Q&A with James R and Tony on the Twin Paradox Experiment

TonyYuan

Gravitational Fields and Gravitational Waves
Registered Senior Member
Tony:
A and B are twins on the earth, they left the earth on the same day, and A and B were exactly the same young when they left.
A and B have exactly the same acceleration and deceleration process, but A returns to the earth after reaching a speed of 0.1 c. B maintains a constant speed after reaching 0.1 c, and flies forward for another 10 ly, and then returns to the earth.
May I ask, when A and B meet again on the earth, which one will be younger?
A and B have exactly the same acceleration and deceleration process, the only difference is that B flies 20 ly more than A at a constant speed. Do you still have questions about the scene I proposed now? If there is no doubt, please tell me when A and B meet, which one is younger?

James R:
I think that in this case they will be the same age when they meet up at the end.

James R, why not continue our discussion? The twin paradox experiment is a good topic. We have also been thinking about your answer, does it mean that acceleration is the key factor causing time dilation.
 
Tony:

I am tempted just to close this thread and issue yet another warning for you trying to reopen a conversation in which you demonstrated zero capacity for analysing the scenario you presented, or even specifying it in an unambiguous way. But I've had a good night's sleep and I'm willing to give you one more chance.

I told you previously that time dilation can be caused by relative motion or by acceleration (which includes the effects of gravity), or both. Fundamentally, time dilation is associated with different frames of reference - observers who are in uniform or accelerated motion with respect to one another.

Please tell me whether you accept this. If you do not, please explain why.

From what you have written in the past, it seems that you do not accept the theory of relativity. If you do not, then there's very little point in discussing scenarios such as this one, unless you have some sort of alternative theory you can use to analyse the problem. If you do have such an alternative theory, then we ought to discuss whether your alternative theory is consistent with real-world experimental results and the like. Because we have 115 years of evidence that says relativity is.

As to the scenario in your opening post here, you have specified that A and B have exactly the same accelerations. To my mind, that means that the situation is symmetrical between A and B. We can consider A to remain stationary and B to move, or consider B to remain stationary and A to move. At different times, both A and B experience identical accelerations, so whatever the effects of those accelerations, in terms of time dilation, they must be the same in each frame of reference. Therefore, I conclude that the twins will, at the end of their trips, be the same age as one another once again. During the trips, they will each see the other aging faster or slower than themselves (at different times), but these effects are symmetrical for both of them.

Please tell me whether you agree with this analysis. If you do not, please present your own analysis.

If it turns out that you're still not able or willing to discuss these things and present any arguments of your own, I will close this thread and issue a further warning.
 
I am tempted just to close this thread and issue yet another warning for you trying to reopen a conversation in which you demonstrated zero capacity for analysing the scenario you presented, or even specifying it in an unambiguous way. But I've had a good night's sleep and I'm willing to give you one more chance.
James R, first of all, you must be clear that the discussions between us are equal and positive, and we are all seeking scientific truth. You can't just because my views don't agree with yours, you think it's a disrespect to you, and you have to use your privileges. How is this different from dictatorship?
I told you previously that time dilation can be caused by relative motion or by acceleration (which includes the effects of gravity), or both. Fundamentally, time dilation is associated with different frames of reference - observers who are in uniform or accelerated motion with respect to one another.

Please tell me whether you accept this. If you do not, please explain why.
From your answer, I can feel that you are full of doubts. You have added velocity, acceleration, gravity, etc. to the queue of reasons for time dilation.
What I can be sure of is that both velocity and acceleration are related to the reference object. If you think that time dilation is related to speed and acceleration, then your second sentence is also logical.


From what you have written in the past, it seems that you do not accept the theory of relativity. If you do not, then there's very little point in discussing scenarios such as this one, unless you have some sort of alternative theory you can use to analyse the problem. If you do have such an alternative theory, then we ought to discuss whether your alternative theory is consistent with real-world experimental results and the like. Because we have 115 years of evidence that says relativity is.
If the premise of discussing the paradox experiment of twins is to accept the theory of relativity, then the discussion under this unequal condition is meaningless. As for the 115-year evidence, GPT can list it, but unfortunately, these cannot prove that SR is correct. Of course, if I say that, you will definitely be unhappy. My question is simply the twin paradox, and you've already answered it.

Judging from your answer, acceleration is the key factor in time dilation, not velocity as SR thinks. I just drew this conclusion from your answer, if you don't think it is correct, then please tell me why B flying at a constant speed for 20 ly does not make B younger?
Before you use your privilege, please answer my question, thanks!
 
Tony:
A and B are twins on the earth, they left the earth on the same day, and A and B were exactly the same young when they left.
A and B have exactly the same acceleration and deceleration process, but A returns to the earth after reaching a speed of 0.1 c. B maintains a constant speed after reaching 0.1 c, and flies forward for another 10 ly, and then returns to the earth.
May I ask, when A and B meet again on the earth, which one will be younger?
A and B have exactly the same acceleration and deceleration process, the only difference is that B flies 20 ly more than A at a constant speed. Do you still have questions about the scene I proposed now? If there is no doubt, please tell me when A and B meet, which one is younger?

James R:
I think that in this case they will be the same age when they meet up at the end.

James R, why not continue our discussion? The twin paradox experiment is a good topic. We have also been thinking about your answer, does it mean that acceleration is the key factor causing time dilation.
James R,
The twin paradox experiment is a good topic. We have also been thinking about your answer, does it mean that acceleration is the key factor causing time dilation. Do you think we have understood your answer correctly?
 
Tony:

I will start by listing what you did not include in your reply:
  • You have not said whether you agree that time dilation can be caused by relative velocity.
  • You have not said whether you agree that time dilation can be caused by acceleration.
  • You have not said that you agree that time dilations has something to do with reference frames in relative motion.
  • You have not suggested any alternative theory that you suggest would be superior to the theory of relativity.
  • You have not told me whether you agree with my analysis of the outcome of the scenario you presented.
  • You have offered no analysis of your own about the scenario you presented.
  • You have not even said what you think the outcome of the scenario you presented would be.
  • You have not said whether you agree that the theory of relativity (special or general) is correct or incorrect.
  • You have given no reasons for anybody to think that the theory of relativity is incorrect.
I asked you explicitly to address these matters, but you have not done so. Why is that, Tony?

Let me move on to the actual content of your latest reply...
James R, first of all, you must be clear that the discussions between us are equal and positive, and we are all seeking scientific truth.
So far in this, Tony, one of us has demonstrated a capacity to at least express his opinion and reasons on a scenario that you suggested, while the other has not. Our discussions are not equal. The lack of any progress on this - even to the point of understanding what you disagree with me about - is not a positive sign.

If, as you claim, you are seeking scientific truth, you will need to gather the courage to share your own thoughts with other people. And by sharing your thoughts, I mean actually discussing the relevant physics. So far, you have not done any of that.
You can't just because my views don't agree with yours, you think it's a disrespect to you, and you have to use your privileges. How is this different from dictatorship?
I have at no time used my "privileges" as a moderator of this forum "just because" your views don't agree with mine.

As a moderator, your views don't bother me. You've barely told me what they are, although you have hinted that you don't accept the theory of relativity (without telling me why you don't accept it). It's not a crime to be wrong, or incompetent, Tony. If your views are wrong or mistaken, that's a learning opportunity for you, becing a man who is all about seeking scientific truth.

I closed your previous thread because you were unable or willing to talk about any relevant physics, despite my asking you to provide analysis and details several times. You did not appear to be posting in good faith.
From your answer, I can feel that you are full of doubts.
Really? What was it in my response that gave you that impression. Be specific.
You have added velocity, acceleration, gravity, etc. to the queue of reasons for time dilation.
I didn't add them. That's what the theory of relativity says about time dilation.

Do you know anything about the theory of relativity, Tony? Or is this all new to you?
What I can be sure of is that both velocity and acceleration are related to the reference object. If you think that time dilation is related to speed and acceleration, then your second sentence is also logical.
I'm glad you think so.
If the premise of discussing the paradox experiment of twins is to accept the theory of relativity, then the discussion under this unequal condition is meaningless.
I have told you what the theory of relativity has to say about the twin paradox. You are free, of course, to disagree and to propose some other theory of your own, which can be tested against experiments and compared with the many successes of relativity.

If you have your own alternative analysis of the twin paradox that you'd like to present for discussion, please do so.

It makes sense that if you think I'm wrong, then you'll be able to tell me why you think I'm wrong. But, so far, you haven't raised any specific objections to what I've told you.
As for the 115-year evidence, GPT can list it, but unfortunately, these cannot prove that SR is correct.
Why not?
My question is simply the twin paradox, and you've already answered it.
Okay. Is that all, Tony?

You asked about the twin paradox. I gave you a correct, useful answer about it, and you accept that answer.

Are we done here? Or do you have something else you'd like to discuss about the twin paradox?
Judging from your answer, acceleration is the key factor in time dilation, not velocity as SR thinks.
I said nothing like that in my answer. I did not mention one "key factor". I told you that both acceleration and constant-velocity motion can affect time dilation.

Do you understand why "special relativity" is called "special"? It's literally because it only deals with one "special case" of a more general theory (called the "General theory of relativity" or "General relativity"). Specifically, SR deals with relative motion at constant relative velocities (i.e. no accelerations).

The twin paradox involves accelerations, so it is not solvable using SR alone. It requires GR.*
I just drew this conclusion from your answer, if you don't think it is correct, then please tell me why B flying at a constant speed for 20 ly does not make B younger?
In whose reference frame? In B's reference frame, he always ages at the same rate as normal, no matter how fast he goes. In A's reference frame, watching B move at high speed, B will appear to age slower than A. But this is symmetrical: from B's reference frame, A will appear to be aging slower than B.

The very first thing to learn in relativity is: always be clear about which reference frame you are measuring things in, because measurements in different frames won't always agree. These disagreements are why the theory is called "relativity".
---

Over to you, Tony. In your next post, be sure to address the matters I have listed as dot points at the top of this post.

If you cannot or will not do this, I will close this thread.

----
* Technically speaking, we can get away without using GR if we're willing to make complicated SR calculations, but even that won't work if there's gravity involved.
 
Last edited:
A and B are twins on the earth, they left the earth on the same day, and A and B were exactly the same young when they left.
A and B have exactly the same acceleration and deceleration process, but A returns to the earth after reaching a speed of 0.1 c. B maintains a constant speed after reaching 0.1 c, and flies forward for another 10 ly, and then returns to the earth . May I ask, when A and B meet again on the earth, which one will be younger?
A and B have exactly the same acceleration and deceleration process, the only difference is that B flies 20 ly more than A at a constant speed. Do you still have questions about the scene I proposed now? If there is no doubt, please tell me when A and B meet, which one is younger?


The above is the question I asked, and James R gave a clear answer: "I think that in this case they will be the same age when they meet up at the end."

Judging from James R's answer, he was very clear about my question and had no objection to the scene I proposed. James R, do you agree with me?

Then according to James R, we can draw the conclusion that acceleration is the key factor affecting time dilation. Because A and B have exactly the same acceleration and deceleration process, the only difference is that B flies 20 ly more than A at a constant speed. But James R has clearly told us "I think that in this case they will be the same age when they meet up at the end.” . This means that the difference in B relative to A does not cause B's time to become slower than A's.

I think our analysis is very logical. James R Do you agree?
 
Tony,

You still haven't addressed the matters I listed as dot points in my previous reply to you. After you have done that, I will reply to post #6.

Last chance.
 
Please do not troll.
Tony,
You still haven't addressed the matters I listed as dot points in my previous reply to you. After you have done that, I will reply to post #6.
Last chance.
I've been around the twin paradox experiment all along, and you've given a definite answer.
We also draw the following conclusions based on your answer: According to James R's answer, acceleration is the key factor affecting time dilation rather than velocity as SR thinks.

I don't understand why you would stray from this topic and start your privilege with irrelevant reasons, which is dictatorship. We've got the answers we want, you can't hide your chaos on SR, do whatever you want, it's your power, you're the emperor here.

A place controlled by a dictator is not worthy of our nostalgia, see U.
 
Relative Velocity --- causes ---> Time Dilation


Acceleration --- causes ---> Relative Velocity --- causes ---> Time Dilation


The second statement is just a more comprehensive version of the first. Introductory SR classes deal almost exclusively with problems in which there is no acceleration. They only cover the behavior of clocks that already have a constant relative velocity. These classes don't explain the role that acceleration plays. Unfortunately, this practice results in many people with good background in undergraduate physics thinking acceleration has no role in time dilation. Then they get on the internet and start broadcasting that misconception.


The Twins Paradox is the only problem at the introductory level where an understanding of the role of acceleration in SR is important. Rather than telling the student it is beyond the scope of an introductory course, different books try to present a resolution to the paradox by using different approximations. Not surprisingly, many undergrad students and most inquisitive laymen are very suspicious of these approximations. After all, an approximation only has validity to the person who knows the real process.


P.S.

I own a textbook entitled "Basic Relativity" written by Richard A. Mould.

The first 7 Chapters cover SR with constant velocity. Chapter 8 covers SR with uniform acceleration. Chapters 9 through 14 cover concepts like rotation, differential geometry and general relativity. And yes, you read the title correctly, "Basic Relativity". I never got past Chapter 8.
 
Moderator note:

TonyYuan has been warned for trolling.

Due to accumulated warning points, Tony has been automatically temporarily banned for 3 days.
 
Tony:

I've been around the twin paradox experiment all along, and you've given a definite answer.
Have you learned anything about the twin paradox in the time you have been around it?
We also draw the following conclusions based on your answer: According to James R's answer, acceleration is the key factor affecting time dilation rather than velocity as SR thinks.
I corrected this misconception of yours in direct replies to you several times, Tony.

Now, I have to conclude that you're aware you're telling lies, but still telling them, like a troll.
I don't understand why you would stray from this topic and start your privilege with irrelevant reasons, which is dictatorship.
I explained what would happen and why. I gave you several chances, including the one in which I allowed this thread to continue, despite closing two of your previous threads because you wouldn't explain your position. As I expected, you have not modified your behaviour in this thread. Instead, you seem to want to play childish games.
We've got the answers we want, you can't hide your chaos on SR, do whatever you want, it's your power, you're the emperor here.
There is no "we", Tony. It's just you. You're on your own.

I'm glad you found my answers useful. I hope this was a valuable learning experience for you.
A place controlled by a dictator is not worthy of our nostalgia, see U.
Are you leaving us again, Tony?

Okay. Bye!
 
Last edited:
twins;


My interpretation of this "twin" scenario:

Ref. frame is Earth. A and B leave E at t=0, and accelerate to .1c at t1, when

A returns to E and B continues for 10 yr before returning.

For the period from 0 to 2*t1, both have the same v, thus the same time dilation. Any difference in time will occur later. For v=.1c 1/gamma=.99.

Time for A is [(10+t1-2*t1)+(10+t1)]*1=20.

Time for B is [(10+t1-2*t1)+(10+t1)] *.99 =19.8.

This is an instance of two clocks separating and later reuniting. The difference depends on the path each takes.

Special Relativity excludes the effects of gravity.

The gamma factor, sqrt(1-v^2) contains v as a fraction of c, which is the standard =1.

Time dilation is NOT a function of acceleration in SR.

twins-tony.gif
 
twins;


My interpretation of this "twin" scenario:

Ref. frame is Earth. A and B leave E at t=0, and accelerate to .1c at t1, when

A returns to E and B continues for 10 yr before returning.

For the period from 0 to 2*t1, both have the same v, thus the same time dilation. Any difference in time will occur later. For v=.1c 1/gamma=.99.

Time for A is [(10+t1-2*t1)+(10+t1)]*1=20.

Time for B is [(10+t1-2*t1)+(10+t1)] *.99 =19.8.

This is an instance of two clocks separating and later reuniting. The difference depends on the path each takes.

Special Relativity excludes the effects of gravity.

The gamma factor, sqrt(1-v^2) contains v as a fraction of c, which is the standard =1.

Time dilation is NOT a function of acceleration in SR.

View attachment 5485
It looks like you came up with a different answer than James R.
 
twins;


My interpretation of this "twin" scenario:

Ref. frame is Earth. A and B leave E at t=0, and accelerate to .1c at t1, when

A returns to E and B continues for 10 yr before returning.

For the period from 0 to 2*t1, both have the same v, thus the same time dilation. Any difference in time will occur later. For v=.1c 1/gamma=.99.

Time for A is [(10+t1-2*t1)+(10+t1)]*1=20.

Time for B is [(10+t1-2*t1)+(10+t1)] *.99 =19.8.

This is an instance of two clocks separating and later reuniting. The difference depends on the path each takes.

Special Relativity excludes the effects of gravity.

The gamma factor, sqrt(1-v^2) contains v as a fraction of c, which is the standard =1.

Time dilation is NOT a function of acceleration in SR.

View attachment 5485
I don’t understand your statement that “ time dilation is not a function of acceleration in SR”. Surely the point about SR is it does not apply to scenarios involving acceleration.

So that would mean that SR is not equipped to deal with such a scenario, rather than that there is no time dilation, according to SR, when there is acceleration.

Or have I misunderstood?
 
And if you agreed, why ?
With all the calculations you did for the precession of orbits, I would think this example would be easy for you.
Let me borrow your analysis.
1. 0----t1, A, B have the same acceleration process (assumed to be a uniform acceleration process), at t1 time, A, B have the same speed, during this period A, B have the same time dilation.
2. t1----2t1, A returns to E, A is a deceleration process (it can be assumed to be a uniform deceleration process), A returns to the earth, and the final speed is 0. But B keeps flying at a constant speed of 0.1c. So during t1----2t1, A and B have different time dilations. But B will go through the same process during (t1+20 ---- t1+20+t1). Therefore, when A is in the period of (t1---2t1) and B is in the period of (t1+20 ---- t1+20+t1), the time dilation of A and B can cancel each other out.

The final difference is that A spends 20 of its time at rest (relative to E), and B spends 20 of its time in 0.1c constant flight.
James R believes that the final total time dilation of A and B is the same, and they will be equally young, that is to say, when B flies at a constant speed of 0.1c, it does not make B's time slower. That is to say, speed is not the main factor affecting time dilation, but acceleration is.
 
I don’t understand your statement that “ time dilation is not a function of acceleration in SR”. Surely the point about SR is it does not apply to scenarios involving acceleration.

So that would mean that SR is not equipped to deal with such a scenario, rather than that there is no time dilation, according to SR, when there is acceleration.

Or have I misunderstood?



You misunderstood.

I am surprised to see you holding the misconception that SR does not deal with acceleration. You are not alone. Many members on many science forums would agree you. When they post, they usually get corrected but the misconception continues. See my post, #9 above.

I don't want to appear condescending to someone with your level of proficiency, but I will repeat.
If time dilation is a "Function Of" velocity and velocity is a "Function Of" acceleration, then time dilation must be a "Function Of" acceleration (albeit indirectly).
That's basic algebra. Time dilation for an inertial/accelerating observer/observed pair requires a different equation from the one required for inertial observer/observed pairs, but it is still part of SR.
In fact, time dilation for accelerating/accelerating observer/observed pairs is also part of SR. But I have never seen the equation for that last condition.

That being said, I do not agree with phyti's analysis. He does not seem to be aware of the time dilation equation for an inertial/accelerating observer/observed pair.
 
You misunderstood.

I am surprised to see you holding the misconception that SR does not deal with acceleration. You are not alone. Many members on many science forums would agree you. When they post, they usually get corrected but the misconception continues. See my post, #9 above.

I don't want to appear condescending to someone with your level of proficiency, but I will repeat.
If time dilation is a "Function Of" velocity and velocity is a "Function Of" acceleration, then time dilation must be a "Function Of" acceleration (albeit indirectly).
That's basic algebra. Time dilation for an inertial/accelerating observer/observed pair requires a different equation from the one required for inertial observer/observed pairs, but it is still part of SR.
In fact, time dilation for accelerating/accelerating observer/observed pairs is also part of SR. But I have never seen the equation for that last condition.

That being said, I do not agree with phyti's analysis. He does not seem to be aware of the time dilation equation for an inertial/accelerating observer/observed pair.
It looks like your answer is also the exact opposite of James R's.

A and B are twins on the earth, they left the earth on the same day, and A and B were exactly the same young when they left.
A and B have exactly the same acceleration and deceleration process, but A returns to the earth after reaching a speed of 0.1 c. B maintains a constant speed after reaching 0.1 c, and flies forward for another 10 ly, and then returns to the earth . May I ask, when A and B meet again on the earth, which one will be younger?
A and B have exactly the same acceleration and deceleration process, the only difference is that B flies 20 ly more than A at a constant speed. Do you still have questions about the scene I proposed now? If there is no doubt, please tell me when A and B meet, which one is younger?

The above is the question I asked, and James R gave a clear answer: "I think that in this case they will be the same age when they meet up at the end."
Judging from James R's answer, he was very clear about my question and had no objection to the scene I proposed.

Then according to James R, we can draw the conclusion that acceleration is the key factor affecting time dilation. Because A and B have exactly the same acceleration and deceleration process, the only difference is that B flies 20 ly more than A at a constant speed. But James R has clearly told us "I think that in this case they will be the same age when they meet up at the end.” . This means that the difference in B relative to A does not cause B's time to become slower than A's.
 
Back
Top