The universe could be infinite in spatial volume and matter content. T or F?

[Martin]

In standard cosmology, matter is assumed to be distributed throughout all space more or less uniformly. So if space is infinite volume, the amount of matter is infinite. If space is a boundaryless finite volume then the amount of matter is finite as well.

 

In neither the finite or infinite case is there any edge or boundary to space, and since the region occupied by matter coincides with the whole of space there is no edge or boundary to the occupied volume either.

 

the question of space infinite or finite has not been resolved yet.

 

What is your opinion? Do you think space volume could be infinite?

[insane_alien]

It could be considered infinite in volume and matter but finite in time.

 

also, it doesn't have to be infinite in volume at any one time to be consdered infinite in volume.

 

it could be like Hilberts Paradox of the Grand Hotel if the radius of the universe is expanding faster than the speed of light.

 

though if we find a way to travel or communicate faster than the speed of expansion then this would be null and void and we would have to consider it finite.

[DrP]

The words "could be" make this statement true. If you were to have used the word "is" instead then it would not be true because no-one knows.

[Royston]

I voted true for the same reason DrP gave. However what I want it to be is finite (positive curvature) so [math]\Omega >1[/math], only because I don't like the idea of infinite matter et.c

[gcol]

As already said, I had to vote yes, because of the word "could".

 

As we do not know, anything could be possible.

[YT2095]

False, if Both are Infinite they are then both the same "amount" and since the universe is not Solid matter, it`s obviously False.

[Skye]

YT, I think you are intuitively doing algebra using infinities, and that's not really possible.

[Severian]

I said true. But if you had phrased the title of the thread as "The universe could be finite in spatial volume and matter content" I would also have said true.

[YT2095]

well since Infinity is by definition Infinite meaning Everything forever and then some, and Matter that occupies this is of the same nature, then even the Smallest gap that is Not matter says that it`s not the Same quantity when compared to Space.

 

since all matter must reside in Space, and since all space is Not filled with matter, it`s only Logical that one is Greater than the other, no matter How "big" you go or continue with into infinity.

 

Space will always be Greater than the Material within it.

 

it`s only Logical!

[DrP]

False, if Both are Infinite they are then both the same "amount" and since the universe is not Solid matter, it`s obviously False.

 

I see you point and agree, but I'm not sure that is what Martin ment. I think he ment is space infinate. (?)

 

I think you (YT) would be very good at the following type of question:

'How far can a dog run into the wood?"

[YT2095]

half way in, then he`s heading out would be the Logical choice I expect.

[Klaynos]

I said true. But if you had phrased the title of the thread as "The universe could be finite in spatial volume and matter content" I would also have said true.

 

Yep, I agree with this.

[gcol]

If quantum mechanics indicates that every smallest particle of matter is surrounded by a "halo" of uncertainty, and at the very edge of the expanding universe the "bow-wave" of this uncertainty may extend an indefinite distance, some precursor effect of matter will always be in advance of anything actually measurable, perhaps?

[YT2095]

you don`t have to go to such extremes, Particles are popping in and out of existence all the while even in a pure Vacuum, these particles are Literally "Borrowed" from the Future, but soon disintegrate again.

you don`t need to go to the edge of universe to know this

[Martin]

No one AFAICS has asked any questions that need answering. I'll just put in my two cents. I agree with DrP, Snail, Skye, Severian, Klaynos (who agreed with Severian)...etc

 

The words "could be" make this statement true. If you were to have used the word "is" instead then it would not be true because no-one knows.

 

I voted true for the same reason DrP gave. However what I want it to be is finite (positive curvature) so [math]\Omega >1[/math], only because I don't like the idea of infinite matter et.c

 

YT, I think you are intuitively doing algebra using infinities, and that's not really possible.

 

I said true. But if you had phrased the title of the thread as "The universe could be finite in spatial volume and matter content" I would also have said true.

 

Like Snail, I also feel personally more comfortable with the finite spatial volume solution that he mentioned. But we don't know which is right, so either could be. In finite volume case space has no boundary or edge and it has no CENTERPOINT either (unless you imagine it embedded in some higherdimensionality for which there is no evidence and then the centerpoint is outside our 3D space.) But it does have finite volume and therefore the matter (assumed to be distributed roughly uniformly) has finite mass. As Severian observes, that could be the case.

 

But the issue hasn't been resolved yet. In modern observational cosmology there are two leading versions of the standard LCDM model, spatial infinite Omege = 1, and spatial finite Omega > 1. The last errorbar I saw was 68 percent Omega in the range [1.010, 1.041]. It slightly favors finite but not to a statistically significant extent. It was in something that both David Spergel and Ned Wright had signed onto---and other top experts.

 

About matter: you can measure it in kilograms or by its energy equivalent in joules, or other ways. If you measure it, say, in joules, then the current best estimate for the density of matter in space is about 0.2 joules per cubic kilometer. If you have an infinite number of cubic kilometers of volume, then naturally you have an infinite number of joules (energy equivalent) of matter.

[Skye]

well since Infinity is by definition Infinite meaning Everything forever and then some, and Matter that occupies this is of the same nature, then even the Smallest gap that is Not matter says that it`s not the Same quantity when compared to Space.

 

since all matter must reside in Space, and since all space is Not filled with matter, it`s only Logical that one is Greater than the other, no matter How "big" you go or continue with into infinity.

 

Space will always be Greater than the Material within it.

 

it`s only Logical!

If space is infinite, and matter is distributed evenly within it, then matter will be infinite too.

 

Imagine that there is one hydrogen atom every meter throughout space. Then you travel through space, every meter hitting a hydrogen atom. Since space is infinite you would hit an infinite number of atoms if you traveled along a path for long enough (infinitely long time).

 

The only difference with solid matter is that the atoms are a little closer together, but it is still a matter of hitting an atom every few Angstroms along an infinite path.

[YT2095]

but is you had Infinite Matter, you would have the Utmost Max joules per Km^3, this is not the case.

 

and as far I know the Max poss would be that borne of an antimater annihilation/2 (or there abouts), and that is NOT the case either.

[Mr Skeptic]

I said true. But if you had phrased the title of the thread as "The universe could be finite in spatial volume and matter content" I would also have said true.

 

I agree with what Severian said, and that was exactly the reason why I voted yes.

 

However, an infinite universe has all sorts of uncomfortable theological and philosophical implications. Basically, it has all the attributes that the "parallel worlds" interpretation of QM has, but in a single world. For example, if it were at all possible for life to evolve, it would have done so infinitely many times, and infinitely many times in every possible way. And if it were at all possible for a more or less omnipotent/omniscient entity that is interested in your sex life to form/evolve/whatever, it would also have done so infinitely many times. Likewise, there would be a world much like our own, where you are a president, criminal, or cyborg, etc, etc.

 

Quite disturbing to think about, so I too would much rather the universe be finite. At the very least, our own portion of the universe is completely cut off from the rest of the (potentially infinite) universe, so we probably wouldn't see the more improbable of the possibilities mentioned above. However, if our universe is cut off from the rest of the universe, would we not say that the universe (as defined by everything we can see, ie everything that could affect us) is finite, but a part of a larger metaverse that is infinite. Then the difference from the "many worlds" QM is that our universe intersects with many more universes which intersect with many more universes, etc.

[Royston]

I agree with what Severian said, and that was exactly the reason why I voted yes.

 

However, an infinite universe has all sorts of uncomfortable theological and philosophical implications. Basically, it has all the attributes that the "parallel worlds" interpretation of QM has, but in a single world. For example, if it were at all possible for life to evolve, it would have done so infinitely many times, and infinitely many times in every possible way.

 

There's no reason why infinite volume and infinite matter necessitates infinite variation. I'm sure somebody brought this up in another thread, and I agree.

[Realitycheck]

If there was infinite matter, there would be no space. You cannot have infinite matter taking up infinite space, there is either more of one or the other and obviously there is more space.

[Martin]

Please read the exact wording of the poll question

 

 

3D space could be infinite in volume and the total amount of matter it contains

 

Nobody is suggesting that 3D space contains an infinite number of joules per cubic kilometer. In fact the average density has been estimated to be about 0.2 joules per cubic km.

 

Clearly then, if the number of cubic kilometers is infinite, so must be the number of joules.

 

Skye already pointed this out with a visual example, I think.

 

So I think there is no more real argument. We are down to intentional or unintentional verbal misunderstanding of what the poll question was asking.

 

Maybe the title of the thread misled some people because it made them think we were talking about a density rather than a total amount.

Sorry about that, I apologize if the title misled you. What I meant to ask is what the poll question says---it's a bit more explicit.

 

Does anyone want to change their vote?

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I should say that the spatially infinite model, with an infinite amount of matter, is the dominant model in cosmology. LCDM has both infinite and finite versions and mathematically the infinite is slightly simpler. So if it is not a big issue, a professional observational cosmologist will just automatically assume the infinite case---or calculate for both cases.

 

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In POPULAR writing for the mass audience authors seem to give the impression that the cosmological singularity is somehow a contained in a finite volume, or even is a single point. But this is not how cosmologists ordinarily think of it. A singularity is where a mathematical model breaks down and that can easily be along a whole region of infinite extent (it doesn't have to be a pointlike singularity). In standard mainstream cosmology you have these two main cases and in spatial infinite LCDM the singularity has infinite extent just like space itself does. In spatial finite LCDM the singularity is point-like.

 

I was thinking people were going to argue that the universe couldn't be infinite because they had been told that the Big Bang Singularity was pointlike, which is finite, and therefore couldnt give rise to spatial infinite case. That argument is WRONG but only because the assumption is wrong about the singularity being pointlike.

 

However nobody seems to have made that argument.

 

Again: anybody want to change their vote?

[fredrik]

A philosophical reflection. At this point, I haven't asked myself this question too frequently, mainly since there are many other questions that hogs my mind.

 

But my first reflection, is how certain I am are on the measure implicit in the question. Since, it should seem clear the the certainty of the preferred measure and question, does change what's the right answer. And in general measure tend to be chose based on particular models.

 

To motivate my opinion I would have to spend time analysing the construction of the measure, and current data. But the easiest motivation is due to the "could be" in the question

 

/Fredrik

[Realitycheck]

What I am reading is that the universe is no longer infinite, that we know the approximate size, boundaries, and total mass involved (in order to determine % of dark matter), even if only by extrapolation of known figures.

[Martin]

... that we know the approximate size, boundaries, and total mass involved (in order to determine % of dark matter), ...

 

the percentages are calculated on a per unit volume basis (normally under the assumption that the whole is either infinite or very large)

 

anyone who is familiar with the technical literature and follows the math knows that we do not know the approximate size

 

the most common model used is the infinite case of LCDM

 

 

a lot is known about the universe on a per unit volume basis

and also we can calculate various horizons that help describe our limited perspective. this is good, but none of this comes close to describing the whole.

 

I don't know of any professional cosmologist who thinks the universe can not be infinite.

 

====================================

 

HERE'S A GENERAL COMMENT NOT DIRECTED AT ANYBODY IN PARTICULAR

 

Certainly there is no scientific reason to rule out the infinite case-----it could turn out either way, at this point we do not know.

 

But it is perfectly all right to have HUNCHES or to have a favorite outcome that you prefer for emotional or psychological reasons. I have a private hunch that within a few years the data will show that a certain parameter Omega is greater than one. Right now the 68 percent errorbar for it is [1.010, 1.041].

Sixty eight percent confidence is not enough to be sure.

That is the most recent errorbar I've seen, in a technical WMAP report, and is based on all the other types of data as well as WMAP. (i.e. supernovae, galaxy counts at various redshifts, etc.).

 

If I had to give odds, I would say that at this point there is a 32 percent chance that the universe is infinite.

 

Top experts like David Spergel and Ned Wright take pains to explicitly point out that the data is CONSISTENT with the infinite universe case. Omega could be > 1, yes, but the case that Omega = 1 is still not ruled out. The data is still statistically consistent with infinite.

[YT2095]

I Personally don`t believe the "Universe" IS Infinite, I think it`s very big and all that, but not Infinite, else what would we be expanding into?

 

if it was already "Maxed out" in size, there would be no room for it to expand.

 

 

you just can`t have Both.