Prospects for contact of string theory with experiments

Nima Arkani-Hamed today gave a “vision talk” at Strings 2019, entitled Prospects for contact of string theory with experiments which essentially admitted there are no such prospects. He started by joking that he had been assigned this talk topic by someone who wanted to see him give a short talk for a change, or perhaps someone who wanted to “throw him to the wolves”.

The way he dealt with the challenge was by dropping “string theory”, entitling his talk “Connecting Fundamental Theory to the Real World” and only discussing the question of SUSY (he’s still for Split SUSY, negative LHC results are irrelevant since if SUSY were natural it would have been seen at LEP, and maybe a 100km pp machine will see something, or ACME will see an electron edm).

He did discuss the string theory landscape, and explained it was one reason that about 15 years ago he mostly stopped working on phenomenological HEP theory and started doing the more mathematical physics amplitudes stuff. David Gross used to argue that the danger of the multiverse was that it would convince people to give up on trying to understand fundamental issues about HEP theory (where does the Standard Model comes from?). It’s now clear that this is no longer a danger for the future but a reality of the present.

In order to go over time, Arkani-Hamed dropped the topic of his title and turned to discussing his hopes for his amplitudes work. The “long shot fantasy” is that a formulation of QFT will be found in which amplitudes are given by integrating some abstract geometrical quantities.

The conference ended with a “vision” panel discussion. Others may see things differently, but what most struck me about this was the absence of any sort of plausible vision.

Update: Taking a look at the slides from the ongoing EPS-HEP 2019 conference, Ooguri seems to strongly disagree with Arkani-Hamed, claiming in his last slide here that a CMB polarization experiment (LiteBIRD) to fly in 8 years, “provides an unprecedented
opportunity for String Theory to be falsified.” I find this extremely hard to believe. Does anyone else other than Ooguri believe that detection/non-detection of CMB B-modes can falsify string theory?

This entry was posted in Strings 2XXX. Bookmark the permalink.

20 Responses to Prospects for contact of string theory with experiments

  1. Tony says:

    I watched the “vision” discussion and I’m not entirely convinced the fate of high energy theoretical physics is in the best of hands given that the owners of those hands struggle with the concept of placing microphones in said hands for the purposes of audibility!

    That said, the language that is being used here and elsewhere seems to me to be better suited to theological discussions, rather than scientific ones. One hears “hope”, “faith” and so on far too often to provide any convincing meta-evidence that these people are on the right track. I worked in neuroscience for nearly 20 years (and trust me, that is a field full of shysters) and never saw anything remotely as shambolic as the current state of theoretical (high energy) physics. I mean, the string landscape story is a morass of no escape and the whole AdS/CFT duality story is not even applicable to our universe.

    I remain absolutely stupefied that people with so much mathematical and technical expertise can get sucked into what has effectively become a cult. In my opinion, senior people in the field, such as Witten, need to show some genuine leadership and say enough is enough, let’s move on. But of course that would require the cult leaders to themselves renounce their own faith and belief system, which they cannot do without admitting to practicing seriously poor judgment.

  2. Peter Woit says:


    There’s a long history of Strings XXXX “vision” talks full of hype and unrealistic claims about the present and prospects for the future. Gross has a lot to answer for in terms of being responsible for many of these things, he was doing this 24 years ago at Strings 1995 and has never stopped. If instead of hype, he and others over the years instead put forward a realistic summary of the state of the field and the problems it was facing, that could have had a very positive effect.

    What struck me as unusual about this year’s version was the lack of any actual vision, with the panelists having nothing much to say when Gross asked them for a vision of the future of the field over the next decades (Doug Stanford’s response was something like “why do we need a vision, as long as we’re having fun?”). Urs Schreiber is on the opposite extreme of string fandom from me, but his response to this was similar:
    “The closing ‘vision’ panel discussion did not take off.”

  3. Alessandro Strumia says:

    I remember a “vision” talk by Gross at HEP 2011. At that time (no new physics in the first 1/fb of LHC data) many good theorists started discussing the reality of data. So I expected a useful discussion, but Gross predicted the discovery of SUSY, of DM, of new Z mesons, a new CERN/US linear collider to explore the superworld. All within 10 years. In the last slide Gross cared about LHC data, telling: “1/fb down, 3000/fb to go”. Some wise guy commented: “1 beat in the head down, 3000 to go”.

  4. Peter Woit says:

    You can watch the talk Alessandro Strumia refers to here
    At 28 min in you can see Gross’s “predictions” for the 10 years post-2011. His track record on these is not good…

    For another such talk from him, way back when, you can take a look at the first substantive post on this blog
    from March 2004, which reported on a Gross “vision” talk I went to. The post included the text:
    “This [LHC startup] is now getting close enough that Gross and others seem intent on ignoring the failures of string theory, desperately hoping that superpartners will pop out of the LHC, thereby providing at least some vindication of the train of reasoning that lead to string theory. What will be interesting to see will be what Gross et. al. do when this doesn’t happen. Will they drop string theory?”

    The answer to this is now conclusively known. A remarkable aspect of Strings 2019 is that the only mention I saw of the LHC was Arkani-Hamed’s rather absurd revisionist claim that the LHC null SUSY results did not change anything. After years of pointing to the LHC results as what would test string theory and vindicate the idea, the string theory community now acts like the null SUSY results at the LHC are not worth mentioning.

  5. Low Math, Meekly Interacting says:

    This isn’t a very technically insightful comment, but if I may make a human observation: All this HEP theorist swagger and arrogance some people complain about seems to have left the building. The younger members of the panel make word choices and display body language that evinced more embarrassment than anything to my ears and eyes. Try to get these guys to talk about something other than their own work and the buzzkill is palpable. Gross is asking about “hopes” and all I could do was feel bad as they struggled to think of something they were willing to own up to.

  6. Peter Woit says:

    I think that’s accurate. Arkani-Hamed was also unusually subdued, I’d guess partly because he isn’t really a string theorist and has no particular positive vision of where string theory research is going. Having just delivered a talk about string theory prospects for connection with experiment in which he hadn’t been able to come up with any can’t have helped. Nati Seiberg also pretty much ignored string theory, sticking to the quite accurate point that there is a huge amount about QFT that we don’t understand, and making progress there is what is most promising.

  7. Dom says:

    It is painful to read the site in question as a human being with empathy for people struggling with an illness but I gather that the reason that the Strings conference was dismal was:
    “It almost looks to me as if the nasty anti-string crackpots were co-organizing the conference and could veto talks if not participants.”

  8. Thomas Van Riet says:

    The suggestion by Ooguri is sensible. Maybe detailed model building and detailed understanding of SUSY breaking is still rather difficult in string theory. Not because of the theory but because, like anything in fundamental physics, it is tough to do detailed computations, especially when conformal and super-symmetries are broken. What string theory sofar seems to tell us is that there are patterns for “low energy” physics coming from string theory. These patterns are the key in order to make predictions. That is the essence of the Swampland program. The question is whether the patterns can be proven or not. The Weak Gravity Conjecture is probably the most rigorous such a pattern, but already consistent with experiment, so no prediction. Large field inflation seems clearly something that does not come for free in string theory. Some are trying to prove this formally. They might succeed, and some Euclidean version of the WGC could be behind it. Not clear yet. But we should be constructive and supportive to the people that are trying instead of complaining about it. I do not see any other framework for quantum gravity and fundamental physics where such endeavors are even possible.

  9. Peter Woit says:

    Thomas Van Riet,
    What exactly is the falsifiable string theory prediction Ooguri is claiming for CMB B-mode polarization?

  10. Peter Woit says:

    I normally try and avoid discussing the latest weirdness from Lubos, but for those who want to indulge, they can go to his website and check out his take on the Strings 2019 vision panel. He seems to agree with me and Urs Schreiber that there was no vision at the vision panel. Blaming this on me as co-organizer of the conference is pretty funny.

    Thinking about it, a couple things that struck me about the panel is that of the five speakers (other than Gross, the moderator), three are currently at the IAS, two are recent products of Stanford. For a conference in Europe, this was very much a US group, focused on a narrow part of the US theory community. When I was a student at Princeton in the early 80s, the field was quite faddish. When I got there everyone was working on instantons. I think this way of working is still going on today, with the center of gravity some very specific questions about AdS/CFT and associated toy models. Lubos has this description of today’s fad:

    “All of the talks are about some French-speaking style general complexity-thermodynamics-AdS-attempts-on-quantum-cosmology issues, with some CFT rather disconnected from the string vacua.”

    As usual, the problem with everyone working on the same question is “what if this doesn’t go anywhere”?

  11. DB says:

    Dom, Peter,
    Trying to blame specific people (which we all know who they are, Peter being one of them) for what happened at Strings 2019 is not just a joke, it’s unfair. Not the least because those people had nothing to do with organizing the conference. Not sure why the author of that web page came up with this ridiculous idea.

    Wouldn’t it be easier to accept that string theory, as is formulated nowadays, has hit a brick wall? Not sure if a temporary one or not, but it’s definitely not progressing as it was expected a decade or two ago…

    Acknowledging limitations is a good thing. Even Witten was asking for something more modest in his comment re the “vision”…

  12. Peter Woit says:

    Part of Lubos’s complaint is that theorists who think they see how to get a unified theory out of string theory were not invited to Strings 2019 and not represented on the “vision” panel. As he discusses, one reason for this is that there is a separate “String Phenomenology 2019” conference where such people were represented.

    I found it remarkable that Arkani-Hamed completely ignored this “string phenomenology” and I don’t see any possible explanation for this other than that he thinks it doesn’t work, is not able to give a viable connection of string theory to experiment. I think Lubos is right that the lack of representation at the conference or on the panel of people claiming to get a unified theory out of string theory probably reflects the views of the organizers. To his mind, they are wrong and have been cowed into submission by me and others, to my mind, they are right to not bring people in to discuss failed ideas.

    The “vision” panel would have been a lot more interesting if the question Gross put to everyone was formulated as “give that string theory unification has hit a brick wall, what should we do?”.

  13. Thomas Van Riet says:

    @Peter, if the dust settles then one might potentially get to “no B-modes” within the detectable range.

  14. Peter Woit says:

    Thomas Van Riet,
    So, in this video
    they should have not only been informing Linde that inflation had been discovered, but at the same time informing Kallosh that string theory was falsified?

  15. The most remarkable thing about this is how hard they avoid saying “we got this wrong” (prospects to experimentally test strings/susy) even though the claims that turned out to be wrong are all over the published literature (and collected here on Peter’s and on my blog), not to mention in the media.

    It’s concerning because without acknowledging that something went wrong in the first place, they’ll never be able to learn from their mistakes. This is particularly obvious when it comes to the claim that now it’s actually good news the LHC hasn’t found susy. (Sure, hahaha.)

    Frankly I think Nima understood the situation long ago, but people like to invite him for motivational speeches, at which he is admittedly good.


    I see a very pronounced generational divide in the responses to my talks (which are not about string theory, I should add, but about the stagnation in the foundations of physics). While there are exceptions on either side, of course, by and large the older people are patently unwilling to even think about what I am saying (will frequently repeat arguments I just explained are wrong, it’s quite comical actually) while the younger people may not agree but at least they see the need to think about what is going on (for the obvious reason that their career prospects depend on them getting it right).

    While that’s good news to some extent, the reality of academia is that it would take at least two more decades for power to shift to the younger generation if that was the only way self-correction in scientific communities takes place. One would hope that it was not the only way.

  16. shantanu says:

    Peter, the only time I have heard a seminar from Ed Witten (in 2005, cf. he talked about proton decay in string theory models.
    Is he or other people still working along these lines and how much recent work is going on? I don’t know how many such talks have been featured in Strings xx meetings.

  17. Peter Woit says:

    As far as I know, neither Witten nor anyone else at the IAS has worked on this kind of “string phenomenology” in a long time, since it is clear that, for instance for proton decay, string theory is completely unpredictive: you can get any result you want. This understanding is widespread among prominent string theorists such as Witten, and that’s why no one was invited to Strings 2019 to discuss such issues.

  18. Hi Peter,

    You mentioned earlier that “Nati Seiberg also pretty much ignored string theory, sticking to the quite accurate point that there is a huge amount about QFT that we don’t understand, and making progress there is what is most promising.”

    Is this talked about at Strings 2019 and what are some of the things Seiberg (or you) found to be worth making progress for on that front?

  19. Math Phys says:

    “Isn’t it just important to have fun now?”.

    How visionary!

  20. Peter Woit says:

    For Seiberg’s views, see his talk

    Also, he is one of the co-organizers of TASI 2019, which focused on problems in QFT. See the videos from that conference, available here

Comments are closed.