I've done a bit of reading about the twin paradox, as well as watched a few videos and the Wikipedia page on it, however, I don’t understand how their explanations explain away the problem. They claim that the acceleration solves the issue, however, don’t we arrive at the same problem? In the earth point of view the astronaut is accelerating, but you might as well see the earth as accelerating in the astronauts view. In other words, same problem, just with acceleration rather than velocity.
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I believe acceleration is mentioned in that an experiment to test Special Relativity can not use accelerated frames. General Relativity was created to handle the complications of accelerations. – C. Towne Springer Jan 23 '18 at 08:32
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Refer to my answer to https://physics.stackexchange.com/q/381276/ – Michele Grosso Jan 23 '18 at 10:35
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2Possible duplicate of How is the classical twin paradox resolved? – Stéphane Rollandin Jan 23 '18 at 11:41
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I exactly see the story as you do! Looking for not a descriptional answer since years. I am surprised that even professionals still argue. I think GR should not be the point as SR should be consistent. But I do not understand the three frames resolution of the paradox – Alchimista Jan 23 '18 at 12:36
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Edward you might read my comments directed to Michele Grosso. Perhaps it is simply like that. No GR required and especially proper acceleration. An accelerometer does the discerning the situation. – Alchimista Jan 23 '18 at 13:06
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Even the term acceleration, can be confusing. If we see a train moving in a straight line at a specific speed, we see that its clocks are running slower than the clocks owned by those that are stationary relative to the train track. And, if the train sticks to the same speed, but is now on a train track loop going round and round, it is accelerating, yet no matter how long it continues to accelerate, we still observe that its clocks are ticking exactly as slow as beforehand. – Sean Jan 23 '18 at 15:57
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In the earth point of view the astronaut is accelerating, but you might as well see the earth as accelerating in the astronauts view. In other words, same problem, just with acceleration rather than velocity.
Lets make the problem simpler. Suppose you have two rocket ships instead of earth and rocket, side by side. One rocket fires off. The man in the firing rocket feels the acceleration pushing him to the seat, the man with the quiet engines does not, so each knows who is moving away. The firing rocket frame is not an inertial frame and can be separated experimentally.
It is similar with the optical illusion when you are stopped in your car next to a stopped bus, and the bus suddenly starts to move forward : you have the optical illusion you are sliding back. You know that you are not moving, because there is no dv/dt (acceleration) , and your body immediately corrects the optical illusion.
anna v
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It seems though that results of relativity are then dependent on what observers feel or notice. – Lambda Jan 23 '18 at 21:47
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So is it the acceleration that creates time effect of SR? What’s weird is it would seem logical that the deacceleration would cancel the acceleration. – Lambda Jan 23 '18 at 22:06
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@Lambda "feel", "notice" is a measurement, rather one could devise a detector to measure the "feel" and "notice". Physics is about measurements and models that fit the measurements and , very important, are predictive of future setups. ( a map can fit a terrain, but cannot predict new terrains). Special relativity describes transformations between inertial frames. https://en.wikipedia.org/wiki/Inertial_frame_of_reference – anna v Jan 24 '18 at 04:07
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@Lambda http://math.ucr.edu/home/baez/physics/Relativity/SR/acceleration.html and also http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html – anna v Jan 24 '18 at 04:10
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In the earth point of view the astronaut is accelerating, but you might as well see the earth as accelerating in the astronauts view.
It is not symmetric. You can clearly say which system is accelerated. Just imagine they guy in the rocket being pressed into his seat. The guy on earth does not feel that.
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I would propose an answer: There is no paradox. When the traveling twin passes the stationary on his way back, he appears to be younger. However, if he stops at the starting point, he looks and is at the same age as the stationary twin. The two clocks (hearts) are tik-tak-ing at the same rythm all the time - according to the principle of relativity. Accelerations are not considered in special relativity. torben
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SR (special relativity) can describe accelerated objects. However in SR an accelerated reference frame can not be used to describe a physical occurrence; that is why the twin paradox is measured correctly only by the twin on the earth. – Michele Grosso Jan 23 '18 at 10:42
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@Michele Grosso. I do have the same problem as OP. GR shouldn't be necessary. But in the frame of SR the paradox is treated by three frames. Earth twin, outgoing ship twin, backgoing ship twin. Why not ship twin, and outgoing and backgoing earth? – Alchimista Jan 23 '18 at 12:32
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@Michele Grosso. Perhaps I got it.After reading your answer: if I would be the ship twin, carefully listen to my body or watching my smartphone I will know that I am the one switching frame. It is as simple as this? :) – Alchimista Jan 23 '18 at 13:03
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@Alchimista. The ship twin is not an inertial reference frame, hence in SR (special relativity) can not describe the complete physical happening, forth and back to earth. That is why, as you wrote, in SR the experience is treated by three reference frames: earth twin, outgoing ship twin and backgoing ship twin, being each of the three an inertial reference frame. When you switch to the backgoing ship twin you discontinuously change the initial time set to measure the earth twin, thus allowing the returning twin to match the observations by the earth twin. – Michele Grosso Jan 23 '18 at 13:11
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Yes. It is the discerning point. Which of the twins isn't in an inertial frame. I mean no way to tell this front doodles or minkosky diagrams. I neglected along these years the idea of proper acceleration that can be felt and measured. – Alchimista Jan 23 '18 at 13:14
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@Michele Grosso. +1 to your A in the old and closed Q.Amazing was the power of your "further note to convince....". These years I was distracted by doppler shift and debates on gr yes gr no. True is that the idea of proper acceleration is inside me or the sensor of my phone but I wouldn't be able to concisely explain it or mathematically describe it . However at the moment I am quite happy :) – Alchimista Jan 23 '18 at 13:23