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Questions tagged [loop-quantum-gravity]

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9
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Does a good path integral exist in Loop Quantum Gravity?

The Hamiltonian operator of Loop quantum gravity is a totally constraint system $$H = \int_\Sigma d^3x\ (N\mathcal{H}+N^a V_a+G)$$ Here, $\Sigma$ is a 3-dimensional hypersurface; a slice of ...
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309 views

Significance for LQG of Sen's result on entropy of black holes?

Sen 2013 says, ...we apply Euclidean gravity to compute logarithmic corrections to the entropy of various non-extremal black holes in different dimensions [...] For Schwarzschild black holes in ...
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1answer
213 views

Discretizing spacetime

It is often claimed in quantum gravity circles (I'm thinking of LQG in particular) that it is "not possible" to discretize spacetime. The issue, as I understand it, is that should one attempt to ...
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171 views

Why is a theory of quantum gravity expected to solve the BigBang singularity problem?

This a follow-up question related to this. A successful theory of Quantum gravity is expected to solve the BigBang singularity problem. Why (and how) is the quantization of gravity supposed to solve ...
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93 views

Physical interpretation of polymer quantization

I have read a bit about polymer quantization, and I want to know what this quantization means physically. I already know that it enables us to incorporate an additional length scale that solves the ...
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83 views

Can loop quantum gravity use known techniques to cure the fermion doubling problem?

It is well known that LQG has a fermion doubling problem and therefore cannot include chiral fermions. https://arxiv.org/abs/1507.01232 However, there are already many known techniques to dealing ...
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102 views

Definition of evolution equation in Rovelli's quantum gravity book or how a function can determine a curve

I'm reading the book Quantum Gravity by Carlo Rovelli. In page 107, he says that the evolution equation of the system can be cast into $f=0$, where $f$ is a map such that $f: \mathcal{C}\times \Gamma \...
3
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133 views

Homeomorphism between the space of all Ashtekar connections and spacetime?

Excerpt from an essay of mine: Let $\Psi(\varsigma)$ be the wavefunction in the loop representation, where $\varsigma:[0,1]\to\mathcal{M}$, where $\mathcal{M}$ is spacetime. Then, let $\mathcal{A}$ ...
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57 views

Can mass still be observed in our universe after moving from a black-hole to a white-hole?

This question is based on the recent papers on LQG black-holes by Abhay Ashtekar. Quantum extension of the Kruskal spacetime and Quantum Transfiguration by Kruskal Black Holes When mass moves from ...
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42 views

Ad-hoc algebraic spin network quantization

In Loop Quantum Gravity, one usually embraces the functorial point of view towards (T)QFT. Canonical and spinfoam formalisms only differ in how the projection operator is defined. Canonical formalism ...
2
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1answer
133 views

Spin networks - resources

I am very interested in studying spin networks. Where can I begin? I want to understand them at their basic level. Which reference is good to get more technical details?
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133 views

Prof Lewandowski's paper about different space time for different particles

I read here http://www.sciencedaily.com/releases/2013/07/130709115344.htm that Prof. Lewandowski's work suggests that different particles may experience different spacetimes. His work is in the ...
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36 views

In loop quantum gravity what is considered the initial conditions?

In LQG, the Universe starts off not from a singularity but of finite size. And there may be the idea of a pre-big bang crunch. Assuming the Universe is symmetric in time about the 'big bang'. What ...
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24 views

In LQG can two bosons occupy the same space?

Apart from the fact the LQG doesn't really have any well accepted theory of how to put matter and particles into it. In theory in LQG can two bosons occupy the same space? Because of course if you put ...
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47 views

Hierarchy problem and loop quantum gravity

According to https://en.wikipedia.org/wiki/Hierarchy_problem#Finite_Groups. Hierarchy problem can be theoretically solved using symmetry of certain bosonic string theory on the Leech lattice (though ...
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55 views

How to describe the strength of gravity in LQG?

In general relativity we have free falling observers who feel no gravity. and equations for geodesics. There are tools that describe the strength of gravitation field for a given observer. In Are ...
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137 views

Is there a connection between Loop Quantum Gravity and the Rishon Model?

In the picture below you can see how the first generation of quarks and leptons is seen in Loop Quantum Gravity. In the Rishon Model of my beloved Haim Harari you can see that the first generation of ...
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296 views

Loop-quantum gravity as cellular automaton

I've been reading Zakopane lectures on loop gravity lately and I only understood a very small part of it, but from the little I understood, I'm wondering if loop quantum gravity isn't close to ...
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85 views

Cosmological inflation in LQG/LQC

I seek the state-of-the-art report on how cosmological inflation is described by loop quantum cosmology. I know that LQG/LQC predicts a big bounce to replace the classical big bang singularity of GR. ...
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260 views

Loop Quantum Gravity and Gauge theory

Are there any connection between Loop Quantum Gravity and Gauge theory? If so, how does the gauge theory is described? When exactly does the spin network of the foam is created in the era around the ...
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17 views

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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13 views

Spin Foam Introductory Texts

What are some good introductory texts on spin foams / LQG for someone specialized in SUSY / string models? I’m somewhat familiar with some of the literature (Topological Amodel and crystal melting / ...
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23 views

Coordinate space of loops in loop quantum gravity

I have a basic and perhaps admittedly misguided question about the loops in LQG. Broadly speaking I think I understand the logic that lead to them, namely that working in the ADM formalism (using the ...
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53 views

Has Loop Quantum Gravity Been Axiomized?

I was just wondering if any work had been done to axiomize loop quantum gravity. If so what are the axioms of LQG? Thanks
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16 views

Conformal dimension of fields over groups

Group Field Theory (GFT) deals with field theory over group space for instance $$S_2 = \int dg_1dg_2 \mathcal{K}(g_1, g_2)\phi(g_1)\phi(g_2) +\int dg_1dg_2dg_3\mathcal{V}(g_1, g_2, g_3)\phi(g_1)\phi(...
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Resource recommendation: Relation between q-deformed groups and non-commutative field theory

I would like to know if non-commutative field theory is related to $q$-deformed groups in any way. There is a relation between non-commutative field theory and group field theory which I understand is ...
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39 views

What is the relationship between Loop Quantum Gravity and Conformal Cyclic Cosmology?

I have heard/read of both of these "theories" or concepts by Roger Penrose (et al.?) - pardon my possible misuse of the word "theory". Is CCC just one possible model of the universe based on the ...
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61 views

Relation of spin networks, graphs, polyhedra and emergence of 3-space in loop quantum gravity

I have some questions regarding the current status of spin networks and their relation to geometry in loop quantum gravity. The picture I got many years ago is that spin networks in LQG are coloured ...
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124 views

What's wrong with lattice quantum gravity?

Assume one can write the metric field on a lattice, so on each lattice point one has a value of $g^{\mu\nu}$. Similar to the way lattice QCD is formulated. Then later taking the distance between ...
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41 views

Could every particle encode the distances to all other particles?

I was thinking about quantum gravity and pre-geometry and wondering this question: "If space does not exist. How does a particle know how far away it is from another particle?" i.e. there are no ...
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40 views

Quantum gravity: should it stabilize inspirals?

Bohr model and Quantum Mechanics stabilize the atoms in order to have a minimum state (due to some effective or centrifugal force) avoiding electrons to hit the nuclei. Thus, electrons (accelerated ...
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80 views

A special path integral

May be $f(\vec{x}), \vec{g}(\vec{x})$ an arbitrary functions dependent on the coordinates $\vec{x}=(x,y,z)^T$. Defining the following function dependent on a 3-dimensional curve $\vec{\gamma(t)}$ ...
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97 views

Loop quantum gravity- is the critical density sufficient to form a 'black hole'?

I think in loop quantum gravity the rate of expansion of the universe is found from: $H^2=\frac{8\pi G}{3}\rho\left(1-\frac{\rho}{\rho_c}\right)$ And I was wondering whether the critical density $...
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1answer
81 views

What are exactly “norms” in spin networks? Are there any non-quantum spin networks?

Roger Penrose proposed a series of networks from which, fundamentally, space-time would emerge, called spin networks (https://en.wikipedia.org/wiki/Spin_network) In this article, it is said: ...
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1answer
111 views

By What Mechanism Does the Universe Expand in Loop Quantum Gravity Theory?

So, the universe is expanding, and, from what I've heard, that expansion is accelerating. However, I'm unclear as to the specific mechanism involved, particularly as would be described in a Loop ...
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1answer
78 views

Time and “fundamenta”l equations

I have been reading articles by Carlo Rovelli. About quantum mechanics, he says: “The Heisenberg and Schrödinger pictures are equivalent if there is a normal time evolution in the history. In the ...