Researchers look beyond the birth of the universe

[RyanJ]

A new study by the a group of physicists has shone new light on the big bang, using a modified form of Einstein’s cosmological equations. They have shown that the big bang may infact have been a a sort of "quantum bounce". This is a stunning revelation, as if it proves to be correct it will mean that there may have been another universe before this one, that may have suffered a fate such as the big crunch.

 

http://www.physorg.com/news66660003.html

 

- Ryan Jones

[Martin]

Ryan, I am glad you noticed this! I had not seen this physorg popular article, only some recent preprints by Ashtekar. I will fetch some links to more technical background that goes with this. Good find! thanks for posting it.

 

Martin

[bascule]

Holy schnikes batman!

 

So what I'm confused about here is if this is compatible with Lee Smolin's fecund universes model or if what they're describing is more akin to our universe being born out of a "big crunch" type of scenario where our universe begins when another big classical universe ends.

[RyanJ]

Holy schnikes batman!

 

So what I'm confused about here is if this is compatible with Lee Smolin's fecund universes model or if what they're describing is more akin to our universe being born out of a "big crunch" type of scenario where our universe begins when another big classical universe ends.

 

It certainly seems like its saying a big crunch may have occured - there was no big bang, simply a rebound when the point reached some critical density... If this proves to be correct it could mean that the universe we know today may be just one in an infinate seriese of universes.

 

Lets hope we can get more details about this, its interesting stuff

 

@Martin: I do try to find interesting articles, not often does one as interesting as this turn up though.

 

Cheers,

 

Ryan Jones

[Martin]

Holy schnikes batman!

 

So what I'm confused about here is if this is compatible with Lee Smolin's fecund universes model or if what they're describing is more akin to our universe being born out of a "big crunch" type of scenario where our universe begins when another big classical universe ends.

 

superficially, if you go by the news reporter account, it is not compatible.

it is not explicitly incompatible either, just sort of tangential to Smolins cosmo reproduction scheme.

 

the reporter was not thinking about that or asking Ashtekar questions about that in the interview.

 

I just took another look at the Ashtekar article in Physical Review Letters. I see that I was wrong.

Earlier, just a few months back, he was choosing his words very carefully and not excluding either possibility.

 

Earlier, the way he was talking, the rebound could have been from a BLACK HOLE GRAVITATIONAL COLLAPSE or it could have been from a BIG CRUNCH GRAVITATIONAL COLLAPSE

both kinds of gravitational collapse are theoretically possible and so far the rebound is just from SOME gravitational collapse.

 

Now, to my chagrin, I see that what what he says is biased in the direction of a whole universe collapsing.

 

What I'd rather emphasize is that Ashtekar's analysis does not give final answers about the overall story. All his analysis says is THERE WAS A BOUNCE.

In reporting this, he really ought to leave himself lots of leeway to go in either direction.

 

In his earlier talks he spoke of the bounce as connecting to a "large classical region of spacetime" (that "large classical region" could be the region around a star that collapses to a black hole, or it could be thought of as much larger, even a whole universe)

 

There are unresolved questions either way:

 

if it was a BH collapse, then the large amount of matter and energy in our universe would need to have arisen during inflation----some inflation scenarios (perhaps all) result in a lot of matter being created when the inflaton field decays and inflation stops. this is one of the puzzling things about inflation.

Alan Guth (inventor of inflation) has referred to it as a "free lunch"---it seems to violate energy conservation in some way that General Relativity allows. this is bizarre but conceivable

 

if it was a Crunch collapse, then other questions arise. As far as is known, with the usual standard cosmological model, our universe is not expected to collapse. the prevailing mainstream "Lambda-CDM" model is not cyclic. It keeps on expanding indefinitely. So if a prior universe crunched, then it must have been different from ours in some essential detail.

 

I would think that Ashetekar's main job would be not to OVER-interpret or over-report.

if the journalist wants to say it was a Big Crunch---he does that on his own responsibility: that is the journalist's look-out.

 

But it looks to me like there has been a shift and he is at least for now coming down on the side of Crunch collapse. Just from the language he himself uses in the journal articles

 

I am confused and unhappy about this. have to read and think about it some more.

[Martin]

this thread has a link to an Ashtekar article

http://www.scienceforums.net/forums/showthread.php?t=20709

but it is written for historians and philosophers of science

 

this is probably better

http://arxiv.org/abs/gr-qc/0602086

Quantum Nature of the Big Bang

Abhay Ashtekar, Tomasz Pawlowski, Parampreet Singh

4 Pages, 2 Figures. Minor changes to match the published version in Physical Review Letters

Phys.Rev.Lett. 96 (2006) 141301

"Some long standing issues concerning the quantum nature of the big bang are resolved in the context of homogeneous isotropic models with a scalar field. Specifically, the known results on the resolution of the big bang singularity in loop quantum cosmology are significantly extended as follows: i) the scalar field is shown to serve as an internal clock, thereby providing a detailed realization of the 'emergent time' idea; ii) the physical Hilbert space, Dirac observables and semi-classical states are constructed rigorously; iii) the Hamiltonian constraint is solved numerically to show that the big bang is replaced by a big bounce. Thanks to the non-perturbative, background independent methods, unlike in other approaches the quantum evolution is deterministic across the deep Planck regime."

 

this would be written for colleagues, the wording would be the most careful

(yes that can mean dull and incomprehensible, but better that than journalistically overplayed:-) )

[Martin]

It certainly seems like its saying a big crunch may have occured - there was no big bang, simply a rebound when the point reached some critical density...

 

rebound is a good word. It never occurred to me. Sounds better than "bounce" in some contexts. I am going to adopt it.

 

I am disgusted right now with Ashtekar for evoking the idea of a series of universes. I dont think there is any real evidence for that.

 

It might have HAPPENED yes, but all he has shown us is a model that has a deterministic evolution through one rebound, from one prior collapse.

It is a big leap from there to imagining a whole series of bounces

 

Other people can party if they want. i am going to go off and sulk.

 

Save me some cake.

[RyanJ]

Its an interesting idea though, it may not have any evidence yet but its going to be interesting to see how this one turns out.

 

@Martin: I would have one question that would relate to the idea of multiple universes and multiple big crunches, if it were to have happened many times before then there are a lot of interesting questions right? Such as why this time does the universal expansion seem to be accelerating rather than slowing down...

 

As I said I look forward to hearing developments about this

 

Cheers,

 

Ryan Jones

[Bettina]

rebound is a good word. It never occurred to me. Sounds better than "bounce" in some contexts. I am going to adopt it.

 

I am disgusted right now with Ashtekar for evoking the idea of a series of universes. I dont think there is any real evidence for that.

 

It might have HAPPENED yes' date=' but all he has shown us is a model that has a deterministic evolution through one rebound, from one prior collapse.

It is a big leap from there to imagining a whole series of bounces

 

Other people can party if they want. i am going to go off and sulk.

 

Save me some cake.[/quote']

 

Don't sulk. I rely on you for good data on this because I am a believer (no proof of course) that this universe was not the only one. This is interesting and I can't wait to see how it pans out. Forget the cake.

 

Bee

[JohnB]

I will consider the awe inspiring implications as soon as my mind stops being boggled.

So if a prior universe crunched, then it must have been different from ours in some essential detail.

different from ours in some essential detail..........

[Severian]

From the article:

 

While the general idea of another universe existing prior to the Big Bang has been proposed before, this is the first mathematical description that systematically establishes its existence and deduces properties of space-time geometry in that universe.

 

That sort of statement just makes me angry. They have not "systematically establish[ed] its existence". They have shown that in certain theoretical frameworks such a scenario is possible.

[Dr. Dalek]

I have read alot of forums on subjects related to this recently. What gives

[Martin]

From the article:

 

 

 

That sort of statement just makes me angry. They have not "systematically establish[ed] its existence". They have shown that in certain theoretical frameworks such a scenario is possible.

 

Perhaps you should complain to the editor or to the journalist.

A lot of science journalism is very bad.

 

One of the co-authors has made a specialty of exploring for ways of testing QG models of the bang or "bounce"

 

different models do have different inprinciple observable "signatures", things that one might look for in the CMB

 

the guy's name is Parampreet Singh. he is one of Ashtekar's Penn State post docs.

 

the journalist COULD have interviewed Singh and gotten some careful statements about mid and longterm prospects for testing. I heard Singh give a seminar talk about this, which is online. the journalist could have listened to it.

 

but presumably the journalist knows what will sell newpapers

or bring lots of hits to the site.

 

Roy Maartens at Portsmouth is also a quantum cosmology (QC) phenomenologist---who plays the whole field, string brane loop you name it. he is smart and moderately charismatic and skeptical of everybody.

 

If you are very concerned, you could probably write to Roy and get some outrageous quote to fling at the editor.

 

However in the end I personally believe (with Singh) that they WILL find ways to test these QC models and some will be shot down---some will fail but also some may pass. And Ashtekar's just might pass.

[Martin]

I have read alot of forums on subjects related to this recently. What gives

 

basically what gives is that singularities do not exist in nature, they are places where MODELS fail

and you can sometimes fix a singularity if you find a new model

which is just as good as the old model AWAY from the singularity

but which can cope with the singularity not blow up or stop computing.

 

so it was always in the cards that eventually somebody might find an alternative to the standard model of cosmology (which is based on Einstein's 1915 Gen Rel, and Friedman's 1920s simplification of it, and which blows up at the start of expansion)

 

somebody named martin Bojowald DID find an alternative, he was a postdoc at Penn State working for Ashtekar. it was 2001. He published.

 

very little notice at that time.

 

Since then some 20 people have gone over the same ground and published a lot more papers about it and it has been discussed at a lot of conferences.

 

Now by the grace of the Almighty, a major scientist, Ashtekar, with a world reputation, has decided that the world is ready to hear about this. Which the quantum gravity/quantum cosmology community has be researching and discussing for 5 years ever since Bojowald's original paper.

 

so what gives?

a small shift in the way the bang (the start of the present expansion phase) is understood, which began in 2001 with the work of a nice young German fellow

 

I picked my SFN name "Martin" to honor him when I became a member here.

 

in case you are interested here are Martin's papers

http://arxiv.org/find/grp_physics/1/au:+bojowald/0/1/0/all/0/1

and here is the key 2001 one

http://arxiv.org/abs/gr-qc/0102069

Absence of Singularity in Loop Quantum Cosmology

 

BTW there are several OTHER cosmology models in which the classical singularity does not show up and something like a "bounce" or rebound from a collapse phase occurs. this will have to be sorted out observationally. the different models predict slightly different stuff that can in principle be observed in the present if you decide to look for it. Bojowald just happened to be working within the context of a certain model which has gained a fair amount of prominence in the years since 2001 but is still far from being a majority or consensus model (!) far from it. It doesnt even use strings. Comparatively it is a rather direct unimaginative straightforward way of quantizing the standard cosmology model. No extra dimensions and very little additional structure. this is not something you have to jump thru hoops about. If you look at the paper you may get the flavor of it.