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.
Questions tagged [loop-quantum-gravity]
172 questions
37
votes
7 answers
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 ideas, probably a change just as fundamental as the…
Deschele Schilder
- 1
- 5
- 45
- 105
37
votes
4 answers
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 assigns Lie groups representations to the edges and…
Marek
- 23,981
34
votes
3 answers
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 Gravity Lagrangian Density (the…
Abhimanyu Pallavi Sudhir
- 6,268
21
votes
1 answer
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 the matter degrees of freedom. How is matter…
twistor59
- 17,244
- 2
- 56
- 84
21
votes
3 answers
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 dimensions, and all these dimensions need to fit…
19
votes
5 answers
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 fields in a space are equivalent to fields on a…
Lawrence B. Crowell
- 9,408
17
votes
3 answers
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 space on the quantum scale. Though, is there an…
Crystal Optics
- 731
14
votes
8 answers
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 approach is whether it picks a privileged frame…
user1355
14
votes
5 answers
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 provided a very nice answer.
Let me summarize…
Marek
- 23,981
13
votes
0 answers
Does a good path integral exist in Loop Quantum Gravity?
The Hamiltonian operator of loop quantum gravity is a totally constrained system
$$H = \int_\Sigma \mathrm{d}^3x\ (N\mathcal{H}+N^a V_a+G).$$
Here, $\Sigma$ is a 3-dimensional hypersurface; a slice of spacetime. Moreover, $\mathcal{H}$ is the…
kryomaxim
- 3,558
12
votes
0 answers
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 four space-time dimensions the macroscopic result…
user4552
12
votes
3 answers
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 theory. Why? Why quantization is not unique?
If you…
kryomaxim
- 3,558
12
votes
1 answer
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 = E^2 \left( 1 + \xi \frac{E}{E_P} + {\cal O}\left(…
Prof. Legolasov
- 16,527
12
votes
4 answers
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 formula for the entropy of the black hole.
Parts of his…
Marek
- 23,981
11
votes
2 answers
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 came across a paper in arxiv whose abstract claims…
Ashwin Balaji
- 625