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Universal 'Now' at Time-Zero


StringJunky
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The universe has a density that suggests it is flat, which means that it is likely to be infinite in extent. What is the probability of a starting universe expanding with infinite speed to create an infinite expanse in a finite amount of time?

 

By infinite in extent, it was my understanding that the universe curves back on itself, and therefore has no finite edges or boundaries, not that it is is literally infinite in size. According to current thinking it is about 93 billion light years in diameter, but again, where are you getting evidence that the unknown is infinite, or that it is the current or standard model that it is?

 

I think we are getting hungup on the scientific use of the term infinite:

 

"The Vardanyan model says that the curvature of the Universe is tightly constrained around 0. In other words, the most likely model is that the Universe is flat. A flat Universe would also be infinite and their calculations are consistent with this too. These show that the Universe is at least 250 times bigger than the Hubble volume."

 

So here we have a team coming up with the latest model...on the one hand they use the word infinite, yet, when it comes down to it, they give a finite estimate, e.g., circa 250+

 

http://www.dailygalaxy.com/my_weblog/2013/02/the-real-universe-is-250-times-bigger-than-the-visible-hubble-volume-todays-most-popular-1.html

 

Also, it seems rather logically absurd to speak of an universe that is infinite in size expanding even more. If you are espousing the Big Bang model, how is it that one goes from a very small point in size to an infinite size in, say 13.9 billion years, while expanding at the speed of light?

Edited by disarray
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Dont see anything about an infinitely old universe.

 

The first sentence is: The universe may have existed forever, according to a new model that applies quantum correction terms to complement Einstein's theory of general relativity.

 

 

However, there is no particular evidence to show that this might be the case.

 

Indeed. This is an initial attempt to include quantum effects. It is, however, consistent with all the evidence we have.

By infinite in extent, it was my understanding that the universe curves back on itself, and therefore has no finite edges or boundaries, not that it is is literally infinite in size.

 

What you are describing is the alternative to infinite in size: "finite but unbounded" (the usual 2D analogy is the surface of the Earth).

 

 

According to current thinking it is about 93 billion light years in diameter

 

That is the observable universe, not the whole universe. The whole universe is expected to be many times larger than that (or infinite). It is also possible that the whole universe is smaller than the observable universe!

 

 

So here we have a team coming up with the latest model...on the one hand they use the word infinite, yet, when it comes down to it, they give a finite estimate, e.g., circa 250+

 

No that is NOT what they say. 250 is a LOWER BOUND.

 

 

Also, it seems rather logically absurd to speak of an universe that is infinite in size expanding even more.

 

Of course it isn't. Take the natural numbers; there are infinite number of them. Now multiply them all by two; you have "expanded" the number line but it is still infinite. Or look at the Hilbert Hotel paradox. Or ...

 

 

If you are espousing the Big Bang model, how is it that one goes from a very small point in size to an infinite size in, say 13.9 billion years, while expanding at the speed of light?

 

Sigh. Expansion is not a speed. Expansion is not a speed. Expansion is not a speed. ...

 

I don't have the time (or patience) to explain the difference between scaling and speed right now. I'll come back to it ...

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The first sentence is: The universe may have existed forever, according to a new model that applies quantum correction terms to complement Einstein's theory of general relativity.

But again, this assumes some sort of contraction theory. I see nothing else in the article

 

Indeed. This is an initial attempt to include quantum effects. It is, however, consistent with all the evidence we have.

So it seems you are not arguing that there was a Big Bang, as according to your article, the theory discards the notion of singularities, and thus, "These terms keep the universe at a finite size, and therefore give it an infinite age." So I don't see how you are having your cake and eating it too; that is, I don't see how you are accepting the idea of expansion (if that is the case), and agreeing with this unorthodox model at the same time.

 

What you are describing is the alternative to infinite in size: "finite but unbounded" (the usual 2D analogy is the surface of the Earth).

Yes, I agree. My point exactly. Are you suggesting it is infinite and unbounded? Again, it seems you are not talking about a standard/current model involving the Big Bang or the expanding universe.

 

That is the observable universe, not the whole universe. The whole universe is expected to be many times larger than that (or infinite). It is also possible that the whole universe is smaller than the observable universe!

I didn't say it was the whole universe.

 

No that is NOT what they say. 250 is a LOWER BOUND.

I'm going to agree with those who say that the number 250 was thrown out there for a reason...and it is a long way from infinity, and does indeed suggest that there is a finite number that one might come up with.

 

Of course it isn't. Take the natural numbers; there are infinite number of them. Now multiply them all by two; you have "expanded" the number line but it is still infinite. Or look at the Hilbert Hotel paradox. Or ...

I'm going to go along with those who say that you can't add on to infinity, by the definition of the word, "infinity", itself, even though mathematically you can have infinities 'greater' than ( some would say different or denser) other infinities, as per Cantor's Diagonal Argument.

 

Sigh. Expansion is not a speed. Expansion is not a speed. Expansion is not a speed. ...

I don't have the time (or patience) to explain the difference between scaling and speed right now. I'll come back to it ...

 

Okay, but my point still holds that you are starting with a small point and expanding at a finite speed. Also, correct me if I'm wrong, but you are sounding a little condescending or supercilious with all this sighing and impatience. Maybe dealing with people who have a sense of curiosity but less knowledge than yourself is not your forte.

 

Edited by disarray
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Okay, but my point still holds that you are starting with a small point and expanding at a finite speed. Also, correct me if I'm wrong, but you are sounding a little condescending or supercilious with all this sighing and impatience. Maybe dealing with people who have a sense of curiosity but less knowledge than yourself is not your forte.

You aren't taking in what he's saying and he is not speculating. People only have a finite amount of patience and Strange is very patient. If he's sighing it means your attitude is pissing him off because you are not listening. You are clearly not liking the answers he's giving you and yet you plead curiosity.

Edited by StringJunky
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Also, correct me if I'm wrong, but you are sounding a little condescending or supercilious with all this sighing and impatience.

 

I apologise. Its been a bad day.

 

 

Not seeing this sentence in the article link I gave

 

That's weird. Try this one: http://www.livescience.com/49958-theory-no-big-bang.html

'"Our theory suggests that the age of the universe could be infinite," said study co-author Saurya Das, a theoretical physicist at the University of Lethbridge in Alberta, Canada.'

 

 

Are you suggesting it is infinite and unbounded?

 

It is either infinite (and therefore, by definition, unbounded) or finite and unbounded. They seem to be the only possibilities in current models.

 

 

I'm going to agree with those who say that the number 250 was thrown out there for a reason...and it is a long way from infinity, and does indeed suggest that there is a finite number that one might come up with.

 

Yes, the number 250 is based on the measured flatness (more accurately, perhaps, the error bounds on that flatness).

 

Giving a lower limit does not exclude infinity (I think we can all agree that infinity is larger than 250 :))

 

 

You can't add on to infinity, by the definition of the word, "infinity", itself.

 

Yes you can. Lets take the infinite set of odd numbers. Now add the number 4 to that set. The set is still infinite. Now add to that the rest of the infinite set of even numbers. The size of the set is still infinite.

 

 

Expansion is not a speed. ...

 

Expansion is a scaling effect. It is easiest to consider this constant in time and space (which is close enough for the moment).

 

Consider a number of galaxies separated by the same distance (far enough apart that the expansion of space is significant and the same between all of them).

 

At time 0, they are 1 unit apart:

A.B.C.D.E.F

 

After some time they are 2 units apart:

A..B..C..D..E..F

 

After the same time again, they are 3 units apart:

A...B...C...D...E...F

 

And so on:

A....B....C....D....E....F

 

Now, if we look at the distance between B and C, for example, it increases by 1 at every time step. But the distance between B and D increases by 2 at every step. So the distance between B and D is increasing twice as fast as the distance between B and C; i.e. the speed of separation is twice as great.

 

Choose any pairs of galaxies and you will see that apparent the speed of separation is proportional to the distance between them. Take two objects far enough apart and the speed of separation will be greater than the sped of light.

 

We can trace back the state of the (observable) universe and calculate the radius at various times in the past. For example, when the CMB was released, the radius was about 4 billion light years. That is about 360,000 thousand years after the (notional) time zero.

 

Off the top of my head, I don't know what the size was at the earliest times we can model but as they are fractions of a second rather than thousands of years it is going to be pretty small.

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You aren't taking in what he's saying and he is not speculating. People only have a finite amount of patience and Strange is very patient. If he's sighing it means your attitude is pissing him off because you are not listening. You are clearly not liking the the answers he's giving you and yet you plead curiosity.

Hmmm. Since when do you read minds. Your trying to blame me as having an attitude or not listening is rather insulting. I am not pleading curiosity...what do think I am doing?. So what if I disagree with his answers. I know that I am trying hard to understand things. As far as I am concerned you are slandering me and my motives. Please refrain.

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Hmmm. Since when do you read minds. Your trying to blame me as having an attitude or not listening is rather insulting. I am not pleading curiosity...what do think I am doing?. So what if I disagree with his answers. I know that I am trying hard to understand things. As far as I am concerned you are slandering me and my motives. Please refrain.

I felt you were insulting Strange.

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I apologise. Its been a bad day.

 

 

That's weird. Try this one: http://www.livescience.com/49958-theory-no-big-bang.html

'"Our theory suggests that the age of the universe could be infinite," said study co-author Saurya Das, a theoretical physicist at the University of Lethbridge in Alberta, Canada.'

No, I was on my article by mistake. Then I went to your article which seems to center on the non-expanding and hence infinitely old universe, so I don't know why you are explaining expansion to me (which I understand) , as an expanding universe does imply one with a definite age as I understand it. So yes, there may be some rationale for believing in a static universe....but again, I think that the phrase "infinite" is being used to suggest that in such a theory we would have no way of determining the age of the universe. However, even in a static universe, I see no reason to assume that it is infinitely old just because we can't determine its age.

 

I follow a bit about your reference to infinities, but I think that manipulating numbers does not necessarily reflect what might be happening in the universe; that is, I don't see that one is actually manipulating any empirical data.


I felt you were insulting Strange.

Not at all. I understand he may have been tired or stressed or whatever. But no, I can't imagine an instructor audibly sighing with impatience when a student is genuinely trying to understand something....that is insulting. It's nice to defend people, but you were making assumptions that weren't true.

Edited by disarray
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Not at all. I understand he may have been tired or stressed or whatever. But no, I can't imagine an instructor audibly sighing with impatience when a student is genuinely trying to understand something....that is insulting. It's nice to defend people, but you were making assumptions that weren't true.

 

We are ordinary people sharing information, not paid employees.

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We are ordinary people sharing information, not paid employees.

 

Point taken. However, I wouldn't make such assumptions about my friend or child in such a manner, even though I am not paid to be civil.

 

But yes we are all ordinary. I tend to assume people are here to learn...but it seems that there are indeed bloggers who go out of their way to irritate and badger others.....I am not one of those people.

Edited by disarray
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Point taken. However, I wouldn't make such assumptions about my friend or child in such a manner, even though I am not paid to be civil.

 

But yes we are all ordinary. I tend to assume people are here to learn...but it seems that there are indeed bloggers who go out of their way to irritate and badger others.....I am not one of those people.

Yes, there are utter a-holes that pass through here and one gets a bit jaded and quick to judge sometimes.

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No, I was on my article by mistake. Then I went to your article which seems to center on the non-expanding and hence infinitely old universe

 

It doesn't say non-expanding. It says, for example:

"Using the quantum-corrected Raychaudhuri equation, Ali and Das derived quantum-corrected Friedmann equations, which describe the expansion and evolution of universe"

 

 

So yes, there may be some rationale for believing in a static universe....

 

The presence of the CMB killed that idea a few decades ago.

 

 

but again, I think that the phrase "infinite" is being used to suggest that in such a theory we would have no way of determining the age of the universe.

 

It isn't. It makes no real difference to the big bang model if the universe is finite or infinite.

 

(And note that when I say "big bang" I am not referring to some (possibly non-existent) moment of creation. It is a model (or family of models) that describes the evolution of the universe from a hot dense state.)

Edited by Strange
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(And note that when I say "big bang" I am not referring to some (possibly non-existent) moment of creation. It is a model (or family of models) that describes the evolution of the universe from a hot dense state.)

To add: possibly, the beginning of a new epoch.

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You aren't taking in what he's saying and he is not speculating. People only have a finite amount of patience and Strange is very patient. If he's sighing it means your attitude is pissing him off because you are not listening. You are clearly not liking the answers he's giving you and yet you plead curiosity.

He has a bad habit of this in other threads, too. Some sort of issue with comprehension, coupled with a bad habit of reading things into comments their authors had no intention of conveying.
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To add: possibly, the beginning of a new epoch.

 

To focus on your original question, since we know so little about the initial Planck epoch is there any point in even attempting to define predecessors?

 

The article previously linked by Strange seems to suggest that there are very few quantities to consider. Just a speck of Bose-Einstein condensate (edit) 'stuff' at the Planck temperature crammed into the infinitesimally tiny Planck volume.

 

There's probably quite a few paradoxes at large here, but one that sparks my interest is what's happening to system entropy. If any physical laws do persist back to such phases, I'm guessing the 2nd Law has as good a chance as any. The old definition

 

dS=dQ/T

 

suggests that under these conditions, though the entropy is 'low' (ie compared to later times) it seems that there's a limiting case where no matter how much energy is added to the system, there's essentially no change to total system entropy. And if entropy is unchanging, haven't we lost our arrow of time? Maybe that 10^-43 second is in some sense an infinitely long asymptotic approach to a time zero singularity that never actually happened since both the singularity and time were imaginary quantities at that point. They just hung around for eternity in GR maths.

 

Just one speculation among many.

Edited by sethoflagos
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The last post makes the most sense.... Yes expansion involves the ideal gas laws at every stage of its evolution. Every particle whether its fermionic or bosonic contributes to expansion. Even gravity itself aids expansion though not in the way many think. Take a homgeneous and isotropic initial condition. As inhomogeniety occurs, the average density of matter drops, due to pooling into large sale structure formation. This means gravity has less influence on the voids away fro the LSS.

 

The very fact that gravity tends to condense into the LSS regions alone aids expansion. However we would need some rules governing LSS formation.

 

For this we will use strictly a non relativistic matter only fluid. Just matter....

 

Well one set of rules has to do with Jeans mass, Primordial density fluctuations expand linearly at a rate slower than the rate of expansion. This induces localized anistropy regions that sets up two possibilities locally. Inflow and outlfow of matter.

 

the dividing line between the two possibilities can be found by the following argument. Let the time of freefall into the overdense region be

 

[latex]t_g=1/\sqrt{G_\rho}[/latex]

 

sound waves in a medium propogate with velocity [latex]c_s=\sqrt{\frac{\partial p}{\partial\rho}}[/latex]

 

so they move one wavelength in the time

[latex]t_s=\lambda/c_s[/latex]

 

when t_g is shorter than t_s the fluctuation is unstable and will continue to grow until it collapses locally setting T_g as equal to T_s we find the Jeans instability, Which correlates the rate of expansion and collapse locally due to gravity itself (locally only)

 

[latex]\lambda_j=\sqrt{\frac{\pi}{G\rho}}c_s[/latex]

 

So we can see from this that expansion and gravity both aid in large scale structure formation. That large scale structure formation in turn helps the rate of expansion by the following equation.

 

[latex]H_z=H_o\sqrt{\Omega_m(1+z)^3+\Omega_{rad}(1+z)^4+\Omega_{\Lambda}}[/latex]

 

as expansion increases and the LSS develop the matter density evolves by the ratio in the last equation. This alters the rate of expansion compared to the rate today by the last equation. You will note radaition and matter both evolve but the cosmological constant does not.

 

If you truly look and study the thermodynamics of particles, you will find nothing is more natural than an expanding or collapsing universe. Expansion is literally a thermodynamic process. (Though were still trying to fit the cosmological constant under thermodynamic process) possible solution is the Higgs metastability.

 

Essentially from the above if the matter wavelength (Jeans mass wavelength) is significantly smaller than the Hubble expansion. Locally gravity will collapse, this local collapse will in turn aid expansion by lowering the global mass density average.

 

So from above we see that a matter only universe can still expand when we involve nothing more than gravity and matter.

 

Radiation has a different ratio of contribution so does the Cosmological constant.

 

ill regardless the rate of expansion still boils down to potential vs kinetic energy relations of the ideal gas laws and thermodynamics.

 

We don't need anything more than GR and thermodynamics to explain expansion. Regardless if the universe is finite or infinite.

Edited by Mordred
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He has a bad habit of this in other threads, too. Some sort of issue with comprehension, coupled with a bad habit of reading things into comments their authors had no intention of conveying.

So now you are into cyberbullying? Again, please refrain from the personal attacks on my writing and reading habits, as well as other personal attacks both here and elsewhere. Thank you.

Edited by disarray
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Mordred,

.

Thanks for that. I almost understood. Like a compression and rarefaction wave moving through the matter.

 

How do you symbolize the intersection of two or more impulses though?

 

Regards, TAR

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Like a compression and rarefaction wave moving through the matter.

 

How do you symbolize the intersection of two or more impulses though?

 

The picture Mordred's post puts in my mind is more of clumps galaxies condensing under their own gravitational force rather like snowflakes forming and growing due to their own forces of attraction in moist air as it rises and cools.

 

Seems to suggest a phase separation between a dispersed, gravity dominated, mass-rich phase of the universe, within a continuous, expansion dominated, mass-depleted phase.

 

This doesn't necessitate 'The Void' blowing through the galactic clusters in any sense, I think. Maybe more just floating in the breeze. And if inflation/expansion is broadly spherical and into 'new space' as opposed to displacing pre-existing space, then there aren't going to be any 'intersections of impulses'. They're forever diverging aren't they?

 

Of course, in no way am I claiming a full understanding of Mordred's post! Just picturing it from a more mundane gas thermodynamics point of view.

Edited by sethoflagos
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Not a bad correlation on the snowflake analogy, the localized hydrodynamic equations assist the filament developments. These are typically covered in decent astrophysics textbooks. A good resource being "Elements of Astrophysics". Jeans equation above is one example of localized hydrodynamics due to gravity and particle movement of pressure less dust.

 

The FLRW metric used in cosmology essentially averages these localized influences onto a global scale.

 

This is where the Cosmological principle takes hold. At some point of volume where a homogenous and isotropic average occurs decides the scale from local to global measurements and influence. This scale being roughly 100 Mpc in the universe today. Less than 100 Mpc that region is not considered uniform.

 

What I described above is essentially showing how a matter dominated universe can expand, however we only considered matter. photons and other forms of radiation influence expansion via their own equations of state. An equation of state correlates density to pressure relations of each particle species.

GR curvature is generally speaking on the localized scale, where universe curvature is a thermodynamic history of expansion rates.

 

This distinction is important when it comes to gravitational redshift, as opposed to cosmological redshift...

 

The universe undergoes three primary eras, radiation dominant BB to time of last scattering (CMB,), matter dominant followed by the current Lambda dominant. Each era has its own thermodynamic relations which is an average dominant influence.

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Every particle whether its fermionic or bosonic contributes to expansion. .

 

I've read a few wiki articles recently, but can't get a clear fix on when the first fermions appeared. Did they 'wait' for enough space to be available to satisfy the Pauli exclusion principle, or did they just appear anyway and perhaps partially drive inflation via degeneracy pressure?

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Good question. As quarks are fermionic this will be when the quark epoch occuurs according to this SO (5) chronology. The lepton family drops out later.

https://en.m.wikipedia.org/wiki/Chronology_of_the_universe

 

 

The supersymmetric model however has earlier possible stages. The exact timing is model dependant.

 

A good coverage between models is

 

http://pdg.lbl.gov/2011/reviews/rpp2011-rev-guts.pdf GRAND UNIFIED THEORIES

http://arxiv.org/pdf/0904.1556.pdf The Algebra of Grand Unified Theories John Baez and John Huerta

 

A good textbook coverage is chapter 3 below

 

http://www.wiese.itp.unibe.ch/lectures/universe.pdf:"Particle Physics of the Early universe" by Uwe-Jens Wiese Thermodynamics, Big bang Nucleosynthesis

 

This chapter does an excellent job covering the Boltzmann aspects and additional degrees of freedom as particles drop out of thermal equilibrium.

 

It details the Bose-Einstein and Fermi-Dirac statistics leading to the Maxwell Boltzmann statistics. It includes GR and the FLRW metric as well.

 

http://www.wiese.itp.unibe.ch/lectures/universe.pdf "Particle Physics of the Early universe" by Uwe-Jens Wiese Thermodynamics, Big bang Nucleosynthesis

Edited by Mordred
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http://www.wiese.itp.unibe.ch/lectures/universe.pdf:"Particle Physics of the Early universe" by Uwe-Jens Wiese Thermodynamics, Big bang Nucleosynthesis

This chapter does an excellent job covering the Boltzmann aspects and additional degrees of freedom as particles drop out of thermal equilibrium.

It details the Bose-Einstein and Fermi-Dirac statistics leading to the Maxwell Boltzmann statistics. It includes GR and the FLRW metric as well.

http://www.wiese.itp.unibe.ch/lectures/universe.pdf:"Particle Physics of the Early universe" by Uwe-Jens Wiese Thermodynamics, Big bang Nucleosynthesis

Good pdf resources are great, but a couple of links (see above) did not work.

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