Any of the various explanations of gravity as a quantum theory, including string theory and loop quantum gravity.
6
votes
0answers
114 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) ...
-5
votes
0answers
83 views
Criticism of String Theory by other string theorists [closed]
*EDIT: Due to policy I will edit this into a question:
Do you know any string theorist that have criticized string theory and if so please could you give me references? thanks.
End of EDIT. ...
0
votes
1answer
90 views
can be exist the negative mass? [duplicate]
I'm not sure about this but I guess there must be negative masses in the universe because of the symmetry. If the gravity is one of the main forces in nature it must has negatives mass to be able to ...
4
votes
1answer
66 views
T-Duality between Type HE String theory and Type HO string theory
My question is regarding T-Duality between the 2 Type H string theories.
I know that the Type II String theories are T-dual to each other because T-Duality changes the sign of the Gamma Matrix so
...
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 ...
1
vote
1answer
70 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 ...
0
votes
1answer
67 views
Why Planck scale is so important?
I know that Planck scale is the scale where both, gravity and quantum effects are relevant simultaneously. Are there more reasons?
0
votes
1answer
68 views
Explanation for the notion that physical laws break down at the Big Bang
I've often heard the phrase "physical laws break down at the big bang".
Why is this? Divide by zero?
Please provide the mathematics.
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.
1
vote
1answer
69 views
What is the smallest existing thing in theory and law?
What is the smallest existing thing in theory and law?
3
votes
2answers
87 views
Are all points in the universe connected?
Is it true that every point in the universe is connected or could be so theoretically? If so how is this mediated?
Is it through the quantum nature of the fabric of space or is it through the ...
1
vote
1answer
29 views
measure higher frequencies then half of Planck-frequency?
The maximum frequency is defined by the Planck frequency $\omega_P$. Also there is the Shannon theorem which tells us that to lossless capture a signal, you have to sample it with minimum of the ...
2
votes
1answer
105 views
Phys.org Spectral geometry to unite relativity and quantum mechanics, restate in laymens terms?
Lingua Franca links relativity and quantum theories with spectral geometry
Could someone give me a short synopsis of this article in laymens terms? What implications does this have in the physics ...
9
votes
2answers
337 views
What is the current state of research in quantum gravity?
I was browsing through this and was wondering what progress in quantum gravity research has taken place since the (preprint) publication.
If anyone can provide some helpful feedback I would be ...
7
votes
0answers
103 views
Why is the Planck length the shortest measurable length? [duplicate]
I quote from the Wikipedia article on Planck length:
According to the generalized uncertainty principle, the Planck length
is in principle, within a factor of order unity, the shortest
...
5
votes
0answers
238 views
Can the laws of quantum mechanics be derived from a more fundamental theory? [closed]
String theory takes quantum mechanics for granted and tries to make it compatible with gravity but if it turns out to be a theory of everything then shouldn't it in principle explain why our world is ...
3
votes
1answer
209 views
How do I quantize a classical field theory
I have not been able to find any information about this on the Internet. I am a middle-schooler, 14, who self-studies physics, and I know up to and including ODEs, and some of the calculus of ...
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 ...
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 ...
0
votes
3answers
234 views
Why isn't the Bekenstein-Hawking Entropy considered the quantum gravitational unification?
Based on the Bekenstein-Hawking Equation for Entropy, hasn't the relationship between quantum mechanics and gravity already been established.
19
votes
3answers
592 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 ...
5
votes
2answers
324 views
The Uncertainty Principle and Black Holes
What are the consequences of applying the uncertainty principle to black holes?
Does the uncertainty principle need to be modified in the context of a black hole and if so what are the implications ...
2
votes
3answers
274 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 ...
10
votes
1answer
387 views
Why one-dimensional strings, but not higher-dimensional shells/membranes?
One way that I've seen to sort-of motivate string theory is to 'generalize' the relativistic point particle action, resulting in the Nambu-Goto action. However, once you see how to make this ...
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 ...
4
votes
1answer
176 views
Is the quantization of gravity necessary for a quantum theory of gravity? Part II
(At the suggestion of the user markovchain, I have decided to take a very large edit/addition to the original question, and ask it as a separate question altogether.)
Here it is:
I have since ...
15
votes
3answers
496 views
Why is gravity so hard to unify with the other 3 fundamental forces?
Electricity and magnetism was unified in the 19th century, and unification of electromagnetism with the weak force followed suit, bringing into play the electroweak force.
I've been told that ...
3
votes
1answer
220 views
Deriving the reduced Green's functions in Polchinski's volume 1
In equation 6.2.7, Polchinski defines his reduced Green's functions $G'$ on the 2-manifold to satisfy the equation,
$$ \frac{-1}{2\pi \alpha '}\nabla ^2 G'(\sigma_1, \sigma_2) = ...
1
vote
1answer
170 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 ...
2
votes
1answer
134 views
What happens to atoms inside the black hole?
Black holes have very high gravitational force intending to crush everything. So as we know atoms in a molecule have inter atomic spacing between then and further electron,s also revolve at a certain ...
6
votes
0answers
141 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 ...
4
votes
3answers
282 views
Higgs-Boson/Graviton
The Higgs boson gives particles mass. And the graviton is the theoretical force-carrier of gravity. Gravity depends on mass. So if the Higgs Boson gives things mass, it therefore gives them gravity. ...
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 ...
14
votes
7answers
593 views
Is the quantization of gravity necessary for a quantum theory of gravity?
The other day in my string theory class, I asked the professor why we wanted to quantize gravity, in the sense that we want to treat the metric on space-time as a quantum field, as opposed to, for ...
1
vote
1answer
107 views
Divergence in Supergravity
I'm not familiar with supergravity so here's my question: I've heard in talks that if one finds divergence for five-loop 4-graviton scattering amplitudes in five dimensions this translates to a ...
1
vote
1answer
200 views
Dirac Equation in General Relativity
Dirac equation for the massless fermions in curved spase time is $γ^ae^μ_aD_μΨ=0$, where $e^μ_a$ are the tetrads. I have to show that Dirac spinors obey the following equation:
...
5
votes
4answers
300 views
What is the “foamy space” hypothesis that has been debunked recently?
In "Space-Time Is Smooth, Not Foamy", a Space.com article, it is stated:
In his general theory of relativity, Einstein described space-time as fundamentally smooth, warping only under the strain ...
1
vote
0answers
113 views
Approaches to Quantum gravity [closed]
I'm going to start my graduate studies in theoretical physics. My supervisor wants me to work on quantum gravity. He gave me the liberty to chose a particular approach to Quantum gravity (Excluding ...
3
votes
3answers
220 views
Question on inflation
I have two particular questions regarding the inflationary scenario. They are:
1.) What is the physical origin of the inflaton field?
2.) Why has the potential of the inflation field its particular ...
4
votes
1answer
88 views
Where and how is the entropy of a black hole stored?
Where and how is the entropy of a black hole stored?
Is it around the horizon? Most of the entanglement entropy across the event horizon lies within Planck distances of it and are short lived.
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 ...
3
votes
1answer
124 views
Question on inflation as a phase transition
I have just finished watching the following video http://www.youtube.com/watch?v=beQ9fZ0jVdE where Laughlin, Gross and some students discuss e.g. about inflation. The following question is risen:
Is ...
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 ...
3
votes
1answer
99 views
Why are some extra dimension theories known as strongly coupled and others as weakly coupled?
I was looking at pdf file of the presentation of a conference talk. The speaker discusses two types of "mechanisms" for stabilizing the weak scale and calls them "weakly coupled" and "strongly ...
11
votes
2answers
401 views
Extremal black hole with no angular momentum and no electric charge
A black hole will have a temperature that is a function of the mass, the angular momentum and the electric charge. For a fixed mass, Angular momentum and electric charge are bounded by the extremality ...
5
votes
0answers
124 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 ...
1
vote
1answer
96 views
What are all the approaches that have been tried for a theory of quantum gravity? [closed]
I am aware that that the most researched approach is that of string theory. I have also heard about quantum loop gravity. What other approaches are there to unify gravity and QFT? Also, please include ...
0
votes
3answers
160 views
The Role of Gravity among the Fundamental Forces of Nature
If we look at the standard model, we have 4 fundamental forces which include
Gravity,
Electromagnetism,
Nuclear weak force,
Nuclear strong force.
I would like to look at Gravity for a minute. ...
5
votes
1answer
357 views
Do all the forces become one?
Were the forces of nature combined in one unifying force at the time of the Big Bang?
By which symmetry is this unification governed?
Are there any evidence for such unification of forces?
Has ever ...
4
votes
2answers
136 views
What is the motivation for assuming “Page” scrambling for Hawking radiation?
What is the motivation for assuming "Page" scrambling for Hawking radiation?
Obviously, at the semiclassical level, we want the outgoing Hawking radiation to look thermal and mixed. However, surely ...
