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I always wondered what the description of Big Bang would be like in string theory.

How is it different from QFT version of Big Bang?

Thanks.

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There isn't a QFT version of the Big Bang. QFT takes us back to the electroweak symmetry breaking, which was about 10$^{-12}$ seconds after the big bang. What happened before then isn't known, though hopefully the LHC will tell us soon. Incidentally http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang is an interesting related article.

String theory doesn't have a lot to say about the Big Bang at the moment. This area is known as string cosmology, but it's all pretty speculative at the moment. Googling for "string cosmology bounce" finds a couple of books on Google books, e.g. this book and this review. I don't know enough about the subject to know how this work is regarded.

Loop Quantum Cosmology predicts the universe did not shrink to a singularity at the Big Bang, but instead reached a minimum size then bounced. So winding time back you'd see the universe shrink down then expand again. Again, most of us would regard this as pretty speculative.

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It's not much more clear in loops what cosmology looks like, the bouncing idea is strange. But inflation is all long before the electroweak breaking, and it's experimentally established. –  Ron Maimon May 1 '12 at 22:00

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