In Einstein's theory of relativity, if motion is truly relative, then why would somebody in a rotating space station experience (artificial) gravity? I mean, I get why they experience gravity IF the space station is rotating, but what I do not get is how can you say it is rotating in the first place? Would you not need to define its motion in relation to another point in space?
So let's say we have two space stations and in our hypothetical universe they are the only two things that exist in the entire universe.
- In space station 1, there is no sensation of gravity.
- In space station 2, there is a sensation of gravity.
So we know that space station 2 is rotating and space station 1 is not because of the sensation of gravity we feel in station 2.
To an observer in station 2, they would feel gravity and see station 1 appearing to orbit around them. An observer in station 1 would feel no gravity and see station 2 spinning but staying in one spot. I think everyone would agree with all of those observations thus far.
But here is where it breaks down, I think, you have to have some fixed reference point in space to be able to say that station 2 is spinning and it is not station 1 orbiting in order to get the sensation of gravity on station 2. Newton seemed to have an answer to this because he said there was a fixed "at rest" but according to Einstein, I don't think there is a fixed at rest?
Does my question make sense? My confusion also applies to acceleration, it seems you have to have some fixed reference frame to say anything is accelerating at all. We know you would feel the effects of acceleration if in a space ship in deep space, but why if all motion is relative. I mean, how can you even say you are accelerating and it is not everything else in the universe accelerating and you are actually standing still without a fixed “at rest” point in space?