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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Black Hole and Loop Quantum Gravity

According to LQG, in a stellar Black Hole, a region A where the collapsing matter density is plankian and another region B which is horizon and also reaches plankian at the end of evaporation process. ...
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Square of Volume of Tetrahedron in Loop Quantum Gravity

In the subsequent statement about the geometry of Tetrahedron in Carlo Rovelli's book, there is a formula as follows: $$V^2 = \frac {2}{9}(\vec L_1 \times \vec L_2)\cdot \vec L_3$$ Where $\vec L_a$ is ...
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Please explain statement in a book on Loop Quantum Gravity

In a book by Carlo Rovelli on Covariant Loop Quantum Gravity, I struggle to understand a statement on Tetrahedron as follows: What is the dimension of the matrix? How to derive the given matrix ...
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Just how small a point is required for the Pauli Exclusion Principle to apply when looking at LQG?

In Loop Quantum Gravity, the thought is that the smallest possible point is 10^-35 meters. But it is recognized that this is still not a singularity, which basically has no dimensions. So when it ...
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Is there a wave function in loop quantum gravity?

In the postulates of quantum mechanics, http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/qm.html a wavefunction is fundamental. Is there a wavefunction - or an analogon - in loop quantum gravity? As ...
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Does loop quantum gravity explain the dark matter effect without dark matter?

Does loop quantum gravity explain the dark matter effect (the rotational curves of the galaxies, the increased velocitoes of galaxies within galaxy clusters) without using dark matter? As far as I ...
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Simple explanation on 'How vacuum is treated in the different quantum gravity theories?' And is there a theory where there is NO space without matter?

Could you please make an easy-to-understand synopsis on how the different quantum gravity theories (loop quantum gravity, causal dynamic triangulation, and the many other) treat empty space? That ...
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Are there quantum gravity theories in which spacetime itself is regarded as quantum in nature?

In quantum gravity, it's tried to quantize the gravitation. However, if I got it correctly, most quantum gravity approaches try only to quantize gravity as a force, the curvature of spacetime, not the ...
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Doubts about General Relativity in Ashtekar variables and Thiemann trick - Perez "INTRODUCTION TO LOOP QUANTUM GRAVITY AND SPIN FOAMS"

I am working on the Perez book, INTRODUCTION TO LOOP QUANTUM GRAVITY AND SPIN FOAMS (https://arxiv.org/abs/gr-qc/0409061). In particular, I am interested in the understanding of the Poisson brackets (...
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String Theory, the IKKT model and LQG

In Brian Greene's book The Fabric of the Cosmos (2004) he suggests the possibility that String Theory and Loop Quantum Gravity may be two attempts to construct the same theory from very different ...
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Study Loop quantum gravity [duplicate]

I am a master's final year student in physics. In my curriculum I have courses on qft, qed and string theory but nothing on loop quantum gravity. I want to study the subject but I am not able to get ...
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Good Introductory Text for Quantizing Geometry?

In this video she makes an interesting claim. In loop quantum gravity on can think of the gravity as: $$ G^{\mu \nu} = \kappa T^{\mu \nu} $$ Now in loop quantum gravity one can quantize geometry as ...
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About Loop Quantum Gravity and concerns with its "polymer" quantization. Has it ever been addressed or answered/justified?

Referring to Why is Standard Model + Loop Quantum Gravity usually not listed as a theory of everything Underlying papers are: J. W. Barrett, “Holonomy and path structures in general relativity and ...
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How does LQG solve the problem of the quantization of gravity? [closed]

How does LQG solve the problem of the quantization of gravity? Not only is it a discretization of space with groups of holonomy and diffemorphisms as curved backgrounds?,is that I see that they use ...
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What is holonomy-flux algebra?

I am trying to understand what this algebra is doing, the singularity of the invariant states of difeomorphism in holonomy flow algebras is one of the articles that I could not understand, I am ...
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Why would the validity of UV/IR decoupling imply the explicit constructability of black hole remnants?

A paper written in 2020 by Harlow and Shaghoulian (reference 1) proposes a connection between unitary black hole evaporation and the non-existence of global symmetries in quantum gravity. In passing (...
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Triangulation of the Hamiltonian constraint in Loop quantum gravity

Im trying to obtain regularized (and triangulated) version of Hamiltonian constraint in the LQG. However, one step remains unclear to me. I am starting with the Euclidean Hamiltonian: $H_E=\frac{2}{\...
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GHY term in loop quantum gravity

Does the GHY (Gibbons-Hawking-York) boundary term play any role in loop quantum gravity? If it does where and how does it show up? (I am more interested in 4D)
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Planck-scale curvature in covariant LQG and quantization of length: does LQG apply also to the Planck-regime?

In the covariant approach of loop quantum gravity (see http://www.cpt.univ-mrs.fr/~rovelli/IntroductionLQG.pdf ), the theory is defined on a "lattice", similar to lattice QCD. In this case ...
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Poisson algebra between Hamiltonian constraints in the connection formulation of the loop $f(R)$ gravity

I have a problem with calculation of the Poisson algebra for Hamiltonian in loop $f(R)$ gravity, which is given by: with the smeared version $\int _\Sigma d^3 x N H$. $\tilde{K^i_a}$ is the extrinsic ...
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Since spacetime can bend and form waves, does this mean it must be made of sub-units of matter? How can something bend if it does not have sub-units? [closed]

My question is philosophical, I'm just curious to hear people's opinions. I'm also interested in any resources that are related to this question. Have you read any papers that attempt to investigate ...
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Terminology: "Sum over Geometries" vs. "Sum over Topologies" in Quantum Gravity

I am currently studying loop quantum gravity and related approaches like simplicial quantum gravity, spin foam models, tensor models and group field theories. In texts about this topics, one often ...
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Does Loop Quantum Gravity predict that high-energy photons or light waves will travel faster or slower than low-energy (longer-wavelength) ones?

Matthew O'Dowd, the Australian-born host of PBS Space-Time, insists that high-energy (short-wavelength) photons (or waves) of light will travel slightly more slowly through space than lower-energy, ...
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What are the physical state invariants of loop quantum gravity?

What are the "physical state" invariants for Loop Quantum Gravity? The Wikipedia page talks about "physical states" being invariant, diffeomorphism invariance, "quantities ...
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Is background independence necessary for loop quantum gravity in itself, or only necessary to make LQG compatible with special relativity?

At first look the idea of particulate space in loop quantum gravity would seem to indicate a preferred frame or ether, but theorists have gone to great lengths to prove the background independence of ...
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Diffeomorphism constraint in loop quantum gravity

I am reading Canonical Quantization of Spherically Symmetric Gravity in Ashtekar’s Self-Dual Representation by Thiemann and Kastrup [a] and also the book Modern canonical quantum general relativity by ...
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I would like a simple description of what a sum of geometries means in loop quantum gravity

I have been studying quantum gravity theories. Many theories would have gravity (that is space and time) defined by the exchange of a gravitational quanta. That is simple in sense it is readily ...
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LQG: Why does gravity attract (not repel)?

I read that LQG can (with the spinfoam formalism) give the Einstein equation when $h$ tends to zero. See the metrics created by an object in the sky. The equations of the geodesics contain a parameter ...
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Loop quantum gravity

Is Loop Quantum Gravity trying to bring quantum mechanics from it's principles? Or is it taking ideas from quantum mechanics and merging them with GR to find a theory of quantum gravity?
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What is a particle in loop-quantum-gravity?

What exactly is the underlying mathematical structure of e.g. an electron in Loop-quantum-gravity? And is there a simple way to get the quantum mechanical limit so that one can see how the wave ...
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What is the interaction between quantum fields and Rovelli's particulate space of loop quantum gravity?

I've read Rovelli's book and papers, but he makes little mention of quantum fields. What is the interaction between fields and his particulate space of loop quantum gravity? I know that he says loop ...
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Loop Quantum Gravity falsified?

In the Wikipedia article "Loop Quantum Gravity" one can read ESA's INTEGRAL satellite measured polarization of photons of different wavelengths and was able to place a limit in the ...
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Compactness condition on boundary formalism for loop quantum gravity

I'm going over Rovelli's Covariant Loop Quantum Gravity notes http://www.cpt.univ-mrs.fr/~rovelli/IntroductionLQG.pdf and in section 2.4.2 "Boundary formalism" he briefly develops how to ...
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A Loop Quantum Gravity question

Can someone answer this question, I have chosen this from Bodendorfer's article on 'An Elementary Introduction to Loop Quantum Gravity' from section 3 General relativity in the connection formulation ...
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Is Loop quantum cosmology replacing the Big Bang singularity with a big bounce?

Am I correct in understanding that in the cosmological version of Loop quantum gravity, namely Loop quantum cosmology, the universe in all models starts with a big bounce? Are there other models, for ...
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Loops in Loop Quantum Gravity

Am I correct in understanding that in Loop Quantum Gravity, loops are somehow interconnected with each other or interact, or is there some form of quantum entanglement between them? And if so, can we ...
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Clebsch-Gordan coefficients, spin networks and intertwiners

After spending some time with LQG books and articles i have still some problems regarding concepts of this theory. Spin network is built from lines labeled by spin label $j$ and since angular momentum ...
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Why does combining background independence and diffeomorphism invariance force you to conclude that spacetime must be quantized?

I was recently watching a fermilab video on loop quantum gravity and at about 4:20 it is stated that, when combined, background independence and diffeomorphism invariance force you to conclude that ...
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Sinusoidal shape and continuity of the electromagnetic wave

I hope my question will be understandable. I wonder about the sinusoidal shape of an electromagnetic wave. I have the impression that something fundamental is behind this shape. To simplify things, ...
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Question about quantum gravity and super-fluid vacuum?

I've been reading a lot about super-fluid vacuum/quantum foam/quantum vacuum etc and how quantum gravity (as hypothesized) will emerge out of interaction of these virtual particles that make up said ...
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Relationship between classical $q$-deformed General Relativity and the cosmological constant

The frame-connection formulation of pure General Relativity in 4 dimensions is given by the action $$ S_{4d}[e, \omega] = \frac{1}{2 \kappa} \int \varepsilon_{IJKL} e^I \wedge e^J \wedge F^{KL}, $$ ...
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Would naked singularities have the same gravitational properties as black holes of the same mass? [duplicate]

This is just a thought experiment before someone mentions the cosmic censorship conjecture. If physicists are discussing it in papers and scholarship, I wanna see some of those theoretical angles too ...
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How does detection of Gravitational Waves affect Quantum Gravity Research?

After detection of gravitational waves in 2015, what are it's implications on quantum gravity theories? Are there any quantum gravity predictions validated through GW detection?
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How to get orientation entanglement in network?

Looking at this intuitive description of spinors. Is there a way to add something like this to a network graph. (e.g. the kinds of networks you get in LQG) or any kind of graph? It looks like ...
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Difference between Loop Quantum Gravity (LQG) and Causal Dynamical Triangulation (CDT)

Recently, I have read about Causal Dynamical Triangulation from here and Wikipedia. In Wikipedia it states, CDT is a modification of quantum Regge calculus where spacetime is discretized by ...
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Does Loop Quantum Gravity predict general relativity in semi-classical Limit?

Recently i read about Loop Quantum Gravity in Wikipedia and found this below statement here. Presently, no semiclassical limit recovering general relativity has been shown to exist. But i also ...
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What goes in what spaces in LQG?

I read again the first chapter of Rovelli 2005 quantum gravity book, and I am still puzzled by the different spaces for each concept. It seems spin foams inhabit Hilbert spaces. But i read elsewhere ...
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Discrete spacetime: what does it mean for spacetime fields and vacuum?

Suppose we imagine that the space-time continuum is really a discrete stuff of something. This something could be some kind of particles or "substance"/matter/energy field. Then, I see two conceptual ...
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Gauge invariance of 3-dimensional LQG action

I'm going through C. Rovelli's textbook. On pages 91-93 he defines: $$ U_e = {\cal{P}} \left\{ \exp \int_e \omega\right\} \in SU(2), \tag{4.30} $$ $$ L_s^i = \int_s e^i \in {\mathbb{R}}^3. \tag{4.31} $...
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Immirzi parameter and it’s Critical values

Where does the critical values of the Immirzi parameter, i.e. log(2)/pi(3^1/2), etc. come from? Is there an equation that relates these values to the general immirzi parameter? What is the ...
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