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Infinite Universe Or Not?


litespeed

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That's where the definition of "universe" becomes the problem. If "The" Universe includes everything inside the universe as we know it and anything else beyond it then the question is impossible to anwser. If it refers only to the space and matter within the envelope of the known universe it seems obviously finite. I personally tend to refer to the known universe as the local universe which is only a small part of what I believe is a larger infinite universe that lies beyond our abilities of observation.

 

Good point. It must be established, and I think it already is, that the visible universe is only a part of the universe that we can see. It is not the whole universe. We must extrapolate that there is more beyond the visual horizon, similarly to the Greeks who had extrapolated that there were entities smaller than that which we could see: i.e., the atom.

 

Usage of the world "local" generally refers to the Local Group of galaxies. So to avoid confusion, what you call the "local universe" in standard parlance is called the visible universe.

 

I don't think what lies beyond the visible universe (beyond the visible horizon) is a question impossible to answer. For example, the standard model (currently knows as Lambda CDM) has a period of galaxy formation beyond the horizon. Recall, before the LCDM model (the standard hot big bang model) had galaxy formation inside our horizon, though observations showed that was not the case. So it was extrapolated that galaxy formation occurred very quickly after the big bang. This is just an example to show that it is not impossible to understand what may have occurred at those distance (during a time-period before which we can see).

 

True that whatever is extrapolated will remain based on a model, in lack of observational evidence. That's why we have predictions based on models. Which ever model best fits observations will be the most likely solution.

 

Whether of not the universe is spatiotemporally infinite in the direction of the arrow of time, or in the past, can be determined to some extent based on model-extrapolation when confronted with observations.

 

 

 

Sure, just hold your hands out in front of you and spread them apart. The space between them just expanded. So, obviously, it *can* happen. The question is if it's happening on a universal scale—best scientific evidence says yes. Yes it is.

 

This isn't a case where space between your hands expands. The distance between your hands increases. Galaxies are not thought to be moving 'through' space. The space is thought to be stretching, expanding, growing, between galaxy clusters.

 

Pluto is correct. There is no experimental evidence that can establish the veracity of space expansion. For example in vacuum experiments carried out here on earth we cannot create new space, or make a vacuum expand. It seems, on the contrary, that there is a fundamental limit inherent in nature that forbids such behavior.

 

In other words, it seems to me that space expansion would violate at least two physical principles, if not natural laws: (1) the vacuum cannot be emptied further than a fundamental limit described by zero point energy. There will always be a residual ground energy, even at zero absolute temperature (i.e., an ideal, or perfect, vacuum is unattainable in the natural world, as far as experiments show). (2) Expanding space would violate energy conservation.

 

I realize that in the standard expanding universe model, every newly created cubic centimeter of space emerges with an equal quantity of energy. And that a universe dominated by some mysterious form of energy (whether it be quintessence or lambda) has the capability of continually producing new energy from literally nothing (Goldsmith 2000), again according to standard expanding universe model. Each new cubic centimeter emerges with more energy than the preceding. Newly created space would have no causal connection with the rest of the universe.

 

This, however, is in violation with experimental evidence.

 

 

 

You're talking about the metric expansion of space, I'm talking about distance and we both should be talking about whether the universe is infinite or not.

 

Of course there is a relation with the expansion of space (the creation of space), the impossibility for space to expand, and wether or not the universe is infinite in both directions of time (or finite), since competing models provided different answers which contain these possibilities, leading to differing answers to the question.

 

 

 

CC

One look is worth ten thousand words.

(Proverb from a fortune cookie in a NJ restaurant, 2005)

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I don't think what lies beyond the visible universe (beyond the visible horizon) is a question impossible to answer.

 

And that's not the question I was claiming is impossible to answer. Is what lies beyond the visible universe infinite or not is a question I don't think we could ever answer because we will always be restricted to what is visible to us which is a finite set of a possibly larger set which may or may not be infinite.

 

I am generally of the opinion that space itself is infinite and extends forever beyond the bounds of the observable universe. If it is not then we must ask what lies beyond it's boundary. Further, if it is expanding then what is it expanding into if it is not more space?

 

Matter, on the other hand, could be finite but could consist of an unimaginable quantity many times the matter of the visible universe. I do tend to believe that matter has existed for eternity since it can be neither created nor destroyed. An event like the Big Bang could have changed it's form, and/or redistributed it, but I am not of the opinion that such an event was responsible for the creation of matter in the observable universe. For me it is difficult to imagine how space or matter could have come from nothing.

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This isn't a case where space between your hands expands. The distance between your hands increases.

 

Yes, and that's really all I was saying in this thread. If you put a force on two objects then the distance between them can easily get larger or smaller. The only question is can it happen in a metric, overall, with-all-comoving-observers kind of way.

 

A Friedman universe is an *exact* solution to general relativity's field equations. It says that if you put a homogeneous fluid in a universe of its own and allow it to follow the rules of general relativity then the fluid will either contract or expand with time. Every bit of fluid will measure distance increasing (in an expanding solution) with every other bit of fluid.

 

So, a better answer (that I now regret not giving) would be that space can expand (in a metric expansion of space kind of way) if GR is a good model of reality... and our universe is roughly homogeneous... I just somehow didn't think Pluto was going to go for that.

 

Pluto is correct. There is no experimental evidence that can establish the veracity of space expansion.

 

Pluto is correct that no experimental evidence can *prove* the expansion we're talking about above. I disagree that we cannot "establish the veracity" of such a thing. We have GR and FLRW and many observations that *establish* veracity. But, no theory is ever proven—valid as it may be.

 

For example in vacuum experiments carried out here on earth we cannot create new space, or make a vacuum expand. It seems, on the contrary, that there is a fundamental limit inherent in nature that forbids such behavior.

 

While we can make a vacuum expand, I think that's about equally synonymous with FLRW expansion as my hand thought experiment.

 

In other words, it seems to me that space expansion would violate at least two physical principles, if not natural laws: (1) the vacuum cannot be emptied further than a fundamental limit described by zero point energy. There will always be a residual ground energy, even at zero absolute temperature (i.e., an ideal, or perfect, vacuum is unattainable in the natural world, as far as experiments show). (2) Expanding space would violate energy conservation.

 

In quantum field theory, every point in space has energy. If space is expanding then conservation would be violated. To me, this has more to do with the current incompatibility between GR and quantum mechanics rather than a real violation of conservation laws. Being that the two theories are incomparable, I don't think there is a way to show conclusively one way or the other right now.

 

I realize that in the standard expanding universe model, every newly created cubic centimeter of space emerges with an equal quantity of energy. And that a universe dominated by some mysterious form of energy (whether it be quintessence or lambda) has the capability of continually producing new energy from literally nothing (Goldsmith 2000), again according to standard expanding universe model. Each new cubic centimeter emerges with more energy than the preceding. Newly created space would have no causal connection with the rest of the universe.

 

Perhaps we can debate Goldsmith's account in another thread. I think we could agree that according to GR a universe can expand just fine without Lambda... and indeed, be spatially infinite without it as well.

 

~modest

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Scientifically prove to me how space can expand.

 

Sure, just hold your hands out in front of you and spread them apart. The space between them just expanded. So, obviously, it *can* happen. The question is if it's happening on a universal scale—best scientific evidence says yes. Yes it is.

Seriously - is this what they mean by expansion of space!!??

See my reply in my last post.

 

When two things get further apart there is an increase in measured distance between them with time.

 

In the metric expansion of space (which is I'm sure what you're thinking of) there is "the averaged increase of metric (i.e. measured) distance between objects in the universe with time." or so says wiki.

 

Are these exactly the same thing? No. Would these be exactly the same thing if your hands were the only two things in the universe? Yes. If the universe were made up of nothing but lots and lots of hands, again—it would be exactly the same thing [edit: assuming your hands were subject only to the 'forces' of gravity and were comoving with all the other hands in the universe :)... sorry, I'm cracking myself up here]. So, the distinction is somewhat subtle.

 

But, really, if you want to get deep into it, check out the link:

 

Metric expansion of space - Wikipedia, the free encyclopedia

 

And, make a thread on the topic.

 

~modest

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G'day from the land of ozzzzz

 

I'll come back to my question.

 

What does the expansion.?

 

Space is questionable, so why not look at a realistic idea?

 

I'm just thinking aloud for a sec.

 

If spacetime is the answer than maybe I could hang my hat on that and question it.

 

If its actual distance, than I cannot see that, since I look at all the images, I see clustering of stars and clustering of galaxies.

 

We see matter moving towards the centre of a galaxy, we see dwarf galaxies that are merging with the Milky Way.

 

So far its actual contraction of actual distance.

 

Than we see expansion from stars in the process of supernova and jets from star and black holes ejecting matter and reforming galaxies. This expansion I can understand.

 

Now lets take it one step further, light from distant galaxies, could this be changing in wave length and producing a form of expansion.

 

Is this the same as timespace?

 

If so what mechanism or mechansims could produce such a shift?

 

If I read papers on expansion they give logical expalantions of why, but! there is always an if and a condtion.

 

This link is quite interesting, I hope I have not post it before.

 

[astro-ph/0701358] Dark Matter in an n-Space Expanding Universe

Dark Matter in an n-Space Expanding Universe

 

Authors: Mario Rabinowitz

(Submitted on 12 Jan 2007 (v1), last revised 24 Mar 2007 (this version, v2))

 

Abstract: The total number of degrees of freedom of a d-dimensional body in n-space is derived so that equipartition of energy may be applied to a possibly n-dimensional early universe. A comparison is made of a range of proposals to include free and bound black holes as either a small component or the dominant constituent of dark matter in the universe. The hypothesis that dark matter consists in part of atomic gravitationally bound primordial black holes is closely examined in 3-space, as well as in n-space; and the Chavda and Chavda holeum hypothesis is found to be flawed. Blackbody and Hawking radiation are generalized to n-space, and Hawking radiation is shown to be simply proportional to the black hole density. The importance of quantum gravity in understanding the role of early universe dark matter is undermined because present approaches to a theory of quantum gravity violate the equivalence principle. A general heuristic proof for geodesics on an expanding hypersphere is presented. Classical limits of Einstein's General Relativity are considered. A novel approach to the accelerated expansion of the universe is discussed. An anomalous surprising aspect of 4-space is demonstrated.

 

 

ALSO:

 

[astro-ph/0701750] The Sunyaev-Zeldovich Effect from Quasar Feedback

The Sunyaev-Zeldovich Effect from Quasar Feedback

 

Authors: Suchetana Chatterjee (University of Pittsburgh), Arthur Kosowsky (University of Pittsburgh)

(Submitted on 25 Jan 2007 (v1), last revised

19 Apr 2007
(this version, v2))

 

Abstract: The observed relationship between X-ray luminosity and temperature of the diffuse intercluster medium clearly shows the effect of nongravitational heating on the formation of galaxy clusters. Quasar feedback into the intergalactic medium can potentially be an important source of heating, and can have significant impact on structure formation. This feedback process is a source of thermal Sunyaev-Zel'dovich distortions of the cosmic microwave background. Using a simple one-dimensional Sedov-Taylor model of energy outflow, we calculate the angular power spectrum of the temperature distortion, which has an amplitude on the order of one micro-Kelvin. This signal will be at the noise limit of upcoming arcminute-scale microwave background experiments, including the Atacama Cosmology Telescope and the South Pole Telescope, but will be directly detectable with deep exposures by the Atacama Large Millimeter Array or by stacking many microwave images.
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Amazing how Hypography changes your view of the universe and in fact what you see, and select to see, from the infinite universe, of things there are to see.

A bit like Schrödinger's cat thought experiment really

http://xkcd.com/45/

Schrodinger's cat

 

Take todays' Christmas present ( for someone else -trying to read it first ;) )

Page 5 the introductory paragraph goes:-

 

"Very vast is the expanding rubber sheet of the space-time continum. Should we not call it infinite?

No as a matter of fact, we should not, not unless we want to get into an interminable argument with both physicists and philosophers - the kind of argument where people steeple their fingers and say, very slowly, 'We-ll, it all depends on what you mean by "infinite".'

And go on saying it with variations, till the beer runs out. If you are very unlucky, they will explain how infinities come in different sizes.

 

Buy "The Folklore of Diskworld" By Terry Pratchett and Jacquline Simpson for the rest :QuestionM

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Hi y'all,

This thread has been a very interesting read.

Since Modest is not presently responding to my challenges in the "Spacetime" thread (stuck in the "philosophy of science" section)... as he has been "pressed for time"... and maybe even pressed by contracting time... (if "it" can "inflate")...

 

Anyway, I made copious notes on these five pages of dialogue, some of which I will quote with attending commentaries in bold, in context for direct reference.

 

But, for openers, I think discussion of the meaning of key terms is essential.

 

"Universe": Literally it means One "verse"... all there is, leaving aside the question of "known" or "visible."

 

"Infinite": Well, the "stuff" of the visible,known cosmos as de-fined by whatever shape and expanding size can well be called finite, however large. But the space *into which it is expanding must be infinite.* Why "must?" I challenge anyone to posit a reasonable "end of space"... an obviously ill-conceived notion.

 

Note: I have already distinguished "space" (emptiness), which is infinite, from the stuff *in space* which may be de-fined as finite shape and size, however changing.

 

Well... more company has arrived, so I will just post my notes with brief commentaries.

------------------------------------

Michaelangelica:

"From what I have read, the universe is NOT infinite.

It has a fast expanding 'edge'

"The material of the cosmos is expanding and is not infinite.

 

The intriguing question for me is

"What is on the other side of that edge?"

Infinite space.

 

C1ay:

'Precisely. If it's expanding then it begs the question of "What is it expanding into."

Infinite space.

Tormod:

"Hey Pluto

 

Not sure what you mean. Space as the "fabric" it's made of, or space meaning the entire universe?

 

It has been scientifically proved that space does expand, and that the cosmic expansion has increased over at least the last two billion years."

The stuff in space is "exploding outwardly." Space is emptiness with no properties at all, including being a medium/entity which is expanding.

 

Michaelangelica:

"If you ascribe to the Big Bang theory of the evolution of the KNOWN universe it seems to have an "end" where we seem to be getting lots of static on our radios from."...

The "cosmic event horizon" is as far as we can see into the cosmos. I may well be that the cosmic material is like the rubber of an expanding baloon. Our event horizon might be one small "sphere" of visibility within one small volume of this "balloon membrane."

 

"At first there was nothing;

then it exploded."

Terry Prattchet

Right!! Something from nothing is the way the linear human mind works! (Not to mention the absurdity of positing a "beginning and end of time!" Some version of a oscillating/cyclical cosmos is the only way to explain "where it all came from" before the last in an ongoing, perpetual series of bangs and crunches.

 

C1ay:

 

"That's where the definition of "universe" becomes the problem. If "The" Universe includes everything inside the universe as we know it and anything else beyond it then the question is impossible to anwser. If it refers only to the space and matter within the envelope of the known universe it seems obviously finite. I personally tend to refer to the known universe as the local universe which is only a small part of what I believe is a larger infinite universe that lies beyond our abilities of observation."

Right on!

 

Coldcreation:

'Good point. It must be established, and I think it already is, that the visible universe is only a part of the universe that we can see. It is not the whole universe. We must extrapolate that there is more beyond the visual horizon, similarly to the Greeks who had extrapolated that there were entities smaller than that which we could see: i.e., the atom."

 

Usage of the world "local" generally refers to the Local Group of galaxies. So to avoid confusion, what you call the "local universe" in standard parlance is called the visible universe.

Yes!

....

 

" Originally Posted by modest:

"Sure, just hold your hands out in front of you and spread them apart. The space between them just expanded. So, obviously, it *can* happen. The question is if it's happening on a universal scale—best scientific evidence says yes. Yes it is."

CC:

"This isn't a case where space between your hands expands. The distance between your hands increases. Galaxies are not thought to be moving 'through' space. The space is thought to be stretching, expanding, growing, between galaxy clusters.

"Thought" by whom? Those who would make "empty space" (nothing) into some-thing? the burden of evidence-toward-proof is on those who theorize that space is some-thing... and "time" as well. (See commentaries in my "spacetime[" thread.

 

Pluto is correct. There is no experimental evidence that can establish the veracity of space expansion. For example in vacuum experiments carried out here on earth we cannot create new space, or make a vacuum expand. It seems, on the contrary, that there is a fundamental limit inherent in nature that forbids such behavior."

Exactly!

 

Pluto:

"What does the expanding?

Right. Nothingness does not expand. Stuff in space moves away from other stuff... or 'expands', though this does not mean the 'stuff" itself is expanding... just more space between things.

 

We have space without any form of matter or energy. Does this expand?

Of course not! "expanding spacetime" is a metaphore, a learning aid for visualization of the effects of gravity for students learning relativity.

 

Modest that does not prove that space expands. We are talking about spacetime expansion. I think.

As above.

 

 

As for the universe being infinite, If you define ALL as being the universe than ALL is infinite. If you define the universe as only the observable universe than it becomes finite. Than you have a change in definition of the known universe to a UNITUNIVERSE or part of a multi-universe units."

Agreed.

 

Originally Posted by Pluto:

"Modest that does not prove that space expands. We are talking about spacetime expansion. I think."

Modest:

"You're talking about the metric expansion of space, I'm talking about distance and we both should probably both be talking about whether the universe is infinite or not."

Space is infinite. The stuff in space (our cosmos and other possible cosmi beyond our visible horizon) is finite, each possible cosmos being defined by its shape and size... all in flux.

 

 

Originally Posted by coldcreation View Post

I don't think what lies beyond the visible universe (beyond the visible horizon) is a question impossible to answer.

"Answer" may be relative to what might be imagined as reasonable, but not accessible to observation for verification.

C1ay:

"And that's not the question I was claiming is impossible to answer. Is what lies beyond the visible universe infinite or not is a question I don't think we could ever answer because we will always be restricted to what is visible to us which is a finite set of a possibly larger set which may or may not be infinite.

Yes. though each cosmos must be a finite system occupying infinite space.

 

I am generally of the opinion that space itself is infinite and extends forever beyond the bounds of the observable universe. If it is not then we must ask what lies beyond it's boundary. Further, if it is expanding then what is it expanding into if it is not more space?

Exactly.

 

Matter, on the other hand, could be finite but could consist of an unimaginable quantity many times the matter of the visible universe. I do tend to believe that matter has existed for eternity since it can be neither created nor destroyed. An event like the Big Bang could have changed it's form, and/or redistributed it, but I am not of the opinion that such an event was responsible for the creation of matter in the observable universe. For me it is difficult to imagine how space or matter could have come from nothing."

 

Total agreement here!

 

My family is harassing me to get off the net and join the celebration.

 

Great thread. Thanks. (sorry... no typo edit.)

Michael

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Lunchtime.... gotta run.

 

M~ica, I just saw your Schroedinger's comic above. It made me laugh. :Glasses:

 

M~Mooney,

I care about future generations having the leisure and the capabilities to care about cosmology and evolution.

 

If we don't turn this planet in a sustainable direction, I will be sad that those future generations won't have the leisure time or facilities or coordination to care about cosmology or evolution--they'll be struggling for survival (caring for evolution and cosmology/religion from a very subjective position only).

 

I care for cosmology and evolution objectively, because they force us to use science to discover the complexities of the world.

 

I think this is a good thing because understanding that complexity is what will allow us to evolve into a Type I civilization. We don't have much time and if you've got a great IQ, I don't understand why you don't apply it to helping with real current problems of economics, environment, and education.

...or did I ask you this already?

 

~SA

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