Why is twin paradox a paradox?

Question

We heard that "Twin Paradox" is tested and proved to work, but it is not specified how it works- and that is why it is a paradox?. This means the observer ages faster than the space traveler within the same reference time span, but not specified how it works. If that is the case, it seems two different forces act on the twins differently in the relationship times(two clocks of the twins and one reference clock outside the twins). Is that the case that twin paradox remains paradox because the the source of the two forces are undetermined? would you help on this matter as usual? Kindly.Thanks.

Answer 1

"Why is twin paradox a paradox?"



Because it involves a frame jump... comparing measurements in two different frames of reference.



"We heard that "Twin Paradox" is tested and proved to work, but it is not specified how it works- and that is why it is a paradox?"



No, we *know* how it works. It is a paradox because it is formulated to compare measurements from two separate inertial frames... elapsed time. It is a "first grader mistake" that we then teach you not to do.



"This means the observer ages faster than the space traveler within the same reference time span, but not specified how it works."



No, it means duration measurements in your frame... of the *other* frame, show the other frame to be aging more slowly.



"If that is the case, it seems two different forces act on the twins differently in the relationship times(two clocks of the twins and one reference clock outside the twins)."



No forces. No acceleration is required (the twin paradox can be duplicated with three clocks, and no acceleration in the testing period), only different velocity history. In other words, it is "perspective in 4D spacetime".



"Is that the case that twin paradox remains paradox because the the source of the two forces are undetermined? would you help on this matter as usual?"



http://www.physics.adelaide.edu.au/~dkoks/Faq/Relativity/SR/TwinParadox/twin_paradox.html



I'd recommend you get a good text on this subject, and read up on it. I like "Spacetime Physics" by Taylor and Wheeler, but there are other good choices here:

http://www.physics.adelaide.edu.au/~dkoks/Faq/Administrivia/booklist.html#special-relativity

Answer 2

Atomic clocks have indeed been sent off on aircraft and brought together and it does indeed turn out that they show different times.



The twin paradox states two twins start off at the same age one travels at a high speed relative to the other but both will see each other's clocks running slow. If that's not obvious, consider if you are on a train from your perspective you are not moving forward but the platform is moving backwards. So both are moving relative to each other. Yet when the twins are re-united one has aged more than the other, this is a paradox.



The solution to the paradox though is that one twin had to change reference frames by accelerating and decelerating hence one twin is aged less than the other.

Answer 3

This result appears puzzling because each twin sees the other twin as traveling, and so, according to an incorrect naive application of time dilation, each should paradoxically find the other to have aged more slowly. However, this scenario can be resolved within the standard framework of special relativity (because the twins are not equivalent; the space twin experienced additional, asymmetrical acceleration when switching direction to return home), and therefore is not a paradox in the sense of a logical contradiction.

Answer 4

The simple answer is that the scenario often presented as the "Twin Paradox" is only half of the real paradox!



The actual Twin Paradox comes from the consideration that either twin may regard themselves as moving and the other as stationary, and therefore will be younger when they meet again. Clearly, Alex being younger than Bob and Bob being younger than Alex cannot both be true.



It is resolved, as Zardoz and Paul said, by recognising that the two twins are NOT in the same situation. The one in the rocket is subjected to accelerations.

Answer 5

It is a paradox because all motion is relative, so either twin can be assumed to be motionless. The theory is only valid in a non-accelerating frame of reference. In that case you can't have twins because one would have to accelerate first to get moving. But two random people could be passing each other at high speed, in which case there doesn't have to be any acceleration. Then there is no absolute speed. You cannot say if one is still and the other moving or both are just moving at different speeds. And the theory says each one sees the other one as aging slower. They can't both be aging slower, and that is the paradox.

Answer 6

The Twin Paradox was a paradox because it was thought that since T₁ was moving relative to T₂ and T₂ was moving relative to T₁ they'd each age slower relative to the other. The paradox is resolved when acceleration is taken into account.



T₁ accelerates from F₁ into F₂, spends time in F₂, then accelerated back into F₁ where T₂ spent all of their time. There is no paradox.



(As only one twin is accelerating into another reference frame there need be only one force, by the bye.)

Answer 7

It isn't a paradox, it's simply non-intuitive and therefore often seems to be a paradox.

Answer 8

It is a paradox, because the proof is not convincing.

It is a conjecture at most.

Think about airplane speed vs speed of light, it is not a proof.