I'm kind of a noob who's posted a question or two here before to settle arguments and such. Please don't kill me if this has been covered before. I was reading some stuff about space travel trying to get some creative ideas for a sci/fi book idea I had. Nothing serious and really nothing to do with the twin paradox, but I stumbled accross that and had a thought. I was reading about it on wikipedia and the example used there is one of twin "A" making a trip of 4.45 light years at a speed of .866c. Of course for simplicity they assume that the velocity is reached instantly. Upon twin "A"s return, twin "B" would have aged 10.28 earth years, while twin A would have only aged 5.14. Aside from the complicated (for me) math that they used to generate these results I understand the idea. BUT... What would the twins look like physically? If my thoughts are correct, shouldn't they still be the same height/weight etc? What I'm thinking is the human body ages based on it's own biological clock right? It doesn't trigger growth hormones or the aging process based on it's location on earth right? So the 10 earth years/5 earth years thing doesn't really matter here. I started thinking of it like this: If it were possible for twins to be born at the same instant on opposite sides of the galaxy, and then relocated instantly to a neutral location, wouldn't they be the same? The earth years number is just an arbitrary number that WE use because it's how we understand time. The human body does it's own thing. How far off am I?