[Jan 2007] The "shape" of the Universe, etc.

So this is taken from a writing in 2007, something i posted to an astronomy bulletin board of a general interest group back then.

I tried to answer a q about what "shape" the Universe is, and point the questioner to good sources for this kind of stuff.

-M

---------- Forwarded message ----------

Date: Wed, 10 Jan 2007 

From: Mandeep S.S. Gill 

Subject: Cosmology post on C-surfing

Hey there Caz-  ok...

It's hard to discuss some aspects of cosmology "reasonably", as they don't correspond to our common sense intuitions of "shape" etc. -- the very small and very large get very *weird* compared to our daily lives.  yet -- it *is* the Universe we live in.

Now, as far as what shape the Universe is..  it appears right now that our Universe is of infinite volume, and *always has been* ever since "just after" the Big Bang.  where just after means epsilon after, any number greater than zero. and since we can't really understand the Universe back beyond a certain point with our current physics (certainly before the Planck Time of 10^-42 seconds, and possibly even later than that), we simply can't *ask* those questions at the current moment in physics.

Or rather, you can *ask* (you can always ask of course), it's just that physics won't offer any meaningful answer for you.  It's as good as philosophical theorizing at that point, which is of course how *all* of these kinds of questions were addressed before we could make numerical sense out of parts of the world.  The domain that we can understand has always expanded. It's not clear that there's a limit, or an end whatsoever in fact -- but we already understand a huge amount now about how things work, and what we do get is dazzlingly breathtaking and stunningly beautiful at times.

Ok, let's get back to it:  an infinite Universe can't exactly be said to have a "shape", as it spreads everywhere.  But -- we already know from experiments that the intrinsic geometry of the Universe is very close to "flat" vs. spherical or hyperbolic (these words are in analogy with 2 dimensions), and there are some theoretical (though yet unproven) reasons cosmologists have to believe that is *exactly* so.

As to a pointer to a good book to read on these matters -- well, i've last been reading some of George Gamow's popular work, which is good.  

For something more recent, i guess i'll go ahead and recommend Wikipedia on cosmology, on the whole i've had good experience with info on their site, most often (in science at least) reasonably correct, even if it's at times incomplete.  Always a decent place to begin.

-M