tag:blogger.com,1999:blog-2381900080106522441.post7236703665946473089..comments2017-12-07T10:32:01.848+01:00Comments on relatively quantum: Approaches to quantum gravityNorberthttp://www.blogger.com/profile/04965554394207041308noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-2381900080106522441.post-26351971533305893282016-04-15T12:14:41.739+02:002016-04-15T12:14:41.739+02:00Nice review! I would like to point out that the de...Nice review! I would like to point out that the described approaches are all based on the assumption that the short-distance topological structure of the spacetime is given by a smooth manifold. This is a logical possibility, but somehow I find it difficult to believe. Note that the approaches you refer to as "smaller" are precisely those where the smooth manifold structure is abandoned and one uses a non-commutative manifold, or a discrete set, or a piecewise linear manifold, etc ... Even in the case of CDT, although the theory is defined in the picewise linear manifold case (a triangulation), the goal is to obtain the smooth-manifold limit. More than 20 years ago Chris Isham has described this problem in one of his QG reviews: one starts with a smooth manifold M and a metric g, so the simplest thing is to replace (M,g) with (M,g*), where g* is an operator. A more general quantization is to replace (M,g) with (M*,g*) where M* and g* are some quantum generalizations of M and g.A. Mikovichttps://www.blogger.com/profile/03175906801121515444noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-81717218494102153982016-04-13T11:12:50.517+02:002016-04-13T11:12:50.517+02:00Hi Vedran,
thanks a lot for your input. I incorp...Hi Vedran, <br /><br />thanks a lot for your input. I incorporated it in the post. <br />Norberthttps://www.blogger.com/profile/04965554394207041308noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-55562607441219592862016-04-12T22:45:45.288+02:002016-04-12T22:45:45.288+02:00Hi,
CDT was misspelled as "casual" DT i...Hi,<br /><br />CDT was misspelled as "casual" DT instead of "causal".<br /><br />Also in asymptotic safety you (almost) always go Euclidean.<br /><br />Finally, in asympt. safety spectral dimension apparently goes to 3/2, and not 2 as previously thought. This was confirmed in CDT and very recently Euclidean Dynamical Triangulations (EDT). Note that this result is relevant as it bypasses one usual apriori counterargument against QFTs of gravity.Vedranhttps://www.blogger.com/profile/02194339965441762137noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-27375307889079912012016-04-12T17:30:05.880+02:002016-04-12T17:30:05.880+02:00Dear Jakob,
thanks a lot for your comment. I fix...Dear Jakob, <br /><br />thanks a lot for your comment. I fixed the typo and added a brief explanation for the origins of the name. It originated in the time before it was realised that one needs to go beyond Wilson-loops to have non-vanishing volumes, i.e. to Wilson-"graphs", but it got stuck. Norberthttps://www.blogger.com/profile/04965554394207041308noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-33796708684607819112016-04-12T17:05:37.183+02:002016-04-12T17:05:37.183+02:00Nice review! In the last section an "of"...Nice review! In the last section an "of" is missing in the sentence "The application the main technical and conceptual ideas". In addition, I think a short explanation is missing on why loop quantum gravity is called LOOP quantum gravity at all.<br /><br />Best wishes,<br /><br />Jakob<br />http://JakobSchwichtenberg.com/Jakob Schwichtenberghttps://www.blogger.com/profile/10458230617292717089noreply@blogger.com