A comment on David's 3D Universe: It seems that the Universe must be a
4D manifold as observers traveling at different velocities will observe
S_3_i inside S_3_j and others will observe the reverse. Thus, no
particular S_3 is distinguished sufficiently to be called "The Universe".
I realize this impacts upon free will, but I have a tentative
explanation for that difficulty, but this is not METAPHYS-L.