So if I hop into a spaceship and leave at a very fast velocity, why is it that, upon returning, I will have aged less than my twin who stayed on earth? I've seen the triangle diagrams for this, but I just cannot understand why it seems to be that there is some *absolute* frame of reference here. It seems that we're saying that my velocity was absolutely higher than that of my twin's. If I am leaving the planet at a velocity v, then he's leaving me at the same velocity. If I accelerate away from him at acceleration a, then he's doing the same from my frame of reference. What is it that I'm not seeing?