Back from vacation today, so regular blogging likely to resume. Will start with something quick, a link to material that was posted today.
The Edge web-site annual question feature is out today, with this year’s question What *Should* We Be Worried About?. I wrote something about the “Nightmare Scenario” that HEP is facing if the LHC finds a Standard Model Higgs and nothing else.
Others addressed the same issue, with Lisa Randall writing:
In my specific field of particle physics, everyone is worried. I don’t say that lightly. I’ve been to two conferences within the last week where the future was a major topic of discussion and I’m at another one where it’s on the agenda.
Her specific concern is motivated by her interest in large extra-dimensional theories, for which no evidence has shown up so far at the LHC. If the extra jump by a factor of 6.5/4 in energy that will arrive in 2015 after repairs still shows nothing, this may be the end of the line for such theories for a very long time. The prospects for a higher energy machine are problematic in terms of technology, as well as the political will to pay for them. The overselling of this that went on for many years pre-LHC won’t make it any easier to re-use these theories as an argument for building a new machine.
Amanda Gefter sees no reason to worry. Particle theorists will just move to making progress without experiment, through studying paradoxes of the current theory, with her final example for optimism the recent debate over the “firewall paradox”.
Carlo Rovelli’s contribution explains one problem with this: humans are very good at convincing themselves they have found some wonderful explanation of something (e.g. some resolution of a paradox, like the supposed SUSY solution to the hierarchy problem), when reality actually involves something quite a bit more subtle and unexpected:
A number of my colleagues in theoretical physics have spent their life studying a possible symmetry of nature called “supersymmetry”. Experiments in laboratories like Geneva’s CERN seem now to be pointing more towards the absence than the presence of this symmetry. I have seen lost stares in the eyes of some colleagues: “Could it be?”, how dare Nature not confirm to our imagination?
By the way, when I was in Paris last week I picked up a copy of Rovelli’s wonderful short book that has just come out in France Et si le temps n’existait pas?. It begins with a personal history of how he got into science, from a background in the 1970s disillusion following the flowering of radical ideas in the 1960, a story I found quite interesting, since I’m of the same generation as him. There’s also the story of how some of the ideas of loop quantum gravity developed, and some speculative material about time. Definitely worth looking for if you read French and are interested in these topics.
“the “Nightmare Scenario” that HEP is facing if the LHC finds a Standard Model Higgs and nothing else.”
Well, the current Higgs diphoton rate is not really supporting this scenario, quite the contrary. This should keep people busy at least for some years.
Hello Prof. Woit,
Nima has published two papers with the second one on SUSY and the first one on scattering amplitudes. As a general audience, I’d like to hear some explanation and your comments about these two papers.
In both cases, it’s probably worth making it clear that Arkani-Hamed has co-authors.
I’m far from expert enough to comment intelligently about the amplitudes paper (except that the short section on relations to mathematics is rather wild). At some point soon I’ll probably write more about the latest status of SUSY, and the second paper you mention is part of that story.
Rovelli’s argument is totally bizarre. He criticizes supersymmetry for being too speculative, when in fact it is one of the most conservative ideas about BSM physics. Supersymmetry is not in the same category as the multiverse, nor is it an a priori bad idea that should have been abandoned long ago, as Rovelli implies. It is a very general idea that addresses a range of problems, and it is an important part of quantum field theory regardless of whether it provides a successful framework for BSM physics.
The most ironic thing is that Rovelli is one of the leading proponents of loop quantum gravity. Most of his argument applies pretty well to his own field…
Peter, I don’t want to lead the discussion off topic, but I’m curious to know why you say the relation of Arkani-Hamed’s work to mathematics is “wild”.
To be more explicit, I was referring to section 15.4 of the paper, for which I think the adjective “wild” is pretty appropriate. Again, calling this “Arkani-Hamed’s work” is doing his collaborators a huge disservice. In the case of section 15.4 especially, which pretty clearly was written by the mathematicians in the collaboration (Goncharov and Postnikov). Please though to all, if you want to find a place to discuss this paper, you need to find one moderated by someone more expert in the topic than me.
About Rovelli, I think his point was exactly that the least speculative of these kinds of ideas, weak-scale SUSY, is turning out to have nothing to do with reality, giving a good lesson in why one should be skeptical of imaginative speculations of theorists. Yes, the lesson also applies to LQG.
If anyone is taking bets on where the necessary input for the way forward is going to come from, can I put my money on observational cosmology?
You can put your money there, but people have been making that bet (that something learned from cosmology would tell us how to go beyond the standard model) for more than 30 years now, and so far it has been a losing one.
Thanks for the reality check. It seemed a slightly better and more obvious choice than my second guess which was looking at different systems that occur far away from equilibrium.
“In my specific field of particle physics, everyone is worried. I don’t say that lightly.”
it is interesting how perspective can distort reasoning even for the most emminent of scientists that should have quite a keen sense of how not to fool themselves.
i am in hep theory and i am not worried in the slightest. neither are any of my colleagues. that might be connected to the fact that all of us never believed susy or string theory to be of any use for understanding the weak scale in the first place. so accordingly, we did not indulge in building spectacular models that get killed now by experimental evidence.
quite on the contrary from being worried, i have the sincere hope that department hiring committees will resume to hire based on contributions to physics on not on how well one person can jump on the latest fad that is fashionable but rather very much unlikely in the grand perspective of things.
how preposterous it is for a scientist to be disgruntled by what nature chooses to be. we are supposed to find out, not to satisfy our vanity. the “SM only” results of the LHC are quite healthy to the field and let us not forget that the Higgs (as boring as it might seem to some – i am specifically disregarding the gamma-gamma excess here as this is most probably a systematics issue) is the first fundamental spin-0 we have found – a true prediction not to be sneezed at.
a bit of humbleness would serve us all well
The results from ATLAS and CMS are consistent with a SM Higgs boson.
Yes, they are consistent. However, according to ATLAS the diphoton rate is about 80% the SM prediction. The interesting thing is that the excess grew with luminosity, but of course as chris points out there is still plenty of room to blame this on systematics. I am being optimistic and believing in ATLAS rather than in CMS.
I wonder if theoretical physicists need studying speculations like the firewall paradox or need developping a heuristic firewall to deal with “wild” speculations …
Interesting discussion. I left theoretical physics 30 years ago when Mike Green (now the Lucasian professor) successfully convinced me there were no useful ideas out there. Of course his actual intention was to convince me to join him in String theory research, but the idea that since we had no best fit theory (I was in agreement that SUSY on it’s own looked unconvincing), then the next best option was to provide so many degrees of freedom that somewhere in the resulting vast solution space would be an answer, was enough to make me realise that no one had anything useful to say. Seems like it’s pretty much the same situation, no change.
I do disagree with your comment that 30 years of cosmology research hasn’t shown what’s beyond SM – on the contrary, the only actual experimental evidence we have at all beyond SM is from cosmology as far as I can tell.
Jack, I completely disagree with you that
“the only actual experimental evidence we have at all beyond SM is from cosmology as far as I can tell”, even though that seems to be the current folklore.
from astronomical observations alone. there is not one shred of evidence that cold dark
matter has anything do with WIMPs, SUSY or beyond standard model particle physics
or even with standard model of particle physics.
(the only argument given is WIMP miracle which has been overblown and IMO it is as likely or unlikely as Titus’ Bode’s law)
Regarding dark energy, it may well be consequence of us living in an inhomogenous universe or a breakdown of classical GR.
The only other evidence you may be considering is inflation. In 80’s people were optimistic
that inflation is connected with GUTs and the like. However GUT based models of inflation are ruled out
From cosmology we get that only about 5% of the Universe is baryonic. That means new physics or “beyond standard model” physics is needed to explain what the other 95% is. Admittedly it could be modified general relativity but as far as I understand, people usually mean the “standard model” to include general relativity.
Dark matter is the most promising possibility for a connection between observational cosmology and the SM, and a huge amount of effort for many years has gone into exploring this. The bottom line though is that this has yet to lead to anything. Even if dark matter is due to some new particle not in the SM (an axion, a WIMP, something else), the constraints that cosmology provides on the properties of this particle aren’t enough to either allow definitive experimental tests, or such that they point to a convincing extension of the SM. The SUSY WIMP scenario is the most developed of such things, but it doesn’t seem to be working out.
The SM plus GR does not explain the observed properties of the universe (galactic rotational discrepancy, etc). They do explain every single experiment we have ever done on earth and near space (i.e. to the solar system edge).
Internal inconsistencies (renormalisation, etc) and ugliness and lack of integration between SM+GR is NOT a valid experimental reason for SM+GR to need modification – the universe’s laws could be ugly and inconsistent. The only actual experimental evidence we can detect that is not explained by SM+GR is that obtained by observations of the universe beyond our solar system. Sadly.
I think that’s enough about cosmology, which is pretty much off-topic.
physicsphile, DM could very well be a primordial black hole (which is perfectly consistent with all data), in which case its nothing to do with particle physics, and
is consistent with GR. Also it could be an artifact of backreaction (see 0809.1183)
or some similar misunderstood physics.
But anyhow the main strawman I wanted to destroy which you will hear in almost every
conference is that dark matter is evidence for Weak scale SUSY or any beyond SM
theory which predicts a stable massive particle with electroweak interactions.
There is no evidence for astronomical observations that the cold dark matter is WIMP
It took many years for neutrino mixing/mass to be experimentally proven beyond all doubt… until the early 1990’s and SAGE, the evidence was thought to be as poor as that right now for WIMP dark matter (from DAMA/LIBRA, Cogent, ATIC, etc).
Not that the WIMP evidence is convincing or right, but the point is: if you give up doing experiments, you are guaranteed to discover nothing interesting. The neutrino guys never gave up. And the dark matter searchers must never give up either.
The current ratio of dark to luminous matter is evidence that the dark matter has weak interactions with luminous matter. It is not an airtight case, but it is interesting enough to pursue experimentally.
BTW, the LHC has really interesting and constraining results on light WIMPs, via missing energy. No signal, but very interesting constraints.
> the universe’s laws could be ugly and inconsistent.
They may be ugly but we better hope they are consistent. Actually being able to get 1 = 2 (even if you have to jump through a few hoops for this) is very bad, economic mainstream-level bad.
Sorry if my cosmology comment derailed the conversation. Part of what I had in mind was that if large classes of models predict a negative value for a cosmological constant in stark contrast to the observed value at least cosmology provides a sanity check unavailable elsewhere (and this has been within the past 15 years as opposed to 30).
If somehow we could travel back in time to 1961 and try and get unstuck, I’m not entirely sure anyone would consider it obvious to ask a guy working for the phone company. New ideas on how to move forward seem to come from unexpected places utilizing unexpected analogies.
How is the hep-th job market doing? Looks like pheno modelers are doing fine..
Are sterile neutrinos as dark matter candidates already ruled out ?
The most extreme scenario could then be: SM + 4th neutrino + GR and
For most generic parameters, sterile neutrino satisfies what astrophysicists call
“warm dark matter” (WDM). From fits to cosmological data, WDM constitutes a very small fraction of the matter/density budget.
Having said that, since we have not detected a sterile neutrino or know its mass etc, its entirely possible to cook up sterile neutrinos with non-standard properties so that they could be CDM candidate in which case you are right.
Again astrophysical observations are completely agnostic to nature of CDM.
Astrophysics and Cosmology have taught us that:
– There is dark energy, and it has a specific density. We will soon find out how it evolves with redshift.
– There is dark matter, and its properties are actually quite well constrained, i.e. it cannot be a light particle, hence “WIMPs”, where “M” stands for “Massive”.
– Neutrinos have masses. That comes from observations of the sun and the original SM had massless neutrinos. Actually, I think it was cosmology originally that taught that there were at most 7 neutrino species, which was a surprise at the time.
– The GZK effect is true, a probe of particle physics at 10^20 eV.
In the near-future we’ll have more constraints on dark matter, we’ll know to what extent dark energy evolves and what its equation of state parameter is, more work will be done on the lithium problem, there will be more evidence for (or against) inflation, we’ll directly measure gravitational waves in the labs, we’re approaching tests of gravity at high curvature scales, etc. Currently, cosmological constraints suggest a “4th” neutrino species at 2-sigma significance, and we’ll know more about that soon as well.
Some of you need to pay more attention.
Call me crazy, but as an outsider who can only follow things dimly, it seems to me that stuff like
makes a pretty strong case that the SM is not at all worked out yet and that there are some huge, important unsolved problems in understanding existing accelerator data. There are even hints that multiple anomalies are pointing to some common basic conceptual shifts.
I guess one could say that all this stuff is still not “beyond” the SM, but so what? There are 400% anomalies against current understanding and they get bigger (instead of the expected smaller) with collision energy. Or one could say that these are just problems in calculating the predictions of the theory rather than with the theory itself, but a) how do you know? and b) if so, isn’t doing those calculations a primary job for theorists?
Perhaps there are some anthropological factors that would explain what is or is not considered a big deal to worry about in physics. But even in a “softer” field like finance, where predictions are by their nature much less precise, if it is thought that x is supposed to equal y but empirically x = 4y, where x and y are basic observables, people tend to get exercised about it.
The above paper is obtained at lower rates than post-bailout rent-seeking ones at the DOE:
Puzzles in Hadronic Physics and Novel Quantum Chromodynamics Phenomenology
I believe that in the last 20-30 years, we had a lot of speculations in theoretical high energy physics, but not many frank, critical discussions.
Surely, a big part of our society wants to hear from the physicists bombastic ideas, amazing scenarios, in a words, they should run the show; and, by contrast, we have much less requests of exercising critical sense.
However, it is important to recall that all of us, scientists included, are called to decide whether we want “to exchange a walk on part in the war for a lead role in a cage”. This is what should primarily worry us, in my view.
The same view is expressed in http://arXiv.org/pdf/1206.1466.pdf in somewhat more formal terms.
I’ll confess to being a bit nonplussed by the final paragraph of your Edge contribution, where you seem to think that the current problems of particle physics are somehow going to infect the rest of science. (“Will intellectual progress become just a memory, with an important aspect of human civilization increasingly characterized by an unfamiliar and disturbing stasis?”) I can see no evidence for this in any other field of science.
Yatima: Thanks for the link. This seems a useful reminder that there are still problems in HEP, even though it does not tackle the electroweak radiative corrections which (IMHO) seem more serious, unless I’ve missed some work published recently.
SRP and others: the Standard Model is still quite healthy, despite points referred to above. Like the Copenhagen Interpretation of Quantum Mechanics, it keeps taking the flack from its detractors and continues to generate results in accordance with experiment.
Well, it’s a “worry” about what might happen that was being asked for, not an already serious problem…
As Lisa Randall notes, within particle physics “everyone is worried”. Whether this infects other fields depends a lot on how particle physicists deal with the problem. One particular form of the worry is whether pseudo-science (e.g. the string theory anthropic landscape) will become the dominant paradigm in the historically important field of fundamental physical theory. If this happens and fundamental physics changes from an ongoing successful example of how humans can understand reality to a dismal example of what is wrong with human behavior, there may be larger implications.
Perhaps I should be more optimistic and not worry. we’ll see.
My hope is that Alain Connes is actually onto something with his connection of non-commutative geometry to the Standard Model. However, physicists seem universally either to ignore this or to dismiss it.
Speaking from the perspective of someone who teaches an introductory course in the history of particle physics, I think there is more to the disappointment at lack of evidence for SUSY than arrogance or irritation that our theories don’t match reality (so far).
The idea of super gauge symmetry provided a way around the famous no-go theorems of the 1960s; when theoreticians encountered major problems in extending the unification program to include the strong and gravitational interactions, SUSY suggested a possible escape route. So much so that, as I understand it, it is difficult to see how the fundamental forces can ever be described in a unified framework without some version of this fundamental symmetry. So lack of evidence for SUSY is a little worrying as it could imply that some interactions are unified but not others…which seems strange and also at variance with our favourite cosmological pictures. That said, there are many different versions of SUSY and it’s early days yet…
You wrote that Dark Matter cannot be light. That is not correct. Axions for instance could be very light (and address the Stron CP problem).
My my, reading those “apocalyptic” reactions from physicists just makes me think they are nothing but drama queens. HEP is littered with unresolved problems, inside the standard model and outside the SM. If multidimensional theories are out, pick another problem. Isn’t that what a theoretical physicist is supposed to do ? Or have we arrived at a situation were overspecialization leads to stagnation ? You study 20 years to have the instruments and skills to tackle one problem, and beyond that ? Nothing ? Now this would be catastrophic.
Me, I’d like to see theoretical physicists get another go at axiomatic quantum field theory or something equivalent like that. A theory that from the get-go negates infinities. A proper physical theory where you don’t have to deal with renormalization and other arcane techniques to get rid of things that shouldn’t even be in the theory to begin with.
I think designing a finite quantum field theory is a much more interesting proposition than chasing strings, d-branes and other exotic structures with no link whatsoever to down to earth experimental physics.
I feel there’s some reason to worry over the prospect of loss of “Big Science” in HEP. This branch of physics, to many, represents an ideal few other disciplines can rival, and an exemplar of “pure” research. Can anyone think of a more impractical scientific discovery in the past thirty years which has attracted so much attention as the Higgs boson? I do fear a world in which that discovery may be the end of new discoveries in fundamental physics for a very long time. Without this exemplar, or any obvious path to pursue it, will science as a whole veer more and more toward the “practical”? Will science, as a whole, lose the tradition of curiosity for its own sake needed to sustain it?
*A proper physical theory where you don’t have to deal with renormalization and other arcane techniques to get rid of things that shouldn’t even be in the theory to begin with.*
This is one of those scurrilous rumors that just won’t die. The modern formulation of quantum field theory — the one Wilson et al got off the ground in the 70s — is free of unphysical infinities. The textbook presentations, unfortunately, are littered with them.
Please, no more about renormalization. It’s off topic, and blog comments here about it are not unlikely to enlighten anyone about anything.
For all your criticism of string theory, you are clearly a product of the 70s and 80s culture in which somehow particle theory was the ‘fundamental’ area of physics and the intellectual backbone/heavyweight of the field. As someone who has spent equal time on your side of the fence and on the other side in condensed matter, soft matter etc in the last 10 years, I can tell you that the culture of particle theory today is to first order irrelevant to the rest of physics and science.
It is a very isolated narrow field with little intellectual heft today even within physics departments. Other physicists work on as many interesting novel ideas & systems in a year as string theorists work on in a decade – and these physicists know it.
The days of Gell-mann & hep-th towering over physics and science culturally are long dead.. I am sure Peter knows this in his head but his worry about the culture of hep-th affecting the rest of science shows some remnants of Peter’s upbringing. Trust me, other scientists don’t give a damn..
I think you’re right, as far as some physics departments go, and someday even the IAS may hire a non-particle theorist (although the time-frame of particle physics dominance goes back to the 50s and 60s, before my time, and it’s not as weak now as you claim).
Non-physicists though often encounter physics through curiosity about “what is the world made of?”, “what are these fundamental physical laws that govern this?”, as well as through taking courses where they learn the standard historical narrative. From this point of view, particle physics and cosmology are likely to always seem like central topics (and to always get a lot of press), so degeneration of research in these areas is going to look to outsiders like degeneration at a core location of modern science.
Some of us find exact solutions in statistical mechanics and quantum field theory deeper and more fundamental than theoretical high energy physics as it currently stands. A typical talk on current high energy theory sounds as theoretically ad hoc as a talk on civil engineering.
The best parts of modern string theory (topological strings and AdS/CFT) and Yang-Mills theories (non-perturbative dualities and exact solutions) are essentially new applications and extensions of ideas from the theory of integrable models.
I’m pretty sure axions are not consistent with growth of structure and galaxy rotation curves.
Light particles don;t gravitationally settle into halos, they travel at relativistic speeds and are spread evenly across the universe.
However, there could still be axions, and they could in principle be inferred astrophysically, for example as a cooling mechanism for white dwarfes.
@chris: the worry isn’t that our theories aren’t working. The worry is that if new physics doesn’t show up at this scale the governments won’t fund expensive new experiments to probe beyond the standard model. I’m also a high energy physicist, and many particle physicists I know, even ones who don’t like string theory, are very concerned about this possibility.
If nature tells us something else is responsible for stabilizing the hierarchy than the theories we’ve come up so far – great! Nature is telling us something. But the concern is that we won’t learn anything really new at the LHC and funding for high energy experiment will screech to a halt.
Physicists of your type have many physical systems to study, and there are many more of you than there are string theorists (it’s not even close), so it’s not surprising that you come across more physical systems. High energy physicists are, by definition, interested in one physical system, though they may apply their “novel ideas” (in the sense of abstract theoretical ides) to many physical systems.
Which bring me to my main point, to correct somewhere where you’re off. Your statement about novel ideas is absurd, assuming by that you mean some more abstract ideas that may or may not be immediately applicable to already-known-to-exist real world physical systems. Regardless of the eventual fate of string theory’s ability to describe the one system high energy physicists are (by definition) interested in,
nearly all abstract conceptual breakthroughs in the last thirty years in gravity, quantum field theory, or string theory have been made by string theorists or people who at one point called themselves string theorists. In this sense, nearly all of the “intellectual heft” to use your phrase is coming out of theoretical high energy physics.
In my experience at top 20 U.S. institutions in physics, between giving seminars at many of them and researching as a member of a number of them, the reason “particle theory today is to first order irrelevant to the rest of physics and science” is because the average condensed matter theorists lacks the theoretical backbone to understand what we are talking about. The very best do, absolutely, I agree with you, but it’s just downright offensive and incorrect to make your claim in the way you have.
One of the big reasons that many physics departments are now treating particle theory as irrelevant is the incredibly arrogant behavior and attitude of theorists like yourself. Instead of showing some humility and admitting that things have not gone well in recent years, too many string theorists think that it’s a good idea to go on about how brilliant they are, how wonderful their “conceptual breakthroughs” are, and how the problem is just that non-string theorists are ignorant and stupid (i.e. lack “theoretical backbone to understand what we are talking about”). If you want to know why virtually no string theorists are getting jobs in the US, this has a lot to do with it.
Apologies for the tone of the previous post, I am a confident competent theorist, not an arrogant one. Sometimes this comes out the wrong way when I find someone’s arguments silly, incorrect and damaging, or offensive.
High energy physicists acknowledge some difficulties faced in using one of their theories (strings) to uniquely address issues in TeV scale physics. You and I have discussed this many times.
However, hiring in physics departments should be based on quality of work and scientific though, either conceptual and abstract or applying known ideas to a new system (or ideally new ideas to a new system). You yourself made the argument that it is made based on hurt feelings and perceived arrogance, and unfortunately this is sometimes true. High energy physicists readily acknowledge when real conceptual breakthroughs come from people in other fields (e.g. Kitaev, Wen (though formerly a string theorist), C. Kane, others, etc.), but when high energy physicists stress their many conceptual breakthroughs in the last 30 years, we are calling a spade a spade, not being arrogant. This is scientific endeavor; we should be honest about progress and it is a shame when good ideas and confidence in them are perceived as arrogance, particularly when this affects hiring decisions. Hiring of scientists should be based primarily on the quality of their ideas, not their sometimes bad attitudes.
Arrogance by itself isn’t the issue, if physics departments didn’t hire anyone arrogant, they’d be a lot smaller. What is the issue is that people don’t want colleagues who are both arrogant and delusional, convinced that their work is highly successful and important (when it isn’t), and that everyone around them is just too dumb to see this.
David you are wrong. axions are perfectly consistent with a vanilla CDM.
axion is a non-thermal relic so its perfectly fine. note that something as heavy as a WIMPzilla (worked on by Rocky Kolb et al) could also be a vanilla CDM.
again astrophysical observations alone provide no guidance for the mass or the interaction
“The worry is that if new physics doesn’t show up at this scale the governments won’t fund expensive new experiments to probe beyond the standard model.”
and they are right. i myself do not see the need of a multi-billion-$ collider to extend our energy range by a factor of 5 when there is no compelling argument that new physics should show up there.
in such a situation the money is probably better spent elsewhere. where? well, i currently don’t know, but people will have ideas i am sure.
what i perceive as the real problem here is the same problem that infests us at the individual level: the success-metric driven system that science is slowly turning into makes many of us think that the ultimate goal of science is to divert ever increasing streams of external funding into our direction. this is just plain wrong.
if we have learned all that we can reasonably hope to learn through current accelerator technique, then let’s be happy that we learned it and turn to something else. and if a thousand people have invested 3 decades of their lifes into this particular topic that turns out to be a dead end then it is a dead end still. no amount of money will ever convince nature to change its laws so as to make them accessible to us.
now please don’t get me wrong – i am not arguing against a next collider. i actually think that a linear collider “Higgs factory” would be well worth building at least. but i seriously dislike the gut reaction of many physicists that lament the decreased chances of future funding now that the SM is confirmed as if it was the ultimate goal of physics to finesse out as much tax money as possible.