This is something that interested me after reading about time dilation. For the point of making it simpler, ignore relativity relating to gravitational fields Lets say for example, that the Earth does not orbit the sun, and the solar system doesnt orbit within the galaxy etc (makes it easier to explain, but the point is the same),... and the Earth is just spinning on its axis in free space, having no resultant movement ( other than rotating) in the universe. So if someone were to be in outer space, looking down at the Earth, can we assume that they age "quicker" than someone standing on the Earth, as the person in space would have 0 velocity, and the people on the Earth would be moving with a velocity equal to the rotation of the earth. Now, what if someone were to run on the earth in the opposite direction to the earths rotation, with a speed equal to the earths rotation? So within the free space that person would have 0 resulant velocity. The question is that with reference to free space, that running person would be aging "quicker" than someone who is sitting still on the earth, but is this true? Because from the earths point of reference, the running person is travelling very quickly, so time wouldn't apper "slower?" for that person compared to someone sitting still? Does the absolute true value for γ hold only if you take velocities from a point which has no velocity at all ( the idea of free space). And finally, am I correct in saying you would age slower if you are nearer the equator, ( as your speed would be greater?) I appreciate anyone who can enlighten me on this. I apologize if I have missed a obvious point here, but I've been thinking about it for a few days and I can't get my head around it! Thanks!