Relative Motion and the Twin Paradox

[circa 1991]

Question:  Why does one twin age more slowly in the famous "twins paradox"?
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Well, That is the whole point of the paradox!  From the point of 
view of the twin who is in the space ship, that is exactly what happens.  
However, everything breaks down if the twin in the space ship decides to slow 
down, turn around, and come back and visit his twin back on earth.  During 
that deceleration and turning phase, he suddenly sees his twin on earth get 
older and older and older, while he does not age much at all.  Actually, 
motion in our universe really is not all that relative.  Position is relative, 
and different positions in our universe have different average velocities of 
all the matter in that area (the velocity of the Hubble expansion), so if you 
think about the physical universe, relativity seems a little less than 
obvious.

Arthur Smith
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