Cosmology without inflation (Peter and Pinto-Neto, bibliography, change in cosmo)

1. Sep 16, 2008

marcus

It's been pointed out already at Cosmo forum that a revolution, or at least a minor insurrection, is brewing in cosmology. This paper is part of that. It comes from a different direction compared to some of the other research in nonsingular cosmology. For instance it is not specifically a Loop cosmology bounce paper. But indeed there seem to be half a dozen converging lines of thought in nonsingular or bounce cosmo. One useful thing the authors do is compile a substantial body of references to other work. They provide their own ideas of how a quantum bounce removes the singularity and also removes the need for inflation. The riddles that inflation scenarios were made up to answer go away by themselves, according to Peter and Pinto-Neto, making inflation scenarios unnecessary extra baggage. Since the conjectured physical mechanisms underlying inflation scenarios are entirely made up, support for the scenarios depends on there being no other more natural way of addressing the several puzzles. Peter and Pinto-Neto devote themselves to yanking out the rug.

http://arxiv.org/abs/0809.2022
Cosmology without inflation
Patrick Peter, Nelson Pinto-Neto
8 pages, Phys. Rev. D 78, 063506 (2008)

"We propose a new cosmological paradigm in which our observed expanding phase is originated from an initially large contracting Universe that subsequently experienced a bounce. This category of models, being geodesically complete, is non-singular and horizon-free, and can be made to prevent any relevant scale to ever have been smaller than the Planck length. In this scenario, one can find new ways to solve the standard cosmological puzzles. One can also obtain scale invariant spectra for both scalar and tensor perturbations: this will be the case, for instance, if the contracting Universe is dust-dominated at the time at which large wavelength perturbations get larger than the curvature scale. We present a particular example based on a dust fluid classically contracting model, where a bounce occurs due to quantum effects, in which these features are explicit."

Among their many other publications, the authors have a couple of earlier papers specifically related to this:

http://arxiv.org/abs/hep-th/0203013

http://arxiv.org/abs/hep-th/0610205

Peter previously did string research. He now works in astrophysics (Paris), Pinto-Neto's main interest is cosmology (Rio De Janeiro)

Last edited: Sep 16, 2008
2. Oct 7, 2008

hurk4

Marcus, I am very happy with this as you can understand from my earlier posts. This is what I was waiting for.
Thanks

3. Oct 17, 2008

marcus

I share your sentiments. One thing that would be very helpful is people coming us with TESTS of whether inflation actually occurred. And in fact just yesterday I saw a paper by Paul Steinhardt that addresses this.

The reason is that we only tolerate inflations scenarios because they solve some puzzles, like near-flatness, temperature near-isotropy,...
But now we realize there are other ways to answer the same riddles.

Inflation is suspect because it requires one or more exotic fields which we don't have any other reason to believe really exist---"inflatons". If we find some other more economical way to explain flatness etc, then we don't have to dream up inflatons.

Paul Steinhardt was motivated by wanting to get rid of inflation so he made up the brane-clash cosmology, which I think is pretty far-fetched. But at least it was a try. Now Peter and Pinto-Neto are discussing something considerably simpler.

In the meantime, Steinhardt has come up with ideas for testing----tests that he says could rule out inflation or make it much less believable.

But of course, fair is fair! The tests might tend to confirm inflation!
Either way, I think it is extremely interesting. It would settle a lot of issues if we could get some tests of whether this imagined episode of exponential expansion actually happened.

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

Yes, here it is:

http://arxiv.org/abs/0810.2787
Proving Inflation: A Bootstrap Approach
Latham Boyle (CITA), Paul J. Steinhardt (Princeton)
4 pages, 2 figures
(Submitted on 16 Oct 2008)

"We propose a way to test the essential idea underlying the inflationary paradigm: that the universe underwent a brief period of accelerated expansion followed by a long period of decelerated expansion."

4. Oct 17, 2008

sysreset

Any thoughts as to how Peter and Pinto-Neto view dark matter/dark energy in their paradigm?

5. Oct 17, 2008

marcus

I don't understand why they call the idea a paradigm, or if it is properly theirs. Maybe there is a historical priority issue.
It seems to me that (no matter who first proposed it when) the bounce cosmology picture has been dominated since about 2001 by Bojowald Ashtekar and their co-authors.
What interests me about the Peter&Pinto-Neto paper is that it shows total strangers converging from other directions on the same idea.

This is not a long paper (only 6 pages) and it is not their first. I think I remember seeing that Pinto-Neto goes back to the 1990s with this idea.

In this paper they list a number of questions they are leaving open. My impression is they don't have as full a picture as you get in some other research. DE is mentioned at top of right column on page 3 and listed as an open question on page 6. DM is mentioned at top of right column on page 6.
========================

In case anyone wants a broader view of nonsingular quantum cosmology research, here's a search of stuff since 2005
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+COSMOLOGY+AND+DATE+%3E+2005&FORMAT=www&SEQUENCE=citecount%28d%29 [Broken]
you will see here some Topcite 100+ and numerous Topcite 50+ papers, almost all of them (loop) bounce cosmology.
But there are some 180 papers and if you go further down the less you will find several other approaches.

BTW I think an interesting question would be how loop cosmology deals with dark energy, since there is a large much-cited literature, even more interesting than how this 6 page paper does.

Last edited by a moderator: May 3, 2017
6. Oct 18, 2008

wolram

Who's tests are the best tests, who should we be listening to.

http://arxiv.org/abs/astro-ph/0210007

Boomerang, Maxima, DASI, CBI and VSA significantly increase the case for accelerated expansion in the early universe (the inflationary paradigm) and at the current epoch (dark energy dominance), especially when combined with data on high redshift supernovae (SN1) and large scale structure (LSS). There are 7 pillars of Inflation'' that can be shown with the CMB probe, and at least 5, and possibly 6, of these have already been demonstrated in the CMB data: (1) a large scale gravitational potential; (2) acoustic peaks/dips; (3) damping due to shear viscosity; (4) a Gaussian (maximally random) distribution; (5) secondary anisotropies; (6) polarization. A 7th pillar, anisotropies induced by gravity wave quantum noise, could be too small. A minimal inflation parameter set, \omega_b,\omega_{cdm}, \Omega_{tot}, \Omega_Q,w_Q,n_s,\tau_C, \sigma_8}, is used to illustrate the power of the current data. We find the CMB+LSS+SN1 data give \Omega_{tot} =1.00^{+.07}_{-.03}, consistent with (non-baroque) inflation theory. Restricting to \Omega_{tot}=1, we find a nearly scale invariant spectrum,

7. Oct 18, 2008

marcus

Offhand I'd be inclined to listen to Paul Steinhardt, if only on the basis of reputation! At first sight, that 2002 paper by those 10 folks doesn't impress me personally. But that's just my reaction. You have to decide for yourself.

Another way to answer your question who *should* we listen to is to see who gets listened to by members of the active research community. That is, pick up clues from the collective intelligence of the tribe. Here are the cites:

http://arxiv.org/cits/astro-ph/0210007

What this says to me is that this 2002 paper was never cited very much and in the past 5 years only got cited TWICE. That is, after 2003 it dropped out of the picture almost entirely.

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

Ultimately each person makes up their own mind. I can't advise you. But I will tell you my own thoughts. I don't like the paper because it confuses actual TESTS with things we already knew that inflation was made up to explain, or which there might be other explanations for.
A test is a prediction of something definite that if you might find in future and if you go look and don't see it then you throw the theory out.

I don't see where they put inflation on the line and say "it predicts we will see suchandsuch and if we don't see this then it is wrong."

Maybe someone else can show me something like that in the paper.
====================

Look at what they say on page 2, wolram:
"This paper is an update of [1] to take into account how the new data have improved the case for primordial acceleration, and for acceleration occurring now. The simplest inflation models are strongly preferred [preferred to what?] by the data. This does not mean inflation is proved, it just fits the available information better than ever[but so might alternatives be fitting better than ever]. It also does not mean that competitor theories are ruled out[what competitors, they never say!],.."

In other words, their paper is logically inconclusive. It is not constructed to prove anything. The data they present could, as far as I can see, just as well be taken as evidence for a bounce cosmology model---or any model that provides an alternative explanation for microwave background features.

the reason I like Steinhardt's approach is that he is really trying to test primordial acceleration, not merely argue that it is plausible. He focuses on the essential features (a brief period of acceleration followed by a long period of deceleration) and says "let's see whether or not this actually happened".

Just so people know what we are talking about. I will recopy the Steinhardt paper abstract. I could be wrong but I think it is the first case of a proposal to really test inflation. Not just to point out things for which inflation is one possible explanation.

http://arxiv.org/abs/0810.2787
Proving Inflation: A Bootstrap Approach
Latham Boyle (CITA), Paul J. Steinhardt (Princeton)
4 pages, 2 figures
(Submitted on 16 Oct 2008)

"We propose a way to test the essential idea underlying the inflationary paradigm: that the universe underwent a brief period of accelerated expansion followed by a long period of decelerated expansion."

Last edited: Oct 18, 2008
8. Oct 18, 2008

wolram

May be a bad example, but there are many more like,

http://www.journals.uchicago.edu/doi/abs/10.1086/510378 [Broken]

Last edited by a moderator: May 3, 2017
9. Oct 18, 2008

marcus

this all seems to be about presentday effects of dark energy----evidence for gradual acceleration going on now.

that is different from early universe inflation scenarios.