Friedrich Hirzebruch 1927-2012

The German mathematician Friedrich (Fritz) Hirzebruch passed away a couple days ago, at the age of 84. Hirzebruch was perhaps the most important mathematician in the Germany of the postwar period, responsible for the founding of the Max Planck Institute in Bonn, as well as the yearly Bonn Arbeitstagung conference. The Mathematics Genealogy Project lists him as having 52 Ph.D. students and 368 descendants. There’s a wonderful interview and article about him at the Simons Foundation web-site.

Hirzebruch’s first great mathematical achievement was the proof in 1954 of the generalization of the classical Riemann-Roch theorem to higher dimensional complex manifolds, now known as the Hirzebruch-Riemann-Roch theorem. This used the new techniques of sheaf cohomology and was one of the centerpieces of the explosion of new results in geometry and topology during the 1950s. Further generalization of this led to the Grothendieck-Riemann-Roch theorem, and the Atiyah-Singer index theorem. Hirzebruch’s monograph on the subject Topological Methods in Algebraic Geometry was the essential textbook in this area for many years.

The last time I heard Hirzebruch talk was at the celebration of Atiyah’s 80th birthday in Edinburgh, where Hirzebruch gave a talk about his interactions with Atiyah. He displayed some of their correspondence from this period, which makes fascinating reading and is now available here.

With the loss of Raoul Bott a few years ago, and now Fritz Hirzebruch, the math and physics communities are deprived of two of the great figures who built parts of modern mathematics that appear crucially in the structure of the Standard Model. Much of this connection between math and physics remains a mystery, and it’s too bad they won’t be around to help make progress unraveling it.

Update: The New York Times has a very good obituary of Hirzebruch here.

Posted in Obituaries | 10 Comments

Welcome to the Multiverse

Multiverse Mania makes the big time this week, with a cover story Welcome to the Multiverse by Brian Greene in Newsweek. While the title indicates that the Multiverse is here and part of our scientific world-view, the subtitle is a bit cagier: “The latest developments in cosmology point toward the possibility that our universe is merely one of billions.”

The article is pretty uniformly a promotional piece for multiverse mania, although buried fairly deep in the piece is something a bit more skeptical:

because the proposal is unquestionably tentative, we must approach it with healthy skepticism and invoke its explanatory framework judiciously.

Imagine that when the apple fell on Newton’s head, he wasn’t inspired to develop the law of gravity, but instead reasoned that some apples fall down, others fall up, and we observe the downward variety simply because the upward ones have long since departed for outer space. The example is facetious but the point serious: used indiscriminately, the multiverse can be a cop-out that diverts scientists from seeking deeper explanations. On the other hand, failure to consider the multiverse can place scientists on a Keplerian treadmill in which they furiously chase answers to unanswerable questions.

Which is all just to say that the multiverse falls squarely in the domain of high-risk science. There are numerous developments that could weaken the motivation for considering it, from scientists finally calculating the correct dark-energy value, or confirming a version of inflationary cosmology that only yields a single universe, or discovering that string theory no longer supports a cornucopia of possible universes. And so on.

I don’t see how we’re anywhere near finding such a version of inflation or getting rid of the string theory landscape, so the only hope of getting any evidence against the multiverse seems to be to calculate the cosmological constant. The multiverse thus looks to be pretty much impregnable and immune to any conceivable scientific challenge. A few years ago, pieces like this would hold out hope that the LHC would discover something encouraging for the multiverse, but now the LHC isn’t even mentioned. The only possible positive evidence suggested is seeing remnants of bubble collisions in the CMB, but the very likely eventuality of not seeing such a thing doesn’t count as evidence against the multiverse idea.

So, I fear Brian is right: Welcome to the Multiverse, physics is going to be stuck with it for a very long time…

Posted in Multiverse Mania | 94 Comments

Higgs Update

The announcement of new Higgs results from the LHC is now scheduled for about a month and a half from now, July 7th, 9:30 and 10am Melbourne time, at ICHEP2012. The LHC is performing well, with nearly 2.5 fb-1 of integrated luminosity/experiment. With only 2-3 weeks more of data collection before the cutoff for what can be analyzed in time to be made public July 7, one can expect the July announcements to be based on perhaps 4-5 fb-1 per experiment. Rough estimates show that, combining last year’s 5 fb-1 at 7 TeV and this year’s expected data, if the SM Higgs really is there at 125 GeV, each experiment should see a signal of 4 sigma significance. This is not quite the 5 sigma significance traditionally set for a discovery claim, but very close.

It thus looks possible that a discovery claim will require combining the results from CMS and ATLAS. The LHC Higgs Combination Group has been hard at work for the last couple years, developing methods for combining results from the two experiments. This time, they will be ready to quickly combine all the data from the two experiments, and maybe this will be what gives the 5 sigma needed for CERN to claim discovery. I don’t know what the plan is for when they will be provided with the CMS/ATLAS data, or when they plan to announce a result.

The LHC-HCG is competing with Philip Gibbs, who today released a Higgs Combination Java Applet which allows anyone to produce their own data combinations. If the LHC-HCG can’t produce a combination by 10:30am July 7, CERN should perhaps consider getting Philip’s applet properly set up and having DG Heuer publicly press the right button, allowing CERN to claim the Higgs discovery before Philip does.

Posted in Experimental HEP News | 15 Comments

Latest from the Rumor Mill

There’s at least one thing about string theory that has changed dramatically since my book was written back in 2002 or so. At the time I accumulated various numbers showing the way hiring in particle theory at leading institutions in the US had been dominated by string theory hires. Overall, at that time about 20 people/year were getting tenure-track positions, roughly half in string theory half in phenomenology. This data came from the Theoretical Particle Physics Jobs Rumor Mill, and Erich Poppitz has done an excellent job of putting some statistics together based on this data (see here). In recent years Erich’s data shows a much lower number of such positions (10-15/year), due to some combination of the bad economy and lack of enthusiasm for particle theory by other physicists. The number of string theorists getting positions had come down to about 2/year, then down to only one last year.

The hiring season is not yet over and not all the data is in, but so far the Rumor Mill shows no job offers to string theorists at all. Job offers are going pretty exclusively to phenomenologists and cosmologists, with phenomenologists allowed to stray into formal theory if they work on topics related to N=4 SYM and its superconformal invariance (including the hot topic of amplitudes). Marcus at PhysicsForums has patched some of the Rumor Mill links for better accuracy.

One thing hasn’t changed though since 2002: there’s a much larger number of talented and accomplished candidates than there are jobs, and departments are playing it safe, offering the few jobs available only to people working in a small number of areas that are conventionally agreed to be “hot”. As always, if you’re working on some idea that’s not in the narrow mainstream, there’s no chance you’ll get hired into a permanent position at a US institution.

Update: There is one string theorist now with a job offer it seems, with Princeton making an offer to Simone Giombi, who works on the hot topic of higher spins. So, at least Princeton has not given up….

Posted in Uncategorized | 26 Comments

The Smell of SUSY

The implications of the failure to find SUSY at the LHC are beginning to sink into the particle physics community: the paradigm that dominated the subject for the past 30 years has collapsed in the face of experimental (non)-evidence, threatening to take down the life’s work of hundreds if not thousands of theorists. For some recent attempts to quantify what is going on, from some people with much more statistical expertise than me, see Philip Gibbs and Tommaso Dorigo. By now a significant number of SUSY analyses of the full 2011 dataset have been completed, with negative results. By the end of the year there will be more data, but just a factor of 2-3 more, at about 14% higher energy. To believe that these sorts of increases will turn no signal into a signal requires a willingness to engage in a rather large amount of wishful thinking. The 62% jump in 2014 to 6.5 TeV/beam is more significant, but it’s hard to see an argument for why this should do the trick, and the wait for these results will be discouragingly long, probably until 2015. How many SUSY enthusiasts will keep the faith?

A small number of theorists though still claim all is well, with one group producing a new paper claiming the full 5 inverse femtobarn results show Chanel No5 (fb^-1): The Sweet Fragrance of SUSY. Last year the same authors were claiming to detect Profumo di SUSY in the first inverse femtobarn, and argued that 5 times more data would be conclusive. To quantify the SUSY smells they are advertising, one can plot as a function of time their published predictions for the parameter $M_{1/2}$ which determines the gluino mass.

arXiv:1007.5100 455 GeV (“Golden Point”)
arXiv:1009.2981 455-481 GeV (“Golden Strip”)
arXiv:1111.0236 512 GeV (“Universe F-U2”)
arXiv:1111.4204 518 GeV (“Profumo di SUSY”)
arXiv:1203.1918 610 GeV (“Aroma of Stops and Gluinos”)
arXiv:1205.3052 708 GeV (“The Sweet Fragrance of SUSY”)

It’s rather easy to extrapolate to the future what these authors will be claiming the SUSY masses are, harder to extrapolate how they’ll be describing the smell. The rest of the particle physics community I suspect is already using very different terms for this.

Update: According to this report from Pheno 2012

As pointed out by Rahmat Rahmat (yes, that’s his name—in my notes I list him as Rahmat2) and Csaba Csaki, respectively from University of Mississippi and Cornell University, the LHC should have detected some signature of SUSY by now, especially if the MSSM is correct. As Csaki said, “SUSY is a wonderful woman who does not return my letters. It makes you wonder if she even exists!”

Posted in This Week's Hype | 19 Comments

Igor Frenkel 60th Birthday Conference

This week Yale is hosting a conference on Perspectives in Representation Theory, in honor of Igor Frenkel’s 60th birthday. I’m planning to take the train up there and attend some of the talks tomorrow and Wednesday. Frenkel has been a pioneer in the field of representation theory, especially in the area of infinite-dimensional algebras whose representations are significant for understanding low-dimensional QFT, string theory and topological QFT. He started his career in the early 1980s, with many important results relevant to understanding affine Lie algebras. These became central in the explosion of interest among physicists in 2d conformal QFTs after 1984 due to their importance in string theory. Frenkel’s later work has covered a wide variety of topics, with one theme that of trying to understand higher-dimensional generalizations of affine Lie algebras and their potential application to QFTs in higher space-time dimensions than 2. He has also promoted the themes of “categorification” and geometric incarnation of representations that are now central to much research in this area.

Pavel Etingof and other students and collaborators of Frenkel have put together a wonderful document, On the work of Igor Frenkel, which gives much more detail about the many topics of his mathematical research.

Update: Videos of the talks are now available here.

Posted in Uncategorized | 1 Comment

Why Does the World Exist?

With a lot of attention these days (see here for instance) going to an argument between philosophers and physicists about the “Why is there Something rather than Nothing?” question, this is the perfect time for Jim Holt’s new book Why Does the World Exist? An Existential Detective Story. While the argument between Krauss, Albert and their fellow combatants was mind-numbingly dumb, boring, narrow, petty and ill-mannered, Holt’s discussion of the topic is brilliant, entertaining, and wide-ranging as well as generous in spirit to all points of view. The only unfortunate thing here is that the book won’t be out until July. I’ve checked with him though, and he doesn’t mind if I write about it now, since I just read an advance copy. In July I’ll try to remember to repost this.

Holt first sets the stage by explaining some of the history of the question “Why is there Something rather than Nothing?” and why it’s one he finds compelling (as well as explaining why one might reasonably think otherwise…). He first ran across the question as a high school student fascinated by Existentialism and trying to read Heidegger’s Introduction to Metaphysics.

(Personal digression:

Around the same time I was also trying to read that book as a college freshman. I just found my old copy, where I underlined lots of things that seemed of significance at the time, as well as putting exclamation points around the paranoid nationalist ravings that appear at one point. I soon decided Heidegger wasn’t for me, and some years later learned of a personal reason to dislike him, see this from the Wikipedia entry on Heidegger and Nazism:

Heidegger also denounced or demoted several colleagues for being insufficiently committed to the Nazi cause.

On September 29, 1933, Heidegger leaked information to the local minister of education that the chemist Hermann Staudinger had been a pacifist during World War I. Heidegger knew this would cost Staudinger his job. The Gestapo investigated the matter and confirmed Heidegger’s tip. Asked for his recommendation as rector of the university, Heidegger secretly urged the ministry to fire Staudinger without a pension.

Hermann Staudinger was my great-uncle (on my father’s side of the family). Despite Heidegger’s efforts, he managed to keep his job, survived the war, and went on to win a Nobel prize. I never really got to know him since he died when I was rather young, but got to know very well his widow, my great-aunt Magda. Decades later, she was still quite upset by the Heidegger business.

End of personal digression.)

Holt then moves on to contemporary thinker’s takes on the subject, including entertaining descriptions of his trips to visit some of them, starting with some philosophers. These include Adolf Grünbaum who takes the position (to which I’m sympathetic…) that this is a pseudo-problem, and derisively refers to worries about Nothingness as the “ontopathological syndrome”. Another visit is to Richard Swinburne at Oxford, who goes for the “God did it” explanation.

The first physicist he visits is David Deutsch, also at Oxford, and Holt’s description of the experience and account of their conversation is quite wonderful. As you might expect, lots about the deep significance of quantum physics and Many-Worlds. After a discussion of Robert Nozick and his principle of fecundity (“all possible worlds are real”), it’s on to Alexander Vilenkin and the cosmological multiverse mania that has gotten so much attention from physicists in recent years. Here the sort of “something from nothing” that Krauss was discussing in his recent book comes into play.

The most intellectually powerful figure Holt talks to might be Steven Weinberg, who has this to say about the multiverse:

“Vilenkin is a really clever guy, and these are fascinating conjectures,” Weinberg said. “The problem is that we have no way, at present, of deciding whether they’re true or not. It’s not just that we don’t have the observational data – we don’t even have the theory.”

and this about string theory:

When I brought up string theory, a melancholy strain became detectable in Weinberg’s voice.
“I was hoping that with string theory things would fall into place much more rapidly than they have,” he said. “But it’s been rather disappointing. I’m not one of those people who bad-mouth string theory. I still think it’s the best effort we’ve made to step beyond what we already know, but it hasn’t worked out the way we were expecting it would.”

About Susskind’s claims that the Many-Worlds and string theory multiverses may be one and the same, Weinberg is having none of it, describing the two ideas as “completely perpendicular” and saying:

“I found it [Susskind’s claims] puzzling too,” he said. “I’ve spoken to other people about it, and they don’t understand it either”… “I don’t agree with Susskind on that,” Weinberg told me, “and I don’t know why he said it.”

The discussion with Weinberg brings up the whole question of a “Final theory”, a truly unified fundamental theory of physics, and what its significance for the question of existence might be. After Weinberg, Holt describes a meeting with Sir Roger Penrose, and explains Penrose’s “Platonism”, the philosophical point of view that mathematical objects actually are real things that exist (in some sense…). Penrose attempts to also bring the question of consciousness into this, which seems to me a mistake, but the questions raised here about the relation of mathematics and our fundamental ideas about the physical world are dear to my heart. To the extent that to me there’s a sensible question behind “Why is there Something rather than Nothing?”, it’s bound up with this great mystery of the origin of the fundamental laws of physics. Mathematics and physics have a completely unexpected and still not understood congruence at their deepest levels, and this mystery seems to me not only a very real one, but one that we can hope to further elucidate. I realized from Holt’s discussion that maybe my own mystical views on this subject are best described as “Pythagorean”. While he does a reasonable job of raising some of these issues, to me he dismisses them too quickly in favor of moving on to other topics much less worth taking seriously. But I would think that, wouldn’t I?

The later part of the book reverts to the philosophers. For his discussion with John Leslie about “axiarchism”, you can watch the two of them here on Bloggingheads. His final philosophical encounter is with Derek Parfit, in the imposing venue of All Souls at Oxford. Novelist John Updike is his last interviewee, and Updike also isn’t so happy with string theory:

“But this whole string theory business… There’s never any evidence, just mathematical formulas, right? There are men spending their whole careers working on a theory of something that might not even exist.”

Holt ends the book on a personal note, telling the story of the death of his mother and his return to the place he grew up. Throughout the book, he weaves in accounts of time spent in Paris, reading at Sartre’s Cafe de Flore, and wandering the city contemplating aspects of his great philosophical question, as well as life in general. Some might find this distracting and not so serious, but I enjoyed those parts of the book a lot. Of course, this may largely be due to the fact that I’m a sucker for Paris and know well and love the locations he was describing.

If you have even the slightest interest in the “Why is there Something rather than Nothing?” question, be sure to get yourself of a copy of this wonderful book when it comes out. My interest in the question has always been rather minimal (I got grief from some of my commenters recently for my dismissive attitude on the topic), but this didn’t keep me from getting a lot out of the book. It’s philosophy of a high level, pursued in an unusual and personal manner, and it’s a pleasure to follow along with the author as he tells a fascinating and thought-provoking story.

Posted in Book Reviews | 45 Comments

Phenomenology 2012

This week at the University of Pittsburgh the Phenomenology 2012 Symposium has talks reviewing the current situation in particle physics phenomenology. Not much new, but there is one plenary talk on string phenomenology, Cumrun Vafa’s Stringy Predictions for Particle Physics. Mostly this deals with Vafa’s ideas about F-theory “predictions” for the fermion mass and mixing matrices. Quite a few assumptions and rather little string theory (the predictions are “stringy”) goes into this, and except for the one recently measured neutrino mixing angle, these are all postdictions, not predictions. I suspect that most string theorists are no more sold on these as predictions of string theory than they are on Kane’s Higgs mass prediction. For example, Vafa’s colleague Andy Strominger in recent talks (and not so recent ones) gives string theory an “F” in the area of making unambiguous testable predictions, and I assume he’s well aware of Vafa’s work.

Pre-LHC, Vafa had been claiming F-theory predictions for SUSY at the LHC (see for example here, here and here). The most dramatic one, the focus of the Harvard Gazette story, was for a stable stau. One of the papers linked to has various detailed calculations for what such an stau would look like, with typical masses around 200 GeV.

At the conference on Monday, this talk gives recent CMS results relevant to such an stau, listing new mass limits of 314 GeV for a “cascade-decay” scenario, 223 GeV for a “pair-produced” one. Vafa only briefly mentions SUSY at the end of his talk, with his final slide “We will wait to see if SUSY plays any role at the weak scale!” I’m guessing he’s getting resigned to the idea that the answer is probably No.

Update: Also on the No SUSY news front this evening, there’s a preprint entitled Should we still believe in constrained supersymmetry? analyzing the current situation with one popular version of SUSY, the CMSSM, which concludes:

We find that LEP and the LHC strongly shatter our trust in the CMSSM (with M_0 and M_{1/2} below 2 TeV) reducing its posterior odds by a factor of approximately three orders of magnitude.

Posted in Uncategorized | 3 Comments

Half Hour to Midnight

Matt Strassler posts here about a recent panel discussion of phenomenologists talking about the implications of the latest results from the LHC. You can listen to the thing for yourself, and see what Matt has to say at his blog, but here are some things that I noticed from watching the discussion:

  • I don’t recall string theory even getting mentioned once. The extent to which string theory is now agreed to be thoroughly irrelevant to LHC physics is kind of striking. The few people like Kane claiming otherwise are being ignored as an embarrassment. If evidence for SUSY or extra dimensions had shown up, this would be very, very different.
  • Arkani-Hamed is probably the dominant personality in this field, and as Matt mentions, he embodies the conventional wisdom of the subject, expressing it at length and with brio. Back in 2005 he was claiming we would know whether SUSY solves the hierarchy problem within a year of LHC turn-on. Somewhat more than a year after LHC turn-on, in February 2011, he was saying that we’d have to wait until 2020. Now he’s putting it differently: it’s the “eleven and a halfth hour” for the idea of SUSY solving the hierarchy problem.

    The only remaining hope for this is that there’s a light stop, which has so far escaped detection, and gluinos just above the current bounds. He sounds willing to bet against this, and is arguing that the idea may soon be toast, to be finally put to bed as results from better stop searches come in over the next few months. If there’s no sign of SUSY in the 2012 data set, it sounds like he’s willing to concede that SUSY can’t be what stabilized the weak scale.

  • On the other hand, he argues that a 125 GeV mass for the Higgs is evidence for SUSY. Here the argument is that such a low-mass Higgs must be an elementary scalar, not the sort of thing you get in technicolor or extra-dimensional models. “SUSY” is here equated with the SM, without comment. I’m not sure what the reason for this is other than the sociological reason that it’s the dominant remaining paradigm for BSM physics, I don’t see a positive scientific argument.

    The 125 GeV value is also described as uncomfortably inconclusive for the idea of SUSY explaining the hierarchy. It’s somewhat too high for this, but not so high as to make it impossible.

  • If the SM continues unvanquished at LHC energies, it sounds like conventional wisdom will move to “it still has to be SUSY, even though our main motivation for SUSY is gone, since we don’t have any better ideas.” Best guess for the SUSY breaking scale will move up to be just high enough to be unobservable at the LHC.
  • Clearly a lot of theorists are looking at the failure of the last quarter century of BSM ideas and trying to figure out what else they can work on. The idea of “back to working on QCD” was repeatedly mentioned. Arkani-Hamed has over the past few years dropped BSM work and moved to a radical speculative program about new ideas for QFT based on a different point of view about amplitudes. One of the speakers jokingly accused him of becoming a mathematician. Maybe that’s where things are going…
Posted in Uncategorized | 51 Comments

Correction

A while ago I wrote here about a recent “conference of Nobel Laureates” convened by Jeffrey Epstein in the Virgin Islands. This was based upon stories in boston.com (Boston Globe) and marketwatch.com (Wall Street Journal), which were based upon this press release from Epstein’s foundation. The foundation also has stories about this on their web-site (see for instance here).

Looking into it more carefully, it appears that everything in the press release refers to something that happened not this spring, but back in 2006. More details about the 2006 event are in a piece by Lawrence Krauss at Edge.org. The pictures and quotes are the same as in the 2012 press release. Still available on-line here is a schedule of talks from the 2006 conference.

When I saw this I was wondering why it didn’t give a specific date for the conference, and how Epstein had gotten the same prominent people as in 2006 to return this year, despite his well-known problems with the law in the interim. I have no idea why the Epstein Foundation recently issued this peculiar press release.

Epstein is a rather curious story, for some background, see this New York Magazine profile from 2002, and this Harvard Crimson piece about him when he donated $30 million to establish a Program for Evolutionary Dynamics in the Harvard math department. At the time of the 2006 conference, Epstein was under investigation by the police for having hired under-aged women for sex, and he ended up serving 13 months in prison as a result. He was arrested soon after the conference. Some recipients of donations from Epstein returned the money, but not Harvard.

Update: About the Program in Evolutionary Dynamics, I should point out that after losing Epstein to the penal system, it has landed on its feet, with a $10.5 million grant from Templeton.

For another article about Epstein, from 2003, see this at Vanity Fair.

Update: Another strange Epstein press release has appeared: Jeffrey Epstein’s Involvement With the Edge Foundation. It’s an endorsement of John Brockman and his Edge Foundation, with text that was also posted on all sorts of odd internet sites back in 2010. Very strange…

Posted in Uncategorized | 7 Comments