Any of the various explanations of gravity as a quantum theory, including string theory and loop quantum gravity.
15
votes
3answers
918 views
Is decoherence even possible in anti de Sitter space?
Is decoherence even possible in anti de Sitter space? The spatial conformal boundary acts as a repulsive wall, thus turning anti de Sitter space into an eternally closed quantum system. Superpositions ...
2
votes
3answers
272 views
Could all strings be one single string which weaves the fabric of the universe?
This question popped out of another discussion, about if the photon needs a receiver to exist. Can a photon get emitted without a receiver? A universe containing only one electron was hypothetically ...
9
votes
2answers
211 views
How is causal patch complementarity compatible with behavior during inflation?
Causal patch complementarity is the conjecture that in de Sitter space with a positive cosmological constant, the states within the causal patch are sufficient to fully describe the universe with the ...
4
votes
2answers
314 views
Is spacetime an illusion?
In consistent histories, for gauge theories, can the projection operators used in the chains be not gauge invariant?
In quantum gravity, for a projection operator to be gauge invariant means it has ...
4
votes
2answers
355 views
Why is Mendel Sachs's work not taken seriously? Or is it?
Back in college I remember coming across a few books in the physics library by Mendel Sachs. Examples are:
General Relativity and Matter
Quantum Mechanics and Gravity
Quantum Mechanics from General ...
9
votes
1answer
180 views
What does the equivalence principle mean in quantum cases?
We know that electron trapped by nuclear, like the hydrogen system, is described by quantum state,and never fall to the nuclear.So is there any similar situation in the case of electron near the ...
2
votes
1answer
243 views
Does a complete theory of quantum gravity require anthropic post-selection?
Does a complete theory of quantum gravity require anthropic post-selection? Certainly the black hole complimentarity and causal patch conjectures highlights the essential role of observers, at least ...
1
vote
1answer
67 views
What are the implications of the Nesvizhevsky experiment and followup experiments with ultracold neutrons?
I remember reading about the groundbreaking experiment by Nesvizhevsky (et al. 2001) some 12 years ago using ultra-cold neutrons which showed the first experimental evidence of quantum gravity. It is ...
1
vote
1answer
201 views
Special relativity paradox and gravitation/acceleration equivalence
One of the features of the black hole complementarity is the following :
According to an external observer, the infinite time dilation at the horizon itself makes it appear as if it takes an ...
1
vote
1answer
318 views
Does spacetime really exist in quantum gravity?
If there are no localized observables in quantum gravity, does spacetime really exist, or might spacetime really be an illusion?
1
vote
1answer
450 views
What is the smoking gun signature of string theory?
What is the smoking gun signature of string theory? Suppose we have a complete and consistent model of quantum gravity with a zero or negative cosmological constant, but all we are given is its ...
-2
votes
1answer
202 views
A quanta of time
A question of Quantum Time: Does a minimum interval of time cause wave-like behavior?
If we think about the uncertainty principle, could it derive from a quanta of time? Does plank’s constant somehow ...
9
votes
0answers
156 views
How is Matter Modelled in Loop Quantum Gravity?
I have a basic understanding of how gravitational degrees of freedom are modelled in loop quantum gravity, but as far as I know, the main machinery - spin network states and observables, does not ...
7
votes
0answers
86 views
gauss-bonnet gravity constraints from string theory
recently there has been advances in observational constraints of gravity theories that contains scalars coupled to the gauss-bonnet topological term:
http://arxiv.org/abs/0704.0175
...
6
votes
0answers
97 views
Is the 125 GeV Higgs boson some kind of a “almost-commutative graviton” at the electroweak scale?
The expression "almost-commutative graviton" is provocative. I use it on purpose, as some kind of a "propagandon", to ask to the physics community if the observation of only one Higgs (scalar boson) ...
6
votes
0answers
94 views
Is it believed that all UV completions have “Maldacena duals”?
I have heard occasional rumors that effective field theories have gravity duals. For example, I've been told that UV momentum cutoffs in N=4 SYM become finite radii in AdS. I've heard speculations ...
6
votes
0answers
140 views
Does local physics depend on global topology?
Motivating Example
In standard treatments of AdS/CFT (MAGOO for example), one defines $\mathrm{AdS}_{p+2}$ as a particular embedded submanifold of $\mathbb R^{2,p+1}$ which gives it topology ...
6
votes
0answers
87 views
Hawking radiation for closely orbiting black holes
Suppose we have two black holes of radius $R_b$ orbiting at a distance $R_r$. I believe semi-classical approximations describe correctly the case where $R_r$ is much larger than the average black body ...
5
votes
0answers
123 views
Finite quantum gravity?
I'm working through an article that has some questionable assertions. The article is by Frank Tipler, "The structure of the world from pure numbers". (I'm going to ignore the fact that some of ...
5
votes
0answers
88 views
Geometric entropy vs entanglement entropy (dependent on curvature coupling parameter)
I have a quick question. In hep-th/9506066, Larsen and Wilczek calculated the geometric entropy (which I believe is just another name for entanglement entropy) for a non-minimally coupled scalar field ...
5
votes
0answers
119 views
When periodic solutions are combined with timelessness, do we get closed timelike curves?
In quantum gravity, ADM wavefunctional solutions have to satisfy the Wheeler-DeWitt equation. This leads to timelessness. What happens if we have a time periodic solution? In classical general ...
4
votes
0answers
130 views
Implications of Unruh-inertia to theories of gravity
If it turns out to be true that the galaxy rotation curves can be explained away by Unruh modes that become greater than the Hubble scale at accelerations around $10^{-10} m/s^2$ as proposed in here, ...
4
votes
0answers
114 views
Can we have consistent histories inside a black hole?
A consistent history is a POVM set of observables corresponding to a time-ordered product of projection operators. For gauge theories, not any old operator will do, only gauge-invariant observables. ...
3
votes
0answers
71 views
Pohlmeyer reduction of string theory for flat- and AdS- spaces
The definition of Pohlmeyer invariants in flat-space (as per eq-2.16 in Urs Schreiber's DDF and Pohlmeyer invariants of (super)string) is the following:
$ Z^{\mu_1...\mu_N} (\mathcal{P}) = ...
2
votes
0answers
50 views
Status of Teleparallel Quantum Gravity
There are several approches to incorporate torsion into a theory of gravity.
According to this article, requiring a consistent coupling to Dirac fields leaves us with the Einstein-Cartan approach or ...
2
votes
0answers
54 views
Wick rotation for FRW in quantum gravity
There is no timelike Killing vector for FRW cosmologies. In the path integral formalism, is it possible to Wick rotate for quantum cosmology in quantum gravity? If yes, how? If no, how does one work ...
2
votes
0answers
102 views
What results from particle collision would ensure the existence of the graviton?
I understand that particles are smashed together to try to enable us to detect some sort of graviton presence but we can't actually detect a graviton due to the fact that it 'exists' in some extra ...
2
votes
0answers
26 views
What methods are there to deal with quantum spatiotemporal chaos?
By now, there has been enough grasp on quantum chaos for systems with a small number of degrees of freedom. The major tool used is periodic orbit theory to approximate the spectral distribution. Is ...
1
vote
0answers
68 views
Black hole entropy from collapsed entangled pure light
Consider the following scenario, very similar to the one proposed in this question, but this time, the pure quantum radiation used for the black hole collapse, is now being split with down-converter ...
1
vote
0answers
183 views
Curiosity episode with Stephen Hawking. The Big-Bang
In an episode of Discovery's Curiosity with host Stephen Hawking, he claims the Big Bang event can be explained from physics alone, and does not require the intervention of a creator.
1) His ...
1
vote
0answers
165 views
't Hooft's landscape of conformally constrained QFTs
As described in "A class of elementary particle models without any adjustable real parameters", "The Conformal Constraint in Canonical Quantum Gravity", and "Probing the small distance structure of ...
1
vote
0answers
57 views
Thermal gravitational radiation and its detection
To my poor knowledge on the topic, the gravitational waves that are most likely to be detected by LIGO or other experiments do not have thermal spectrum. But I'm not certain.
I know that Hawking's ...
1
vote
0answers
87 views
Euclidean quantum gravity and gravitational instantons
I have some questions concerning the calculations made by Hawking in the 80-90's using Euclidean (canonical) quantum gravity on gravitational instantons. Were those tunnelings only between identical ...
1
vote
0answers
82 views
Canonical quantum gravity
I am looking for an introduction (textbook or paper, or if someone wouldn't mind writing a memo on it) to canonical quantum gravity, specifically the concept of minisuperspaces. I have been reading ...
1
vote
0answers
257 views
Quantization of Gravitational Field: Quantization conditions
I'm begining to study Quantization of field with the second quantization formalism. I've studied phononic field, electromagnetic field in the vacuum and a generic relativistical scalar field.
I ...
1
vote
0answers
228 views
Are virtual photons affected by effective gravity in non-linear quantum electrodynamics?
Quantum electrodynamics based upon Euler-Heisenberg or Born-Infeld Lagrangians predict photons to move according to an effective metric, which is dependent on the background electromagnetic field in a ...
0
votes
0answers
83 views
How can it be seen that ST unifies GR and QM as the quantum gravity scale is not directly accessible
I am a newbie to superstring theories, but I came into this question:
so superstring theories purport to unify general relativity and quantum theory.
However, there is yet no definitive way to test ...
0
votes
0answers
62 views
Why there can't be infinitely small existing?
Why there can't be infinitely small existing?
I am not suggesting it can or cannot. I am asking can there be an absolute or reasonable answer to that question.
0
votes
0answers
54 views
What is the physical mechanism for the subjective rapid vanishing of the firewall on such a short notice?
Suppose there is an astronomical sized black hole. There is an observer Alice. She jumps into the black hole after it has emitted 2/3 — or 3/4, the exact number doesn't matter — of all the ...
0
votes
0answers
142 views
Newton Gravitational constant $G$, Plank constant $\hbar$ , Speed of Light $c$ : The Dream Team of moderators?
The 3 great constants of Nature are well known :
The Speed of light $c$ (special relativity)
The Plank constant $\hbar$ (quantum mechanics)
The Newton ...
0
votes
0answers
19 views
In the Hartle-Hawking boundary condition, what should we set as the initial values for the scalar fields?
In the Hartle-Hawking boundary condition, what should we set as the initial values for the scalar fields? Fields like the Higgs assuming it's fundamental, and the inflaton fields.
0
votes
0answers
254 views
Gravitation and the QFT vacuum
I'm asking this to get yet another lessson in the inability of QFT and GR to cohabit. Many people believe GR must yield to quantization. The question here is as to why the activity of the vacuum ...
0
votes
0answers
147 views
Do spacelike singularities really exist in quantum gravity?
Do spacelike singularities really exist in quantum gravity? If the memory of anything which falls into a black hole can't get out, is there any sense in which the interior of the black hole is real? ...
