What Do Canonical Quantum Gravity Models Tell Us About the Big Bang?

In summary, most people here agree that in order to understand what happened at the big bang, we most likely need a quantum theory of gravity. There are various models of cosmology that attempt to sidestep this requirement, but looking at quantum gravity seems to be the mainstream approach. One potential approach is string theory, which has been suggested to be supported by evidence from the big bang. Another possible approach is the LQG model, which is based on the idea that the big bang resulted in a 'bounce' of the universe. There are several other possible approaches as well, including acoustic metric models, causal dynamical triangulation, causal sets, group field theory, Hořava–Lifshitz gravity,
  • #1
skydivephil
474
9
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.
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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  • #3
Hi thanks for that , I don't have this book, if you have any comments on what the canonical QG implies for the big bang, would love to hear it.
 

What is quantum gravity?

Quantum gravity is a theory that attempts to unify the principles of quantum mechanics and general relativity in order to explain the behavior of matter and energy at very small scales, such as the subatomic level, and at very large scales, such as the universe as a whole.

What is the current understanding of quantum gravity?

Currently, quantum gravity is still a theoretical concept and has not been fully proven or accepted by the scientific community. However, many physicists believe that it is necessary for a complete understanding of the universe and are actively researching and developing theories to explain it.

What is the relationship between quantum gravity and cosmology?

Cosmology is the study of the origin, evolution, and structure of the universe. Quantum gravity is a key element in understanding the fundamental laws of the universe and is therefore closely related to cosmology. It is believed that quantum gravity plays a crucial role in the early stages of the universe and may hold the key to understanding the Big Bang.

What are the challenges in developing a theory of quantum gravity?

One of the main challenges in developing a theory of quantum gravity is reconciling the principles of quantum mechanics and general relativity, which are currently incompatible. Additionally, there is a lack of experimental evidence to support any particular theory of quantum gravity, making it difficult to test and validate these theories.

What impact could a successful theory of quantum gravity have?

A successful theory of quantum gravity would have a profound impact on our understanding of the universe and could potentially lead to new technologies and advancements in fields such as space exploration and quantum computing. It could also help to bridge the gap between our current understanding of the universe and the mysteries that still remain, such as the nature of dark matter and dark energy.

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