Any of the various explanations of gravity as a quantum theory, including string theory and loop quantum gravity.

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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 ...
2
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1answer
97 views

What's the recent released 750GeV particle's spin?

I was told that it has recently been confirmed to be spin-2 particle, and potentially to be graviton. I'm pretty interested in how this has been examined. Edit: During the Moriond 2016 conference, ...
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38 views

I wondered what proof exist for the existence of gravitons?

It seems from my perspective that gravity is an indirect trait of matter; meaning that gravity is a trait of spacetime itself and that when matter interacts with spacetime, a bend occurs producing ...
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2answers
134 views

How exactly does string theory make general relativity and quantum mechanics compatible?

Correct me if I'm wrong, but the reason that quantum mechanics and general relativity are incompatible is because the quantum foam at Planck scales renders space-time discontinuous and doesn't allow ...
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2answers
72 views

Zero gravity at center of astronomical bodies [closed]

All theories agree that the net gravity at center of all astronomical bodies is zero. Are black holes exception to this? Is gravity zero at the center:) of singularity? Is anything like center of ...
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1answer
68 views

What is the difference between Quantum Gravity, Loop Quantum Gravity, Quantum Geometrodynamics, and Relativistic Quantum Mechanics? [closed]

What is the difference between Quantum Gravity, Loop Quantum Gravity, Quantum Geometrodynamics, and Relativistic Quantum Mechanics? As far as I know, they are all theories made to unify QM and GR. But ...
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2answers
201 views

Are massive gravitons as the dark matter fluid more correct than the notion of WIMPs?

Accepted at APS Physical Review D: Massive gravitons as dark matter and gravitational waves Precursor: Bigravitons as dark matter and gravitational waves The massive graviton is a viable ...
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1answer
52 views

Are there any numerical predictions of the Newtonian gravitational constant $G$ from modern theories?

There are no established relationships between the Newtonian gravitational constant $G$ and other fundamental constants, so there is no way to derive its value from other quantities. Its value must be ...
3
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1answer
32 views

Does the Bekenstein entropy bound present problems for unitarity in cosmological models that invovle a collapse or bounce?

If we expect the Bekenstein bound, or something like it, to hold in a collapsing universe, will that not eventually force us to accept some loss of information, or is there something I'm missing?
4
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2answers
135 views

What is the black hole information paradox really? [closed]

Preliminaries What is the black hole information paradox really? Is it a sophisticated way to ponder and debate the existence of an operator on the boundary that can tease out the interior of a ...
9
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3answers
603 views

General relativity vs graviton discovery

Will the discovery of the graviton lead to the redundancy of general relativity even though it has been so well established. If not, will it mean that gravity will have two separate theories that ...
5
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2answers
146 views

What does string theory predict for the singularity inside a black hole?

The usual explanation for what's going on inside a black hole goes something like "General Relativity predicts a singularity with infinite curvature, but when matters gets so tightly compressed we ...
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1answer
85 views

Exotic differentiable structures in physics

When reading a bit on exotic spheres and exotic $\mathbb{R}^4$'s, I came across some papers of Carl H. Brans and Torsten Asselmeyer-Maluga: "Exotic differentiable structures and general relativity" (...
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53 views

Does gravitational radiation have a formalism similar to Wheeler-Feynman electrodynamics?

Binary systems radiate energy away in gravitational waves as the orbits of the two masses spiral in towards each other. My understanding of gravity is that we think of it as a mediator of particle-...
2
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1answer
128 views

What is the relation between the metric tensor and the graviton?

In Zee's quantum theory in a nutshell, at the end of chapter I.10, he states that the graviton is of course the particle associated with the field $g_{\mu\nu}$. My understanding of quantum ...
4
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2answers
147 views

Preparatory knowledge to study Quantum Gravity

I am an old (41-Years-old) physics graduate. I pretty much quit to "frequent physics" 10 years ago and my ability to manage physics is a bit rusty. I was fascinated with Quantum Gravity (QG) theory ...
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2answers
95 views

Is the spacetime for gravity described with gravitons flat?

Gravity has two equivalent descriptions. One is general relativity, the other is the mechanism by the exchange of gravitons. Is in the latter the spacetime flat?
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41 views

Can we express QFT in R^8 where the spacetime can be embedded in?

A smooth, 4-dimensional manifold can be embedded in $R^8$. Isn't it a natural selection of space for QFT when we try to extend QFT with gravity?
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60 views

Which quantum gravity theories do predict a growing number of space dimensions?

In this 2013 Nature article there is a short presentation of the causal dynamical triangulations approach to quantum gravity, where it is said Intriguingly, the simulations also hint that soon ...
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24 views

Causal networks and “local” entanglement

On his Opus Maximus, a new kind of Science, Stephen Wolfram suggests that causal networks can create behaviour similar to entanglement because the local structure of space is only an averaged ...
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1answer
56 views

Could gravitational waves have a large entropy in quantum gravity?

The question is broad, and we still don't know what is quantum gravity. But let me be more specific. In the question (on this site, see below) on whether gravitational waves have entropy the answers ...
6
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2answers
254 views

From Quantum Mechanics to Quantum field theory to String theory?

Today during a very "unique" study session, I might have internalized why Quantum mechanics was not enough, and Quantum field theory makes sense. It seems the reasons are that When a potential is ...
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21 views

LIGO Gravitational Wave Discovery and Gravitons [duplicate]

Now that gravitational waves have been detected, how hard will it be to detect a graviton? Will the equipment have to be more sensitive or are the difficulties more complicated than that?
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151 views

What kind of fundamental interaction is gravitation?

Einstein showed that gravitation is not a force but a effect caused by curvature of space time. Then why does theories of quantum gravity treats gravitation as one of fundamental force?
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42 views

What is quantum foam?

Can someone please explain me what quantum foam is? Is it the space-time fabric or just any other field? Also please explain this image
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40 views

Has anyone explored a possible duality between quantum gravity and statistical mechanics?

There is a well known duality between quantum mechanics in D dimensions and classical statistical mechanics in D+1 dimensions. Specifically, the Euclidean version of the path integral in D dimensions ...
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44 views

Scale invariance

Physically why should scale invariance break down at the Planck limit? If not what are the other possibilities to save the quantum granularity of spacetime? I would really appreciate professional ...
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2answers
109 views

A doubt regarding Black Hole Complementarity

A friend was explaining Black Hole Complementarity to me, and at one point he said that to get a (horrendously) mixed quantum state, i.e. a thermal density matrix without a heat bath, one takes a ...
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122 views

A spin zero graviton?

Why can the graviton not be a spin 0 particle? On a similar note why can it not be a spin 4, spin 6 particle?
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18 views

Why is graviton not found yet? [duplicate]

Why is graviton not found yet? Newton said gravity pulls us, Einstein said space is bent and it pushes us, hawking predicts the existence of graviton and 'hawking radiation'. How far are we from ...
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39 views

What´s the physical foundation of the assumption that the curvature of spacetime can be quantised? [duplicate]

At the moment different paths (by percentual very few people in the world) are taken to arrive (that is, if an arrival exists) at a theory that can quantise the curvature of spacetime. Considering the ...
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9 views

Is viscosity excluded by Lorentz symmetry in spatio-temporal discreteness?

"In the case of spatio-temporal discreteness, viscosity is excluded by Lorentz symmetry". This statement is from here. Can anyone explain why this is the case? I'm looking for an intuitive way to ...
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1answer
142 views

Why are string theorist so indifferent to the gauge structure of gravity? [closed]

Gravity shares many of the characteristics of Yang-Mills gauge theory. For example, the affine connection plays the similar role as the gauge potential in gauge theory, the Riemann tensor plays the ...
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1answer
54 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
169 views

What is the problem with quantizing GR in the Effective Field Theory approach?

In the modern view due to Wilson, the cut-off $\Lambda$ is an intrinsic property of a theory and renormalization just means that the theory is invariant under scale transformations below $\Lambda$. ...
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If gravitons are 'real' and analogous to photons are they also being 'stretched' by the universe's expansion?

Since photon wavelengths are stretched by our expanding universe, appearing to us as a redshift, would graviton wavelengths similarly be stretched? For that matter, do gravitons even have a ...
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142 views

The integration of Einstein's equations [closed]

Einstein's equation is $$G_{\mu\nu} + \Lambda g_{\mu\nu} = {8 \pi G \over c^4} T_{\mu\nu}$$ where $G_{\mu\nu} = R_{\mu\nu} - (1/2)g_{\mu\nu}\,R$ is the Einstein tensor, which combines the Ricci tensor,...
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69 views

Why is quantising gravity so difficult? [duplicate]

Since gravity is so similar with the Yang-Mills theory, the Christoffel connection is the gauge potential, the Riemann curvature is the field strength, then why is quantising gravity so difficult when ...
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110 views

Heisenberg's uncertainty principle at the Planck scale

A particle of mass has a reduced Compton wavelength $$\overline{\lambda}_{C} = \frac {\lambda_{C}}{2 \pi} = \frac {\hbar}{m c}$$ Schwarzschild radius of the particle is $$r_s = \frac{2Gm}{c^2}=2\,\...
2
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2answers
95 views

Can gravity prevent quantum superposition of positions for a massive object?

Theoretically, nothing prevents a really massive object to be in a superposition of two spatial locations, even far away one from the other. Then I guess spacetime would also show the superposition of ...
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101 views

What is the justification for continuing to model space-time as a manifold in string theory?

Background The question I have arises from taking seriously the idea that, in a physical theory, one should first define all physical quantities via (thought) experiment. Justification and ...
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1answer
93 views

Quantum Gravity vs. Quantum Field Theory in Curved Space-time [closed]

I'm a freshman on Physics course, espite of this fact I have a quite interest on Gravitation. My question is: What is the difference between Quantum Gravity and QFT in curved space-time? The great ...
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2answers
94 views

Could there be a “massive gravity” theory?

If we talk about a "quantum theory" of General Relativity, we know that the particle that mediates the gravitational force would be the so called Graviton, a massless particle with spin $2$. I ...
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57 views

Wave function of the universe - universes similar to ours [closed]

According to this image, the first peak in the graph corresponds to our universe while the other peaks correspond to other, less probable universes. But what do points slightly right (or left, doesn't ...
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181 views

Singularity - exactly what is it?

In quantum mechanics and gravity theories one always meets the word "singularity" in connection with talks about black holes and the big bang, etc. Now in mathematics a singularity is well defined – ...
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2answers
133 views

How do people go about looking for asymptotic safety in quantum gravity?

Do we have (proposed?) methods to look for fixed points in the renormlaization group flow of the Einstein-Hilbert action? My understanding of the RG is still somewhat sketchy at this point and I am ...
5
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1answer
138 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 (...
3
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1answer
97 views

Is there a path to go from GR, to Gravitational Waves, to Gravitational Particles (Gravitons), to Quantum Gravity?

The articles on the subject often say : a part of the mass of the 2 celestial bodies became energy for gravitational waves after merging : E(gravity waves) = (M1 + M2 - M_merged).c^2 Intuitively I ...