As a thought experiment, you can certainly arrange whatever initial conditions you like. We already discarded the rest of the universe, after all. You're absol

As a thought experiment, you can certainly arrange whatever initial conditions you like. We already discarded the rest of the universe, after all. You're absolutely correct that I'm assuming the current understanding of how inertia works. It would be fascinating if we were to somehow perform the experiment and didn't get the usual result. Your symmetry argument is excellent and well-stated. I have no complete counter. To extend the argument: If just one astronaut is in an otherwise empty universe, can she tell whether or not she is spinning at 100 RPM by extending her arms to sense centrifugal force? The usual laws of physics would say that she can. A laser-gyro should work too. I think Mach would guess that she can't. Because I can't make an empty universe, I don't know how to do the experiment, but it's interesting to ponder.