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Questions tagged [quantum-gravity]

Any of the various explanations of gravity as a quantum theory, including string theory and loop quantum gravity.

Any of the various explanations of gravity as a quantum theory, including string theory and loop quantum gravity. NOT to be confused with .

A requirement of quantum gravity springs from the fact that classical gravity and quantum matter cannot go along together, due to the Einstein Field Equation $G_{\mu\nu}=\frac{8\pi G}{c^4}T_{\mu\nu}$.

However, quantising gravity in the traditional way, leads to a non-renormalisable theory.

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When periodic solutions are combined with timelessness, do we get closed timelike curves?

In quantum gravity, ADM wavefunctional solutions have to satisfy the Wheeler-DeWitt equation. This leads to timelessness. What happens if we have a time periodic solution? In classical general relativity, a time periodic solution just means that and…
user1902
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What specifically does the phrase "continuum limit" mean?

I'm interested in the meaning of the phrase "continuum limit" specifically as it is often used in expressions relating to the ability of a quantum gravity theory to recover GR in the continuum limit. I believe I understand the meaning but want to…
inflector
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Does a UV completion of gravity necessarily need to be so drastic as String Theory or LQG?

First of all I, it is my understanding that the problems one encounters with the non-renormalizability of gravity are very similar (if not the same) as one encounters in any non-renormalizable theory. As long as you are doing your calculations…
DJBunk
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Is it possible that there is no theory of quantum gravity?

{{Under Construction}} Short question: What published works and what research groups are investigating the possibility of non-existence of gravity at quantum level? Long question: I am no physicist, but of what I read and understand of the…
lvella
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Status of Teleparallel Quantum Gravity

There are several approches to incorporate torsion into a theory of gravity. According to this article, requiring a consistent coupling to Dirac fields leaves us with the Einstein-Cartan approach or the rules of general relativity. The latter can be…
Christoph
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On fluctuations of the gravitational potential?

In the book "Gravitation", written by Charles W. Misner, Kip S. Thorne, and John A. Wheeler, in § 43.4, p.1192 "Fluctuations in geometry", and in § 44.2, p.1200, by analogy with electrodynamics, the following formula (43.29) is obtained for the…
Alexander Klimets
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Is the Causal Set Theory a QFT of gravity?

It's hard for me to tell if the Causal set theory is a quantum field theory of QG. There really isn't that much information on the subject.
user164839
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Does the universe need Quantum Gravity?

A lot of supporters of string theory say that it has to be right because the quantum gravity is necessary for the universe, is this true? Does the universe need quantum gravity?
user86072
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What specifically are the measurements that correspond to fixing the infinite number of counterterms in quantum gravity?

I understand that quantum gravity is nonrenormalizable because there are an infinite number of counterterms. In QED the counterterms correspond to the loop corrections to the vertex function as well as the electron and photon self-energy. This…
user1247
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Where are the gravitons in the Wheeler-de-Witt formalism?

As I understand it, in the Wheeler-de-Witt formalism you sum over the spaces bounded by a start space and and end space. What I want to know is where do gravitons fit into this picture? I understand where they come from in string theory since you…
user84158
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Sir Roger Penrose's claim on quantum gravity in relation to brain function

I'm hoping that this board may be able to offer an explanation. First, my apologies for quoting a slightly lengthy fragment but I wanted to provide the full context for my question. I'm reading Artificial Intelligence - A Modern Approach1 where I…
Konrad
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What are the implications of the Nesvizhevsky experiment and followup experiments with ultracold neutrons?

I remember reading about the groundbreaking experiment by Nesvizhevsky (et al. 2001) some 12 years ago using ultra-cold neutrons which showed the first experimental evidence of quantum gravity. It is my understanding that these experiments has been…
Mr X
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Why can we detect single photons, but not single gravitons?

Everybody can buy a single photon counter. Why are there no single graviton counters? Obviously, graviton sources are rare. But why are graviton detectors so hard to make? Is it just because the typical gravitons (say, from black hole mergers) have…
frauke
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Time is the potential?

Perhaps time can be expressed as $$ t = \frac {Gh} {c ^ 4} \int \frac {dS} {r} $$ Where S is the entropy of entanglement of an arbitrary closed surface. r is the radius to the surface point. Integration over a closed surface. This is very similar to…
Kuyukov Vitaly P.
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Gravity-Induced Quantum State Reduction

Roger Penrose (along with two other co-authors) recently released a paper on the arXiv which proposes a test of quantum gravity with a Bose-Einstein condensate acting as a very massive 'particle'. The aim is to investigate some interactions and…
psitae
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