Never Give Up

Alok Jha has a piece in the Guardian yesterday about the failure to find SUSY. His conclusion I think gets the current situation right:

Or, as many physicists are now beginning to think, it could be that the venerable theory is wrong, and we do not, after all, live in a supersymmetric universe.

An interesting aspect of the article is that Jha asks some SUSY enthusiasts about when they will give up if no evidence for SUSY appears:

[Ben] Allanach says he will wait until the LHC has spent a year or so collecting data from its high-energy runs from 2015. And if no particles turn up during that time? “Then what you can say is there’s unlikely to be a discovery of supersymmetry at Cern in the foreseeable future,” he says.

Allanach has been at this for about 20 years, and here’s what he has to say about the prospect of failure:

If the worst happens, and supersymmetry does not show itself at the LHC, Allanach says it will be a wrench to have to go and work on something else. “I’ll feel a sense of loss over the excitement of the discovery. I still feel that excitement and I can imagine it, six months into the running at 14TeV and then some bumps appearing in the data and getting very excited and getting stuck in. It’s the loss of that that would affect me, emotionally.”

John Ellis has been in the SUSY business even longer, for 30 years or so and he’s not giving up:

Ellis, though confident that he will be vindicated, is philosophical about the potential failure of a theory that he, and thousands of other physicists, have worked on for their entire careers.

“It’s better to have loved and lost than not to have loved at all,” he says. “Obviously we theorists working on supersymmetry are playing for big stakes. We’re talking about dark matter, the origins of mass scales in physics, unifying the fundamental forces. You have to be realistic: if you are playing for big stakes, very possibly you’re not going to win.”

But, just because you’re not going to win, that doesn’t mean you have to ever admit that you lost:

John Ellis, a particle theorist at Cern and King’s College London, has been working on supersymmetry for more than 30 years, and is optimistic that the collider will find the evidence he has been waiting for. But when would he give up? “After you’ve run the LHC for another 10 years or more and explored lots of parameter space and you still haven’t found supersymmetry at that stage, I’ll probably be retired. It’s often said that it’s not theories that die, it’s theorists that die.”

There may be a generational dividing line somewhere in the age distribution of theorists, with those above a certain age likely to make the calculation that, no matter how bad things get for SUSY and string theory unification, it’s better to go to the grave without admitting defeat. The LHC will be in operation until 2030 or so, and you can always start arguing that 100 TeV will be needed to see SUSY (see here), ensuring that giving up won’t ever be necessary except for those now still wet behind the ears.

For another journalist’s take on the state of SUSY, this one Columbia-centric and featuring me as skeptic, see here.

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60 Responses to Never Give Up

  1. Giotis says:

    SYSY is a fundamental symmetry of Nature. There is no doubt about it. You must be a theoretical physics imbecilic not to acknowledge that.

    Now, how it breaks, at which energy scale breaks and whether it solves some problems of the SM is another issue.

  2. Peter Woit says:

    Giotis,
    I suppose another way to deal with losing is by not only refusing to admit that you’ve lost, but claiming that you’ve really won. Good luck with that…

  3. Giotis says:

    Ok, then I would really like to know your theoretical arguments against SUSY being a Symmetry of Nature. Let me guess, you don’t have any. You just sit there crossing your fingers hoping LHC doesn’t find anything. That’s pathetic…

  4. The point hidden in Giotis message is a real issue: people are ever careless about language in what should be exact science, and it leads to endless confusion.

    All mentioning of “supersymmetry” in posts like this is really “low energy supersymmetry”. Hence the term “supersymmetric universe” above is quite misleading. Supersymmetry may or may not be a fundamental symmetry of nature, indeedm and what is currently happening at the LHC is quite unrelated to that question. What the LHC sees or does not see is global supersymmetry unbroken at rather low energy. That to exists is — or would be — about as striking as global Lorentz symmetry in the universe, which would be bizarre, even though Lorentz symmetry is a fundamental symmetry of the universe.

    Speaking of universes, that’s another example of how careless language damages the scientific discourse: if people had remembered to correctly say “observable universe” instead of just “universe” that awful term “multiverse” would have been neither necessary nor the cause of wasted much bandwidth that it currently is.

  5. Peter Woit says:

    Giotis,
    See Chapter 12 of Not Even Wrong, which was written more than ten years ago.

    The Columbia Magazine story didn’t really quote the arguments I explained to the writer of the article. The simplest is that SUSY explains nothing at all about the SM, since it gives no relations between different objects in the SM, instead relating each SM object to a hypothetical new one. A symmetry argument that explains nothing isn’t a very good symmetry argument.

  6. Peter Woit says:

    Urs,

    The problem is more your use of language, since if you made it clear to people that when you said “supersymmetry”, you meant something that can’t ever be tested, they wouldn’t take you very seriously. I think you’re right that some string theory/SUSY enthusiasts post-LHC will argue that nothing has shown them to be wrong, and nothing in their lifetime ever possibly can, but to the extent that they make this situation clear they will have a serious credibility problem.

  7. fuzzy says:

    in my view the problem is worse than pointed out above. even giotis admits that he/she has no idea where this hypothetical symmetry is realized. in this way, he/she is speaking frankly, but i wonder whether this status of affairs was so clearly acknowledged even before lhc—or it was not.

    in particular, i saw that some experts of susy have been mentioned above; let me ask whether, in the past 30 years, they begun their speculative papers by saying “we do not have an idea where susy is broken but let us try 1 tev or so”. if they did not (i think they did not) i should conclude that they have misled their field and themselves (which is worse); or, they have believed in some wrong argument. in the last case, i would appreciate very much if they did not rush to tell us what we should think.

  8. emile says:

    Giotis: SUSY is a fundamental symmetry of Nature? how do you know this fact about Nature? where is the experimental evidence?

  9. Giotis says:

    Emile,

    We live in the 21th century; physicists are in a position now to theoretical deducing properties of Nature. The discovery of Higgs is a great example. They don’t have to be guided by experiments, like little kids, to put 2 and 2 together. I’m not in a mood to explain to you why SUSY *has* to be a symmetry of Nature, if you can’t figure out why is that just open a text book (indeed SUSY is text book material) and stop wasting your time reading blogs…

  10. Indeed, the worldline theory of any spinning particle, such as the electron, is locally supersymmetric. So supersymmetry as such has been experimentally tested since Stern-Gerlach.

    What is under discussion re LHC is some very special aspect of supersymmetry namely “global low energy spacetime supersymmetry”. This is the precise term. You may not want to say this each time, but it’s good not to forget what you are talking about.

  11. Florin says:

    Hi Urs,

    Can you give some more details on “the worldline theory of any spinning particle, such as the electron, is locally supersymmetric” ? I don’t follow that.

    As for finding superpartners at LHC.. I don’t know but this was never presented as being a “special” aspect of supersymmetry, but the main feature of supersymmetry.

  12. Peter Woit says:

    Florin,

    Urs is just trying to muddy the waters by talking about 0+1 d SUSY when the discussion is actually about 3+1 d SUSY.

    In 0+1 d, you’re just doing quantum mechanics, and in cases where your Hamiltonian has a square root, you can call this a supersymmetry. The Dirac operator is an example, so if you want you can say that it generates a supersymmetry, and that SUSY was discovered to work experimentally back in 1928. No need for the LHC! Of course, that’s something completely different than what everyone else means when they are discussing supersymmetry (i.e. an extension of the 3+1 d Poincare algebra that mixes fermions and bosons)

    One place that has something about this is a chapter of my book in progress. See chapter 23 of
    http://www.math.columbia.edu/~woit/QM/qmbook.pdf

  13. emile says:

    Giotis, you wrote: “The discovery of Higgs is a great example. They don’t have to be guided by experiments, like little kids, to put 2 and 2 together. “.

    The Higgs is a great example for not having to run experiments? You knew for sure, that there was a SM-like scalar before it was found? You think we did not need to run the LHC after all? Can you tell me if there are other scalars? an extended sector, 2 HDM? an ewk singlet?

  14. Peter Woit says:

    Thanks JG, fixed.

  15. Brian says:

    Ellis: “Obviously we theorists working on supersymmetry are playing for big stakes. We’re talking about dark matter, the origins of mass scales in physics, unifying the fundamental forces.”

    Funny kind of roulette when the barrel is totally empty and you’re guaranteed to win. Funnily enough, I heard recently that Ellis was not very interested in the new twistor scattering techniques because it did not fit the priorities of the department … perhaps those senior theorists really should be having a word with department heads.

  16. Seth Goldberg says:

    Somewhat Off topic: Speaking of other physical contexts of supersymmetry, there is also a condensed matter/disorder model. Has anyone here read Supersymmetry in Disorder and Chaos by Konstantin Efetov Cambridge University Press (September 13, 1999)?
    See e.g. http://www.amazon.com/Supersymmetry-Disorder-Chaos-Konstantin-Efetov/dp/0521663822/ref=sr_1_1?ie=UTF8&qid=1375921527&sr=8-1&keywords=supersymmetric+solid+state
    Anyone willing to comment as to the appropriateness of the mathematical physical analogy (in Maxwell’s sense)?

  17. Peter Woit says:

    Seth,
    This has nothing at all to do with the topic of this posting, and it’s also a topic I know very little about. Fermionic variables have all sorts of interesting uses in stat-mech, and I gather this book is about some of them, but this is a very long ways away from 3+1 d space-time supersymmetry and its uses in particle physics.

  18. Chris W. says:

    We live in the 21th century; physicists are in a position now to theoretical deducing properties of Nature. The discovery of Higgs is a great example. They don’t have to be guided by experiments, like little kids, to put 2 and 2 together.

    Giotis, that’s just laughable. An undergraduate that made such a statement would deserve to be told they don’t belong in physics or any other scientific field in which empirical observations must be accounted for. In such fields, properties of nature are deduced using theories or hypotheses, and those theories can be wrong. That is why we test them. If you want a theory that can’t be wrong, stick to mathematics or metaphysics and stay the hell out of physics. Period.

  19. Mitchell Porter says:

    Giotis said

    “SUSY is a fundamental symmetry of Nature. There is no doubt about it. You must be a theoretical physics imbecilic not to acknowledge that… Ok, then I would really like to know your theoretical arguments against SUSY being a Symmetry of Nature… I’m not in a mood to explain to you why SUSY *has* to be a symmetry of Nature, if you can’t figure out why is that just open a text book”

    There is no textbook on Earth which explains why supersymmetry “has to be a symmetry of nature”. There isn’t even a proof that string theory has to be supersymmetric.

  20. Thomas Larsson says:

    Both Michelson and Morley kept looking for the ether wind well into the 1920s. They never, never, never gave up.

  21. Alex says:

    Were Michelson and Morley convinced that there must be an ether wind for them to find, or were they doing their measurements in the spirit of the modern-day physicists who keep doing precision measurements to push the limits on Lorentz violations out another decimal place? I’m pretty sure that these folks will never find anything, but I’m happy to see them trying anyway, and getting published in PRL for their efforts. It’s important to the culture of physics that we always have people testing assumptions, and that I can show my students that the people who test assumptions are recognized in prestigious publications for pushing the boundaries out another decimal place.

  22. Bee says:

    Sociologists call it an “escalation of commitment”. If I were a sociologist, my next paper would be on “the susy community in the LHC era”. Only half joking, it’s quite interesting to watch.

  23. N. Nakanishi says:

    Giotis,

    Three decades ago, I proved that SUSY cannot be the fundamental symmetry of physics. The reasoning is as follows.
    Evidently, SUSY, if it exists, must be spontaneously broken, but there is no Nambu-Goldstone fermion. Hence, one must assume that super-Higgs mechanism works. That is, supergravity must be encountered. However, quantum supergravity cannot be consistent with SUSY. This is because the global super-charge generators have no space-time index, while the translation generator P_mu does have a space-time index in contradiction with the SUSY anticommutation relation.
    The essential problem of Poincare invariance in the framework of gravity is that the general coordinate transformation, which is nothing but the local version of the translation, already contains the Lorentz transformation. The local Lorentz transformation is an internal symmetry; indeed, Dirac field is a scalar field in the framework of gravity. Only after spontaneous breakdown takes place, Dirac field becomes a world spinor. Thus, Poincare invariance is not a fundamental but secondary symmetry. Since SUSY is an extension of Poincare symmetry, it cannot be a fundamental symmetry!

  24. Yatima says:

    The very first post.

    1) Fact-free dogmatic statement.
    2) Reinforce the fact-free dogmatic statement.
    3) Ad hominem attack while claiming the high ground, throw in an argumentum ad populum.
    4) Follwup by “I don’t know what the hell is going on”.

    Sure is a formula for success :-(

  25. LogicFan says:

    I am very pleased that when I was an undergraduate considering the PhD I decided to go into philosophy rather than physics. The intellectual standards of your discipline are abysmal.

    You have failed to make any significant theoretical advance in, say, over 30 years. That’s pretty bad. Perhaps you will retort that philosophy has failed to make any significant theoretical advance in over 2,000 years, but I do not believe that that is true, and in any case we have maintained our standards when it comes to the pursuit of truth via careful analysis and dispassionate reasoning.

    The ad hominem attacks issued from the string theory camp are appalling; its uninterest in the scientific method is baffling; and its emotional attachment to a theory that has virtually zero empirical support is depressing. What has happened to you guys?

  26. gedankentroll says:

    LogicFan said

    “… physics. The intellectual standards of your discipline are abysmal. You have failed to make any significant theoretical advance in, say, over 30 years.”

    Whereof one is totally clueless, thereof one should be silent.

  27. Ted Danson says:

    Of course I have no idea who ‘Giotis’ really is but I have seen this kind of mentality amongst a number of people employed as researches in physics departments (and more than one commenter here). I’m not sure they realize how strange some of their comments seem to those who have (god forbid) been in the business of seriously confronting a model against experiment. Look at this comment for instance:

    Giotis:
    ‘Ok, then I would really like to know your theoretical arguments against SUSY being a Symmetry of Nature. Let me guess, you don’t have any. You just sit there crossing your fingers hoping LHC doesn’t find anything. That’s pathetic…’

    What a bizarre comment! It would seem to imply that in the mind of ‘Giotis’, physics beyond the standard model *must* involve supersymmetry. No choice in it. This seems much more like a ‘faith-based’ statement than something a scientist would write.

  28. LogicFan says:

    gedankentroll:

    That is a good paraphrase of Wittgenstein, who in turn is suggesting something important. But what he is not suggesting is that criticism by thoughtful, unbiased, and educated people be ignored.

    I have noticed many parallels between string theory advocates and postmodern/Continental “philosophers”. Both camps claim special access to profound truths; both camps are highly insular; both camps are resistant to critical inquiry (string theorists disregard calls for empirical verification and postmodern thinkers refuse to subject their “theories” to logical analysis); both camps use ad hominem attacks to defend themselves against calm criticism; both camps write in incomprehensible jibberjabber; both camps have an inflated sense of self-worth; and both camps have utterly, totally failed to add to the sum of human knowledge. The two groups have actually been counterproductive, on my view.

    Instead of just working in service of your own ego, don’t you want to help figure stuff out about this fascinating universe in which we live?

  29. gedankentroll says:

    Of a long Time I have suspected, that these modern Analytics were not scientifical!

  30. emile says:

    LogicFan: I’m afraid you are being distracted by a relatively small group of people whose notion of science has nothing to do with what 99% of working physicists would accept. To say that the field has low standards is not based on a good knowledge of what is going on. In particle physics, the standards are also high: get educated on what it takes before a paper is even submitted to a journal if you work on CMS or ATLAS. Physics in general is doing great: attend a few colloquia in various subfields and you will be impressed. In particle physics, we just found that the Universe has a scalar field with a non-zero average value. This is significant. The associated particle is a new type of particle never before observed. Not finding anything else at those energies is disappointing to some but it is also an important finding (as you can see from the way many react to this). Just 15 years ago we learned that the Universe is expanding. That’s a major, major find. Not too long ago we confirmed that neutrinos oscillate and have now measured the associated mixing matrix which looks very different than its counterpart in the quark sector. I could go on. Lots of progress and lots of questions to answer. A few high profile people and a few bloggers can give the wrong impression. Another thing regarding SUSY: from an experimental point of view, the search will go on for years to come not because experimentalists are necessarily wedded to the idea, but because those searches cast a very wide net in terms of possible final states (these searches can catch many other things from other BSM models) and because you never know what is going to show up in the phase space you have not yet explored.

  31. Mike Mathison says:

    Hello Logic Fan – I think emile has more or less just said this already, but here’s my take on your comments:

    Earlier, of philosophers, you said “we have maintained our standards when it comes to the pursuit of truth via careful analysis and dispassionate reasoning” but then later you said of your Continental school that they are “[...] resistant to critical inquiry [...] refuse to subject their theories to logical analysis [...] [and have] totally failed to add to the sum of human knowledge”.

    I guess we all have our mad aunties in the attic – perhaps some of ours are string theorists and perhaps some of yours are post-modernists. However, if you’re someone who likes big cool machines then I think you probably made the wrong choice going with philosophy rather than physics.

    Earlier, of physicists, you said “you have failed to make any significant theoretical advance in, say, over 30 years”. However, as a big fan of physic myself, I don’t think that can be entirely correct as I understand there have been many advances in fields such as astrophysics, solid state physics and so forth, as well as a steady stream of speculative big-question theoretical ideas proposed around gravity/quantum-mechanics/Standard-Model-refinement/HEP in general – and at least some of these are/have-been susceptible to falsification either via experiment or observation. Most of us still hold onto the quaint idea that concocting theories that are none the less subsequently shown to be wrong by Nature is *not* actually a waste of time and *does* actually constitute a kind of progress – if only because the knowledge that a plausible/appealing theoretical idea is actually *wrong* is in and of itself very useful knowledge to have gained as it further constrains future theories and is probably telling us something important about our deeper assumptions. I believe such ideas and reasoning are also prevalent in philosophy, though I’m no expert. Anyhow, although it may not be in accordance with the extraordinary rigors of your discipline, I for one would certainly count the failure so far of super-symmetric particles to appear at LHC energies (and the mainstream theories’ resulting entry into the arena of the decidedly unwell/coughing-up-blood) as an important advance for physics, both experimental and theoretical.

  32. lucretius says:

    Before I ask my question I think I should make a disclosure.

    I am a mathematician with a rather detached attitude to “physical truth” but actually quite excited about the contribution mathematical physics (including the part you refer to in the title of your book and this blog) has made to my own subject. For me the discovery of Witten-Seiberg invariants, Chern-Simons-Witten theory, Gromov-Witten invariants, supermanifolds, superalgebras, Mirror Symmetry etc, more than justifies everything that has gone into the study of the physics. Moreover, I am quite confident that even if the physical theories (like SUSY) do not find experimental confirmation during the next 100 years, the mathematical ideas they have stimulated will find their way into physics via another route. So, quite naturally I think, I am certainly rooting for SUSY physics crowd and hoping that the LHC will bring them some good news. I think it will be good for science, mathematics, almost everyone … which brings me to my question.

    The question is, would you agree that by your public stand on this matter, the success of your book and the reputation it has given you among your readers and journalists, you have inevitably turned yourself into “a partisan of failure” in this matter? Isn’t it true that if LHC does find evidence of SUSY you will find yourself in a rather difficult position? Isn’t it rather like the situation of an out of power politician who finds himself in the situation where, from his point of view, “the worse is the better”?

  33. Dom says:

    Probably going off-topic but aren’t you misrepresenting Peter’s position which seems essentially to be “Show me the evidence via testable predictions” which then gets hijacked into a meta argument about what science is that we’ve all heard a million times.

  34. Zathras says:

    To answer lucretius, I think one has to recognize a spectrum of theories out there from empirically testable to completely untestable. SUSY is somewhere in the middle, since experiments can confirm or rule out large swaths of the parameter space, but there is still the theoretical possibility of SUSY at energies which cannot be tested. If SUSY is confirmed (looking unlikely, but let’s just say…), then there are testable predictions to look at. On the other hand, string theory is something which makes no testable predictions, and has no hope of doing so. And there is no science. Woit’s and Smolin’s books are not anti-SUSY books; they oppose ideas masquerading as science which make no testable predictions. To the extent SUSY does so, Peter would have no problem with it.

  35. Peter Woit says:

    Dom/Zathras,

    The SUSY issue right now isn’t so much about testability, but about whether one can get that part of the theory community that for decades has been pushing a specific idea about particle physics to admit that it has been falsified, draw the implications of this, and move on to try and find something more promising. If you know nothing about the scale of SUSY breaking, it’s an empty, untestable idea. Pre-LHC, the argument was that SUSY breaking should be at the weak scale, stabilizing it with respect to the Planck scale. This wasn’t a very good idea and it didn’t explain much, but it got a huge amount of attention and had a great influence on the field. Now the question is whether the fact that it has been experimentally shot down will get acknowledged or evaded.

    About issues raised by lucretius, a separate comment will follow.

  36. Peter Woit says:

    lucretius,

    I don’t think I’m a “partisan of failure”, since I don’t think the LHC results ruling out SUSY extensions of the SM broken at the electroweak scale are a “failure”. They’re actually a huge success of the scientific method. A machine has been built and operated successfully to study nature at distance scales nearly an order or magnitude smaller than ever done before, and one proof of the pudding of this great success is that certain not very good speculative ideas were ruled out. The only possible failure here is if some theorists manage to evade the implications of the LHC results and convince others to keep pursuing the same ideas.

    Sure, if the LHC all of a sudden turns up evidence of the kind of SUSY I’ve been arguing against, then my arguments were misguided and people should take that into account. At this point though, I think if you look at what I had to say in my book (written mostly in 2002), it holds up very well in light of LHC results, especially compared to typical other books of that era which enthused about string theory and SUSY ideas which it’s now clear haven’t worked out.

    It’s important to distinguish between the SUSY models that are being shot down and the mathematics that you mention, most of which has nothing at all to do with them. Quantum field theories and superalgebras have all sorts of very interesting mathematics behind them, well worth pursuing (so much so that I included some of this in the course I taught last year), but this doesn’t mean that one specific, quite complicated and ugly, example of these is worth much attention. For me the argument against SUSY extensions of the SM has not just been that there’s no experimental evidence for them or that they’re not as predictive as one would like, but that the ones on sale are hideous and don’t really explain anything. I wouldn’t be surprised at all if there is some better unified theory that has an interesting super-algebra of symmetries, but just don’t think that the ones we know about could possibly work. Hopefully the LHC success at ruling out bad ideas will encourage people to look for better ones. This includes mathematicians, who should pay attention to what the class of theories is that they were often told was of great physical importance, but didn’t turn out to be, and decide where to direct their attentions accordingly.

  37. Florin, for an extensive list of references on the local worldline supersymmetry of spinning particles, see here: http://ncatlab.org/nlab/show/spinning+particle#WorldlineSupersymmtryReferences .

    Generally, local supersymmetry is generic in low dimensions, while global supersymmetry is the opposite: non-generic and unlikely.

    Historically, people lifted the worldline formalism of spinning particles to the worldsheet formalism of what back then were called “spinning strings”, which is 2d gravity coupled to fermions. It turns out that the most natural Lagrangian for this is automatically locally supersymmetric — this is how the concept of supersymmetry was _found_ in the West. People didn’t look for it, it jumped at them when they wrote down fermions in 2d gravity. Ever since, the former “spinning string” is known as the “superstring”.

    The miracle that happens then is that while the second quantization of spinning particles is not itself locally supersymmetric, the second quantization of spinning strings is itself locally supersymmetric. And this is how perturbative string theory implies that if there are fermions at all, then there is local supersymmetry.

    As I keep saying, and as our host is now acknowledging too, it is crucial to distinguish local supersymmetry from global supersymmetry. That we don’t find global supersymmetry at the LHC says nothing about whether “the universe is supersymmetric”. It may or may not be, and it is good to know the difference.

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  39. Peter Woit says:

    Urs,
    I don’t think that global vs. local SUSY is relevant, or that a statement like “the universe is supersymmetric” the way you are trying to use it is meaningful, rather than an empty slogan.

    The Dirac operator and spinors show us that there’s an interesting superalgebra at work in fundamental physics, but this has nothing to do with SUSY extensions of the SM. One should stop sloganeering, and pay attention to what exactly it is that works as good physics and good mathematics, and what doesn’t.

  40. One should stop sloganeering. We can agree on that. A good move is to stick to precise scientific language and avoid imprecise sweeping statements.

    There is so much confusion about string theory out there that in all the confused criticism the discussion never gets to what might be good, substantial criticism.

  41. Giotis says:

    The only way to extend Poincare algebra and still respect Lorentz invariance is the super-Poincare algebra. You do that and the existence of fermions is imposed to you by the algebra. SUSY in this sense *explains* fermions which are inherently Quantum mechanical! Similarly in the Superspace formalism you take the ordinary space time and the super-Poincare group forces you to extend it to a Superspace by adding fermionic degrees of freedom to the usual bosonic.

    What deeper theoretical reason you want to acknowledge that SUSY is symmetry of Nature? Nature is crying out that it is Supersymmetric at a fundamental level.

  42. Nex says:

    No theoretical reasons ever suffice to prove something is a part of Nature.

  43. CWJ says:

    Seth,
    The supersymmetry in Efetov’s book is really just a useful tool for carrying out certain Gaussian integrals. Using “normal” numbers, the integral of the Gaussian exp(-ax^2) is proportional to 1/sqrt(a), but if you take the same integral with Grassmannian (fermionic) variables, then it is proportional to sqrt(a). This turns out to be useful in computing Green’s functions of random matrices, for example.
    (Sorry for being off-topic, Peter–but at least it’s on a technical issue and not a rant! And since I happened to laboriously work through the technique some 15 years ago but never published anything…might as well put that knowledge to use.)

  44. Armin Nikkhah Shirazi says:

    Giotis,

    I think when one is deeply committed to a particular point of view it can sometimes be very difficult to be aware of the assumptions one makes. In your first sentence ” The only way to extend Poincare algebra and still respect Lorentz invariance is the super-Poincare algebra.” I could detect at least three.

    Assumption 1: One needs to extend Poincare algebra in order to resolve certain issues with the SM that SUSY addresses
    Assumption 2: Any approach to understanding these issues potentially conflicts with Lorentz Invariance

    Assumption 3: Lorentz Invariance should be respected in a deeper theory

    Of course, the assumptions differ in how confident one can be in them, for example I am vastly more confident in the third one than the first two but my point is this:
    The strength of one’s argument depends on the strength of one’s assumptions, and if one is either not aware of them or has a quasi-religious belief that they are correct, one is unlikely to recognize the points at which one’s argument could break down.
    To someone who does not share all of your assumptions it may not necessarily seem that “Nature is crying out that it is Supersymmetric at a fundamental level.”

  45. Peter Woit says:

    Armin,

    There’s another problem, that “The only way to extend Poincare algebra and still respect Lorentz invariance is the super-Poincare algebra.” isn’t actually true. Presumably Giotis is actually talking about the extension of Coleman-Mandula to include SUSY, so one could figure out what he intended to say, but if you’re going to base your argument on a no-go theorem, it would be a good idea to get the theorem right…

  46. lucretius says:

    If you look at section 10.3.3 of Efetov’s book you will find that he speculates that there might be a possible relation of the “sigma model” with string theory and quantum gravity. He concludes: “Anyway, the unification of these, at first glance, completely different theories from different branches of physics looks very exciting”. Two conclusions:
    1. The original question was only about 99% off topic.
    2. Some people find “unifications” very exciting even if they do not seem to lead to any now empirical discoveries.

  47. Giotis says:

    Come on, you know what I mean. In fact if you want to be pedantic there are two theorems: Coleman-Mandula and Haag-Lopuszanski –Sohnious.

    So you could say the SUSY is the most general symmetry you could have according to these two no-go theorems.

  48. N. Nakanishi says:

    Giotis,

    You are wrong. HLS’s no-go theorem holds only f0r the physical S-matrix symmetries, that is, for unbroken symmetries. Evidently, SUSY, if it existed, is broken in the actual physical S-matrix. Hence HLS’s theorem does not give any priority to SUSY. There is no no-go theorem for the Lagrangian symmetries which we really want to have.

    By the way, have you understand my proof of the proposition that SUSY cannot be a fundamental symmetry?

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