Thread: Space cannot be infinite

My understanding is that general relativity essentialy says that space time is a solution of the Einstein field equations. There are lot's of solutions.

As far as I know, the standard ones are finite but unbounded. Think of the surface of a sphere as a finite but unbounded space: an ant could start walking on it and never run into a boundary. EDIT: and yes UM, eventually come back to its starting point.

I do believe I recall, but could not find quickly find reference too, infinite solutions. At anyrate, as I recall, the infinite solutions had space time expanding in such a manner that anything beyond the edge of the visible universe would be moving faster then the speed of light so that photons would never reach us to begin with.

As Spockman pointed out though, the beauty of science is that it is all theory. Any theory we cook up will be superceded by a better one. Unless we have empirical confirmation of something that a theory says, It is only a potential failing point for our current theory.

UM, I think that we can get from point A to B "faster" than light speed, not by traveling faster than light (Depends on the reference system I guess) but from bending space-time.

Very similar to the question proposed on http://hypography.com/forums/physics...tion-pass.html

The paper folding analogy describes how it can be conceptualized-

That's called a worm hole.

The way I prefer to think of space, is that it's neither fenite nor infinite.
Think of a sphere (or a circle). The sphere is the universe, all the stars, galaxies, dark-matter and energy is located within this sphere. So comes the dilemma: What's outside the sphere?
The answer is (as in can be) "nothing". There's no matter, no electromagnetic waves, no energy. And therefore, what's outside the sphere does not exist. But if you imagine you're in a spaceship, and travel out past the sphere's "edge", you're not actually moving outside of the "edge". You're simply expanding the sphere itself. In this interpretation there're no limit, you could travel forward without getting looped back for our entire concept of time. And if you turned around and went back, the sphere would shrink until you were no longer the only energy located at the boundary. I think that's the easiest approach.

That's one way to say it, but hasn't it been proven that Space is still expanding? The aftershock of the big bang? I saw a History channel thing about that... After it went BOOM-CLANK-KAPOW on us, it kept expanding.

To me, it makes sense that it's like a balloon: You breath out, ushing air into the balloon. You breath back in, the air comes out of the balloon. Then we havesuper-small space, again, and then bigbangagain to make it big, big crunch to make it small. See where I'm going?

Originally Posted by [SomeGuy]

That's one way to say it, but hasn't it been proven that Space is still expanding? The aftershock of the big bang? I saw a History channel thing about that... After it went BOOM-CLANK-KAPOW on us, it kept expanding.

To me, it makes sense that it's like a balloon: You breath out, ushing air into the balloon. You breath back in, the air comes out of the balloon. Then we havesuper-small space, again, and then bigbangagain to make it big, big crunch to make it small. See where I'm going?

The universe is still expanding, but that's not a problem with the explanation I gave. Just as you in a spaceship can expand space, so can all other forms of energy. However it's pretty much identical to the balloon analogy.
However it's unlikely that space will start contracting. I've read that it the expansion is accelerating.

Wouldn't it eventually get too stretched out and thin out? Wouldn't it destabilize? Imagine a giant ball of silly putty. With your mind, stretch that sucker out millions of miles. IT's thin as hell now, right? That's spacetime. Now imagine galaxies and planets on top of that. and in that. What do you think will happen? I think because of that, there are laws we don't know about that say that the universe will contract.

Originally Posted by [SomeGuy]

That's called a worm hole.

Yes, it can be called that.

Originally Posted by [SomeGuy]

Wouldn't it eventually get too stretched out and thin out? Wouldn't it destabilize? Imagine a giant ball of silly putty. With your mind, stretch that sucker out millions of miles. IT's thin as hell now, right? That's spacetime. Now imagine galaxies and planets on top of that. and in that. What do you think will happen? I think because of that, there are laws we don't know about that say that the universe will contract.

It's possible that the universe will stop expanding, but I don't think it will contract to a new "big bang". And there's no real reason that it should get too thin. No matter how far apart to "blubs" of energy are, it'll always be a finite distance.

But think, if the Universe is finite, there is a finite amount of spacetime. Eventually, that will thin out and the Universe will...break I guess.

Originally Posted by [SomeGuy]

But think, if the Universe is finite, there is a finite amount of spacetime. Eventually, that will thin out and the Universe will...break I guess.

In all models that I'm aware of with any experimental backing, spacetime is not thought of as a substance but as merely existing: Their is no it to stretch out. It is sort of a problem that none of our theories can construct 'spacetime'.

Originally Posted by [SomeGuy]

But think, if the Universe is finite, there is a finite amount of spacetime. Eventually, that will thin out and the Universe will...break I guess.

What exactly do you mean by 'spacetime'?
And what do you mean when you say the Universe is finite? That there's a set amount of energy in it, that cannot be changed? If so I agree with you, but I don't see why spreading this would bring about the End of World.

I guess that makes sense.

Originally Posted by khh

What exactly do you mean by 'spacetime'?
And what do you mean when you say the Universe is finite? That there's a set amount of energy in it, that cannot be changed? If so I agree with you, but I don't see why spreading this would bring about the End of World.

Spacetime...is spacetime. Look it up. The universe has a definite size, yet it expands. Therefore, there is a set amount of energy and matter in it.


I figured that eventually spacetime would stretch out and become thin enough to rip.

Originally Posted by [SomeGuy]

Spacetime...is spacetime. Look it up. The universe has a definite size, yet it expands. Therefore, there is a set amount of energy and matter in it.

I figured that eventually spacetime would stretch out and become thin enough to rip.

*Wikipedia* Ah, that. Why didn't I just do that to begin with >.<
I don't really imagine that as something finite. I mean, it's basically just matter itself. Barring black holes, all mass has space, and where there's mass and space, there's time. It's kind of a concept more than a, er, thing, isn't it?

You can't talk about a finite amount of space-time, but you CAN talk about a finite amount of matter.

With an expanding Universe and finite matter (The matter in the Universe is pretty much non-changing) the mass density will lower, the current average density of the univers is 0,25 atoms per cubic meter.

With the Universe expanding the density will get eventual get so low that no star, planet or any objects with temperatures above ~0 Kelvin will exist. The last of the bigger structures in the Universe will be black holes, after 2&#215;10^99 years all supermassive black holes would have evaporated.

Long before that, 10^14 years from now would all stars have ceased to exist.

The current science give an estimate to the half-life of protons to 10^37 years, this mean when the Universe is around 10^40 years protons would have halved about 1000 times.

We are then left with zero protons.

10^100 years from now the Dark Era (practically empty Universe) will rule until either the Big Crunch, Big Rip, Big Bounce or true heat death would be achieved.

If we still exist we might alter some parametre, changing our "destiny" or play with dimensions and such, we can only speculate..



This bring us to the last question!

Ah, right. I forgot about that part :p
Wow that's big stuff...

Yes, it's big stuff.

To avoid cataclysmic mass brain meltdown we have to watch this.

I agrfee with that. My views have been altered.

Originally Posted by Universal Mind

If you travel far enough away from Earth, you reach Earth?

Probably not, but I like the idea.

Well.. as a technicality, I'd say probably yes, but only after an infinite amount of time.

But you can pretty much interpret "infinite amount of time" as something impossible (for human beings), so..

Originally Posted by SleepyCookieDough

Space cannot be infinite because then there would be an infinity of solar system, meaning an infinity of planets resulting in an infinity of peoples. There cannot be an infinite of peoples because there cannot be an infinity of spirits.

Infinity is not a number. It just never stop going but that is impossible. Only numbers go to infinity but most numbers will never be used since they go to infinity meaning that trillions of trillions of trillions of number will not be used. Actually, what I just said is wrong. infinity doesn't represent a large number. An infinity of numbers will never be used. That's the actual statement. And time might be infinite too.

Its sorta hard to explain though..

infinity isnt static its movement, the universe is expanding infinitely, thats what we mean.

I just wanted to add something before going to bed.

In quintessence (first time I use that word ) the concept of infinity has no root in reality, infinity is a concept created because of the limiting capacity of the human mind, we say infinity because we can't really grasp the "it" we are calling infinity.

Bear in my that I an talking about reality, and not a scientific or mathematical model of reality.

Goodnight.

I know this thread is a little bit old, but my high school math teacher ALWAYS talked about "the limit". Here's his example from what I can remember:

"If I stand x amount distance from the wall, and then decrease my distance by 50&#37;, will I ever hit the wall?"
"No."
"But will I appear to be touching the wall eventually? The answer is yes. I may be physically touching the wall, however if we go down on an atomical level, I will never, ever, touch the wall."

Space is infinite.

Who's to say it is limited to one universe, and not a multiverse, anyway?