The “SUSY Bet” event in Copenhagen took place today, with video available for a while at this site. It appears to be gone for the moment, will put up a better link if it becomes available. An expensive bottle of cognac was presented by Nima Arkani-Hamed to Poul Damgaard, conceding loss of the bet. On the larger question of the significance of the negative LHC results, a recorded statement by Gerard ‘t Hooft (who had bet against SUSY), and a statement by Stephen Hawking (not in on the bet, but in the audience) claimed that if arguments for SUSY were correct, the LHC should have seen something, so they think nature has spoken and there’s something wrong with the idea.
The losers of the bet who spoke, (Arkani-Hamed, David Gross and David Shih) demonstrated the lesson about science that supersymmetry and superstring theory have taught us: particle theorists backing these ideas won’t give up on them, no matter what. They all took the position that they still weren’t giving up on SUSY, despite losing the bet. In more detail:
- Arkani-Hamed was not a signatory of the original bet in 2000, but signed on to the later 2011 version. He explained today that at the time he thought chances of SUSY visible early on at the LHC were just 50/50 (with his 2004 work on split SUSY motivated by realizing that pre-LHC the conventional picture of SUSY at the electroweak scale was already ruled out). He attributed his decision to take the pro-SUSY side of a 50/50 bet to “optimism”, implying that this took place at a conference dinner where there may have been too much to drink. In his split-SUSY scenario, SUSY may yet show up at the LHC, or it could even be invisible there, requiring a higher energy accelerator. So, he’s not giving up on SUSY based on LHC results.
- David Gross also is not giving up, arguing that fine tuning of a factor of 100 or 1000 is not a problem (invoking the large ratios that appear in the fundamental Yukawa couplings). He did say that young people might want to take this as reason to look for new ideas, but, for himself, felt “I’m too old for that”.
- David Shih isn’t giving up either, arguing that there still was lots of data to come, plenty of room for SUSY to appear at the LHC, still believes we’ll discover SUSY, at the LHC or elsewhere.
One piece of misinformation promoted by several of the speakers was the idea that “everyone” back around 2000 believed in SUSY as the next new physics to be found. In my book (written in 2002-3) I wrote a long section about the evidence against SUSY, and, of course, if you look at the bet under discussion, in 2000 many more people (16 vs. 7) were taking the anti-SUSY vs. pro-SUSY side (at least in Copenhagen, but I think this reflects the general range of opinions).
No one today asked the obvious question “Is there any forseeable experimental data that would cause you to decide that SUSY was an idea that should be abandoned?”. I’m now not seeing any prospect in my lifetime of anything that would cause these or other SUSY proponents to give up (John Ellis has also announced that no matter what the LHC says, he’s not giving up). Unfortunately “Not Ever Wrong” is clearly the slogan of the (minority) segment of the particle theory community that long ago signed up for the vision of fundamental physics in which SUSY plays a critical part.
Update: There’s a blog entry from Natalie Wolchover about this. She has more detail about the final remarks from Gross that I mentioned:
“In the absence of any positive experimental evidence for supersymmetry,” Gross said, “it’s a good time to scare the hell out of the young people in the audience and tell them: ‘Don’t follow your elders. … Go out and look for something new and crazy and powerful and different. Different, especially.’ That’s definitely a good lesson. But I’m too old for that.”
Update: Video of the Copenhagen event is available here.
Update: I happened to be looking at Michael Dine’s 2007 Physics Today article on string theory and the LHC, noticed the side remark that “The Large Hadron Collider will either make a spectacular discovery or rule out supersymmetry entirely.” I wonder if he still thinks this, and whether we’ll ever see Physics Today publishing something updating its readers.
Update: Yet another news story about this, from Science News.
So… what experiments should experimentalists do, Peter? Should we fold up shop and give up because some theorists lose bets?
I think there has never been doubt that going to the energy frontier is always the best experiment to perform. Mel Schwartz used to emphasize this point; he did lots of clever experiments, from being the prime mover in the nu_mu discovery to (pi mu) atoms to very clever exploitations of the SLAC facility in doing K0L physics.
The argument for the energy frontier among experimentalists never depended on some theoretical bets… primarily it depended on discovery potential for something completely new. To the extent theorists have enabled marshalling resources through hype to get the machines built, they are useful. If they are wet blankets they should be ignored.
If they overhype… well… James Watson’s rule kicks in… if you overhype and are wrong, the only penalty is embarrassment, and there is always a chance your wrong hype will stimulate the right idea. If you underhype you risk 1)the right idea might never germinate and 2)the needed experimental work might very well never get performed.
How hilarious it has been to read “Tunnel Visions” and read some of the rationale in 1993 for killing the SSC. The need to focus on economically remunerative research was a big argument. Meanwhile, the single biggest economic force since 1993… the world wide web… was invented at CERN to assist particle physics. Irony factorial.
The non-signals at the LHC tell us that a proton collider should be the next energy frontier machine, not a lepton machine. Precision Higgs studies are the role of e+e- in the future. Prepare, Peter, for all the hype from people you find frustrating to get those projects done. It will take decades, but the allure of the energy frontier will never die.
Meanwhile lots of clever low energy experiments are underway. Likely, though, that there will be the usual fights to cease basic research and spend all scarce research funds on a new Facebook or something. Perhaps that is what the result of your negativity might be, Peter.
It is good to remember the difference between the variants of “low” energy susy checked at LHC, and high energy susy, namely supergravity. No known mechanism exists which would force a supergravity theory to settle in a vacuum that preserves a global supersymmetry (which is what the LHC could see), while there are excellent theoretical arguments for supergravity itself, i.e. for high energy susy: Besides sugra being a prediction of spinning strings (the spectrum of the spinning string miraculously exhibits spacetime supersymmetry) there are some strong general mathematical arguments, such as Deligne’s Tannakian theorem on tensor categories and its implication for supersymmetry.
Hi, Goleta Beach,
I don’t think you’re being realistic here, and Watson’s nonsense about overhyping is directly refuted by the example of the SSC. In retrospect, it actually took outrageous hype to defend the thing, and it still got killed. By the standards of any other field in science, SUSY has completely and utterly failed as a “natural” explanation for the Higgs mass, and it has failed equally to supply a realistic WIMP. It’s only in HEP, apparently, that a theory can crater so dramatically and still be tweaked in such a way as to receive endless and unconditional support. One never encounters anywhere else such boundless trust in “beauty”, as judged by a miniscule fraction of the overall physics community.
They may be right. The universe may indeed be supersymmetric. But at what energies should it be sought for, if not the TeV scale? The LHC got funded because there was such a high degree of confidence that the Higgs (be it fundamental or composite) would be discovered at accessible energies. And there was a ton of hype about SUSY to ice that cake. Now the Higgs has been discovered, and it’s not supersymmetric. Rather, it’s super-standard. If SUSY exists, it’s fine-tuned to at least some degree, we now know that much. But by how much? How can anyone answer with confidence anymore, except to say it could be any value up to energies we will never be able to probe? Has anything of the scale of the next-generation collider been funded based on such uncertainty of discovery?
I personally would gladly vote to build such a machine anyway, just in case. Sadly, people like me aren’t in charge, and the example of the SSC tells me HEP researchers have a vertically-steep uphill battle ahead of them to convince those who hold the purse strings to commit to such an expense. And they will need a better argument than “well, you never know…” The overhyping of SUSY will likely factor directly and powerfully into the skepticism of the funders those future researchers will face, and I’m inclined to predict it will be the field’s undoing unless a much better idea is discovered, and soon.
Goleta Beach,
I think what experimentalists should do is pretty much ignore unconvincing beyond the SM models, and go about the business of exploring the energy frontier as best they can. Such models may have some useful role in motivating ideas about what searches to do, but, especially given how they haven’t worked out, people should be careful to not let them have too much influence over what searches get done and what don’t.
As for the next collider, I do think there should be one, but that considerations of what to build should not be significantly influenced by arguments like “this machine is better because it will have better reach for superpartner X”. In terms of selling a machine to governments, some hype is unavoidable, but if you’re going to engage in over the top hype, you should avoid blowback to your own community, not engage in it at technical conferences for instance. The main problem I’m concerned about is theorists believing their own hype.
The politics of a new collider are going to be very tricky. All that’s clear to me is that this is hopeless in the US right now, there’s no way that is going to happen, no matter how much hype you engage in. I have zero understanding of what the Japanese and Chinese situation is. In Japan, with negative interest rates, you might think that building a very expensive machine would make money, not cost money… As for CERN, I also don’t know much, but if I had to guess, I’d guess any project that could fit in the envelope of the current level of funding should be salable, anything that would cost a lot more will likely be hard to sell (no matter how much hype…). More specifically, I’d guess that a new 100km ring is going to be hard to get, but anything you can imagine putting in the LHC ring (ep machine, HE-LHC) much more plausible.
To Low Math… well, “Tunnel Visions” tells a quite different story of the demise of the SSC. A bit more realistic about how things actually work, as opposed to a theoretical guess as to how US funding works.
The theorists (as serious as Steven Weinberg) were hardly listened too… meaning, overhype didn’t kill the SSC. Much stronger budget winds, the demise of the Soviet Union, and the reconciliation of HEP v. billion dollar project management styles in the US forces were all way more important than the hype was. Basically the theory hype has to be there but in politicians minds the difference between Steven Weinberg saying “This is important” and him saying “If you fund this you will get the Starship Enterprise built before Russia does” is squat. Both arguments saturate the “science good” meter.
As for SUSY being unnatural, I disagree, as I said earlier:
“A 1 TeV neutralino is perfectly fine for even the absolutely simplest SUSY phenomenologies, with all other superpartners out of reach of buildable colliders. That neutralino might be seen in the direct dark matter experiments or the indirect ones.. no problem.
https://idm2016.shef.ac.uk/indico/event/0/contribution/32
Or it might not. Whichever it is, all perfectly natural, because natural always is what nature chooses.”
My decades in physics have taught me how right Watson was. His view is not nonsense at all… the reason being, the path to truly important discoveries is usually circuitous and not linear at all. Thinking that it is easy to predict the serendipity of discovery the real nonsense.
Increasing beam energy is always the best route to a fundamentally new discovery, whether it is SUSY or not. Integrated luminosity at a hadron machine does help because in essence (the parton distribution functions) it does slowly increase the available energy. But slowly. Getting more energetic beams in the long run is needed, no matter what.
Thanks Peter. Probably the kind of thinking that is needed… if the field can think of a way to get, say, 3X the energy for the same cost as the LHC, that should trigger a new collider. Innovation is essential to achieve that. That the direct work product of collider physics has economic value has always been a ruse.
On the other hand, the indirect work product, from every light source in the world to the world wide web, are rather powerful arguments to keep the endeavor going.
Remember what Planck said.
“A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.”
It was true a hundred years ago; and, it is true now. David Gross is onto something with the remark you attribute to him.
Goleta Beach:
1) The U.S. got the benefits of the web without tossing the additional billions that were still needed into the SSC.
2) Glad you may be seeing the light on the need for accelerator innovation. It would be encouraging to this non-physics taxpayer if the particle community would stop trying to build scaled-up versions of what they already know how to do and invest at least a few hundred million dollars in advanced accelerator concepts, if only to rule them out. Both rational and sales-oriented considerations make it desirable to pursue new technologies offering the potential to drastically cut the cost of the energy frontier.
Hi, Goleta Beach,
I’m pretty familiar with the sad story of the SSC, though I’m sure not as much as yourself. What I meant by “in retrospect” is that anyone looking back will think themselves justified in ignoring the eggheads with their expensive toys and killing the thing even when, back then, the scientific argument looked substantially better. Because those eggheads got it rather wrong anyway.
As for the question of naturalness, I’m also looking at history and seeing decades of vehement arguments in favor of SUSY appearing long, long ago, and ever since. Clearly there’s always a place where “natural” SUSY can hide, and, if I understand correctly, that will be true forever, given how many knobs SUSY has to twist. I imagine it must be possible to craft a SUSY theory in which SUSY is perfectly natural and 100% undetectable by the LHC, just by having an extreme version of the model in the Quanta article. But why, then, were so many incredibly smart people (including several Nobelists) so thoroughly convinced that the LSP simply had to appear in the LEP? Then the Tevatron. Then in the first run of the LHC? Then they talk about one-part-in-a-thousand fine tuning as being perfectly OK, obviously. And, hey, what does it really mean to be “natural” anyhow? Etc. This has been going on literally for decades. I know of no parallel in science, anywhere. I’ve seen wrong ideas. I’ve seen failures. I’ve seen outright fraud (embarrassing amounts in my own field, in case anyone thinks I lack any perspective at all). But the failure-proofing of the SUSY paradigm seems outlandish. I’m perfectly aware of my own limited intellect; that’s why I rely on the testimony of those much smarter people. But their story keeps changing, and my ability to trust their judgment is simply gone.
I don’t think it’s reasonable to expect continued financial support based on an infinite regression of models “explaining” why the sure bet wasn’t, and why we should look just a little bit harder, over and over again. Much better to use your other argument, which is simply “push the frontier”.
That said, if I understand correctly, an order-of-magnitude increase in energy will be staggeringly expensive even by the standards of “big science”, barring some revolutionary technological breakthroughs (I fantasize about the muon collider, which I’m told is likely a pipe dream). I think without a much more compelling argument for a new discovery than the SSC had going for it back in the day, I’m with Peter: Zero chance in the USA of it passing the laugh test in Congress. The next generation hadron collier will probably have to be in China, mostly for nationalistic reasons. So let’s hope the PRC stays stable over the next 40 years or so.
Lino D’Ischia,
One problem here is that SUSY enthusiasm isn’t just something common in Gross’s generation. Several generations of theorists since have been trained from their student days in this ideology. Of the comments from the bet losers, it was David Shih who seemed most unconcerned about not seeing SUSY so far, and he is the youngest of them.
Jesus, the same story again and again.
SUSY is there; it is alive, well and unbroken at some high energy scale. It’s almost a necessity of Nature to be there for strong *fundamental* theoretical reasons.
It is just that along the way people thought that the presence of the Symmetry (if appropriately broken at certain scale) can be justified also from effective field theory point of view using some bottom-up arguments based on naturalness.
So what people are trying to see in LHC now is how much it is broken using bottom-up low energy effective field theoretic arguments based on naturalness.
It is naturalness that is failing here (to the extend that it is failing at the specific LHC scales), but naturalness is just a general strategy used to guess at which scale new Physics is expected to appear; it is unrelated to SUSY per se.
The fact that no new Physics (not just SUSY) seems to appear at LHC just means that the effective field theory doesn’t have a clue why Higgs is so light and it’s a question for the fundamental theory to answer (this also depends on how much fine tuning someone is willing to accept).
So be it, all it’s nice; SUSY should not carry the burden to justify the usage of naturalness by Physicists as a working hypothesis to construct BSM phenomenological models.
I’m sure this is what Gross had in mind and reporters must stop misleading the public with similar eye catching hype.
Giotis,
“SUSY is there; it is alive, well and unbroken at some high energy scale.”
The problem is that such a statement is a religious one, not a scientific one. Gross and the other losers of the Copenhagen bet were betting that SUSY was science, with particular testable experimental implications. Unfortunately for that point of view, they lost. This really is now the question for the future of HEP theory: is it really all right if the field becomes based on a series of untestable claims like yours (which, by the way, I strongly disagree with)?
I think you will find that, post LHC results, your religious views are now those of a small minority of the field.
In 1986 I attended a summer school of physics, where John Ellis was one of the tutors, and had a lecture on SUSY. Asked about experimental prospects of finding it he responded, quote “I will not commit suicide if SUSY is not found at LEP. But if it is not found at the SSC then maybe…”. OK, LHC is lower energy than the SSC, but I’m a bit afraid…
I feel I repeating my self so for the last time I will state the obvious.
SUSY as a fundamental symmetry doesn’t make any top down low energy BSM predictions or the scale at which it is broken.
It is naturalness that makes these predictions and not just for SUSY but for any potential new Physics that can be used to explain the Higgs lightness.
These are two completely unrelated issues.
On a more mundane level, we can at least test David Shih’s optimistic claim that by spring, the LHC will have up to five times the data it had at ICHEP giving 12×5 = 60\fb. Personally, I believe David’s being overly optimistic as with SUSY based upon how things are going right now, and it will be a rather more modest 35\fb.
Also, despite the optimism of Nima and David Gross about this being a great opportunity for newly minted PhDs to come up with new ideas to challenge SUSY, the main problem remains: No new physics has shown up at the LHC to show the way and we need to wait until then.
srb… of course no-one predicted the web would come from the expenditures justified for CERN between 1954 and 1993….
What no-one knows is… what innovation did we miss out on by *not* pursuing the SSC… and would it have been as lucrative as the web was? The point is…. serendipity.
Of course much of the condensed matter community was vociferously opposed to the SSC as impractical, focused on wasteful intellectual curiosity that would never lead anywhere. Not one of those SSC antagonists credit high energy physics with inventing the web, though.
There have been intense efforts in accelerator innovation for at least 30 years. In fact, the LHC did benefit from some of the very practical magnet innovations developed for the SSC…. and the LHC ignored some other of the SSC lessons; had they paid attention to them the magnet problems the LHC experienced might have been avoided.
But accelerator physicists are often prevented by practical matters from innovation… they must deliver the beam and aren’t always given enough freedom and support to play with instruments like the LHC and benefit from some serendipity.
Low Math… doesn’t the argument for the SSC look even stronger today? At first glance, the LHC didn’t have sufficient energy to discover new physics. The SSC might have had sufficient energy.
As to why Nobelists predicted evidence for SUSY at PEP-I, SppS, KEK, LEP, Tevatron, LHC… they are optimists. Optimists have a huge evolutionary advantage over pessimists, because optimists make things happen. And sure, we’ll need innovations to keep future collider costs within a reasonable envelope. I’m optimistic that we’ll get them.
As for fine tuning… the universe is already amazingly fine tuned… see
https://en.wikipedia.org/wiki/Fine-tuned_Universe
which omits the surprising fine-tuning of G_fermi, which controls the rate of pp fusion in the Sun.
The only sensible definition of naturalness is: if nature chooses it, it is natural.
@GoletaBeach, if dark matter consists of 1 TEV neutralinos, wouldn’t LHC, Lux, PandaX, or upcoming Xenon1T detect it?
@Peter Woit – what about neutron and electron EDM measurements? it is conceivable they can find a EDM consistent with SUSY or rule out EDM to SM values, ruling out SUSY, and do not require multibillion dollar colliders.
best
wimp,
The problem is that these are just two numbers, and if you manage to measure a value too large to be the SM value, you have found evidence for BSM physics, but very little information about what it is, in particular no evidence that it is SUSY.
On the other hand (and this is where we are now), when you find a lower bound on an EDM inconsistent with “generic” SUSY models, SUSY proponents will just say that this doesn’t rule out SUSY, only puts a single constraint on the large parameter space of SUSY models. These EDM numbers have been inconsistent with generic SUSY models with TeV-scale superpartners for a while, but that has had little effect on getting anyone to give up on looking for SUSY at the LHC (although it was one of the motivations for split SUSY).
This is the general problem with low energy experiments that give very indirect access to high mass scale physics. So far all they give is a small number of complicated constraints on BSM models, and if you observe something non-SM you may justifiably get a Nobel prize, but the only information you’ll have about BSM physics is one number, a complicated function of the huge parameter space of BSM models.
Peter Woit,
i understand what you are saying, but what about an exclusion? finding EDM does not prove SUSY, but a sufficiently low EDM might be able to falsify it.
is it possible in principle that a sufficiently low measured value of electron/neutron EDM – both- on the order of 10^-32 or less, can rule out SUSY, since SUSY generically predict values of EDM much higher than this? i.e if electron, neutron, proton EDM – all three- are measured to less than 10^-32, would that falsify SUSY (assuming no other evidence of SUSY in LHC, rare decays, dark matter searches)?
regards
wimp,
The problem is that you are falsifying a particular notion of “generic” SUSY model. Given the kind of EDM limits you mention, SUSY enthusiasts could just say
1. SUSY might be “generic”, at high enough energy scale.
2. SUSY might be at lower energy scales but “non-generic”, or “fine-tuned”, just happening to be such that the EDMs are much lower than expected by dimensional analysis.
In any case, the main point I was trying to make is that ruling out SUSY models at higher mass scales might be something you can do with a new collider, but it’s not a good motivation for building one. We already know all sorts of problems with such models, and they don’t really explain anything, so ruling them out is not an interesting goal. Understanding what physics looks like at multi-TeV scales (and whether it is SM or non-SM) is a good motivation.
Peter, your response only points out the wisdom of Planck’s statement; i.e., only now, after two unsuccessful attempts to see anything of SUSY, will the younger generation begin to distrust this approach. And it will have to be the generation behind the present one. This might take some time. OTOH, I believe that at least some of the youngest generation will begin to look in unchartered areas, and should something prove promising, who knows,maybe the whole field will latch onto that. I think the problem in modern-day science is that opposing viewpoints are so quickly suppressed.
But I can’t help feel that all of this should be part of some learning curve for scientists.
Urs,
you say that supergravity might be the way to go. How many parameters (instead of the about 20 of the standard model) does it have? Are they fewer than the 105 of usual supersymmetry?
Nature didn’t read the paper of Wess and Zumino. Too bad.
Claudio Merati,
The SUSY models under discussion are generally assumed to be supergravity models, this aspect of them doesn’t solve the fundamental problem Urs and Giotis want to ignore: the supposed beauties of the models are wrecked by the necessity of breaking SUSY since you see no evidence of it in the observed particle spectrum.
There are good motivations for SUSY. But the main motivation, that weak-scale SUSY makes the weak scale naturally small, is dead. If future data will show evidence for sparticles, it would be like discovering a dead body.
I am a HEP theorist myself and about 30% of my published work deals with new physics searches.
If I had to decide, I would not fund a new collider today.
I am surprised that many of my colleagues still would. They seem to be blinded by some strong observational bias or put sociology over interest in nature. Because if the LHC has told us one thing it is that everything points towards a “dessert” (i put the word into quotation marks as I am again quite surprised that the working of our theories over many orders of magnitudes should be labeled by a derogatory term).
So, let us look at the big picture. Aside from all speculative thoughts there was one big argument why the LHC had to be built: In its energy range there had to be the Higgs or otherwise S-matrix unitarity would be violated. And remember, when we started out the upper mass bound for the Higgs (from triviality) was ~600-800GeV. That is a solid reason to sink O(10) billion.
What has happened now? The Higgs is found and its mass indicates that our vacuum is metastable and something will happen at ~10^12GeV. So again we are in a situation where there is a new energy where we have to see some sort of new physics, just like before. Only this time around it happens to be 9 or so orders of magnitude beyond our current technical capabilities.
Leaving egos, careers, technical expertise and all these aside, what can one conclude from that? I think the logical decision would be that accelerator physics should start confronting the challenge of bridging the gap of 9 orders of magnitude in energy and while they are busy doing that the big money should go to other areas of fundamental physics where progress is just happening at breakneck speed like e.g. cosmology.
As individuals – especially those stuck in the field – we might not like it, but that seems to be the only logical conclusion. Some people seem to prefer to hype their specific model and want to convince the public to commit substantial resources towards investigating if their ideas are correct. But in all honesty, a scientist should know better and clearly separate established fact (like someting new has to show up at around 10^12 GeV) from fantasy (like “SUSY is around the corner”).
AGT tells that Nekrasov’s instanton partition functions in 4D N=2 SYM can be used to compute conformal blocks in non-supersymmetric 2D critical systems, including the humble Ising model.
These surface critical systems are studied since decades in many different ways, using various analytic methods including 2D conformal field theory, numerical methods, as well as experimentally. The AGT correspondence, which originates in very stringy ideas, leads to results that are in perfect agreement with everything that we know. 4D SUSY is absolutely necessary to obtain these results in 2D non-SUSY systems, and no SUSY-breaking or any approximation of any type is involved in these computations.
If only for this reason, 4D supersymmetry cannot be a totally wacko idea. However, SUSY simply does not appear in high energy physics.
chris,
Arguments like “we know there’s no BSM physics up to 10^12 GeV” from theorists are just as worthless as the “we know from naturalness there has to be BSM physics at the TeV scale” ones. I hope experimentalists have the sense to ignore both of them.
Mathphys,
I agree that d=4 N=2 SUSY is a fascinating theory, (besides the AGT stuff you mention, this is the theory that gives Donaldson invariants and a very deep connection between 4d geometry and topology and physics). People should study SUSY theories like this, while noting that the ones leading to beautiful mathematics are different than the ones used in the failed program to connect SUSY to experiment (e.g. N=2, twisted, vs N=1). I wouldn’t be at all surprised if thinking about SUSY and QFT led to some new classes of theories providing new insights into the world, I just think it’s clear that the particular class used so far doesn’t work.
As someone who worked on SUSY for years, and even did my Ph.D. on a SUSY model, I have to admit that I never was able to see anything particularly compelling or beautiful about the whole idea. I know, I know, the square root of the Poincaré group and all that, but as beautiful and inevitable as I find the mathematics of gravity or gauge theories, SUSY always seemed ugly to me. Personal esthetics, I guess.
Chris, though it would be very nice for this glutton if everything pointed to a dessert, I think you meant to say desert.
With SUSY, you really can have your cake and eat it too.
To chris… I don’t really agree that cosmology is proceeding at breakneck speed. A simple cosmological constant fits the dark energy just fine… B-modes promise to be a long hard slog. Maybe we’ll get the average neutrino mass out, that will be good. But hardly breakneck speed.
The arguments you mention about the Higgs & LHC were really arguments for the Higgs & SSC. The LHC got interesting when precision electroweak indicated a light Higgs. The no-lose theorem never applied to the LHC and a heavy higgs.
What you miss is the exploratory aspect of high energy physics. A prominent motivation for experimentalists and machine builders is the unexpected. No theorist predicted the muon, parity violation (actually seen in the 1930’s, it is a wonderful story), strangeness, CP violation, neutrino flavor, the bottom quark, the tau lepton… well, the charm quark, the Z0, the W, the top quark, and CP violation in the B system, the Higgs and its mass (roughly)… they did get predicted by theorists.
A requirement of theoretical prediction would, in the past, have resulted in missing about 1/2 of particle physics discovery. Luis Alvarez wrote a wonderful essay in the early 1970’s about the necessity to politely and congenially disregard theory regularly (but not always).
Sure, $10 billion ain’t easy. But accelerator builders haven’t figured out how to get factors of 10 or 10,000 in beam energy because they are lazy. Nobody has figured out economical flying cars either in the past 50 years. Some technological problems are rightfully hard.
There has been however a very nice adiabatic continuous improvement in accelerator abilities. The field needs to support machine guys and not burden them with ideas of flying cars… and don’t ever think that innovation is not intensely pursued in the accelerator business. It is, but often theorists are a big ignorant about it.
Just a quick question about your book. Are you going to keep the latest free PDF version of the final draft online, even after it is printed? Would the publisher permit that, since it might just reduce sales? (On the other hand, seeing what you’re getting like this may be a way to promote and popularise the book, just as browsing in bookstores works.)
anon2,
My contract with Springer specifies that I retain copyright, as well as the right to make the final draft version available on my web site, which I intend to do (I did learn something from the experience of my first book…)
Right now rereading from beginning, fixing minor things and making various improvements based on comments and suggestions from readers. Pretty thoroughly sick of working on this, hope it’s over soon.
All,
I’m deleting further tired general discussion of topics like particle accelerators and their funding, and hoping for a return to the topic of the posting.
I actually was curious about what the current state of SUSY and general BSM physics betting might be, in light of the current LHC results. Maybe the dust hasn’t settled enough yet, but it was quite entertaining a few years ago to see all the personal odds estimates being thrown around, as well attempts at generating aggregates for different outcomes. Useless scientifically, of course, but a very interesting sociological exercise.
Well, the accelerator discussion (as well as EDMs) was targeted to the topic of “in your lifetime”. But it is your blog and if it is tiresome to you, that is alright.
To stay on topic: “Not Ever Wrong” and “Not in Your Lifetime” are inequivalent. Ever is forever. Your lifetime may be forever for you, but it is not forever for everyone else.
Not Ever Wrong makes current particle theorists sound like theologists. I don’t think they are. I think that their belief is that eventually empirical evidence will decide whether SUSY is wrong or right, it is just that the time frame may be 1000’s of years, or however long it takes to do a complete set of experiments up to the Planck Mass. Speculation about how long it will take to perform that set of experiments is… well… tiresome to you.
The current particle theorists view is not the same as theology. In theology the concept is that the theology is correct independent of empirical evidence.
Congratulations to you too on this in recognition of you standing up to the Zeitgeist of the day. Bravo!!
As an experimentalist in HEP, I think the community should focus on testing the SM and not on testing unmotivated theories. It is entirely natural that sometimes theory needs to wait for some hint from experiment and this is the current case.
And there is no reason to be pessimistic about the field, there are a lot of obvious areas to test the SM such as neutrino masses, CP violation in the lepton sector, proton decay, confinement and muon g-2 to name just a few. These don’t require a bigger collider, but that doesn’t make them any less important or likely to provide the necessary hint.
And it would be best if theorists create theories to fit these new hints, not only look for some version of an old, no longer motivated, model that is not ruled out by the new ‘constraint’.
If all the obvious places to test the SM result in trivial extensions and no hint about future physics, then it might be time to become pessimistic.
I had a slightly different take on David Gross’s comments, following on those of ‘t Hooft, than Peter. I understood him to be saying that the emphasis on SUSY as a central issue is actually misplaced [except perhaps for some String theorists], and a distraction from dealing with our lack of understanding of some true fundamentals of particle physics and of space-time in general. (From ‘t Hooft: The resolution of whether super-symmetry exists or not isn’t just about whether some new particles show up at a particular energy in a particular experiment, but rather about the nature of space and time: is space-time super symmetric?) To summarize:
– The underlying issue is one of “naturalness”, or the lack thereof, in the heirarchy of masses and their couplings with the Higgs field.
– There have been a whole series of issues with “big numbers” and “small numbers” during the development of the Standard Model, all of which appeared to be completely “unnatural” at the time. Some have been dealt with in the theory, in QCD, and are calculatble (if you understand the dynamics properly) and some have just been accepted as “just the way it is” — such as the heaviest quarks having 50,000 times the mass of the quarks that make up the proton. There’s no fundamental explanation for that – just measurement. In 1960, that would have been considered insanity. Today, it’s “So what?”
– We should not try to apply the same methods to other, perhaps totally unrelated “problems of large numbers” just because they worked before. Every such problem is its own separate case and will probably require its own particular solution, as we better understand the underlying physics. E.g., the Cosmological Constant problem is probably unrelated to the hierarchy problem, and will need its own separate solution, to be able to calculate anything.
– Super symmetry offers the possibility of handling the hierarchy problems by turning them into logarithmic effects, just like we learned from QCD that couplings vary logarithmically with energy, not linearly. Some type of super symmetry still seems like the best hope for doing that.
– So super symmetry doesn’t show up at the LHC, or only shows up very tentatively over the next few years? That’s probably just a sign that there are small numbers involved, just like there were in the quark-lepton mass spectrum. So what? It’s likely that we don’t understand the parameters of super symmetry buried in the couplings with the Higgs just like we don’t understand other paramters of the Standard Model: we are missing something fundamental.
– This doesn’t mean that it’s right, just that it’s the only explanation we have come up with so far that addresses this particular large number issue. So he’s sticking with it, as something that will need to be considered in more fundamental explanations.
– What we really should be worrying about is identifying the underlying dynamics of more fundamental physics, that better explains those unexplained parameters in the Standard Model and lets us do actual calculations in regimes where we currently cannot. And the younger generation should not be shy about throwing out the preconceptions of the prior generation of physicists in order to do so.
While I can’t claim to agree with “believing in” SUSY just because it’s the only game in town, this seems like a much more nuanced, rational approach than Peter suggests.
Yeah, as johnnythelowery says, congratulations. This is probably the nearest you’re ever going to get to official confirmation that SUSY is dead.
Don’t worry Peter, that’s exactly what Thomas Kuhn descriped. Some theory only dies when their participants die. It would be worrying if many new people join SUSY/Strings, but i guess that doesn’t happen. At our universities, string theoretists are not taken serios anymore, and the groups mainly consist of a few old guys, and senior-postdocs which cant find permanent positions. no PhD students mainly.
I guess thats a good sign. 🙂
Peter,
I strongly disagree with the statement that arguing for the desert is the same as arguing for low-energy BSM physics on grounds of naturalness. First of all, the desert is not a thing, but actually the absence of a thing (BSM physics below the GUT scale). Hence, the default assumption should be to stick with the SM and put the burden of proof on anyone who claims there are violations just round the corner.
johnnythelowery and anon,
Thanks, but in this case I don’t think my skepticism about SUSY at the LHC is a “standing up” to anything, since I think most HEP theorists have always shared this skepticism (as I keep pointing out, it’s the losers of this bet who were in the minority). So, on this one I’m in the majority, now kicking the losers while they are down…
WLM,
I didn’t discuss Gross’s comments about SUSY/naturalness getting too much attention, while our complete lack of understanding of the SM parameters at all gets very little. I completely agree with those comments.
I do though also completely disagree with his argument that one should have faith in SUSY, because it promises a solution to the naturalness problem, even if you have to fine tune things somewhat. This argument claims to solve a conceptual “fine-tuning problem” by extending the SM by something complicated, adding in over a hundred new parameters. And then you find it doesn’t really solve the problem, you still need some fine-tuning. I’ve always been of the opinion that this never was a solution to the problem (adding a huge number of new parameters is not a plausible explanation of a puzzle about one parameter), but the LHC could have vindicated this. It didn’t, so now the disturbing situation is that proponents of this have decided to stick to a bad “solution to a problem” and keep promoting it, without any hope now of experiment resolving the issue.
The bet I’m really looking forward to is the Lubos-Jester one. Boy, am I looking forward to that one!
The LHC has recorded ~20\fb making ~30\fb by mid-October a realistic possibility. Make the blog post a good one, Peter 😉
Mr. Anon Anonymous,
I think that bet was a good indication that skepticism about SUSY at the LHC was always very widespread (Jester offered 100 to 1 odds, betting it wouldn’t show up).
I hear Lubos is doing his best to refuse to admit defeat, now claiming he won’t pay up until all analyses in all channels by CMS/ATLAS based on 30 inverse fb are completed, which could be quite a while.
One reason I never got interested in searching out such a bet was that I suspected I’d never see the money if I won. I would have predicted that some sort of anomaly would show up in LHC data that SUSY enthusiasts could point to as a possible SUSY signal, have been surprised that that hasn’t happened.
Opinion: Nature has spoken on more than one level here, for example on the matter of which speaks the most for human naturel, neo-philosophical notions of Critical Rationalism as exemplified by Karl Popper and currently David Deutsch on Karl Popper; or is it the more traditional mixture of common experience with a peppering of self-honesty and awareness of the facts of history.
We don’t change our minds. It may not even be possible to change our mind. Not about core hard-won whole-life insights. The reason this is not apparent to us is because it’s a relatively tiny subset of the fulsome summary of all the real or possible things we think we have (or had, or would’ve).
Everyone is [usually] more-than-happy to abandon, or switch sides, on the vast majority of our opinions because we attach little real value to them. So it looks like changing our minds is something humans do all the time, when in reality we do not, ever.
Science on the theoretical side is almost always about the hard-won insights and whole-life lessons. It cannot, and has never, depended on this sort of notion. What has changed relatively recently is the level in scientific affairs at which positions are decided. Everywhere else the positions that really matter are attributes of groups not individuals. Science uniquely managed to heave this trait in the direction of the individual far enough that the consensus and ultimate course became on-balance, and ultimately settled objectively by objective reality, via measurements.
That has now changed, it has reverted back to the base-energy state of human nature in which it is relative power that has the final word, not truth. Not because humans are cynical or attach little value to the virtue of objective truth, but because that is the objective truth in human affairs.
I assume people are aware of this: at collaborations like ATLAS, the limits on BSM physics can move to publication quickly; however, unexpected/expected excess could take much longer to go through the internal review and politics. This is just the reality of the life in big collaborations. With this in mind, you might want to hold your bet for a little longer and it is very sensible to me that you do want to see majority of the results with full 2016 LHC data.
Dull discussion accompanying the bet. Just a load of big shots (who in this case were proven categorically wrong) exchanging platitudes about new physics and naturalness. The final speaker literally agreed with everything said previously. With respect, what was he there for? I wanted something more adversarial. Unfortunately, these kinds of discussions are somewhat ceromonial and reverential, and don’t challenge the ideas or the logic of their special esteemed guests. As a result, we hear the same old things and nothing changes. I suppose at least they had the video message from ‘t Hooft.
anon,
I think the idea was to just have as panelists those who had lost the bet, with the idea that they might have something interesting to say about how losing the bet had changed their point of view (winners of the bet were likely to not have much to say except “told you so”). This didn’t really work out, since the attitude of the losers was pretty uniformly “So what? I still believe SUSY rules, no matter what experiment says”.
Can you explain this attachment to SUSY? What is so compelling about it?