If the universe is constantly expanding...

If the universe is constantly expanding, then is it correct to say the universe is not infinate? And never can be?

My head hurts. http://boards.straightdope.com/sdmb/newthread.php?do=newthread&f=7#

No it’s still infinite. It’s that the distance between things is expanding.

I should say can still be infinite. The point is that the expansion is determined by the distance between finite points.

But how can anything be infinite?

Depends on your definition of ‘universe,’ for one thing.

The stuff that was created from the big bang is ever-expanding. Recent theories are that ‘space’ may exist beyond the edges of where we have expanded to - that is, space is as plainly-three-dimensional as any child would guess.

Also depends on what you mean by “anything.” Matter, I’ll agree, is hard to imagine as infinite. But simple volume? The ‘void’ into which matter expands? Why not infinite? Time? Why not infinite?

Oh, I kinda forgot to fill out what I meant by ‘depends on your definition of universe.’ ‘Universe’ has been defined by all the stuff that was created by the big bang.

That seemed natural, given that until recently there was a large cosmological consensus that time, volume, and matter didn’t exist ‘before’ the big bang (although ‘before’ in that model would be a meaningless concept).

Universe might be that infinite space I was talking about that’s all the rage on the Parisian Cosmological runways this year.

I can remember hearing about space being “finite but unbounded”, that space is simply relations between “things” (matter, various mass-less particles), and as such cannot exist without those “things”–that space was potentially infinite, even though there is only a finite amount of stuff, and thus only relations of a finite nature.

I know I stated that terribly, but is that still an accepted interpretation?

So I gather there can be infinity…something that can go on and on infinitely.
But can there be anything before that infinity.
(And my headache is getting worse.)

Our cosmological horizin is, of course, finite, and growing all the time.

To extrapolate beyond the horizon using our current best-candidate model of the Big Bang and what came after suggests an infinite, almost perfectly flat universe. Whether one can be reasonably sure spacetime lacks some non-trivial topology beyond our cosmic horizon probably depends on who you ask.

Again, apparently it depends on who you ask. Questions about what came “before” the Big Bang, once pretty much off-limits to serious speculation, as theory could say nothing about the putative Big Bang singularity, are among the big ideas of modern quantum gravity and cosmology. Some people think we have no good theory for Planck-scale physics, and hence it’s still a total non-starter. Some think we’ve got some good first drafts of a theory or theories, but there’s considerable disagreement even then about what exactly these theories are going to look like in the future. Maybe it’s meaningliess, like asking what’s north of the North Pole. But perhaps it might not be completely nutty to talk about “before” the Big Bang, if you interpret that word somewhat loosely. That’s what I can glean from the popularizations, anyway.

Or whom you ask.

Some cosmologists think that the universe extends quite a bit beyond our “light”
horizon, but that since nothing past that point (which is 13 mly away-i.e. as far away
in light years as the universe has existed in years) can causally interact with us it
doesn’t much matter-for now.

I don’t believe so; space these days is regarded at a thing in itself, not just the relationship between objects.

These days, “finite but unbounded” refers to a spherical universe ( well, technically a hypersphere ); just like the surface of a globe, there is a finite area but no edges. That is what you would get if there was enough matter to cause the universe to collapse in a Big Crunch.

To put what uglybeech said in different words, spacetime is stretching; Galaxy A and Galaxy B end up farther apart because there is, literally, more space between them. That’s why the expansion of the universe isn’t limited by lightspeed; the lightspeed limit refers to things/information travelling through space, not space itself.

This subjest used to confuse me, until I understood that it is space itself that is expanding. Now picture this, if there is an infinite amount of stuff out there and the observable universe is finite, then somewhere there would be a exact duplicate of our entire observable universe, or actually an infinite number of them.

Even worse, there really wouldn’t be any fundamental distinction between a
duplicate universe which exists a googolplex number of light years away, and one
which “existed” 100 billion billion years ago.

I heard the Universe was just part of a Quantum wave? Plus something to do with the 11th dimension, that and string theory.

There are different levels of infinity, believe it or not.

An infinite number of levels of infinity, as it happens.

To quote** Der Thris**, in part, “These days, “finite but unbounded” refers to a spherical universe ( well, technically a hypersphere )”

So in order for me to catch a better grasp on relieving my headache, I looked to define
what a ‘hypersphere’ is.

" noun - The set of points a distance r away from a center point in n dimensions. It is the n-dimensional analog of the circle in planespace, the sphere in realmspace, and the glome in tetraspace. Sometimes the term hypersphere is used to refer only to the glome. See the chart under rotatope."

Vodka, maybe vodka with the aspirins!

We can find out the answer to this question - from the Google ad

I wonder how much over $49 a baby universe is. :slight_smile: