What Was the Force Holding Matter Together Before the Big Bang?

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The discussion centers on the forces that might have held matter together before the Big Bang, with emphasis on Loop Quantum Cosmology (LQC) as the leading research framework. Participants argue that traditional cosmology cannot adequately address pre-Big Bang conditions, suggesting that LQC models indicate a "bounce" from a prior collapse rather than an explosion into empty space. The conversation also touches on the implications of entropy and the Second Law of Thermodynamics in this context, questioning their applicability during the transition from collapse to expansion. There is skepticism about the need for inflation to explain the universe's flatness, with some suggesting alternative explanations. Overall, the dialogue highlights the complexities and ongoing debates surrounding the nature of the universe's origins and the theoretical frameworks attempting to explain them.
  • #31
Thanks Marcus, I skimmed through the abstracts you quoted. I don't fully understand everything, but it sounds like information in the form of gravitational waves is theorized to survive from before the Big Bang. If so, then it will be a long time indeed before any observational tests are realized (Given LIGO has been 20 years in the making and still no detection).

I am unfamiliar with "tensor perturbations", and Chaplygin's equation of state. Is there a layman's explanation? (Even though I completed physics grad school, I never took a course in general relativity or cosmology, instead specializing in experimental work with atoms and lasers.)[/size]
 
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  • #32
Redbelly98 said:
... I skimmed through the abstracts you quoted...

I'm glad you skimmed the abstracts. It's good to have someone else to talk to who might be interested in keeping track of this part of the literature. To me, the most revealing paper on the list was this one:

http://arxiv.org/abs/0904.2835
Matter Bounce in Horava-Lifgarbagez Cosmology
Robert Brandenberger (McGill University and CERN)
6 pages, 1 figure
(Submitted on 18 Apr 2009)

I'll quote some excerpts to give an idea of content.

"...Since the curvature perturbation R grows on super-Hubble scales, a matter bounce leads to a larger amplitude of non-Gaussianities than slow-roll single-field inflation. Since it is a different mode of R which dominates, the shape of the non-Gaussianities is also different from what is obtained in slow-roll single-field inflation models.

The specific predictions for the amplitude and shape of the three-point function (the “bispectrum”) were worked out in [21]. In particular, the predicted amplitude of the bispectrum is very close to the level which could be detected using the Planck satellite experiment.

...

...Thus, one of the main messages of this Note is that it is not necessary to force a period of inflationary expansion into Horava-Lifgarbagez cosmology. The alternative matter bounce scenario predicts an amplitude of the normalized bi-spectrum is the order of 1, and a specific shape of this three-point function, as studied in detail in [21].

These specific predictions are potentially within the reach of upcoming CMB missions such as PLANCK.

To obtain a successful late-time cosmology, the model presented here must be supplemented with a mechanism to transfer the energy at late times to Standard Model matter and radiation..."

In case anyone is unfamiliar with Brandenberger's standing, he was co-organizer of a 3week workshop at Kavli ITP Santa Barbara which brought LQG and String people together to study resolution of the cosmo singularity, and spacetime singularities in general (The Quantum Nature of Spacetime Singularities).
This year at the big Paris meeting (Marcel Grossmann 12) he is the one chosen to chair the parallel session on bounce cosmologies.
To put it crassly, he is a respected old boy of the inner circle.
=====================

I was unfamiliar with the Chaplygin equation of state.
Just took a look at the introduction to this paper, which has something about it:
http://arXiv.org/pdf/gr-qc/0202064v2
p = - A/rho
where A is some positive constant.
If anyone has some better sources please share them. This seems to be just another type of inflation, with a different kind of exotic matter for the inflaton field. This time the "exotic fluid" postulated to drive the inflation has an equation of state of that particular form.
"...
thereby avoiding the above mentioned fine-tuning problems. This is achieved via the introduction, within the frame work of FRW cosmology, of an exotic background fluid, the Chaplygin gas, described by the equation of state... "
Fortunately only one of the papers listed depends on the universe tanking up on Chaplygin gas so I'm going to focus on some of the others.

I like Brandenberger's because among other things it obviates inflation. This puts Willy the Razor in high good humor, grinning from ear to ear.
 
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  • #33
I guess the general lesson is that when you test an early universe model you test the model against what we can see in the present.

This is apt to be of stuff like the CMB.

You don't test the idea of a bounce. You test a model of how the universe works, and if it has a bounce...well, then it has a bounce.

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

At some level it doesn't matter very much whether it is a HoravaLifgarbagez model or a Loop Cosmology model. The important thing is to have some signature in the CMB that the Planck spacecraft can look for. Or else say how much finer resolution than Planck's you want to get.

Planck is supposed to launch May 6. Just a couple of weeks!
http://www.esa.int/SPECIALS/Operations/SEM45HZTIVE_0.html
http://www.esa.int/esaSC/120398_index_0_m.html
=================

Everybody seems to be talking about Horava-Lifgarbagez quantum gravity---not just Robert Brandenberger, a dozen or so papers by others have appeared recently. But none have pointed out the obvious shortened terminology---taking the initial and final syllables.
 
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  • #34
Why are cosmologists putting so much efforts into trying to find ways around the singularity at t=0? Isn't it a better idea to first make sure we know for certain what kind of a universe we find ourselves in - is it a 2D hologram, 11-dimensional, N-dimensional or 3-dimensional?
 
  • #35
marcus said:
I guess the general lesson is that when you test an early universe model you test the model against what we can see in the present.

This is apt to be of stuff like the CMB.

You don't test the idea of a bounce. You test a model of how the universe works, and if it has a bounce...well, then it has a bounce.

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

At some level it doesn't matter very much whether it is a HoravaLifgarbagez model or a Loop Cosmology model. The important thing is to have some signature in the CMB that the Planck spacecraft can look for. Or else say how much finer resolution than Planck's you want to get.

Planck is supposed to launch May 6. Just a couple of weeks!
http://www.esa.int/SPECIALS/Operations/SEM45HZTIVE_0.html
http://www.esa.int/esaSC/120398_index_0_m.html
=================
...

Planck launch date has been set back to May 14.

Wavejumper, the standard model cosmologists work with is spatial 3D. You seem to want everybody to put off doing ordinary cosmology until extra dimensions (for which there is no experimental evidence) have been conclusively ruled out.
 
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  • #36
Planck launch will be a big event for many reasons. I foresee it as one of the most important experiments ever conducted. Let's wait a month or three and see what it reveals. I expect mostly the expected, and a few very unexpected results. The Herschel will also be launched on this mission. See the NASA site for details. We live in exciting times. This is the golden age of science. We've already seen WMAP and gravity probe B, and it keeps getting better. Imagine what we could do if we did a better job averting indulgence in needless conflicts.
 
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