Fascinating how one thing sparks off another in this sort of thread. After asking you (Socratus) if you could identify a F of R for the Universe, I thought about the Cosmic Microwave Background. In a way that provides a universal inertial frame. It approaches every point in the Universe from every direction at a uniform speed. The motion of the Milky Way through the CMB has been measured. This must be as near as one can get to identifying absolute motion.

There never was nothing.