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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 ...


4

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 ...


4

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 ...


3

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 ...


2

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 $\frac{\textbf{1}}{\textbf{2}}$ ...


2

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 ...


1

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 ...


1

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 ...


1

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, ...


1

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 ...


1

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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