Is the Universe infinite?

[Airbrush]

8 hours ago, beecee said:

The best one can say is that the Universe is at least near infinite in extent and content.

The concept "near infinite" is meaningless because the difference between infinite and very, very big is INFINITE.  These 2 concepts have an infinite difference.

If this universe is infinite, then where does the adjacent universe begin?  If you need to go to infinity seeking the edge of our universe, where does the next one begin?

Edited August 15, 2017 by Airbrush

[swansont]

4 hours ago, Airbrush said:

The concept "near infinite" is meaningless because the difference between infinite and very, very big is INFINITE.  These 2 concepts have an infinite difference.

If this universe is infinite, then where does the adjacent universe begin?  If you need to go to infinity seeking the edge of our universe, where does the next one begin?

You're thinking in 3 (spatial) dimensions. What if each universe was simply occupying a different set of dimensions?

[Manticore]

8 minutes ago, swansont said:

You're thinking in 3 (spatial) dimensions. What if each universe was simply occupying a different set of dimensions?

Or - each universe occupies the same 3 dimensions but each is offset in one or more further dimension(s).

Imagine a 2 dimensional universe like an infinite sheet of paper - then stack as many as you like in the 3rd dimension.

(Very old idea - certainly pre-dates the coining of the word 'Multiverse'.)

[Mordred]

lol This is under the assumption of an infinite universe, you are quite right that the universe may be finite.

We simply don't know which is the case

[Airbrush]

4 hours ago, Mordred said:

lol This is under the assumption of an infinite universe, you are quite right that the universe may be finite.

We simply don't know which is the case

If you were forced to bet on one or the other, infinite universe within an infinite multiverse, or finite universe within an infinite multiverse, what would you bet on?

Edited August 15, 2017 by Airbrush

[Airbrush]

6 hours ago, swansont said:

You're thinking in 3 (spatial) dimensions. What if each universe was simply occupying a different set of dimensions?

That is changing the rules of the game.  In terms of 3 spatial dimensions only, how can more than one infinite universe occupy an infinite multiverse?

[Strange]

28 minutes ago, Airbrush said:

That is changing the rules of the game.  In terms of 3 spatial dimensions only, how can more than one infinite universe occupy an infinite multiverse?

Perhaps you are trying to apply "common sense" to the concept of infinity. That won't work.

Take the number line again. There are an infinite number of negative integers, then there are an infinite number of positive integers. So two infinite "universes" in the multiverse of all integers.

[swansont]

33 minutes ago, Airbrush said:

That is changing the rules of the game.  In terms of 3 spatial dimensions only, how can more than one infinite universe occupy an infinite multiverse?

Why is that a reasonable constraint to put on the problem?

[Carrock]

36 minutes ago, Airbrush said:

That is changing the rules of the game.  In terms of 3 spatial dimensions only, how can more than one infinite universe occupy an infinite multiverse?

Take one infinite multiverse. Chop it in two (rather difficult in practice) and you have two infinite universes. You can repeat this an unlimited (but not necessarily infinite) number of times for as many universes as you want.

Alternatively, simply say that the (infinite) multiverse is twice as big as the (infinite) multiverse or infinitely many times as big.

This is a verbal description of perfectly valid maths. See e.g. http://gizmodo.com/5809689/a-brief-introduction-to-infinity

 

Edited August 15, 2017 by Carrock
Spelling

[Airbrush]

1 minute ago, swansont said:

Why is that a reasonable constraint to put on the problem?

Then what you are saying is that there CAN be multiple universes that are infinite in size, but only if they exist on different dimensions?

What if there were no other dimensions for other infinite-sized universes, how do more than one infinite-sized universes occupy a multiverse, all on the same dimension?

[swansont]

5 minutes ago, Airbrush said:

Then what you are saying is that there CAN be multiple universes that are infinite in size, but only if they exist on different dimensions?

No, I asked why that constraint was reasonable. Strange and Carrock have already addressed the other issues.

 

[Airbrush]

10 minutes ago, Carrock said:

Take one infinite multiverse. Chop it in two (rather difficult in practice) and you have two infinite universes. You can repeat this an unlimited (but not necessarily infinite) number of times for as many universes as you want.

Alternatively, simply say that the (infinite) multiverse is twice as big as the (infinite) multiverse or infinitely many times as big.

This is a verbal description of perfectly valid maths. See e.g. http://gizmodo.com/5809689/a-brief-introduction-to-infinity

 

Very interesting explanation and I plan to spend more time studying "A Brief Intro to Infinity".

Can we agree for my example to exclude other dimensions from this discussion of universes? 

So you can chop an infinite universe in half on any plane you choose.  On each side of your "chop plane" there are 2 infinite universes that are butt up against each other at the "chop plane".  Each of these half universes are half as infinite as the two were together, right?  How do you select your next chop plane?  Do you chop your 2 universes into 4 on an intersecting perpendicular plane?  Ok, you now have 4 quadrants to the universe.  But that is not a natural configuration for big bangs.  Big bangs do not neatly butt up against each other in 4 quadrants.  Big bangs should be an amorphous blob or even roughly spherical shaped.  Right, don't we see animation CGI of big bangs, and they are roughly spherical in shape?  Also how does something infinite in size pop out of a point smaller than a proton?

[Mordred]

3 hours ago, Airbrush said:

If you were forced to bet on one or the other, infinite universe within an infinite multiverse, or finite universe within an infinite multiverse, what would you bet on?

I wouldn't accept the bet, I recall one line by Migl that is appropriate. Our observable universe is finite, and we will never receive signals beyond the cosmic event horizon. So for all practical purposes it only matters what we can understand about our finite observable portion of the universe. 

 

[Airbrush]

15 minutes ago, swansont said:

No, I asked why that constraint was reasonable. 

Sorry, only as a thought experiment.  I agree with you that infinite universes may co-exist on different, overlapping dimensions.  But I am trying to understand how it can make sense without the aid of other dimensions.

[Airbrush]

2 minutes ago, Mordred said:

 ......for all practical purposes it only matters what we can understand about our finite observable portion of the universe. 

That is true, but don't you think we may someday be able to INFER whether the universe (our big bang) is finite or infinite?

[Strange]

13 minutes ago, Airbrush said:

Each of these half universes are half as infinite as the two were together, right? 

Half as infinite is still infinite.

 

13 minutes ago, Airbrush said:

But that is not a natural configuration for big bangs.  Big bangs do not neatly butt up against each other in 4 quadrants. 

I don't think this is being suggested as a way that universes could be created, just to help you understand that there is no reason why an infinite space cannot be (infinitely) subdivided into infinite sub-spaces.

[Mordred]

8 minutes ago, Airbrush said:

That is true, but don't you think we may someday be able to INFER whether the universe (our big bang) is finite or infinite?

The only viable method to address that question remaining to us is to solve how our universe began.

The two major alternative methods we tried, (Universe curvature and signals in the CMB) have failed to provide conclusive data.

It was once the belief in Cosmology that we could use curvature to determine if our universe is finite or infinite. However this turned out to be wrong.

Lets play assume for a moment and assume expansion stopped. With our current ever so slight curvature , if we were to send a signal, that signal will theoretically take 880 billion years arrive back on Earth. 

( as curvature affects light paths, this remains true in both the finite and infinite case).

 

Edited August 15, 2017 by Mordred

[Manticore]

1 hour ago, Airbrush said:

Each of these half universes are half as infinite as the two were together, right? 

There is an old mathematicians joke about infinity - it goes something like this:

Question: You find an infinitely long piece of string. Where do you cut it to get two equal pieces?

Answer: Anywhere you like.

Question: How do you get three equal pieces?

Answer: Cut it anywhere you like. Then run alongside it for an infinite distance and cut it again.

[Carrock]

1 hour ago, Airbrush said:

Very interesting explanation and I plan to spend more time studying "A Brief Intro to Infinity".

Can we agree for my example to exclude other dimensions from this discussion of universes? 

So you can chop an infinite universe in half on any plane you choose.  On each side of your "chop plane" there are 2 infinite universes that are butt up against each other at the "chop plane".  Each of these half universes are half as infinite as the two were together, right?  How do you select your next chop plane?  Do you chop your 2 universes into 4 on an intersecting perpendicular plane?  Ok, you now have 4 quadrants to the universe.  But that is not a natural configuration for big bangs.  Big bangs do not neatly butt up against each other in 4 quadrants.  Big bangs should be an amorphous blob or even roughly spherical shaped.  Right, don't we see animation CGI of big bangs, and they are roughly spherical in shape?  Also how does something infinite in size pop out of a point smaller than a proton?

The non bolded points have conveniently been dealt with while I took a break.

The finite observable universe originated (probably) in a volume smaller than a proton but because of the lack of observable edge effects the big bang is either spatially infinite or too large to measure. 'Originates' here really means 'this is the earliest time when plausible physics can be invoked.'

Inflation is an explanation of why the observable universe is so smooth but I doubt anyone will ever come up with a remotely plausible smoothing mechanism to ensure the big bang was of infinite extent.

So while the universe may or may not be infinite in time and/or space I believe the big bang was finite in space. If the universe is spatially infinite I'd expect an infinite number of big bangs.

[beecee]

15 hours ago, Airbrush said:

The concept "near infinite" is meaningless because the difference between infinite and very, very big is INFINITE.  These 2 concepts have an infinite difference.

I believe it describes a state that is probably finite, but also humongously big and in realty beyond  human measuring capabilities. I have been taken to task over it before, but I also believe the definition I gave, would be obvious to most people. 

[Airbrush]

On ‎8‎/‎15‎/‎2017 at 1:25 PM, beecee said:

I believe it describes a state that is probably finite, but also humongously big and in realty beyond  human measuring capabilities. I have been taken to task over it before, but I also believe the definition I gave, would be obvious to most people. 

Yes now I see what you mean, like a figure of speech.

On ‎8‎/‎15‎/‎2017 at 0:00 PM, Manticore said:

There is an old mathematicians joke about infinity - it goes something like this:

Question: You find an infinitely long piece of string. Where do you cut it to get two equal pieces?

Answer: Anywhere you like.

Question: How do you get three equal pieces?

Answer: Cut it anywhere you like. Then run alongside it for an infinite distance and cut it again.

Ha, that is a good one!  How else can you cut an infinite string into 3 equal pieces?

Ok, I just thought of a way to stack an infinite number of universes, each of which is infinite in size.  If they are flattened like a stack of pancakes or galaxies, each of which extends out to infinity on the x and y axes, but the z axis is a finite thickness.

Edited August 16, 2017 by Airbrush

[Tub]

On 01/08/2017 at 2:32 PM, dordle-loddle said:

Is the Universe infinite or just really, really big?

I'd be happier believing that the Universe is infinite, that's a comforting thought, but i can't help feeling that it's finite, simply because what we can see of it is still expanding in space/time. If the Universe was already infinite,( and eternal ),wouldn't that prevent any further expansion of space/time?  I hope i can be shown to be completely wrong.

[Carrock]

52 minutes ago, Tub said:

I'd be happier believing that the Universe is infinite, that's a comforting thought, but i can't help feeling that it's finite, simply because what we can see of it is still expanding in space/time. If the Universe was already infinite,( and eternal ),wouldn't that prevent any further expansion of space/time?  I hope i can be shown to be completely wrong.

Exponential expansion can continue for unlimited but finite time.

A/the universe has finite or infinite (i.e. aleph-null) units of volume. If this universe doubles in size an infinite number of times in infinite time it contains 2^(aleph-null) units of volume. This is equal to aleph-one units of volume (assuming the continuum hypothesis). That is, there would be as many units of volume in this universe as there are dimensionless points. This is topologically inconsistent with current physics.

 Philosophy of Science Vol. 32, No. 1 (Jan., 1965), pp. 21-31  has a good description of this. (The article was very aggressively peer reviewed but some on this forum are convinced it is too old to be correct.)

Of course the universe is not constrained by what seems to be (im)possible....

Edited August 17, 2017 by Carrock
Included case of an initially finite universe.

[Tub]

37 minutes ago, Carrock said:

Exponential expansion can continue for unlimited but finite time.

A/the universe has finite or infinite (i.e. aleph-null) units of volume. If this universe doubles in size an infinite number of times in infinite time it contains 2^(aleph-null) units of volume. This is equal to aleph-one units of volume (assuming the continuum hypothesis). That is, there would be as many units of volume in this universe as there are dimensionless points. This is topologically inconsistent with current physics.

 Philosophy of Science Vol. 32, No. 1 (Jan., 1965), pp. 21-31  has a good description of this. (The article was very aggressively peer reviewed but some on this forum are convinced it is too old to be correct.)

Of course the universe is not constrained by what seems to be (im)possible....

Thanks, Carrock. Can i assume, then, that an infinite Universe would have to be a steady-state Universe, or have i misunderstood your post? ( I'm not a mathematician. )

[Handy andy]

On ‎01‎/‎08‎/‎2017 at 2:32 PM, dordle-loddle said:

Is the Universe infinite or just really, really big?

The question is philosophical and gives rise to various answers. Static space, Dynamic space etc

I assume you are referring to space being infinite or finite dimensions.

From the philosophical point of view it is a chicken or egg question between infinite space or no space and which existed first, perhaps both could exist at the same time, with all points in space being connected via a common wormhole. Quantum entanglement allows separated particles to be influenced instantly via a theoretical  wormhole connecting points in space. Space has no observable edge and is expanding between galaxies as a quantum foam, without which there would be no space. The gravitational field regardless of if you assume it to be governed by relativity or caused by the expansion and contraction of quantum foam flowing towards mass causes the existence of space, ie no field = no space. A zero Space separates producing virtual particles of opposite polarity, these move around, possibly entangled possibly not? etc etc  

An actual fact about space, is it is really big from the human point of view, and from the quantum entanglement point of view, separated parts are or can be connected, this is best visualized with the wormhole concept, but a mathematical equation works also

 

Edited August 17, 2017 by Handy andy