Relativity, classical Galilean relativity, special relativity, and general relativity, all say that all inertial frames of reference are equivalent. Accelerated

Relativity, classical Galilean relativity, special relativity, and general relativity, all say that all inertial frames of reference are equivalent. Accelerated frames of reference are not equivalent to inertial ones, nor to each other. That is, there is a difference in all of these theories between an observer who is at rest with a train accelerating towards them, and the same observer accelerating towards a train that is at rest. This doesn't mean that you can't do coordinate transforms to look at the world from the point of view of the accelerated observer, and get apparent forces. But different accelerated observers will come up with different apparent forces, while all intertial observers agree on the same forces experienced by any object.