The Nightmare Scenario

Now back from a short vacation, and there seems to have been a lot happening on the debate over fundamental physics front. From the experimentalists, news that the Standard Model continues to resist falsification:

  • At ICHEP, as expected, new data from ATLAS and CMS ruled out the supposed 750 GeV state that would have indicated new physics.
  • Also at ICHEP, significantly stronger bounds on SUSY: gluinos ruled out up to 1.9 TeV, stops up to 900 GeV.

Recall also the recent results from LUX and PandaX (discussed here) putting stronger bounds on the sort of WIMP dark matter supposedly a feature of SUSY models.

In addition, there was news from IceCube ruling out the possibility of certain models of light sterile neutrinos (paper here, a Nature news story here).

For what it all means, you should of course consult Resonaances (and read a profile of Jester, The Rogue Blogger Who Keeps Spoiling Physics’ Biggest News) as well as Tommaso Dorigo (and some coverage from Physics World featuring him).

From an even wider perspective, see Sabine Hossenfelder for The LHC “nightmare scenario” has come true and Natalie Wolchover’s piece on the “nightmare scenario”, What No New Particles Means for Physics (by the way, congratulations to Wolchover on some well-deserved awards, including this one). My own views on this are well known: this was in some sense a major theme of my book, and among other places I’ve written about this, see for example a 2013 Edge essay.

My perspective on this is in some ways similar to Hossenfelder’s, but I draw very different conclusions, strongly disagreeing with her criticism of “reliance on gauge symmetry”, and “trust in beauty and simplicity”. This hasn’t been what theorists have been doing for 30 years. The string theory unification ideology has led to an emphasis on extremely complex and ugly models, with gauge symmetry not a fundamental feature at all. Yes, she’s right to point to “A failure of particle physicists to uncover a more powerful mathematical framework to improve upon the theories we already have”, but I’d argue that that failure is due to an insistence on looking in the wrong place.

Wolchover’s piece captures some of the current angst well, for instance quoting Maria Spiropolu about SUSY as follows:

“We had figured it all out,” said Maria Spiropulu, a particle physicist at the California Institute of Technology and a member of CMS. “If you ask people of my generation, we were almost taught that supersymmetry is there even if we haven’t discovered it. We believed it.”

Arkani-Hamed is as quotable as ever, saying the lesson of all this failure is

“There are many theorists, myself included, who feel that we’re in a totally unique time, where the questions on the table are the really huge, structural ones, not the details of the next particle. We’re very lucky to get to live in a period like this — even if there may not be major, verified progress in our lifetimes.”

I suspect that there are quite a few physicists, of my generation and later, who don’t necessarily feel “very lucky” to get to live in a period of no significant progress in the past 40 years, with the prospect of none in our lifetimes. It would be great if the “huge, structural” questions really were on the table, but I’ve seen little interest among theorists in such questions, beyond whatever the fad of the day related to AdS/CFT might be.

Also finishing up while I was away was the Strings 2016 conference, and for the state of the subject you might want to watch David Gross’s “Vision” talk (video here, I had to download the whole thing to watch it, streaming was unusable). I think Gross was right in pointing to work on the so-called “Sachdev-Ye-Kitaev” model as perhaps the most interesting thing being discussed at the conference. This is an exactly solvable large-N quantum mechanical model exhibiting features of holography. A good place to start learning about it is Kitaev’s KITP lectures here and here.

Gross also went over some history, noting that some current topics in string theory echo back to 1967 work of Mandelstam (and that Gross himself had written a paper at that time on this material, so next year will be a 50th anniversary of his engagement with the subject). As for the current state of the theory, his take is much the same as that he has talked about at many earlier Strings conferences: string theory is now a “framework” encompassing QFT and most of the rest of fundamental physics, but we don’t really know “what string theory is”. To me it’s very unclear why one is supposed to believe so strongly in the overarching role of a set of ideas that aren’t well-defined and have been an utter failure at explaining anything about particle physics. Soon he’ll have to pay off his SUSY bets, but this doesn’t seem to have changed his conviction that superstring theory unification is on the right track. He ended with his usual sign-off “The best is yet to come”, but this time added a parenthetical “I hope it comes quick”.

Another new Wolchover piece well worth reading is about Miranda Cheng and her work on modular forms and string theory on K3 surfaces. I think this sort of work on the boundary of mathematics and physics makes clear the problem with string theory and mathematics: things are complicated and ugly if you try and make the theory look like the real world. You get beautiful ideas and great mathematics when you ignore the supposed connection to the real world and go in another direction. The problem is that often, instead of pursuing good mathematical ideas where they lead, people doing this feel the need to stick to some connection to the failed idea. Here’s what Cheng has to say:

I personally always have the real world at the back of my mind — but really, really, really back. I use it as sort of an inspiration for determining roughly the big directions I’m going in. But my day-to-day research is not aimed at solving the real world. I see it as differences in taste and style and personal capabilities. New ideas are needed in fundamental high-energy physics, and it’s hard to say where those new ideas will come from. Understanding the basic, fundamental structures of string theory is needed and helpful. You’ve got to start somewhere where you can compute things, and that leads, often, to very mathematical corners. The payoff to understanding the real world might be really long term, but that’s necessary at this stage.

For another physicist still enthusiastic about string theory, see this interview with Brian Greene, somehow motivated by a sci-fi horror series, Netflix’s “Stranger Things”.

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42 Responses to The Nightmare Scenario

  1. Justin says:

    As the most influential string theorists like Witten approach retirement, should we expect to see a whole new generation of independent research ideas coming from the young theorists? Or will the influence of strings carry over into the next generation preventing research in other ideas? And how are we supposed to ever make progress if we are limited in what we can work on? Also, is this a problem unique to the US or do strings have a stranglehold in Europe as well?

  2. Bob says:

    To me, that fact that people are disagreeing about what should be fundamental and what we have too much of really means we need a period where everything is challenged and everything is explored.

    Here’s hoping we move into a period where wild speculation and exploration of new ideas is actually encouraged rather than sticking to paradigms that may be leading us nowhere fast.

    When you reach a dead end in a maze, you have to take a few steps back to find another branch, no matter how gold-gilded the walls are.

  3. Bee says:


    I suspect the reason you are disagreeing with me is that I am not referring to string theory, but primarily to all the hep-ph clutter you find on the arXiv. If the diphoton story has demonstrated on thing it’s that you can cook up hundreds of models to fit any bump that comes up as a fluke. This type of construction is hence arguably seriously underdetermined.

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  5. Thomas Larsson says:

    Has anybody considered the possibility that the reason why the LHC found no trace of BSM physics might be that there is no BSM physics? Except for gravity, which is a separate story. With the Higgs mass right at the edge of the stability region, there seems to be no compelling theoretical reason why there has to be anything beyond the SM. On the contrary, the fact that the SM is living on the edge makes it more compelling to me than if it were deep inside the stability region.

    The standard counter-argument is that visible matter only makes up 5% of the universe’s mass. However, recall that medieval astronomers knew that the universe was a clockwork with at least thirteen epicycles. Experimental data are always interpreted within some framework, be it epicycles or QFT+GR. QFT and GR are of course on much stronger footing than epicycle theory ever was, but we know that their marriage is an unhappy one, and if they break down anywhere , the large-scale structure of the universe is as likely a place as any.

  6. Bee says:


    The problem with your idea is the statement that the “unhappy marriage” of QFT and GR is as likely to break down on (cosmologically) large scales as anywhere. On cosmologically large scales joining GR and QFT works just fine. The problems only become noticeable at very short distances, or high energies respectively. This doesn’t mean that a combination of GR and QFT does *not* lead to long-distance modifications, but at least it isn’t presently clear how or even why that should be so. And in any case, that would also constitute new physics.

    Having said that, of course it’s been considered that there isn’t any new physics until the Planck scale, it’s called the “big desert”. But you don’t read much about it in the pop sci media because there isn’t much to be said about it.

  7. Dave Miller says:


    It sounds as if you agree with Miranda Cheng’s comment?

    Personally, it sounds sensible to me: the basic ideas of string theory are sort of intriguing, and it will be interesting to see them explored and fleshed out. Alas, connecting them to experimental physics seems to be a project for the distant future.

    Maybe the “string wars” will end in a truce along the lines Cheng suggests.

    Dave Miller in Sacramento

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  9. Navneeth says:

    Thomas Larsson: Has anybody considered the possibility that the reason why the LHC found no trace of BSM physics might be that there is no BSM physics?

    Why are so many people so quick to dismiss BSM physics so soon, despite the experimentalists’ repeating that we have so far gathered only a fraction of the data the LHC was designed to generate?

  10. Maurice Carid says:

    The crucial question is “what do we learn from the unholy mess that the particle physics community got itself into?”.
    I agree with Peter that I cannot comprehend the lessons Sabine suggests.
    Neither do I comprehend her answer to Peter:

    >I suspect the reason you are disagreeing with me is that I am not referring to string theory, but primarily to all the hep-ph clutter you find on the arXiv.

    Sabine, do you consider the “hep-ph clutter” you’re referring to, to rely overly on gauge symmetry or to be beautiful and/or simple?! If not, it is no example for cases of too much “reliance on gauge symmetry” or “trust in beauty and simplicity” in the last decades, that Peter challenges you to cite.

  11. Jan Reimers says:

    Hi Peter, I am curious if you think the recent progress on amplitudes is a counter example to pessimistic statements like:

    Yes, she’s [Sabine’s] right to point to “A failure of particle physicists to uncover a more powerful mathematical framework to improve upon the theories we already have”,
    but I’d argue that that failure is due to an insistence on looking in the wrong place.

    It would be great if the “huge, structural” questions really were on the table, but I’ve seen little interest among theorists in such questions,
    beyond whatever the fad of the day related to AdS/CFT might be.

    In particular we can now calculate complex gluon tree amplitudes using a starting point (Grassmanian + twistor variables etc) that has no locality or unitarity and we see these features emerge in the final answer. At least for tree level we can’t just wave this off as only applying to a toy model (planer N=4 SYM). For me this really does seem to be uncovering a more powerful mathematical framework to improve upon the theories we already have. At least it is a definitive step in that direction which can be rigorously checked against known results. Does this work also not count as a step towards the huge structural questions (emergent space-time and emergent QM)?


  12. Low Math, Meekly Interacting says:

    Hi, Naveenth,
    Based on my read of the popular literature on the subject, while the quoted experimentalists are maintaining an admirably agnostic stance, the theoretical picture is pretty grim. Since the LHC has turned on (and arguably well before), the favored theory for BSM physics, SUSY, has been shown to be all-but-irrelevant to the major problems it was purported to solve. If SUSY kept the Higgs mass “natural” and supplied a candidate for WIMPs, at the very worst a credible bump should have appeared somewhere by now. Instead there’s NOTHING. If anything like SUSY exists in nature, it either has to be horribly ugly to meet its original demands, or it’s fine-tuned. The former seems unlikely, and the latter just adds exponentially to the mystery of nature’s apparent “unnaturalness”. There’s little reason to think that SUSY will appear at energies accessible to any conceivable experiment. At best, there’s no reason to think that feasible experiments are probing nature at energies that are in any way special. We would simply have to be extremely, incredibly, ludicrously lucky to live in a universe where BSM physics is accessible.
    Presently, there’s simply no compelling reason to think the LHC will see anything deviating from the SM. Maybe it will, but why should it? And if we are to build another, more powerful collider, what would it be for? Perhaps all we can hope to do is learn more about the SM Higgs. Is that enough to justify the tens or hundreds of billions of dollars that will be needed to build this machine? Can a vibrant field of theoretical and experimental particle physics be sustained by such an endeavor? I guess these are the major, and deeply troubling questions that need to be faced even now. Unless, again, we are very, very, very, VERY lucky.
    Do I have this right?

  13. Radioactive says:

    Thomas – there is all that Dark Matter floating around in space…

    Peter – Ads/CFT is a very long lived fad, going strong since 1997. And I am not sure what you expect theorists to do when there’s a popular and promising direction, other than to pursue it and then give talks about it at conferences.

  14. Anonyrat says:

    IMO, we have to figure out “beautiful and simple” rather than “arbitrary and underdetermined” symmetry-breaking, if the fundamental theory is built with symmetries and dimensions that aren’t apparent in our world.

  15. Peter Woit says:

    There are now many generations of string theorists of all ages, the problem isn’t Witten (whose influence is not what it used to be). Actually, Witten and those of his generation had a much wider training than many younger theorists, who often ended up with a rather narrow perspective.

    These days, even “string theorists” mostly don’t work on actual string theory. The faddishness of the field remains an ongoing problem, even as the fads evolve. The nature of the fads and prospects for doing other things vary a lot from place to place, hard to generalize much about “US vs. Europe” for instance.

  16. Peter Woit says:

    We agree about hep-ph. I think a problem may be that lots of hep-ph work starts with a motivational claim about how beautiful SUSY is, how beautiful GUTs are, but then goes on to extremely complicated and ugly constructions (because the simple, beautiful ones don’t look at all like nature).

  17. Peter Woit says:

    Dave Miller,
    I don’t agree or disagree with Miranda Cheng’s comment, I quoted it as a good example of how string theorists working in that area think about their work. They realize there is no hope of doing something that connects with experiments (which is good, keeping them from working on failed ideas), but at the same time, the goal of getting such a connection to string theory motivates their research direction. The danger here is that this keeps them from pursuing directions that are mathematically promising (because they clearly don’t lead to anything related to physics), while at the same time encouraging research directions that are mathematically unpromising, but promise some sort of physics connection (although I think these are mirages).

    A good example of what I mean is Cheng’s recent talk at the Strings 2016 conference, where one of her topics was counting IIB flux vacua, a subject motivated by dubious physics, and leading into a thicket of complicated mathematics.

  18. Peter Woit says:

    Jan Reimers,
    Some of the amplitudes ideas you mention are an example of new structural ideas, and I’m sure that’s something Arkani-Hamed had in mind. So, yes, that’s a good example of an interesting research program. At the same time, there’s a huge disjunction between what is actually going on in that subject, and claims that one is going to get something like “emergent spacetime and QM” out of it. Arkani-Hamed himself acknowledges that the long hype-filled motivational intros to his talks about this are something he does to keep himself from getting discouraged, more than actually grounded in reality. At the latest Strings, his technical talk was “Towards deriving string theory as the weakly coupled UV completion of gravity”, and, like the Cheng example above, I suspect this is an example of devotion to string ideology sending someone in a direction quite different than where the actually interesting things being learned about amplitudes might be pointing.

  19. Peter Woit says:

    I don’t know if “fad” is the right word for something going on for nearly 20 years (or, even more so, something like SUSY extensions of the SM, at over 40 years). What I meant to indicate is a huge overemphasis on one idea, partly because everyone else is working on it. After 20 or 40 years, claims about “promising” are highly problematic, arguably one might instead take the point of view that once tens of thousands of papers and decades have been devoted to an idea, if its initial promise hasn’t worked out, it never will.

  20. John says:

    The real life reason it’s called the nightmare scenario is because the funding dollars will start to dry up and jobs will be lost. Governments and taxpayers will start to question why we need to keep funding the LHC if there is nothing else to find.

    On the bright side some funding should free up for new concepts and ideas that are different from the direction that has been pushed for 20+ years.

  21. Hi Peter,
    as I said elsewhere, I remember Dad used to worry quite a bit about the possibility of a ‘desert’ in accelerator physics after the discovery of the Higgs (unlike his colleague Julius Wess, who felt that the first SUSY discovery was just around the corner).
    The frustration is understandable from a theorist’s point of view but the situation is a little different for the experimentalist. After all, it’s reasonable to explore the next energy frontier and see what shows up, at least for a while. As my old supervisor used to say, experimental physics works primarily by ruling things out.
    Of course, it’s possible particle physics may find itself in the same situation as GR in the 40s and the 50s for some years. After all, we can’t expect experiment to always track faithfully, there will always be periods of drought. And maybe it won’t be such a bad thing if more theoreticians and experimentalists focus on other areas such as condensed matter physics for a while. Many important breakthroughs were made there before, as you know.
    My feeling is that the next big discoveries may come in observational cosmology – hopefully these will show the way for the next generation of particles
    Regards, Cormac

  22. WLM says:

    It would seem that one aspect of this “ultimate catastrophe” is that, as recently as a couple of years ago, almost everybody in hep-ph thought that finding the proverbial needles in the haystack would be easy: you just had to sit down on that metaphorical haystack (the energies at the LHC) and the needles (new particles) would poke you in the ass. Turns out that was wrong. Super-symmetry isn’t just harder to find, it may not even exist. So BSM physics got much harder to identify; if the LHC is going to expose anything, it will probably be fairly subtle, maybe not at all obvious. One of the things that David Gross said recently applies here (paraphrasing): If we are now going to find maybe only a single needle hidden within a single straw somewhere within that haystack, we need to understand the haystack very, very well. That’s what the LHC can help to provide, including the Alice experiment, not just CMS and ATLAS.

    On the other hand, the push to investigate N=4 super-symmetric, non-interacting, infinite color charge, conformal versions of QCD, as something that’s sort of close to the real world if one could only somehow insert quarks into it and break super-symmetry to get it back to reality, seems like the “more of the same” that both you and Bee are referring to. The main reason that this approach is “interesting” and “shows promise” seems to be that it looks like it may someday have some connection to a version of String Theory, not that it is actually about physics. Seems like what an old federal judge friend of mine used to refer to as “mental masturbation” — something that used to appear to be more common in the law and in philosophy than in physics :-).

  23. Radioactive says:

    I guess I would agree with that Peter. However if you dislike hep-ph and hep-th ‘clutter’ then the academic environment is much more at fault than any perverse desire on the part of the average researcher to doggedly pursue failed ideas. The non-stop treadmill of competition for new PhDs, new postdocs and new staff with very little flow out the top and the pressure to publish 2-3 papers a year and get cited means no time to start whole new research directions or take risky decisions. With a healthy experimental situation – eg. the 70s in particle physics, right now in gene editing – this environment probably works quite well for making rapid progress.

    Regarding switching from elementary particle theory to condensed matter. Many people, young and old, I have interacted with seem to view theories about fundamental particles as not just intellectually, but morally superior. I think the continued existence and even growth of apparently moribund ideas will continue as long as this view persists.

  24. anon says:

    I wouldn’t consider the situation in life sciences (e.g., gene editing) as quite that good. There’s a huge oversupply of recent PhDs who are slaving in low-paid (usually a paid a lot less than in physics) postdoc positions for years. And there’s no shortage of of bad (inconsequential, plain wrong or in worst cases downright fraudulent) papers.

  25. Mitchell Porter says:

    WLM, see e.g. arxiv:1607.02843 for fruits of N=4 research.

  26. Thomas Larsson says:

    Yes, the LHC have only gathered a fraction of the data at full energy, but IIRC statistical errors only decrease with the square root of the integrated luminocity, so error bars will only go down with one order of magnitude or so. Besides, there are other experiments, like PEDM and proton decay, which also point at no BSM physics.

    As I said, 95% of the universe’s mass is dark, *if* you interpret the observations within the framework of QFT+GR. But my impression is that most plausible models of dark matter lead to BSM physics at LHC scales, so there is a cognitive dissonance with the null results from LHC. But a modification of the QFT+GR framework would of course also be a kind of BSM physics.

    People talked about the Big Desert back when I was a student, but nobody believed in it then. And it is incompatible with the standard interpretation of dark matter and energy, right?

    My argument against BSM physics, apart from the obvious fact that it is disfavored at the LHC, was the criticality of the Higgs mass. This is not my idea – the authors of arXiv:1307.3536 call it the principle of living dangerously.

  27. Jonas says:

    Thomas Larsson,
    As far as I understand things the non-zero neutrino mass is BSM, so we already have such data. It’s just not related to SUSY or similar things.

  28. NoGo says:

    Perhaps one more direction where BSM physics might come from (apart from colliders, comsology, and neutrno detection):

  29. Shantanu says:

    Thomas, forget dark matter. But don’t neutrino oscillations already tell us there must be BSM physics? After all that’s why last year’s nobel was given

  30. Peter Woit says:

    The neutrino mass story is complicated, I don’t think “BSM/non-BSM” is very useful. One project planned for when I have some time is to get unconfused about some aspects of that story, maybe will write about it here if I manage that.

    For, this, there’s the ever reliable and topical Natalie Wolchover, with
    which includes

    “Still, Pohl is highly skeptical that the puzzle is evidence of new fundamental physics.”

  31. Anonymous says:

    “I suspect this is an example of devotion to string ideology sending someone in a direction quite different than where the actually interesting things being learned about amplitudes might be pointing.”

    What is the direction that the actually interesting things being learned about amplitudes might be pointing? Is there any technical reason for this comment?

  32. Peter Woit says:

    I’m no expert on amplitudes, so,it would be silly of me to claim to know technically what people studying amplitudes should be doing. It seems to be a rich subject with many possibilities. The point of the comment was just that using the subject to try and find a way to make a dubious nogo argument for string theory is the kind of thing you get into if you are enthralled by a dubious ideology rather than the logic of the subject itself.

  33. Hi Peter,

    thanks for the link. Maybe something that other commenters have not pointed out here is the importance of the present status of things for the next forty years. We are in a difficult situation as we need to plan the next big machine now, and we do not know what is the right thing to do. Since experiments are not giving any hint of what direction to take, it seems natural to go for a precision machine that will measure the Higgs boson properties in detail – an e+e- collider reaching several hundred GeV but not more. That thing will improve our knowledge of what we know already, but will most likely not discover anything new, like the much glorified LEP and LEP-II.

    If no investment is made in the near future in a big new hadron collider (which should have one order of magniture larger energy to make any sense) or an entirely new-concept muon collider (which is very challenging and probably as of yet unmotivated), we risk that humanity remains stuck for a long while; in the meantime, we will lose a whole generation of machine developers and detector builders, without a chance of transferring their know-how to the new generations.

    (I must say that regardless of the above threat, I remain of the opinion that no choice should be made now, as we should rather keep waiting for new developments in the neutrino sector and in other related fields of experimental physics before committing to building some new big toy that might not be the right thing).

    In summary, the situation may look good to NAH, but experimentalists have little to rejoice here.


  34. vmarko says:

    Hi Tommaso,

    “Since experiments are not giving any hint of what direction to take, it seems natural to go for a precision machine that will measure the Higgs boson properties in detail”

    It seems to me that the experimental results from the LHC are actually giving a very strong hint which direction to take next — study IR physics, maybe also Higgs precision measurements, and abandon high energies for now. Certainly, it’s a gloomy prospect, but a precision-measurements machine can maintain the knowledge base and the craft of building particle colliders until there is a development suggesting there is something to be found at higher energies.

    In my opinion, we are better off developing methods to study the high energy frontier by catching cosmic radiation. Only there we stand a chance to find out that there is something interesting to look for, and at which energy scale to expect it. And only once we find that out, it makes sense to build another collider, at the appropriate energy scale to study it. I know, it’s tough, luminosity from cosmic rays sucks, but the no-new-physics situation at the LHC leaves us little choice, IMO.

    Best, 🙂

  35. Peter Woit says:


    My impression is that it’s not just that the luminosity from cosmic rays sucks, but that, at center of mass energies above the LHC scale, it’s useless for since you’re highly unlikely to see any events probing very short distances.

    To get more precise information about the Higgs, one needs a new high-energy machine. A lepton collider that could produce and study Higgs particles would have lower beam energy than the LHC, but still would be higher than LEP, extending collider technology to higher energies.

  36. NoGo says:


    Thanks for the link to Natalie Wolchover’s piece. Indeed, it is very informative, and is far more level-headed than other coverage of these experiments I’ve seen.

    Still I wonder, perhaps naively, if some significant progress towards BSM can be made by improving sensitivity of detectors, and increasing calculation power of computers used, rather than “smashing things harder”. (I confess that the sensitivity achieved by LIGO still blows my mind… Of course it’s a different area of research, but demonstrates how far one can go). Isn’t it true that the effect of “heavier” quantum fields can be in principle detected even if colliders lack the energy to actually create particles of such fields?

    I admit that what made me jump up and down about muonic deuterium experiment is that, if it turned out BSM physic, it might shed some light on generation problem. As a non-physicist, again perhaps naively, I find the generations to be the most unsatisfactory part of SM, evidence for something else. I can in principle buy (with cringed nose) anthropic explanation for the rest of SM feathers, but not that one…

  37. Peter Woit says:

    In essence what these experiments are doing is creating a highly excited state (by colliding protons), then looking at the long-lived states this decays to, and using this to study the physics at a high energy scale (in principle one might indirectly even get information about scales higher than the accelerator is producing). The detectors are quite sensitive in the sense of identifying the decay products, more sensitivity of this kind I don’t think would help much. The problem is the large number and complexity of the decay products, making it very challenging to extract useful information about the processes that produced them. So, the sensitivity challenge is that of extracting a small interesting signal from a much larger uninteresting one. This is what HEP experimental analyses are all about, and their methods are highly sophisticated, using as effectively as they can a huge amount of computational power.

    Yes, the generations are a great mystery and in principle a different behavior than expected of muons could shed light on it. But it’s very hard to think of what could plausibly explain such different behavior, at low energy scales that we think we understand well. Thus the skepticism about a non-Standard Model explanation of this.

  38. GoletaBeach says:

    Nature is natural by definition, and if there are no thresholds of new physics crossed at the LHC, that must be perfectly natural.

    It is perfectly fine for the neutralino of SUSY to be far lighter than all the other superpartners. The photon, mostly the neutralino superpartner, is far lighter than all the normal partners.

    A 1 TeV neutralino is perfectly fine for even the absolutely simplest SUSY phenomenologies, with all other superpartners out of reach of buildable colliders. That neutralino might be seen in the direct dark matter experiments or the indirect ones.. no problem.

    Or it might not. Whichever it is, all perfectly natural, because natural always is what nature chooses.

  39. TS says:

    I am reading the exchange to say that no one around believes that B-factory experiments will discover anything worthwhile? Well, make that singular, as there’s only going to be Belle II. Anyway, did the biggest new particle accelerator experiment slip everybody’s mind?

    I can’t help wondering what B-physics could achieve if as much brain power was devoted to it on the theory side as is to high-energy phenomenology or string theory.

  40. Francis says:

    David Gross video at Strings 2016 is now available in youtube

  41. I know that high energy folks are desperate for some new physics, but let’s hold off on the ritual sacrifices for now, ok?

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