Witten Interview

Posted on May 2, 2019 by woit

Graham Farmelo has posted a very interesting interview he did with Witten last year, as part of his promotion of his forthcoming book The Universe Speaks in Numbers.

One surprising thing I learned from the interview is that Witten learned Calculus when he was 11 (this would have been 1962). He quite liked that, but then lost interest in math for many years, since no one gave him more advanced material to study. After years of studying non math/physics subjects and doing things like working on the 1972 McGovern campaign, he finally realized physics and math were where his talents lay. He ended up doing a Ph.D. at Princeton with David Gross, starting work with him just months after the huge breakthrough of asymptotic freedom, which put in place the final main piece of the Standard Model.

If only back in 1962 someone had told Witten about linear algebra and quantum mechanics, the entire history of the subject could have been quite different. It seems quite possible that within 5 years he would have picked up quantum field theory and maybe started thinking about Yang-Mills generalizations of QED, perhaps, at 16, beating Weinberg and Salam to the electroweak theory. Surely he could have figured out how to do one loop calculations in gauge theory, beating Gross/Wilczek/Politzer to asymptotic freedom and a Nobel prize, possibly a few years early. If he had done this at Princeton, he would have overlapped with John Schwarz, who surely would have then been more interested in pursuing gauge theory than string theory. So, no superstring theory or 1984 “revolution”, and who knows what different sort of path the history of the field would have taken.

A lesson for all parents: if your child is an off-the-scale genius, learning Calculus at age 11, don’t even think about trying to give them a normal childhood. Push them, hard, to skip grades, get to college/grad school early. Do whatever it takes.

I did though find some of the later parts of the interview quite depressing. While acknowledging that neither he nor anyone else has been able to figure out what string theory actually is, this hasn’t shaken Witten’s faith that it’s the only viable path towards a unified theory. Most disturbing, on the topic of the landscape he says that he has gone from finding it upsetting to reconciling himself to the idea. For years, whenever asked about how evidence could be found for string theory, he would point to the naturalness arguments indicating that something like SUSY had to happen at the electroweak scale. Now that the LHC has falsified this and there’s nothing to point to as any sort of “test of string theory”, he shows no signs that this falsification has in any way shaken his faith.

Looking to the near future, he’s most optimistic about the “It from Qubit” business. Maybe he’s right and something will come of this, but I’ve seen no indication of a path to a unified theory in this direction (how do you get the Standard Model? Or has he just completely given up on that?).

I don’t have time right now to transcribe the most relevant portions of the interview, might find time later, or maybe Farmelo will make available a transcription.

Update: As explained in the comments, the advice to parents was not meant to be taken seriously. No, your child is not going to grow up to be Edward Witten, and they do not need to hurry up to revolutionize physics before it is too late.

Sabine Hossenfelder had posted a transcript of the interview here. I’ll add some extracts and some more comments about the interview.

About the landscape:

These two puzzles although primarily the one about gravity which was discovered first are perhaps the main motivation for discussions of a cosmic landscape of vacua. Which is an idea that used to make me extremely uncomfortable and unhappy. I guess because of the challenge it poses to trying to understand the universe and the possibly unfortunate implications for our distant descendants tens of billions of years from now. I guess I ultimately made my peace with it recognizing that the universe hadn’t been created for our convenience.

GF [00:20:43] So you come to terms with it.

EW [00:20:45] I’ve come to terms with the landscape idea and the sense of not being upset about it. As I was for many years.

GF [00:20:49] Really upset?

EW [00:20:50] I still would prefer to have a different explanation but it doesn’t upset me personally to the extent it used to.

GF [00:20:56] So just to conclude what would you say the principal challenge is all down to people looking at fundamental physics.

EW [00:21:01] I think it’s quite possible that new observations either in astronomy or accelerators will turn up new and more down to earth challenges. But with what we have now and also with my own personal inclinations it’s hard to avoid answering new terms of cosmic challenges. I actually believe that string slash M theory is on the right track toward a more deeper explanation. But at a very fundamental level it’s not well understood. And I’m not even confident that we have a good concept of what sort of thing is missing or where to find it.

If you theory is not well understood, you don’t even know what sort of thing is missing, and a multiverse is being invoked to explain away why it can’t be tested, the situation seems clear: you have a failed theory. Yes, failure may be personally upsetting to you, but, that’s science.

GF [00:23:20] There’s a famous book about night thoughts of a quantum physics. are there night thoughts of a string theorists is where you have a wonderful theory list developing you know unable to test it. Does that ever bother you.

EW [00:23:31] Of course it bothers us but we have to live with our existential condition. But let’s backtrack 34 years. So in the early 80s there were a lot of hints that something important was happening in string theory but once Green and Schwarz discovered the anomaly cancellation and it became possible to make models of elementary particle physics unified with gravity. From then I thought the direction was clear. But some senior physicists rejected it completely on the grounds that it would supposedly be untestable. Or even have cracked it would be too hard to understand. My view at the time was that when we reached the energies of the W, Z and the Higgs particle we’d get all kinds of fantastic new clues.

EW [00:24:11] So. I found it very very surprising that any colleagues would be so convinced that you wouldn’t be able to get important clues that would shed light on the validity of a fundamental new theory that might in fact be valid. Now if you analyze that 34 years later I’m tempted to say we were both a little bit wrong. So the scale of clues that I thought would materialize from accelerators has not come. In fact the most important clue possibly is that we’ve confirmed the standard model without getting what we fully expected would come with him. And as I told you earlier that might be a clue concerning the landscape. I think the flaw in the thinking of the critics though is that while it’s a shame that the period of incredible turmoil and constant experiment and discovery that existed until roughly when I started graduate school hasn’t continued. I think that the progress which has been made in physics since 1984 is much greater than it would have been if the naysayers had been heeded and string theory hadn’t been done in that period.

“34 years later I’m tempted to say we were both a little bit wrong”??? No, others had good arguments and were right about this (string theory is untestable and has nothing to do with LHC-scale physics), and you had bad arguments and were quite wrong. That this clear result is not being acknowledged and is having no effect on faith in string theory is disturbing.

Update: For another interview with an influential theorist, Sean Carroll has an interview with Leonard Susskind. I don’t think this is a good thing, but Susskind has been very influential in blazing the path that Witten now seems headed down (invoke the multiverse to justify giving up on unifying particle physics, hope very general “it from qubit” considerations will explain gravity). The interview explains in detail Susskind’s point of view.

Update: Farmelo has another interview with a string theorist up, this time it’s Michael Green. When asked if he’s troubled by string theory not being experimentally testable, Green says (19:20):

I don’t think at the moment there’s anything directly to test, because we don’t know what its predictions are.

and says that string theory should really be called “string (not yet a) theory”. Earlier (16:40), he explains

The ingredients of something are there, but it’s clearly not formulated in the right language, and because it’s not formulated in the right language, we don’t really know how to even make sense of its predictions. It doesn’t have any really genuine rigorously derived predictions yet.

Green has been working on string theory for forty years, an entire professional lifetime during which string theory has gone from a relatively simple “(not yet a) theory”, with a true theory seeming not far away, to a much more complicated “(not yet a) theory”, with no progress towards an actual theory in sight. Farmelo doesn’t ask the obvious question of why people shouldn’t interpret this story straightforwardly as the story of a failed speculative idea that never worked out.

Posted in Multiverse Mania, Uncategorized | 38 Comments

The Scientific Attitude

Posted on April 29, 2019 by woit

Just when I thought I was done for now with the “falsifiability” business, in our local book store I found a new book, The Scientific Attitude: Defending Science from Denial, Fraud and Pseudoscience, by Lee McIntyre. This won’t be a review of the whole book, much of which is concerned with what to do about the serious problem of the role of science in our increasingly post-truth society. I’ll just address the few pages of the book that deal with string theory, in which a quote from me appears in a misleading way.

The problem here is almost exactly the same as the problem with the Symmetry article discussed in the last posting. Both authors believe that string theory is a conventionally predictive theory, one with predictions that just happen to be hard to test. According to them, critics of string theory just don’t understand that there can be value in a theory which is testable in principle, even if a practical test is far away. Unlike the Symmetry piece, McIntyre at least names critics and links to their words, writing:

If one reads these kinds of criticisms closely one finds careful phrasing that string theory “makes no predictions about physical phenomena at experimentally accessible energies” and that “at the moment string theory cannot be falsified by any conceivable result.”23 But these are weasel words, born of scientists who are not used to taking seriously the distinction between saying that a theory is “currently” testable versus whether it is “in principle” testable. The practical limitations may be all but insurmountable, but philosophical distinctions like demarcation live in the difference.

The quoted words are mine, with footnote 23 referring to my 2002 article in American Scientist. Of course I was and am well aware of the distinction between testable “in principle” and “currently”. Bizarrely, the author has chosen to edit out from what I wrote the sentence that precisely addresses the issue I’m supposedly weaseling on. Here’s the full quote:

String theory not only makes no predictions about physical phenomena at experimentally accessible energies, it makes no precise predictions whatsoever. Even if someone were to figure out tomorrow how to build an accelerator capable of reaching the astronomically high energies at which particles are no longer supposed to appear as points, string theorists would be able to do no better than give qualitative guesses about what such a machine might show. At the moment string theory cannot be falsified by any conceivable experimental result.

As the deleted language make clear, by “any conceivable experimental result” I was making a claim about “in principle”, not “currently”. Furthermore, near the beginning of the article I explain the problem of principle:

First, string theory predicts that the world has ten space-time dimensions, in serious disagreement with the evidence of one’s senses. Matching string theory with reality requires that one postulate six unobserved spatial dimensions of very small size wrapped up in one way or another. All of the predictions of the theory depend on how you do this, but there are an infinite number of possible choices, and no one has any idea how to determine which is correct.

This article started out as an early 2001 arXiv posting and was published in early 2002, about a year before the now famous KKLT claim to have a string theory model with fully stabilized moduli. Back then, the problem I was pointing to was the basic one that, to have a self-consistent string theory model that you can confront, in principle, with experiment, you need to solve the problem of “moduli stabilization”. 6d compactifications come in families with a lot of parameters (the “moduli”) governing their size and shape, and the physics depends crucially on those parameters. You need to somehow give the moduli dynamics, and get a ground state with a correct fine-tuned vacuum energy.

KKLT claimed they could do this, but with an exponentially large “landscape” of solutions that removes the ability to get well-defined predictions from the theory. Their construction is so complicated, and non-perturbative string theory so poorly understood, that it remains controversial to this day whether these are really solutions to whatever the conjectural well-defined version of string theory might be. This is what the current “Swampland” argument is about.

I’ve put together a FAQ entry answering the Doesn’t string theory make predictions at very high energy? question. What causes all the confusion here is the common claim from string theorists that “string theory is testable at high energy”. If you ask them to tell you what the “test” is, they tell you about one of the characteristic features of the perturbative superstring (Veneziano amplitude, Regge trajectories, 10 space-time dimensions). What they are really saying is “if we did experiments at a high enough energy scale and saw one of these characteristic phenomena, we would have a successful test of string theory”, which is true enough, but not a specific, falsifiable prediction. What they are not telling you is that they are ignoring the compactification problem as well as that of not having a well-defined non-perturbative theory, and that many “string theory” models wouldn’t exhibit these characteristically perturbative features.

The main point of the new book seems to be to argue that a better way to characterize science is by whether those supposedly engaging in it are exhibiting the “scientific attitude”, which

can be summed up in a commitment to two principles:
(1) We care about empirical evidence.
(2) We are willing to change our theories in light of new evidence.

It seems to me there are lots of problems with this formulation. Sticking to the string theory question, undoubtedly string theorists “care about empirical evidence” and would like to have some. The problem though is they don’t have any, and don’t have any significant prospects for getting any. As for being willing to change one’s theories in light of new evidence, if there’s no new evidence, your willingness to change your theory won’t ever get tested.

My impression is that most people, this author included, are just fundamentally unwilling to believe that, given the high scientific profile of “string theory”, it could really have a serious problem of being inherently untestable. The technical issues involved are so formidable that non-experts don’t have any hope of understanding them. But there really is a serious problem here, and those who worry about the string theory fiasco damaging the credibility of science in a dangerously post-truth world are right to be worried.

Posted in Book Reviews | 16 Comments

Falsifiability and Physics

Posted on April 23, 2019 by woit

Symmetry magazine today published an article on Falsifiability and physics, yet another in the genre of defense of current HEP theory against its critics. As usual, only defenders of the status quo are quoted, the critics remain unnamed and their actual arguments ignored. I don’t completely understand this journalism thing, but if you are writing about a controversy, aren’t you supposed to contact people on both sides?

The problems with this article begin with the misleading subtitle: “Can a theory that isn’t completely testable still be useful to physics?” The problem here is not theories that aren’t “completely testable”, but theories that aren’t testable at all, that make no testable predictions at all.

The article starts out by discussing Popper and the supposed “falsifiability” criterion for what is and isn’t science, leading up to:

But where does this falsifiability requirement leave certain areas of theoretical physics? String theory, for example, involves physics on extremely small length scales unreachable by any foreseeable experiment. Cosmic inflation, a theory that explains much about the properties of the observable universe, may itself be untestable through direct observations. Some critics believe these theories are unfalsifiable and, for that reason, are of dubious scientific value.

Who are these “some critics”? Where do they say that the reason there is a problem with string theory is “unfalsifiability”? For the case of one critic I’m pretty familiar with, chapter 14 of his book is all about how “falsifiability” is not something that can be used to decide what is science and what isn’t.

We’re then told that:

At the same time, many physicists align with philosophers of science who identified flaws in Popper’s model, saying falsification is most useful in identifying blatant pseudoscience (the flat-Earth hypothesis, again) but relatively unimportant for judging theories growing out of established paradigms in science.

Unclear who “many physicists” are, who the “philosophers of science” are, and what flaw in Popper is being referred to.

In an odd move, the article then turns to the topic of SUSY, where the problem isn’t that well-advertised SUSY models (with electroweak scale SUSY breaking solving the “naturalness” problem) aren’t falsifiable, it’s that the LHC has falsified them. As usual in science, if your model gets falsified, instead of giving up and doing something else you can change your model to something less desirable that hasn’t been falsified (SUSY models with symmetry broken at higher energy scales) and keep on going. This is though what philosophers of science call a “degenerating research program”, which is not a good thing.

There’s more in the rest of the article, but actual critics remain invisible and their actual arguments unaddressed.

Update: Will Kinney has some appropriate comments.

Update: Massimo Pigliucci has posted here his contribution to the “Why Trust a Theory?” volume, which discusses “falsifiability” and the “String Wars”.

Posted in Uncategorized | 33 Comments

This and That

Posted on April 16, 2019 by woit

Since you’ve read about the black hole image elsewhere, here are a few other items that might be of interest:

  • I was sorry to hear today of the death on April 11 of Geoffrey Chew. Throughout the 1960s, Chew’s S-matrix/bootstrap philosophy was the dominant paradigm in high energy theory. It went into eclipse with the success of gauge theories in the early 1970s, but in recent years the (S-matrix) “amplitudes” program has to some degree revived it a bit, with hopes that it may be relevant to formulating quantum gravity.
  • I thought the string wars were at times rather brutal, but it seems that they may have been a picnic compared to what astronomers get up to when there is a lot of money involved. See here for the bizarre story of what happened to Richard Easther when he started criticizing the plan for a New Zealand component of the Square Kilometer Array.
  • For some recent and upcoming conference sites giving an idea of what is new in math and physics, Microsoft is hosting Physics Meets Machine Learning, the Eighth New England String Meeting had lots of interesting talks, hardly any strings to be seen, and MSRI last week hosted a “Hot Topics” workshop on Recent Progress in the Langlands Program.

For some news related to new books, there’s:

  • Lee Smolin has a new book out, Einstein’s Unfinished Revolution, arguing that quantum mechanics is likely incomplete, since it continues to lack a successful “realist” version. He will be giving a public lecture about this at Perimeter tomorrow.
  • John Baez advertises on Twitter a forthcoming volume about “New Spaces in Mathematics and Physics”. For some of the content, see here. Also, the original conference these articles are based on has videos here.
  • I’m looking forward to seeing Graham Farmelo’s forthcoming The Universe Speaks in Numbers, about which I suspect there will be parts I’ll strongly agree with, others about which I’ll equally strongly disagree. The book evidently is based mainly on interviews, some of which Farmelo is putting up on his website. Jon Butterworth has a review this week in Nature, entitled A struggle for the soul of theoretical physics. He describes the Farmelo book as “a riposte” to critiques from a group I’m identified as being part of, but I have to keep pointing out that my point of view is not at all that the problem with string theory/supersymmetry has been “too much math”. I think progress in fundamental physics is going to require more mathematics, not less.
  • There’s a new edition of the Kiritsis String theory in a Nutshell textbook available from Princeton. Looking at the introduction, I’m glad to see that Kiritsis points out the problem with the usual “string theory works, at the Planck scale” argument:

    A big “hole” in string theory has been its perturbative (only) definition. With the advent of nonperturbative dualities, it was hoped that this shortcoming can be bypassed.Although the nonperturbative dualities have shed light in many obscure corners of string theory (obscured by strong-coupling physics), they never managed to bypass the Planck barrier. The Planck scale is always duality invariant, and any dual description is well defined for energies well below that Planck scale. We have no clue from string theory what happens near or above the Planck scale, as the relevant physics looks nonperturbative from any point of view.

    I’ve added this to this FAQ entry.

Posted in Uncategorized | 23 Comments

Why Trust a Theory?

Posted on April 5, 2019 by woit

I noticed today that Cambridge University Press has recently published Why Trust a Theory?, a volume of articles based on a December 2015 conference held in Munich. The book is available online here (if your university is paying for it…), and preprint versions of many of the contributions are on the arXiv.

The conference had its origins in a piece published a year earlier in Nature by George Ellis and Joe Silk, entitled Scientific method: Defend the integrity of physics. Ellis and Silk made a forceful case that widely advertised but inherently untestable string theory and multiverse research does damage to the public understanding of science and is a threat to the credibility of science at a time it is under attack. The piece suggested:

A conference should be convened next year to take the first steps. People from both sides of the testability debate must be involved.

Looking through the proceedings volume, there’s lots of abstract discussion of philosophy of science and some diversity of points of view on the multiverse. When it comes to string theory though, the organizers interpreted “people on both sides” to mean bringing in one person willing to point out that there is a problem with string theory, and an army of string theorists to defend the theory. On the issue of the problems of string theory, the volume contains nearly 100 pages of pro-string theory hype, from Polchinski (two contributions), Silverstein, Kane and Quevedo. As usual with Kane, there’s a string theory “prediction” of the gluino mass (1.5 TeV +/- 10-15%) which has already been falsified. All I could find on the side of substantive criticism of string theory was in Carlo Rovelli’s contribution (preprint version here), and mainly in a single paragraph:

String theory is a living proof of the dangers of excessive reliance on non-empirical arguments. It raised great expectations thirty years ago, promising to compute all the parameters of the Standard Model from first principles, to derive from first principles its symmetry group SU(3)×SU(2)×U(1) and the existence of its three families of elementary particles, to predict the sign and the value of the cosmological constant, to predict novel observable physics, to understand the ultimate fate of black holes, and to offer a unique, well-founded unified theory of everything. Nothing of this has come true. String theorists, instead, have predicted a negative cosmological constant, deviations from Newton’s 1/r^2 law at sub-millimeters scale, black holes at the European Organization for Nuclear Research(CERN), low-energy super-symmetric particles, and more. All this was false. Still, Joe Polchinski, a prominent string theorist, writes [7] that he evaluates the Bayesian probability of string to be correct at 98.5% (!). This is clearly nonsense.

I won’t spend more time here discussing the conference and the articles in this volume, mainly because I’ve already written a lot about this in previous posts. For a contemporaneous discussion of the conference and Polchinski’s String Theory to the Rescue paper, see here and here. There are also interesting blog posts about the conference from Massimo Pigliucci, see here, here and here, and a Quanta piece by Natalie Wolchover here. For a discussion of Sean Carroll’s Beyond Falsifiability contribution, see here (and discussion here and here). For a discussion of Eva Silverstein’s contribution, see here.

Update: A few more links to material about the Munich conference: Jim Baggott here and here, Andrew Gelman here, Davide Castelvecchi here, and the conference website (with videos) here.

Update: Looking at the Preface, I notice that the editors claim:

Additional contributions were solicited by the editors with the aim of ensuring as full and balanced presentation as possible of the various positions in the debate.

With regards to string theory, the one additional contribution in the volume is from string theorist Eva Silverstein, so evidently the editors felt that balance required yet more on the pro-string theory side….

Update: I mischaracterized Polchinski’s calculation of the probability that string theory is correct as 98.5%. More accurately, he claims that the probability is “over 3 sigma” (i.e. over 99.73%).

Update: I finally got around to watching the videos of the panel discussions at the workshop (all videos available here). What most struck me about these discussions was the heavily dominant role of David Gross, who was on two of three panels, participating from the audience in the third. On the panels he was on, Gross was speaking far more than anyone else, and rarely if at all would anyone disagree with him. Gross’s point of view is that there is a testability problem with the multiverse, but all is well with string theory (although probably not at Polchinski’s “over 99.73% sure to be true” level). He’s a powerful intellect and a forceful speaker, so it’s not surprising that no one would take him on. But on the topic of string theory I think there are very serious problems with many of the claims he makes (for his arguments of 15 years ago, see the first substantive post of this blog), and the organizers should have found someone willing to challenge him on those.

Posted in Book Reviews | 26 Comments

Not Even Wrong 2.0

Posted on March 31, 2019 by woit

This blog has just passed its 15th anniversary, and there hasn’t been a lot of change in format since the first postings in March 2004 (there hasn’t been a lot of change in string theory either, but that’s a different topic…). I’ve been hearing a lot in recent years from people who have urged me to update the format of the blog, moving to formats more in tune with the way people now use the internet. One innovation in recent years has been that the blog content is available through Apple News.

I’ve decided to follow some more of the advice I have been getting, and have started up a Not Even Wrong Facebook site. No longer will you have to navigate to my WordPress site to access the blog content, instead it will be available the same way most people are now getting their news, through your Facebook News Feed. This will make it much more convenient for everyone to get notified about new posts and share these with others. I’m looking forward to the expanded readership and connections to the rest of the world that becoming part of the Facebook information eco-system will provide.

Update: Just unblocked a lot of comments that somehow were stuck in a moderation queue. Some people don’t seem to understand that for an international blog like this, the date is best calculated according to UTC.

The uniformly hostile response here to the Facebook idea has been extremely reassuring. No, I don’t intend to move the blog to Facebook. The fact that a sizable fraction of the US population in recent years has been getting its news off their Facebook News Feed seems to be one of the main factors in the 2016 collapse of democracy here, and the same thing is happening all over the world. This has also significantly moved along the ongoing destruction of the economic viability of conventional journalism. Going through the exercise of putting up a Facebook site made me aware of some aspects of how Facebook works I’d never realized. For example, on a Facebook post you can only hyperlink text to other Facebook material, not to the outside world.

It has become all too clear just how ugly the world created by Facebook is, that it is a sociopathic organization, and a danger to a healthy democracy. If you must stay in contact with friends and family this way, avoid any engagement with anything else on the Facebook site. Best would be to delete your Facebook account, now.

Update: For a book-length explanation of why you should be concerned about Facebook, see Roger McNamee’s Zucked, reviewed here.

Posted in Uncategorized | 116 Comments

This Week’s Hype

Posted on March 31, 2019 by woit

This week’s hype comes to us courtesy of Scientific American, which, based on this preprint, tells us: Found: A Quadrillion Ways for String Theory to Make Our Universe.

As usual in these things, the only physicists quoted are the authors of the article, as well as some others (Cumrun Vafa and Washington Taylor) who are enthusiastic about the prospects for getting the Standard Model out of “F-theory”. No one skeptical of the idea of F-theory compactifications of string theory (such theorists would not be hard to find…) seems to have been consulted. If such a person had been consulted, he or she might have pointed out:

  • Models like this have been around for over two decades, see for instance this from 23 years ago.
  • They have always come with claims that some sort of connection to experiment was right around the corner. A decade ago there were papers like this one (and promotional pieces like this one) explaining F-theory “predictions” for what would be seen at the LHC, “predictions” that never worked out.
  • This new work doesn’t even bother trying to make “predictions”. It just works backwards, trying to match the crudest aspects of Standard Model, ones determined by a small set of small integers. Given the huge complexity and number of choices of these F-theory constructions, that some number of them would match this set of small integers is not even slightly surprising.
  • The authors seem to argue that it’s a wonderful thing that they have found quadrillions of complicated constructions with this kind of crude match to the SM. The problem is that you don’t want quadrillions of these things: the more you find, the less predictive the setup becomes. What’s being promoted here is a calculation that not only predicts nothing, but provides evidence that this kind of thing can’t ever predict anything. A peculiar sort of progress…

Update: This hype has now been supplemented by the now common phenomenon among string theorists of having their university’s press office put something out promoting string theory. This time it’s the University of Pennsylvania, with a headline assuring us that their university’s physicists are Making sense of string theory, with a discovery that “might change the course of the field.”

Posted in This Week's Hype | 8 Comments

Some Quick Items

Posted on March 25, 2019 by woit

A few quick items:

  • This past weekend I went to see the new film Out of Blue, which sounded promising: a murder mystery based on a Martin Amis book, set in New Orleans, starring Patricia Clarkson, with a plot involving lots of deep ideas about physics. Unfortunately, the film was pretty awful, for a review from a professional, see here. There was a lot of physics, I think intended to add philosophical depth, but it was just the usual Schrodinger’s cat, black holes, dark matter, multiverse mumbo-jumbo. The Variety reviewer appropriately ends her review with

    It makes one feel a little bit embarrassed for the multiverse.

  • Sticking to the sophomoric, I was searching through old boxes of stuff and turned up a paper I wrote, Quantum Theory and Reality, about the interpretation of quantum mechanics for an expository writing class during my first year (1976) of college. While it was my first year, I did have sophomore standing. Rereading the thing, I’m glad to see that I’ve learned a few things since my sophomore year, but on the other hand, some of my views haven’t changed (I still don’t think “hidden variables” work…).
  • Ethan Siegel at Forbes has This is Why The Multiverse Must Exist. By now, all I can do is refer to this FAQ.
  • Results using the full datasets of the LHC Run 2 are starting to appear, some of them in talks given at last week’s Moriond conference in La Thuile. There are summaries available from CMS, ATLAS and LHCb. Referring to the absence of any significant evidence of new particles or anything inconsistent with the SM, in these results and in a new result from BELLE, Jester comments:

    La Thuile: Where Hopes Melt Away.

    This week, there’s another ongoing “Winter” HEP conference (“Winter” I guess means you can go skiing…), at Aspen.

  • I was sorry to hear of the recent death of Jean-Marc Fontaine, at the age of 74. Frank Calegari has an appreciation of Fontaine and his work here.
  • For more positive recent developments in arithmetic geometry, I recommend Peter Scholze’s lecture series at UCLA on Prismatic Cohomology, discussed by Terry Tao here. In related news, this week at MSRI there’s an interesting workshop on Derived Algebraic Geometry and its Applications.
  • For an interview with Eric Weinstein, who, like Sabine Hossenfelder, is always thought-provoking on the great question of why fundamental physics has gone off the rails, see here. I think he may have a point about Tom Lehrer.
Posted in Film Reviews, Uncategorized | 13 Comments

The Shape of a Life

Posted on March 23, 2019 by woit

I just finished reading The Shape of a Life, which is the great geometer Shing-Tung Yau’s autobiography, co-authored with Steve Nadis. It’s quite fascinating, and an essential read for anyone interested in the history of modern mathematics. Yau has been for a long time a central figure in the field of geometric analysis, so this is in some ways as much an autobiography of the subject as well as of the man.

Back in 2010 I wrote here about an earlier volume by Yau and Nadis, The Shape of Inner Space. What I really liked about that book (and discussed in some detail there) was the autobiographical material about Yau. Much of the book though was devoted to topics like string theory attempts to get physics out of Calabi-Yaus, with a discussion that was detailed and accurate, but to my mind often not of great interest (since these attempts don’t work…).

The new book seems to have been written specifically to appeal to me, greatly expanding the autobiographical material of the earlier book, while limiting the discussion of dubious speculative physics. There is still a fair amount about physics, but this time more focused on another of Yau’s interests, the mathematical theory of general relativity.

The book begins with the story of Yau’s early years in Hong Kong, how he managed to survive an impoverished childhood, avoid becoming a duck farmer, and ultimately find a way to get to the US and graduate study in mathematics at Berkeley. It’s a compelling story of that period and those places. It’s also about the best example I can think of to show how bringing someone with undeveloped talent into the environment of a first-rate research university can change their life, liberating them to accomplish great things, with dramatic impact on their intellectual development as well as that of a whole field.

Yau has always had a deep interest in the history of mathematics, and the story he tells of his intellectual development explains in detail how his own work and ideas grew out of earlier strands of thought. Even as a graduate student, he had started to develop the point of view that has been so fruitful in geometric analysis, using the study of non-linear partial differential equations to prove theorems about geometry and topology. Besides his proof of the Calabi conjecture, this ultimately led to the proof of the Poincare conjecture, a story Yau explains in detail.

Over the years Yau has been involved in various controversies over priority for mathematical results. In this book he doesn’t shy away from discussing these, but generally gives a measured explanation of his point of view on what happened. There’s also a fair number of often amusing stories about mathematicians and the math community that liven up the history. For one sort of example, there are Yau’s descriptions of his culture clash with the long-haired, pot-smoking Berkeley of 1969. For another, here’s a story about Richard Hamilton (of whom Yau has a very high opinion) and his 1982 lectures at the IAS:

Hamilton, who had come from Cornell, stayed for a week in an IAS apartment. At the end of his stay, the chief math secretary was livid because Hamilton had made a huge mess of the apartment, and it took a long time to clean up the place. On the other hand, he had given some wonderful talks, and collaborations between Hamilton, my students, and me picked up from that time forward. So, on balance, his visit would have to be called a great success. Hamilton may have posed some challenges to the cleaning and janitorial staff, but he had posed even more consequential challenges to the mathematics community, some of which were taken up by members of my group.

Yau is generally considered a major figure not just for his research, but also as a politician of the mathematics community, deeply involved for many years in efforts to build or expand research centers, here and in China. A recent example is the creation of the CMSA at Harvard. He has a lot to say about the stories of these efforts, and he definitely does not do so with the style of the politician careful to offend no one. In this book you get Yau’s honest, unvarnished version of what happened, as well as his analysis of some general problems, and I won’t be surprised if some people take offense at this material.

One thing there’s perhaps a bit too much of in the book are the references to his conflicts with his advisor Shiing-Shen Chern (which I’d somehow never heard about before). A major touching theme though throughout the book is that of fathers, sons and traditions of filial piety. There’s a lot about Yau’s father (who Yau very much looked up to) and quite a bit about his sons. On the mathematical side, there’s a lot about his numerous students, many of whom have gone on to important academic careers. As his academic father, Chern also fits into this theme, although not so felicitously. At the end of the book, Yau looks forward to his own future as, like Chern before him, the grand old man of the field. He’s planning more teaching and less research, and taking pleasure in his mathematical legacy and progeny.

Posted in Book Reviews | 7 Comments

This Month’s Hype

Posted on March 14, 2019 by woit

Physics Today seems to have decided to deal with Sabine Hossenfelder’s criticism of a future collider by publishing the least credible possible response: a column by Gordon Kane arguing that string theory predicts new particles of just the right mass to be likely beyond the LHC reach, but accessible to a higher-energy proton-proton machine.

In the column, we learn that:

In recent years there has been progress in understanding those [string theory] models. They predict or describe the Higgs boson mass. We can now study the masses that new particles have in such models to get guidance for what colliders to build. The models generically have some observable superpartners with masses between about 1500 GeV and 5000 GeV. The lower third or so of this range will be observable at the upgraded LHC. The full range and beyond can be covered at proposed colliders. The full range might be covered at a proton–proton collider with only two to three times the energy of the LHC. One important lesson from studying such models is that we should not have expected to find superpartners at the LHC with masses below about 1500 GeV.

Kane has a long history with this kind of thing at Physics Today, publishing there back in 1997 much the same sort of argument, in an article entitled String Theory is Testable, Even Supertestable. According to the Kane of 1997, a generic “prediction of string models” was a gluino at around 250 GeV, just beyond the Tevatron limits of the time. Thirteen years later, Physics Today had him back, publishing an article entitled String theory and the real world. I don’t have the time to do a full search, but, by 2011 after the first LHC results came in, Kane had a string theory prediction of a gluino mass at 600 GeV, or “well below a TeV”.

As better LHC results have come in, each time Kane has issued a new “string theory prediction” that the mass is a bit higher, just about to appear at the next round of LHC results. The last version of this I had seen (see here), was from 2017 and predicted “that gluinos will have masses of about 1.5 TeV”. This is already disconfirmed and out of date, with Kane now telling us “between about 1500 GeV and 5000 GeV.”

For some other evidence of how Kane deals with the problem of having predictions falsified, one can compare the 2000 and 2013 versions of his popular book on SUSY, an exercise I went through here.

At this point, the argument that we need a new collider because “string theory predictions” say that it will see gluinos has zero credibility. I don’t know of any other theorist besides Kane who believes such a thing. That Physics Today is publishing this is just mystifying. Perhaps a collider skeptic there has come up with this as a clever way to back the Hossenfelder side of the argument.

There are some other odd things in the piece, one that stuck out for me was this bizarre claim about recent history:

We now know that if Fermilab and the US Department of Energy had taken the Higgs physics more seriously, the Tevatron would have discovered the Higgs boson years before the Large Hadron Collider did.

I see Will Kinney has more about this on Twitter.

Update: More commentary on this from Jon Butterworth and Sabine Hossenfelder.

Posted in This Week's Hype | 31 Comments