Recent content by Cepatiti

Sure you can get the Einstein field equations from string theory. One way they arise is as consistency equations to make the Weyl anomaly vanish. Note that string theory is not just a theory of quantum gravity, it is a TOE (Theory of Everything), meaning it does not only describe (quantum)...

Are you referring to this paper: The fate of four dimensions ? Personally, I didn't know that paper. I didn't check, but does it have a lot of follow-up papers? Some remarks related to your question: As far as I know, there is no well-established model in string theory explaining why some...

No one knows, but sure there are ideas. One idea for example is brane cosmology, which states that our universe is restricted to a 4D brane existing in a higher dimensional space, like the setting you have in type II string theories. This higher dimensional space could contain more than one...

I know. But I think the original author's concerns were specifically about the Nambu-Goto action, which he seems to believe restricted to flat Minkowski space. For quantization, you would normally use the Polyakov action anyway. If the question was however about how curved spacetime arises in...

(i) Not sure I got the question correctly, but I would say this: proper time corresponds to the length of the worldline, hence it is a very natural parameter to use to parametrize the worldline. As for the Lorentz invariance, observations indicate that Lorentz symmetry is preserved in nature...

Just to briefly come back to the notion of "geometrical object": I don't think this notion is rigorously defined in physics, that's why I put it between quotation marks. However, I believe it is attached to the notion of "physical" degrees of freedom, i.e. degrees of freedom that cannot be...

I was taught in GR that a tensor ought to be a "geometrical object". Hence in particular, it cannot be annihilated by a mere coordinate transformation. What would you say about pseudovectors, then? They are not geometrical objects, but still transform like vectors under certain...

In the past, I came across the paper by Webb et al., "Indications of a spatial variation of the fine structure constant", published in Phys. Rev. Lett., 107, 191101, 2011, that seems to report the observation of a spatial variation of the fine structure constant, using the Keck observatory in...