String theory might be about to finally be killed off

News site TechEye is reporting that String theory might be about to finally be killed off, with a story that starts off

The world’s top boffins are debating finally killing off one of the more elegant scientific theories about the nature of reality.

This isn’t exactly the most reliable information source, with one problem that the story is about supersymmetry, with the only connection to string theory this:

For ages the world’s cleverest physicists have been divided over the concept of supersymmetry – a theory which stipulates that all known fundamental particles have heavier, supersymmetric counterparts called sparticles. It appears to be based on the theory that the universe is made out of string which was teased into shape by cats which are potentially dead or alive [are you sure about this? Ed.]

The writer seems to have gotten the material for the story from a more reliable source, the Economist, which recently had A bet about a cherished theory of physics may soon pay out. That story starts by explaining about Ken Lane’s 1994 bet with David Gross that the LHC would not see supersymmetry. As mentioned here, this year’s data should be enough to resolve the question they were betting about. It is likely that results from SUSY searches using most of this year’s data will be presented at the usual mid-December LHC Jamboree at CERN, and unless there’s dramatic news my sources are keeping from me, these results will be negative.

The bet was for an expensive dinner at Girardet’s, a three-star Swiss restaurant which has now closed, and

Dr Lane says it is time for Dr Gross (who won the Nobel prize in 2004) to cough up—if not with dinner at Girardet’s then at another suitably ritzy venue. After receiving no response to several e-mail prompts, however, Dr Lane is growing impatient. “David appears to be welshing [misuse of language, see here] on our bet,” he says.


Dr Gross is not ready to concede quite yet. The data are in, but their analysis is not complete. “It looks like I will lose this bet by the end of the year,” he says, “but we should await the word from the experimenters themselves.” (Dr Lane says the original terms have been met and Dr Gross should throw in the towel.)

As for whether this really kills off SUSY, there’s a pithy quote from Sabine Hossenfelder:

Sabine Hossenfelder, a theoretical physicist at the Frankfurt Institute for Advanced Studies, is one of many who think it is time for theorists to focus on other problems—how gravity behaves at the very small scales of quantum mechanics, for instance. If the LHC finds no trace of sparticles in this year’s data, she believes the last thing the field needs is another round of Susy model adjustments. “That’s not science,” she says. “That’s pathetic.”

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23 Responses to String theory might be about to finally be killed off

  1. John McAllison says:

    I agree with Gross on this: wait until ICHEP 2017 when the recorded 40fb from 2015-2016 has been fully analyzed. The news coverage will be far greater on the demise of SUSY, than on the the state of the diphoton excess at ICHEP 2016.

    Talking of bets… I’m hoping Jester does a series of blog posts over the coming months on how his bet with Lubos is finally being concluded at long last.

  2. Another Anon says:

    If SUSY dies, surely string theory dies as well?

  3. Another Anon says:

    There’s no fermions in bosonic string theory without SUSY.

  4. Jeff M says:

    Being a mathematician, not a physicist, I’m curious – any story about what the first bet like this was? Also, isn’t SUSY essentially unkillable, I mean can’t you adjust the energy up by at least several orders of magnitude?

  5. Kenneth Lane says:

    1)From my iMac’s built-in dictionary:

    welsh |welSH| (also welch)
    verb [ no obj. ] (welsh on)
    fail to honor (a debt or obligation incurred through a promise or agreement): banks began welshing on their agreement not to convert dollar reserves into gold.

    Sorry, my Welsh friend. As far as I know, it is not meant as a national slur, but I don’t have my OED handy.

    2) At ICHEP, in Chicago in August, the largest statistical support for supersymmetry was about 3-sigma; see the plenary talk by Dave Charlton. At that time, the LHC had delivered a total of about 55 inverse femtobarns to ATLAS and CMS, of which about 90-95% was recorded by each detector. There is now about 65 inverse femtobarns delivered to them. There is no way on God’s green earth that the additional 1o inverse femtobarns can turn a 3-sigma fluctuation into a 5-sigma discovery. As any decent physicist knows.

  6. Kenneth Lane says:

    p.s. For those unfamiliar with the LHC: Those 55 and 65 inverse femtobarn refer to EACH detector. The bet called for only 50.

  7. Peter Woit says:

    Kenneth Lane,

    I think you’re counting both 8 TeV and 13 TeV data. Presumably David’s argument is that the 8 TeV data doesn’t count, only data at or near the design energy counts. In any case, he’s only got a month left before (negative) results with 50 inverse fb at 13 TeV appear, so you should be able to collect soon.

    As in many etymology questions, the one here may be not so clear, but online one finds explanations like this:

    “.Even worse is the verb ‘to welsh,’ meaning ‘to renege on a bet,’…The term welsher became common in Britain during the eighteenth and nineteenth centuries in the argot of race-track bettors. But from a reader came a comforting word for all Welshmen, one which gives a touch of logic to the use of the term: ‘It was ENGLISH bookies who, having too many long shot winners against them, fled over the border to ‘boondock’ Wales to become the original welshers and escape irate bettors looking for their payoff.'”

  8. Eric Weinstein says:

    [This is really weird. Something must have changed for me to be writing a pro-SUSY comment.]

    To state the obvious, nature either uses SUSY, or it does not. So, let’s leave that aside at first.

    What irritates so many about SUSY, is that SUSY supporters often act like it just HAS to be true and then somehow get an indulgence from the usual standards of science to take a massive advance on experimental reality.

    So while it is really satisfying to see the most strident of the SUSY cheerleaders lose their bets, this isn’t really about SUSY. It’s a morality play about representing a particularly insufferable flavor of triumphalist group arrogance in speculative physics.

    But what if, for argument’s sake, SUSY is real, yet nature instantiated in a totally different framework than the one expected? It’s not SUSY which should be on trial. Instead, it’s really the specificity with which the current top physics echelon claimed it could specify the future of the field.

    SUSY is one of the few areas in which physicists pointed mathematicians at something that mathematics should have seen but even now can’t really intuit. Sure you can write down axioms, but the SUSY structures are surprisingly rich and difficult to motivate.

    If we lose SUSY, we are going to lose a lot of genius thinking about spinors that has not yet been fully incorporated into the core of pure mathematics. I for one hope that SUSY is real but that the current instantiation will come to be seen as wildly off. That will end up, in practice, seemingly vindicating both the cheer-leading David Grosses of the world and their grumpy critics. In truth it will validate neither.

    I don’t believe in the sparticles we are supposed to see at LHC. I also don’t believe that SUSY is nowhere to be found in nature. My guess has been that we did something brilliant and then messed it up. And this is why SUSY won’t die and also isn’t progressing to confirmation. Let’s let the morality play finish, but realize that it is triumphalism rather than SUSY which is about to have its comeuppance.

  9. Peter Woit says:

    I agree that there’s a problem here, since the term “SUSY” can mean several different things. Particularly a problem to my mind is that what doesn’t get distinguished are

    1. SUSY = use of super Lie algebras (i.e. Z2-graded Lie algebras)

    2. SUSY = Extension of the Lie algebra structure of the Standard Model by a specific extension of the Poincare Lie algebra by a Z2-odd spinor (N=1 minimal supersymmetric extension of the SM).

    The second of these has been problematic from the beginning (no superpartners= states you would get by acting by the Z2-odd spinor operators on known states, theory gets ugly very quickly if you try and introduce new physics to push these states to unobservably high masses). The first is a very general idea, and I think likely will be part of any deeper understanding that goes beyond the SM.

  10. Barry Badge says:

    I obviously don’t know, but a phenomenon like String Theory looks to me more historically similar to a political movement than a scientific theory, in that the key to the status of that community is very much to do with the dominance it holds in key institutions and the links it has to the major sources of funds.

    I am hopeful String Theory will die off but the signal will, I think, be that of the funding drying up. Even then, with institutions like Templeton in play, String Theory will leave the mortal coil of science very much like the proverbial ‘old hippy’.

    That said, the last couple of years feels like a sea change with many more people coming out against it. You’re obviously much more informed and in-touch with events and if you think it’s a maybe, maybe it is.

  11. Peter Woit says:

    Barry Badge,

    The real news is the failure of the 13 TeV LHC to see supersymmetry, with the way the TechEye story brings string theory into it kind of silly. It is true that no SUSY at the LHC removes the best hope that those devoted to string theory unification models had for seeing some sort of experimental vindication. Other than SUSY, hopes for an experimental result indicating string theory are now pretty much “maybe a miracle will happen.” This isn’t at all though a new situation.

    I don’t want this to turn into the same discussion as usual of the state of string theory, but I’ll just comment that funding has never really been the way to look at this: amounts of money going into theoretical physics, string theory or otherwise, have always been and always will be rather small compared to other topics.

  12. Barry Badge says:

    “amounts of money going into theoretical physics, string theory or otherwise, have always been and always will be rather small compared to other topics.”

    Sure but that surely translates the allocation of resources up the list of what determines outcomes. Presumably the problem is not String Theory in itself, in that if there were 20 string theorists worldwide on a shoe string budget, there would be no problem.

  13. Anon says:

    The December CERN jamboree is cancelled to preserve the sanity of the experimentalists. Expect the 40 fb-1 results for Moriond early next year.

  14. Peter Woit says:

    Thanks for the news. So, the likely date for the funeral of SUSY and fine-dining for Ken Lane now seems to be four months away, mid-March.

  15. Entropic gravity says:

    We’ll enjoy the event better during the spring break… 🙂

  16. NumCracker says:

    BTW, one can not experimentaly kill SUSY or even superstrings, they can survive even this ridiculous limits:

  17. Ford says:

    Dear Peter

    I would like to see your comments on approaches like this, where SUSY disapears from observable spectrum:


  18. Peter Woit says:


    I think Sabine Hossenfelder’s comment was aimed at this kind of thing, and I agree with it.

  19. Kenneth Lane says:

    To Peter Woit and what data at what energy counts: As you can see from the original bet (whose picture I believe you posted) there is no mention of what energy the 50 inverse fb must be. There is not even mention of whether it is 50 inverse fb per detector of 50 total for the two. A reasonable interpretation is that it is 50 inverse fb for each detector and all the data from Runs 1 and 2 count toward the 50. (After all, the Higgs boson was discovered in 2012 with — as I recall — somewhat less than 20 inverse 5b of 8-TeV data.) The job of interpreting the bet is on the other three physicists, and they agree that the conditions of the bet have been met. BTW, I do not think there will be a total of 50 inverse fb of 13 TeV data; it is more like 42 or so.

    As for the ethnic slur, I was unaware of its origin and I sincerely apologize for using it.

  20. Peter Woit says:

    Kenneth Lane,
    Unfortunately the terms of your bet are somewhat imprecise, and I can see a technical argument from Gross’s side to wait a bit more before conceding. He has though clearly lost the bet, with the only thing that could save him a SUSY discovery in this year’s data, and that doesn’t seem to have happened (although we’ll have to wait until March it seems for fully analyzed, released, results). It sounds like you’ll be able to collect, on a time scale of months from now.

    I’m more interested though in whether we’ll see a consensus in the HEP community that SUSY is dead, or whether it will continue to live on as a zombie form of physics. One question is whether Gross will admit not just that he lost a bet, but that this was a wrong idea. Another thing I wonder about is whether the field will keep training students in this subject, even after it is dead. One thing to watch will be the upcoming IAS summer school on particle phenomenology, see
    Will there be lectures there aimed at training the grad students and postdocs in the lost cause of SUSY phenomenology, or will there be an acknowledgement that this was a failure, and a move on to other topics?

  21. Nakanishi says:

    SUSY is dead: Nature is natural!!
    Since some decades ago, I have continuously claimed that SUSY should not be a correct symmetry. The reason for this belief is that SUSY as a symmetry at the Lagrangian level is inconsistent with quantum Einstein gravity, which implies that the Poincare symmetry cannot be a primary symmetry but is a secondary symmetry derived as a consequence of spontaneous breakdown, just like the electromagnetic U(1) symmetry in the electroweak theory.

  22. Scott Church says:

    Peter, forgive me if this is a naive question but…

    What’s being killed off here is minimal SUSY. We can of course keep looking for it at ever-higher energy scales. Now IMHO searching for increasingly massive sparticles to preserve increasingly lop-sided symmetries with their lighter Standard Model partners only makes it more subject to Occam’s Razor. But a string theory enthusiast could respond by playing the “elegance” card, and say that a theory this “beautiful” justifies doing that… indefinitely (quoting Einstein, “If the facts don’t fit the theory, then so much worse for the facts…”).

    It seems to me that questions of “beauty” vs. Occam’s Razor are about as objective as arguing about who’s wife is hotter. I’ve seen Sean Carroll go so far as to refer to the AdS-CFT duality as “our best understanding of quantum gravity…” even though it’s a toy model duality based on an AdS universe we don’t live in. If the word “understanding” can be stretched to limits like these it’s difficult to see what would be ad-hoc enough to offset what’s “beautiful” to string theory enthusiasts.

    So… how can we be sure it’s even possible to kill off string theory? Is this really any different than trying to convince Linus not to waste yet another Halloween night waiting in the cold for the Great Pumpkin to appear…?

  23. Peter Woit says:

    Scott Church,
    Yes, string theory unification is compatible with anything, and so is SUSY, by pushing the SUSY breaking scale up to unobservably high values. But, for the last 30 years or so, whenever asked about how string theory was going to connect to experiment, the standard answer has been by finding SUSY at the LHC (and a SUSY dark matter particle). Now that that has collapsed, there is nothing left as justification for string theory unification except claiming that ugly scenarios are really beautiful, and hype about AdS/CFT (which has nothing at all to do with string theory unification).

    The point is not that seeing nothing at the LHC falsifies string theory/SUSY, but it falsifies the one viable heavily sold scenario for connecting these ideas to experiment.

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