Time before and during the Big Bang

[Martin]

(classical 1915 General Relativity breaks down and gives an unphysical result called a "singularity"---this is not a sign of a break in nature, but rather a failure of the theory. The quantized theory reproduces Gen Rel as its classical limit away from the former singularity, but does not break down. Time evolution continues from a prior contracting classical regime through the former singularity to an expanding classical regime.)

 

A good way to catch up on current QG thinking about time evolution before and during the Big Bang is to watch the video of Abhay Ashtekar's talk, given 14 October at the Albert Einstein Institute (MPI-Potsdam).

 

Ashtekar is a world authority on classical and quantized Gen Rel. His abstract is here

http://loops05.aei.mpg.de/index_files/abstract_ashtekar.html

 

Besides the summary, it has two links one for the video of the recorded talk

http://loops05.aei.mpg.de/index_files/Video/ashtekar.wmv

 

and the other for the slides/lecturenotes

http://loops05.aei.mpg.de/index_files/PDF_Files/ashtekar.pdf

 

You will find Ashtekar is rather careful to qualify what he says, and to indicate uncertainties and questions which remain open. Listening to him is a way to get a feel for how this area of quantum cosmology is advancing.

Much that is being discussed now is preliminary, but quite interesting, or so I think.

 

If you would like to see the program for the whole October conference it is here

 

http://loops05.aei.mpg.de/index_files/Programme.html

 

there are also video recordings and PDF files of the slides for many of the other speakers available for download from this page

[Bettina]

I'm watching and listening but his accent makes it hard to get every word...and the cameraman should take lessons.

 

I'm still listening...

 

Bettina

[Martin]

as a shortcut, in case anyone else is into this:

 

before you start watching the video, look at his slides #11, 12, 13, 14

 

Slides #11 and 12 are PICTURES of the contraction, the bounce, the re-expansion. in particular slide #12 is a QUANTUM WAVE FUNCTION for the simple model (homogeneous isotropic universe with matter)

 

so it shows a schematic of the bounce in a simplified case

 

Slide #13 is RESULTS from the analysis and computer modeling that Ashtekar and coworkers did

 

Slide #14 is tentative CONCLUSIONS that they draw

 

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

 

then when you download and watch the video, you can FAST FORWARD until you see slides #11 and 12 up on the screen, and then slow down and watch it. That way, if you want, you can skip all the beginning and get to the interesting conclusions.

 

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

 

my compliments to you Bettina, it takes admirable determination for a Highschool Senior, I think, to be essentially walking into a room that is all experts, specialists in Quantum Gravity, and sit down and listen and try to understand. I will try to help out some. I know it is not easy to follow---even if his Indian accent werent a problem!

[sunspot]

Space/time are often said in the same breath but do they always exist proportionally together? For example, a black hole is not a point in space-time but only a point in space with an extension of time since it last longer than an instant while occupying only a point in space. The reverse of a black hole would have an instant of time within extended space, which sounds like a rapid expansion in distance without time. It is sort of like space expanding without time.

[Martin]

...For example, a black hole is not a point in space-time but only a point in space with an extension of time since it last longer than an instant while occupying only a point in space. The reverse of a black hole would have an instant of time within extended space, which sounds like a rapid expansion in distance without time. It is sort of like space expanding without time.

 

Hi sunspot,

sounds like you are especially interested in black holes. You might be able to FIND A THREAD at SFN that is specifically about black holes. The search engine might help. That way you could find out what other SFN posters have to say that relates to your questions.

 

Or you could start your own black hole thread.

 

I guess i would recommend looking in Wikipedia first, and then at the Black Hole FAQ at John Baez site. When time permits, maybe I can get you some links.

 

the main point in this thread is that IF ONE ONLY HAD VINTAGE 1915 GEN REL, then one might think that time stops at the big bang, because the theory broke down there and put out physically meaningless results (a "singularity")

 

but it isnt automatic that a theory HAS to break down right at that moment, in fact more modern models do NOT break down

 

so AS FAR AS WE KNOW time extends back before big bang

we have no rigorous proof of this but we have NO CONCLUSIVE EVIDENCE THAT IT DOESN'T

 

That is what this thread is about, and also it is about Abhay Ashtekar's talk, which you can watch the video.