Debunking the Big Bang Theory: Colliding Branes as a Possible Alternative

[marcus]

Comments on this thread remind me that LQC has progressed quite a bit in the past 2 or 3 years and it is not so easy to keep abreast. So I want to call attention to a Abhay Ashtekar's recent review paper---a kind of status report---and quote some interesting passages just to get the latest stuff out on the table.
http://arxiv.org/abs/1108.0893
Loop Quantum Cosmology: A Status Report
Abhay Ashtekar, Parampreet Singh
(Submitted on 3 Aug 2011)
The goal of this article is to provide an overview of the current state of the art in loop quantum cosmology for three sets of audiences: young researchers interested in entering this area; the quantum gravity community in general; and, cosmologists who wish to apply loop quantum cosmology to probe modifications in the standard paradigm of the early universe. An effort has been made to streamline the material so that, as described at the end of section I, each of these communities can read only the sections they are most interested in, without a loss of continuity.
138 pages, 15 figures. Invited Topical Review, To appear in Classical and Quantum Gravity.

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

The paper is long and covers many topics. We already had a discussion here at PF forum of one of the key equations. Equation (5.7) as I recall. I forget who was asking about it.
Yes! It was (5.7) on page 73. This is the modified form of the Friedman equation which comes out of quantizing it and it shows clearly why you get gravity repelling at high density and causing a rebound (with an interval of super-exponential expansion called super-inflation).

That however is not new, one sees that modified Friedman derived already in 2007 basic LQC papers. (Together with a figure for the critical density at which the quantum corrections dominate.) So I won't copy that here.

What I want to take note of is some more recent stuff about generalizing and extending the model that they go into around page 67. Don't have time right now but hope to get back to this later today.

 

[marcus]

...
I should have perhaps said "we have no good theory of QG". But yes, there is no reason not to do research into the consequences of LQG on the CMB. Apart from the fact that it's using an unproven theory on as yet uncollected data. .

See the paper by Wen Zhao and two people at Cambridge which is in the search listing of LQC phenomenology-related papers which I gave earlier. In effect they confront LQC bounce cosmology with 7 years of WMAP data (using NASA's WMAP7 report to constrain).

It is as you know customary to make predictions which can be tested by FUTURE data and this on the whole is what is being done. I expect some more constraints to accrue from the European Planck spacecraft observations now in progress. But higher resolution (especially polarization of CMB) will be needed, again see Wen Zhao's paper. It's hardly a criticism to note that a lot of the testing literature is aimed at future possible data collection---although of course some relates to past and current.

Generally speaking, I do have reservations about the search for "signatures" of any kind in the CMB - remember that paper by Penrose a couple of years ago? It was widely regarded as pretty dodgy. I think that the search for signatures in the CMB needs to be *very carefully* done - you can find almost anything in noise if you look closely enough.

Yes indeed We should all be *very careful*. It also helps to have professional phenomenologists with no stake in your theory who see their job as testing it and will be just as happy if the data disprove as they would be if the data support the theory. (Penrose seems to have had just one guy who looked like he was collaborating with Sir Roger to find supportive evidence, rather than objectively putting the theory to the test.) I fail to see the analogy here. Perhaps you can discover some analogy if you take a critical look at some articles in the Inspire search list. By some of the people I mentioned.

Here is the link again.
http://inspirehep.net/search?ln=en&...Search&sf=&so=d&rm=citation&rg=100&sc=0&of=hb

The one by Wen Zhao I mentioned is as I recall #22 on the list.

 

[stglyde]

Markus, the universe in a grain of sand is assuming classing GR.. but quantum GR says the density can't be high so not only can all energy of the universe in Planck volume not possible, even atomic volume not possible. So based on your reading and experience, what is the surest bet of the minimize size of the initial universe. Do you think it was once maybe about a Ping Pong ball size or a baseball size or building size or the size of Texas? What is your estimate from non classical GR calculations and theoretical projection of rewinding the universe down to smaller and smaller size?

 

[marcus]

Markus, the universe in a grain of sand is assuming classing GR.. but quantum GR says the density can't be high so not only can all energy of the universe in Planck volume not possible, even atomic volume not possible. So based on your reading and experience, what is the surest bet of the minimize size of the initial universe. Do you think it was once maybe about a Ping Pong ball size or a baseball size or building size or the size of Texas? What is your estimate from non classical GR calculations and theoretical projection of rewinding the universe down to smaller and smaller size?

Glyde, it's nice of you to ask! I appreciate you asking my opinion. There was a Nasa report called WMAP5 (cosmology implications from the 5-year WMAP data) which said that in the simplest case where the U had a finite size, with 95% certainty it would be AT LEAST 10 times larger than the observable portion. (And it could just as well be 100 or 1000 times larger, the estimate was just a lower bound that it had to be at least that.)

Their number was more precise than 10. I am just speaking approximately. Their lower bound was roughly that. I can get the link to the report if you want. It's online.

Many cosmologists think of the U as spatially infinite, and therefore it would be spatially infinite at the start of expansion. And they do their calculations based on that assumption. You get approximately the same fit to the data whether you say infinite or finite-but-very-large.

So the first thing is always to remember that when people talk cosmology OBSERVABLE universe is just a small portion of the full universe that one has to model with the equations or the computer simulator. What one models is the full thing and this can be spatially infinite (even already at "bang" time) or in any case very large.

Don't confuse observable universe with the whole thing. I'm sure you know this, but people forget. It has to be made explicit to avoid confusion.

In standard cosmology, as you probably know, the universe has no edge or boundary, and matter is distributed approximately evenly throughout. So if space is infinite volume then matter must be infinite---because it is throughout all space.
===================

That is just preliminaries. Are you OK with all that?

 

[stglyde]

Glyde, it's nice of you to ask! I appreciate you asking my opinion. There was a Nasa report called WMAP5 (cosmology implications from the 5-year WMAP data) which said that in the simplest case where the U had a finite size, with 95% certainty it would be roughly 10 times larger than the observable portion.

But the universe could as well be 100 times larger than the observable universe. Their factor of 10 was just a lower bound.

Many cosmologists think of the U as spatially infinite, and therefore it would be spatially infinite at the start of expansion. And they do their calculations based on that assumption.

You get approximately the same fit to the data whether you say infinite or finite-but-very-large.

So the first thing is always to remember that when people talk cosmology OBSERVABLE universe is just a small portion of the full universe that one has to model with the equations or the computer simulator. What one models is the full thing and this can be spatially infinite (even at "bang" time) or in any case very large.

Don't confuse observable universe with the whole thing.

In standard cosmology, as you probably know, the universe has no edge or boundary, and matter is distributed approximately evenly throughout. So if space is infinite volume then matter must be infinite---because it is throughout all space.
===================

That is just preliminaries. Are you OK with all that?

Good you emphasize on the observable universe vs actual extent. Anyway. Do you know how many Planck volume can fit in say the hydrogen atom up to the electron orbital? You really think that if the observable universe energy were contained in the hydrogen atom. The Planck volume would merely hold a few micrograms. This would make the Planck scale unimaginably small. I wonder if your analogy is valid (ignoring quantum gravity and HUP).

Or for a radius of 40 Billion light years, how many meters or miles across would be the Planck length? Any ideas?

 

[marcus]

Good you emphasize on the observable universe vs actual extent. Anyway. Do you know how many Planck volume can fit in say the hydrogen atom up to the electron orbital? You really think that if the observable universe energy were contained in the hydrogen atom. The Planck volume would merely hold a few micrograms. This would make the Planck scale unimaginably small. I wonder if your analogy is valid (ignoring quantum gravity and HUP).

Or for a radius of 40 Billion light years, how many meters or miles across would be the Planck length? Any ideas?

Answer to blue question is yes. Actually much less than a few micrograms. A hydrogen atom is very big. To get PLANCK density you must compress observable down to something like the size of a proton, the nucleus of the hydrogen atom.

This is around 100 thousand times smaller than the atom, if I remember right.

 

[marcus]

BTW Glyde, Brian Powell said something useful a few posts back.

Science is a dispassionate pursuit that does not benefit from preconceived notions of what "exceeds the imagination". It is an incorrect picture to imagine Planckian energy densities somehow confined to a small region, fighting against this confinement with outward pressure. It is true that both density and pressure determine the gravitational properties of the stress-energy, and, when you place near-Planckian energy densities into the Friedmann equation, you get a perfectly well-behaved cosmological solution.

Sure, such high densities have not been tested in the lab. But we understand the equation of state of radiation, and we have lots of observational evidence that supports the Friedmann model. Extrapolation of these physical theories into untested regimes (as long as the theory is appropriate to these regimes) is a perfectly reasonable and substantiated practice.

I have to go. I want to remark on something in Brian's post. Back later.

OK I'm back. BTW the conventional ideas of the radii of proton and observable U differ by a factor of 10⁴¹. My feeling is that this is not so surprising. I wouldn't say a proton is very SMALL compared with the photons of highest energy light. Indeed a proton is kind of mediumsized as things go. But the observable U is very large. So between medium size and large there are these 41 powers of ten.

If you want to find out some about Planck scale----energy, volume, density, mass, length etc.----Wikipedia is not too bad.
http://en.wikipedia.org/wiki/Planck_units

The linear size associated with the proton is 10^-15 meters. You can read what the Plancklength is and see what their ratio is. The corresponding volumes would be related by the cube of that ratio, whatever you find it to be.

Ive got some other stuff to attend to, but see what you can find out meanwhile on your own.

 

[stglyde]

Answer to blue question is yes. Actually much less than a few micrograms. A hydrogen atom is very big. To get PLANCK density you must compress observable down to something like the size of a proton, the nucleus of the hydrogen atom.

This is around 100 thousand times smaller than the atom, if I remember right.

Energy units are electrovolts.. for example.. the possible mass of Higgs boson to be 125 TeV. I wonder what is the electron volts of the energy of the entire "observable" universe. Now it's still unbelievable that when you put it in the diameter of the nucleus. The Planck volume is almost negligible. But then energy doesn't have pauli exclusion so I wonder why a certain volume should hold certain energy or in what sense is the statement that the energy of the observable universe is put into the size of a hydrogen nucleus and the Planck volume holds only a few microgram since energy doesn't have spatial extension. Anyone else can explain? Thanks (this paragraph is ignoring quantum gravity and HUP for sake of discussion of energy Tev of the universe and containment of it in a limited spatial extension like in a hydrogen nucleus).

 

[Chronos]

I believe the most recent estimates on higgs mass are around 125 GeV.

 

[ThomasT]

... I wonder why a certain volume should hold certain energy ...

That would seem to me to depend on what's being talked about (ie., a certain volume of ... what?), and what it's assumed (or observed) to be doing.

... or in what sense is the statement that the energy of the observable universe is put into the size of a hydrogen nucleus ...

Why would anybody want to suppose that the energy of the observable universe was ever the "size of a hydrogen nucleus"?

Regarding the title question of the thread, and your OP, the standard 'big bang' theory accounts (in a necessarily limited way) for the evolution of our universe from a point (the 'big bang') beyond which (ie., further into the past) backward extrapolation from current observation and theory is impossible.

Whether it's 100% true is a question/consideration that can't be answered. But it makes sense and it's internally consistent (afaik), and (also afaik) it doesn't say or imply that the observable universe was ever the size of a hydrogen nucleus, or the head of a pin, or whatever (also just afaik).

Kudos to bapowell and marcus for their usual informative replies, and to Astronuc for putting the (sophisticated) cosmological speculation into (imo) the proper perspective.

Would I bet my life on the standard big bang theory being 100% true? No. But it certainly makes sense insofar as it's relevant. If somebody comes up with a better account, I feel sure that they'll publish it.

 

[marcus]

Glyde what you said about radiation energy (light, UV, gamma etc) not having Pauli exclusion is very important. The shorter the wavelength the more energy, too. There is no limit to how many photons fit in the box AND the smaller they are the more energy each one carries.

Can't you estimate how many Planck volumes are in a proton volume?

Planck length is about 10^-35 meters and proton scale is about 10^-15 meters. So cube their ratio.

Proton volume is about 10⁶⁰ times Planck volume. Like I said, the proton is kind of medium sized.

The standard metric unit of energy is a JOULE. It is the amount you expend if you lift a (kilogram) book about 10 centimeters off the table. It is the amount of thud you hear when you drop it back onto table.

The energy density of the U, with all matter converted to the common currency of light, is 0.22 nanojoules per cubic meter. What would density be if the volume of the observable were replaced by the proton volume but with same amount of energy. You know the linear size ratio (I gave it earlier).

I hope you get the hang of doing some simple physics arithmetic on your own soon if you have not already. Go ahead risk making mistakes. If you do someone will probably catch them, no harm done.

 

[stglyde]

Markus, I'll ponder on the above. But I need to know something now and the reason why I wrote this thread. Remember Lorentz when he tried to explain the reason for the null result of the Michelson-Morley Experiment. He claimed length can contract and time can shorten when something moving in the ether, that's why the MMX produced null result and all experiments up to the present can't distinguish between Lorentz Ether Theory and Special Relativity because they both use the Lorentz Transformation (which was invented by Lorentz before Einstein discovered SR). I think you are pretty familiar with LET. Now let's not debate about LET. What I want to know is whether the Big Bang is compatible with Lorentz Ether or how the Big Bang can give birth to Lorentz Ether. If no experiment can distinguish LET and SR. Can LET perhaps be refuted by strong evidence of the Big Bang.. assuming Big Bang and Lorentz Aether is totally incompatible. If not. Any papers or models of how the Big Bang can give rise or give birth to the Lorentz Ether?

 

[marcus]

Markus, I'll ponder on the above. But I need to know something now and the reason why I wrote this thread. Remember Lorentz when he tried to explain the reason for the null result of the Michelson-Morley Experiment. He claimed length can contract and time can shorten when something moving in the ether, that's why the MMX produced null result and all experiments up to the present can't distinguish between Lorentz Ether Theory and Special Relativity because they both use the Lorentz Transformation (which was invented by Lorentz before Einstein discovered SR). I think you are pretty familiar with LET. Now let's not debate about LET. What I want to know is whether the Big Bang is compatible with Lorentz Ether or how the Big Bang can give birth to Lorentz Ether. If no experiment can distinguish LET and SR. Can LET perhaps be refuted by strong evidence of the Big Bang.. assuming Big Bang and Lorentz Aether is totally incompatible. If not. Any papers or models of how the Big Bang can give rise or give birth to the Lorentz Ether?

Glyde, this is something of a new line of questioning. I will try to carry it along so we don't forget it. Maybe someone else will respond in a useful way, who knows more and has thought more about it than I have.

But before I try to understand the new I want to finish the discussion of Planck energy density and how to picture it.

People have different conjectures about the start of expansion---the actual start, that very moment, is not covered by classical GR and standard cosmology. So people are working on various models and they typically do involve densities around Planck.

One very concrete and definite model of the start of expansion is the (LQC) BOUNCE and when they study different cases and either solve the equations or run the computer simulations with various inputs it typically happens that the bounce occurs when the density is 41% of Planck.

In effect we always face the need to picture Planck energy density, with whichever model.
If you iike to picture stuff in your mind, as many do. The simplest is to think of that density of LIGHT filling the universe. Imagine that ordinary matter boiled away into light already at lower density. Nothing that occupies any space is left. Only photons. You know from LASERS that you can put as many photons as you want on top of each other like sardines without limit.

The typical photon in the mix has wavelength equal Planck length. (the smaller the more energetic, the hotter the light). That is wavelength equal to 10^-35 meter. So within the space of a proton sized 10^-15 meter he has room for a lot of ripples. A proton is a huge space for these photons because, being such hot and energetic light their wavelength is very small. And they have no Pauli territoriality, they welcome each other's company.

So let's put some numbers. The energy equivalent of 22 micrograms (i.e. Planck mass) is 1.9 billion joules or in round numbers 2 billion joules. It's like the energy equiv of a tank of gas. It is the Planck energy unit.
So at Planck density, or at 41% of Planck energy or whatever, everything is pure energy and we can picture the U filled with very hot bright light with about a billion joules in each Planck volume. Or two billion, if we are imagining Planck density instead of 41% of it.

...

...estimate how many Planck volumes are in a proton volume?

Planck length is about 10^-35 meters and proton scale is about 10^-15 meters. So cube their ratio.

Proton volume is about 10⁶⁰ times Planck volume...
The standard metric unit of energy is a JOULE. It is the amount you expend if you lift a (kilogram) book about 10 centimeters off the table. It is the amount of thud you hear when you drop it back onto table.

The energy density of the U, with all matter converted to the common currency of light, is 0.22 nanojoules per cubic meter...

So a proton volume has 10⁶⁰ Planck volumes each of which contains a two billion joules of light. So it contains 2x10⁶⁹ joules.

Lets compare that with (the energy equivalent of) the observable universe. The Hubble distance is about 13.8 billion light years. If you type that into google you get
1.3 x 10²⁶ meters. Radius of the observable is about 3.3 times Hubble distance so say 4x 10²⁶ meters. I think that makes the observable volume about 2.5 x 10⁸⁰ cubic meters. You might check that with a calculator.
So what do we get if each cubic meter of today's universe has on average the matter equivalent of 0.22 nanojoules? I get around 5 x 10⁷⁰ joules.

This has been quick and sloppy, it is not good enough to quote in another post. anyone who cares to do so could improve the accuracy and the result might change by up to an order of magnitude. But it gives the right idea. If you think of the proton volume as a room containing jillions of photons of very high temperature short wavelength light, and you imagine that the energy density is Planck,

then that proton volume contains about the same as the energy equivalent of the observable universe volume. This is admittedly kind of clunky. Anyone who wants is welcome to make it neater and more precise.

 

[Tanelorn]

Marcus, Re Proton energy ratios, that is very interesting that they are so close. It can't be any more than a mathemetical curiosity can it? Also how can all the protons in the observable universe have similar values of energy to just one proton?

 

[marcus]

Hi T., I did not see your post when I was typing this. Not sure how to respond to your question though. What I wanted to say was it's important to stress a point that Brian Powell made earlier. Not to think of the UNIVERSE as the size of a proton at the start of expansion.
We were talking about the observable and what is destined to expand to form the part that is currently observable to us.

The whole universe (at expansion start) is presumably quite a lot bigger than a proton!
And energy is all over the place. You cannot carve out and mentally isolate a little protonsized pocket of it and say "this energy in this pocket is what is going to make our observable universe".

You could only do that if everything held still and remained nicely compartmentalized. But it is all over the place.

So all this mental exercise with the proton volume does for us is give us practice imagining the ENERGY DENSITY we think the U had, as a whole, at the start of expansion. At that moment the "observable" part was not well defined and was all over the place without clear boundaries, so it had as yet no meaning. So the exercise is simply about visualizing a density.

There is no meaningful entity that had, at that time, "the size of a proton". So one cannot say that what is now our observable U started out as something the size of a proton. It is not so neat and compartmentalized.

The actual energy is all over the place and we can't lay claim to some definite chunk of it as ours. But we can talk about the density. In each protonsize volume there was at that time AFAIK enough to be equivalent to what now is in our observable region. That gives an idea how much is in any given volume at the time expansion started.

The whole universe should be pictured as (probably much) much larger than a proton. All of that same density. And of course boundaryless. No edge and no outside.

Particular bounce cosmology models would give you different estimates of the exact density (like LQG fairly consistently says 41% of Planck) but whatever the different models they tend to say something that is within an order of magnitude or so of Planck density. So that is what the mental exercise is really about imagining.
===========
Tanelorn AFAIK the proton is just an arbitrary choice to establish a visual image of a scale of size and volume. AFAIK it primarily comes up in cosmo popularizations where they have to give the reader something to visualize, like an atom, or the nucleus of an atom, or in this case the nucleus of a hydrogen atom (i.e. proton). To establish an idea of scale.

So it's probably just completely arbitrary. And as you know from the point of view of the three little quarks inside, a proton is just this big empty space with three flies buzzing around in it. The flies think that THEY are fundamental, not the big room they are buzzing around in. So the proton is here just a nice way to imagine a convenient amount of nearly empty space that has a definite size.

That's what I think anyway. Could be wrong.

 

[Tanelorn]

Hi Marcus, I just reread and saw that you said each cubic meter contains the same energy as a proton and not the whole observable universe. Thats what happens when you go speed reading!

Anyways seasons greetings to you and all at PF!

 

[Notwen7]

The standard big bang model purports that the big bang happened everywhere at once, not at a single point. This is an important misconception to straighten out. The colliding branes theory is a proposal that seeks to explain the physical mechanism for the big bang itself. Therefore, it is not in opposition to the standard big bang model; rather, it seeks to extend it. The colliding branes theory is still only hypothesis. The colliding branes theory has the rather unfortunate name of "ekpyrosis" in case you wish to read more about it.

Can you explain how it happened at multiple points at once? Also how do scientists arrive at these hypotheses?

 

[Tanelorn]

Notwen you are being misled by a bad name. I dislike Big Bang the name a great deal for that reason.
It is not an explosion from a point.
Inflation from a state of very high density and high temperature takes place everywhere at the same time.
The universe was almost infinite then and much much bigger now!

 

[Notwen7]

Notwen you are being misled by a bad name. I dislike Big Bang the name a great deal for that reason.
It is not an explosion from a point.
Inflation from a state of very high density and high temperature takes place everywhere at the same time.
The universe was almost infinite then and much much bigger now!

Indeed, I am. So in a sense it is almost like the dew point of a liquid? I'm imagining the small little vapor bubbles forming simultaneously being similar to the release of energy and matter from many places of the universe?

 

[Drakkith]

Indeed, I am. So in a sense it is almost like the dew point of a liquid? I'm imagining the small little vapor bubbles forming simultaneously being similar to the release of energy and matter from many places of the universe?

No. Imagine being a raisin inside a muffin in the oven. As the muffin starts to rise, all the other raisins seem to get further away from you as the muffin bakes. The muffin is like space and the raisins are like galaxies. The big difference is that a muffin occupies a finite volume. The universe is thought not to. Imagine being inside an infinitely large muffin mix. The raisins 10 miles from you would be receding from you at a much higher rate than the raisins next to you. This is all the "Big Bang" is. It is simply that the universe was once in a much denser state than we are now, similar to how the muffin mix is much thicker before cooked. No explosion, no bang.

 

[stglyde]

No. Imagine being a raisin inside a muffin in the oven. As the muffin starts to rise, all the other raisins seem to get further away from you as the muffin bakes. The muffin is like space and the raisins are like galaxies. The big difference is that a muffin occupies a finite volume. The universe is thought not to. Imagine being inside an infinitely large muffin mix. The raisins 10 miles from you would be receding from you at a much higher rate than the raisins next to you. This is all the "Big Bang" is. It is simply that the universe was once in a much denser state than we are now, similar to how the muffin mix is much thicker before cooked. No explosion, no bang.

How about spacetime.. isn't the fact that redshift occurs is because space is being expanded.. so can't we say spacetime was getting bigger from the initial core or Big Bang gave birth to spacetime? If not.. and if spacetime already exists. Can it also support the observation that redshift occurs and even the microwave background radiation becomes 3 degrees kelvin because the wavelength got expanded too. Can they do it without space being expanded?

 

[Drakkith]

How about spacetime.. isn't the fact that redshift occurs is because space is being expanded.. so can't we say spacetime was getting bigger from the initial core or Big Bang gave birth to spacetime? If not.. and if spacetime already exists.

You can say whatever you want. The theory that the Big Bang was conceived from says nothing about this, it only says that the universe was once in a very dense state.

Can it also support the observation that redshift occurs and even the microwave background radiation becomes 3 degrees kelvin because the wavelength got expanded too. Can they do it without space being expanded?

Can what support this?

 

[stglyde]

You can say whatever you want. The theory that the Big Bang was conceived from says nothing about this, it only says that the universe was once in a very dense state.



Can what support this?

Isn't it that microwave background radiation 3 Kelvin temperature was a result of the wavelength being expanded due to spacetime being expanded from the Big Bang? So logic says spacetime was once smaller perhaps the same size as whatever bang...

 

[Cosmo Novice]

Isn't it that microwave background radiation 3 Kelvin temperature was a result of the wavelength being expanded due to spacetime being expanded from the Big Bang? So logic says spacetime was once smaller perhaps the same size as whatever bang...

This is completely moot if the U is infinite. If it is infinite now then it always infinite.

 

[stglyde]

This is completely moot if the U is infinite. If it is infinite now then it always infinite.

Is this your own speculation as a novice or did you hear it elsewhere? Can other non-novice confirm if it's true?

 

[bapowell]

Isn't it that microwave background radiation 3 Kelvin temperature was a result of the wavelength being expanded due to spacetime being expanded from the Big Bang? So logic says spacetime was once smaller perhaps the same size as whatever bang...

Your wording isn't very clear, so I'm not certain of your question. The photons that make up the cosmic microwave background have been redshifting with the expansion of the universe since they were "created" at decoupling.

 

[Cosmo Novice]

Is this your own speculation as a novice or did you hear it elsewhere? Can other non-novice confirm if it's true?

This is a mathematical conjecture; if something is infinite now then it was always infinite. This is not to say that infinities cannot grow. This is more to do with number theory than cosmology but this is what I have deduced from a lot of independent research into the matter.

I may be incorrect and open to any challenges/corrections to my statement.

If the Universe is infinite, it must have always been infinite; the reason being; if you could pause expansion right now and move quickly across the Universe, you would cross an infinite amount of Universe without ever encountering the same patch of Universe twice. Now as we know the Universe is just in a less dense state, if you could have traveled across it 10 billion years ago it would still have been infinite just also a lot more dense. Its very logical if you think about it. This is of course assuming a spatially flat and infinite U.

 

[Calimero]

...if you could pause expansion right now and move quickly across the Universe, you would cross an infinite amount of Universe without ever encountering the same patch of Universe twice.

Not quite. You would encounter same patch infinite amount of times. Read this, if you have time and will, interesting stuff!

 

[ThomasT]

So, wrt recent replies, it seems to me that it isn't, and can't be, known whether our universe is infinite or not. It also seems to me that this is irrelevant to the OP question of whether the mainstream big bang theory is true or not. There's no way to know. Period. So, might as well close the thread.

But then there is that interesting thing about evidence for the expansion of the universe. And I have to ask myself: why would an infinite universe appear to be expanding?

 

[nazarbaz]

Cantor proved that we could always conceive of bigger infinities...
But what do we mean by infinity in this particular case ? What does it imply both on the ontological (perhaps I must say ontical) and phlosophical levels ? Causality still holds ?
It's dubious...