Bojowald in July Nature Physics, probing before bigbang with quantum cosmology

[Martin]

http://www.science.psu.edu/alert/Bojowald6-2007.htm

 

he's making the rounds of major international conferences now

 

his article on "Before the Big Bang" will be in the July issue of Nature Physics online

and then in the August hardcopy issue.

 

the press release (above link) goes into quite a lot of detail, but it would still be a good idea to try to get ahold of the actual article

[foodchain]

I knew it!

 

JK, but wow, a brave new world.

[Martin]

a science information site called Eureka Alert put the release out in a format that is better for printing on just two sides of a sheet of paper

http://www.eurekalert.org/pub_releases/2007-07/ps-whb062907.php

 

 

the actual online article is here

http://www.nature.com/nphys/index.html

but it requires a subscription

 

I won't know what to make of it until some of the dust settles.

I think it might be interesting.

He has identified two complementary quantities around the bounce---

with an uncertainty tradeoff (like in simple quantum mechanics is a tradeoff between making precise the position and momentum of a particle---the two quantities are called complementary----you can only buy knowledge about one by paying with uncertainty about the other)

 

He seems to have uncovered a hint of some kind of complementarity between the Before-bounce and After-bounce

in some department (maybe it is total mass or energy, I am not sure)

the more precisely you nail down the After quantity the less certainty there is about the Before quantity.

 

this could, of course, be wrong. he is developing a certain quantum cosmology model and following out the consequences

 

other people are working on finding ways to test the model.

still a ways to go. but interesting...

[[Tycho?]]

While interesting, I'd have to get some sort of quantifiable evidence of loop quantum gravity before I put too much stock in something like this.

[Martin]

Lee Smolin has weighed in at Sean Carroll's blog (Sean has been having fits about Bojowald's article in Nature Physics)

http://cosmicvariance.com/2007/07/02/against-bounces/#comment-294116

 

There is an article about the Loop cosmology bounce in Physics World

that is a lot better journalistically than the earlier press-release-based things.

The reporter interviews Bojowald directly rather than relying on Penn State PR department quotes. Tries for clarity and balance

http://physicsweb.org/articles/news/11/7/1/1

 

they give a current snapshot of Bojowald, from the Penn State physics website

He looks like a cousin of mine, back when we were both younger

http://www.phys.psu.edu/people/display/index.html?person_id=417

same expression and same dorky round plastic glasses frames too.

[lucaspa]

http://www.science.psu.edu/alert/Bojowald6-2007.htm

 

he's making the rounds of major international conferences now

 

his article on "Before the Big Bang" will be in the July issue of Nature Physics online

and then in the August hardcopy issue.

 

the press release (above link) goes into quite a lot of detail, but it would still be a good idea to try to get ahold of the actual article

 

I see you are still cheerleading Bojowald.

 

As I read the article, a new question pops up.

 

Bojowald is saying that prior to the Big Bang (or Big Bounce as he calls it) was a contracting universe. This universe contracted down to the very small and very dense state at the Bounce, then shows up as our expanding universe.

 

So, now where and how would you get a very large universe so that it can contract? That's even, in many ways, more miraculous than the BB. Our universe isn't going to contract, so either our universe is the end of the cycle of expanding/contracting universes (very unlikely) or somehow there was already a completely formed universe prior to this one. The BB and its aftermath at least gives us a series of causes to get a universe the size it is now. But the prior universe that Bojowald is saying is there doesn't have that.

[lucaspa]

Lee Smolin has weighed in at Sean Carroll's blog (Sean has been having fits about Bojowald's article in Nature Physics)

http://cosmicvariance.com/2007/07/02/against-bounces/#comment-294116

 

And it appears that many of Sean's criticisms are valid. I find these 2 comments by Sean and Smolin interesting:

 

Sean "Lee, I never expressed doubt that the formulation was well defined, only that there’s any reason to expect it to relate to the real world. At least, no such reason is given. You can’t restrict to the spatially homogeneous case, and then claim there is no fine tuning. That is an infinite amount of fine tuning, which needs to be justified.

 

I seem to be saying the same thing over and over, but I’ll try one more time. Unlike cosmologies in which the Big Bang is a boundary condition, bounce cosmologies feature a pre-bounce contracting phase. You need to tell me what happens during that phase, and why. Are there perturbations that are in their growing mode as they approach the bounce? If no, why in the world not? Generic gravitational collapse is expected to be highly non-linear and inhomogeneous, what is so special about this? And if yes, why don’t the perturbations grow and destroy the smoothness? Why in the world would we expect a homogeneous expanding cosmology to emerge from the other side?

 

These are not annoying technical issues that can be addressed later. They are the Whole Big Problem that must be confronted by any attempt to honestly address the issue of initial conditions."

 

Smolin: "I agree with you, the LQC models are only models, and the big question is if the singularity is replaced by a bounce also in the full quantum theory. This is under investigation, there are arguments but no firm results yet. And I also agree that it will be very interesting to know what happens to inhomogeneous degrees of freedom during the bounce.

 

One should be cautious of reasoning that is too classical. One can see from the LQC models already that near and during the bounce the geometry is quantum and far from classical. There are also arguments, due to Markopoulou, that near Planck temperatures there is a phase transition to a non-geometric phase where locality is lost completely, see gr-qc/0702044 for more on this, hep-th/0611197 for a model of the phase transition and astro-ph/0611695 for possible consequences for CMB spectra. If this is the case then inhomogeneities may be lost during the phase transition for the same reason that you can melt down a sculpture and then get a homogeneous hunk of metal that when it cools again. "

 

Smolin gives a possible answer to the inhomogeneities, but these appear ad hoc and not part of Bojowald's original work. I like that "if this is the case then homogeneities may be lost ..." As I read this it is even more tentative than the usual scientific tentativeness. Not only may Markopoulou arguments not happen but, even if they do, the inhomogeneities remain!

 

Bojowald has a lot of work to do yet. Remember, Smolin is the main proponent of LQG. His support is very lukewarm considering that.

[Royston]

Bojowald is saying that prior to the Big Bang (or Big Bounce as he calls it) was a contracting universe. This universe contracted down to the very small and very dense state at the Bounce, then shows up as our expanding universe.

 

Lucaspa, could you please quote where it says this in the article...all I can see is collapsing 'state', not collapsing 'universe.'

 

EDIT: Doh, nevermind...it's on the first paragraph.

 

EDIT2: So my question is, is the first paragraph misleading i.e the collapsing state is considered to be our universe, rather than a whole universe collapsing i.e the interior of a blackhole is considered as the collapsing beginnings of our universe ? (Physicsweb article)

[Martin]

Has anyone read the actual article in Nature Physics?

 

http://www.nature.com/nphys/index.html

 

It is in the current (July 2007) online issue and will be available in next month's (August) hardcopy.

[Royston]

Unfortunately I'm not subscribed to Nature, so I can't access the article. Also, I'm very under the weather today, so ignore my previous rambling.

[Martin]

... I'm very under the weather today, so ignore my previous rambling.

 

Sorry to hear that.

As for the availability of the article, it should be at university and college libraries by early next month----the August paper edition of Nature Physics has the Bojowald article (the online edition does advance publication).

 

So it should be on the shelves in a few weeks.