Originally Posted By: Joey
That's correct (although the one traveling is the younger one in the end). The thing is that the one traveling away and then back changes his inertial system (e.g. by accelerating) which in the end cuts down his time consumption. The acceleration itself doesn't have an effect, though, as you're accelerating and decelerating. If you could change your inertial system without acceleration this would have the same effect.

This would allow us to build a time machine. *want*

vec_set( player, vector(x,y,z) )?
Since "inertial system" is just a fancy word for "we take this point as the origin of space", I could argue that space is just a made-up concept and our entire universe is defined by accelerations, thereby acceleration is the effect. But you could just as easily argue back your point of view tongue.

What interests me is when you take the cosmic background radiation as inertial system. Then the space in our universe shrinks inwards instead of extending outwards!

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