## Thursday, November 06, 2014 ... /////

### A string landscape conference in Madrid

Four weeks ago, there was a conference at ITP of UAM/CSIC in Madrid, Spain. The title of the conference was

Fine-Tuning, Anthropics and the String Landscape (click here for the page with videos)
In the table, columns are describing the timing, speaker name, title, video URL (pairs of the talks are often clumped together), and PDF URL of the talks. The topics covered the most controversial and the least solid aspects of string theory – string cosmology, the string landscape (well, at least the shape of the non-SUSY landscape fails to be solid), and its popular (and hated) anthropic interpretation (and the anthropic "explanation" of the apparent fine-tuning in Nature).

To help you to decide whether you want to open the conference website, it may be a good idea to list all the speaker names: Guth, Hogan, Break (she gave 5 talks, quite a hard-working madam, and I am not counting her brother Lunch Break and their uncle Reception), Vilenkin, Brown, Blanco-Pillado, Randall, Kleban, Meissner, Donoghue, Banks, Bousso, Bena, Sethi, Danielsson, Ruderman, Freivogel, Bousso as the host of the main discussion, Denef, Vercnocke, Watari, Westphal, and McAllister.

Some of the physicists' talks covered topics that you might expect; sometimes the topics were somewhat unexpected. I don't plan to discuss all these questions because I've done it too many times, even recently, and if those things are going to get some room on this blog soon, it will be some newer technical results.

I was also told that my PhD adviser Tom Banks would be the main speaker during a dinner and he would recommend the local Spanish graduate students to work on "alternatives" to string theory – the latter is no longer the best candidate for theory of quantum gravity, Tom thinks. My sources were exactly as shocked as I was years ago when I would learn about this evolution of Tom's.

(See some of the history of my interactions with Tom's idiosyncratic ideas since 1999.)

It is not quite clear to me what we should imagine behind the word "alternatives" but if they're supposed to be ideas similar to Tom's talk about the "multiverse of holographic spacetime" and his "holographic axiomatics", well, I would strongly discourage Spanish and all other graduate and not only graduate students from such experiments.

As far as I can see, these propositions are connected with an honorable and nice man but they lack any solid beef. Fifteen years after the first moment when I experienced Tom Banks' excitement about these claims, the percentage of sharp insights, valid logical or mathematical derivations, and equations in his "HST" papers has actually decreased, not increased – and be sure that it was already bad in 1999. Some future breakthrough formulation of quantum gravity may resemble Tom's words in some way but what I see today seems like a mixture of demonstrably incorrect claims, some random guesses, and some completely vacuous words. I don't see any new answers to the question how the observables of quantum gravity should be calculated and indeed, what they are.

Of course that I respect Tom more than any researcher of loop quantum gravity, to mention a notorious example of an "alternative", but I think that his particular "alternative" may be even more content-free than LQG. Graduate students who have studied at least several chapters from a string theory textbook should also read one Tom Banks' paper on "HST" – for them to understand what is meant when people say that there are no alternatives to string theory. Seeing what someone actually calls "alternatives" is a great way to get the point, I think.

#### snail feedback (7) :

Well, he has his own personal agenda of promoting his theory.

What I don’t like about Tom Banks is his constant whining that people don’t take his theory seriously or that they don’t put any effort to delve into it.

Has he ever thought that maybe there is a good reason for that?

What are your main objections to LQG Lubos? I'm quite rusty on it but originally Ashtekar's approach to quantization of gravity seemed worthy of some research, if I'm not completely off track.

I don't see how an alternative escapes the landscape, which to me is ST greatest contribution which to some is an indication of its failure. Now SUSY looks like a likely failure to "solve the naturalism problem." That's fine. Naturalism is perhaps our problem not the Universe's. Science explains everything it can and accepts its limitations. Tell me how any alternative derives the variable ratios from first principles?

Last thing that I remember, and I was not really following it (or Physics in general) closely in those days, is that Rovelli apparently managed to calculate the propagator. I haven't heard about anything exciting since then.

Dear Tony, see e.g.

http://motls.blogspot.com/2004/10/objections-to-loop-quantum-gravity.html?m=1

http://motls.blogspot.com/2006/01/review-of-loop-quantum-gravity.html?m=1

I've spent way too much time with that.

It inevitably breaks the Lorentz symmetry which is in conflict with observations. It has absolutely no potential for a gentle resolution of the information loss paradox. It doesn't allow other forces to be added.

In contrast with Ashtekar-inspired claims, it is in no way formally equivalent to gravity because crippling extra quantization/compactness conditions are imposed on the Wilson lines.

In no way, it solves the problem of nonrenormalizability of gravity because there are still infinitely many undetermined coefficients.

Most terribly, it doesn't allow nearly smooth space to exist.