Hm. I'll use the Twin Paradox to phrase me question. if you need a refresher, http://en.wikipedia.org/wiki/Twin_paradox Everything I read about it seems to make a blatant claim that "the twin on Earth will be older". Are such texts missing the point, or am I? Suppose I'm twin A (so I'm on Earth as the frame of reference). My brother, B, is orbiting the Earth near light speed. Of course, from my inertial frame, I'm stationary and he's moving. It seems to me as if time moves slower for him. So when he sends me a picture of himself each year, I'm surprised how young he looks. Great, so good so far. But let's start from the beginning again. This time, I'm B. The Earth seems to be moving around me near the speed of light. Naturally, time seems to be going slow for them. So, when I receive a picture of my brother each year, I'm surprised to see that HE is the younger one. Yet, I've generally read that the twin that leaves Earth is objectively younger-- which assumes that the Earth's frame of reference is the most important. On a similar note, suppose I orbit near light speed with a clock. When I get back, I find that Earth's clocks are all behind mine, since the Earth was moving rapidly compared to my inertial frame. Yet, my boss who sent me up on the mission will look at my clock and tell me that it's behind, right? So if we put the clocks side by side and look at them, then what? Sorry, just started with this branch of physics an hour ago or so. But, I wouldn't be able to get sleep tonight without asking.