Arkani-Hamed Colloquium

Nima Arkani-Hamed was here at Columbia yesterday to give the physics colloquium, which clocked in at a bit over 1 hour and 45 minutes. He did reveal the secret of why his talks are this long: when invited to give a 1 hour colloquium, he plans on talking for at least 1 hour 30 minutes. The content of the talk was similar to many others he has given recently that are available on the web, see for instance this one at the IAS, this recent one at BNL, or for a written version, see here.

As a performer, he’s a powerful speaker: smart, vigorous, and supremely self-confident. His arguments lead to “inevitable” conclusions, not just implying results but “nailing” them. It’s clear why he’s the most influential person in the field these days. With most theorists made worried and unsure by 40 years of failure to get anywhere in their efforts to improve on the Standard Model, he knows exactly what he thinks and will tell you forcefully what you should think. 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, and he has a professorship at the IAS and a $3 million prize from Yuri Milner to back him up.

Despite his long-time advocacy of SUSY, according to Arkani-Hamed, the negative results from the LHC are “not making many of us worried about SUSY”. He (accurately) points out that he’s not one of those like Gordon Kane who for decades has been predicting the discovery of superpartners to be six months away. It has long been clear that the simplest versions of SUSY should have shown up at LEP and the Tevatron, and pre-LHC the lack of any indirect evidence for SUSY indicated to him that it was unlikely to show up at the 8 TeV LHC. So, by his lights, there’s no reason that LHC results so far should cause any new worries about SUSY, beyond those he already had pre-LHC. On the more limited question of whether a “natural” version of SUSY will work out, one where the superpartner masses just barely avoid large amounts of fine-tuning, a year ago (see here) he was saying we were at the “eleventh and a halfth hour” for this possibility. Now that the 8 TeV results are here (and negative), he argues that it is only with the 2015 data that the results will be decisive. The current wisdom about “natural SUSY” I guess is summarized in slide 8 here: Keep Calm and Wait for 14 TeV.

The main point of the talk was one that Arkani-Hamed has been consistently making for nearly a decade, that the role of the LHC is to decide between two possible futures for fundamental physics:

  • The small value of the Higgs mass (in Planck units) has a “natural” explanation, most likely using SUSY, in which case we spend the rest of our lives unraveling the complexities of a SUSY-extended Standard Model.
  • The small value of the Higgs mass (in Planck units) indicates “fine-tuning” that can only have an anthropic explanation, just like the one for the CC. In that case, we live in a multiverse, with physics determined by something like the string theory landscape. About this whole conceptual framework, he says the “ideas are so poorly defined, not clear if they make any kind of mathematical sense”, and it’s “not clear progress will happen anytime soon” but, no need to worry or get discouraged, since this is an “attractive problem”.

Based on the LHC results so far, it looks like all evidence is that we’re headed to the second alternative.

Arkani-Hamed’s talk was structured so as to present a long chain of argument (needing at least 1h 30 min to explain) leading to these two alternatives. One of the alternatives (SUSY naturalness) is essentially already dead, with the die-hards intent on hanging on a couple more years. The other is essentially what David Gross has called “giving up”: you just announce that the problems you haven’t been able to solve can never be solved. In this vision, the 20th century with its huge success at finding a highly predictive, mathematically beautiful fundamental theory was an aberration caused by only being able to see physics at energies way below the Planck scale. In this new 21st century physics, you just postulate that at higher energies things are much more complicated, in ways we can’t hope to ever know, and theorists devote their lives to making excuses, not predictions. Witten may end up being right that “string theory is 21st century physics that fell into the 20th century”, in a much more negative way than he intended.

If a long, complicated argument leads you to the conclusion that the only viable alternative is to give up, then it seems to me you have two choices: give up, or examine more carefully your argument. A much more interesting and more useful talk than Arkani-Hamed’s would be one less devoted to forcefully insisting on the conventional chain of argument based on the technical problem of sensitivity of the Higgs potential to the cut-off, instead looking carefully for weaknesses in the argument (one possibility is discussed here). Arkani-Hamed is a brilliant physicist, but this may be a time when what is needed is not self-confidence in the power of one’s arguments, but instead a suspicion that one has been making a mistake somewhere for quite a while now.

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45 Responses to Arkani-Hamed Colloquium

  1. Nex says:

    Science advances one funeral at a time.

  2. BB says:

    ” A much more interesting and more useful talk than Arkani-Hamed’s would be one less devoted to forcefully insisting on the conventional chain of argument based on the technical problem of sensitivity of the Higgs potential to the cut-off, instead looking carefully for weaknesses in the argument (one possibility is discussed here). ”

    I think it is simply preposterous to present the work of Lykken at your link as a valid alternative, as I have already explained in the comments to that post. Conformality cannot be invoked, per se’, as a solution to the hierarchy problem as long as other scales exist in the deep UV and your CFT isn’t screened from them (as it happens instead e.g. in RS or SUSY theories).

  3. Neil says:

    I’m not a physicist, just an interested bystander, but surely there are more than two futures, one of them depressingly bleak. There is BSM physics to explore at the high precision, high intensity frontier and at the cosmological frontier. It will not all end at 14 TeV, I hope.

  4. Shantanu says:

    Peter, did someone ask any of these hard questions after the talk?
    or there was no time for questions, given the length of the talk?
    shantanu

  5. Dave Miller in Sacramento says:

    Peter,

    Isn’t part of the issue here unrealistic expectations about the pace of progress?

    The first three-quarters of the twentieth century saw an unprecedented explosion in the rate of discoveries in physics, partly because of the early revolutions in relativity and quantum theory, and, then, after WW II because of the huge influx of government funds to pay all of us and to build bigger and bigger accelerators.

    For reasons we all know, that post-war boom just could not continue — in particular, we could not keep exponentially growing the size (and cost) of accelerators. So, it seems to me that the present slower pace is really a return to historical normalcy. We had a period where we frantically grabbed all the low-lying fruit, and, now, we need to sit back and digest the fruit.

    Personally, I think we have a lot to digest concerning the structure of QFT and even QM itself. It took quite a while to go from Maxwell to QED and even longer to go from Newton to Einstein. Why should we expect any progress forward from the Standard Model to be fast or easy?

    Dave

  6. Jeff says:

    “Armani-hamed is a brilliant physicist” – what exactly does that mean? I’m a mathematician, math is hard because we actuallly have to prove things. I’ve always thought physics was hard because things had to WORK. Arkani-Hamed doesn’t have to prove anything, and from what I can tell he hasn’t come up with anything that works.

  7. Peter Woit says:

    Nex,

    If you’re referring to Arkani-Hamed, he’s about the youngest person of any prominence active in this field, and very influential on those younger than him. On the other hand, if you’re referring to me, yes I’ll likely be long gone while he’s still around…

  8. Am I Lloyd says:

    It’s a little troubling to hear a scientist speak of so many results as “inevitable”, especially in a field like string theory.

  9. Peter Woit says:

    BB,
    I wasn’t claiming Lykken’s talk as a solution to the problem, just pointing it out as an example of ideas about solutions to the problem that it would be more fruitful to examine, in preference to arguing that no SUSY at the LHC implies anthropics as the only way out.

    I avoided going on here about my own take on this, since I do this endlessly, most recently in the last posting a couple days ago. There seem to me many more serious problems with the Higgs field than its quadratic sensitivity to the cutoff, and the argument from that technical issue to anthropics via the philosophy that the SM is just an effective theory, with something quite a bit more complicated at a high scale, is one I keep pointing out as likely flawed.

  10. Peter Woit says:

    Neil,

    Arkani-Hamed near the end did quickly go over his favored scenario for BSM physics we might hope to see (mini-split SUSY), but didn’t seem particularly optimistic that there was really a significant chance of the that scenario working out.

  11. Peter Woit says:

    Shantanu,

    Little time for questions after such a long talk, and nothing like a “hard question” was asked.

  12. Peter Woit says:

    Am I Lloyd,

    This talk didn’t really deal with string theory at all, although in some sense failed string theory ideas motivate the overall framework.

  13. Bob Jones says:

    A much more interesting discussion of supersymmetry recently appeared on the arXiv:

    http://arxiv.org/abs/1304.7798

  14. Georges says:

    I am really shocked at the chutzpah of that person explaining that his “secret” is to plan a one hour thirty minutes talk when invited to give a one hour colloquium. And then he even talks for fifteen mors minutes! This is despicable behaviour, encouraged by the audience not leaving the room in protest. I know that this happens frequently, but I have decided to no longer tolerate such misbehaviour and encourage you to do likewise.

  15. Peter Woit says:

    Georges,

    To be fair to Arkani-Hamed, I shouldn’t have called it a “secret”. At the beginning of the talk he warned people basically that he intended to go on for at least an hour and a half, and said that he didn’t mind at all if people left while he was still talking. But, yes, the word “chutzpah” did come to mind…

  16. P says:

    Bob,

    The article you cited is a detailed analysis of superstring perturbation theory, and the results have no immediate / obvious connection to the N=1 field theory story Nima discusses.

    Cheers

  17. Bob Jones says:

    P.,

    Yes, I know.

  18. Nathalie says:

    Dear Peter,

    Thank you for the reference to Arkani-Hamed’s IAS talk. It was a nice talk.

    AH argues that in all possible worlds with proper long distance behavior you have (assuming the validity of local quantum field theory ) consistent theories only for fundamental particles with spins 0, ½, 1, 3/2 and 2. Because those with 0, ½, 1 and 2 have already been seen the 3/2 must also exist. Hence supersymmetry.

    It seems to me that one could just as well argue that since nobody has ever seen the spin 2 the spin 3/2 will also be invisible to us humans. We must humbly admit that we don’t know what we are talking about when we make such strong statements.

    Another comment is that the proper long distance behavior of electromagnetism is due to the fortunate fact that matter happens to be electrically neutral at large distances. Otherwise, AH could not have presented his talk.

  19. piscator says:

    Jeff: It means he is a charismatic speaker who has a lot of power in the community. Seriously, you are totally correct. Physics is about stuff that works and agrees with experiment. People whose reputation is built on models that do not work and do not agree with experiment are not brilliant physicists whatever other qualities they may have. Anyone who thinks otherwise needs to recalibrate their BS detectors.

  20. JJ says:

    Arkani-Hamed is NOT a brilliant physicist; he is in fact a good car salesman. Of course he knows a lot about his cars, but he couldn’t care less about customers. All he really cares about is to make money, and he has proven his ability to do that. The way he does this, as all good car salesmen do, is to blow his customers away by his show business skills. So DO NOT listen to him, as he is full of BS.

  21. M. Wang says:

    In most professions in the US, the best bullshiters rise to the top. The only conclusion here is that particle physics is no longer science but just a profession, but this should not be news to readers of your blog.

  22. Sum Perspektive says:

    JJ (and Peter, as the moderator)

    These personal attacks on N. A-H. are really inappropriate, and foolish. There is an element of truth in the claims that Nima is a good showman, this cannot be denied. But anyone who denies his brilliance, in terms of an incredible track record of remarkably creative approaches to very (Very!) difficult problems, is simply foolish (or possibly jealous, I suppose). Think back to before large ED’s, Little Higgs and Dimensional Deconstruction, and you had a situation where almost everyone worked solely on SUSY models. Nima was one of the leaders whose originality opened up whole fields, that were justifiably of immense interest. Sure, these things didn’t work out, and Nima has largely moved on to other topics, like a good scientist would. But without his ideas it seems likely that many more people would have been working on the same old (failed) SUSY ideas. Nima’s ideas were precisely the kind of fresh and original approaches that (I understand) Peter would advocate (ie exploring more general possibilities, which are hard to come up with).

    (For the record, I completely disagree with the “SUSY or anthropic/tuning” divide that NAH discusses of late, and suspect there is another way of understanding the issue of E/W naturalness. But my dislike for these ideas does not prevent me from recognizing his abilities).

    M Wang: The presence of “non purists” in science is as old as science itself. Read Einstein’s talk at Planck’s birthday, where he describes Planck as one of the few (presumably like himself) who would not be equally happy in some other ladder-climbing profession, as one who instead worships at the temple of science, so to speak. Most in the field are trying to get great jobs, and are willing to spew rubbish in the name of their cause, but this is not a recent development.

  23. Peter Woit says:

    Sum Perspective,

    I don’t disagree. It’s interesting to note that for the last few years Arkani-Hamed has mostly abandoned BSM phenomenology and concentrated on working on a mathematical physics topic, that of understanding the mathematical structure of certain scattering amplitudes in terms of the cell structure of the positive Grassmanian. He advertises that with some of the same showman techniques (and the same tactic of taking up to two hours for a scheduled one hour talk…), but it’s a much more interesting and fruitful thing to be pursuing than failed ideas about BSM physics.

    It’s too bad though that he maintains his other career as promoter of those failed ideas, where, unlike Kane who just denies reality, he is following them to their logical and empty conclusion.

  24. piscator says:

    I’ll say this again: brilliance in physics comes from discovering stuff that works and agrees with experiment. I find talk of incredibly creative approaches to difficult problems a bit creepy and fawning to be honest. It’s like calling a mathematician brilliant because he made twelve different attempts to prove the Riemann hypothesis and none of them worked.

    And for the record, I don’t think the ideas you mention are actually particularly good. Really good ideas tend to have an impact trajectory that grows over time as their profundity becomes appreciated and more and more applications are found (eg AdS/CFT). Something like LED is a more like a pump-and-dump stock.

    There’s nothing wrong with not being a brilliant scientist, that’s the situation pretty much everyone is in, but we have to be honest about what is necessary for first rate science (agreeing with experiment) and what is not (being charismatic and giving great talks).

  25. A says:

    If a mathematician came up with 12 original ideas to prove the Riemann hypothesis, none of which were obviously wrong, I think a lot of people would call that mathematician brilliant, whether or not the proofs actually worked out.

    I’m not really a big fan of how Nima presents things, and a lot of his ideas can be pretty half-baked, but the fact that he’s actually producing new ideas (even if they’ve all been completely wrong) puts him ahead of the game for most of the field these days.

  26. Bill says:

    A, this is complete nonsense. There is a big difference between “none of which were obviously wrong” and “even if they’ve all been completely wrong”. I don’t know one example of a mathematician that fits your description and has the same stature as NAH.

  27. different fields says:

    Math \neq physics, otherwise experiment wouldn’t be needed. Theoretical physics isn’t just about proving “theorems” about the real world, nor is it *just* describing experimental results. Look at the history of 20th century theoretical physics, there were a myriad of wrong directions that still led to a lot of progress in understanding our universe. There were also many things that were proposed as an incorrect description of the phenomena they intended to describe, e.g. Yang-Mills Theory, but as we all know they turned out to be pretty important much later. Instead of all the vitriol and what sounds like Fox news pronouncements in the comment section about personalities, it might be useful for people to understand the field a little better before jumping to such strong conclusions.

  28. Bill says:

    different fields,
    I do appreciate the difference between math and physics, and I do appreciate the way physicists think. Mathematics would not be anywhere near where it is today without physics. But we are talking about some fairness and balance (speaking about Fox News). Yes, it is not all “natural selection” in mathematics and there is some “breeding” by way of awards and recognition of certain people, results and areas. But nothing like this. At least, Witten is a genius who contributed enormously to mathematics even if string theory turns out to be completely irrelevant to physics. But can you say the same about NAH? If string theory turns out to be a failure, what exactly will be left to justify the Fundamental Physics Prize?

  29. Nex says:

    @7 Peter: It’s just a quote due to Max Planck which aptly describes how prominent people in science are unwilling to change their established views even in the face of contradictory evidence. It takes new generations to really move on.

    And we will likely all be dead by the time string theory is completely abandoned.

  30. David says:

    Bill,
    If string theory is proven wrong that will have minimal relevance to Nima’s work and the Fundamental Physics prize would still be justified. Nima’s work on scattering amplitudes is an example of how ideas from ST can help develop and lead to advancements in our understanding of QFTs and gauge theory, as is evident just by looking at the kind of talks given at Strings conferences. You can’t completely untangle the two.

    Also I think the comparison to mathematics is unfair in that physicists really have to deal with the arbitrariness of nature. It would be like a mathematician finding 12 different solutions to a problem and having their result rejected by his/her fellow mathematicians because they don’t like the method. In physics there are plenty of legitimate answers to open questions, but to a certain extent it becomes a matter of luck if its actually realized in nature.

  31. Bill says:

    Does anybody know what NAH is talking about after 1:34:10 mark in this video?

    http://www.youtube.com/watch?v=rKvflWg95hs

    What are those “new remarkable mathematical structures” related to number theory?

  32. Jim Akerlund says:

    I just saw the video and the “new remarkable mathematical structures” comment occurred at the 1:36:10 time mark for me. The video was released on youtube on 4/12/13 and looks to be about a six months old so I am guessing that the mathematical structures he is talking about is based on his recent paper about positive Grassmannian, arXiv:1212.5605 It is his only paper in recent years that was cross posted into these math subjects Algebraic Geometry (math.AG); Combinatorics (math.CO).

    Jim Akerlund

  33. chris says:

    “In physics there are plenty of legitimate answers to open questions, but to a certain extent it becomes a matter of luck if its actually realized in nature.”

    excuse me for stating this so bluntly, but that and exactly that is the kind of unscientific laissez-faire approach towards understanding nature that stalled the advance of science from Aristotele to Copernicus for almost 2 millenia.

    physics is not an intellectual game of abstract brilliance. physics is about understanding nature. there is a very definite line between true and false and this is experiment. a theoretical concept, however brilliant it might seem, is just plain wrong if disproven. it might still serve as advice for future generations how one can fail. but that is it.

    wrong is wrong and faliure, as spectacular as it might be, is still flaiure. i mean, please, just reflect for a second on the hubris of a statement like “but to a certain extent it becomes a matter of luck if its actually realized in nature”. i could understand it kind of if you had said something like “but to a certain extent it becomes a matter of luck whether one can guess the correct laws of nature” – even if i strongly disagree already with that statement. but the thought of physics as a purely intellectual effort that might or might not have to do something with the world outside (and whether it does – coincidentally i suppose – not having any bearing on the brilliance and admirability of the ideas) sort of lets me loose faith in our discipline.

    just to get things straight: it is a choice one makes early in a particle physics career if one indulges in unfounded speculations and produces model after model that can be searched for and falsified. there is the alternative path of sticking close to experimental fact and doing the hard, grinding groundwork of amassing new knowledge. of course the first one is more sexy and of course the grandiose ideas get more media attention (which seems to be so central these days), but working science needs to weed out failed branches mercilessly and fast once they have died. there are too few people willing to provide this essential service to the community today. this blog being one notable exception.

    once all the fuss has cleared, i hope things will be back to normal again and theoretical particle physics will be once more be about understanding nature and not about intellectual ego trips.

  34. Mitchell Porter says:

    “there are too few people willing to provide this essential service to the community today”

    In his talks, Arkani-Hamed says technicolor is dead, focus point supersymmetry doesn’t work, and infrared modifications of gravity are outlandish. Is he one of the few people boldly rejecting failed hypotheses, in your opinion?

  35. Peter Woit says:

    Mitchell Porter,

    There’s never been a shortage of prominent theorists willing to denounce unpopular theoretical ideas. Yes, Arkani-Hamed puts tombstones with “Technicolor RIP” in his talks and announces that he’ll kill himself if the Higgs is a technidilaton, but interest in technicolor has always been a minority viewpoint. The real question is when if ever he’ll start denouncing mainstream ideas that have failed.

  36. Bill says:

    Jim Akerlund,
    Between 1:34:10 and 1:36:10 he is talking about deep connections to number theory and, in particular, Riemann hypothesis. The introduction to the paper you mentioned, arXiv:1212.5605, sounds very grandiose and mentions “remarkable new structures” too, but I did not see anything connected to number theory.

  37. Peter Woit says:

    Bill,

    I think this is the sort of thing he is referring to

    http://arxiv.org/abs/1105.2024

    As usual with Arkani-Hamed, you might want to take some of his claims with a grain of salt….

  38. Bob Jones says:

    Bill and Peter,

    I think Arkani-Hamed is probably referring to some connection between gauge theory scattering amplitudes and Grothendieck’s standard conjectures on algebraic cycles.

    http://en.wikipedia.org/wiki/Standard_conjectures_on_algebraic_cycles

    As Peter has already pointed out, there are results from the theory of motives that allow physicists to simplify expressions for these amplitudes. This is the “symbol” technique of Goncharov, and the original reference is

    http://arxiv.org/abs/1006.5703

  39. Peter Woit says:

    Bob Jones,

    If you know of any significant connection between new techniques in gauge theory scattering amplitudes and the Grothendieck conjectures you link to, I’d be curious to see a reference for it, since I’ve never seen such a thing.

    To the extent that these new techniques involve use of the cell-structure of the Grassmanian, it’s not surprising that one gets connections to quite a few areas of mathematics. Connections to deep conjectures about algebraic cycles in general, and specifically arithmetic aspects would be a lot more surprising (and interesting…)

  40. Bob Jones says:

    Peter,

    There was a talk by Goncharov at this conference

    http://www.birs.ca/events/2012/5-day-workshops/12w5053/videos

    where I think he mentioned something about the standard conjectures. Unfortunately, the video is not online, so I don’t really have a reference.

    But yeah, the cluster algebra stuff that people are using to study the Grassmannian arises in many other parts of mathematics and physics. I’ve also heard Arkani-Hamed suggest in some of his talks that there might be physical reasons for the ubiquity of cluster structures since all of the theories that he and his collaborators are studying come from the six-dimensional (2,0)-theory.

  41. David says:

    Chris,

    Sorry if you misunderstood me. You wrote

    wrong is wrong and faliure, as spectacular as it might be, is still flaiure. i mean, please, just reflect for a second on the hubris of a statement like “but to a certain extent it becomes a matter of luck if its actually realized in nature”. i could understand it kind of if you had said something like “but to a certain extent it becomes a matter of luck whether one can guess the correct laws of nature”

    What I meant was the latter, that its a matter of luck in guessing the correct laws of nature. What I had in mind was pure SU(2) Yang Mills theory as was pointed out earlier. Its a beautiful idea but phenomenologically is off. The only point I was trying to make is that you cannot compare physics and mathematics in terms of how you define success because of the different ways in which we say something is true. In mathematics it has to be a logically consistent and rigorous solution. In physics it has to be a logically consistent (not rigorous obviously) solution and be observed. Its having your model be the right model of all the ones created that I think has an element of luck to it.

    Also I think you have a distorted view on what most particle theorists do. I’m sure that the number of people looking hard at the data and numerical work for the LHC and other particle experiments is much larger then the people who work on the sexy topics of SUSY, ST, and what have you. Its just the latter you’ll hear more about on this blog and in the media (which makes sense).

  42. Mitchell Porter says:

    Do the people complaining about the supersymmetric hegemony actually read hep-ph? There are about a hundred non-susy, beyond-standard-model papers there, every month.

  43. Julian Frid says:

    Ready for a smart, free, in-depth conversation with Nima Arkani-Hamed? Visit the Ideas Roadshow interview.

    Please email me if you should any comments and we’ll post them. Actually email my colleague since this should be his job: taylor@ideasroadshow.com

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