Finite Universe

[DancZer]

Can be the Universe finite?

I draw this once. What do you think about it?

If you think about the Universe as 2D World, the finite would be a surface of the sphere. We are in 3D. Can be the finite Universe a hypersphere?

[Bill Phil]

Wha.... What?

[Jovus]

The universe must be finite, given current theories of universe creation.

To wit: take the measure of one dimension of the universe as the furthest distance from point to point between two objects. At one time, all objects in the universe were constrained in a finite sphere. (Big Bang theory; doesn't matter how large the sphere is.) All objects have a finite velocity. (Increasing, sure, but at any given moment finite.) Therefore, for all times, the universe is finite in extension, since any infinity is always larger than any finity. (You can't 'move through' finitude to infinitude, e.g. you cannot count to infinity.)

Under this definition, the universe is of a finite but indefinite size.

Now, there are two possible other ways I can see to talk about the 'universe' that bring up the possibility of finity or infinity. The first is to talk about the possible extension of space - not 'outer space' as colloquially thought of, i.e. some kind of very extensive 'place', but of the mathematical concept of space. Space as such must necessarily be infinite.

The second is to ask what 'kind of space' best describes the actions of the observed universe, i.e. what mathematical rules govern motion and what we can therefore say about the manifold along which motion takes place. This manifold might be either infinite or finite; I don't know. Personally I think the universe is highly unlikely to be a Hilbert space; I'd guess it's hyperbolic. (I don't know if this has been conclusively decided or not, sadly.) Funnily enough, any hyperbolic space can be represented by a finite transform.

[worir4]

The Universe has to be finite.

Ill just drop this thread link here:

http://forum.kerbalspaceprogram.com/threads/107575-Infinite-Universe-Impossible

[ZetaX]

The Universe has to be finite.

Ill just drop this thread link here:

http://forum.kerbalspaceprogram.com/threads/107575-Infinite-Universe-Impossible

If you read that thread carefully you will see that there was actually no good reason given why it should be finite.

[Majorjim!]

If you read that thread carefully you will see that there was actually no good reason given why it should be finite.

If the universe was infinite and light has had an infinite amount of time to travel then the sky we see would be bright white light everywhere as every point in space would lead to a star.

The universe has no boundary but is finite. It had a beginning. An infinite universe has no begging and no end.

[kStrout]

the big band doesn't happen at one end of the sphere, the sphere coming into existence and rapidly expanding is the big bang.

[Majorjim!]

the big band doesn't happen at one end of the sphere, the sphere coming into existence and rapidly expanding is the big bang.

I think this was implied by the op but his diagram is a 2 dimensional representation.

[ZetaX]

If the universe was infinite and light has had an infinite amount of time to travel then the sky we see would be bright white light everywhere as every point in space would lead to a star.

a) The universe could still be infinite in either space or time. You are assuming that both are infinite, while being finite means that both are finite.

That infinite brightness argument is wrong anyway. Just add a little bit of dust everwhere (and we know there is) and photon travel distances become finite on average.

The universe has no boundary but is finite.

For time one might argue by Big Bang (yet there could be time before it), but we are lacking evidence for space being finite.

[LABHOUSE]

Time was CREATED, the universe is finite so far in time, but it still has eternity to go.

There is no proof nor disproof of the universe being finite or infinite yet​.

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If the universe was infinite and light has had an infinite amount of time to travel then the sky we see would be bright white light everywhere as every point in space would lead to a star.

The universe has no boundary but is finite. It had a beginning. An infinite universe has no begging and no end.

But stars die, and there is cosmic dust blocking some light, and the sun outshines the stars, even at night the sun reflects off of the moon and planets which outshines the stars.

[Woopert]

Well, more precisely, spacetime was created. I've also learned that the universe is flat. That's quite interesting.

I think what it is is that the bounds of space and the universe are infinite, but the amount of matter is finite. Or at least it should be like that.

[ZetaX]

I think what it is is that the bounds of space and the universe are infinite, but the amount of matter is finite. Or at least it should be like that.

That would contradict the cosmological principle. You cannot have finite matter in infinite space while still having homogenity and isotropy.

[Linear]

I find the idea of an infinite universe pretty silly really. Everything else is governed by so many rules, each minute detail is accounted for....oh yeah and the universe is infinite which makes little to no mathematical sense bye.

[Bill Phil]

Maybe infinite in the sense of being the circumference of a circle. Technically there are an infinite number of radians in a circle, but for one rotation it's 2pi. Maybe the universe is like that?

[ZetaX]

I find the idea of an infinite universe pretty silly really. Everything else is governed by so many rules, each minute detail is accounted for....oh yeah and the universe is infinite which makes little to no mathematical sense bye.

It makes perfect mathematical sense. Maybe we some day discover a law of nature that forbids it, but mathematics itself won't be the problem.

[Majorjim!]

Time was CREATED, the universe is finite so far in time, but it still has eternity to go.

There is no proof nor disproof of the universe being finite or infinite yet​.

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But stars die, and there is cosmic dust blocking some light, and the sun outshines the stars, even at night the sun reflects off of the moon and planets which outshines the stars.

Those are the words of Steven Hawking. I will take his view over most. Also, dust obstruction and star death is moot as light has had an infinite amount of time to travel, there too would be an infinite number of stars. This is the intrinsic problem with infinity. it is fraught with paradoxes.

It is thought that infinity is merely a product of our poor mathematics.

To say there was anything before the big bang is meaningless. It isn't within the realms of science.

Edited March 27, 2015 by Majorjim

[ZetaX]

Also, dust obstruction and star death is moot as light has had an infinite amount of time to travel, there too would be an infinite number of stars.

So what? We can safely assume that every star absorbs all the light it gets hit by, so we cannot see more than one star in a given direction.

And anyway, you ignored the part that finite means that both time and space are finite. I am not objecting to time having been finite in the past (and lets ignore the future). All those infinite light arguments become moot as soon as we consider a universe of finite age with a finite speed of light (i.e. the one we probably live in).

[Ethanadams]

Ummm if the universes is finite then what's outside?

(time dosnt exist)

[ZetaX]

Ummm if the universes is finite then what's outside?

There is no outside. And yes, that's simply the answer. A more detailed elaboration can be found in some other threads (probably the one linked above).

(time dosnt exist)

Umm.. it obviously does? At the very least: citation/argument needed.

[Ethanadams]

I have made a thread proving that time is not natural but just a human measurment of the movement of the earth see time thread don't have a link sorry

[Majorjim!]

So what? We can safely assume that every star absorbs all the light it gets hit by, so we cannot see more than one star in a given direction.

And anyway, you ignored the part that finite means that both time and space are finite. I am not objecting to time having been finite in the past (and lets ignore the future). All those infinite light arguments become moot as soon as we consider a universe of finite age with a finite speed of light (i.e. the one we probably live in).

In the exact words of Steven Hawking:

"In an infinite and everlasting universe, every line of sight would end on the surface of a star. This would mean that the night sky would have been as bright as the surface of the Sun. The only way of avoiding this problem would be if, for some reason, the stars did not shine before a certain time."

I'm afraid you are not in a position to realistically argue this point. Sorry but he is a lucasian professor of mathematics!

Your second paragraph doesn't seem to have anything to do with my statement. Care to elaborate?

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I have made a thread proving that time is not natural but just a human measurment of the movement of the earth see time thread don't have a link sorry

Your Nobel prize is in the post I assume?

[ZetaX]

In the exact words of Steven Hawking:

"In an infinite and everlasting universe, every line of sight would end on the surface of a star. This would mean that the night sky would have been as bright as the surface of the Sun. The only way of avoiding this problem would be if, for some reason, the stars did not shine before a certain time."

He and you are ignoring dust. Which I mentioned several times now.

Maybe you can still conclude such a thing, but the argument would be less simple: but then the correct conclusion would be that most of the sky is of similiar brightness, but that brightness may be significantly below the sun's.

Edit: and thinking about it, the stars being infinitely old would mean infinite energy everywhere, so that brightness I speak if is infinite and we are all gone by now. So now one should somehow account for stars being finite things while still allowing infinite time...

I'm afraid you are not in a position to realistically argue this point. Sorry but he is a lucasian professor of mathematics!

So you are going with arguments from authority now? Can we please not go that low? This is (theoretical) science, where things are based on fact and argument, not on what somebody with a title says.

And I still find the argument moot anyway because:

Your second paragraph doesn't seem to have anything to do with my statement. Care to elaborate?

You are always assuming that both space and time are infinite for your argument to work. It could very well be that only space is infinite while time is finite. That would still be an infinite universe, but we would obviously not have the brightness argument. So the "the stars did not shine before a certain time" part is fulfilled, i.e. nothing is contradicting what Hawking said. We could still have a universe that is, at this very moment, of infinite size in regard to space.

Edited March 27, 2015 by ZetaX

[BlueCosmology]

I have made a thread proving that time is not natural but just a human measurment of the movement of the earth see time thread don't have a link sorry

Even if that were true (hint: it's not), in what way does that mean time either does not exist or is not natural? The movement of the Earth both exists and is natural.

Also, you have a strange definition of proof. The entire extent to what you said is " I was told that time is just a measurement of distance of an orbit like 24 hours of time on earth is equivalent to I rotation is this true?".

You haven't even attempted to make it plausible. Let alone attempt to justify it. Let alone actually justify it. Let alone prove it.

Edited March 27, 2015 by BlueCosmology

[Majorjim!]

You are always assuming that both space and time are infinite for your argument to work. It could very well be that only space is infinite while time is finite. That would still be an infinite universe, but we would obviously not have the brightness argument. So the "the stars did not shine before a certain time" part is fulfilled, i.e. nothing is contradicting what Hawking said. We could still have a universe that is, at this very moment, of infinite size in regard to space.

No, no I am not. I have never stated this directly or even implied it. I believe that neither space nor time are infinite in as much as what is reasonable to assume given that it is not reasonable to even discuss what came before or after. We can never know this. and therefore it is not within the realm of science as it lays outside of our experienced reality.

Space can have no boundary and still be finite. Like the surface of a sphere. Or saddle shaped as theorised by physicists.

I don't mean to be rude but you cannot reasonably argue with what someone like S.H says as his views are based on years of complex mathematics and study. Yours is based on, what?

Edited March 27, 2015 by Majorjim

[ZetaX]

No, no I am not. I have never stated this directly or even implied it.

To quote you:

If the universe was infinite and light has had an infinite amount of time to travel then...

That's where you assume both parts of spacetime to be infinite to get the brightness conclusion. Only one of them won't suffice.

I believe that neither space nor time are infinite in as much as what is reasonable to assume given that it is not reasonable to even discuss what came before or after. We can never know this. and therefore it is not within the realm of science as it lays outside of our experienced reality.

We can observe if the universe continues existing forever. We can also observe if space goes on forever by flying straight or just waiting for light from further away. Neither of them completely proves that something is truly infinite (it might just be larger/older than we know for sure). But that kind "does not prove" is the same as in "we cannot know for sure of gravity really exist, maybe it was all just a huge coinceidence so far". Science cannot make absolute statements; but it can say if something is very probable.

In other words: the universe being infinite in space or existing for forever is something that can be tested.

Space can have no boundary and still be finite. Like the surface of a sphere. Or saddle shaped as theorised by physicists.

I am pretty sure I know how manifolds work

I don't mean to be rude but you cannot reasonably argue with what someone like S.H says as his views are based on years of complex mathematics and study. Yours is based on, what?

On the very same. I am a working mathematician.