[pzkpfw]

Twin A finds twin B as younger than himself, hence he says that B experience time dilation.

No. While in relative motion they both consider/know that time is slow for the other. That's what is called "Time dilation".

And it goes both ways - it's reciprocal. After all, that is what puts "paradox" in "twins' paradox". (But to be clear, it's not actually a paradox, there's is no argument about that. The term comes from a naive partial understanding.)

On the other hand, Twin B finds twin A as older than himself, hence he says that A experience time contraction.

That one turns out a different age than the other is usually called "differential aging".

[hamdani yusuf (OP)]

As I said before, doing it via frame changes just adds complications, requiring multiple formulas, some of those being more complicated.

Using what I showed, no frame change is made ever. You pick just one and stick with it.

If you dismiss frame changes, you should get reciprocal time dilation. And there will be nothing to tell which twin is the younger when they reunite.

[hamdani yusuf (OP)]

The situation was never symmentrical, and if it is (like the one in one of your recent threads), then the result is very much symmetrical. But adding more characters just adds more complications which is inadvisable if you cannot in any way understand even the simplest case.

I'll get to the symmetrical version of this problem later, after we sort out some of current scenario at hand.

[hamdani yusuf (OP)]

I didn't touch on a paradoxical part because there isn't one.
The misunderstanding can be best avoided if we avoid switching inertial frames altogether, as I suggested in post 1.It only leads to confusion if you don't understand how to do it right, and doing it right that way is considerably more complicated than sticking to one frame as I suggested.

I just want to know how to do it right, and what makes it hard to explain.
STR requires that all inertial frames are equally valid frame of reference. Let's see if it can be satisfied. If you dismiss it, you are no longer using STR.

[hamdani yusuf (OP)]

The first is a terrible video. It has many errors, such as asserting that they see each other age more slowly, which is only true when they watch each other recede. The twins scenario is not in any way about what anybody sees. Then they try to explain things via gravity which is utterly wrong. This is a special relativity scenario in which gravity is never taken into consideration.

Minutephysics' video also depicts both twins see each other age more slowly during constant velocity motion. Only when the travelling twin turns around, he sees the staying twin ages much faster. He mentions acceleration as the cause, instead of gravity. But GR says they are equivalent.
Then on returning leg, travelling twin sees staying twin to age more slowly again.

[hamdani yusuf (OP)]

The second video isn't much better. It say 'time slows down as you approach the speed of light'. That's just wrong. 'I move at nearly light speed relative to a muon created in the upper atmosphere. It doesn't make time slow down to me. He then attempts to reference an invalid frame of a light-like worldline, which is obfuscation at best, and wrong at worst. He never actually gets back to the twins after that.

He is one of the most famous astrophysicist and science communicator at present. If even he fails to get it right, it's no wonder that many others also fail.

[hamdani yusuf (OP)]

There are good videos out there, but hunting down bad ones seems a favored pasttime to those that don't want to learn. Take the advice of other posters and find a good physics text if you actually want to learn this, which I suspect you don't. Stay away from you-tube, pop sites, and especially social media.

The format of the information source should not prevent the content to be delivered correctly. IMO, the video format is much richer than paper printout for its ability to show motion and audio information simultaneously. Interactive video/simulation would be better.
If you think there are good videos, you can just put the link here, so we can compare with the bad ones and analyze what makes them better.

[hamdani yusuf (OP)]

Relative to that frame, which we've called 'A's frame', Alpha Centauri moves closer to twin A at 0.4c. There's no suggestion that it needed to accelerate to do so since it was always moving at that speed relative to that frame, as was Earth. Yes, twin A needed to accelerate to a halt in that frame, but that fact is irrelevant since he spent zero duration at that alternate speed. Acceleration computations do not figure into the simplified method I suggested in at the top.

I agree. 
I am trying to help Hamdani understand this but it is very difficult because he asks question after question either ignoring or not understanding the answers.  I have no idea if he even understood the original answer in reply #1.

It almost seems that his goal is to sow confusion, I doubt that is the actual goal but that seems to be what happens in all his posts. 

You agree with Halc, but disagree with me, even when what we say is the same thing. It seems like you are the one who's confused.

[hamdani yusuf (OP)]

Ignoring, yes. Understanding seems not to be his goal, and most can see that and simply stop responding to the brick wall.
I chimed in because we all this talk of acceleration requiring a change of frames was running contrary to my suggestion to keep things simple and never choose to switch frames. Hamdani pays enough attention to notice when we give non-unified answers. So his goal is perhaps to find the differences between the ways different people correctly approach the same problem, and then spin those differences as contradictory, which they are of course not.

Without frame switching, both twins are equally valid observers, and there would be no physical age difference between the twins. The discrepancy in observed age would be fully covered by relativity of simultaneity.

Professional physicists commonly say that it's the frame switching which causes the age difference. Some say that it's the same as acceleration, while some other say that acceleration is not necessary, hence treating frame switching differently than acceleration.

Some critics of STR say that the confusion is caused by many supporters of STR have their own versions of the theory which are incompatible with one another, but claim that they are the standard STR.

[hamdani yusuf (OP)]

As I said, his goal doesn't seem to be to give the appearance of understanding anything.

Understanding how nature works accurately is an instrumental goal to achieve the universal terminal goal.
I'll just let ideas to come up, and then let natural selection to do its job. Shutting down ideas prematurely can prevent us from getting the correct answer. We need reasons to accept or reject ideas.

[pzkpfw]

Possibly there's some talking past each other in regards to "frame switching".

You are right (in short) that the explanation of the (not) paradox is that the scenario is not symmetrical, the reason for that being one observer remaining in a single frame, and the other not. *

But there's another kind of "frame switching" ... someone trying to analyse the thought experiment who willy-nilly flips from frame to frame (Alice, Bob going, Bob returning ...) without rigour and confusing themselves and everyone reading their words.


(* I prefer the triplet version: B passes A, later C passes B, back towards and eventually passing A. Nobody accelerates ever. Makes it clearer, I think, especially in the "frame switching" sense.)

[Origin]

You agree with Halc, but disagree with me, even when what we say is the same thing

When did I do that?

[hamdani yusuf (OP)]

You agree with Halc, but disagree with me, even when what we say is the same thing

When did I do that?

This statement is incorrect.  Twin A does not stay in his own constant inertial frame.

[hamdani yusuf (OP)]

I asked Google Bard about Twins Paradox.

What is the twin paradox?

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 centers on the contention that, in relativity, either twin could regard the other as the traveler, in which case each should find the other younger?a logical contradiction. This contention assumes that the twins' situations are symmetrical and interchangeable, an assumption that is not correct.

The key to understanding the twin paradox is to realize that the twins' situations are not symmetrical. The traveling twin undergoes acceleration during the turnaround phase of the journey, while the stay-at-home twin does not. This asymmetry is what allows for the difference in aging.

Another way to think about it is that the traveling twin's worldline is not a straight line in spacetime, but rather a curved line. The stay-at-home twin's worldline, on the other hand, is a straight line. This difference in worldlines is what accounts for the difference in aging.

The twin paradox has been experimentally verified using atomic clocks. In one experiment, two atomic clocks were synchronized and then one was flown around the Earth on a jet aircraft. When the clock was returned, it was found to have lost a tiny fraction of a second. This was due to the time dilation effect predicted by special relativity.

The twin paradox is a fascinating example of how special relativity can lead to counterintuitive results. It is also a reminder that the universe is not as simple as it seems.

[Origin]

Quote from: Origin on Today at 05:09:24
Quote from: hamdani yusuf on Today at 03:16:06
You agree with Halc, but disagree with me, even when what we say is the same thing
When did I do that?
Quote from: Origin on Yesterday at 13:19:58
This statement is incorrect.  Twin A does not stay in his own constant inertial frame.

Halc pointed out that what I said was incorrect.  I was agreeing with him.

[Halc]

You're making up facts. There's no conflict when different physicists explain it in different ways since none of the explanations are wrong. But the way I showed seems the most simple, and requires but the one equation.

Not just a different way, but different interpretation of the cause.

But one interpretation of 'the cause' doesn't invalidate any of the others. Personally I don't think there is a cause. Asking for one is like asking what causes a table to be longer than it is wide. It is perhaps caused by which dimension one decides to designate as the length.

Lorentz' relativity interpretes time dilation is caused by relative motion against stationary aether. Thus no paradox is generated.

But that's pretty much the answer I gave in post 1, except without the aether, which has no method of detection. Instead there is just a preferred frame. You choose one, and exactly like the Lorentz case, no paradox is generated.

Einstein's 1905 Relativity dismissed aether  ...
Since there is no more universal reference, it's no longer clear which clock ticks faster.

Nobody ever claimed that a clock ticked faster. Your problem for suggesting otherwise, but don't blame relativity theory when making such a blunder.

Einstein's 1921 relativity reintroduced aether, with some modifications. It no longer carries some physical characteristics. It was then renamed to space-time continuum.

'Spacetime' was coined by Minkowski in 1908. Einstein never wrote the term "space-time continuum:, which seems to be a pop term introduced as early as 1930 in a fiction story. I am unaware of a physics paper that uses the term ever, but if you have a quote from Einstein, that would really help illustrate that you're not just making up your own facts. And no, he never reintroduced aether either, but GR does introduce a preferred (non-inertial) frame relative to which cosmological time (adjusted for potential) is constant at simultaneous events, something that can be measured since cosmological time is an empirical measurement. None of that has anything to do with a proposal of a medium through which light travels.

If you dismiss frame changes

Nowhere do I dismiss them. I just said that computations are more complex if you choose to do them. Please try to actually read what I say and not make up your own crank story about what you hoped I said. The computation in posts 1 and 9 did no frame changes, and they both arrived at the same answer of 8 and 9 1/6 and they did it with only the one equation instead of several that would have been required to do the same thing with frame changes.

I just want to know how to do it right

This is very apparently a lie. If you wanted to know how to do it, there are many correct ways to do so, but I illustrated probably the easiest way. I invited you to work out yourself how to do it in the frame of the B's 2nd leg. That's how you learn, by doing, or at least attempting. You declined. You show no indication of wanting to learn how to do it, so the above statement is false.
It is this obvious lack of desire to learn that makes myself and other ignore the majority of any of your posts.
Prove me wrong and attempt the calculation using the 3rd frame and the numbers already provided in posts 1 & 9.

STR requires that all inertial frames are equally valid frame of reference.

That it does, but it doesn't say you are required to use them all. You can if you want, but it's a lot more work since transformations are required every time you change frames.

Minutephysics' video also depicts both twins see each other age more slowly during constant velocity motion. Only when the travelling twin turns around, he sees the staying twin ages much faster.

If it doesn't say that each of them sees the other twin age faster when approaching, then the video is wrong.
An explanation based on what people see is not wrong, but again, more complicated than this simple situation needs to be. You again need more than one formula to get the correct answers.

He mentions acceleration as the cause, instead of gravity. But GR says they are equivalent.

This is wrong, and the video is wrong if it says this. GR says the two are equivalent only locally, not over any significant distance. The two are very distinguishable over distance.
The problem with using videos for education is so many of the videos have no peer review.

The format of the information source should not prevent the content to be delivered correctly.

No, it shouldn't, but only peer review helps ensure the content is correct, and almost no video undergoes such review. I've pointed out blatant errors in videos by very respected, famous and popular authors.

If you think there are good videos, you can just put the link here

I've never had the time to search for good ones, and I've never chosen any to do the actual learning.
Watch out for any video that claims to be the one correct way to explain the situation.

Without frame switching, both twins are equally valid observers

First of all, it is you that needs to do frame switching or not, not the twins, who require no more intelligence than the ability to read the clock that's strapped to their wrist.
Secondly, all people and devices for that matter are valid observers. Frame switching doesn't somehow cancel the ability of a thing to make a measurement, but in the twins scenario, the only measurement is the local consultation of one's watch. There are other scenarios where actual observation beyond clock watching is necessary, but the twins scenario doesn't require observers at all. It can be (and has been) done by just zooming clocks around without people serving any purpose other than that of a courier.

confusion is caused by many supporters of STR have their own versions of the theory which are incompatible with one another, but claim that they are the standard STR.

There is one STR, and it is mathematically perfect, meaning it cannot be falsified from an armchair, only by empirical means. If somebody actaully alters the theory, that person is wrong, but most just convey the concepts in different ways. I've seen no wrong replies to you for instance. You're the only one making blatantly incorrect assertions.

I asked Google Bard about Twins Paradox.

Should be entertaining since it, like chatGPT, uses all the disinformation online as part of its training material. I would never trust an answer from a chatbot.

What is the twin paradox?

Bad start. You didn't ask about your scenario specifically (asking it for the ages at the end of your experiment in the OP, nor did you ask it about 'the cause' of the differential aging. So you're now asking a far more generic question. But you're in luck since it does directly attribute the potential differential aging to asymmetry, and the asymmetry to non-symmetric acceleration. So the answer is actually quite good this time. It says that asymmetry 'allows for' differential aging, but correctly doesn't go so far as to say it causes it, since there are plenty of asymmetric situations where there is no differential aging.

Another way to think about it is that the traveling twin's worldline is not a straight line in spacetime, but rather a curved line. The stay-at-home twin's worldline, on the other hand, is a straight line. This difference in worldlines is what accounts for the difference in aging.

This is quite close to the explanation I gave in the 'what is the cause' topic that has so many of your posts.
This answer is less intuitive and more complicated, but also more generic (can be applied to any situation), something not true of the first explanation.

The twin paradox has been experimentally verified using atomic clocks. In one experiment, two atomic clocks were synchronized and then one was flown around the Earth on a jet aircraft. When the clock was returned, it was found to have lost a tiny fraction of a second. This was due to the time dilation effect predicted by special relativity.

This part is a little off, since GR was needed to predict the results. The entire experiment took place at various altitudes in a gravity well. SR was not up to making any prediction better than the fact that the westbound clock would accrue more time than the eastbound one.

[hamdani yusuf (OP)]

But one interpretation of 'the cause' doesn't invalidate any of the others. Personally I don't think there is a cause. Asking for one is like asking what causes a table to be longer than it is wide. It is perhaps caused by which dimension one decides to designate as the length.

The cause is how people commonly define length and width.

[hamdani yusuf (OP)]

Quote from: Origin on Today at 05:09:24
Quote from: hamdani yusuf on Today at 03:16:06
You agree with Halc, but disagree with me, even when what we say is the same thing
When did I do that?
Quote from: Origin on Yesterday at 13:19:58
This statement is incorrect.  Twin A does not stay in his own constant inertial frame.

Halc pointed out that what I said was incorrect.  I was agreeing with him.

The statement you said to be incorrect is Halc's statement which I paraphrased. Which means you didn't agree with him.

[hamdani yusuf (OP)]

And no, he never reintroduced aether either,

He used the word ether in his lecture in 1920. You can't just deny history.
"According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time"
He just modify some of its characteristics to comply with known experimental results.

[hamdani yusuf (OP)]

GR says the two are equivalent only locally, not over any significant distance.

How much distance is considered significant?