# Turn around point with respect to twin paradox

Just as I thought I was done with the issue of what takes place at turn around point of the twin heading back to Earth, I am finding myself at square 1 again as they say.

So I mumbled to myself and that I should find out what the man Einstein himself said in regard to it. I figured it is the right thing to do. I looked very close only to find out he didn't have much to say about it. It appears that he pointed that SR wasn't complete.

All the experiments with respect to SR has been done in at rest frame unless I have that wrong.

The letter of SR's non-preferred reference frame relativity says neither frame can tell who is at rest or who is moving. There seem to be no other frame mentioned here, such as an existing rest frame must be there to determine the actual trajectories of the two frames.

Furthermore the basic Twin paradox has multiple frames. A twin on a planet with respect to another destination object as at rest frame. The other twin moves between the two.

GPS satellites have the center of the Earth as the preferred rest frame, ( Earth centered inertial frame) which is the idea of Lorentz/Poincare, preferred reference frame relativity.

What I like to know if there has ever been an experiment in SR that shows what happens at the turn around point, or an experiment that did not have at rest frame? How can it even be possible?

If that is one too many questions please ignore the last one.

• What happens at the turn around point is that the doppler effect for the stationary twin's clock changes the frequency of the received time ticks for the twin that moves, while absolutely nothing happens to the clock signal of the moving twin as received by the stationary twin. It's really trivial. Oct 6, 2022 at 22:52
• This comment has nothing to do with this particular question. I have noticed that you have been deleting your questions that get downvoted. (Your last three, I think.) My understanding of how this site works is that deletion is not a productive strategy. I think it is making it more likely that you may receive a temporary question ban. Oct 19, 2022 at 23:31
• @Ghoster, When I see a single downvote anywhere, be it in regard to my post or comment or an answer, to me it means someone does not want me around. I am not interested in upvotes either. I am only interested if I am getting something or I am not. To me it is the only kind of reward I am after. It won't bother me if someone says something that is distastful at all. But the red negative sign combined with the policy of unananumousness is basically an act of agression to me. That is not a word, it is an act to me. I have my own policy. Oct 20, 2022 at 4:14
• @Ghoster if this site had the policy that I could not delete abrasive in my face symbolism and I detect that I am to put up with it or else. I won't be here for one moment. The internet is a huge place. No site has that much power that they alone have the real answer. In fact most real answers takes far more than just few commentaries you find here and there. What you find in most sites is just few bones thrown at you if you happen to be lucky be at the right place at the right time. Oct 20, 2022 at 4:20
• @Ghoster, today I got lucky big time. Someone gave me a name of a book on relativity, free online. Better yet, I can actually follow the book, the author, the style of writing. That is a big deal to me. It is meaningless if read the most awesome find, except you have no idea what the person is saying and you try hard to follow it until your hair falls apart, not good. Some folks I can't follow period and when I see it, I instantly know it. Oct 20, 2022 at 4:25

I like to know if there has ever been an experiment in SR that shows what happens at the turn around point

The turn around “point” is a mathematical fiction for making the math easier for students. It would require an infinite acceleration, which is not possible for any device.

Instead, realistic twin paradox style experiments all have some large but finite acceleration. The one that comes immediately to my mind is Bailey’s muon storage ring experiments.

Bailey et al., "Measurements of relativistic time dilation for positive and negative muons in a circular orbit," Nature 268 (July 28, 1977) pg 301.

Bailey et al., Nuclear Physics B 150 pg 1–79 (1979).

They were highly relativistic and also used accelerations around $$10^{18} \mathrm{\ g}$$. Thus it was a twin paradox experiment with multiple reunions. All of the relativistic predictions were correct, and this experiment confirmed the clock hypothesis that there is no time dilation due to acceleration beyond that which is already accounted for by speed.

or an experiment that did not have at rest frame

This part of the question doesn’t really make sense. All experiments involve some measuring device so all experiments have a rest frame. The only way to not have a rest frame would be to not have any matter.

I mumbled to myself and that I should find out what the man Einstein himself said in regard to it. I figured it is the right thing to do.

Not closely related to the rest of your question, but this is almost never the right thing to do. In the intervening 117 years there has been considerable improvements in mathematical formulation, professional understanding and pedagogical techniques. You will almost always be better off with a good modern treatment than reading the seminal works

• "This part of the question doesn’t really make sense. All experiments involve some measuring device so all experiments have a rest frame. The only way to not have a rest frame would be to not have any matter." In other words the two inertial frames can not determine the actual. Only another frame (lab frame, presence of another matter) can determine the actual events for the two. Two frames in empty space can never know on their own. If this be case, it perhaps means that SR can never be proven in the two frame only context as stated. Oct 6, 2022 at 21:56
• @Ali A muon in a circular particle accelerator is not in a rest frame. Oct 6, 2022 at 22:54
• @FlatterMann You mean the accelerator and the scientists are not at rest frame in which muon is viewed as being in motion? It appears I have assumed wrong. Oct 7, 2022 at 1:20
• @Ali You need to read the fine print. All rest frames are equivalent, accelerated frames are not. Oct 7, 2022 at 4:34
• I really like the last paragraph :D Oct 7, 2022 at 20:34