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Apr2-11, 11:40 AM
Sci Advisor
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P: 2,361
It isn't gravity that causes the (time)age difference, but the speed at which the space twin travels. For the space twin to age 10 yrs while his Earth twin aged 20, he would have had to make the trip at 0.866c.

I'm not quite sure about what your last question is asking, but I'll take a guess. When they reunite, the Earth twin will have aged 20 yrs and be 30 years old and the Space twin will have aged 10 yrs and be 20 yrs old.