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

learn more… | top users | synonyms

3
votes
3answers
165 views
+50

Could future experiments on “Gravitational Casimir Effect” confirm the existence of gravitons?

From Casimir effect, we know that when two plates are placed very close to each other in vacuum, they attract each other because the quantum fluctuations that press on the two plates' outer surfaces ...
2
votes
3answers
362 views

Are length contractions limited by Planck length?

While we are getting closer to speed of light our length in the direction of the movement is according to Lorentz transformation getting shorter. But we can not (even theoretically) consider length ...
2
votes
3answers
50 views

How does one experience single gravitons and/or Planck-force?

Moving sufficiently far away from a light source one would not be able to measure a steady stream of light, but only single photons every now an then. The experience would be a very faint blinking. ...
17
votes
5answers
2k views

Why doesn't matter clump together such that it can't be taken apart again?

Given the inverse square law force of gravity shouldn't two particles that are infinitely close to each other be infinitely attracted to one another? For example, suppose the hands of some super deity ...
2
votes
2answers
77 views

Gravity as a particle-based force vs space-time warp

I'm interested to understand the interpretation of gravity as a result of exchange of force particles (ie gravitons) vs General Relativity-based warping of space-time. Related to this is while a ...
3
votes
1answer
659 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 ...
0
votes
0answers
35 views

Would a directional “graviton” emitter violate any known laws of physics?

Setting aside that we don't known what the mediating partial in quantum gravity looks like and have no way to manipulate it, what would the implications be of a directional graviton source be? Would ...
2
votes
1answer
118 views

How does this new theory of a possible infinitely old universe not violate the second law of thermodynamics

I read the following article: http://phys.org/news/2015-02-big-quantum-equation-universe.html And followed it back to this journal reference : http://arxiv.org/abs/1404.3093 It appears to be ...
4
votes
1answer
84 views

Theories that predict the number of space-time dimensions

My impression in that most theories assume three spatial dimensions and one temporal dimension, though could in principle be formulated in others numbers of dimensions without inconsistencies. I know, ...
0
votes
0answers
50 views

What does quantum gravity look like at or beyond the Planck scale?

I am reading an article called The fundamental nature of space and time by Gerard 't Hooft. On page 3 he writes the following: Physically, however, the perturbative approach fails. The difficulty ...
32
votes
2answers
3k views

Why is gravity such a unique force?

My knowledge on this particular field of physics is very sketchy, but I frequently hear of a theoretical "graviton", the quantum of the gravitational field. So I guess most physicists' assumption is ...
7
votes
1answer
136 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 ...
0
votes
0answers
14 views

Is black hole complementarity compatible with canonical quantization?

Suppose at time $t$, Alice and Bob are hovering just outside the event horizon of a black hole, sharing the same position, velocity and acceleration. Shortly afterward, in less than the Schwarzschild ...
1
vote
0answers
20 views

Ground state energy in a simple quantum gravity situation

I found this problem in an MIT undergrad QM problem set; it is problem number 2, part a, number iv. I'll summarize everything below, but here's the link: ...
7
votes
2answers
291 views

Is quantum gravity, ignoring geometry, the theory of a fictitious force?

This question is motivated by this question and this one, but I will try to write it in such a way that it is not duplicate. In short, I don't understand the motivation for a "quantum theory of ...
1
vote
0answers
49 views

Gravitational singularity

Is it possible that the gravitational singularity actually turns out to be a genuine singularity once we have a true theory of quantum gravity in place. There is a lot of talk about singularity but ...
7
votes
2answers
675 views

Does anyone take the Wightman axioms seriously?

Does anyone take the Wightman axioms seriously? Mainly with respect to quantum gravity or gauge theores, abelian or non-abelian? Anyone doing any research on axiomatization of QFTs in some way?
3
votes
1answer
329 views

The cap on massive particles's speed is below the speed of light due to Planck length?

This answer http://worldbuilding.stackexchange.com/a/8525/1991 claims that no particle can accelerate further after its de Broglie wavelength becomes Planck length. Given that speed at this point is ...
4
votes
1answer
110 views

Renormalization in Classical Field Theory

1) The statement that general relativity (GR) is not renormalizable - is it a statement only about the quantization of GR or is it non-renormalizable also as a classical field theory? 2) More ...
1
vote
0answers
38 views

Information loss from entanglement and cosmological horizons?

Suppose we have a qubit P in an unknown quantum state. Unknown as in we didn't prepare it, and don't know how it was prepared either. Without measuring the qubit in any way, we encode it into two ...
3
votes
1answer
521 views

Introductions to discrete space-time

It's comparatively easy (cum grano salis) to grasp the following concepts: Euclidean space-time (continous space and continuous time) classical mechanics (discretely distributed matter in continous ...
2
votes
0answers
46 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 ...
6
votes
2answers
121 views

Dirac bracket and second class constraints in first-order gravity formalism

In the first order formulation of general relativity, the frame field $e_{\mu}^a$ and $\mathrm{SO}(3,1)$ spin connection $\omega_{\mu c}^b$ are independent variables. In the Hamiltonian formulation of ...
5
votes
0answers
92 views

Are there any proposed alternatives to quantum mechanics as there are alternatives to general relativity?

There are a lot of alternatives to general relativity and one of the motivations is attempting to formulate a working theory of quantum gravity. In some limit they reduce to general relativity. But ...
15
votes
2answers
2k views

Why don't we have a theory of everything?

What is currently stopping us from having a theory of everything? i.e. what mathematical barriers, or others, are stopping us from unifying GR and QM? I have read that string theory is a means to ...
0
votes
1answer
82 views

Can Einstein's 'Theory of General Relativity' exist in Harmony with 'Quantum Mechanics'? [closed]

From the Book 'In Search of Schrodinger's Cat': Coordinates in space-time represent position; causality depends on knowing precisely where things are going, essentially on knowing their momentum. ...
-3
votes
3answers
365 views

Incommensurability between different observers describing the same universe?

According to black hole complementarity, if there is a black hole and Alice falls into it carrying a qubit, but Bob stays out, then Alice can measure the qubit inside the black hole, and confirm it ...
-3
votes
2answers
615 views

Since when were Loop Quantum Gravity (LQG) and Einstein-Cartan (EC) theories experimentally proven?

Can this template at Wikipedia be true? It seems to suggest that Einstein-Cartan theory, Gauge theory gravity, Teleparalleism and Euclidean Quantum Gravity are fully compatible with observation! It ...
1
vote
0answers
23 views

How would gravitons be detected? [duplicate]

How would gravitons be detected indirectly or directly, in space or on earth? And what experiments are going on to find gravitons?
8
votes
1answer
2k views

What happens to atoms inside a black hole?

Black holes have very high gravitational force that tends to crush everything. So as we know atoms in a molecule have inter-atomic spacing between them and further electrons also revolve at a certain ...
0
votes
0answers
34 views

Does infinity really exist? [duplicate]

Does infinity really exist, or is it just part of the fabric of our imaginations? Great mathematicians, like Gauss or Pointcaré, said that actual infinity does not exist.infinity is mathematical ...
5
votes
2answers
117 views

Bekenstein bound for electron?

Using the Wikipedia version of the Bekenstein bound, and substituting the Wikipedia values for electron mass and radius, one obtains 0.0662 bits. Does this really mean that a system, any system, ...
0
votes
0answers
39 views

No Hair systems and black hole entropy

To my understanding, a black hole is a no hair system. So it can be described just by its mass, spin and charge. In other words it does not differentiate where its mass comes from, so it could be made ...
1
vote
1answer
465 views

Black-hole firewall and holographic principle [closed]

Can the firewall be viewed as the holographic boundary? Naively a hologram 3d image can not cross the hologram 2d surface that produces that image. According to the metaphor the boundary - 2d field ...
1
vote
0answers
84 views

What exactly is black hole complementarity and why is it necessary for solving black hole information paradox?

What exactly is black hole complementarity and why is it necessary for solving black hole information paradox? The first question is about the story of vacuum fluctuation causing Hawking radiations. ...
3
votes
1answer
70 views

Why is the value of the action integral in general relativity the same on all regions that are homologous?

In their famous paper Action integrals and partition functions in quantum gravity, Gibbons and Hawking argue that in order to avoid the singularity of a Schwarzschild black hole you can complexify ...
2
votes
2answers
159 views

Why isn't our universe symmetric?

Why were random variations introduced in the spherically symmetric universe after Big Bang which made it non-symmetrical. Since the outcome of a coin toss depend on factors such as torque applied, air ...
0
votes
0answers
59 views

That the gravitational mass equals to inertial mass can imply that only Einstein-Hilbert action is satisfied

I read Spacetime and Geometry by Sean Carroll. In p. 166 there is a comment that GR's action is nonlinear because if it is linear like the EM field, then graviton will not interact with each other, ...
0
votes
0answers
45 views

Regarding Randall Sundrum model

In Randall Sundrum model 2, that is the one with non compact fifth dimension, there is only one brane, which is the Planck brane. The TeV brane is removed by taking the radius of the fifth dimension ...
29
votes
2answers
4k views

What are Stephen Hawking's main contributions to research-level physics?

Without a doubt, Stephen Hawking is the most famous living scientist; indeed, his public visibility in all of history seems to be rivaled only by Einstein and easily eclipses giants of physics such as ...
2
votes
0answers
32 views

Should the answer to Einstein & Quantum gravity be found in conditions of our local observable universe? [duplicate]

It seems like the discourse over a unified Einstein and Quantum Gravity disregards the phenomena encountered in our local observable universe, such as we find throughout the Intergalactic Medium. One ...
5
votes
3answers
169 views

Gravity - Force or Result?

I am no Physicist, but I enjoy reading about Physics. However reading about leading theories such as M-Theory and others they speculate about the existence of the Graviton. In my past reading of ...
0
votes
0answers
68 views
77
votes
5answers
24k views

What is the actual significance of the amplituhedron?

The news that physicists have discovered a geometrical object that simplifies a lot our models of quantum physics has recently became viral. For an outsider like me, it is difficult to actually ...
2
votes
0answers
39 views

CFT calculation of the Partitionfunction of $2+1$ dimensional gravity

I want to reproduce formula (4.29) in http://arxiv.org/abs/0804.1773v1 given by: $$ Z=Tr(q^{L_{0}}\bar q^{\bar L_{0}})=|q|^{-2k} \prod^{\infty}_{n=2}\frac{1}{|1-q^{n}|^{2}} $$ Where the trace is ...
4
votes
0answers
42 views

What is the status of gauged gravity [duplicate]

The Standard Model of elementary particles is a gauge theory with gauge group $SU(3)\times SU(2)\times U(1)$, which is really a successful theory. We might be able to quantize gravity similarly. ...
2
votes
1answer
89 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 ...
6
votes
1answer
131 views

Regarding Non-renormalizatibility of GR

I've been doing some reading trying to get to a better understanding of some renormalization issues with the Einstein-Hilbert action. But, something odd came into mind that I'm hoping some users may ...
0
votes
0answers
145 views

Does space expand locally without restriction in freefall to central region of black hole?

It is often stated that a distant observer will observe a freefalling object as experiencing an infinite journey to the event horizon, but that a traveler in the local frame will experience a ...
0
votes
1answer
138 views

Does Newton's first law apply also to non-newtonian physics?

I think I understand than an example of Newton's first law (intertial frames) would be a single asteroid in vaccum with no other bodies around, a comet in such free space or likewise. Then I think the ...