Is rotating with whatever angular velocity we want in a vacuum, it and you being the only objects around (assume no intrinsic properties like charge/mass). How do you tell that it's doing so? And if it has perfect rotational symmetry, does it even make sense to say that it's rotating? This has been gnawing at me for a few months but I never thought about asking. Any ideas? What if it has charge or mass? Could you apply any studies of say, the lens-thirring effect to deduce anything useful? I am baffled.