Hello. Last semester in PHYS151, our instructor said that if a rocket is travelling at .90c relative to the Earth, then time will flow slower for it. That's fine, but there's one thing that annoys me. 1. The Earth is standing still, and a rocket is travelling at 0.9c away from it. 2. A rocket is standing still, and the Earth is travelling at 0.9c away from it. So in situation (1), time flows slower on the rocket than on the Earth, and in situation (2), time flows slower on Earth than on the rocket. A dude on Earth should think that (1) is true, but wouldn't a dude on the rocket think that (2) is true (or at least, "might as well be true")? Is time travelling slower for the rocket just because it went through acceleration for a period of time, meaning that acceleration is what causes contraction?