Comparing Candidate Theories of Quantum Gravity

In summary, this person is looking for an introduction to quantum gravity theories so that he can decide which one to pursue further. He recommends a book called "Introduction to Quantum Effects in Gravitational Fields" which is not about quantum gravity theories themselves, but about Hawking radiation and related effects.
  • #1
Bertin
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Hi, you all,

I have been for a couple of semesters interested in quantum gravity as a problem, but truth is I never have been properly introduced to any of the candidate theories. Actually, there are multiple candidates and I would like to compare them. The question then is the following: do you know of any monograph or small set of articles I can read to get a impression of the main ideas and "philosophy" behind each of the most common theories, in order for me to find the one that pleases me more? Despite how useful it is for other things, I really don't like using Wikipedia in this case.

Thank you in advance!
 
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  • #5
Bertin said:
Is this book "approach independent"? Why do you recommend it?

This is a wonderful book, but it is not about theories of quantum gravity, it is about Hawking radiation and related effects, e.g., in expanding spacetimes. Standard QFT is about quantum fields in the a fixed spacetime that is Minkowski spacetime. This book is about quantum fields in other fixed (non-quantized) spacetimes. In my opinion this book is the best short, pedagogical introduction to Hawking radiation and related effects.
 
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  • #7
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  • #8
malawi_glenn said:
There are plenty of other useful references in the wiki article.
Ok, thank you very much. I'll look further into the references there, sorry for not having checked better!
 
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FAQ: Comparing Candidate Theories of Quantum Gravity

What are the main candidate theories of quantum gravity?

The main candidate theories of quantum gravity are String Theory and Loop Quantum Gravity (LQG). String Theory proposes that the fundamental particles are one-dimensional "strings" rather than point particles, and it incorporates gravity through vibrating strings. Loop Quantum Gravity, on the other hand, attempts to quantize space-time itself, suggesting that space-time has a discrete structure at the smallest scales.

How do String Theory and Loop Quantum Gravity differ in their approach to unifying general relativity and quantum mechanics?

String Theory unifies general relativity and quantum mechanics by positing that all particles are different vibrational states of fundamental strings. It requires additional dimensions beyond the familiar four (three spatial and one temporal) to be consistent. Loop Quantum Gravity does not introduce extra dimensions but instead focuses on quantizing the fabric of space-time itself, using a network of loops to describe the quantum state of space-time.

What are the key challenges faced by String Theory and Loop Quantum Gravity?

String Theory's key challenges include the lack of experimental evidence and the difficulty of making testable predictions due to the theory's complexity and the requirement of additional dimensions. Loop Quantum Gravity's challenges involve mathematical difficulties in solving the equations exactly and the problem of connecting its predictions to observable phenomena in the low-energy regime where classical general relativity is well-tested.

What experimental evidence is there to support or refute these theories?

As of now, there is no direct experimental evidence that definitively supports or refutes either String Theory or Loop Quantum Gravity. Both theories remain largely theoretical constructs. Efforts are ongoing to find indirect evidence, such as through the study of black hole entropy, cosmic microwave background radiation, or potential quantum gravitational effects at very high energies, but conclusive results have yet to be achieved.

How do these theories impact our understanding of black holes and the early universe?

Both String Theory and Loop Quantum Gravity offer insights into the nature of black holes and the early universe. String Theory suggests that black holes could be described by D-branes and offers a framework for understanding black hole entropy. Loop Quantum Gravity provides a potential resolution to the singularity problem in black holes and the Big Bang, suggesting that space-time may be quantized and that singularities are avoided. These insights could lead to a deeper understanding of the fundamental nature of the cosmos.

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