Rotation of the universe?
I understand that there are several solutions to Einsteins equations that consist of a rotating universe. I have a few questions. If the universe is composed of everything that exists, how can the universe rotate in the absence of space, since all space is contained within the universe? And, as a Machian, how can the universe rotate if there is nothing for it to rotate relative to (no "fixed stars", as in the case of Newton's bucket). Also, would rotation of the universe imply an axis of rotation, and if so, couldn't this be construed as a preferred frame of reference?