Questions tagged [loop-quantum-gravity]
A theory of quantum gravity, which aims to merge quantum mechanics and general relativity, postulating that the structure of space is composed of finite loops woven into an extremely fine fabric or network.
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Relationship between the Quantum Tetrahedron, V4 geometry in topological photonics, and The Cobordism Hypothesis?
Looking for someone with a background in TQFT/related to answer a question over a posited relationship on a few concepts that tie in together.
First - John Baez's early research into LQG via the ...
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What are particles (both fermions and bosons) composed of and explained as in Loop Quantum Gravity? [duplicate]
From my understanding of LQG, spacetime emerges from discrete quantum assumptions that come first, and I'm wondering how matter and energy particles are related to this (for example, string theory ...
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Decomposition of a gauge-invariant $3$-dimensional spin network state over the Wigner matrix elements
Below follows the passage of Rovelli and Vidotto's Covariant Loop Quantum Gravity that I do not understand. To give the context, let me clarify that a state $\psi$ is a function in $L^2[\text{SU}(2)^L]...
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What does it mean to say that Loop quantum gravity bouncing models "connect" two "classical" universes?
According to these papers in Loop quantum gravity models of bouncing cosmologies the two "sides" or universes passing through the bounce are classical (or have a classical description of ...
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A "structure" encompassing all quantum gravity approaches?
In a recent question that I made on this site, one of the answers mentioned the following (emphasis mine):
Non‐critical string theories (like the 26D bosonic string or 2D “non‐critical” strings) do ...
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Symplectic structure of Holst action
I'm reading the article "background independent quantum gravity: a status report" (Ashtekar, Lewandowski).
Here are some definitions given:
Half-flat connection:
$\omega^+_{IJ}=\frac{1}{2}\...
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Problems with hypothetical discreteness of spacetime
Have some questions about reasoning in following answer indicating problems with compatibility of hypothetical discretizing specetime with known observations.
L. Motl argued there:
A discrete ...
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Eigen-spin-networks of the volume operator
To prove a result, I need to show that there exists a class of spin networks (most likely those with large spins) which are eigenvectors of the $W$ operator (squared) as defined by Rovelli et Al. as ...
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Diffeomorphism-invariant representation of the Hamiltonian constraint in LQG
I seem to recall that there was a theorem (due to probably some subset of Lewandowski, Thiemann, and Ashtekar) which said that the Hamiltonian constraint could not be implemented in the diffeomorphism-...
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Impossibility of building quantum gravity theory from the bottom?
I heard recently in a talk by Alain Connes that a certain Woodword (or Woodward or Woodard, not sure with reccording quality) showed an important result that a quantum theory of gravity cannot be ...
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How do we explicitly prove that the induced covariant derivative on non-expanding horizons (NEH) reduces to the rotational one-form connection?
I have been studying the formulation of Isolated Horizons recently. As a reference I will follow Isolated horizons in classical and quantum gravity by Engle and Liko. But, I will be using the notation ...
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Is loop quantum gravity an $S$-matrix theory?
I interested in different approaches to quantum gravity.
Insofar I understand string-theory correctly, it constitutes a $S$-matrix theory. E.g., David Tong writes
The object that we can compute in ...
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Does Loop Quantum Gravity predict variable speed of light according to intensity of light?
I have read somewhere that Loop Quantum Gravity predicts a variable speed of light. According to the theory, high energy photons travel ever so faster than low energy photons. I wonder, how big is the ...
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Will LISA be able to detect quantum corrections to the waveforms of gravitational radiation?
My main motivation for asking this question is this paper, in which the authors calculate the periodic orbits of a
small celestial object around a supermassive quantum-corrected black hole and the ...
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What does the word "Observable" mean in Quantum Gravity?
I have seen the statement in several places that the only "observables" in general relativity or Quantum Gravity are measured at temporal or spatial infinity. This is often used as a ...
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