Questions tagged [loop-quantum-gravity]

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8
votes
3answers
986 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 ...
33
votes
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 ...
4
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1answer
815 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 ...
16
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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 ...
6
votes
1answer
492 views

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 ...
2
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3answers
4k views

How much energy does a photon need to form a black hole?

I was wondering if it is possible for a single photon to form a black hole if it has a small enough wavelength.If so, what would this wavelength be? I came across this question because I am reading ...
12
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1answer
298 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 = ...
32
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7answers
3k views

Dirac once said that renormalization is just a stop gap procedure, and there had to occur a fundamental change in our ideas. Did something change?

Once, Dirac said the following about renormalization in Quantum Field Theory (look here, for example): Renormalization is just a stop-gap procedure. There must be some fundamental change in our ...
20
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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 ...
14
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7answers
2k 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 ...
6
votes
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.
11
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4answers
2k views

Question regarding the validity of the big bounce

I have several questions regarding the "big bounce" theory. It appears to be popular among LQG researchers. My questions are as as follows. 1) How one reconciles it with the fact that it is now ...
8
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2answers
245 views

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 ...
2
votes
1answer
776 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 ...
2
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0answers
1k views

Loop-Quantum Gravity versus String Theory [closed]

Basically asking what were the motives behind each theory. What was it that led physicists toward these ideas?
1
vote
1answer
838 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 ...
28
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3answers
3k views

Why is Standard Model + Loop Quantum Gravity usually not listed as a theory of everything

I have often seeen statements on physics.SE such as, The only consistent theory of everything which we know of to date (2013) is string theory. Why exactly is this so? Adding the Loop Quantum ...
19
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1answer
1k views

How is matter modeled in loop quantum gravity?

I have a basic understanding of how gravitational degrees of freedom are modeled in loop quantum gravity, but as far as I know, the main machinery, spin network states and observables, does not encode ...
15
votes
5answers
2k views

What is the role spin-networks play in Loop Quantum Gravity?

This is a second question (in what will probably become a series) in my attempt to understand LQG a little. In the previous question I asked about the general concepts behind LQG to which space_cadet ...
9
votes
1answer
1k views

Are there any versions of LQG that claim to not violate Lorentz symmetry?

LQG formulations have a minimum length/area. Since say, a Planck area can always be boosted, any minimum area in space can be shrunk. Do LQG proponents worry about local Lorentz invariance violation, ...
4
votes
2answers
847 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, ...
10
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0answers
323 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 ...
6
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1answer
364 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 ...
3
votes
3answers
790 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 ...
5
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1answer
474 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 ...
2
votes
1answer
84 views

Was $\kappa$-Minkowski model falsified by gamma ray burst measurements?

I'm considering the $\kappa$-Minkowski space – a certain model from non-commutative geometry which reduces to the usual Minkowski space in the limit $\kappa \rightarrow \infty$. The parameter $\kappa$ ...
5
votes
1answer
844 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?
1
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1answer
82 views

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 ...
0
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0answers
49 views

How does LQG explain attractivity? [duplicate]

Newton said that attraction was due to forces at a distance. RG said that matter fields change the metrics of space time Rovelli says the fields ARE space time (not enbedded in it). How does ...
0
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0answers
100 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 $...
-3
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3answers
1k views

Have any of the new predictions made by LQG been experimentally verified?

A wikipedia template lists under the heading "fully compatible with observation": Einstein-Cartan theory, Gauge theory gravity, Teleparalleism and Euclidean Quantum Gravity. Does this claim generally ...