The Universe - infinite or not ?

[Neandethal00]

Cosmo Novice is correct. Standard spatially flat models of the universe are spatially infinite but have only existed for a finite time.


This is incorrect. Here is a good explanation: http://www.astro.ucla.edu/~wright/cosmology_faq.html#XIN

From your link:

"Everything that we measure is within the Universe, and we see no edge or boundary or center of expansion. Thus the Universe is not expanding into anything that we can see, and this is not a profitable thing to think about".

I'm sorry, but this type of statements just turn me off from main stream science.
There is a group of 'know all' scientists who have the audacity to claim 'we already know what we wanted to know'.

There is nothing wrong in saying "We DO NOT know, yet".

 

[Ken G]

I think you are missing a crucial element of what he said-- he did not say we know it isn't expanding into anything, he said "this is not a profitable thing to think about." That's quite an important element of science, noticing what models are profitable to think about, and what ones are just idle speculation. In science, the proof is in the pudding-- models are good not because they are right, they are good because they actually guide our observations and allow us to make successful predictions. Too many people want science to be some kind of "oracle of truth", and they get mad when their pet theories are not getting attention. It isn't because the pet theories are wrong, it is simply because they bear no fruit. You just have to kind of deal with it, you want science to be something that it isn't, and then you blame the scientists.

 

[apeiron]

As a simplistic example, under the right conditions, a fog appears everywhere with no starting point. Sure, the analogy breaks down if you get into the nitty gritty, but to me, it's a very rough analog of how the universe formed - one difference being that the "right conditions" were not localized.

This is definitely an alternative way of viewing the issue. As a phase transition. Time and space as something definite would have been born out of something far less definite. You could call it a fog, a vagueness, a pre-geometry, a perfect symmetry.

What would be "infinite" or unlimited in the fog is degrees of freedom. So there just is no issue about the size of the space that the universe emerged from, or the one it is growing into. The beginnings are defined by their lack of such dimensional organisation, and the universe by it being a state of organised, or globally constrained, dimensionality.

 

[DavidMcC]

Cosmo Novice is correct. Standard spatially flat models of the universe are spatially infinite but have only existed for a finite time.


This is incorrect. Here is a good explanation: http://www.astro.ucla.edu/~wright/cosmology_faq.html#XIN

You (and UCLA) are making the same mistake as George (IMO), in equating black holes to the classical theory of them, which does not allow for an LQG BH, in which it is a mass quantum effect (just like superfluids and supeconductors, etc).
Also, flatness cannot be measured to zero error, so a large, but finite, curvature is necessarily a possibility, no matter how accurate the measurement.

 

[narrator]

You (and UCLA) are making the same mistake as George (IMO), in equating black holes to the classical theory of them, which does not allow for an LQG BH, in which it is a mass quantum effect (just like superfluids and supeconductors, etc).
Also, flatness cannot be measured to zero error, so a large, but finite, curvature is necessarily a possibility, no matter how accurate the measurement.

The uncertainty principle is well established in scientific method.

 

[bcrowell]

Also, flatness cannot be measured to zero error, so a large, but finite, curvature is necessarily a possibility, no matter how accurate the measurement.

Cosmological solutions with negative spatial curvature are also spatially infinite but have existed for a finite time. You simply have an issue about cosmology that you don't understand properly, as in this quote:

That doesn't make an infinite big bang a physical possibility, though. The only way the universe could be infinite is if it never had a beginning, ie that its beginning was an infinite time ago. Not plausible.

Go to the library and pull a freshman gen ed astronomy text off the shelf. Read the chapter on cosmology. This is basic stuff that you've simply gotten wrong.

You (and UCLA) are making the same mistake as George (IMO), in equating black holes to the classical theory of them, which does not allow for an LQG BH, in which it is a mass quantum effect (just like superfluids and supeconductors, etc).

The text you quoted wasn't about black holes.

It sounds like you have some ideas about black holes and cosmology that are nonstandard. Since they're nonstandard, you can't expect other people to telepathically figure out what they are when you just make vague references to "cosmic BHs" ( https://www.physicsforums.com/showpost.php?p=3347236&postcount=73 ).

If you want to discuss your ideas about black holes and cosmology, and explain why Ned Wright doesn't know what he's talking about, I suggest you start a separate thread on that in the Independent Research forum. Lay out your ideas coherently so that they can be discussed. But please do yourself a favor and step back and try to more realistically evaluate your own knowledge. There is an extreme mismatch between the elementary mistakes you're making and your assessment of your own expertise as being superior to that of professional cosmologists like Ned Wright.

 

[Neandethal00]

This is definitely an alternative way of viewing the issue. As a phase transition. Time and space as something definite would have been born out of something far less definite. You could call it a fog, a vagueness, a pre-geometry, a perfect symmetry.

I can live with this foggy phase transition analogy.

Unfortunately, in no branch of science 'common sense reality' is replaced by 'mathematical reality' as much as it did in astronomy/astro-physics/astro-anything.

 

[Cosmo Novice]

You may have to re-invent physics for that, Cosmo!

Open and spatially euclidean flat cosmological models with 0 curvature are spatially infinite and temporally finite. This models assumes that the BB began geometrically at all points in space/time and does assume spatial infinity. This is well within the laws of physics and if space was determined to have 0 curvature then this would be the current model.

 

[dougal217]

The quadrupole and octupole modes of WMAP seem to have an interesting orientation along the ecliptic plane... A bounded, finite Universe with a center of gravity would account for a number of things, including the Pioneer anomaly, and wouldn't require either a hot BB, Inflation (which is in big trouble), but most of all, doesn't need a Cosmological Principle, which is unprovable

 

[Ken G]

But would it instead require the tooth fairy? That's not really facetious-- the problem with forming entirely new theories to fix some of the bugs in the old one is invariably that the bugs get replaced by gorillas.

 

[zahero_2007]

Infinity is an ill defined concept so the universe is not infinite

 

[DavidMcC]

Zahero, infinity is well defined, but it is a pure mathematical concept, and not useful in physics, except as an approximation (since 1/infinity = 0).
The mathematical singularity of a classical black hole is a good example.

 

[Tanelorn]

I understand that all finite universe possibilities have space time wrapping around around. Which is the most correct space or space time wrapping around?

 

[bcrowell]

Infinity is an ill defined concept so the universe is not infinite

No, this is incorrect. We have a FAQ on this: https://www.physicsforums.com/showthread.php?t=507003

I understand that all finite universe possibilities have space time wrapping around around. Which is the most correct space or space time wrapping around?

Only space.

 

[Primtall]

The last part wasn't exactly true. -

... The set of positive integers is infinite. The set of positive integers divisible by 2 is also infinite, and half the size. The set of positive integers divisible by any known prime number is infinite , and expanding (everytime a new prime number is discovered).

 

[Neandethal00]

... The set of positive integers is infinite.

No they are not infinite. They are finite but unbounded.

Added Later: Numbers are not physical entities, the universe is.

 

[Fuzzy Logic]

Whether one believes the universe is infinite or not, one must believe in infinity.

If one believes that the universe is finite, then what is beyond the universe (both in time and space)? And what was before the universe?

One cannot say that there was no before or beyond because there was no time or space. The mere notion of a singularity directly contradicts that concept. The existence of a singularity implies a void of some kind that the singularity itself resided in and expanded into.

If it is insisted that all of existence was within the singularity then how could space and time expand? What did it expand into? How does one conceive expansion of something into itself? Wouldn't it be more accurate to say that all of the matter in the universe got smaller?

If one now accepts that infinity must be possible, then why is it more plausible to have an infinite void instead of an infinite universe?

 

[revo74]

From my understanding we have indirect evidence of virtual particles. No one is debating whether they exist or not. What is speculative however is this notion that virtual particles could become Universes.

Assuming that Krauss is correct that our Universe was a virtual particle with the right conditions that underwent expansion and became a Universe, there is something I am confused about, which I'm hoping someone can address.

Krauss says that empty space or the vacuum of space at extremely small scales is not truly empty or "nothing". Instead there lies a brewing sea of energy where virtual particles pop in and out of existence in a fraction of a second. This suggests that this sea of energy is a feature of our Universe. It is not a separate entity. Now, it is my understanding that Krauss is claiming that our Universe spawned from this sea of energy, which suggests to me that one independent entity (our Universe) came from a separate entity (sea of energy). So does this mean that there are two entities? One which is a feature of our Universe and the other a realm of existence outside of our Universe where it came from.

 

[Primtall]

No they are not infinite. They are finite but unbounded.

Added Later: Numbers are not physical entities, the universe is.

Need to nail down some terminology : Finite to me , means that it can be measured using a Real number. Unbounded means that it has no "end". There is no real number that allows you to measure the set of positive integers thus it is infinite. The set of known prime numbers on the otherhand is Finite , as there is a definite amount of them. According to Euclid the number of prime numbers is infinite. What we have therefore is a finite set (the known primes) expanding into the infinite (the primes ). This is a good model for the expanding universe, expanding into the infinite

 

[Primtall]

"Added Later: Numbers are not physical entities, the universe is"
The post related to an assertion that 'only FINITE things can expand' . Logically this isn't so, and the example of an infinite set of numbers, expanding , supports (actually proves) this point, logically.
In the mathematical universe ,logic and physically realized logic, are one and the same thing. Without getting mystical, it can be said that the the universe is a symphonic expression of the logical - but that's a different thread.

 

[Fuzzy Logic]

No they are not infinite. They are finite but unbounded.

Added Later: Numbers are not physical entities, the universe is.

Why wouldn't real numbers be infinite? How can they be both finite and unbounded? At what value does real numbers end?

 

[Primtall]

Agree with you fuzzy logic. Finite things are supposed to be measurable by a real number and the set of real numbers can't be. I think the 'finite but unbounded' business relates to ants on spherical surfaces, or the way n-dimensional beings would experience n+1 dimensions ... from the perspective of a higher dimension , all of space-time might well be an ink blot on its fabric and finite in that sense.

 

[Neandethal00]

Assuming that Krauss is correct that our Universe was a virtual particle with the right conditions that underwent expansion and became a Universe, there is something I am confused about, which I'm hoping someone can address.

Krauss says that empty space or the vacuum of space at extremely small scales is not truly empty or "nothing". Instead there lies a brewing sea of energy where virtual particles pop in and out of existence in a fraction of a second. This suggests that this sea of energy is a feature of our Universe. It is not a separate entity. Now, it is my understanding that Krauss is claiming that our Universe spawned from this sea of energy, which suggests to me that one independent entity (our Universe) came from a separate entity (sea of energy). So does this mean that there are two entities? One which is a feature of our Universe and the other a realm of existence outside of our Universe where it came from.

The other late night I was listening to a talk radio (guess!) where one physicist for an hour kept babbling "the universe came from nothing, things can come from nothing", etc.
Sometimes I wonder why some simple things do not come to some brilliant minds. If something comes from a place, that place is NOT nothing. Just because we do not see or do not know yet, does not mean that place is nothing.

Krauss is right, Space is a medium. Empty space is not empty. We do not yet know the true nature and structure of this medium. Sometimes, I'm afraid we may never know. That's why to us it appears things come from nothing. Energy explanation of Krauss is a possibility.

 

[Neandethal00]

Why wouldn't real numbers be infinite? How can they be both finite and unbounded? At what value does real numbers end?

A few posters including me are insisting the universe is finite. It does not matter how many ways, in how many words we write this, many of you will not be able to figure out exactly where this argument comes from until you start visualizing any physical object and taking it (or its properties) to infinity. Where ever you stop, it is finite.

The post related to an assertion that 'only FINITE things can expand'

Primtall.

No, the assertion is all physical things are finite.

 

[Primtall]

A few posters including me are insisting the universe is finite. It does not matter how many ways, in how many words we write this, many of you will not be able to figure out exactly where this argument comes from until you start visualizing any physical object and taking it (or its properties) to infinity. Where ever you stop, it is finite.

Primtall.

No, the assertion is all physical things are finite.

Again, not true.
My fingernail is Infinite. It is composed out of the infinite by the imposition of an arbitrary boundary condition, in the same way that the perfect circle bounds infinity
(pi being 3.14159 ... ad infinitum). What we call the Finite is just some demarkation or
Limit imposed on the infinity of the infinitesimally small (to us). This applies equally whether you are talking about the size of the universe or the size of the coastline of Ireland (scale and Zoom being just arbitrary parameters). In the case of the expanding universe,the discussion is really about expanding Limits. Infinity is already there (your container) , and the limit of the universe as t goes to infinity , is infinity. The model of the 'set of known primes' expanding into the 'set of primes' captures the relationship quite well.

 

[Primtall]

Further, there's been a lot of nonsense posted about 'something' co-existing alongside 'nothing'. It's not like light and pockets of darkness. Nothing means 'nothing at all, ie. no potential , no quantum flux, no entropic chaos, no fuzz on the tv screen before the coherent signal is received, Nothing AT ALL. It really is one or the other - as apart from 'something' there is nothing. Prof. Hawking was surely wandering when he said that m-theory solved the mystery of 'why there is something instead of nothing'. If you define 'nothing' as any of the above then yes , but you may as well go mystical and say that the material world emerges spontaneously from the non-material etheric realm. "Why is there m-theory instead of nothing ? " professor ?

 

[minio]

I doubt that it could not be determined. I personally agree with theories that our universe in 3D has currently some 80 billions ly across. However if time is considered as another dimension then we cannot say if universe is finite because we have just one limit (big bang 14 bilion years ago), but not other and thus is IMHO not possible to make conclusions unless we hit the end of time. However I am not physicist nor matematician, so I might be wrong :)

 

[Primtall]

just logically, if 3D can be measured by a real number (80 bil in this case) then it would be finite. Can it be though, when the thing being measured is expanding ? i would have thought not but maybe there is some convoluted definition somewhere, that makes it, according to that definition, Finite.

 

[Neandethal00]

Again, not true.
My fingernail is Infinite. It is composed out of the infinite by the imposition of an arbitrary boundary condition, in the same way that the perfect circle bounds infinity
(pi being 3.14159 ... ad infinitum). What we call the Finite is just some demarkation or
Limit imposed on the infinity of the infinitesimally small (to us). This applies equally whether you are talking about the size of the universe or the size of the coastline of Ireland (scale and Zoom being just arbitrary parameters). In the case of the expanding universe,the discussion is really about expanding Limits. Infinity is already there (your container) , and the limit of the universe as t goes to infinity , is infinity. The model of the 'set of known primes' expanding into the 'set of primes' captures the relationship quite well.

Whatever...

Numbers have no meaning until you use (physical) them.
This arguments will go no where.. Let's not waste our mental energy.

 

[Primtall]

all right