What happened before the Big Bang? (professional journal style)

[Martin]

Bojowald's What happened before the Big Bang? article in the August 2007 issue of NATURE PHYSICS is now available to non-subscribers

http://npg.nature.com/nphys/journal/v3/n8/index.html

During August it was accessible only if you paid, but they just made it free.

 

The link gives the TOC for the August issue.

Scroll halfway down the page to where it says LETTERS and click on the PDF for the Bojo piece.

 

Or get the article directly in HTML

http://npg.nature.com/nphys/journal/v3/n8/full/nphys654.html

 

In this piece Bojowald derives (in the context of his quantum cosmology model) some definite limitations on what can be known about the universe prior to the beginning of expansion. Even though the singularity is no longer there, in the Loop Cosmology model, a Heisenberg-like principle of indeterminacy limits knowledge in some (but not all) respects.

 

Bojowald was just awarded the Xanthopoulos prize for his work in quantum cosmology. This was presented at the international conference of General Relativity and Gravitation (GRG) people that is held every three years.

In past years (1993 and 2001) famous string theorists have been awarded the prize. I think it is nice to see Bojowald (and Thiemann who was honored along with him) get the recognition----they do nonstring quantum gravity.

 

I suppose part of the news about the Nature Physics article is that it is unusually prominent among peer-reviewed journals specializing in physics.

It is a subsidiary of the weekly NATURE, and it has an unusually high rate of citations per article published. It's a good place to publish---prestige and visibility-wise. Bojowald normally publishes in Physical Review Letters (PRL) and in Physical Review series D (PRD). These are good solid journals but his piece in Nature Physics caused a bigger splash.

 

===commentary on the Bojo article===

 

Carlo Rovelli is one of the founders of Loop Quantum Gravity and the author of the book Quantum Gravity published in 2004 by Cambridge University Press.

 

He had some comments on Martin Bojowald's article in the August issue of NP.

Here is Rovelli's commentary, just over one page

http://npg.nature.com/nphys/journal/v3/n8/full/nphys690.html

 

Here is a sample:

 

Science has frontiers; sometimes these frontiers move. One of the most impressive of science's frontiers is the Big Bang, and now a quantum theory of gravity — loop quantum gravity — is providing equations with which to explore it. Although these equations are still tentative, and rely on drastic approximations, they introduce a definite method of exploration, and are capable of describing the Universe not only close to the Big Bang but also beyond it. It is in this context that Martin Bojowald reports, in this issue, on the possibility of a peculiar limitation to our ability to observe fully the 'other side' of the Big Bang — whatever that expression might mean (Nature Phys. 3, 523–525; 2007).

[Reaper]

Interesting. We may yet be able to actually describe what happens before the big bang.

 

So, from my understanding of the article, does this model here suggest that the universe is constantly expanding and contracting in (virtually)never ending cycles?

And if so, would it even be possible to determine the properties of the "previous" universe? It seems to me that this theory is suggesting that at the so-called singularity, all information about the state of the universe before and after the big bang either pinches off or is suppressed somehow, in which case we are still back at the question "What did happen at or before the Big Bang?"

[BenTheMan]

Lockheed---this is an interesting quesion. I think I have seen some research into relic gravitational waves. If you think about it, if the big bang is really a ``big pinch'', then the only things that can propogate across would be gravitational waves, so I'm not sure how much we could learn about a previous universe.

[Martin]

Interesting. We may yet be able to actually describe what happens before the big bang.

Yes, quite a number of people are working on this now. Bojowald is the one with the most highly cited recent papers, and he has attracted bunch of young researchers into the field. Ashtekar is another major figure. It is getting hot as a field of research.

 

So, from my understanding of the article, does this model here suggest that the universe is constantly expanding and contracting in (virtually)never ending cycles?

 

I wouldn't extrapolate so far. Loop cosmology is one quantum cosmology (QC) model. Much of current work is aimed at extracting predictions from it of things that future experiments will be able to observe (e.g. in the CMB as it is measured more and more precisely, in the expansion history as it is determined more precisely at greater redshifts).

 

If the Loop QC model is RIGHT---or if it passes its first tests of prediction against observation and gets some credibility---then one can start talking about conditions before the bounce.

 

but there are a lot of issues to investigate simply about what was immediately before the bounce (assuming Loop model is right, which it might not be)

So even if you confirm the idea of a bounce---a prior contracting phase---you still don't want to jump to conclusions about where this contracting phase came from. My attitude would be cautious step by step. I wouldnt assume a "cyclic" picture. At that point all it would say is that somehow there was a contracting phase of unknown cause.

 

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

an important point is that in Bojowalds model it is not that ALL information is lost in the bounce. It is that certain specific information is lost and he can say precisely what kind of information. His model permits a certain amount of extrapolation back in time. (again assuming the model is verified by its predictions of what we can observe in our present surroundings)

 

 

And if so, would it even be possible to determine the properties of the "previous" universe? It seems to me that this theory is suggesting that at the so-called singularity, all information about the state of the universe before and after the big bang either pinches off or is suppressed somehow, in which case we are still back at the question "What did happen at or before the Big Bang?"

 

the model permits some extrapolation back in time to determine prior conditions---but not full 100percent.

 

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

 

there is a common misconception that you cant tell anything about before bang because you cant receive any SIGNALS from it.

but that is not how extrapolating back in time works.

To take an analogy, the oldest light we see, the CMB, dates from the time of last scattering about 380,000 years before bang when temperature was about 3000 kelvin.

 

Therefore, just using signals from the past, so far we cannot "see" back past 380,000 years, because no signals. (In future we will have primordial neutrinos but that is another issue.)

 

HOWEVER we still extrapolate back to the first second from start of expansion, and further, because we can use TRUSTED MODELS that can be and have been frequently checked against observation in the present.

Like we cannot "see" back to the formation of hydrogen, helium, deuterium nuclei because we cannot yet receive signal from that time.

But we can "know" back to that time because we can test GR in present and GR tells us expansion history and temperature and density.

And then experimental nuclear physics tells us about the nuclear reactions at that temperature etc etc.

 

What we want from Bojowald and people like that is a QC model that, on the one hand is TESTABLE against new observations of largescale structure, CMB, and expansion history---things we can measure---and on the other hand makes the transition back to the prior contraction phase allowing us to extrapolate back in time to before bang. It has to become a trusted model like the classic GR we use to get back to the first second or so. the scientific progress here is exciting to watch but requires patience.

[spider1]

If there is no future contraction then wouldn't everything remained tiny particles just floating away from the initial big bang. The contraction seems to be the only model that gives a clear explanation of gravity. You cant roll dough on water.

[pioneer]

Like we cannot "see" back to the formation of hydrogen, helium, deuterium nuclei because we cannot yet receive signals from that time.

 

This has a conceptual problem. If you were sitting on the formation of hydrogen, when this energy was in existance, even if our reference was expanding rapidly, the energy will still go faster. The speed of light would still be the same even in the expanding reference of the original universe. The only place one would have a shot at seeing, this energy, is at the outer edge of the matter, before the energy heads off into empty space.

 

Maybe I am missing something. The matter traveled faster than energy during the expansion, without requiring infinite energy to do so??? It sort of like shining a flashlight in a relativistic ship and beating the light to the end of the ship. Without adding new laws of physics, I would bet on the light, everytime.

[Martin]

Pioneer, I will try to reply. but if I dont understand your question and don't give a suitable response, please rephrase your question.

 

My response is that we CAN see back to a time when neutral hydrogen formed out of partially ionized hydrogen-----the fairly opaque 3000 kelvin gas.

That is where the CMB comes from. from a time around age 380,000 years when the plasma settled down and became neutral and therefore transparent.

 

the light from that epoch DOES get to us.

 

note that it is not OUR hydrogen that we see forming, it is the other guy's, we see an event that happened here too (we can infer) but we see it far away and the light has taken 13 billion years to get to us.

 

there is no question of the HYDROGEN atoms traveling to us and outracing the light. when we look at CMB microwaves we see light coming to us from stuff crud hydrogen etc that is still very far away (and getting farther). So nobody outraced the light!

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

 

the reason we dont also see light coming from crud that is in the process of forming stable protons and neutrons, is that THAT LIGHT WAS SCATTERED AND BLOCKED by the partially ionized hot stuff that filled space before 380,000 from start. there was light, but it couldnt get through!

 

probably some day we will have neutrino telescopes able to detect the Cosmic Neutrino Background of neutrinos coming from that era. and that will be like the CMB and we will be able to study that era with the help of signals

 

but it will still not be a case of the crud outracing the neutrinos. it will be the other guy's protons and neutrons and deuterium nuclei etc that we see forming. THEY didnt come to us, outracing the neutrinos. Only the signal from them will be coming.

 

here is WIKEPEDIA about the CNB cosmic neutrino background

http://en.wikipedia.org/wiki/Cosmic_neutrino_background

its temperature is expected to be around a millikelvin* if and when we are able to detect and measure

just like the temperature of the CMB has been measured at 2.7 kelvin

 

I'm oversimplifying and equating the era of formation of protons and deteriums with the moment of release of the CNB but they happened very close to the same time if not technically at exactly the same instant. CNB dates from about 2 second age.

2 second from start of expansion IIRC.

 

*Wikipedia has an estimate that amounts to about a tenth of a millikelvin, rough order of magnitude, depending on what the masses of the neutrinos turn out to be. this is an unfamiliar topic for me----mention it just to illustrate that it may well be possible to get signal which is older and from farther than the CMB. so push boundary of observable back some

 

gravity waves too, might be a way of seeing further back.

[bascule]

an important point is that in Bojowalds model it is not that ALL information is lost in the bounce. It is that certain specific information is lost and he can say precisely what kind of information.

 

From my gut feeling (which is pretty much all of those who don't learn the underlying math are forced to go on) I really like models that incorporate some pre-bang temporal (and thus spatial/informational) context as an explanation for the non-uniformity of the big bang. I just have considerable trouble attributing it to quantum fluctuations (alone), but then again I have trouble accepting (in my "gut", mind you) that quantum indeterminacy cannot be attributed to hidden variables, even when it's been experimentally demonstrated to the contrary. I guess you can group me with the creationists in that respect *shrug*

[Mr Skeptic]

The Big Foreplay.

 

While one might expect the laws of conservation (or mass-energy, charge, momentum, angular momentum) to hold, they have not been tested at these scales, and it is unclear how these things came to be from whatever was there before.

[Martin]

The Big Foreplay.

 

While one might expect the laws of conservation (or mass-energy, charge, momentum, angular momentum) to hold, they have not been tested at these scales, and it is unclear how these things came to be from whatever was there before.

 

the aim is to get a model of spacetime and matter that fits the data as well or better than the current setup

and where you have the option of running it back in time---on a business as usual basis---without having it blow up.

 

and also the same model should be one that doesn't boggle at black holes, with a good fit to bursts of whatever-type radiation we can detect being released during stellar collapse

 

so the idea is to have a testable model which fits what we can see and measure-----and which ALSO doesn't have the irritating habit of blowing up at high-density events. In a way it is just routine science. You always want to improve theories so as to eliminate singularities (places where they don't compute properly)

 

Then you, if you want, can always object and say "no no it can't be that theory, it has to be something else! the laws have to change in some way we can't fathom! it is impossible to run a business-as-usual model back past this particular bump, my intuition tells me so!"

 

And that is fine. Everyone is free to doubt models. theories can never be proven, only disproven.

 

but it looks to me as if progress towards a quantum gravity theory (basically a quantum dynamics of matter and geometry) is going along at a good clip just now. so I expect some kind of improvement of GR, leading to an improvement of Cosmology---with the expected elimination of singularities---before terribly long. and to have it predictive enough to test against present available astronomical data.

[Luminal]

Should I assume Martin Bojowald is not the same Martin posting in this thread?

[Martin]

Different Martin. I've exchanged email several times with him. Guess I'd call myself a fan. Certainly not the guy himself!

[Realitycheck]

I'm not a big fan of bounce theory, but who really knows. Martin, you recently stated that WMAP info is more conclusively stating that the universe is more likely not in bounce mode, and more into infinite expansion, right? This concludes that this report offers more about question marks and quantum uncertainty and things that nobody really knows than anything, right? (Though I missed a bunch of stuff mixed in with all of that math.) I know that he got around locking himself into any one corner, such as using a mandatory Bounce, but what does it mean, in light of the latest evidence?

 

Without a bounce, we have all of this superhot stuff boiling about before the Big Bang, but no idea what it is doing there, why it is there, nor why it is so condensed and hot. Any ideas to offer?

[kaneda]

This assumes that there was a big bang. There are many problems with the big bang idea, which have been filled in with fudges. Even some professional astronomers doubt the BB happened (27 wrote an open letter to New scientist some years back detailing some of the problems with it and why they did not believe in it).

[swansont]

This assumes that there was a big bang. There are many problems with the big bang idea, which have been filled in with fudges. Even some professional astronomers doubt the BB happened (27 wrote an open letter to New scientist some years back detailing some of the problems with it and why they did not believe in it).

 

And this is not the place to raise your objections to it. Do so in another, more appropriate, thread.

[Martin]

I'm not a big fan of bounce theory, but who really knows. Martin, you recently stated that WMAP info is more conclusively stating that the universe is more likely not in bounce mode, and more into infinite expansion, right? ...

 

Not sure what you mean by "bounce mode".

 

Infinite expansion is quite consistent with modeling the big bang as the result of the collapse of a prior region.

 

Picture an infinite hour-glass shape if you want.

 

To answer your question, "you recently stated that WMAP...[indicates]...the universe is more likely not in bounce mode, right?"

the answer is: wrong, I did not state this.

 

And it would be incorrect to say that. The recent WMAP data is consistent with a big bounce which leads to indefinite expansion.

 

Please don't put words in my mouth that I didn't say, Agent.

Try asking questions directly, instead of making a false statement and then putting a ", right?" at the end. Like saying "Pigs have wings, right?"

or "You recently stated that pigs have wings, right?"

[Realitycheck]

Forgive me for sounding abrasive or misintrepreting your statements, but the impression that I have is that either the universe bounces or it expands indefinitely, unless of course it already bounced once but is expanding indefinitely on this particular occasion, which, as far as I can tell, is unknowable. Even if the universe is prone to bounce back into cycles of expansion and contraction, it still had to start somewhere.

[Martin]

Forgive me for sounding abrasive or misintrepreting your statements...

 

Apology accepted.

 

...either the universe bounces or it expands indefinitely...

 

or it does both. The two are certainly compatible!

 

Before the big bang is a new area of cosmology research. There is lots to find out. I should probably get some links. It is too early to favor one picture over another. There is a 600 page book on this coming out this year, with about 20 authors. Beyond the Big Bang, edited by R. Vaas. German academic publisher.

 

At this point it would be intelligent not to try to second guess----especially if you don't know anything about it. The overall field, if you want to do some reading, is called quantum cosmology.

 

Here is a keyword search at the Stanford database for all the quantum cosmology research published since 2005, ordered by citation count (most important or highly cited papers listed first)

http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=find+k+quantum+cosmology+and+date+%3E+2005&FORMAT=WWW&SEQUENCE=citecount%28d%29