I A version of the twin paradox without accelerations

[PeroK]

I have no objection to that, but perhaps nature hides surprises as is often the case from the point of view of quantum physics, and a (reliable?) experiment that combines the two theories will test the "twin paradox" in a few years, as long as it does not have the luck of similar experiments that have been abandoned in the past:

That is just a complete and utter intellectual cop-out! Testing the twin paradox is not something that has any relevance to physics in 2020. The whole of modern physics is built on SR, including the models of spacetime and energy-momentum that are tested every day in particle collisions. If you don't understand SR then that's no problem - it's not the easiest thing to learn. But don't pull the "SR might be wrong card" out of your pocket - that doesn't achieve anything.

 

[Ibix]

But don't pull the "SR might be wrong card" out of your pocket - that doesn't wash!

Indeed - in particular, the experiment cited seems to be a test of GR and quantum physics. If I understood right they're building a single-atom interferometry experiment and allowing the two paths to have different flight times due to gravity. This certainly isn't an "intro to SR" twin paradox scenario - it's something much subtler. It can't make the twin paradox anything other than what it is (we've already done that experiment), but may reveal something interesting about the interaction between quantum particles and gravity.

 

[George Plousos]

Agree. At least I've learned a lot here and the range of my doubts about Relativity is now more limited.

 

[vanhees71]

That is just a complete and utter intellectual cop-out! Testing the twin paradox is not something that has any relevance to physics in 2020. The whole of modern physics is built on SR, including the models of spacetime and energy-momentum that are tested every day in particle collisions. If you don't understand SR then that's no problem - it's not the easiest thing to learn. But don't pull the "SR might be wrong card" out of your pocket - that doesn't achieve anything.

Of course you are right, the kinematic effects of SR (and also of GR by the way) including the twin paradox have been tested by experiment to a very high precision. That does not imply that new tests using other contexts have no relevance to physics. The quoted test of time dilation in the context of quantum theory is at least interesting. Of course, I don't expect any surprises here, but still it's interesting and no such test of well-established theory is irrelevant.

Of course, the arguments of the typical "Einstein cannot be right, because it's contradicting my common sense", are unlikely to bring forward anything substantial ;-(.

 

[Isaac0427]

Agree. At least I've learned a lot here and the range of my doubts about Relativity is now more limited.

If you need some resources to help you understand relativity better, I'm sure some people here can help you out with that. I can also let you know some pointers I found helpful when I first learned it (I did do a fairly intensive study of relativity, I just had to get a refresher in this thread as it had been a year and a half since I did a relativity problem). If explained the right way, the "paradoxes" start making sense, to the point where they stop seeming like paradoxes.On a different note:

Of course, the arguments of the typical "Einstein cannot be right, because it's contradicting my common sense", are unlikely to bring forward anything substantial ;-(.

I just laugh at the irony of that argument, as it was precisely Einstein's argument in the EPR paper.

 

[vanhees71]

Well, it's well known that Einstein was not very satisfied with this infamous EPR paper, but that's another story.

 

[Tomas Vencl]

I will study your notes, Ibix. In the meantime I have prepared this thought experiment:
I think I can show that the answer to the original question may be different. ……..

Here is Minkowski diagram of your new experiment. Generally it is nothing more then Ibixs picture, maybe with more explanations. It is without scale.

You can arrange the synchonization of Alice and Bobs (Alex and Helens )clocks before, and set it up so, that Bob,Tom and Alex has the zero time at the same event.
You can see, that from Alice, Bob and Tom point of view Helens clocks started earlier (and symmetricaly Alices).
When Bob and Helen meets, Bobs clocks shows 1.x and Helens 2.x , but from Bobs point of view Helens clocks started much earlier, so even if from Bobs view Helens clocks are slower, they shows more.
At the end of experiment, when Alice Tom and Helen meets, Toms clocks show 4, Alice and Helen 4.x, but again their clocks ticks slower (from Toms view), but they started earlier. And also From Toms view Bobs and Alexs clocks show less (3.x) .

 

[PeroK]

Actually, if we want to have more than two observers we should have Carol and Ted in addition to Bob and Alice:

https://www.imdb.com/title/tt0064100/