Gravitational Wave Predictions

I think I can confidently predict that tomorrow morning either one of two things will happen:

  • The first observation of gravitational waves will be reported by the LIGO experiment.
  • A large fraction of the scientific community will be really, really angry at members of the LIGO collaboration.

I’m betting on the first of these two alternatives, and like everyone else will be watching to see what happens tomorrow. If you want some informed commentary on what it all means though, this isn’t the place (what I know about gravitational radiation is basically the little that I learned in a GR course about 40 years ago…), so for now I’ll leave comments closed.

One place advertising a live feed is Nature. I’ll be happy to list better possibilities here if people let me know about them.

Update: Another place to try for the webcast is here.

Update: Big event here at Columbia. Roone Arledge auditorium packed.

Update: Quite amazing, just as predicted, observation of two black holes coalescing, a historic discovery. That stuff I was taught 40 years ago really works. More details many places as the embargo is lifted, with some good examples Natalie Wolchover at Quanta, Dennis Overbye at the New York Times, and Davide Castelvecchi and Alexandra Witze at Nature. The paper has been refereed and is here at PRL.

: Better info about the waves is available elsewhere, but I can report here on something pretty amazing: my graduate school roommate’s gravitational wave soup bowl.

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Stacks Project Party

Last night I got to attend a major event of the Manhattan social season, a party celebrating the fact that the Stacks Project has reached the milestone of 5000 pages. As far as anyone knows, no one has ever printed out the whole thing, but to give an idea of scale, the party featured a large stack of reams of paper totaling about 5000 pages.

I was going to include a party report, describing the various celebrities there, their outfits and conversations, but one of them (Mathematics Without Apologies) has its own blog, so I’ll just refer you there.

For some background about this amazing project, from when it was a mere 4000 pages, see here.

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Rutgers Talk

Slides from my talk at Rutgers are now available here. The idea was just to advertise to physicists there the point of view that is all too familiar to regular readers here. The final speculative comments about relations to mathematics shouldn’t be taken too seriously, these are things I hope to work on and write about much more in a few months once my current book project is completed.

Update: Interestingly, my Princeton advisor Curt Callan yesterday gave a talk at the KITP with a bit of a similar theme, starting off by arguing that the success of the standard model made future progress in HEP very difficult. His answer to the problem is quite different than mine (his involves trying to make contributions to biology). The first question at the end (from David Gross) is about the relation to new mathematics.

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Some News

Not much time for blogging at the moment, with one reason that I’ll be giving a talk at Rutgers on Wednesday, and need to get that prepared. A few quick items:

  • As some commenters have mentioned here, talks from the recent Munich conference (discussed here) are now available. From the little time I’ve found to look at them, I think Rovelli’s is the talk that makes the point about all of this most worth making, with Massimo Pigliucci good at explaining the wider implications.
    While interesting comments on the talks are encouraged, for reasons that I can’t explain publicly, discussion here of the Polchinski contribution is not welcome.
  • Besides watching Gordon Kane in Munich on string theory predictions, he also has a paper about this out now.
  • Congratulations to Bert Kostant on the award of the 2016 Wigner Medal. Kostant has been one of the major figures over the years in developing many deep ideas about the intersection of mathematics and physics, as well as a leading figure in the algebraic approach to Lie algebras and their representations.
  • A lot of mathematicians and physicists want you to use TurboTax.
  • Steven Weinberg’s sensible opposition to guns in UT Austin classrooms has gotten a lot of media attention (for instance here). Of the many obvious reasons why this is a bad idea, he correctly points out that it may well make it difficult for UT to recruit faculty.

Update: A commenter points out that more videos from the Munich conference are available here.

Update: John Horgan has a wonderful interview with the remarkable and ubiquitous Sabine Hossenfelder. Highly recommended.

Update: For news from the LHC, see last week’s Chamonix LHC performance Workshop. From the summary, the goal is about 30 inverse fb of pp collisions this year.

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More From Polchinski

Joe Polchinski has a rather odd preprint on hep-th, more of a blog posting than a paper, summing up his views on string theory and the multiverse. This is a revised version, wisely dropping a really unfortunate section. The material previously here explaining the background to what was in that section has been moved, and I’ve renamed the posting.

I’ve never personally met Polchinski, and from those who know him I’ve heard that he’s a nice guy. I’ve also recently heard that he’s ill, wish him the best.

Update: It seems that I misunderstood why Polchinski removed the section about me from his arXiv article. He’s now claiming that it was just because, since he’d gotten trackbacks to my blog banned, it would be unfair that there would be no trackback to his article (true enough…). This whole situation is a level of bizarre beyond the heights reached way back when during the string wars.

For those reading the version of Polchinski’s article on his website rather than the current one on the arXiv, to understand what this is about, please read the material here.

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Hitler doesn’t get a postdoc in High Energy Theory

I recognize that this is a genre that is a bit tired, and arguably in poor taste, but the commentary on the HEP theory postdoc job market in the video Hitler doesn’t get a postdoc in High Energy Theory is insightful. As far as I can tell the HEP Theory postdoc/junior faculty market has been the same for the last 45 years or so: far more people than jobs, and if you want one you better be working on one of a small number of “hot” topics. One might speculate that this correlates with the lack of progress in the field during this time. I’m a bit better informed about the mathematics job market for fresh PhDs, which is much healthier, as is the intellectual state of the field.

A recent trend does seem to be fewer jobs in the US, more in Europe. Anyone with better information about what is going on is encouraged to comment here (and, condolences if this is because you’re on the market).

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Back at Work

It’s been a while since the last posting here, mostly because I’ve been away on vacation, but also because I haven’t seen anything that newsworthy. But, since I’m back in the office and there have been complaints, here are a few items:

  • For the first time in a very large number of years, a new volume has appeared in the series of Bourbaki treatises, dealing with algebraic topology (table of contents here). From the table of contents, it appears to be a rather modern treatment mostly of the fundamental group, but still in the Bourbaki style of exhaustive coverage and abstract point of view (I don’t see any mention there of actually computing the fundamental group of anything…).
  • While in Paris I attended some of the Seminaire Bourbaki talks. You too can watch via Youtube, or read the written versions.
  • Far from mathematics and physics, one thing I did in Paris was stop by a store selling Breton products, and had a discussion with the owner about Kouign Amanns. He had a short hand-written list of a few places they could be had in the US. When I got back here, the next morning I went out to my local bakery (Silver Moon, at Broadway and 105th), and found that while I was away they had started selling them.
  • On the Mochizuki front, there’s a new paper by Vesselin Dimitrov, claiming that if Mochizuki’s argument is correct, it implies something even stronger than Mochizuki claims, an effective version of the abc conjecture. The next workshop about this will be in Kyoto in July. One mathematician who has gotten interested in this and is listed as planning to attend is Edward Frenkel.
  • If you can’t get enough of the “Is HEP physics dead or what?” debate, see John Horgan on How Physics Lost its Fizz.
  • Among the things going on here at Columbia this semester, there are Eilenberg Lectures on geometric representation theory (starting in a few minutes…) by Roman Bezrukavnikov, a course by Michael Harris on Lafforgue’s recent work on the Langlands correspondence for function fields (also the topic of one of the Seminaire Bourbaki talks), and a conference celebrating Dusa McDuff’s 70th birthday.

Better leave now to get a seat at the talk…

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Various and Sundry

Some short items on a wide variety of topics:

  • The Hawking/Perry/Strominger paper on a new idea about the black hole information paradox (see here for an early discussion) based on BMS supertranslation symmetries has now appeared on the arXiv. I’m no expert on the intricate arguments about this paradox, so have no idea what the implications of this paper for that really are. However, it does seem to be a very interesting approach to quantum gravity questions (although the paper mostly deals with simpler gauge theory calculations). The ideas are squarely in the mainstream of what has been the most successful way of making progress in fundamental theory: identifying new implications of symmetries that are at the center of our core theories (the standard model and GR). Such a new understanding looks like a far more promising way forward than much of what is currently popular in the subject.
  • For an example of what is currently popular, the KITP is hosting a workshop this week of the the It from Qubit Simons Collaboration, on Quantum Error Correction and Tensor Networks. I gather this is supposed to somehow explain AdS/CFT, but I’ve never understood how this is supposed to come about. Evidently I’m not the only one wondering about this. John Presskill reports that, in his talk leading off a series of lectures on this, Patrick Hayden commented that

    I’m unsure what we are trying to learn from these tensor network models of holography.

  • Tonight PBS will be showing the film Particle Fever, which I wrote about here. It’s a great film, highly recommended, despite the larding with comical nonsense about the multiverse (if you believe the theorists in the film, the multiverse is supposed to be tested by its prediction of a mass of 140 GeV for the Higgs). The capsule summary in the New York Times TV listing this morning for the film is “Scientists recreate conditions from the big-bang theory”. While the LHC has nothing to do with the big-bang theory, maybe this summary refers to the comedy of the theorists and another well-known TV show, in which case viewers may be a bit disappointed.
  • In other LHC related news, the AMVA4NewPhysics project now has a blog, latest posting explains the basics of b-tagging.
  • I’ve never been able to really make sense of many of the arguments about “Bayes’s Theorem”, and the recent attempts to justify string theory using this just seemed bizarre. John Horgan has a great explanation of what is going on here, including this take on the Bayes/string theory/multiverse business:

    In many cases, estimating the prior is just guesswork, allowing subjective factors to creep into your calculations. You might be guessing the probability of something that–unlike cancer—does not even exist, such as strings, multiverses, inflation or God. You might then cite dubious evidence to support your dubious belief. In this way, Bayes’ theorem can promote pseudoscience and superstition as well as reason.

    Embedded in Bayes’ theorem is a moral message: If you aren’t scrupulous in seeking alternative explanations for your evidence, the evidence will just confirm what you already believe. Scientists often fail to heed this dictum, which helps explains why so many scientific claims turn out to be erroneous. Bayesians claim that their methods can help scientists overcome confirmation bias and produce more reliable results, but I have my doubts.

    And as I mentioned above, some string and multiverse enthusiasts are embracing Bayesian analysis. Why? Because the enthusiasts are tired of hearing that string and multiverse theories are unfalsifiable and hence unscientific, and Bayes’ theorem allows them to present the theories in a more favorable light. In this case, Bayes’ theorem, far from counteracting confirmation bias, enables it.

  • The recent Munich conference trying to justify string theory by Bayesian methods wasn’t the only example of European funding for philosophers to weigh in on the latest in fundamental physics. Another just announced European LHC-related project is a 2.5 million Euro research unit aiming to investigate the LHC “from an integrated philosophical, historical and sociological perspective.”
  • I just ran across a recent paper by Kristian Camilleri and Sophie Ritson on The role of heuristic appraisal in conflicting assessments of string theory. It is very good, unlike almost every other discussion of this topic, I think it gets right the central serious argument of the “string wars”: how does one evaluate the prospects for the string unification idea? There is no simple answer to this, you need to understand what the state of efforts to connect a hoped for unified string theory to reality really are, how they have evolved, and try to make a sensible judgment about whether this is a failed idea or whether there is hope left. I highly recommend reading this for those who are not completely tired of this subject.
  • In the same journal I noticed another quite good article, by Porter Williams on naturalness. He carefully explains the different incarnations of “naturalness” and I think comes to the right conclusion that it is best thought of as the idea that physical behavior at widely different distance scales should not be correlated. By the way, the name “naturalness” for this is a bit of marketing genius (how could “nature” not be “natural”?).
  • In geometric representation theory news, the Simons Center is running a program on the topic this month, videos here. Here at Columbia Roman Bezrukavnikov will be the Spring 2016 Eilenberg lecturer, with his topic “Geometric categorification in representation theory”. I believe talks will be Thursdays at 2:40, watch the Columbia math department website for more news.
  • Personally, I’m about to head out tomorrow night on vacation, so expect minimal blogging and possibly even shutting off of comments. When I get back, I’ll be teaching our spring semester graduate course on groups and representations, see here. Also trying to finish my book on quantum theory and representation theory. Current state (see here, comments always welcome) is that I’ve gone over and rewritten the first 34 chapters (except the introduction), planning on rewriting and adding material to the rest of the manuscript this semester. This better be done by this summer, partly because that’s when it is supposed to be delivered to Springer, partly because I’m already quite tired of this project and want to work on other things…

Update: Any mention of Bayesianism seems to attract a large number of people who want to discuss it, especially aspects that have nothing to do with the string theory/multiverse business. Please discuss this topic with John Horgan at his blog.

Update: Sabine Hossenfelder has more on the Hawking/Perry/Strominger paper here.

Update: Scientific American has an interesting interview with Strominger, who explains some of the ideas behind Hawking/Perry/Strominger. Jacques Distler has come out of retirement at Musings to object that this work violates two central ideological tenets: one should not pay attention to gauge invariance, and the answer to all questions should be string theory or AdS/CFT.

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End of Year Links

A collection of links to round out the year:

  • The Seminaire Bourbaki talks this January look unusually interesting. Luckily I’ll be in Paris at that time.
  • For an end of year present, Jacob Lurie has posted a version of his unfinished next book, Spectral Algebraic Geometry. It’s advertised as much more user-friendly than previous versions of the same material and that’s quite true after reading the first chapter.
  • If 850 pages or so of this sort of thing isn’t enough to keep you busy during the break between terms, try Lurie’s Harvard colleague Dennis Gaitsgory’s A study in derived algebraic geometry, a book project with Rozenblyum, also in a preliminary version (around 1100 pages), with more to come. I’m hoping for the more user-friendly version of this one…
  • Also from Harvard, videos of last month’s Current Developments in Mathematics talks are now available here. At least the first of Peter Scholze’s talks is rather user-friendly.
  • Very, very user-friendly (especially if you read Japanese) are the Japanese television versions of Edward Frenkel’s talks earlier this year at MSRI, available here.
  • If you just can’t get enough of the new 750 GeV particle, you probably should read Tommaso Dorigo’s take on it.
  • Back when I was writing about the AMS’s role as a mouthpiece for the NSA in its attempts to mislead people about their role in backdooring an NIST crypto standard (see here and here), one thought I kept in mind was that since this standard supposedly was never used in anything important, maybe one shouldn’t get so upset. Recent news (see Matthew Green for an explanation) is that this bad crypto actually was used in something quite important: widely used firewall/VPN hardware from Juniper Networks. Quite likely this was used by the NSA to get access to much of the traffic on a wide variety of networks.

    The story is actually much more complicated than one can believe, with a still unclear sequence of changes in the software indicating that others, possibly a foreign government, took advantage of the NSA backdoor to compromise these systems. Green points out that this makes very clear the problem with government-mandated backdoors: even if you trust the government, they make it much easier for others to take advantage of the security problems they have introduced:

    One of the most serious concerns we raise during these meetings is the possibility that encryption backdoors could be subverted. Specifically, that a backdoor intended for law enforcement could somehow become a backdoor for people who we don’t trust to read our messages. Normally when we talk about this, we’re concerned about failures in storage of things like escrow keys. What this Juniper vulnerability illustrates is that the danger is much broader and more serious than that.

    The problem with cryptographic backdoors isn’t that they’re the only way that an attacker can break into our cryptographic systems. It’s merely that they’re one of the best. They take care of the hard work, the laying of plumbing and electrical wiring, so attackers can simply walk in and change the drapes.

  • If you just can’t get enough of my and other people’s views on string theory, Ben Winterhalter has a piece on the Jstor blog, telling the story of his attempts to figure out what’s going on with extra dimensions.
  • Among the many great articles at Quanta, I can recommend this one, which features my Columbia colleague Wei Zhang.

Happy New Year!

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Why String Theory?

I recently got a copy of Joseph Conlon’s new book Why String Theory? and was pleasantly surprised to find that it’s quite good. Conlon is a lively, entertaining writer, generally sensible about the scientific issues involved, and I think does a great job of explaining the point of view of typical physicists now working on string theory. He also very ably explains the “sociology” of the field, the different kinds of people who work in this area and their varying sorts of goals and motivations.

The book is explicitly motivated by the desire to answer a lot of the criticism of string theory that has become rather widespread in recent years (wasn’t always so…). For a typical example from the last few days, see Why String Theory is Not a Scientific Theory at Starts With a Bang. I have mixed feelings about this sort of thing. It gets the main point quite right, that string theory unification is untestable, having failed to make any predictions, and by the conventional understanding of the scientific method, it’s past the time at which most theorists should have abandoned it and moved on. On the other hand, I don’t see at all the point to arguing about the term “scientific theory”. Sure, it’s a scientific theory, a failed one. I’ve personally never noticed any consistent usage by physicists of terms like “theory”, “model” and “hypothesis” in ways that accurately indicate degree of experimental support, don’t see why some writers insist that there is one. I also very strongly object to the article’s standard move of trying to make a failed theory a “mathematical theory”. Mathematics is about well-defined ideas, and there is currently no such mathematical construct as “string theory”. The problems with string theory have nothing do with mathematics, rather have to do with a physical idea that didn’t work out.

To a large extent the problems Conlon is struggling with are ones that the community of string theorists has inflicted on itself. The great majority of writing for the public by string theorists is characterized by large amounts of outrageous hype. For a very recent example, see Daniel Harlow here, who seems to think string theory is a huge success at explaining the standard model

although it hasn’t quite managed to reproduce the complete standard model of particle physics, it comes very close and the obstructions seem more or less technical. I want to emphasize that postdictions are just as good formally as predictions for testing a theory; the distinction is purely sociological.

and that it is also much more (did you know that string theory is what explains the existence of black holes?)

the main reason to work on (or be inspired by) string theory from a scientific point of view is that it may provide explanations of phenomenon that have ALREADY been observed: the existence of black holes, the small positive cosmological constant, and the evidence for an inflationary phase of the early universe.

As for the problem with the multiverse making no predictions, that’s just wrong. We just don’t know what the theory is, when we figure it out, surely it will make predictions:

the issue is not that it doesn’t make predictions. The issue is instead that we do not yet understand it well enough theoretically to know what the predictions are!

I’ve always found reading this kind of thing quite puzzling. My impression of most string theorists is that they’re smart and rather sensible, well aware of the difference between ridiculous hype and an actual scientific argument. Unfortunately such sensible string theorists also have seen no point in trying to write for the public until now, and I’m glad that Conlon’s book finally changes that.

If you followed the reports from the recent Munich conference, you likely heard that the assembled philosophers and physicists nearly unanimously found the anthropic multiverse point of view Harlow advertises to not be legitimate science. Conlon expresses his opinion in this way, and I think it’s the majority one among string theorists, whatever you might have heard:

The most serious problem with the anthropic landscape is that it provides a cheap and lazy explanation that does not come from hard calculation and also has no clear experimental test. It sounds exciting, but does not offer lasting sustenance, and may even act as a deterrent against necessary hard work developing new calculational tools.
Of course, this does no mean that the anthropic approach is necessarily wrong. However the triumph of science has been not because it contains ideas that are not necessarily wrong, but because it contains ideas that are, in some important sense, known to be true: ideas which have either passed experimental test or are glued together by calculation. The anthropic landscape is neither of these. It represents incontinence of speculation joined to constipation of experiment.

Instead of Harlow’s claims that string theory makes lots of postdictions, coming very close to reproducing the complete standard model, modulo some technical issues, Conlon deals with the situation in a much more honest and straightforward fashion. Of the fourteen chapters of the book, chapter 7 is entitled “Direct Experimental Evidence for String Theory.” Here’s the entire content of chapter 7:

There is no direct experimental evidence for string theory.

Conlon’s point of view is different than that of the majority of string theorists in one way, which he explains in detail.

My interest in string theory is in what it can offer to physics that can be probed by experiment.
This view is far from universal. It may seem odd, but most of those who work on string theory are essentially uninterested in any connections with experiment, any public claims that they may make to the contrary notwithstanding.

He backs this up by the observation that less than 10% of talks at recents Strings 20XX conferences have any connection to observable physics.

Here, I’m again in the majority, with his colleagues, who I think have made an accurate evaluation that connecting current string theory to experiment is a failed and hopeless project (I differ with them on prospects for this changing). Conlon has a research program to investigate potentially observable effects of moduli fields, something his colleagues are skeptical about. While I’m also skeptical about this, it does seem like a reasonable thing to investigate, especially since such things may be generic to all theories with extra dimensions, not just string theory. The chapter of the book describing this research is one with material you won’t find in other popular books.

Many of his colleagues have adopted the attitude that, while connecting string theory to experiment is hopeless, it deserves investigation purely as an idea about quantum gravity. While Conlon devotes a fair amount of space to the arguments about quantum gravity and string theory claims about them (including some criticism of loop quantum gravity) he avoids much of the usual hype, and also makes it clear that he himself isn’t interested in pursuing this because of the lack of any hope of ever testing one’s ideas. In some sense I think he and I agree here: it is only if one’s idea for quantizing space-time degree of freedom connects up somehow to our successful theories of other quantized degrees of freedom that one will have any hope of ever knowing whether one has the right theory of quantum gravity. Absent a connection of this kind, one is doomed to become just another cog in an endless fruitless ideological argument about whose quantum theory of gravity is better (or at least, whose sucks less).

Conlon claims that at this point, most string theorists are interested in string theory not as a theory of quantum gravity, but because of applications of ideas that have emerged from string theory to other fields (e.g. AdS/CFT). Here he gives a reasonable account of attempts to use AdS/CFT to say something about condensed matter physics. One place in the book where he, unusually, descends to conventional incantations of hype is his account of applications of AdS/CFT to heavy-ion physics, where he says nothing about the fact that this doesn’t work very well, just repeating some rather stale hype.

There’s a lot else to like in the book, for instance a chapter of highly perceptive descriptions of the different kinds of theorists and the different ways they work, including some rather amusing and mostly friendly caricatures of common behavior. For an example of the kind of thing you’ll read here but not in any other popular string theory book, he notes that certain persons have recently received multi-million dollar prizes based upon model-building ideas that didn’t work out.

There’s a lot more in the book than I have time to discuss, some of which I agree with, some of which I don’t. Obviously I have a different point of view than Conlon’s, but his at least I find to be one with serious arguments behind it, unlike all too much of the popular string theory literature. One thing I found rather discouraging after my book came out ten years or so ago was what seemed to me a lack any serious response from sensible string theorists. Quite a few years later, it’s great to see that Conlon has written such a thing, and I recommend it highly to anyone who cares about these issues.

And, Happy Holidays!

: Sabine Hossenfelder has a posting with a similar take on the Siegel piece. I also like her description of the Munich workshop:

There was, however, not much feud at the workshop, because it was mainly populated by string theory proponents and multiverse opponents, who nodded to each other’s talks. The main feud, as always, will be carried out in the blogosphere…

I haven’t seen the full piece, but New Scientist now seems to be covering the multiverse as theology, which is about right.

Update: Over on Facebook Dan Harlow explains the “technological problems not relevant for questions of principle” needed to get string theory predictions

the idea is that in order to view string theory as a theory of nature, we need to view it as providing a unique probability measure on the space of low energy theories. This would be computed by understanding both the structure of the landscape and the dynamics of eternal inflation. We can then compare our observations to the predictions of this measure, and if they are atypical the theory is ruled out. We are far from doing this though, except for the imprecise cartoon that seems to more or less work for the cosmological constant. This seems just as scientific to me as quantum mechanics, except that we don’t yet know how to compute the probabilities.

I see a bunch of problems of principle here, starting with not knowing the underlying non-perturbative theory and going on from there. Some commenters over there think “It’s hard to even begin to imagine how one can even take Woit seriously.”, but it looks like they take seriously Harlow’s claims that this “seems just as scientific to me as quantum mechanics”, with the minor difference that you can’t calculate anything.

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