# Tag Info

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Well, an heuristic solution would be that it is actually impossible for anybody to cross the event horizon. As you noticed, Schwarzschild black hole is dual (at least locally, that is, if you don't make full turn) to Rindler's observer (the uniformly accelerated one). The stationnary observer in the Schwarzschild case is the uniformly accelerated one in ...

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The question whether primordial B-mode detection says something about quantum gravity or not may be subjective, but one can give an unambiguous and objective answer why people were even bringing up quantum gravity in connection with B-modes (and BICEP2). Here, I will try to answer that question. My answer is mostly based on an excellent (guest) blog post by ...

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This is rather subjective. But I'll volunteer my answer: Would the presence of B-modes in the CMB provide evidence for quantum gravity? No. And recent argument is that they don't even provide evidence for gravitational waves. I don't know if you saw the recent Horizon program, but note that what didn't come out is that the gravitational waves date from ...

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There seems to be some confusion. In the referenced paper there is no temporal direction, and even though there is curvature there, it has nothing to do with gravity (there is no time). Where as when you compare with $2D$ gauge theory, one of those $2$ dimensions is temporal in deed. So if you wanted to carry the analogy you should consider two dimensions, ...

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Let us suppose the holographic principle is indeed correct and that there is a (3+1)-dimensional quantum gravity theory that explains our universe, which has an equivalent description as a (2+1)-dimensional system. This simply means that the two descriptions cannot be distiguished so there is no physical experiment that could determine if we "actually" live ...

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Tononi's theory, even if recognized, is pretty naive. Dont take it seriously, there are better ones. Read for instance the work of Hans Moravec ("pigs in cyberspace" is online). In his view consciousness is not a local phenomenon.

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My take on the subject is slightly non-standard, but it conforms to both the many world hypothesis and the Mathematical Universe hypothesis advanced by Max Texmark, and the final conclusion is not too far from conventional beliefs. The Anthropic principle loosely constrains the underlying local evolution propagator to have a low-energy effective functional ...

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Even if we come up with a TOE there is no way to prove that it is the only one let alone the best one. A big philosophical problem which is usually swept under the carpet.

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The problem is that there are too many possible theories of everything with no way to eliminate any of them. General relativity predicts everything on a large scale, quantum physics predicts everything in on a small scale, and both predict everything on a medium scale. There's more than one way to reconcile the two, and all of them are experimentally ...

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My guess would be that almost always in physics $x$ stands for a dimensionful quantity, then the logarithm cannot be well defined unless for a dimensionless ratio, i.e. log $(x/x_0)$. In which case you can apply the given formula which becomes perfectly convergent -\text{log }\left(\frac{x}{x_o}\right) =\int_0^{\infty}\frac{dt}{t}\left(e^{-tx} - e^{-tx_o} ...

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I'm not aware of any reason that nonlinearity necessitates superluminal signals. I disagree with the existing answers. Certainly classical field theories can be nonlinear without inducing superluminal signals, e.g. General Relativity. I also see nothing in the quantization procedure of a classical field theory that would add superluminal signals. The ...

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you can say the same thing about the emitted electromagnetic radiation, especially for a neutral spherically symmetric black hole, where classically there can not be any radiation. The explanation to both phenomena is that the source of fluctuation is quantum mechanical, and the statement that the power of gravitational waves is proportional to the second ...

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You should think of it the following way: for each field (scalar field, Maxwell field, gravitational, etc), there are linearized perturbations off the black hole which vary in time and in space (both the radial direction and along the horizon). Since black holes radiate, each of these linearized perturbations are "turned on" or present, as you say. In ...

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GR predicts gravitational waves, which hence exist without violating it. By the wave-particle duality, there must be a particle (or at least a quasi-particle) associated with (the quantization of) such waves. We arbitrarily name them gravitons. Whatever aspect of them may be found to violate GR simply indicates how we need to amend our theory on the way to a ...

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Here the object $\chi_\alpha$ has an explicit 2D vector index, as well as an implicit 2D spinor index. There for it is in the $\textbf{1}\otimes\frac{\textbf{1}}{\textbf{2}} =\frac{\textbf{1}}{\textbf{2}}\oplus \frac{\textbf{3}}{\textbf{2}}$ representation of the $SO(1,1)$ group. Now the question is how do we isolate the $\frac{\textbf{1}}{\textbf{2}}$ ...

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For energies below the scale where gravity becomes strongly coupled, the paradigm of QFT is applicable and teaches us that gravity is due to the exchange of massless spin-2 particles we call gravitons, and that the whole picture of curved space time is nothing but a nice way to equivalently represent the collective effect of a huge number of gravitons ...

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The key to the effect is the idea - really just a conjecture, and as the paper states, "these ideas have not been met without controversy" - that there are materials that are opaque to gravity waves in the same way that conductors are opaque to EM waves. If that's true, then the cavity between parallel plates will contain a reduced set of modes of the ...

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I have read the paper and the gravitational explanation of the Casimir effect is not the main point, it's the experiment that provides evidence of the graviton's existence. The paper starts by drawing a macroscopic analogy between Maxwell's equations and Einstein's linearized field equations (known as gravitoelectromagnetism). The author uses GEM because of ...

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The Planck length is a quantum effect (among others). SO the answer is: yes, speeds in the universe are limited by c, and also by the Planck length, indirectly. However, this latter limit has never been measured nor achieved, so that in practice, the limit by c is sufficient. All Planck values are limits. There is no way to get a measurement result lower ...

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While we are getting closer to speed of light our length in the direction of the movement is according to Lorentz transformation getting shorter. This are two misconceptions here. One is that the way this is written implies that velocity is absolute. This is not the case. The "relativity" in relativity theory means exactly the opposite. Velocity is ...

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But we can not (even theoretically) consider length shorter than Planck length. This is a popular misconception. Treating Planck units as special is really more numerology than anything else. For example, the Planck mass is about the mass of a single biological cell. Does that mean physics doesn't apply to anything smaller (or is it larger?) than a ...

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Quite probably gravitons can cause similar effects as photons. The reason I believe so is that gravitons arise by quantizing linearized gravity (linear approximation to GR), the procedure is very similar to quantization of electromagnetism. Individual gravitons have the usual relativistic energy and momentum relation to frequency (energy-density is ...

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One doesn't. We haven't even detected gravitational waves, much less single quanta of gravitational waves. As of now, gravitons are a theoretical idea derived by extending quantum mechanical ideas to general relativity.

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From what I understand gravity is similarly quantized and transmitted via gravitons. Well, we don't know that. There is no accepted quantum theory of gravity, only approximations like semiclassical approaches. We cannot give you a "mental picture" at the moment because we don't have one. We can speculate all day, and extrapolate from all the other ...

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I cannot answer to all the questions but would like to stress something regarding what the Casimir effect tells us and what it doesn't. If you look at how it is derived for the usual EM interaction, an experimental verification of the standard Casimir effect tells us that: the EM field can have standing waves between two plates and outside them There ...

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