Chris L Peterson:
Is radial symmetry a condition of having a center? I would think the
Universe must have a center in some higher dimension, regardless of its
shape and topology (even if that center isn't a simple point).

Brian Tung:
I suppose it depends on what you mean by "center." If you just mean
something like "center of mass," then you're probably right. I was
thinking more of a geometric center, obviously.

I can think of no reason why the Universe can't have a central region
in three-dimensional space if the Big Bang theory is correct. If the
Universe exhibits perfect radial symmetry, then the center is a simple
point in three-dimensional space; if, due to quantum fluctuations, the
Universe has minor bumps at its edge, like the surface of a rocky
planet, then the center in three-dimensional space would need to be
spread out; a central /region/ rather than a point. I have trouble
seeing the Universe having taken the shape of a banana or

The problem is the edge. I can at least grasp the /concept/ of a
center. In my version of the balloon analogy the balloon is perfectly
spherical (or very nearly so, considering the above-mentioned quantum
fluctuations it doesn't need a stem because it is self-inflating.
Every point is moving away from a common center, which is where those
points started out (wrapped in a single dimension?) when the balloon
was infinitely small. But the /edge/ of the Universe? From inside the
balloon I can move to the edge and encounter a material substance that
I cannot penetrate. My balloon is transparent, and I can see what is
outside that object. But I can't get my mind around an immaterial edge
beyond which is nothing whatsoever, not even empty space. One
cosmologist, half joking, said "It could be a brick wall, for all we
know."

Physicists used to say that, ultimately, the Universe could and would
be explained by a few simple laws that everyone could understand at
least in a rudimentary way. I think that all hope for such an
explanation has been abandoned. String theory, Inflation, the notion
that gravity is so weak because it is Not of This World, but is just
leaking in from another dimension; the Universe may be a hologram; the
Universe may not exist at all except in our minds; the physicists
themselves don't agree on or understand this stuff. That doesn't bode
well for me understanding it.

Here is my one prediction, however: There will not be a Theory of
Everything that unifies gravity with the other forces. Gravity, it will
be decided, is distinct, and must be understood on its own terms.

Davoud

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