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Arguments against LQGby jdstokes
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#19
Jan1909, 03:53 AM

PF Gold
P: 1,961

I will post a thread about that later. 


#20
Jan1909, 07:20 AM

PF Gold
P: 3,685

I do not know if this is the best paper but it is the best i can find, nor do i pretend to even understand all of it, but it doe's seem to give a good overview.
http://arxiv.org/abs/grqc/0501053 G. AmelinoCamelia, C. Lämmerzahl, A. Macias, H. Müller (Submitted on 17 Jan 2005) Abstract: We give an overview of ongoing searches for effects motivated by the study of the quantumgravity problem. We describe in greater detail approaches which have not been covered in recent ``Quantum Gravity Phenomenology'' reviews. In particular, we outline a new framework for describing Lorentz invariance violation in the Maxwell sector. We also discuss the general strategy on the experimental side as well as on the theoretical side for a search for quantum gravity effects. The role of test theories, kinematical and dymamical, in this general context is emphasized. The present status of controlled laboratory experiments is described, and we also summarize some key results obtained on the basis of astrophysical observations. 


#21
Jan1909, 07:32 AM

PF Gold
P: 1,961

I found this one, among the citations for the above article:
Quantum Gravity Phenomenology Authors: Giovanni AmelinoCamelia (Submitted on 2 Jun 2008) http://arxiv.org/abs/0806.0339 Abstract: I review the present status of the development of Quantum Gravity Phenomenology. Among the accomplishments of this young research area I stress in particular the significance of studies which established that some appropriate data analyses provide sensitivity to effects introduced genuinely at the Planck scale. The objective of testing/falsifying theories that provide comprehensive solutions to the quantumgravity problem appears to be still rather far, but we might soon be in a position to investigate some "falsifiable quantumgravity theories of not everything". 


#22
Jan1909, 11:52 AM

P: 2,828

The weak anthropic principle and the landscape of string theory The case for background independence 


#23
Jan1909, 03:18 PM

Astronomy
Sci Advisor
PF Gold
P: 23,235

"It is interesting to note that while the understanding of the string landscape is evolving, present evidence on the nature of the landscape allows such an argument to be made, leading to the conclusion that the WAP favors a negative value for the cosmological constant, Lambda, in contradiction to the result of astronomical observations. The viability of applying the WAP to string theory then requires that either there are found an infinite discretum of anthropically allowed vacua for Lambda >0, or the recently found infinite discretum of solutions for Lambda <0 be reduced to a finite value." Smolin's coauthor on this one is George Ellis, a wellknown cosmologist who earlier coauthored The Large Scale Structure of Space Time with Stephen Hawking. Basically they argue that applying the Weak Anthropic Principle to the String Landscape tends to discredit string/M as a whole. The argument goes as follows. Suppose one assumes that our universe was chosen at random from the habitable sector of the String Landscape as presently understood. Then it is infinitely more likely to have Lambda < 0at least as things stand presently. (Only a finite discretuum with Lambda >0 and an infinite one with negative cosmo constant.) Therefore String/M predicts negative Lambda. But at least so far, observations point to positive Lambda. This would seem to discredit String/M at least with it's present Landscape of possible vacuua, if one follows Anthropic reasoning. My impression is that this paper does not "pave the way" towards a reconciliation. Nor is it really a serious attack on Stringy thinking. At least I do not consider it antistring. What I do see is that Ellis and Smolin disapprove of resorting to Anthropic Landscape argumentsand in that they agree with a considerable part of the string research community itself! I think the main thing their paper is intended to show is what a liability the Anthropic Landscape is to string/M. 


#24
Jan1909, 03:48 PM

P: 2,828

Not even to mention the fact that, a situation which I would find wonderful, if one could prove that the landscape has a unique solution compatible with any known experimental fact, that would not by itself disprove string theory because the infinite (?) remaining landscape is wrong. That would mean that we have found a sufficient constraint for string theory to become fully predictive ! 


#25
Jan1909, 04:11 PM

Astronomy
Sci Advisor
PF Gold
P: 23,235

Exactly! In that case Anthropic reasoning would be superseded and laid to rest. I was just about to add that the other paper (Case for B.I.) does make a constructive suggestion to string theoristsworking on a nonperbative background independent versionand in that sense does pave the way to more collaboration. I didn't realize that is the recent paper you meant.
But I see you already made that point. A propos of prospects for linkage, Smolin is one of a dozen or so Loop community people (Loop and allied approaches) that will be taking part in an interesting weeklong symposium in early July (if all goes as planned) bringing together roughly the same number of String/M and Noncommutative QFT people. This is the 25th Max Born symposium at Warsaw. What you say in general terms (not about the Smolin/Ellis paper specifically) I think is very truethe time is ripe for an exchange of ideas and methods. A lot of people in several areas seem eager for this and ready to take the initiative. I will get the link to the XXV Max Born preliminary list of speakers Warsaw 29 June3 July http://www.ift.uni.wroc.pl/~planckscale/ http://www.ift.uni.wroc.pl/~plancksc...?page=speakers http://www.fuw.edu.pl/~meissner/home.html 


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