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7 votes

Where does Planck's constant come from in non-renormalizability of quantum gravity?

One way to think about it is in terms of the path integral. For perturbative quantum gravity around flat space, we expand the metric as $$ g_{\mu\nu} = \eta_{\mu\nu} + h_{\mu\nu} $$ where $h_{\mu\nu}$ ...
Andrew's user avatar
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2 votes
Accepted

How do hyperbolic tessellations like {7,3} in Anti de-Sitter space relate to our intuition of 3D space (or 4D structure if you include time)?

AdS/CFT does not usually involve the hyperbolic plane. The original examples due to Maldacena involve higher-dimensional hyperbolic spaces. The best known example features string theory in a five-...
Mitchell Porter's user avatar
-1 votes

What would one use a theory of quantum gravity for?

Has anyone mentioned the graviton? A QG would showcase this as a fundamental force. It would then be left to delineate the limit of GR as a geometry to the discreteness of this fundamental particle of ...
Mark Thomas's user avatar
0 votes

What would one use a theory of quantum gravity for?

A bunch of areas in which QG would be needed: Primordial Cosmology Black hole singularities Development (or finding a no-go theorem against) of time-machines and faster-than-light travel. ...
Rexcirus's user avatar
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0 votes

What would one use a theory of quantum gravity for?

I suggest you take a look at Oriti's discussion of the Bronstein hypercube of QG meta-thelries. The different vertices of the cube correspond to the target theory one gets based on the number of ...
starseed_trooper's user avatar
0 votes

Is the background independence of dynamics a necessary condition for physical theories?

It depends on the meaning of physical theories. E.g., classical electrodynamics and classical Newtonian are examples of physical theories that are not completely background independent. Of course, ...
Lukas Nullmeier's user avatar
0 votes

Does information always gravitate?

If we have a photon and black hole with the same size, the photon can not be lowered to the hole. So all the energy must go to the hole with the photon. If we have a book and a black hole, the book ...
stuffu's user avatar
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0 votes

Low-energy string effective action valid for large dilaton field?

The above action is not valid for large (positive) dilaton values, but that's not the end of the story. The perturbative expansion for the partition function of the string worldsheet schematically ...
11zaq's user avatar
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2 votes

What would one use a theory of quantum gravity for?

Others have answered in terms of theoretical achievements. But there also could be practical, technological benefits. What would they be? Who knows? Could the early researchers into quantum mechanics ...
Barmar's user avatar
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0 votes

Renormalizability of Quantum Gravity

As QMechanic said, when Griffiths says gauge theory he really means Yang-Mills theory, of which gravity is not an example. Also, regarding it's renormalizability, it's worth mentioning that in three ...
11zaq's user avatar
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5 votes

What would one use a theory of quantum gravity for?

Currently, the conceptual need for a quantum theory of gravity (or a theory that combines gravity and quantum physics) is to a large extent induced by the fact that we don't know what gravity does ...
flippiefanus's user avatar
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1 vote

Does information always gravitate?

There's a few things at play here. The increase in entropy you're mentioning is related to the Bekenstein bound $$S \leq \frac{2\pi RE}{\hbar} $$ where S is the entropy of a given region of space, R ...
11zaq's user avatar
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2 votes

What would one use a theory of quantum gravity for?

I want an anti-gravity machine. When we get a workable theory of quantum gravity, I expect that it well tell me that I can't have the machine; it would be nice, however, if it gave us some insights ...
Simon Crase's user avatar
3 votes

What would one use a theory of quantum gravity for?

You've (re)discovered a somewhat awkward fact: even if one day we do discover the correct theory of quantum gravity, and we develop vastly more precise experimental apparatuses than exist today, then ...
tparker's user avatar
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5 votes
Accepted

What would one use a theory of quantum gravity for?

I understand that one might hope to get some kind of insight over dark matter or dark energy problems. But shouldn't a theory of quantum gravity by construction reproduce general relativity at large ...
TimRias's user avatar
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8 votes

What would one use a theory of quantum gravity for?

Suppose you have an electron in a superposition of two measurably different locations. The electron has mass so it interacts with the gravitational field, so what does the gravitational field look ...
alanf's user avatar
  • 8,066
21 votes

What would one use a theory of quantum gravity for?

The two standard answers are: Resolving the singularity at the Big Bang Resolving the singularity in Black Holes Both of these have large spatial curvature within very small regions.
Allure's user avatar
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5 votes

What would one use a theory of quantum gravity for?

The first case is more of a "particle physics–like approach". We just want to understand what things are made of, and this involves reaching larger energy scales. The Planck scale surely ...
Níckolas Alves's user avatar
2 votes

What do we learn from quantizing the relativistic point particle?

I will give a different perspective on the worldline formalism. Yes, the worldline formalism is perturbative, where the worldline proper time is the Schwinger proper time. However, once we use BRST ...
Nogueira's user avatar
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0 votes

Planck-scale measurements of sub-light-speed motion

We have no idea about how physics works at the Planck scale. Any answer to this question would be tremendously speculative.
Níckolas Alves's user avatar
2 votes

What do we learn from quantizing the relativistic point particle?

The theory of a relativistic point particle is insufficient for the same reason that the theory of a relativistic string is insufficient! Specifically, the former can compute the amplitude for a ...
Connor Behan's user avatar
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-1 votes

Is quantum gravity research implying that gravity is actually a force and not spacetime curvature according to GR?

In short, no. Or, read on for curious intrigues in the quest for (QG)... Quantum Mechanics (QM) shares a set of physical axioms with General Relativity (GR). These are foundational (sine qua non) ...
Jeltz's user avatar
  • 11
5 votes

Is quantum gravity research implying that gravity is actually a force and not spacetime curvature according to GR?

There is no conflict between being a manifestation of spacetime geometry and being a quantum force. Fields, classical or quantum, are spacetime geometry. The gauge fields of the Standard Model can be ...
benrg's user avatar
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22 votes

Is quantum gravity research implying that gravity is actually a force and not spacetime curvature according to GR?

Disclaimer: I am mainly a relativist, and I think science has benefitted much more by thinking of gravity as a geometrical entity than as a "force". It is impossible to answer this question ...
Níckolas Alves's user avatar
6 votes

Is quantum gravity research implying that gravity is actually a force and not spacetime curvature according to GR?

I don't understand the statement that ``gravity is geometry and not a force". It is a force, but it isn't some magical phenomena where things are just attracted to each other. That is, gravity ...
VaibhavK's user avatar
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22 votes

Is quantum gravity research implying that gravity is actually a force and not spacetime curvature according to GR?

First, the concept of "force" is not as easy as it might seems. It is inherited from Newtonian mechanics in which it is defined as a vector sourcing the motion of the particles. In a sense, ...
Léo Vacher's user avatar
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