In Guth's book he says that the observable Universe is a "tiny speck" of the total size. I saw somewhere more reciently where it was stated that it was "at least 30 times larger" than we can see, but I don't remember where. I think it was concerning the latest C.B.R. data.

What's the current wizdom on the subject?

Take a peek here.

A different figure.

http://www.newscientist.com/news/news.jsp?id=ns99994879

That article, I think, speaks to the proper distance to the "edge" of the observable universe. That is, objects (or in this case, the cosmic background radiation) observed whose light orginated at very high redshifts is NOW something like 46 billion light years away. The 78 billion light years number quoted is, I believe, the distance to the "event horizon", given the present combinations of cosmological parameters favored today. The cosmic event horizon is the maximum proper distance that we will ever see, and its existence is peculiar to universes with an accelerating expansion rate. However, I thought that number was closer to 62 billion light years (for the so-called "concordance" expansion parameters), so again, I am not quite sure where the quoted number comes from.

If you'd like to try your own hand in computing "distances" in cosmology, go to Ned Wright's "cosmocalculator" web page.

However, the poster of this question, I think, is wondering about just how large our universe really might be. The above describes the distance at a "cosmic now" of an object on our cosmic horizon. i.e., something akin to the size of our observable universe. However, our Universe is FAR larger, and may even be (if inflation or something like it is correct) FAR, FAR larger in size.

A lot of this is discussed in Brian Greene's Fabric of the Cosmos when writes about inflation. It's possible that what we see of the universe is only a fraction of the whole thing, and that many "local" big bangs/inflation periods could have happened.

Of course -- I posted it just to offer some perspective.

If inflation theory is valid, the quantum jitters were stretched during inflation allowing for the formation of the WMAP results. I wonder if enough is known about the quantum jitters to take a stab at the size based on this alone?

__________________
Lighten up! This is a stellar board!

Doesn't inflation theory require flat spacetime cosmology? And doesn't that mean that the universe is infinite in size?

__________________
"Stupidity gets denser in a crowd" - Old Finnish saying. [My website and My BLOG] [Nimblebrain forums]

As I understand it, the inflationary hypothesis or scenario and their kin do not require the universe to be infinite in size. Inflation merely makes the universe spatially flat on very large scales (i.e., far, far beyond the current horizon). What you suggest was true for expansion that doesn't include an early inflationary phase, and in the old "density is destiny" scenarios. When you throw in very early inflation and a late accelerated expansion rate, things aren't quite as cut and dry. To give you a more concrete example....if we consider the planet Earth to be the entire Universe of a virus sitting on a Walmart parking lot, its 'universe' (the Walmart parking lot) is spatially flat, even if its Universe (the planet Earth) is finite and curved. The analogy isn't perfect, but I am just trying to make the point....

On the other hand, when you hear just how inflated the universe might be due to the early inflationary phase, you'll conclude that the universe might just as well be infinite in size....To George -- the number of e-foldings in the size scale of the universe that took place during inflation isn't pinned down by the various inflationary scenarios. All we 'know' is that it had to be done and over with by 10^-12 seconds, and probably much earlier (< 10^-30 seconds).

Well, it's quite possible that I either have misunderstood it or remember it wrong. I just remember reading something about inflation theory which quite clearly stated that inflationary theory requires the omega to be exactly 1. But it's long time ago, so for now I just take your word for it and do some reading about it to check.

Maybe some early version of inflation theory had this requirement?

__________________
"Stupidity gets denser in a crowd" - Old Finnish saying. [My website and My BLOG] [Nimblebrain forums]

Omega=1, steady state.

Omega less than one, Big Crunch.

Omega greater than one, expanding universe in which we find our selves.

__________________
I have grasped the bull by the tail and am lookin' 'im right in the eye.

Omega = 1, flat

Omega < 1, closed

Omega > 1, open

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

In the context of the big bang theory, omega=1 means that universe expands forever at an ever-slowing rate. But perhaps you mean this (from this John Gribbin article):

Spaceman Spiff, here's another thing from that same article (emphasis mine):

So it looks like it indeed was an early version of inflation theory that made the prediction and my knowledge needs updating.

__________________
"Stupidity gets denser in a crowd" - Old Finnish saying. [My website and My BLOG] [Nimblebrain forums]

Omega_total is indeed 1 in the inflation scenario and so the spatial geometry is indeed flat, but the same scenario does not require that the universe be mathematically infinite in size. Only VERY large.
At least that is how I understand it. The "solutions" mentioned by Ari and others above result from expanding universes following the FRW equations of motion without a previous episode of inflation. Inflation makes the observable universe, and FAR beyond, as FLAT as Illinois along I-57 and effectively nearly infinite in size. But our particular "bubble" needn't be mathematically infinite. Splitting hairs.