I’m really enjoying this course, great presentation. Stretches the imagination.

With space contraction and time dilation, how the velocity of different objects is determined and agreed upon among different observers?

I presume it’s like this: the velocity for both is the same, only the direction is opposite. The rocketobserver will say that the earth is moving away at speed v while the observer on earth will say that the rocket is moving away in opposite direction at speed v. However there also is a difference: the rocketobserver feels a force (accelleration) and the observer on earth doesnot.

But if you will take GR in account, then none can cliam that they are in state of rest? I wonder does the ‘net’ time dilation incorporate both the effects for so called”Stationary objects”?! What ya think?