Question

Explain how the The Twin Paradox paradox arises when we use our everyday experience of space and time as absolutes. To the best of your ability, resolve the The Twin Paradox paradox.

Answer 1

Essentially Twin paradox means lets say two twins on the face of the earth.One of them has a space ship and he went to space with that space ship with a very high velocity while the other stayed in earth.Now lets say after 20 year in earths frame the twin with the space ship came back to earth.Now the question is what will be relative age between the two twins?

Now we know from the prediction of STR that moving clock runs slow.That means as the twin with the space ship is going with a very high velocity the clock associated with his frame must go slow with respect to the earths clock.Hence he will be ageing slowly as compared to the other twin who is on the earth.Now the paradox comes because of the fact that someone would argue that with respect to the rest frame of the twin in the ship the one on the earth is actually moving and he should age slowly.Hence by symmetry when they meet they should have the same age.

But this is not true because the two twins are really not symmetrical.Its true that both are moving in each others rest frame but to compare their ages on of them has to comeback and comeback means reversing velocity implies acceleration.On the other hand the twin on the earth never will feel any acceleration.Hence two motions are really not equivalent(Not symmetrical ).

There is a nice way to setup this problem mathematically and indeed it shows that the one with the space ship ages slowly as compared to the other and when they meet on earth after 20 year the twin with the space ship indeed will be younger than the one on the earth.