Time and relativity

[Stclaim]

If a person flies off in a rocket then returns, that person has aged less than the starting point?

If two people fly in opposite directions and return they are both younger than the starting point?

Because they have travelled away from each other at twice the speed/distance as from their starting point, is not one then younger than the other?

[Tim88]

1. Yes

2. Yes

3. No: the direction does not matter. If they otherwise do exactly the same, the result (comparison of their age with the stay-at-home) must be exactly the same too.

[Delta1212]

If a person flies off in a rocket then returns, that person has aged less than the starting point?

If two people fly in opposite directions and return they are both younger than the starting point?

Because they have travelled away from each other at twice the speed/distance as from their starting point, is not one then younger than the other?

If the two flying in opposite directions have symmetrical trips, that is, fly the same distance at the same speed, turn around after the same amount of time and reach their starting point at the same time, they will have aged the same amount.

 

The difference in aging comes when you have asymmetrical travel at relativistic speeds. The starting point never undergoes acceleration. Because the traveler does, and changes speed and direction, the experiences of the traveler and the starting point are not symmetric and therefore the elapsed time for each is not the same.