Most people here I think will agree that in order to understand what happened at the big bang we most likely need a quantum theory of gravity.(adsbygoogle = window.adsbygoogle || []).push({});

There do appear to be models of cosmology such as CCC or Baum/Frampton that seem to try and sidestep this requirement, but looking at quantum gravity seems to be the mainstream approach.

I would like to keep this post open to have a directory for what different approaches to quantum gravity imply about what happened at the big bang. The main approaches I have listed below with articles that are as easy to understand as I can find regarding what they predict happened 13.8 bio years ago

String/M theory:

Pre big bang model of Veneziano

www.cyberastronomo.org/LinkClick.aspx?fileticket

Bounce model also from Veneziano

http://arxiv.org/abs/hep-th/0312182

Ekpyrotic model of Steinhardt and Turok

http://wwwphy.princeton.edu/~steinh/npr/

LQG:

Big bounce

http://phys.org/news126955971.html

But according to the Wikipedia page there are may other approaches to quantum gravity other than the main two (string theory and LQG). Can anyone fill in the blanks as it were with what they predict and any useful articles? I have made a start with Horava Liftshitz gravity. But more are welcome.

Acoustic metric and other analog models of gravity

Asymptotic safety in quantum gravity

Causal Dynamical Triangulation[41]

Causal sets[42]

Group field theory[43]

Hořava–Lifshitz gravity

Matter bounce

http://arxiv.org/abs/0904.2835

MacDowell–Mansouri action

Noncommutative geometry.

Path-integral based models of quantum cosmology[44]

Regge calculus

String-nets giving rise to gapless helicity ±2 excitations with no other gapless excitations[45]

Superfluid vacuum theory a.k.a. theory of BEC vacuum

Supergravity

Twistor models[46]

Canonical quantum gravity

E8 Theory

Geometrodynamics

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# Quantum gravity and cosmology

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