Our new version of Newton’s law makes no reference to ‘absolute space’ or to any ‘rest frame’, and so it is tempting to think that we can stop talking about absolute space altogether. But we need to be cautious. Recall the definition of an inertial frame: it’s a frame moving at constant velocity relative to absolute space. If we excise absolute space from the theory, we seem to have lost the ability to say what an inertial frame actually is.
inertial frame
