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I was browsing through this and was wondering what progress in quantum gravity research has taken place since the (preprint) publication.

If anyone can provide some helpful feedback I would be greatly appreciative.

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    $\begingroup$ An update in 2004 <br/> It came up quite easily in this search. $\endgroup$ – user2307487 Apr 24 '13 at 11:12
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    $\begingroup$ @UGPhysics, You have to be specific. There are different research groups doing different research in different areas to address same topic- quantum gravity: String Theory, Quantum Loop Gravity being major. They have meetings, briefings on progress and so on. "The State" if research is definitely different from 2001 when focus was mainly on String Theory which has sifted towards LQG. But, I am not an expert, not even a physics major. $\endgroup$ – user16682 Apr 24 '13 at 11:21
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    $\begingroup$ @Dinesh The Carlip paper is quite nice because it gives a overview over most of the popular topics. Maybe he should ask for a similar but more up-to-date review paper... $\endgroup$ – ungerade Apr 24 '13 at 14:24
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    $\begingroup$ I don't know whether you can call this progress, but the AMPS paper shows that there are significant problems with the "complementarity" idea for resolving the black hole information paradox (which Carlip's paper calls "not very convincing," along with the rest of the ideas for a resolution). $\endgroup$ – Peter Shor Apr 24 '13 at 15:04
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    $\begingroup$ @user2307487: The Ashtekar paper is available on arxiv without a paywall: arxiv.org/abs/grqc/0404018 . It's only about LQG. $\endgroup$ – Ben Crowell Apr 25 '13 at 0:55
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A few developments since 2001:

There is the new field of loop quantum cosmology, which shows some promising signs of being able to actually calculate things that might conceivably be testable by observation.

The LHC hasn't found any evidence of supersymmetry, which may reduce the appeal of string theory.

There have been some high-precision tests of dispersion of the vacuum: http://arxiv.org/abs/0908.1832 . The results have been negative. This was at one time though to be a potential test of LQG, but now it looks like LQG doesn't yet make any definite prediction.

LQG has been reformulated in the last 10 years, so if you're going to try to learn it, you want to learn it from more recent references. A presentation of the new LQG is given in Rovelli, 2011, "Zakopane lectures on loop gravity," http://arxiv.org/abs/1102.3660 .

In 2004 there was an internet debate between Smolin and Susskind on Smolin's claim that "the Anthropic Principle ... cannot yield any falsifiable predictions, and therefore cannot be a part of science:" http://www.edge.org/3rd_culture/smolin_susskind04/smolin_susskind.html

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  • $\begingroup$ what references do you recommend about the recent reformulation? $\endgroup$ – lurscher Apr 29 '13 at 10:04
  • $\begingroup$ @lurscher: Added a link to a review paper by Rovelli. $\endgroup$ – Ben Crowell Apr 29 '13 at 12:36
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    $\begingroup$ Does the recent reformulation of LQG respect Lorentz invariance? $\endgroup$ – anna v Jul 30 '13 at 4:10
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In string theory, string phenomenology has been gaining interest, with the eventual aim of figuring out the experimentally compatible vacuum in the string theory landscape. An example of the success of the field is the MSSM's (which was shown by Kumar, Kane and Acharya to arise in realistic M(atrix) theory vacua, see e.g. [1]) correct prediction of the Higgs mass prior to its actual empirical discovery*. See e.g. TRF.

*As noted in the comments, the KKA paper I linked to came after the discovery -- however, the original paper [2] was from earlier, as pointed out by Matt Reece, and of course the MSSM prediction was known for much earlier than the observation.

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    $\begingroup$ -1 it's misleading to claim that experimental observation did not have an effect on the paper. there was already 3 sigma evidence for a higgs boson at 125 GeV in December 2013. $\endgroup$ – luksen Jul 29 '13 at 16:23
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    $\begingroup$ The first Kane et al. paper on the Higgs mass was arxiv.org/abs/arXiv:1112.1059, posted on December 5, 2011, slightly before the ATLAS and CMS announcement on December 13. They had the result even earlier-- I was at Michigan on November 16, 2011, and Gordy told me their result then. At that point I hadn't heard the rumor, which doesn't mean none of them had. In any case, it's a straightforward prediction of having heavy scalars in the range they had been advocating for years, although emphasizing the larger tan beta values may have been a choice made in light of the data. $\endgroup$ – Matt Reece Jul 30 '13 at 2:33
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    $\begingroup$ last point before this get's too excessive: the remaining window not excluded was already very narrow and first hints that the higgs mass would be below 130 were known already in august 2011 after Lepton Photon 2013, e.g. blog.vixra.org/2011/08/29/… in any case I think it's a stretch to claim the higgs mass was predicted $\endgroup$ – luksen Jul 30 '13 at 10:27
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    $\begingroup$ Just to give some perspective on the Kane et al paper: People were saying that the Higgs mass should be less than 125-130 GeV in the MSSM, years before this, and without appealing to string theory. The arguments made by Kane et al are somewhat similar, they just work in a different part of MSSM parameter space - that's the part they motivate using M theory... $\endgroup$ – Mitchell Porter Jul 30 '13 at 11:35
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    $\begingroup$ Some reactions from String Pheno 2012: x-sections.blogspot.com/2012/06/string-phenomenology-day-2.html $\endgroup$ – Mitchell Porter Jul 30 '13 at 11:35
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Approaches to Quantum Gravity: Toward a New Understanding of Space, Time and Matter by Daniele Oriti.

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