since there are no light lines in the picture. If the twin looks at Earth when turning around, he sees the same thing just before and just after the acceleration. The observation only changes in redshift, but no time jump is observed. What is observed would be physical fact, and nobody regardless of where they are could contest it.OK. I agree that this is not an observation, which should also consider light transit time. It's just a mental model of physical reality to calculate and predict the outcome. But if these time jumps are ignored, we get the wrong results.
Nevertheless, the reverse time jump is as real (or as unreal) as the forward time jump in the analysis of twin paradox using space-time diagram.
Post by: hamdani yusuf on 27/12/2024 02:26:16
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A rotational version
Twins Bob and Alice inhabit a space station in circular orbit around a massive body in space. Bob suits up and exits the station. While Alice remains inside the station, continuing to orbit with it as before, Bob uses a rocket propulsion system to cease orbiting and hover where he was. When the station completes an orbit and returns to Bob, he rejoins Alice. Alice is now younger than Bob.[36] In addition to rotational acceleration, Bob must decelerate to become stationary and then accelerate again to match the orbital speed of the space station.
https://en.wikipedia.org/wiki/Twin_paradox#A_rotational_version
Post by: hamdani yusuf on 27/12/2024 14:08:26
Every now and then I checked if there's someone upload a reasonable effort to explain about the twin paradox worth sharing. I think this one will do.
Twin Paradox is NOT a Paradox: An Explanation that Makes SenseQuoteEinstein's Theory of Special Relativity is confusing. It?s even harder to grasp when all the explanations disagree about how to interpret it. And to top it all off, the explanations all use a PARADOX.
I decided I needed to step in and give one more explanation to destroy the paradox once and for all. Did I succeed? Let me know in the comments what I should clarify in my next video.
Chapters:
00:00 - Intro
00:48 - The Story
03:03 - The Paradox
04:56 - The Problem
07:59 - Breaking the Symmetry
10:15 - Constructed Inertial Frames
12:27 - Video Evidence
15:21 - There is No Paradox
17:33 - Connecting the Dots
Here's an addendum to the previous video.
How to Read a Spacetime Diagram - A Crash Course
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Spacetime diagrams are great tools for understanding Relativity.
This is a crash course in how to read one.
Post by: alancalverd on 27/12/2024 14:46:04
If you start with relativistic physics there is no paradox and the answer converges to the classical result if v << c.
Why do people waste time with this stuff?
Post by: hamdani yusuf on 28/12/2024 08:27:24
Once again, it's only a paradox if you start from classical physics and try to guess what happens in extreme circumstances.You can't expect to find the solution if you can't see the problem in the first place.
If you start with relativistic physics there is no paradox and the answer converges to the classical result if v << c.
Why do people waste time with this stuff?
Post by: alancalverd on 28/12/2024 11:04:52
If you are brought up to believe that π = 3, you will be amazed by the "tape measure paradox". You might even become a philosopher!
Post by: hamdani yusuf on 29/12/2024 15:04:08
There isn't a problem, just a common misconception that Δt = 0 for all systems, simply because it is a near-enough approximation for many purposes.How can rejecting that Δt = 0 for all systems solve the paradox?
If you are brought up to believe that π = 3, you will be amazed by the "tape measure paradox". You might even become a philosopher!
Post by: alancalverd on 30/12/2024 09:39:08
Post by: hamdani yusuf on 30/12/2024 10:46:34
If you show that Δt→0 as v→0, there is no paradox, just a convenient approximation.In the case of original twin paradox, one twin travels at high a speed, significant portion of light speed, to emphasize the relativistic effects.
Post by: alancalverd on 30/12/2024 11:46:31
There's an old saying that a teacher explains a subject he understands, so that a child can understand it; an educationalist obfuscates a subject he doesn't understand so that nobody else can understand it. So it is with the philosophy of science.
one twin travels at high a speedMore correctly, accelerates to a high speed. If there was relative motion at the start of the experiment, they couldn't synchronise identical clocks.
Post by: hamdani yusuf on 01/01/2025 12:48:32
The "original" was not a paradox but the testable (and now demonstrated) solution to a relativistic equation. Only a philosopher could call it a paradox.Your statement here implies that your are trying to redefine the word paradox, or you are trying to rewrite the history of science.
Post by: hamdani yusuf on 01/01/2025 13:01:46
More correctly, accelerates to a high speed. If there was relative motion at the start of the experiment, they couldn't synchronise identical clocks.The space time diagram as in the Wikipedia article and Minutephysics' video shows that accelerating observer doesn't observe significant time jump of the observed object when they are close to each other. The calculated time jump is only significant when they are separated in space.
Post by: alancalverd on 01/01/2025 14:34:28
Your statement here implies that your are trying to redefine the word paradox, or you are trying to rewrite the history of science.Neither.
If I state that the world is round, G is a constant, and some atoms disintegrate, am I rewriting the history of science or merely stating a fact that wasn't obvious 2000 years ago?
Paradox:
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a seemingly absurd or contradictory statement or proposition which when investigated may prove to be well founded or true:
Heavy objects fall at the same rate as light ones. Paradox or observation?
Scientific knowledge is continuously rewritten. That is the distinguishing feature of science.
I don't want to rewrite history, but I do want to teach what we know, and when we can use a convenient approximation.
Post by: alancalverd on 01/01/2025 14:38:47
The calculated time jump is only significant when they are separated in space.And if vrel < ∞ that implies that significant time has elapsed since the point of synchronicity.
Post by: hamdani yusuf on 02/01/2025 03:35:41
I don't want to rewrite history, but I do want to teach what we know, and when we can use a convenient approximation.Historically, the problem of asymmetry of time dilation between travelling clock and stationary clock was called clock paradox.
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https://en.wikipedia.org/wiki/Twin_paradox#History
In 1911, Paul Langevin gave a "striking example" by describing the story of a traveler making a trip at a Lorentz factor of γ = 100 (99.995% the speed of light). The traveler remains in a projectile for one year of his time, and then reverses direction. Upon return, the traveler will find that he has aged two years, while 200 years have passed on Earth. During the trip, both the traveler and Earth keep sending signals to each other at a constant rate, which places Langevin's story among the Doppler shift versions of the twin paradox. The relativistic effects upon the signal rates are used to account for the different aging rates. The asymmetry that occurred because only the traveler underwent acceleration is used to explain why there is any difference at all,[17][18] because "any change of velocity, or any acceleration has an absolute meaning".[A 3]
Max von Laue (1911, 1913) elaborated on Langevin's explanation. Using Hermann Minkowski's spacetime formalism, Laue went on to demonstrate that the world lines of the inertially moving bodies maximize the proper time elapsed between two events. He also wrote that the asymmetric aging is completely accounted for by the fact that the astronaut twin travels in two separate frames, while the Earth twin remains in one frame, and the time of acceleration can be made arbitrarily small compared with the time of inertial motion.[A 4][A 5][A 6] Eventually, Lord Halsbury and others removed any acceleration by introducing the "three-brother" approach. The traveling twin transfers his clock reading to a third one, traveling in the opposite direction. Another way of avoiding acceleration effects is the use of the relativistic Doppler effect (see ? What it looks like: the relativistic Doppler shift below).
Neither Einstein nor Langevin considered such results to be problematic: Einstein only called it "peculiar" while Langevin presented it as a consequence of absolute acceleration.[A 7] Both men argued that, from the time differential illustrated by the story of the twins, no self-contradiction could be constructed. In other words, neither Einstein nor Langevin saw the story of the twins as constituting a challenge to the self-consistency of relativistic physics.
Post by: hamdani yusuf on 02/01/2025 03:40:33
Heavy objects fall at the same rate as light ones. Paradox or observation?Do heavy rain drops fall at the same rate as light rain drops?
Post by: alancalverd on 02/01/2025 09:27:38
Science is bunk, and the Pope is Infallible!
Post by: hamdani yusuf on 02/01/2025 21:00:47
Post by: hamdani yusuf on 02/01/2025 21:27:48
The Wikipedia article also shows some methods to determine how each twin observes the age of the other twin, like by sending signal at a constant interval, say once a year. For example, the journey takes ten years in earth frame, and the time dilation makes the travelling twin to age only eight years. The earth twin sends ten signals and receives only eight. While the travelling twin sends eight signals and receives ten.No it doesn't. In fact, it doesn't mention observation at all since there are no light lines in the picture. If the twin looks at Earth when turning around, he sees the same thing just before and just after the acceleration. The observation only changes in redshift, but no time jump is observed. What is observed would be physical fact, and nobody regardless of where they are could contest it.OK. I agree that this is not an observation, which should also consider light transit time. It's just a mental model of physical reality to calculate and predict the outcome. But if these time jumps are ignored, we get the wrong results.
Nevertheless, the reverse time jump is as real (or as unreal) as the forward time jump in the analysis of twin paradox using space-time diagram.
This scenario unambiguously tells that travelling twin ages less than stationary twin, from the perspective of both twins. It doesn't matter how many times the travelling twin changes his reference frame, as long as he maintains his speed almost constant during the journey.
The stationary twin sends signals at the constant rate, but receives signals at different rate between outgoing and incoming legs of the journey.
Post by: hamdani yusuf on 25/01/2025 06:03:38
The Wikipedia article also shows some methods to determine how each twin observes the age of the other twin, like by sending signal at a constant interval, say once a year. For example, the journey takes ten years in earth frame, and the time dilation makes the travelling twin to age only eight years. The earth twin sends ten signals and receives only eight. While the travelling twin sends eight signals and receives ten.This thought experiment can be used to distinguish between Einstein's theory of relativity and Lorentz' theory of relativity.
This scenario unambiguously tells that travelling twin ages less than stationary twin, from the perspective of both twins. It doesn't matter how many times the travelling twin changes his reference frame, as long as he maintains his speed almost constant during the journey.
The stationary twin sends signals at the constant rate, but receives signals at different rate between outgoing and incoming legs of the journey.
IMO, Lorentz' is easier to simulate. It doesn't involve any time jump. But being easier doesn't necessarily mean more accurate.
For time symmetry, let's make the stationary twin send signals to the travelling twin at t= 0.5, 1.5, 2.5, ..., 9.5 years in his frame of reference.
The traveling twin send signals to the stationary twin at t= 0.5, 1.5, 2.5, ..., 7.5 years in his own frame of reference, which is a journey of 10 years in earth time, but only 8 years in his frame of reference.
When does the twins receive the signals from the other twin?
Post by: alancalverd on 31/01/2025 10:39:31
It doesn't matter how many times the travelling twin changes his reference frame, as long as he maintains his speed almost constant during the journey.Something of a selfcontradiction?
Post by: hamdani yusuf on 31/01/2025 14:36:46
Which part contradicts which other parts?It doesn't matter how many times the travelling twin changes his reference frame, as long as he maintains his speed almost constant during the journey.Something of a selfcontradiction?
Changing velocity without changing speed can be done by following a circular path, thus change the direction.
Post by: alancalverd on 31/01/2025 16:04:52
Post by: hamdani yusuf on 01/02/2025 10:47:06
But that means he is changing from an inertial to an accelerated reference frame. Relativity applies to velocity, not speed.In time dilation formula, the velocity is squared, which makes it indistinguishable from speed.
How do you think the acceleration affects the aging of the twins?
What's the quantitative difference between changing the direction once and twice?
Post by: alancalverd on 02/02/2025 13:41:56
How do you think the acceleration affects the aging of the twins?If there was never any acceleration, either there is no relative velocity or they were never twins.
Post by: hamdani yusuf on 02/02/2025 13:53:19
Does accelerating twin age slower than inertial twin? How much slower is it?How do you think the acceleration affects the aging of the twins?If there was never any acceleration, either there is no relative velocity or they were never twins.
Post by: alancalverd on 02/02/2025 19:33:39
Post by: hamdani yusuf on 03/02/2025 03:19:53
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Yes, according to Einstein?s theory of relativity, the accelerating twin in the famous twin paradox ages more slowly than the inertial twin who stays on Earth. However, the precise calculation of how much slower the accelerating twin ages requires a proper relativistic treatment.It basically says that acceleration effect on aging is negligible compared to the effect from high speed travelling phase. But in the twin paradox case, somehow it can reverse the effect of time dilation on the stationary twin when observed from the perspective of the travelling twin. In other words, it turns time dilation into time contraction.
The acceleration during the turnaround does not directly cause time dilation but is necessary to change frames. During the turnaround, the traveling twin briefly exists in a non-inertial frame, which leads to an asymmetry in the twin paradox. However, the net effect on aging is still dominated by the time dilation from the high-speed travel phases.
Conclusion
The accelerating twin ages less than the inertial twin due to the relativistic time dilation effect. The exact amount of aging difference depends on the velocity and duration of the trip but follows the Lorentz factor formula.
Post by: hamdani yusuf on 03/02/2025 03:22:18
Here's the space-time diagram of this signal exchange between stationary twin and travelling twin, according to Lorentz' theory of relativity.The Wikipedia article also shows some methods to determine how each twin observes the age of the other twin, like by sending signal at a constant interval, say once a year. For example, the journey takes ten years in earth frame, and the time dilation makes the travelling twin to age only eight years. The earth twin sends ten signals and receives only eight. While the travelling twin sends eight signals and receives ten.This thought experiment can be used to distinguish between Einstein's theory of relativity and Lorentz' theory of relativity.
This scenario unambiguously tells that travelling twin ages less than stationary twin, from the perspective of both twins. It doesn't matter how many times the travelling twin changes his reference frame, as long as he maintains his speed almost constant during the journey.
The stationary twin sends signals at the constant rate, but receives signals at different rate between outgoing and incoming legs of the journey.
IMO, Lorentz' is easier to simulate. It doesn't involve any time jump. But being easier doesn't necessarily mean more accurate.
For time symmetry, let's make the stationary twin send signals to the travelling twin at t= 0.5, 1.5, 2.5, ..., 9.5 years in his frame of reference.
The traveling twin send signals to the stationary twin at t= 0.5, 1.5, 2.5, ..., 7.5 years in his own frame of reference, which is a journey of 10 years in earth time, but only 8 years in his frame of reference.
When does the twins receive the signals from the other twin?
(https://www.thenakedscientists.com/forum/index.php?action=dlattach;topic=86675.0;attach=34566)
As usual, horizontal axis represents space while vertical axis represents time.
In left picture, the stationary twin sends light signal every year, starting from t=0.5y. He sends 10 signals in total. The travelling twin only receive 2 signal before he turns around. The other 8 are received during return journey.
In right picture, the travelling twin sends light signal every year in his reference frame, which corresponds to 1.25 years in earth reference because of time dilation. He sends 8 signals in total. The stationary twin only receive 2 signal before half time of the journey period, 1 right at half time, and the other 5 are received after that.
Post by: alancalverd on 03/02/2025 08:35:39
It basically says that acceleration effect on aging is negligibleNo. It implies that acceleration is essential otherwise there cannot be a relative velocity between twins.
The traffic lights turn green. One car accelerates to a constant velocity, the other stays still. Obviously the distance between them increases with time, but only if the initial acceleration is not zero.
Post by: hamdani yusuf on 03/02/2025 11:04:29
It basically says that acceleration effect on aging is negligibleNo. It implies that acceleration is essential otherwise there cannot be a relative velocity between twins.
Read this part.
However, the net effect on aging is still dominated by the time dilation from the high-speed travel phases.
Post by: hamdani yusuf on 03/02/2025 11:08:15
The traffic lights turn green. One car accelerates to a constant velocity, the other stays still. Obviously the distance between them increases with time, but only if the initial acceleration is not zero.In some explanations, the need for acceleration were removed, and replaced with constantly moving ships, only synchronized their clocks when they are passing nearby.
Post by: alancalverd on 03/02/2025 16:57:06
Post by: hamdani yusuf on 04/02/2025 08:48:11
You cannot, by definition, synchronise clocks that are in relative motion. You can set them both to zero as the ships pass, but neither can say that the other is ticking at the same rate, so they are not in sync.In Einstein's Special Theory of Relativity, each observer sees the other's clock ticks slower than their own.
They only tick at the same rate when they are in the same frame of reference. To avoid unnecessary complication, the clocks were built identically using precise mechanism, such as atomic clock. In the thought experiments, the effect of time dilation are usually chosen to be significantly larger than error margin of the clocks.
Post by: alancalverd on 04/02/2025 23:09:18
Post by: hamdani yusuf on 05/02/2025 01:59:44
So no "paradox" if no acceleration. And thanks to Einstein's neat explanation, no paradox anyway.Congratulation. You might just solved a problem that had caused disagreements among physicists for more than a century.
Post by: hamdani yusuf on 05/02/2025 02:22:37
In Lorentz' theory of relativity shown by the diagrams, the stationary clock ticks faster than any other moving clocks, regardless of their directions. There is no constraints about symmetry, regarding the reference frame of the observers.Here's the space-time diagram of this signal exchange between stationary twin and travelling twin, according to Lorentz' theory of relativity.The Wikipedia article also shows some methods to determine how each twin observes the age of the other twin, like by sending signal at a constant interval, say once a year. For example, the journey takes ten years in earth frame, and the time dilation makes the travelling twin to age only eight years. The earth twin sends ten signals and receives only eight. While the travelling twin sends eight signals and receives ten.This thought experiment can be used to distinguish between Einstein's theory of relativity and Lorentz' theory of relativity.
This scenario unambiguously tells that travelling twin ages less than stationary twin, from the perspective of both twins. It doesn't matter how many times the travelling twin changes his reference frame, as long as he maintains his speed almost constant during the journey.
The stationary twin sends signals at the constant rate, but receives signals at different rate between outgoing and incoming legs of the journey.
IMO, Lorentz' is easier to simulate. It doesn't involve any time jump. But being easier doesn't necessarily mean more accurate.
For time symmetry, let's make the stationary twin send signals to the travelling twin at t= 0.5, 1.5, 2.5, ..., 9.5 years in his frame of reference.
The traveling twin send signals to the stationary twin at t= 0.5, 1.5, 2.5, ..., 7.5 years in his own frame of reference, which is a journey of 10 years in earth time, but only 8 years in his frame of reference.
When does the twins receive the signals from the other twin?
(https://www.thenakedscientists.com/forum/index.php?action=dlattach;topic=86675.0;attach=34566)
As usual, horizontal axis represents space while vertical axis represents time.
In left picture, the stationary twin sends light signal every year, starting from t=0.5y. He sends 10 signals in total. The travelling twin only receive 2 signal before he turns around. The other 8 are received during return journey.
In right picture, the travelling twin sends light signal every year in his reference frame, which corresponds to 1.25 years in earth reference because of time dilation. He sends 8 signals in total. The stationary twin only receive 2 signal before half time of the journey period, 1 right at half time, and the other 5 are received after that.
On the other hand, constraints about symmetry of relativistic effects between relatively moving observers is postulated in Einstein's Special Theory of Relativity. To produce asymmetric result like in the case of twin/clock paradox, there must be a symmetry breaker somewhere down the line of reasoning in the thought experiment. Currently mainstream physics explanation, like shown in Wikipedia article, introduces time jump during turn around period, which effectively reverse the effect of time dilation of stationary twin in the perspective of traveling twin into time contraction.
How can this model be demonstrated in space-time diagrams to show the sequence of events in relativistic journey of the travelling twin when it's tracked with signals exchange?
Post by: alancalverd on 05/02/2025 10:54:25
Congratulation. You might just solved a problem that had caused disagreements among physicists for more than a century.God knows what they disagree about. The theory of relativity predicts a phenomenon that is supported by measurement, which is the way of physics. Anything else is philosophy.
Post by: hamdani yusuf on 05/02/2025 12:23:48
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Einstein's conclusion of an actual difference in registered clock times (or aging) between reunited parties caused Paul Langevin to posit an actual, albeit experimentally indiscernible, absolute frame of reference:
In 1911, Langevin wrote: "A uniform translation in the aether has no experimental sense. But because of this it should not be concluded, as has sometimes happened prematurely, that the concept of aether must be abandoned, that the aether is non-existent and inaccessible to experiment. Only a uniform velocity relative to it cannot be detected, but any change of velocity ... has an absolute sense."[37]
In 1913, Henri Poincar?'s posthumous Last Essays were published and there he had restated his position: "Today some physicists want to adopt a new convention. It is not that they are constrained to do so; they consider this new convention more convenient; that is all. And those who are not of this opinion can legitimately retain the old one."[38]
In the relativity of Poincar? and Hendrik Lorentz, which assumes an absolute (though experimentally indiscernible) frame of reference, no paradox arises due to the fact that clock slowing (along with length contraction and velocity) is regarded as an actuality, hence the actual time differential between the reunited clocks.
In that interpretation, a party at rest with the totality of the cosmos (at rest with the barycenter of the universe, or at rest with a possible ether) would have the maximum rate of time-keeping and have non-contracted length. All the effects of Einstein's special relativity (consistent light-speed measure, as well as symmetrically measured clock-slowing and length-contraction across inertial frames) fall into place.
That interpretation of relativity, which John A. Wheeler calls "ether theory B (length contraction plus time contraction)", did not gain as much traction as Einstein's, which simply disregarded any deeper reality behind the symmetrical measurements across inertial frames. There is no physical test which distinguishes one interpretation from the other.[39]
In 2005, Robert B. Laughlin (Physics Nobel Laureate, Stanford University), wrote about the nature of space: "It is ironic that Einstein's most creative work, the general theory of relativity, should boil down to conceptualizing space as a medium when his original premise [in special relativity] was that no such medium existed ... The word 'ether' has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum. ... Relativity actually says nothing about the existence or nonexistence of matter pervading the universe, only that any such matter must have relativistic symmetry (i.e., as measured)."[40]
In Special Relativity (1968), A. P. French wrote: "Note, though, that we are appealing to the reality of A's acceleration, and to the observability of the inertial forces associated with it. Would such effects as the twin paradox (specifically -- the time keeping differential between reunited clocks) exist if the framework of fixed stars and distant galaxies were not there? Most physicists would say no. Our ultimate definition of an inertial frame may indeed be that it is a frame having zero acceleration with respect to the matter of the universe at large."[41]
Post by: paul cotter on 06/02/2025 21:29:05
Post by: Halc on 07/02/2025 02:29:11
Concerning some misunderstood wiki page on absolutism:
TheNo it doesn't since neither twin has any way of knowing which of the two is stationary, and when.
This scenario unambiguously tells that travelling twin ages less than stationary twin, from the perspective of both twins.
This thought experiment can be used to distinguish between Einstein's theory of relativity and Lorentz' theory of relativity.No it cannot since the two are supposed to be empirically identical.
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IMO, Lorentz' is easier to simulate. It doesn't involve any time jump.Which reduces it to the method described by the very first reply to the "What is the exact cause of the time dilation of the twin?" thread, except the method described there doesn't require one to know an unknowable thing.
The absolutist interpretation is vastly more complicated, and took over 100 years to generalize, as opposed to 11 for the relative interpretation.
I asked ChatGPTYea, it actually said that. chatGTP is wrong as usual. Excellent source of obfuscation, which seems to be your purpose.
...
It basically says that acceleration effect on aging is negligible compared to the effect from high speed travelling phase.
In Einstein's Special Theory of Relativity, each observer sees the other's clock ticks slower than their own.Not true. You're making up nonsense facts. This assertion actually contradicts your spacetime diagrams showing signals being sent between the twins.
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They only tick at the same rate when they are in the same frame of reference.Also wrong, and it is impossible to not be in a frame of reference under SR.
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To avoid unnecessary complication, the clocks were built identically using precise mechanism, such as atomic clock.How the clocks work is an engineering problem. It's a thought experiment. Clocks are assumed to not be broken. The twins are the clocks. That's the whole point. Twins are presumed to appear the same age given normal situations, and that appearance is the precision of the experiment, else all you'd need to do is skip the twins and just send clocks. Oh right, they actually did that (a lot, and at super high speeds). Those were not thought experiments.
I think that was another made up fact, unless it refers to the disagreement as to how best to explain the scenario, especially since there's so many correct ways to do it, apparently none of which are described clearly in this thread.CYou might just solved a problem that had caused disagreements among physicists for more than a century.God knows what they disagree about. The theory of relativity predicts a phenomenon that is supported by measurement, which is the way of physics. Anything else is philosophy.
https://en.wikipedia.org/wiki/Twin_paradox#No_twin_paradox_in_an_absolute_frame_of_referenceAh, the page for the denialists. Figures that wiki would given them that. Let's critique some of what wiki says.
Quote from: wiki
In 1911, Langevin wrote: "A uniform translation in the aether has no experimental sense. But because of this it should not be concluded, as has sometimes happened prematurely, that the concept of aether must be abandoned, that the aether is non-existent and inaccessible to experiment. Only a uniform velocity relative to it cannot be detected, but any change of velocity ... has an absolute sense."Translation: Aether is like Russel's teapot: Makes zero difference, utterly undetectable, and complicates the model for no reason. So yes, let's do it.
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In that interpretation, a party at rest with the totality of the cosmos (at rest with the barycenter of the universeI love this one. They give the universe a barycenter, which implies there's a direction you can point to the center of the universe (which is always Earth of course, God would have it no other way)
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would have the maximum rate of time-keepingNot if you don't know how deep in a gravity well you are, which also cannot be known.
And now one of the favorite quote for the cranks. I see one like this on every denialist site. Great guy, plenty of cred to his name, and he's not wrong, but the comment is always taken wrong.
Quote
In 2005, Robert B. Laughlin (Physics Nobel Laureate, Stanford University), wrote about the nature of space: "It is ironic that Einstein's most creative work, the general theory of relativity, should boil down to conceptualizing space as a medium when his original premise [in special relativity] was that no such medium existed ... The word 'ether' has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum."Yes, under GR, space is indeed endowed with some physical qualities, and special relativity attempted to avoid that.. However, velocity is not one of these qualities. When aether is introduced in forum threads as it has here, quotes like the one above is usually used specifically to incorrectly introduce that property.
Given that all versions of the aether theories endow it primarily with the property of velocity, it seems entirely inappropriate to label something without it as aether, as you seem to be suggesting.
Quote
In Special Relativity (1968), A. P. French wrote: "...Our ultimate definition of an inertial frame may indeed be that it is a frame having zero acceleration with respect to the matter of the universe at large."French here seems to suggest that acceleration is relative (to matter), and not absolute. It seems that if there were no stars in view, you'd not be able to tell if your rocket engines were on or not.
OK, this guy is actually wrong if he actually said this.
As there is ZERO proof or disproof of an aether it has no role in positive science.I suppose so. Take quantum interpretations. Most consider them to have a role in science, albeit a metaphysical one. A good grad course in quantum theory might spend part of one lecture reviewing the various interpretations, but none of them has anything to do with the theory proper (the whole shut up and calculate attitude).
Some interpretations are utterly simple, and some get super complicated in attempt to hold on to classical assumptions as long as possible. Aether interpretation is much like Bohmian mechanics in that way: Max complication to serve the purpose of rationalizing your intuitions rather than finding rational alternatives to your intuitions.
Post by: hamdani yusuf on 07/02/2025 10:44:34
No it doesn't since neither twin has any way of knowing which of the two is stationary, and when.The Wikipedia quote is in context of Lorentz' theory of relativity, which asserts that time dilation is experienced by objects moving through aether. The twin that age slower should be the one who moves faster.
Post by: hamdani yusuf on 07/02/2025 10:48:44
No it cannot since the two are supposed to be empirically identical.They are not identical. The difference between them is in the determining of reference frame where v=0, which causes no time dilation nor length contraction.
Post by: hamdani yusuf on 07/02/2025 12:31:33
Which reduces it to the method described by the very first reply to the "What is the exact cause of the time dilation of the twin?" thread, except the method described there doesn't require one to know an unknowable thing.How do you draw the space time diagram for signal exchange between the twins?
The absolutist interpretation is vastly more complicated, and took over 100 years to generalize, as opposed to 11 for the relative interpretation.
Post by: hamdani yusuf on 07/02/2025 12:35:35
Yea, it actually said that. chatGTP is wrong as usual. Excellent source of obfuscation, which seems to be your purpose.It distilled the information from the training datasets. They were trained mostly with mainstream sources.
Post by: alancalverd on 07/02/2025 12:37:41
neither twin has any way of knowing which of the two is stationary, and when.Which is why you need to introduce acceleration, to identify the travelling twin.
Post by: hamdani yusuf on 07/02/2025 12:38:48
Not true. You're making up nonsense facts. This assertion actually contradicts your spacetime diagrams showing signals being sent between the twins.It's a logical consequence from the postulate that there's no preferred frame of reference.
My space time diagrams showing signal exchange are based on Lorentz Lorentz' Theory of Relativity, not Einstein's STR. You seem to be confused between the two.
Post by: alancalverd on 07/02/2025 12:39:49
It distilled the information from the training datasets. They were trained mostly with mainstream sources.For "training dataset" read "untraceable and unverified sources including unspecified and unfiltered garbage".
Post by: hamdani yusuf on 07/02/2025 12:45:10
An observer can observe objects in different reference frame. That's what Lorentz' transformation is for. The formula suggests that ther will be time dilation when the observer and the observed object are in different reference frame.QuoteQuoteAlso wrong, and it is impossible to not be in a frame of reference under SR.
They only tick at the same rate when they are in the same frame of reference.
Post by: hamdani yusuf on 07/02/2025 12:51:18
So let's just use identically manufactured atomic clocks.QuoteTo avoid unnecessary complication, the clocks were built identically using precise mechanism, such as atomic clock.How the clocks work is an engineering problem. It's a thought experiment. Clocks are assumed to not be broken. The twins are the clocks. That's the whole point. Twins are presumed to appear the same age given normal situations, and that appearance is the precision of the experiment, else all you'd need to do is skip the twins and just send clocks. Oh right, they actually did that (a lot, and at super high speeds). Those were not thought experiments.
Post by: hamdani yusuf on 07/02/2025 12:59:07
Given that all versions of the aether theories endow it primarily with the property of velocity, it seems entirely inappropriate to label something without it as aether, as you seem to be suggesting.I'm not suggesting anything about aether. What I'm trying to do is comparing two versions of relativity theories in the case of twin paradox.
Post by: hamdani yusuf on 07/02/2025 13:02:32
French here seems to suggest that acceleration is relative (to matter), and not absolute. It seems that if there were no stars in view, you'd not be able to tell if your rocket engines were on or not.He wrote it in his book.
OK, this guy is actually wrong if he actually said this.
Post by: alancalverd on 07/02/2025 15:39:53
Would such effects as the twin paradox (specifically -- the time keeping differential between reunited clocks) exist if the framework of fixed stars and distant galaxies were not there?Not sure about the credentials of the writer, but there are no fixed stars! "Fixed stars" is a good-enough approximation for navigational purposes. but they aren't attached to anything, just a very long time away from the solar system.
Post by: hamdani yusuf on 09/02/2025 22:34:25
It seems to rely on conservation of momentum in a closed system. With larger system, its momentum tends to be more stable.Would such effects as the twin paradox (specifically -- the time keeping differential between reunited clocks) exist if the framework of fixed stars and distant galaxies were not there?Not sure about the credentials of the writer, but there are no fixed stars! "Fixed stars" is a good-enough approximation for navigational purposes. but they aren't attached to anything, just a very long time away from the solar system.
Post by: alancalverd on 09/02/2025 22:42:56
You can do better, but not if you use crap sources like chatbots and youtube.
Post by: hamdani yusuf on 11/02/2025 15:28:14
Word salad, I'm afraid.I'll take whatever information sources available and accessible, and then compare their strength and weaknesses. They include people's posts in science forums.
You can do better, but not if you use crap sources like chatbots and youtube.
How would you depict time jump shown in common space time diagrams explaining asymmetry in the twin paradox for the case with signal exchanging twins?
Post by: alancalverd on 11/02/2025 22:21:47
Post by: hamdani yusuf on 13/02/2025 09:06:05
Your travelling twin has accelerated, thus breaking symmetry.Symmetry breaking is necessary but inadequate to explain twin paradox. The explanation must show how the time dilation of the stationary twin must be reversed into time contraction according to the travelling twin.
Post by: paul cotter on 13/02/2025 15:31:07
Post by: alancalverd on 14/02/2025 17:04:55
Post by: hamdani yusuf on 17/02/2025 08:56:11
"Time contraction"? Where did you get this from?In standard explanation for the twin paradox, the stationary twin observes the travelling twin ages less than himself. He perceives that travelling twin experiences time dilation.
On the other hand, the travelling twin observes the stationary twin ages more than himself. He perceives that stationary twin experiences time contraction. It's simply the antonym for dilation. Do you have a better terminology?
Post by: hamdani yusuf on 17/02/2025 09:21:04
Same place as he got "paradox" and "time jump", I think.You can find them in Wikipedia and YouTube videos, including from those who are considered mainstream scientists.
Wikipedia called it as "the plane of simultaneity jump".
Post by: alancalverd on 17/02/2025 09:27:23
In standard explanation for the twin paradox, the stationary twin observes the travelling twin ages less than himself. He perceives that travelling twin experiences time dilation.OK, that makes sense.
On the other hand, the travelling twin observes the stationary twin ages more than himself. He perceives that stationary twin experiences time contraction. It's simply the antonym for dilation. Do you have a better terminology?
BUT the fact that A thinks B has undergone an expansion and B thinks A has undergone a contraction is very, very significant! It means that you can't base any explanation on "a continuously travelling" twin, i.e. a situation in which the relative velocity has "always existed", because if there is nothing in their motion history to distinguish between the twins, the effects must be symmetrical.
Therefore the "travelling twin" must have undergone an acceleration since their clocks were synchronised.
Once again, the "paradox" only exists if you think there is (or should be) such a thing as absolute velocity, i.e you are trying to derive an observed relativistic effect from a classical axiom. Physics doesn't work that way. So your "mainstream" physicists are not worthy of the title.
Post by: paul cotter on 17/02/2025 09:44:38
Post by: alancalverd on 17/02/2025 12:24:33
Post by: Halc on 17/02/2025 12:36:25
In special relativity there is time dilation and length contraction. There is neither time contraction nor length dilation.There is also relativity of simultaneity. I see almost no mention of it anywhere, and yet this accounts for all of the stuff that Hamdani finds so confusing, and finds so many unofficial terms for in various pop sites.
Here's the space-time diagram of this signal exchange between stationary twin and travelling twin, according to Lorentz' theory of relativity.Actually, the picture you post illustrates relativity theory, not LET theory, for three or four reasons:
1) There is no spacetime under LET. It is a theory used for 3D space existing in time (presentism), not 4D spacetime.
2) The picture presumes that the Earth people can determine that they are stationary. There is no way to determine that, so the presumption is unwarranted.
3) There are red lines of simultaneity in the picture. Lines of simultaneity are always horizontal under LET.
4) The universe of LET can have no gravity, so it is not a model of reality. Lorentz never came up with a model that included gravity, which is good because if he did, there's be no way to tell actual time even if you magically knew which clock was stationary.
Under LET, many coordinate effects (the ones Paul mentions above, the RoS, mass, etc. all become real. But so many things that are real under relativity (what clocks measure, what rulers measure) all become coordinate things. Translation: you cannot measure anything at all under LET because none of your tools work, and all the things that are real are undetectable. So why defend this? I know two reasons why, but I've only mentioned the one.
Post by: hamdani yusuf on 18/02/2025 09:33:56
Actually, the picture you post illustrates relativity theory, not LET theory, for three or four reasons:It's a picture of 1D space against 1 D time. Just like classical mechanics in uniform straight motion.
1) There is no spacetime under LET. It is a theory used for 3D space existing in time (presentism), not 4D spacetime.
Post by: hamdani yusuf on 18/02/2025 09:35:32
2) The picture presumes that the Earth people can determine that they are stationary. There is no way to determine that, so the presumption is unwarranted.It was assumed to have something to calculate.
Post by: hamdani yusuf on 18/02/2025 09:36:55
3) There are red lines of simultaneity in the picture. Lines of simultaneity are always horizontal under LET.They're not lines of simultaneity. They're laser signal trajectory.
Post by: hamdani yusuf on 18/02/2025 09:41:40
4) The universe of LET can have no gravity, so it is not a model of reality. Lorentz never came up with a model that included gravity, which is good because if he did, there's be no way to tell actual time even if you magically knew which clock was stationary.Why not?
Lorentz didn't thought about it doesn't mean that someone else can't add it.
It's just a coincidence that general theory of relativity was written by the same person as special theory of relativity.
Post by: hamdani yusuf on 18/02/2025 09:44:23
Under LET, many coordinate effects (the ones Paul mentions above, the RoS, mass, etc. all become real. But so many things that are real under relativity (what clocks measure, what rulers measure) all become coordinate things. Translation: you cannot measure anything at all under LET because none of your tools work, and all the things that are real are undetectable. So why defend this? I know two reasons why, but I've only mentioned the one.I don't defend LET. I was comparing it's implications in contrast to STR to see which one is better for explaining the twin paradox.
Post by: Halc on 18/02/2025 18:49:08
They're not lines of simultaneity. They're laser signal trajectory.So they are. My mistake. From that standpoint, the picture works with either theory.
It was assumed to have something to calculate.They can calculate, sure, but they've no way to measure anything, so any calculation is abstract.
Length of anything cannot be measured. Time cannot be measured, even if one has impossible access to knowledge of being stationary. Proper acceleration is real under relativity and abstract under LET. Coordinate acceleration can be computed from a chosen frame under relativity. Acceleration under LET is absolute (real), and totally incalculable.from empirical measurements.
Lorentz didn't thought about it doesn't mean that someone else can't add it.He did thought about it, and never completed the task. Yes, it was eventually done, but it took a century, and I suspect you don't know the name of the one that did it. Predictions from relativity go away, so no more black holes or big bang theory. There is no absolute time, even if there somehow was a magical velocity meter and a magical objective gravitational potential meter.
The theory supports two new things, neither of which in any way can be measured at all. It is far more complicated, and I see it referenced only by other denialist papers. But yes, it was eventually generalized.
The theory can be falsified by suicide, but the dead cannot publish the results.
I don't defend LET. I was comparing it's implications in contrast to STR to see which one is better for explaining the twin paradox.And how is that going? How does LET explain the scenario any better than the very first reply to the "What is the exact cause of the time dilation of the twin?" topic, which uses Einstein's theory?
Most topics are answered correctly within the first few replies. Ones that turn into blogs of hundreds of posts do not serve to answer any questions, and serve only to obfuscate any reasonable answers. You for instance choose to rebut any good answer with some counter point rather than actually learn something from it. I cannot find a place in any of your topics where you actually appear to learn something not known at the start of the topic.
You will not learn anything from this post. But I just have to butt in occasionally to remind the 3rd part reader what nonsense is being peddled in these blogs.
Post by: hamdani yusuf on 19/02/2025 08:58:10
The theory can be falsified by suicide,Death of the author is independent from the falsification of their theory.
It can be falsified by showing contradictory implications of the theory, or showing some observation which is incompatible with the theory.
Post by: hamdani yusuf on 06/04/2025 15:09:06
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How does velocity time dilation work if two observers are both traveling at velocity v in the same direction and one of the observed slows down to 1/2v? Which of the two observers experiences time at a slower rate after the deceleration?
Post by: alancalverd on 06/04/2025 23:35:30
Post by: hamdani yusuf on 07/04/2025 03:45:42
The question assumes the existence of absolute velocity.It's not assumed by the question. It's assumed if you answer that the observer keep moving at v will experience time at a slower rate.
Post by: alancalverd on 07/04/2025 04:08:36
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two observers are both traveling at velocity v in the same directionis meaningless unless there is such a thing as absolute velocity, which there isn't, or a third observer, which isn't stated or relevant to the question.
The only fact is that one of the observers has undergone an acceleration from 0 to v/2 relative to the other.
Post by: hamdani yusuf on 04/07/2025 05:41:27
It only means that their relative positions don't change with time. This can be determined even when there is no absolute velocity.Quotetwo observers are both traveling at velocity v in the same directionis meaningless unless there is such a thing as absolute velocity, which there isn't, or a third observer, which isn't stated or relevant to the question.
The only fact is that one of the observers has undergone an acceleration from 0 to v/2 relative to the other.
Post by: A-wal on 04/07/2025 14:37:39
Here's the space-time diagram of this signal exchange between stationary twin and travelling twin, according to Lorentz' theory of relativity.You are perfectly free to posit an ether frame that defines motion relative to it and everything still works in exactly the same way but there is no preferred ether frame, you're free to use any frame you like. That's not a different model, that's just special relativity using one arbitrary coordinate system for every observer.
In standard explanation for the twin paradox, the stationary twin observes the travelling twin ages less than himself. He perceives that travelling twin experiences time dilation.Other way round! Less time passes for the more accelerated twin so the more accelerated twin has been time contracted with respect to the less accelerated twin (what you called stationary) and the less accelerated twin has been time dilated with respect to the more accelerated twin.
On the other hand, the travelling twin observes the stationary twin ages more than himself. He perceives that stationary twin experiences time contraction. It's simply the antonym for dilation. Do you have a better terminology?
The whole time dilation length contraction terminology is an absolute mess. Length, wtf is that? So there's no lengths of time then? Length doesn't exclude a duration. It's the contraction of space with respect to bodies in motion relative to the observer.
But then time dilation is the extended time on the observer's own clocks with respect to bodies in motion relative to the observer, you don't see your own clocks as dilated! You see clocks in motion relative to you as contracted so why frame in in the context of unobservable dilation?
That's why I use space contraction and time contraction, time dilation is reserved for the observable speeding up of clocks that the observer is accelerating relative to which is officially called a simultaneity shift.
This time dilation is the only thing responsible for the age difference in the twin paradox because unlike space contraction and time contraction, observable time dilation is non-reciprocal in that it only applies to bodies that you accelerate relative to.
It's caused by but not proportional to acceleration so acceleration is the cause but not the direct cause. It's proportional to the change in relative velocity scaled by the distance between the observer and the clock that the observer is accelerating relative to.
So they're at rest relative to each other then, so the question is just: How does each observer measure the tick rate of the other observer's clocks if two observers are at rest relative to each other and one of them then accelerates relative to the other? Which of the two observers experiences time at a slower rate after the acceleration?It only means that their relative positions don't change with time. This can be determined even when there is no absolute velocity.Quotetwo observers are both traveling at velocity v in the same directionis meaningless unless there is such a thing as absolute velocity, which there isn't, or a third observer, which isn't stated or relevant to the question.
The only fact is that one of the observers has undergone an acceleration from 0 to v/2 relative to the other.
The answer is that after the acceleration when they are in constant motion relative to each other each sees the other clock as time contracted (running slower than their own clock) by T = t(√((c^2−v^2)/c^2)). During the acceleration the observer that is accelerating relative to the other observer sees the other observer's clock as time dilated.
This is caused by changing to a frame in which the distance between the observer that they're accelerating relative to and other bodies at rest relative to that observer become shorter in their new frame so it takes less time to travel those shorter distances.
If you like I can post a screenshot of the general formula I derived that works for simultaneity shifts of any acceleration profile regardless of how unsmooth it is.
Post by: paul cotter on 04/07/2025 18:22:10
Post by: A-wal on 04/07/2025 19:00:08
An ether frame works but it works for any frame, so if there's no preferred ether frame it's just special relativity using the same frame for every observer.
The confusion for terms like time dilation is the fault of the official terms being very misleading, so clarity about the context is important.
The twin paradox time difference is caused by the traveling twin accelerating to a frame in which the distance between the Earth observer and the turnaround point becomes shorter while the traveling twin is in motion relative to them so it takes less time to travel that shorter distance.
This causes a non-reciprocal time dilation (speeding up) of Earth's clocks from the perspective of the accelerating twin but only at the turnaround point, not the initial and final accelerations because simultaneity shifts are proportional to distance.
Post by: paul cotter on 06/07/2025 11:08:45