[quote] Same fam. What college? I'm Cornell[/quote] URI. Not as prestigious, I know, but they have a good physics program, and I'm biting the bullet of being an idiot in high school. [quote]Also, there are two twins, exactly the same age, Bob and Jill. Bob is on Earth and Jill decides to take a near-light-trip around the local supercluster. Jill travels the 4 lightyears to Alpha Centauri and back at just below the speed of light. To Jill, it takes 8 years to travel to the star and back moving at almost light speed. [b]As you probably know, the faster something is moving the slower time seems to flow to [u]it.[/u] [/b][/quote] Reread that sentence I bolded. [quote]To Bob everything Jill does is in slow motion[/quote] This is false. We see photons move very fast. They don't see us move at all. Apply same logic. [quote] and thus to him Jill appears to age less and by the time she returns, only eight years have passed to her and much more have passed to Bob. Now according to Einstein's Theory of Relativity all motion depends on your point of view. Jill can just as surely claim that she herself isn't moving, but rather everything else is moving and she is staying still.[/quote] Jill would be sorely mistaken. Obviously Jill cannot move at the speed of light, so she is still moving through time slower than the rate at which time passes, so she is still moving along with everything else, just relatively slower. Bob can also not claim that he is standstill, as he has mass and is on a mass. What special relativity proves is that Bob will have aged more than Jill, as he is moving slower therefor less symmetric in spacetime. Not both sides.

Well you are right and wrong. You are right that Bob is correct and Jill is wrong, but the reasons behind it are different. (And yea I did word it very strangely. The seeing it in slow motion was just for reference but actually that would be impossible as you said). As you know, Gravity has an effect on time, and the higher the gravity on something the faster time seems to move for it. In order to reach that near speed of light, Jill would have to accelerate and acceleration creates a sort of artificial gravity (think taking off in a plane). Now apparently artificial gravity is actual gravity in some meaning of the word and effects time as gravity would. So the acceleration and deceleration needed to reach the speed and get down from it are mathematically (not gonna write it out) just enough to counteract the effects of her speed (or Bob's speed when you look at it like that) so to her 8 years passes, and to Bob that acceleration and deceleration made him older than 8 years by the time the predicament was over. Ta da!

But you never said she was going to slow down, or that she started from rest. :)

I guess it was sort of assumed since if you start on Earth and she wasn't born on the ship and her twin wasn't.

Well I like to keep assumptions to the minimum until we get to the quantum scale, haha.