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

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Can weakness of gravity explore new dimensions

Since gravitational force is weakest force out of the four fundamental fources at the microscopic level. Is it possible that gravitational force is strong in a particular direction at a new ...
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1k views

Wouldn't angular momentum of a binary star system decrease?

Consider a binary star system, as these stars go around one another they would emit gravitational waves. Since, the graviton is a spin 2 particle. Wouldn't the angular momentum of the stars decrease? ...
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3answers
199 views

Are there any QM effects where charged particles are not intimately involved?

Are there any QM effects that have been/could be measured from interactions involving non-charged particles? Elementary QM is all about the electron energy levels in the atom, photon - atom ...
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25 views

In a theory of quantum gravity, does the gravitational coupling “constant” actually depend on the scale of the systems involved in the interaction?

In the following I will give some arguments that will indicate that the gravitational coupling "constant" actually depends on the scale (space and time) of the interacting systems. The question is: ...
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61 views

Derivation of metric of space time with a point source in 2+1 dimension using ADM formalism

In "Quantum Gravity in 2+1 dimension" by S Carlip, Sec 3.1 (where the metric of a spacetime with a point source is derived, using the ADM formalism), equation 3.8 states that (this is the momentum ...
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177 views

The BICEP2 data are evidence of gravitational waves and of inflation. Are they also the first observation that requires quantum gravity?

It strikes me that the recent announcement of data from BICEP2 contains two really Big Deals: the first evidence of gravitational waves the first evidence of inflation. Is there also a third? ...
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113 views

What does BICEP2's results tell us about gravitation waves and quantum gravity?

The BICEP2 results, unless I am mistaken, are a measurement of CMB polarization, i.e. photon polarization. That is, taken at face value they say nothing about gravity directly. Now, we can start to ...
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16 views

Clarification about “projections and correlations” in Heller's Quantum Gravity

The footnote (bottom) for the following paragraph from “Creative Tension: Essays On Science & Religion” by Michael Heller, has “such a projection, being always “onto,” switches off all possible ...
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667 views

Why quantising gravity necessarily give us gravitons?

Gravitons are supposed to be the quanta of gravitational field My question is, if we do not know how to quantize gravity yet, how do we know that quantizing it in principle should give us gravitons, ...
3
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1answer
55 views

How can Planck units be consistent with conflicting dimensions of mass?

I suspect I'm missing something obvious, but I'm coming up blank. I've gotten pretty comfortable with so-called natural units over the years: in doing quantum mechanics/QFT, it's common to set $c = ...
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60 views

Local degrees of freedom in QUGRA lead to black holes

I am reading Jan Boer's review of the AdS/CFT correspondence and I quote from end of page 1, where he is talking about equivalence of (d+1)-dim gravity to d-dim field theory “If true, it implies ...
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3answers
231 views

Is it possible that there is no theory of quantum gravity? [closed]

{{Under Construction}} Short question: What published works and what research groups are investigating the possibility of inexistance of gravity at quantum level? Long question: I am no ...
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95 views

What do we learn from gravity in three spacetime dimensions?

The last decades there has been a lot of research going on in the the area of three dimensional gravity. The motivation, I understand, is threefold: Whereas gravity is not perturbatively ...
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38 views

Proof of uniqueness for holographic assumption

Is it proved that the over-counting of the degrees of freedom in a field theory of gravity has as only solution the "axiom" of holography? While I understand the behaviour of the area vs. volume ...
2
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0answers
125 views

what is 't Hooft up to? [closed]

apart of the 't Hooft diagrams that you all love (and find all sort of dualities starting with them) one of the venues 't Hooft works nowadays is apparently some sort of "deterministic representation ...
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1answer
402 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?
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1answer
100 views

Two small objects are placed at rest in an empty universe a great distance apart. Given an infinite amount of time will gravity cause them to meet? [closed]

Let's say the objects are marble size or even single atoms or quarks. They are placed in an otherwise empty universe(expanding or non-expanding) at opposite ends of the universe with an arbitrarily ...
75
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3answers
19k views

Why does Stephen Hawking say black holes don't exist?

Recently, I read in the journal Nature that Stephen Hawking wrote a paper claiming that black holes do not exist. How is this possible? Please explain it to me because I didn't understand what he ...
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0answers
155 views

What prediction led to the vacuum catastrophe?

The disagreement between predicted and measured energy density of the vacuum is one of the great unsolved problems of science. According to this book the predicted energy density was obtained as ...
6
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1answer
142 views

Is Poincare recurrence relevant to our universe?

If the theory of everything indicates a singularity-free and finite universe, will Poincare recurrence be relevant to the universe? If so, is there any interesting physical consequence, e.g. in ...
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0answers
56 views

Squashed 3-sphere?

What is a squashed 3-sphere? In context of quantum gravity. I stumbled upon a term 'squashed 7 sphere' but that's concerning supersymmetry. Is it just normal 3-sphere metric, that is just 'squashed' ...
3
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0answers
61 views

Homeomorphism between the space of all Ashtekar connections and spacetime?

Excerpt from an essay of mine: Let $\Psi(\varsigma)$ be the wavefunction in the loop representation, where $\varsigma:[0,1]\to\mathcal{M}$, where $\mathcal{M}$ is spacetime. Then, let ...
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190 views

Superspace as the Hilbert Space for Quantum Gravity

Let $\mathcal{A}$ be the Ashtekar connection. Since $^{(3)}g_{AB}=i\frac{\delta}{\delta\mathcal{A}^{AB}}$ (see R. Penrose, 2004: Road to Reality. Vintage Books, 1136 pp.), the Ashtekar connection, in ...
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63 views

Timelike Loop Spaces as Projective Null Twistor Spaces

Let $\mathcal{M}$ be a spacetime, and let $\Omega\mathcal{M}$ denote the loop space of the spacetime. My idea is that the set of all closed timelike curves of $\mathcal{M}$ forms the projective null ...
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46 views

Stringy corrections to Friedmann equation

Does anyone know a reference or a paper which discusses string theory correction to Friedmann equations?
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1answer
216 views

The most general procedure for quantization

I recently read the following passage on page 137 in volume I of 'Quantum Fields and Strings: A course for Mathematicians' by Pierre Deligne and others (note that I am no mathematician and have not ...
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1answer
65 views

How does a gauge theory probe a spacetime singularity?

Within the framework of string theory, I have read in numerous articles such as the introduction of this this in which it is stated that the gauge theories living on a stack of D-branes can be used to ...
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113 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 ...
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57 views

Normalizability of the Hartle-Hawking state in Liouville theory

I'm confused about how to normalize the Hartle-Hawking state in 2D quantum gravity. We can compute the HH state for two circles of length $\ell_1$ and $\ell_2$ in the matrix model as $\langle ...
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36 views

Black hole entangled with the cosmological horizon

Maldacena and Susskind recently proposed a interesting and very suggestive duality between entanglement and topological identification: http://arxiv.org/abs/1306.0533 But are such ideas applicable to ...
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2answers
188 views

How do gravitons and curved space time work together? [duplicate]

I've heard two different descriptions of gravity, and I'm wondering how they work together. The first is Gravitons: "The three other known forces of nature are mediated by elementary particles: ...
5
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1answer
189 views

What are the arguments for gravity not being a force? (in quantum gravity)

In quantum gravity the standard assumtion is that gravity is a force, although there is a small but persistent group of theorethical physicists who think otherwise. What gives us the motivation to ...
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101 views

Holographic principle and holograms

Holographic principle or Maldacena's duality is a theory that says that the volume of space can be described by just looking the information encoded on a boundary to the region of that space. ...
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1answer
64 views

Gravitational interactions by energy?

The mass-energy equivalence, first established by Einstein is an important and highly discussed phenomenon in physics. Without claiming much knowledge about high-end discussions on this topic, I would ...
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137 views

Why an infinitely measuring apparatus in gravity is not possible?

In the discussion of the amplituhedron paper (arXiv:1312.2007), there is the following discussion in paragraph 14.outlook (page 28): Quantum mechanics forces us to divide the world in two pieces - ...
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2answers
120 views

Continuously feeding an evaporating micro-black hole?

What would happen if you created a micro-black hole and could continuously feed it as quickly as it evaporates? Is it possible that it would remain relatively stable? If so, how might such a thing ...
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0answers
27 views

Lower bound bound on the mass of scalar bosons

Is there any lower bound bound on the mass of scalar bosons in nature. I know that a massless scalar boson would lead to a fifth force which would violate the equivalence principle. But is there any ...
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1answer
97 views

Quantum Theory as a framework for other theories of nature

We know that Quantum Theory should be considered as a framework in which all other theories/forces (Strong, Weak, EM and Gravity) exist. For example, we have the Quantum Chromodynamics, Quantum ...
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2answers
186 views

Fundamental Constants in a theory of everything (TOE)

Do physicists ever expect to be able to derive the fundamental constants of nature from theory? For example, if string theory or some other theory unites the four forces, would the theory be ...
11
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1answer
255 views

What is the CFT dual to pure gravity on AdS$_3$?

Pure $2+1$-dimensional gravity in $AdS_3$ (parametrized as $S= \int d^3 x \frac{1}{16 \pi G} \sqrt{-g} (R+\frac{2}{l^2})$) is a topological field theory closely related to Chern-Simons theory, and at ...
1
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2answers
363 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 ...
3
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1answer
170 views

Can universal continuity be experimentally falsified?

It is an unresolved question whether the universe is discrete or continuous in its intricate quantum level structure. See for example: Is the universe finite and discrete? How could spacetime become ...
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1answer
101 views

How does Hawking radiation grow as a black hole evaporates?

The temperature of Hawking radiation is inversely proportional to the mass of a black hole, $T_{\rm H}\propto M_{\rm BH}^{-1}$, and so as the black hole shrinks the temperature of the radiation should ...
3
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1answer
145 views

What happens when you apply the path integral to the Einstein-Hilbert action?

The Einstein Field Equations emerge when applying the principle of least action to the Einstein-Hilbert action, and from what I understand the path integral formulation generalizes the principle of ...
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92 views

Can the vacuum be filled with virtual micro-black holes?

Since the vacuum is thought to be virtual particles, is it possible that there might be virtual micro-black holes with virtual horizons and virtual hawking radiation which form and evaporate at a rate ...
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2answers
183 views

Is inflation deterministic?

In some theories inflation is supposed to be able to turn quantum fluctuations into macroscopic inhomogeneities. I don't understand how an isolated system such as the universe can undergo such a ...
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2answers
916 views

Is the firewall paradox really a paradox?

The firewall paradox is a very hot topic at the moment (1207.3123v4). Everyone who is anybody in theoretical physics seems to be jumping into the action (Maldacena, Polchinski, Susskind to name a ...
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212 views

Is a QFT in a classical curved spacetime background a self-consistent theory?

EDIT: Better rewording by Chris White: Is it possible to have a theory that treats both GR and QFT (e.g. QFT on a curved spacetime dynamically influenced by the standard QFT fields)? Is such a theory ...
3
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1answer
543 views

What is known on violations of unitarity or locality?

Recently the amplituhedron become a hot topic. I realized that two of the central pillars that QFT is based on, unitarity and locality, are no longer playing an important part (due to gravitational ...
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265 views

Naive quantum gravity

My question involves an analogy I have to point out. Consider the Lagrangian density for the a complex scalar field: \begin{equation} ...