Gross on Outlook for String Theory

David Gross just finished giving the closing talk at Strings 2008, on the outlook for string theory, following a talk by Hirosi Ooguri summarizing the conference. Strings 2009 will be in Rome next June, and it appears that there is a tentative plan to have Strings 2010 in College Station, Texas.

Gross began his talk by recalling his days as a postdoc at CERN in the late 60s, working on an early version of string theory (e.g. trying to extend the Veneziano model). At the time he felt CERN was a great center of theory, but somewhat of an experimental backwater, with the real action he was interested in happening at SLAC. Now, forty years later both string theory and CERN have flourished. CERN is in the process of becoming the single world umbrella lab doing particle physics, driving all the others out of business. Unfortunately, Gross sees the same thing happening in particle theory and seems rather pleased about it, saying that only one umbrella in theoretical physics will survive, string theory, eating up everything else. Except LQG, which he says has not yet been brought under the umbrella, and “we’re not sure we want to”.

I found this display of string theory triumphalism truly appalling. The fact of the matter is that string theory has failed miserably to do what it was supposed to do, explain unexplained features of the standard model and predict what happens beyond it. Under the circumstances, to claim victory and write out of particle theory anything that doesn’t fit under the string theory “umbrella” is completely inappropriate. The message to any young particle theorist from Gross was clear: fall in line with string theory ideology, or there will be no place for you under the “umbrella”, i.e. no job for you (the phenomenologists have their own umbrella, you better try that one). The fact that HEP experiment is being forced to consolidate in one lab by economic realities is a really unfortunate one. There is no similar reason for HEP theory to be forced to consolidate around one topic.

Later on in the talk, Gross started channeling Lee Smolin and me, urging young people to stop sticking to the same well-worn ideas, to stop looking under the same lampposts, and to go out and search for something really new. He argued that they would find wandering in the darkness less competitive since few people were doing it. It was unclear whether one is allowed to get out from under the umbrella when one goes out to investigate the darkness, presumably not.

While he made lots of positive comments about current work in string theory in order to rally the troops, much of his talk was rather pessimistic and critical of trends in string theory research. He acknowledged that there hadn’t been any “great breakthroughs” in the field in quite a while. String phenomenology was described an attempt to make string theory “a predictive, or at least imitative” framework. He didn’t comment on what it means for theorists to give up on predicting nature, and settling for imitating it.

About the LHC, he acknowledged that it is unlikely to have anything to say about string theory. He finds the idea of seeing black holes, strings, etc. “extremely unlikely”, but is betting that the Higgs and supersymmetry will show up. Unfortunately, even if supersymmetry is found “it’s not clear that we’re going to learn enough”, this won’t answer any deep questions about string theory or prove that it is relevant. His “most optimistic hope” is that the LHC will see something unexpected, and “we will realize that this was an obvious prediction of string theory”. He notes that this is “almost our last chance”, if nothing relevant to string theory shows up at this energy scale, it is unlikely that anything relevant will show up at any energy scale accessible for an extremely long time.

Gross commented on two topics that hadn’t been mentioned in the talks. He’s still hoping for a non-anthropic explanation of the CC, and noted that no speaker had brought up the anthropic landscape explanation of the CC, with it getting a mention only at one after-dinner talk. Despite what Susskind claims, perhaps the battle between the anthropicists and their opponents is not going so well for the anthopic side. They may get pushed out from underneath the umbrella…

The second topic was the still unsolved question of “what is string theory?”. Gross noted that there were no talks on string field theory, since it and most other ideas about how to define string theory non-perturbatively have gone nowhere. The one thing that is still alive is AdS/CFT, which now completely dominates the subject. More and more, particle theory research under the umbrella is focused only on things related to the duality of N=4 SSYM and string theory on AdS5 x S5. Gross noted the progress toward showing this duality, with the planar limit perhaps being done within the next few years.

By the way, in Ooguri’s talk, he mentions an AdS/CFT discrepancy that has been resolved, saying he was surprised that some blogger didn’t claim this discrepancy as disproof of AdS/CFT. Lubos in his commentary helpfully explains that Ooguri was referring to “numerous pigs and Woits”. Since I’ve never argued that there’s a problem with AdS/CFT duality, I guess he must be talking about someone else. Maybe Jacques Distler has some postings about problems with AdS/CFT that I missed.

Gross takes the attitude that there is no more value in working on “tests” of AdS/CFT, that the conjecture is now well-tested and it is time to move on to try and understand what AdS/CFT is good for, especially what it says about the question of “what string theory is?”. The planar limit is just the classical limit, and he discusses prospects for moving beyond it [and beyond AdS/CFT, to other backgrounds]. On the QFT side, this means deforming the gauge theory by non-renormalizable operators, so it is not clear what to do.

Update: More summary commentary and prizes at Resonaances. Clifford Johnson watched Gross’s talk and summarizes it as follows:

David Gross summed it all up, took stock of where we are, and where we aren’t, and looked forward. A sort of “state of the union” speech if you like. And the state is good. Very good indeed.

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55 Responses to Gross on Outlook for String Theory

  1. Kea says:

    Most of the talks are now up on the CERN webcast site, but frustratingly not Gross’s talk, although a page linking his talk is there.

  2. Marcus says:

    Yes, too bad video of Gross’s talk is missing from the collection at CDS.
    However the video of Rovelli’s talk is there. I watched it and was impressed
    by the level of interest shown. The hall was packed—people were standing. After the 30 minute presentation there were several excellent questions—and the Q/A dialog went on for another 13 minutes. After which the moderator asked that they continue outside during the break. I counted 8 questions from the audience during the Q/A period. All genuinely constructive, it seemed to me. It spoke well for those attending the conference, and the tone set by the organizers.

  3. I can offer some perspective of research strategies for solving XXX problem, based on personal experience.

    I got some good advice in grad-school:

    “Don’t do yyy, it’s mature field & well understood. Try something in a new area”

    So, I tried a new area. Turns out, the entire field (incl my PhD advisor & current grad students) were STUCK. Everyone was doing the same thing (“followers”): the typical Clustering Phenomena in research.

    “In the game of Life [ or Research ], there are Drivers [ leaders ] & there are Passengers [ followers ]. Which are you?”
    — Volkswagen commercial

    Aka, the classic “cluster f**k” in Research. All fields run into this periodic bottleneck, where there is a stagnation of results. Also, known as temporal pessimism.

    “I’m locally pessimistic, GLOBALLY OPTIMISTIC!”
    — Dr. Jordan Pollack, Brandeis Univ/CS Dept
    [ my grad-school colleague in Artificial Intellgence, his PhD advisor D. Waltz ended up at Thinking Machines, the same company R. Feynman worked at 1 summer ]

    It appears as if String Theory is in this lull, with some dissidents (P. Woit & L. Smolin) raising concerns about any Global Optimism (they ain’t!) So, D. Gross is basically saying, “keep on keepin’ on”. T. Dorigo has an interesting condom/penis analogy with the theme “ST is F**D!” In New York sland, he is saying “Fahgetaboutit!!”. If it were me, I would certainly be investigating Alternative Models, like LQQ (or anything else). If the best minds haven’t cracked it yet (Witten, et al), it seems unlikely a newbie could do it. However, there are Historical examples of newbies “cracking the safe”

    “They’re really smart guys, right? Everyone’s been trying to unlock the safe (solve the problem) from the front. But, eventually someone tries an “end around” (football term) & tries to unlock it from the rear”
    — Leon Lederman

    It happened at the 2007 Fiesta Bowl, an “end around play” won it for Boise State. Could String Theory engineer such a miracle play?

    I was that newbie in my chosen PhD research field 25 yrs ago, who led a breakthrough in my field. The Establishment was pretty much embarassed & shown up by a grad student (me)! I _singlehandedly_ took a global exhaustive search of research strategies, & found a commonality between 2 constraint equations. I found them to be the consequence of ONE geometrical topological structure. The computations were simply 3D vector computations in a homogeneous (n+1) space, within the capabilities of a high-school student! I achieved the “Simple answers, to simple questions..turned out to be REALLY EXCITING” mantra (Murray Gell-Mann). Simple/Elegant solution, a minimalist solution was achieved thru a true reductionist approach

    Of course, I was a threat to the Establishment & my research was NEVER published in journals (due to political back-stabbing). Well, actually there was 1 (early on). However, they were widely published in conference proceedings & I achieved a lot of notoriety.

    My advice to the field:
    Continue on as per David Gross, in the chance that there might be a breakthrough (nobody is holding their breath, apparently, except a few fanatics). I would put a LOT of effort in a _global search_ for that magical TOE model: through the process of Convergent Evolution (multiple path solutions converging to ONE), it could be found. The latter is how I pulled off the coup in my field (single handedly)

    I might be a player in this wacky game of Theoretical Physics. My competition in my field 25 yrs ago, were some physicists including H.C. Longuet-Higgins (do a Google search on Gell-Mann & Longuet-Higgins, you may recall that MGM was dabbling in Psychology. My research field was the Computional Theory of Vision). If I could summarily waste these guys as a grad-student, maybe I can do it again.

    “Out of the Blue” lightning strike, Research area punked!

    (example) Geophysics
    The classic case was Geophysics in the early 1900s. Everything in status-quo “get along mode”. Until, a wayward researcher (German meteorologist) by the name of Wegener came onto the scene. He had an incredibly simple theory termed Continental Drift (a child who builds puzzle could see it), that had some corroborative data from paleo-archaelogy. Naturally, he was laughed off as a crackpot by the so-called establishment (peer reviewed experts, in complete political control of research journals). Of course, Wegener was right & we now know it today as Plate Tectonics. Turns out, it took nearly 60 yrs for the “crackpot theory” to catch on. Time was needed to gather additional corroborative data (Paleo magnetism, from sea floor spreading), Technology played a part. Interesting point: a female grad student (Tanya Atwater, aka Mrs. Plate Tectonics) @Scripps was a critical player in the feverish activity in the 60’s. “She was sent up the pole” (male sexist comment, about she was used as a guinea-pig for the crackpot idea), but she came thru with flying colors & defended the new theory against the backdrop of the male-establishment.

    “If you don’t play [ new wave of research or Technology ], YOU GET LEFT BEHIND”
    — xx, comment on Video on Demand revolution (stimulated by Apple video iPod)

    — Dr. Marcia McNutt/MIT (now Director of Monterey Bay Aquarium)

    Theoretical Physics is on the cusp, of getting hit by “Lightning Bolt out of the Blue”. Somebody (or group) will come up with some “crackpot idea”, which will eventually be shown to be the “Final Solution”.

    “It’s not a matter of IF, but WHEN [ & Who ]”

    Would it be Kea & her Category Theory? Any other candidates?

  4. Marcus says:

    Chimp: “Any other candidates?”

    Sure. there is evidence of a global convergence—the kind of thing you suggested one could look for.
    Add et al after each name mentioned here:

    Renate Loll has constructed a new 4D continuum (not a diff manif) in which dimensionality varies with scale. De Sitter space arises from it at large scale in the absence of matter.

    Laurent Freidel has modified spinfoam—loop gravity path integral—dynamics so that it fits better with Loll’s approach. Convergence you were talking about.

    Yidun Wan has shown how particles could arise in the Loll continuum as topological variation in how blocks are joined. This needs more work.

    The Loll continuum is a fundamentally new continuum. They don’t come along too often (new mathematical models of the continuum.) When a new model of spacetime appears, with fundamentally different properties at a microscopic level, it’s a good idea to check it out. Loll et al have a piece in July 2008 Scientific American. It has references to their papers if you want more information.

  5. Kea says:

    Gross’ talk is now up on the CERN site. Wow. The first 15 minutes was indeed the most absolutely appalling waffly flattery of string theorists, but the second 15 minutes was completely different, and excellent, managing to mix the basic message of a need to attack basic questions with a concrete illustrative example of our ignorance in terms of deformations of exact solutions to AdS/CFT.

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