(January 19, 2010 at 7:38 am)Tiberius Wrote: If it is expanding at a measurable rate, it isn't expanding infinitely, and therefore cannot be infinitely sized (and is therefore finite).

Can you explain this a little further. If the rate isn't decreasing as time goes to infinity then wouldn't it be divergent and therefore it is expanding infinitely? I agree that at any given time it is finite, but as long as the rate doesn't decrease and eventually go to 0, it should continue to go to infinity.

The explanation was why the universe isn't infinitely sized. If something is expanding, it can't be infinitely sized. That was all my point was about.

As for expanding to infinity, there are theories about entropy that state that the universe will eventually reach maximum entropy, and therefore cease to expand (reaching heat-death). There are alternate theories that state heat death is impossible in an expanding universe, since an expanding universe's maximum entropy increases faster than the universe gains entropy. It's a tricky subject; I daresay nobody knows the answer yet

(January 19, 2010 at 1:55 pm)Tiberius Wrote: The explanation was why the universe isn't infinitely sized. If something is expanding, it can't be infinitely sized. That was all my point was about.

An opportunity to disagree again!

As confirmed by the WMAP probe the universe is generally believed to be flat. Flat in the sense of a 2D analogon. If the universe is infinite, then it should appear flat. But with a flat universe there are still two possibilities, infinite or finite. This is hard to get your head round, I know. But something that is infinite can indeed expand. The expansion of space itself is not dependent on the finiteness of the universe.

There could be reasons why the universe appears flat and yet is not infinite. And of course, it could be that it appears flat because it is infinite. We have no definite proof.

Obviously it is flat and if you get to one end you just wrap around to the other end duh! Haven't you ever played, "Asteroids"? You also get an extra ship every 10,000 points, but watch out for the UFO's.

(January 19, 2010 at 2:44 pm)Purple Rabbit Wrote:

(January 19, 2010 at 1:55 pm)Tiberius Wrote: The explanation was why the universe isn't infinitely sized. If something is expanding, it can't be infinitely sized. That was all my point was about.

An opportunity to disagree again!

As confirmed by the WMAP probe the universe is generally believed to be flat. Flat in the sense of a 2D analogon. If the universe is infinite, then it should appear flat. But with a flat universe there are still two possibilities, infinite or finite. This is hard to get your head round, I know. But something that is infinite can indeed expand. The expansion of space itself is not dependent on the finiteness of the universe.

There could be reasons why the universe appears flat and yet is not infinite. And of course, it could be that it appears flat because it is infinite. We have no definite proof.

That site mentioned the word "infinite" in the title and nowhere else. Could you point to some source that describes the idea properly? I can't see how in a finite amount of time you can go from no space and a singularity to an infinitely sized universe. Something doesn't make sense in the calculation...

Plus, every time a physicist hears the word "infinite" they cower. Someone once said that mathematicians handle infinities, but physicists simply can't, since it means their theories come falling apart. It's why singularities and black holes aren't well understood, because the equations involve physical infinities which can't exist according to other laws.

(January 19, 2010 at 3:14 pm)Tiberius Wrote: That site mentioned the word "infinite" in the title and nowhere else. Could you point to some source that describes the idea properly? I can't see how in a finite amount of time you can go from no space and a singularity to an infinitely sized universe. Something doesn't make sense in the calculation...

Plus, every time a physicist hears the word "infinite" they cower. Someone once said that mathematicians handle infinities, but physicists simply can't, since it means their theories come falling apart. It's why singularities and black holes aren't well understood, because the equations involve physical infinities which can't exist according to other laws.

You have to keep in mind three things:
1) we can only have knowledge of the observable universe
2) the universe could have been infinite at the beginning of the big bang
3) the big bang is not an explosion of matter in an already existing space but a stretch of spacetime

I'll use the 2D analogon.

The scenario for the infinite universe
Now visualize yourself an infinite flat sheet of paper. The sheet represents the 2D analogon of the universe at T=T0 (the beginning of the big bang). One could draw a grid of parallel and rectangular lines a meter apart. The observable universe we see now was a tiny tiny speck (Planck width) on this sheet much smaller than a meter.

Now suppose the sheet suddenly stretches everywhere evenly. The lines of the grid are still parallel and rectangular. The stretching is of really epic proportions. The tiny speck blows up to humongous proportions at T=now. The observable universe has dimensions much greater than a meter.

Still from within the speck that blows up, you at no point in time can see what is going on beyond the circle that makes up the visible universe. This is because light is restricted to the speed of light (sounds acceptable that one) and relatively slow when compared to the rate in which spacetime stretches. The whole universe is bigger than the portion we can see (the observable universe).

Maybe this is helpful.
Or maybe this.
Or http://www.youtube.com/watch?v=yD1qAEeyets

Did someone edit my last post rather than quote it?

Quote:but are unable to describe the nature of the universe prior to this time

It is this where I keep an open mind and wonder if my appreciating that there might be a 'higher force' makes me an agnostic.

All other points taken into account I am probably an agnostic atheist.

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(January 19, 2010 at 12:10 am)Tiberius Wrote: It took me a while to wrap my head around it, but you'll get it eventually.

Do people 'get it'?

Or do they have faith in the science? Which is another theory I developed when reading Hawkings book.

I wonder if one day in centuries, they'll say: "Damb! I can't believe the universe was round, we went through this with Earth so long ago it should have occured to us".

(January 19, 2010 at 7:40 pm)TruthWorthy Wrote: I wonder if one day in centuries, they'll say: "Damb! I can't believe the universe was round, we went through this with Earth so long ago it should have occured to us".

I thought scientists already came up with this.

So you can't fall off the edge of the universe;