Questions tagged [quantum-gravity]
Any of the various explanations of gravity as a quantum theory, including string theory and loop quantum gravity.
1,318 questions
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Is there a quantum gravity theory that postulates a gravitational field with the equivalent of the Schwinger limit for electric charge?
The Schwinger limit arises because electron-positron pairs get created instead of virtual photons at high charge density imposing a maximum value on electric field strength. Quantum gravity theory ...
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Could Negative Mass Explain White Hole Elusiveness? A Photon Repulsion Model [closed]
Theory Proposal: If white holes are mathematically valid solutions in GR but remain undetected, could their apparent "missing" nature arise from negative mass effects? Specifically: ...
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Implications of Reeh–Schlieder theorem for gravity
The Reeh-Schlieder theorem shows entanglement always happen in relativistic quantum theories even for vacuum states. The assumption it takes are existence of field operators and vacuum state ...
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Could the distance between particles in a black hole be the Planck length? [duplicate]
In classical general relativity, the gravitational collapse of matter inside a black hole leads to a singularity—a point of infinite density where space and time break down. However, quantum gravity ...
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Noncommutative geometry (NCG) in the foundations of physics (SM and QG)
I came across the applications of noncommutative (NCG) geometry to quantum field theory (QFT) and quantum gravity (QG). I'm trying to understand the status of the field so that I can evaluate if I ...
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Orbital angular momentum operator in QFT
I am reading Subleading soft dressings of asymptotic states in QED and perturbative quantum gravity, written by Choi and Akhoury. At some point in Section 4, they define the orbital angular momentum ...
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How far can an object be zoomed in? If we shrink far smaller than a Planck (~$10^{-35}$ meter), what would we see? [closed]
I'm curious about the fundamental limits of zooming into an object. We know that modern technology allows us to observe individual atoms, and quantum mechanics sets limits such as the Planck length (~$...
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On the meaning of quantizing gravity
Quantum mechanics has two main statements: The physical quantities can have discrete values under some circumstances. For example, the possible energy values of a harmonic oscillator in stationary ...
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How does the near-horizon approximation derivation of the Hawking radiation correspond to the general "in" and "out" modes picture?
I'm working on a semi-classical derivation of the Hawking effect for my BSc thesis. I started with the paper Rindler Space and Unruh Effect by Socolovsky, in which he basically derives the Unruh ...
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Redshift of photons due to gravity by another photon
Imagine two photons starting from origin and travelling in opposite directions. Can they redshift each other due to the gravitational potential between them? Lets modify it even more to make the ...
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Where does the string theory’s exponentially damped propagator come from?
I was reading Quantum Gravity and Quantum Cosmology (edited by Gianluca Calcagni, Lefteris Papantonopoulos, George Siopsis, and Nikos Tsamis, p. 6), and I came across this interesting statement about ...
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Relation of the background spacetime and graviton states in String Theory
I am having trouble to understand the following concept from String Theory (ST): According to my knowledge, ST is often defined on a flat Minkowski background spacetime. If one does so, the curvature ...
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Is it possible that gravitational waves emanating from matter have a "current" flowing in the opposite direction, leading towards the source matter?
In the case of electric current, we consider a conventional direction opposite to the natural movement of electrons. Would it be possible for something similar to happen with gravity? Do gravitational ...
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What is the ensemble approach in quantum gravity? What is the "ensemble" composed of?
There has been some work in quantum gravity somewhat similar to AdS/CFT but with the difference that instead of being a correspondence between two systems, there is one between one system and an ...
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Energy of the ground state in quantum gravity
In a quantum field theory of gravity, wouldn't the ground state be just flat space? But we know that the vacuum has non-zero energy if the quantization is made using the harmonic oscillator scheme. ...
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