In it for the Long Haul

The CERN Courier today has a long interview with the omnipresent Nima Arkani-Hamed, discussing the current state of HEP physics. About the motivations for a next-generation collider project, I’m pretty much in agreement with him: the main argument is for a Higgs factory that would allow a much more detailed study of the Higgs, and if at all possible, an appropriate machine should be built (see more here). He agrees that the SUSY and extra dimensions models used to get people excited about the LHC can’t reasonably be used again for a higher-energy machine:

Is supersymmetry still a motivation for a new collider?
Nobody who is making the case for future colliders is invoking, as a driving motivation, supersymmetry, extra dimensions or any of the other ideas that have been developed over the past 40 years for physics beyond the Standard Model. Certainly many of the versions of these ideas, which were popular in the 1980s and 1990s, are either dead or on life support given the LHC data, but others proposed in the early 2000s are alive and well.

The last reference is to his favored split SUSY models, which I think few people besides him find compelling.

About WIMP dark matter he seems to be claiming that a 100 TeV machine has always been what is needed to find it:

There is a funny perception, somewhat paralleling the absence of supersymmetry at the LHC, that the simple paradigm of WIMP dark matter has been ruled out by direct-detection experiments. Nope! In fact, the very simplest models of WIMP dark matter are perfectly alive and well. Once the electroweak quantum numbers of the dark-matter particles are specified, you can unambiguously compute what mass an electroweak charged dark-matter particle should have so that its thermal relic abundance is correct. You get a number between 1–3 TeV, far too heavy to be produced in any sizeable numbers at the LHC. Furthermore, they happen to have miniscule interaction cross sections for direct detection. So these very simplest theories of WIMP dark matter are inaccessible to the LHC and direct-detection experiments. But a 100 TeV collider has just enough juice to either see these particles, or rule out this simplest WIMP picture.

I don’t remember ever hearing, pre-LHC, from him or anyone else, this argument that the most likely WIMP dark matter models are inaccessible to the LHC or to direct detection experiments. For many years, most of the direct detection experimental results came with plots showing a “prediction” of SUSY WIMP dark matter (see for example here, figure 5), in a mass range of 100-500 GeV, at a cross section measurable (and now ruled out by) experiments like XENON1T (see here).

Arkani-Hamed likes to make the following argument, which I think most current HEP theory graduate students may find hard to swallow:

How do you view the status of particle physics?
There has never been a better time to be a physicist. The questions on the table today are not about this-or-that detail, but profound ones about the very structure of the laws of nature. The ancients could (and did) wonder about the nature of space and time and the vastness of the cosmos, but the job of a professional scientist isn’t to gape in awe at grand, vague questions – it is to work on the next question. Having ploughed through all the “easier” questions for four centuries, these very deep questions finally confront us: what are space and time? What is the origin and fate of our enormous universe? We are extremely fortunate to live in the era when human beings first get to meaningfully attack these questions. I just wish I could adjust when I was born so that I could be starting as a grad student today!

There’s something to be said for entering a field at a time when it is finally able to “meaningfully attack” difficult and fundamental questions. The issue though is whether anyone has any good ideas that will make headway against such questions. The Standard Model was in place by the mid-70s, and by the time I was a graduate student in the early 80s, the “what are space and time? what is the origin and fate of our enormous universe?” questions were already on everyone’s mind as the next things to be thinking about. Starting in 1984, the superstring revolution promised a way to answer these questions.

35 years later, the current generation of graduate students has the same questions to think about, but a long history of failed attempts to consider. In addition, there’s the sad story of the unwillingness of leading figures of the field to admit to the failure of the 1984 revolution, and widespread multiverse pseudo-science (often promoted by Arkani-Hamed) to overcome. The only argument that I can see that this is a good time to start an HEP theory career is that it’s hard to see how things can get worse…

For some commentary about the interview by Tommaso Dorigo, concentrating on the positive case for a new collider as a tool to study the Higgs, see here.

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34 Responses to In it for the Long Haul

  1. SFD says:

    ” the main argument is for a Higgs factory that would allow a much more detailed study of the Higgs.” I find it difficult to believe that the civil authorities, and scientists in other research fields, will think that this argument is enough to justify the $10B tag.

  2. Peter Woit says:

    SFD,
    Yes, but that’s going to be what the serious debate is really about: now that the Higgs has been discovered and we have some information about its properties, is it worth building a next-generation machine to study it in detail, or should we just give up, deciding this is something that humans can’t afford to try and learn about?

    I don’t disagree that this is going to be hard to sell to some people, especially scientists who believe that the money would be better spent on their own field.

    But, to all potential commenters, the “is a bigger collider worth it?” question has already been beaten to death recently, and there isn’t even yet a specific proposal from CERN to argue about. Unless someone has something new to contribute, I’d rather not host the same tedious discussion again right now, it’s one that there will be many opportunities to go over in years to come.

  3. Tom says:

    Nima Arkani-Hamed is regularly described as a “superstar theoretical physicist” (Dorigo). But why? To quote from this blog: “The fact that none of the ideas about BSM physics he is famous for (large extra dimensions, split SUSY, Little Higgs, etc…) have ever worked out doesn’t seem to slow him down”

    The trick which allowed Arkani-Hamed to become so famous boils down to taking established ideas and making them more “hypey”.

    * Extra dimensions -> large extra dimensions
    * Extra dimensions -> little Higgs
    * Susy -> Split susy
    * New methods for scattering amplitudes -> amplituhedron

    And he hypes his favorite pet peeves using whatever argument sounds good no matter if it really makes sense.

    * everyone knows electroweak charged dark-matter particle sit @1TeV, right? If only he had shared this wisdom earlier….
    * “There has never been a better time to be a physicist. […] I just wish I could adjust when I was born so that I could be starting as a grad student today!” Really? What exactly changed in, say, the last 40 years for theoretical physicists?

    All this, combined with his whole „memorable character thing“ (see below) allowed him to get so influential although upon closer inspection none of his ideas turned out to be worth the hype.

    Lately he hyped the proposed China collider to the extent that people started calling it Nimatron. This, of course, was what he was hoping for. This was his/is his chance to leave a legacy since so far, no one will remember his contributions to physics in, say, a hundred years.

    Now since the China collider will probably not be built, he hops onto the next opportunity and repeats his arguments. This is his chance to be remembered in the history books as the guy who helped particle physics survive when “ex-particle-phenomenologist-cum-still-blogger“ (Dorigo) tried to destroy it.

    Everyone who ever met him in person knows that he tries very hard to be remembered, at least, as an extremely unconventional character. (The boots, the whole “I sleep only 3 hours each night and drink 22 espressi each day”, his “Impresario”-Style talks in which he “nails” each argument.) And it seems to be working because journalists love to interview him.

    But people should really stop paying so much attention to media fame and showboating and instead with a calm head reassess the arguments at hand.

    And maybe journalists should ask instead a few young physicist who are starting “as grad student today” if they share his enthusiasm (so far I don’t know a single one who does) and how they think the future of particle physics should look like.

  4. Lonely Physicist says:

    Dear Peter,

    In my opinion, it seems that by frequently reporting in your blog all the nonsense this guy is spouting in interviews and conferences, you are yourself supporting him and his compaign!

  5. Peter Woit says:

    Lonely Physicist,
    You may be right.

    Tom,
    I don’t think Arkani-Hamed just impresses the press, for instance you can see from Tommaso Dorigo’s posting that he’s quite impressed. For another random example, I just saw this
    https://twitter.com/preskill/status/1104449921363529728
    on Twitter from John Preskill
    “Nima is a magician — he gets my pulse racing over the prospect of measuring the self-interactions of the Higgs particle at a future collider.”

    I don’t think it’s helpful to criticize Arkani-Hamed’s persona or argue that he’s not honest, that he has other motives for what he’s saying than that it’s what he believes. I don’t doubt that he believes the “best time in history to be an HEP theory graduate student” line even though it’s way over the top (so much so that I think it seriously hurts his credibility with his colleagues whenever he uses it).

    One reason for his influence is that he’s legitimately very smart and well-informed, and the everything’s fine, positive, full-speed-ahead enthusiasm is a lot more appealing to most people than being told that times are tough and they should be making difficult and unpleasant decisions about how to change their ways. Another reason is that while his own work on how to extend the SM has all failed, it’s not like anyone else has done better. Traditionally the field looks for leadership to those whose ideas have succeeded, credentialed by a Nobel Prize. Right now, the youngest of these, Frank Wilczek, is getting to the traditional retirement age, and all the others (Gross, Glashow, Weinberg) are much older. With 40 years of failure under its belt, where does a field look for leadership?

    A fascinating conflict here is between Arkani-Hamed and Sabine Hossenfelder. He dismisses her here in a really tasteless way
    “It would be only to the good to have a no-holds barred, public discussion about the pros and cons of future colliders, led by people with a deep understanding of the relevant technical and scientific issues. It’s funny that non-experts don’t even make the best arguments for not building colliders; I could do a much better job than they do!”
    basically arguing that she’s not competent to be worth listening to (by the way I’ve seen this tactic used before…). I disagree with her conclusions about whether a new collider would be worth it, but the arguments Hossenfelder is making are serious, widely shared, and she’s quite competent to be making them, every bit as competent to do this as C.N. Yang, whose arguments are actually similar to hers (although China-specific).

  6. Schrodinger's Rat says:

    “…the everything’s fine, positive, full-speed-ahead enthusiasm is a lot more appealing to most people than being told that times are tough and they should be making difficult and unpleasant decisions about how to change their ways…”

    “…where does a field look for leadership?”

    Well, look somewhere else! This behavior is pretty much my definition of the exact opposite of leadership.

  7. parisien says:

    As a student I find his comments about being a student a bit naive. Try finding a position anywhere by saying that what you want to do is to think about what is space and time. I think that the current state of academia doesn’t really allow for anyone new to even come in and find a new approach to those questions because they’re so bogged down with trying to actully find a position of some stabillity and to start any kind of career. Perhaps instead of daydreaming about being a grad student, I feel he should use his position of a public figure to point out the actual problems in academia students coming into it are facing, because if he really wants someone in the next generation to have new idea or approach, better conditions for them are neccessary.

  8. Tom says:

    Peter,

    True. It’s not just the press. Students and professors alike get starstruck when they meet him.

    And, of course, you’re right that criticizing Arkani-Hamed’s persona is not helpful. The discussion should focus on substantial arguments and nothing else. But if we subtract from the interview all the hypey yada yada, we are left with: “We should measure the properties of the Higgs as precisely as we can because we might learn something interesting. We might discover dark matter. We can’t allow that fundamental knowledge is shoved in old dusty books.”

    These are solid arguments. (Maybe except for the dark matter argument). But at the same time there are several good arguments against a new collider (monoculture, opportunity costs, physics case, etc.). And while he claims that he thinks a “no-holds barred, public discussion about the pros and cons of future colliders” would be good, we all know that this will never happen.

    The only person who currently seems to be willing to argue publicly against a new collider is dismissed as a “non-expert”. So who is left to “make the best arguments for not building colliders”?

    There is a strong sense of community in particle physics. (A few weeks ago I witnessed how an eminent professor during his talk in a full lecture hall called Hossenfelder “our current nemesis” and no one disagreed.) And while Hossenfelder’s arguments may be widely shared (especially among younger physicist), no one seems to be willing to go public. The only chance to hear people’s true opinion on these issues seems to be during coffee breaks. Hossenfelder made the conscious choice to waive here “hopes of ever getting tenure”. This is, most likely, the price you have to pay if you go public with your concerns.

    One final comment on Arkani-Hamed I would like to add. A few years ago I attended a summer school where during a break he told a group of students (I’m paraphrasing): “To make a career in physics you truly need to convince yourself that what you’re doing is the best and most important thing in the world, even if you think it isn’t.” (Make of that what you will.)

  9. Jesper says:

    @ Tom, Peter: as much as I enjoy reading this blog and as much as I appreciate the important work it represents, I do feel that Tom has a point. In the present world of theoretical high energy physics everyone seems to be looking at the top of the hierarchy for new ideas. But the main thing you’ll find up there are people who have spent their lives working on and promoting ideas which have not worked out and which we must now conclude are most likely wrong.

    I think that its necessary to spend time discussing and promoting new ideas too. People who think in new directions. There may not be many of them around but by paying attention — and not ridiculing and belittling them — we just might help create a culture where its cool to think more for yourself and not just work within one of the main scientific clusters in contemporary high energy physics.

    If we only pay attention to those at the top of the hierarchy — regardless whether this attention is positive or negative — then we feed all our energy into a system that hasn’t worked well for the past decades. By directing all your attention to the top of the hierarchy you indirectly signal that its only those people who are worthy of that attention. But the truth is that those people are the least likely to lead us in a new direction.

    I believe that high energy physics used to be characterised by rebellious minds. People who didn’t give a f… about hierarchy and what you might risk if you go against the current. I don’t see that anymore. I see a lot of people who are afraid of loosing their status and — if they are younger — of not getting a job. I think that this lack of rebellion is a part of our problem.

    @ parisien. I agree with you. I think that in the present system its almost impossible for a young independent physicist who works on her or his own ideas, to make it. For this reason I have on my blog encouraged young physicists to ‘go rogue’ — if a young, ambitious researcher is faced with a choice between a career and working on her or his own ideas, then I think this researcher should consider whether it might be best to work outside of academia. This isn’t perfect but the world isn’t perfect either. People can do this in other professions — see for instance the arts and literature — so why can’t scientists? I think that this whole idea that we can only do serious research within a given framework — academia, the universities — is wrong. I also think that it makes us smaller than we are.

    I have done that. I chose to work on my own ideas, which eventually pushed me out of academia. Its not great but its a hell of a lot better than the alternative. And it certainly isn’t something that prevents me from doing the research that I want to do. The truth be told, I find it in many ways easier to do research in this way.

  10. DB says:

    I must say that I´m a bit awestruck by everything that has been happening in theoretical physics lately.
    I have to acknowledge that I was one of those that, since ten or twelve years ago approximately, I tended to think that everything that “string theorists” were saying was close to the absolute truth, and that we were pretty close to what people used to call a “final theory of everything”.
    But thoughts and wishes are one thing, and reality is another one.
    Since the last two years I´ve been having lots of serious doubts about string theory being that so much sought TOE, and reading posts like this one (plus the comments from Tom and the rest), and even listening to people like Nima (who used to be my idol together with Witten), plus some comments Ed himself has been making lately, I think I really need to give a serious thought about all my previous ideas.

    One more thing: it seems clear that A-H himself has almost (90%?) forgotten about SUSY and extra dimensions, which is quite a lot to say.

    Time to go off for a while and double check my thoughts.

    Thanks to Peter for the post, and for all the comments.
    And good luck to everyone.

  11. Yatima says:

    “True. It’s not just the press. Students and professors alike get starstruck when they meet him.”

    That is the mark of a good, energetic Persuader. I haven’t watched Nima give interviews but does he wield Jedi mind tricks – consciously or not – as those described in the little blog post by Scott Adams about Mr. Trump: Clown Genius?

  12. a reader says:

    Dear Peter, I appreciate your blog very much, and I respect your opinions. I have been a reader for many years, probably longer than a decade. As a (rank-and-file) (ex-)physicist, I would like to ask you…
    Don’t you think that writing “with 40 years of failure under its belt, where does a field look for leadership?” is rather misleading? I guess I know what you mean, but… Your blog has a wide and large readership, I guess, so when you and others write “with 40 years of failure under its belt, where does a field look for leadership?” or something similar, would you please specify which field? Because some or may be many among your readers without a background in physics will may be guess that you are talking about all physics or all high energy physics rather than (several) subfields of high energy physics theory.
    I mean, has experimental high energy physics 40 years of failure under its belt? Do the large collaborations, I mean all the human beings who built LHC, LEP, Tevatron, RHIC, Super Kamiokande and many other HEP-facilities of the last 40 years deserve that label, failure?
    I think that sort of expression, without specifying, every time, even if it might seem tedious to do so, which particular subfield you are actually talking about, I think that is quite misleading and rather unfair.

  13. Peter Woit says:

    a reader,
    To clarify, the field being referred to is HEP theory, not anything else. I thought this should have been quite clear, since the context is a discussion of the leadership issue with respect to Arkani-Hamed, an HEP theorist.

    A possible source of confusion is that an HEP theorist is also trying to take on a leadership role on the question of what HEP experimentalists should do. Another odd aspect of Arkani-Hamed’s criticism of Sabine Hossenfelder’s views on experimental HEP is that he argues that people should instead listen to HEP theorists Yang and Glashow. Faced with the decision of where to go for advice about the future of HEP experiment, an obvious point to make is that the best answer is not Arkani-Hamed, Hossenfelder, Yang or Glashow, but none of the above. Why not consult instead an actual HEP experimentalist?

  14. Peter Woit says:

    Jesper,

    Yes, in the current environment anyone who wants to pursue a career in this kind of theoretical physics needs to contend with the sad state of the traditional academic hierarchy and career path. That’s not the topic of this posting, and I don’t personally have a good answer for what people should do (which in any case depends on the person and their exact situation). I do hope I can help people trying to find their way by giving a clear-eyed perspective on what the current state of affairs is.

    As for promoting new ideas, I do discuss here what I find interesting, while deleting the large number of comments that come in from those who would like to turn the discussion to something different that they find interesting (for those who would like to discuss new ideas with Jesper, I’m glad to see that he has a blog where you can do this).

    Two reasons for critiquing the current academic HEP theory hierarchy instead of just ignoring it are
    1. This is where students are, for better or worse, now getting trained and will continue to be trained.
    2. The LHC null results, together with the failures of string theory and SUSY as theory (together with the multiverse debacle) I think have opened up many theorist’s minds to the question of whether the subject is in a crisis due to having headed down a wrong path. Some influential theorists may be more willing to think through the implications of the current situation. As discussed here
    http://www.math.columbia.edu/~woit/wordpress/?p=10842
    Arkani-Hamed now seems to exist in a superposition of two very different states: Nima1, who thinks all is well, that current HEP theory an exciting success story, and that split SUSY and the multiverse are the answer, and Nima2, who would like to abandon his old ways and restart life as a mathematical physicist, searching for the deep mathematical question that will give us new insight into fundamental physics. I think it’s worth trying to change the environment so that the amplitude of Nima1 is suppressed, that of Nima2 is enhanced.

  15. a reader says:

    Thank you Peter. I knew well that you meant hep-th, but, please, you all who commendably engage in a public debate, remember that it is very important that you mark the difference between hep-th, hep-ph, hep-ex and (especially if you talk to a very wide audience) physics-all, because the very real risk is, I think, long lasting damage, undeserved in many, but sadly not all, cases.
    As for that Arkani-Hamed, Hossenfelder, Yang, Glashow and others are all theorists (hep-th), I agree with you.
    Experimentalists (hep-ex), be proud of your heroic endeavors and epic achievements of the last 40 years, and speak out!

  16. Amitabh Lath says:

    In addition to being smart Nima is incredibly generous. A few years ago we had a bunch of high school students in our summer Quarknet program, and screened Particle Fever one evening for the students and their parents. Nima came, and took questions for hours upon hours. He answered even very basic questions in interesting and novel ways. Nima’s enthusiasm for physics infected the kids and parents.

    Nima is right to be excited about the state of fundamental physics. It is us humans vs. the universe and although right now our math might not be clever enough and our machines might not have enough energy or luminosity, we will get there and we will crack this. We always have, regardless of politics or personalities.

  17. citely says:

    Wired UK had an article that touched on colliders, whether SUSY is worth another LHC funding round, and quantum computers to process it all. Fluff, but of cultural note (particularly as to where “physics money” is being directed).

    https://www.wired.com/story/inside-the-high-stakes-race-to-make-quantum-computers-work/

  18. Bernhard says:

    Nima is right about the motivation for a new collider (Higgs factory) and that we should learn from past lessons and not invoke hype to sell it. The 100 TeV collider argument for WIMP dark matter is not at all helpful in this respect and he’s, as usual, making stuff up, counting with the fact that is enough intimidatingly smart that nobody will call BS.

  19. Roger says:

    Can someone explain the dark matter argument to me ? Why should the preferred WIMP mass be 1-3 TeV ? I always that it was theoretically unconstrained up to an order of magnitude.

  20. DDOwen says:

    The rather personal attacks on Sabine Hossenfelder combined with the dismissal of condensed matter physics (sure, the failure to explain high-Tc superconductivity would have some weight *if that were the only thing that CMP were concerned with*, but that’s obviously false if you happen to know anything about CMP) do suggest that there’s a certain amount of projection going on in NAH’s argument.

  21. AcademicLurker says:

    This may be drifting off topic, but it’s related to Jesper’s comment above.

    Sabine Hossenfelder’s description of the HEP theorist career path in her book makes it clear that things haven’t changed since Peter and Lee Smolin published their books 13 years ago. The thing that most strikes me as an outsider is the extremely short time frame that’s imposed by the system of postdoctoral grants. If you need to start looking for a new position a year after you start your current one, then you want a paper at least submitted by then, which means you need some publishable results within not much more than 6-7 months.

    I’m curious about people’s impressions of to what extent this is intertia vs a deliberate choice. Do the powers that be in charge of dispensing fellowships & etc. affirmatively believe that this is the best way to select for new theory faculty members? Or is it more a case of “Well, this is the system we have and anyway we have to pick winners somehow so what else are we supposed to do?”?

  22. Peter Woit says:

    DDowen,
    I think you’re misreading Arkani-Hamed. His comment about high-Tc superconductors wasn’t about failure of condensed matter physicists to explain the phenomenon, it was just pointing to the history of unwarranted enthusiasm for the prospects of using high-Tc superconductors to develop much cheaper magnets suitable for a proton-proton collider. This same argument is now being brought up as an argument against the HE-LHC and FCC-hh proposals: why not wait a few years for cheaper high-Tc superconductor magnets before planning a new collider? He just seems to be making the reasonable point that people have been saying this for years, but no viable technology of this kind has appeared, and there don’t seem to be serious prospects for it anytime soon.

    Roger,
    I’d also like to see a reference for this. Arkani-Hamed here and here
    http://www.math.columbia.edu/~woit/wordpress/?p=10824
    seems to be claiming that a naive calculation of a weak interaction strength WIMP with the right abundance to be dark matter gives a mass of 1-3 TeV, and a cross-section too small to be seen in direct detection experiments, but accessible to an FCC-hh machine. I’d never heard such an argument before, curious to know what he’s basing this claim on.

  23. DM theorist says:

    For Peter, Tom, Roger etc

    I’m giving some pre-LHC references below (I even threw in one from Nima, sections 1.2 & 1.3) showing that DM candidates that are defined by their SU(2) representation and gauge interactions alone, typically are required to be very heavy and well out of the LHC range. In the MSSM you actually had to work a bit (see the Nima ref) to get a light candidate that gave you the right relic density.

    https://arxiv.org/abs/hep-ph/0601041
    https://arxiv.org/abs/hep-ph/0610249
    https://arxiv.org/abs/0706.4071

    The general idea is independent of SUSY, and just focused on WIMP hypothesis, taking the weak part, SU(2), to be literal and calculating the thermal relic density. It just so happens that some of the minimal reps, the doublet and the triplet can also be realized in SUSY as the Higgsino and Wino (when you don’t consider mixing etc).

    Theorists were talking about this before the LHC. However, at that time people focused more on what you could see at the LHC rather than what you couldn’t. Obviously when you have an experiment you want to look at everything you can test with it. Nevertheless, this was well known amongst theorists that WIMP DM with basic reps of SU(2) implied masses out of reach of the LHC. As for the last part that Peter asks about with direct detection, when the WIMP mass is higher the number density of WIMPs is going to be lower. This is why the bounds decrease in the the cross section vs mass plain on the standard direct detection results that you see, while at low WIMP mass it’s from threshold effects (there’s a ton of effort on this in the dark matter community now on the low energy side where you can devise new experiments). So this is just the standard systematic problem for a heavy WIMP, but of course if there is something charged under a representation of SU(2), then a higher energy collider could produce it.

  24. Jesper says:

    @ AcademicLurker

    I think that Lee Smolins book “The Trouble with Physics” very accurately describes the situation (and I have written somewhat of an update on my blog), where the short time-frames that you describe makes it very difficult to work on new ideas (especially if they are your own). You need to publish a lot and you need to publish fast. That system very strongly favours the technicians – those who are extremely good at solving technical problems – whereas the visionaries (I believe that Smolin called them the ‘seers’), i.e. those who are good at producing new, creative ideas, are the losers.

    During my career I have been a semi-insider to several of the leading communities in theoretical high energy physics and I have been in close contact with essentially all of them. And it has been my very clear impression that those people, who are at the top of the hierarchies, are predominantly technicians. And it is my impression that they generally think that the present system is fine. After all, it is basically the same system – perhaps a little rougher, perhaps a littler sharper – that they had to fight their way through during their own careers.

    Again, I think that Smolins book describes the situation very well. And I believe that this applies to essentially all fields in theoretical HEP – including LQG. The trouble with physics is that the present system favours researchers who are good at digging very big holes (metaphorically speaking) and disfavours those, who are good at finding the right spot to dig those holes. The result being that everyone digs their holes in the same spot.

  25. Peter Woit says:

    DM theorist,

    Many thanks for the explanations and references!
    Those references led me back to something slightly earlier and simpler, this https://arxiv.org/abs/hep-ph/0512090
    about “Minimal Dark Matter”
    Yes, as Arkani-Hamed claims, the models discussed (pre-LHC) there are in the few TeV range, a range that would require 2-4 times the LHC energy to explore. It’s interesting that these models got so little attention pre-LHC null results.

    Also interesting is that the above paper gives a version of the standard direct detection plot (figure 2), with, besides the usual SUSY CMSSM blob mostly now ruled out, predictions based on these sorts of minimal dark matter models which are at higher mass, with cross sections that the latest generation of experiments should start being sensitive to.

  26. Peter Woit says:

    Jesper/AcademicLurker,
    This has gotten way off topic, it’s an interesting question, but, enough for now.

  27. DM theorist says:

    Hi Peter,

    Glad to help, and yes one of the references was a followup on Minimal Dark Matter (MDM). These focused more on the 5-plet or 7-plet to get stability from the SU(2) rep, instead of having a parity which most models of DM have, and the cross section for direct detection grows like n^4 where n is the size of the representation. I don’t remember the exact differences between the MDM calculation, but I recall 10^-47 cm^2 as the pure Wino case in SUSY, and at ~3 TeV in mass this is below the direct detection bounds even for future experiments. Not to say that this couldn’t ever be tested outside of a collider (indirect detection is also interesting, but with its own uncertainties), just that what Nima said was accurate for the minimal representations.

    I think all decent theorists were well aware of the models. However, I think that sometimes the synergy of being able to test things in multiple ways biases peoples interests, and at least for the SUSY case, they weren’t as “natural” as having a light Higgsino. Now that we’ve seen nature isn’t as “natural”, the WIMP candidates themselves still just have the predictions they have. Some might call this bias in a pejorative sense, I think it’s more just about opportunism. If I have a model that I can test with colliders, direct detection, and indirect detection that’s very cool and super testable. If I lose one of those handles it’s still interesting, but more difficult to interpret. I don’t think there’s a secret theory cabal trying to suppress ideas or not tell the truth about the possibilities, as you see in the Nima paper they were laid out honestly. Experimentalists are just naturally going to be most interested in the models they could see with on-shell experiments and thereby that gets a broader discussion in the community.

  28. Peter Woit says:

    DM theorist,
    Thanks for the further comments. I understand there was no secret theory cabal at work, and people reasonably concentrated on looking at models that the LHC could test, but the way certain models got heavily publicized, despite well-known problems with them, is going to cause a credibility issue going forward.

    The most outrageous example to me was the whole “we may see extra dimensions at the LHC” business, here I suspect if anyone tries this for future colliders they’ll get laughed out of the room. Second though was the “we expect to see “natural SUSY”, with lots of states light enough to be easily seen at the LHC”, even though there was lots of indirect evidence against such states. To his credit, on some days Arkani-Hamed would mention such evidence and talk about split SUSY, on other days though he would go on about how many gazillion gluinos the LHC would produce and how the field needed to get organized to be able to disentangle all the many new states the LHC would see. I gather the WIMP DM story is a variant of this problem.

  29. Dave Miller says:

    Peter,

    I wonder if you (or anyone) can elaborate on what we will get out of more details on the Higgs?

    I myself had also concluded that looking more at the Higgs is the obvious next step. But… can we really get a good handle on the Higgs potential with the next collider? Or if we see something slightly different than we expect, will that merely tell us that the calculations for what to expect were too tough for the phenomenologists to do accurately? And, no matter how accurately we measure Higgs phenomena, will that tell us about anything beyond the Higgs, or will it just satisfy the curiosity of those of us who long ago learned the basic info about the Higgs?

    I honestly don’t know the answers to these questions, but, hopefully, some people actually do have answers to such questions! It seems to me that fleshing out the answers is key to making the case that deeper studies of the Higgs are worthwhile.

    Dave

  30. tulpoeid says:

    Some “superstars” have to understand that standing on the shoulders of giants doesn’t make themselves giants.

    Also, I feel that it’s important to voice a concern regarding Hossenfelder’s treatment: She is by far not the only HEP physicist, and I include experimentalists here, who opposes the next large thing (although a couple of her arguments are hard to swallow but this is not my point here). I’ve been both at LHC and DM experiments; afaik most people in DM and other “small” experiments don’t fear at all that HEP will die without a larger machine right now. There are several of their colleagues at LHC who don’t disagree. There is a number of other smaller collider-based searches, both running and proposed, which at the very least will make us search in smarter ways.

    Imho people who’ve established their careers on the energy frontier are just trying to single out Hossenfelder in an effort to persuade the public that there is only one clown who opposes the mainstream.

  31. ztimashi says:

    Regarding your comment “Traditionally the field looks for leadership to those whose ideas have succeeded, credentialed by a Nobel Prize” I find it very curious, to say the least, that all non-emeritus theorists at IAS are now string theorists.

  32. Peter Woit says:

    ztimashi,
    Arkani-Hamed isn’t a string theorist, and, actually I think that’s a reason his views are quite influential.

  33. Thomas Larsson says:

    ztimashi,
    It is becoming increasingly difficult to look for leadership from people with a Nobel prize, since there is no longer any active HEP theorist with that qualification. Or at least none who is below normal retirement age, which in Europe is 67 or less. Wilczek is 68, I think.

  34. Stephen says:

    “There has never been a better time to be a physicist” Really? Maybe Nima should study up on the history of particle physics between the mid 50s and the mid 70s.

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