Questions tagged [loop-quantum-gravity]

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151 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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2answers
57 views

Notation issue in a paper on loop quantum gravity/geometrodynamics

I was reading a paper and I came across some notation that confused me. This was concerning the extrinsic curvature tensor defined as $K_{ab} = \frac{\mu}{2}K^i_{(a}K^i_{b)}$. I am normally ...
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87 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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94 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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3answers
804 views

Why there is no unique “recipe” for quantization of a classical theory?

I have seen in Wikipedia that different quantization methods exist (see Wiki article with name "Quantization"). Moreover, Wikipedia stated that there is more than one way to quantize a classical ...
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1answer
77 views

What is the meaning of $O(r^{-n})$ odd/even?

I am studying the book "Modern canonical quantum general relativity" written by Thomas Thiemann. In this book, it has been written since $\vec{N}$ is an asymptotic Killing field of $δ_{ab}$ we ...
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1answer
268 views

Experimental bounds on Lorentz-violating dispersion relation

It has been predicted by several background-independent approaches to Quantum Gravity (like LQG or spinfoams) that the physical dispersion relations in vacuum could take the following form: $$ p^2 = ...
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3answers
1k views

What experiment would disprove loop quantum gravity?

Loop Quantum Gravity (LQG) is a theory of quantum space-time that attempts to describe the interconnection between general relativity and quantum mechanics. It's main postulate is the granularity of ...
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434 views

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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186 views

Good mathematical introduction to loop quantum gravity [duplicate]

All websites or papers I could find did only have a mathless introduction for laymen. Does anybody know where to find a precise and mathematical introduction to LQG, for example containing the "...
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162 views

A brief description of a plausible and possible candidate for Quantum Gravity [closed]

I wanted to know the specifics(essence) of a particular theory that is present for quantum gravity (QG),and which seems to have the best potential. I am no expert on field theories and QG, cause ...
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1answer
568 views

Number of free parameters in String Theory and LQG

In the Standard Model, we have these free parameters: 6 quark masses 6 lepton masses 3 coupling constants Higgs mass Higgs VEV 4 CKM parameters 4 PMNS parameters QCD vacuum angle That's 26 in total. ...
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103 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 \...
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1answer
371 views

Zeno effect in quantum gravity?

Given that "the quantum zeno effect can "freeze" the evolution of the system by measuring it frequently enough in its known initial state." Is there any equivalent/similar Zeno effect in quantum ...
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1answer
98 views

Need resource about super-inflation in Loop Quantum Cosmology

In the current model during inflation H remains nearly constant where $ H = \frac{ \dot{a}}{a} $ but the scale factor a grows exponentially and requires a large number of e - folds N where $ N = ln\...
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1answer
943 views

What is the basic idea of loop quantum gravity? [duplicate]

I have researched a little on loop quantum gravity (LQG), but all I got were very ambiguous explanations about loops and nodes that all end with mathematical equations. If someone could give me a non-...
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3answers
2k views

Space-time in String Theory

I would like to understand how Physicists think of space-time in the context of String Theory. I understand that there are $3$ large space dimensions, a time dimension, and $6$ or $7$ (or $22$) extra ...
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1answer
821 views

Is Space-Time Quantisation necessary or even meaningful?

It is believed among people working on Quantum Gravity, that space-time must be quantised at the Planck scale. Although it is very hard to verify such proposition, it is interesting from a ...
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1answer
167 views

Uncertainty relation and quantum gravity

Suppose a quantum version of gravity exists (which I don´t think). What will be the quantities in the uncertainty relation connected with this quantum gravity? Some time ago I sent a letter to Lee ...
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1answer
289 views

How do we choose how to discretise spacetime in loop quantum gravity?

In LQG we choose a two-complex (or other) on which to discretise GR before quantising. I'm a little uncertain about the nature of this choice. Is the two-complex an a priori property of the universe (...
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315 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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7answers
1k views

Does the discreteness of spacetime in canonical approaches imply good bye to STR?

In all the canonical approaches to the problem of quantum gravity, (eg. loop variable) spacetime is thought to have a discrete structure. One question immediately comes naively to an outsider of this ...
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4answers
5k views

Give a description of Loop Quantum Gravity your grandmother could understand

Of course, assuming your grandmother is not a theoretical physicist. I'd like to hear the basics concepts that make LQG tick and the way it relates to the GR. I heard about spin-networks where one ...
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276 views

What are elementary particles according to Loop Quantum Gravity? [closed]

Are elementary particles still excitations of quantum fields in LQG?
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1answer
234 views

Spacetime in Loop quantum gravity

In LQG, does spacetime consist of interconnected loops? Are those loops real? If spacetime does not consist of the aforementioned loops, what it consists of? The definition of real would be: they ...
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1answer
626 views

Variable speed of light in loop quantum gravity

Loop quantum gravity predicts a variable speed of light. What is the range of such a variation in its speed?
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89 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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5answers
6k views

Can Loop Quantum Gravity connect in any way with string theory?

The one difficulty I see with LQG is that it requires an enormous number of degrees of freedom, e.g. these spin variables in the net. This is in contrast to stringy holographic theory where the ...
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1answer
331 views

Can I teach myself physics (LQG specifically)? [closed]

OK I'm a second year undergrad student...have taken the introductory Math, Phys and Computer Science classes. I LOVE physics, and always have since I was a kid and wanted to major in that initially, ...
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1answer
116 views

Distributional Extension of a Hilbert Space

This question comes from the Complexification section of Thomas Thiemann's Modern Canonical Quantum General Relativity, but I believe it just deals with the foundations of quantum mechanics. The ...
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81 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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2answers
112 views

Confused about equations for the Big Bang in general relativity ad loop quantum gravity?

I am trying to get a vague understanding of the mathematical equations for the Big Bang in GR and LQG. My understanding so far is that when the universe is assumed to be homogeneous and isotropic, ...
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99 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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263 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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1answer
1k views

LQG Demystified Book?

Does a similar easy to read introduction like David Mc Mohan's Demystified books exist for LQG? I'd like something easier to start with than a paper but deeper than a popular book.
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1answer
448 views

What are the arguments for gravity not being a force? (in quantum gravity)

In quantum gravity the standard assumtion is that gravity is a force, although there is a small but persistent group of theorethical physicists who think otherwise. What gives us the motivation to ...
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311 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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136 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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1answer
318 views

Are background independence and diffeomorphism invariance the same?

What is the difference between background independence, which loop quantum gravity formalism claims to have, and diffeomorphism invariance?
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3answers
764 views

Does the Opera result hint to a discrete spacetime?

Could the Opera result be interpreted as some kind of hint to a discrete spacetime that is only seen for high enough energy neutrinos? I think I've read (some time ago) something like this in a ...
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1answer
672 views

The future of supersymmetry [duplicate]

Considering the fault of any experimental evidence from LHC for supporting the supersymmetry idea until now, can we say that it is dead? Generally the people who are working on this subject say that ...
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4answers
2k views

Discussion of the Rovelli's paper on the black hole entropy in Loop Quantum Gravity

In a recent discussion about black holes, space_cadet provided me with the following paper of Rovelli: Black Hole Entropy from Loop Quantum Gravity which claims to derive the Bekenstein-Hawking ...
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808 views

Entropy of a naked singularity

According to the wikipedia article http://en.wikipedia.org/wiki/Naked_singularity: "Some research has suggested that if loop quantum gravity is correct, then naked singularities could exist in nature, ...
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1answer
525 views

Area law for Entropy in Loop Quantum Gravity

In connection with the long saga of the (claimed) microscopic calculations of the Hawking-Bekenstein entropy in (3+1) Loop Quantum Gravity (LQG) and related approaches I have the following question: ...
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134 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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451 views

Coherent $U(N)$ intertwiners in Loop Quantum Gravity (LQG) and a measure on the Grassmannian

This is a detailed question about $U(N)$ intertwiners in LQG, and it comes from the the paper by Freidel and Livine (2011 - archive). It is very specific but related to finding a measure on a quotient ...
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1answer
207 views

What are all the approaches that have been tried for a theory of quantum gravity? [closed]

I am aware that that the most researched approach is that of string theory. I have also heard about quantum loop gravity. What other approaches are there to unify gravity and QFT? Also, please include ...
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1answer
160 views

Entropy, Mass and Brane gravity

Does string theory state as vibrational entropy increases, mass increases? Related: What is a D-brane? Reference: Cambridge Relativity
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1answer
771 views

What do “tachionic” neutrinos mean for QG?

Reading about the spectacular Opera claim, I`m (again ;-P) wondering if a confirmation of superliminous neutrinos could help settle some still open quantum gravity issues ...? In this post, Lumo ...
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1answer
730 views

How is the expansion of space itself explained in LQG?

To explain the expansion of space I have often heard people saying that space is continuously created. This picture is usually applied to cosmological scales but I`m nevertheless curious if some ...