1

Physics, Astronomy & Cosmology / Re: Are Black Holes Real? Is Time Travel Possible?

« on: 16/01/2025 16:47:15 »

I was going to start a question here by first saying that there is a wormhole at the center of every black hole.

This is false. A wormhole is a valid solution to Einstein's field equations, but the conditions require exotic matter (say with negative mass) for this kind of thing to work. It has nothing to do with black holes.

There is a "singularity" at the center of every black hole. "A point of infinite density." (How is infinity possible?)

This is also completely wrong. AI has no clue. A singularity means a region where the equations no longer apply. It doesn't mean a point of infinite density. Matter is pulled apart by tidal forces near a large mass, not compressed at all. There is never a time during the fall that compression occurs.

Has one been ever observed?

Yes and no. They have pictures, yes, but the picture shows the X-ray emissions from the plasma surrounding one, not the BH itself, which is, well, black.

And black holes would take you to another time and place in spacetime.

So does sitting at your desk.

So time travel is theoretically possible?

You existed in 2024. You exist in 2025. If that's time travel, then yes. If you don't consider that to be time travel, then no because falling into a black hole is no different.

What about temporal paradoxes? The the grandfather temporal paradox talks about an extreme example.

There is no paradox here since you won't find your young grandfather by going into a black hole any more than you would by sitting at your desk. There is no worldline leading to 'the past' in any black hole.

And what about other ways of going back in time?

There isn't a first way to go back in time. Star Trek is fiction, as is any TV show or movie, including those that supposedly try to keep things plausible like 'Gravity'.

2

Technology / Re: Does cold weather damage the batteries used in an EV?

« on: 11/01/2025 15:37:15 »

First of all, cold means salt, and especially Tesla hasn't shown any obvious awareness of the need to protect parts from corrosion.  That's an issue since batteries are at the bottom of the car where the salt is.

2.     If a rechargeable battery loses some capacity (in the sense of KWh of electrical energy it can store or deliver)  in the cold weather,  where does that energy go?

Capacity and energy are different things.  Sure, you put X energy into the car, it gets cold, and now there's less energy available. It went away with the heat?  Does the full charge return if it warms up or do you need to top off a full battery if it's been cold and it's warm now?  I don't know the answer to that one.

3

Physics, Astronomy & Cosmology / Re: What Is The Final Parsec Problem ?

« on: 06/01/2025 18:47:47 »

    When galaxies collide, their central supermassive black holes (SMBHs) should also eventually merge.
    However, as the SMBHs approach each other within about a parsec (3.26 light-years), the density of stars and gas in the galactic core becomes too low to effectively remove the energy and momentum needed for the final plunge and merger.
    This "energy loss problem" prevents the black holes from spiraling inward and merging within a reasonable timeframe.

So how do Black Holes merge then ?

The quote you give kind of says it.  To get closer, their kinetic energy must go somewhere, else, like Earth, it just keeps orbiting the sun without getting closer.

Thing is, the way this energy is dissipated is by flinging other matter away, giving that matter the orbital energy of the pair. Once the material is all gone, only new (not orbiting) material can contribute further to this process, and that takes a lot of time.

They will eventually merge, just all all planets will eventually fall into the sun given enough time and no external dissturbance.  Any pair of orbiting objects emits gravitational waves and that energy comes from kinetic energy.. Earth for instance emits GWs at the rate of about 200 watts, and the kinetic energy of Earth will run a pair of 100W light bulbs for an awfully long time.  The sun will swallow Earth before that has time to happen, but that's the fate of say Jupiter.

Likewise, all black hole binaries like the undoctored picture you took will eventually merge, but the universe is only 14 billion years old, nowhere near long enough for gravitational waves to do the job at a full parsec away.


Fun fact: Two sheep circling each other will emit Baaavitational waves.

4

New Theories / Re: How does Hamdani explain the twins paradox?

« 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.

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.

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.

#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.

It predicts apparent time jump in the observation by traveling twin

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.

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.

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.

5

New Theories / Re: How does Hamdani explain the twins paradox?

« 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.

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.

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.

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.

Also to see if the travelling twin can be a valid observer

Differential 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.

how he views the  time dilation experienced by the other twin.

Time dilation isn't something anybody experiences, per the first postulate of SR.

6

New Theories / Re: How does Hamdani explain the twins paradox?

« 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?

7

New Theories / Re: How does Hamdani explain the twins paradox?

« 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.

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.

It shows no such thing since your twins are never a different age when co-located.

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)

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.

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.

8

New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 11/12/2024 17:16:13 »

Two people pass each other on the street; and according to one of the two people

This is a nit, I know, but this sort of language has set public understanding of modern science back by decades since the wording seems to suggests that physical reality is dependent on human observation, which is true of neither relativity nor quantum mechanics. That rant said, keep in mind that "according to one of the two people" is a misleading shorthand for "relative to the inertial frame in which one of the two people is stationary".

Humans choose different frames all the time, and not often that one except when checking one's pockets or something.

Secondly, another nit is that using special relativity presumes flat spacetime, and the spacetime between here and Andromeda is not flat.  I'm also willing to ignore that since it is besides the point being illustrated by the example.

an Andromedean space fleet has already set off on its journey,

Third nit is that this statement is a counterfactual, a statement of the state of something unmeasured. Such assumptions are typically assumed in special relativity exercises, but not in quantum mechanics where few consider the principle to be sound.  I am fine with this assumption for this exercise.

None of these nits are fatal to the point, or make it wrong.  Yet.

How can there still be some uncertainty as to the outcome of that decision?

Exactly because it has not been measured. That leaves it uncertain to the measurer, and in fact it will never be measured because by the time the light gets here, the telescopes will long since have ceased to function.

But Penrose assumes both a 3D spatial universe (presentism) and a 4D spacetime universe, and the paradox seems to revolve around these two incompatible models being used at the same time.
In the 4D block model, the entire history of the universe has the same ontology, meaning the invasion is objective fact and is not in any way a function of a reference frame. Presentism is not compatible with relativity of simultaneity. Simultaneity across the universe is objective and not observer or frame dependent. He needs to pick one model and stick with it. This is more than just a nit. It crosses the line into being self-inconsistent.

If to either person the decision has already been made, then surely there cannot be any uncertainty.

Under the block model, all events have equal ontology and the decision very much is part of it. The only thing that the two observers are doing is comparing different pairs of objective events. There is no 'has already been' of anything since that is a reference to the present.

according to one of them, the decision lay in the uncertain future, while to the other, it lay in the certain past.

Here is a blatant reference to presentism, something totally incompatible with the 4D spacetime model his two people are leveraging. Thus Penrose sows the seeds of confusion rather than adding clarification to what SR actually says. Bad form...

So many many light years away, the "paradox" of Andromedeans having launched, or who will launch, a fleet, is well beyond an observational limit.

The observational limit is one's past light cone, and that cone is identical for both observers (well, a couple meters apart actually), but way over at Andromeda, those two different light cones are still only a couple meters apart.


A more correct wording of the Andromeda scenario is that we have these two different inertial frames differing by a couple m/sec in velocity, and we have one event of these two people passing by each other, and another event of the Andromedan fleet launching. Relative to one of those frames, the people passing event occurs first, and relative to the other frame, the fleet launch event occurs first.  Same two events, but ordered differently in one frame as compared to the other. That is a far better wording of the scenario that presumes SR and it utilizes only B-series language.

9

Just Chat! / Re: Help!

« on: 10/12/2024 16:10:06 »

I tried to reply to Hamdani on his "origin of the magnetic field" and it came up as a new topic which I find I cannot delete. Any suggestions?

I fixed it. Not deleted. It is now a reply to that topic.
As for why it occurred, no idea.  Wrong button pushed?  The topic title was different ("field" instead of "force"), so that means it was never composed as a reply in the first place, and suggests the post wasn't opened via the 'quote selected' option.

10

Just Chat! / Re: Theories to start a new world.

« on: 09/12/2024 18:39:48 »

Due to some problem, civilisation is leaving earth and will try to colonise some other planet and start a new world.   You can take the material that describes three theories in science.   Which three theories would you choose to take?

I had a hard time with this and have not until now contributed. I find it pretty implausible that the means to get to another world is somehow feasible but the means to take significant information along is not.

I would think skills would be more important than any scientific theory.  Literacy?  What good does even that do if certain other skills are not yet acquired?  How primitive is our group?  Need to start there if we're to give them something useful to advance.

#1: I'd send some kind of record of where they came from, since that will not easily be gleaned if the information is lost. The ability to read the record can wait in necessary.  This one counts since who knows what scientific theory they'd otherwise come up with to explain their sudden appearance without a nice trail of biological fossils to support something like evolution.


Concerning philosophy.

Questions such as (1) why are we here, (2) why is there good and evil, (3) what is the nature of human consciousness, (4) why does the universe exist, and many others may not trouble a logical being like your good self but a lot of humans seek answers to these questions and science cannot provide the answers.

That's right. Sans answers to these, there seems nothing to send with the ship.
Alan has posted an awful lot of philosophy for somebody who pokes so much fun of it.

Hi.

Religion is all about selling undisprovable hypotheses in order to control people's actions.

   No, that just sounds like human selfishness, corruption and some desire for power by a few people who have come to be in charge of the religion or else in charge of something else and just citing religion as supporting them.

Sorry, but I agree with Alan here. Religion is for herding sheep, and a group of herded sheep is more fit than the same sheep not herded. Hence it is not entirely a good idea to debunk religion as part of our 3 tidbits we take along. People who know what is going on are not so easily herded.

Religion is about not wanting to be alone, left feeling pointless, worried about not existing any longer, seeking the answers to fundamental questions  etc. etc.

AFAIK no other species suffers from any of these.

I would differ. Any social creature suffers from severance from its society. Go to a good pet shop and they'll tell you which species/breeds do well in isolation and which need to be kept with their own kind. Love birds are notoriously on the 2nd list.  I had a budgie which suffered significant stress from severance from his deafening buddies, but he eventually bonded with us and became super friendly.

I'm not sure how religion satisfies loneliness, but I do see it providing purpose. The loneliness is perhaps how they rope you into cults and financial scams and such, a tool for the herders.
.

11

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 07/12/2024 18:53:02 »

I was hoping we could lean towards what an exact reason for the different ages of twins is.

Am I missing something? I was of the opinion that this question was comprehensively answered at an early stage in this query.

That was indeed done in the very first reply, the important part being this:

There are many ways to explain the difference, so there is no one correct way.

That means that anything claiming or asking for 'the correct way' is already presuming something wrong.

The rest of the post lists only one of the ways to explain it, and also provides counterexamples to every one of the 'explanations' mentioned in the videos, both of which were shown to be mistaken in subsequent posts. Takeaway is to use a peer reviewed text to get your information, not pop videos, even those put out by supposedly knowledgeable celebrities.  An arm-chair amateur like me should not so easily be able to find the mistakes in them.

If you want another explanation, it can be something as simple as "That's the nature of Minkowskian geometry". A straight (timelike) path between two spacetime points (events) is longer in length than one that isn't straight. This is unintuitive since in Euclidean geometry, the opposite is true.

12

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 06/12/2024 15:25:33 »

"Einstein based special relativity on the idea that the speed of light is the same for all observers.

That it is the same relative to any inertial frame. It is not true relative to non-inertial frames, and there is no mention of observers in the premises.

That's because a space-time distance that is zero for one observer is zero for all observers.

It's called an interval, not a distance, and any interval (zero or otherwise) between two events or along any worldline is frame independent. Again, observers play no role in this.

So this speed, c, is an invariant speed.

You make it sound like frame invariant light speed is derived from this zero interval, rather than the frame invariant interval (of any value) being derived from the fixed light speed postulate.

You then only move into the time-like direction, and in this direction, you move with the speed of light.

That's like saying that a school bus is parked in my driveway (our reference frame), front bumper against my garage door. 20 ns later the rear bumper is 10 meters away at the street?  Did the bus move at faster than c? No. It's just a different part of an extended object and the thing isn't moving at all. Likewise, you are a worldline, an extended object that is present at both events delimiting the measurement. You don't move from one event to the other, it's just different parts of you that are present at each event, just like the bumpers being different parts of one bus. It isn't motion.

All that said, yes, different definitions are used, and it is commonplace to express motion through spacetime as taking place at c, expressed as a four-velocity, not a normal velocity.

13

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 06/12/2024 01:43:43 »

I had to move the group of posts due to the assertive tone they took, rather than a questioning one.

Einstein, and Feynman have both said that relativity says we move in the time direction. Time isn't really a thing with extent, but it is a direction. We move at the speed of light in that direction.

John Baez, Roger Penrose, say it too.

Actual quotes (and context) would really help. Are these statements in peer reviewed publications or are they casual comments or from pop articles?
What they are trying to say is that time and space are the same thing, meaning time and length can be used interchangably. So for instance, a worldline segment one second long (the worldline of any clock over one second measured by it) is exactly one light-second in length. The statement is one to define this ratio of translating space to time. But to call it 'speed' totally contradicts the definition of speed, as Paul has correctly pointed out. There is no meaningful motion through spacetime except for the one example I posted in the other topic, and that motion is completely undetectable, given that the interpretation posits a completely undetectable thing.
In particular, with motion, when the object gets to the destination, it is no longer at the former location. With a worldline, the object is present at every event along the line. It doesn't move from one event to another, leaving the former event 'vacant' so to speak.

It is also a common shorthand to identify a frame by an observer stationary in it, but it must be made clear at some point that frame selection is an arbitrary abstract choice, not a physical property of an object or observer. If Penrose did not make that clear in his book, then he's not doing a very good job of explaining relativity.
The vast majority of human observers choose a different frame than the inertial one in which they are stationary. It is far more pragmatic to use say the accelerating rotating frame of the surface of Earth when walking past another person.

14

New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 06/12/2024 00:35:48 »

In a universe with four dimensions, you have to move at the speed of light in at least one of them.

In a universe with 4 spatial dimensions, the speed at which some object moves through any on dimension is frame dependent, and less than c (assuming similar rules as our universe).
I presume you're talking spacetime, but speed is defined as spatial change over time, and is not a meaningful concept in spacetime. An object traces a worldline through spacetime and is everywhere present on that worldline, hence there is no motion at all.  The speed of an object at some moment is the slope of its worldline in some selected frame, and that speed is less than c for any valid frame.

The reason you can, and do, move at the speed of light in one dimension--the time dimension--is because time has to vanish from your local frame of reference, if you want to age at all.

That's a weird but true explanation of a theory.

Is is not an explanation at all, and neither Einstein nor Minkowski said anything like that.


The only possible meaning of motion through spacetime is something like moving spotlight theory, one version of presentism, a philosophical stance, not a scientific one. In that interpretation, the universe is a block but the present is defined by a moving pointer (the spotlight) that defines which events are current. Given that model, speed through spacetime would be the speed at which the spotlight advances along a particular line.  Problem is, no physical instrument can measure that rate, so it can be anything: Far higher than c, far less, even negative.

Photons don't "age".

In a way they do. There are a number of waves of a photon between two events (in a given frame, its frequency times its duration between the two events). That is an age of sorts.
If you're saying that the photon does not undergo any physical change from one event to the other, that's true, but also true of something like a proton which doesn't move at c. Protons also cannot recall a past.

Since photons, or electromagnetic radiation in general has this "time equivalence", it should be possible to quotient the total space with it. This is what a Minkowski spacetime diagram represents, a quotient space.

Another assertion resulting in these posts getting moved, on top of an unusable suggestion of relevancy to the twin paradox.

Have you seen Penrose's description of two observers walking past each other? That this means they are literally in different 'spaces', at least according to Minkowski.

This is bending what people say beyond the breaking point. Two people walking past each other tend to use the exact same reference frame, and therefore share the same coordinate system, which includes the exact same space.
Penrose, if he worded his statement correctly, would have explicitly identified a pair of different inertial frames, neither of which necessitates an observer to be defined.

All that said, yes, the events which are simultaneous with a given event relative to one inertial frame are mostly different than the events which are simultaneous with the same given event relative to a different inertial frame. That statement actually derives from Minkowski, and is probably what Penrose means. I have no access to any exact quote.

15

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 29/11/2024 19:12:02 »

The passenger in an accelerating  rocket may read 1 g on his accelerometer because he is being pushed from behind. Having landed on Earth his instrument will read 1 g because he is being pulled from below.

No, both cases are due to being pushed from below. Were it not for this push, both cases would locally experience no proper acceleration. The two cases being locally indistinguishable is the essence of the equivalence principle, and not the below suggestion:

But acceleration does not produce gravity as [chatGTP] implies

I think it's the implication from equivalence principle.

You show signs of not having read the critique at all, since it is that assertion that was colored red every time it was made.  The equivalence principle is not in any way applicable to the mathematics of an accelerating frame, either locally or not. It makes it sound like the mathematics of special relativity was derived from general relativity and not the other way around.

Two balls are connected by a string, floating freely in outer space. They are spun until having a constant angular speed. No energy is expended afterwards, even though the balls are continuously accelerated.

Excellent counterexample.

Consider one ball moving in a straight line at constant speed. If we want to change its direction we need to exert a force perpendicular to the track, so work is done.

A force perpendicular to motion does no work, which is why the 2 balls on a string don't slow in their rotation over time.

16

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 29/11/2024 00:26:06 »

. Having never used supposed "AI"(no intention of doing so-you can't teach an old dog new tricks!), I am in a weak position to criticise. I have seen some atrocious rubbish in replies to questions posed by others and a high degree of suggestibility. In response to a question that requires a blunt "NO", answers will often digress into unsubstantiated speculation with the seeming aim of perpetuating the discourse rather than delivering a straightforward answer.

This is very perceptive.  Yes, the answers always seem agreeable, and if you protest a correct answer by asserting your own sufficiently plausible rubbish, none of the LLMs seem capable of telling you that it's still rubbish. It might seem a bit skeptical, but it will encourage you to explore your line of thinking rather than point out where it contradicts evidence or contradicts itself.

I didn't want to tell copilot that its answers were rubbish. I had hoped that it would figure it out itself after I pointed out inconsistencies in its replies.

We may not need forum moderators in the future, an LLM can analyse and critque the work produced by the forum users LLM well enough.

Moderators are needed to moderate, to recognize and deal with posts not complying with the rules. Being correct is more of a job for site experts, be they moderators or not.
I'm no expert in pretty much any subject, but I know enough to take apart a lot of answers I see from AI.

(I copied and pasted the reply @Halc obtained from Gemini).....   

Actually, Hamdani provided replies from both chatGPT and gemini. I just copied his quotes so I could color them

My replies below are replies to chatGPT apparently agreeing with much of what gemini had to say..

You say that "spacetime is curved due to the acceleration" in an accelerated frame..... It would be better to mention that acceleration causes the perception of curvature, or locally mimics gravitational effects due to the equivalence principle.

But that isn't right. There is no curvature locally, so there cannot be any local perception of it. In the non-local case, most of the effects are due to the accelerated frame. it is quite hard to distinguish curved spacetime from flat since all the effects are present in both, but differently.
For instance, I am under proper acceleration of 1g and dangle a clock on a long rope. In both cases the clock on the rope will run objectively slower, so that effect is not due to curved spacetime. But the two cases differ a bit for how much slower since they differ. Nearby, it differs but a little, but for a gravitational field of a small mass, it can differ a lot over not that much distance.

The equivalence principle does not suggest any of this

In an accelerating reference frame, spacetime itself doesn?t curve in the same way...

It doesn't curve at all. Spacetime curvature is objective, not a coordinate effect, and an accelerated frame is just a coordinate choice. I would have immediately grilled gemini on this point, but I have no access to it.

students using LLM to write the essays and someone else using a LLM to mark and grade them.

They get what they deserve if they commit the same sins. Education should devolve into GIGO. Nobody should pay for any pseudo-education implemented in this manner.


I talked to my AI about black holes and got Newtonian answers in response. It had no clue.
Thought of another one: Sagnac effect is a favorite empirical disproof of anything Einstein.  Let me have a go:


Does light travel west faster than it does east?

Light travels at a constant speed in a vacuum, ... This speed remains the same regardless of the direction in which the light is traveling, be it west, east, or any other direction.

The notion that light could travel faster in one direction over another doesn't hold up according to our current understanding of physics. The speed of light is influenced by the medium through which it travels (such as air, water, or glass), but not by the direction.

So if I create a vacuum tunnel and some mirrors around the world and shine a pulse in both directions, both pulses will return to the origin spot at the same time?

Yes, exactly! In your vacuum tunnel setup, if you shine a pulse of light in both the west and east directions simultaneously, both pulses would return to the origin at the same time. The speed of light in a vacuum is constant and does not depend on the direction of travel.

This constancy of the speed of light is a cornerstone of Einstein's theory of relativity and is true regardless of the motion of the source or the observer. It?s one of the fascinating and sometimes counterintuitive aspects of the way our universe works.

So the Sagnac effect disproves relativity then? It predicts that west and east light go different speeds and measurement of this difference is used to detect absolute rotation. Sure, most Sagnac devices have a far smaller circumference than a planet, but the principle is the same

...The Sagnac effect occurs in rotating reference frames, such as a rotating disk or the surface of a spinning planet like Earth. In these scenarios, if you send two beams of light in opposite directions around a loop, they will take different amounts of time to complete the loop.

So the two pulses do take different times to come back to the emitter then?

Yes, in the context of the Sagnac effect within a rotating reference frame, the two pulses of light would indeed take different amounts of time to return to the emitter.

Not in the context of Sagnac. In the context of what actually happens

Let's break this down in the context of what actually happens with light pulses and rotation.

If you set up a vacuum tunnel with mirrors and shine a pulse of light in both the westward and eastward directions, the two pulses would indeed take different amounts of time to return to the origin if the system is rotating.

So I didn't color anything, but it didn't take much to get it to contradict itself. The LLM did not take into account the rotating frame of reference in the first reply because despite the real-Earth scenario, I didn't word the question in a way that drew attention to the fact that we're working with a rotating frame, despite the fact that west and east are not even defined on a planet that doesn't rotate.

I did word the one query as an attempt to discredit relativity like so much training material attempts to do, and it at least didn't take that bait. I partly wanted to see if I could lead it down a false path if it looked like it was my purpose to do so.

The copilot replies were edited heavily, cutting it down to actual replies, and cutting out all the educational stuff it tried to add on, and of course all the congratulatory stuff at the end about how perceptive my questions are. It tacks that on to ever single reply in some form or other.

17

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 27/11/2024 19:09:27 »

Asking chatbots about relativity is almost always going to get wrong answers.
I can highlight the wrong and particularly correct and really wrong answers.

Is GR needed for accelerated frames of reference?

Yes, General Relativity (GR) is necessary when dealing with accelerated frames of reference, especially when the acceleration is significant or when gravitational effects are involved. While Special Relativity (SR) handles inertial frames (non-accelerating), GR extends the theory to include non-inertial frames, such as those that are accelerating or influenced by gravity.

In GR, gravity is not seen as a force but rather as the curvature of spacetime, and this curvature affects how objects move, including those in accelerated reference frames.  So, for understanding the full effects of acceleration, particularly in the presence of strong gravitational fields, GR is required.

ChatGPT tries to sneak in gravity since yes, GR is needed to deal with gravity. But acceleration does not produce gravity at it implies. It seems to just repeat this comment a number of times.


At least ChatGPT doesn't attempt to leverage the equivalence principle, which I cannot say for the other examples.  Gemini is definitely the worst of the bunch.

The same question for Gemini,

Yes, General Relativity (GR) is crucial for understanding accelerated frames of reference. Here's why:
 * Equivalence Principle: GR postulates that gravity and acceleration are equivalent. This means that an observer in a uniformly accelerating spaceship cannot distinguish between the force of acceleration and the force of gravity. This principle forms the foundation of GR.
 * Curvature of Spacetime: In GR, gravity is described as a curvature of spacetime. This curvature is caused by the presence of mass or energy. In an accelerated frame of reference the spacetime is curved due to the acceleration.
 * Time Dilation and Length Contraction: GR predicts that time runs slower in a gravitational field or an accelerated frame of reference. This is known as gravitational time dilation. Additionally, objects appear shorter in the direction of motion in an accelerated frame, a phenomenon called length contraction.
 * Global Positioning System (GPS): GR is essential for the accurate functioning of GPS satellites. The satellites are moving at high speeds and are at a different gravitational potential compared to Earth's surface. Without accounting for GR, the GPS system would be significantly inaccurate.
In summary, GR provides a comprehensive framework for understanding the physics of accelerated frames of reference. It is a fundamental theory that has been experimentally verified and is essential for many modern technologies.

That was horrible. I would love to have questioned Gemini after that comment and show how it directly contradicts itself.  I tried to do it with copilot, getting this conversation, not as bad as the two above. This is actually my first intentional interaction with any LLM ever.

Is GR needed for accelerated frames of reference?

In some ways, yes. Accelerated frames of reference are closely tied to the principles of General Relativity (GR). Unlike Special Relativity, which deals with constant velocities and inertial frames, General Relativity accounts for acceleration and gravity.

Einstein's theory of General Relativity generalizes the idea of relativity to include non-inertial (accelerated) frames of reference. It essentially states that the presence of mass and energy curves spacetime, which in turn affects the motion of objects. In this context, acceleration can be considered equivalent to gravitational effects?a principle known as the equivalence principle.

So, while you might not need all the complexities of GR for simple cases of acceleration, understanding the full implications of accelerated frames and gravityindeed requires the framework provided by General Relativity. If you're diving deeper into areas like gravitational waves, black holes, or cosmology, GR becomes essential.

Try as I might, I cannot get copilot to mention accelerated frames without dragging gravity into it as well, making the comments ambiguous.

But there is no curve spacetime under special relativity. Are you saying that acceleration creates spacetime curvature?

You're correct that Special Relativity (SR) doesn't involve curved spacetime. SR deals with inertial frames of reference?those moving at constant speeds relative to each other?and doesn?t account for acceleration or gravitational effects.

Note the evasion of actually answering the question.

In General Relativity (GR), however, acceleration and gravity are indeed linked to the curvature of spacetime. The equivalence principle in GR states that locally (in a small region of spacetime), the effects of acceleration are indistinguishable from the effects of gravity. This means that in an accelerated frame of reference, the spacetime can be thought of as curved. So, yes, acceleration is related to spacetime curvature in the context of GR.

Think of it this way: in an accelerating elevator, you feel a force pushing you down, similar to gravity. GR explains this by suggesting that the acceleration causes a curvature in spacetime, akin to how a massive object like Earth curves spacetime, creating what we perceive as gravity.

What do you mean by acceleration being linked to curved spacetime? Does it curve spacetime or not? The equivalence principle indeed says that locally, the effects of acceleration are indistinguishable from gravity, but locally, spacetime is not curved, gravity or otherwise. You seem to imply otherwise when saying "This means that in an accelerated frame of reference, the spacetime can be thought of as curved" when the opposite is true, that locally, even under gravity, spacetime can be thought of (and is) flat.

You bring up an excellent point. You're right?locally, spacetime is considered flat, even in the presence of gravity. Let's clear up the confusion.

The equivalence principle states that within a sufficiently small region of spacetime, the effects of acceleration are indistinguishable from the effects of gravity. In this local sense, spacetime can be approximated as flat, which aligns with your statement that locally spacetime is not curved.

To clarify: acceleration itself does not directly cause spacetime curvature. Instead, in GR, acceleration and gravity are related through the equivalence principle. When we consider larger scales or longer durations, gravity (or the presence of mass and energy) causes spacetime to curve. This curvature affects how objects move, leading to what we perceive as gravitational effects.

So, while an accelerated frame of reference might feel similar to experiencing gravity, this does not imply that acceleration curves spacetime in the same way mass and energy do. Locally, spacetime remains flat, and the equivalence principle helps us understand why the effects of acceleration can mimic gravitational effects in small regions.

There was more, but you get the idea

18

Chemistry / Re: Shrink ray or growth ray, how could they work?

« on: 22/11/2024 22:05:03 »

I recently watched the Movie "Honey I Shrunk the Kids"

Fantastic Voyage was there first, or at least earlier.

explanation was essentially that atoms are 99% empty space, so all you have to do is collapse it down a little bit or expand it a little bit. Tah dah!

That gets you a bug sized thing that masses the same as the original. It would sink into the dirt like a nail being pounded in.

That said, super-dense matter is possible such as in a neutron star, but it takes pressure. The Pauli exclusion principle prevents the explanation given above. It's a classical explanation given to a quantum problem.

One way I thought it might be possible would be y changing the mass of the involved particles.

That eliminates one of the problems I mentioned above, but introduces a whole new zoo of particles with new laws, which you seem to mention in your post,.

Very small effects can be seen in examples of isotope effects--bond length contraction in molecules composed of heavier isotopes compared to equivalent molecules with lighter isotopes.

Isotopes differ in number of neutrons. Nothing is going to shrink significantly just by making isotopes, even if the mass alters a bit.

19

Question of the Week / Re: QotW - 24.11.22 - Why are boat propellers at the rear?

« on: 15/11/2024 12:41:35 »

There are exceptions to both, but in general, a propeller at the front of a boat would put higher velocity water against most of the hull, increasing drag. This is also true of aircraft, but it also increases lift.
An aircraft is more stable if pulled from the front, but a boat is more maneuverable with it at the rear.
The boat relies on the high speed water for its rudder to work, so the rudder needs to be behind the propeller.
A small boat tends to lift its bow out of the water at higher speeds, not a good thing if the propulsion is there.

A reason not to:  If somebody falls overboard, there's very much a danger of being sucked into the propeller flow, not so true if it was up front.

20

Physics, Astronomy & Cosmology / Re: Has anyone heard of tresino theory?

« on: 14/11/2024 21:57:16 »

A tresino is apparently quite stable, and its discovery (a 5th phase of matter, one beyond the 4th:plasma) seems to have implications on all sorts of things unexplained until now, including why the corona of a star gets so much (100's of times) hotter that the surface of the star, and why planets take so long to cool down.

I don't see how a particle can be a phase of matter at all, but apparently this 5th phase involves some proportion of tresinos, like plasma involves nuclei stripped of their electrons, thus destroying their identity as 'atoms'.

It is theorized that tresinos were a common state of matter early in the universe, but no 'very' early since it took many epochs for things like protons to form in the first place.

Apparently cold fusion, not understood well at first, may finally be explained by properties of the tresino. It isn't fusion, but it may still well be a viable energy source. Much to learn first.