Questions tagged [quantum-gravity]
Any of the various explanations of gravity as a quantum theory, including string theory and loop quantum gravity.
1,334 questions
1 vote
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Dimensional reduction check: R^(5) for ds^2 = e^(2A(rho)) gbar_{mn}(x) dx^m dx^n + d(rho)^2 [closed]
Setup Consider the 5D metric with a single warp factor depending only on the extra coordinate: $$ ds^2 \;=\; e^{2A(\rho)}\,\bar g_{\mu\nu}(x)\,dx^\mu dx^\nu \;+\; d\rho^2 , $$ with signature ((+----))...
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4 votes
0 answers
59 views
Under what conditions do functional renormalization group (FRG) limit cycles occur in asymptotically safe gravity? [closed]
In the functional-renormalization-group (FRG) formulation of quantum gravity, the effective average action Γₖ evolves with the RG scale k according to the Wetterich equation $$\partial_k \Gamma_k = \...
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0 votes
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Why is the string worldsheet theory a CFT?
Why do we say that the (gauge-fixed) worldsheet theory in string theory is a conformal field theory (CFT)? Where exactly does this conformal invariance come from? Is it simply because, after gauge ...
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1 answer
280 views
Why does gravity need to be renormalized?
Renormalization was first proposed to solve the selfforce problem of point charges. According to classical electrodynamics, the electric field energy diverges at point charges, which means a single ...
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1 vote
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150 views
Are black holes pure quantum states before evaporation?
I'm studying the black hole information paradox and the Page curve. My professor told us different formulations of the paradox, one of which is: we consider the initial star to be a pure quantum state,...
- 551
-4 votes
2 answers
289 views
Can a spin-2 particle decay into a spin-0 particle?
I wonder if there is any mechanism described in high-energy particle physics by which it is predicted that a spin-2 particle like the hypothesized graviton can decay into a spin-0 particle like the ...
- 4,685
1 vote
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93 views
EFTs in the EFT-hedron and strongly coupled UV-completions?
The EFT-hedron developed by Arkani-Hamed and collaborators encode EFTs that can be UV-complete (https://arxiv.org/abs/2012.15849). But does it only encode EFTs that can be completed by weakly coupled ...
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4 votes
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108 views
Negative geometries and positivity bounds?
Recently, Nima Arkani-Hamed and collaborators have discovered the relation between positive geometries that encode basic features of QFTs called positivity constraints like unitarity, causality, ...
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2 votes
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124 views
A question on Wilson coefficients and UV-theories of fundamental high-energy physics?
In this paper (PDF) the authors tried to use Wilson coefficients which encode the influence of the UV-theory into its low-energy EFTs (which would differ between different fundamental high energy ...
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0 votes
1 answer
144 views
Did time exist before the Big Bang, if converting matter to energy requires motion and motion requires time? [closed]
I’ve been reading about the origin of the universe, and I have a conceptual doubt that I can’t resolve. According to general relativity, time and space both began with the Big Bang. But if matter can ...
2 votes
2 answers
467 views
What does ER=EPR actually mean? Is entanglement really the same as a wormhole?
I’ve been trying to wrap my head around the ER=EPR idea that Maldacena and Susskind proposed — the claim that entangled particles (EPR pairs) might be connected by tiny wormholes (ER bridges). On the ...
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1 vote
1 answer
301 views
Canonical quantization of linearized gravity coupled to matter
I'm looking for references treating the canonical quantization (i.e., Hamiltonian formalism) for point particles coupled to linearized GR. I assumed there was a ton of material on this out there, but ...
-1 votes
1 answer
132 views
Difference between relativistic spacetime and the summation of quantum fields? [closed]
Total amateur physics fan here, so I'd like to ask a stupid question. General relativity and quantum theory are currently irreconcilable, but I've always wondered What keeps spacetime from just being ...
1 vote
0 answers
113 views
Implications of Wald entropy on black hole microstates
Since the black hole Wald entropy is directly obtainable from classical general relativity, leading directly to the area law from the geometric theory, doesn't this imply that the explanation for the ...
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4 votes
2 answers
231 views
Detection of gravitons via excess quantum noise
In the recent paper that won first prize of the 2025 Gravitational Research Foundation essay contest, Probing Quantum Structure in Gravitational Radiation by Manikanden & Wilczek, it is claimed ...
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