Who’s Winning the String Wars and Why Should You Care?

Part two of Gerald Alper’s piece at Smashpipe is now available there, with the title Who’s Winning the String Wars and Why Should You Care?, and some more substantive material than in part one. One of the great things about having a blog is that whenever anyone writes anything about you that you think might not be 100% correct, you can blog about it, and explain yourself ad nauseam. So, here are a few clarifications for readers of that article:

  • About the “horrible sentence”

    The Hilbert space of the Wess-Zumino-Witten model is a representation not only of the Kac-Moody group, but the group of conformal representations [transformations] as well.

    I don’t think it’s a bad sentence, it succinctly conveys the main point about the close relationship of the WZW QFT to representation theory. Like a certain number of things in the book though, it’s not intended for everyone. There were certain things I wanted to explain, and the way I went about this was to try to as clearly write them down as possible, in a way accessible to as many people as possible, but well aware that not everyone would understand everything. Unlike writing “the WZW model is related to mathematics like X is to Y”, where X and Y are things most people would recognize, you’re not going to get fooled into believing you understand something you don’t by what I was writing. Those who do understand the sentence will understand a real idea.

  • I AM VERY CONFIDENT that I AM RIGHT. No one has ever critiqued string theory with the level of detail that I have.

    Not sure exactly how I said this, but I suspect the “no one has ever” wasn’t intended to convey that this was a good thing. I’ve clearly spent too much of my life thinking about this. I also should specify that what I’m confident about is that current “string vacua” models don’t correspond to reality. They’re complicated, ugly, and don’t explain anything. My suspicion is that even Witten might not completely disagree with this, acknowledging that at our current understanding of string theory, there is no convincing model. I think a more accurate way of characterizing where Witten and I disagree here is with how promising it is to pursue this particular vision of unification. I am not at all confident that Witten or someone else pursuing it might not come up with something really new and successful some day. I just think it’s a relatively unpromising route to keep heading down, although I acknowledge it’s possible it might lead to finding a more interesting path. Doubtless Witten feels the same way about things I find more promising.

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Beyond Experiment: Why the scientific method may be old hat

This week’s New Scientist has an article by Jim Baggott and Daniel Cossins entitled Beyond Experiment: Why the scientific method may be old hat, which deals with the recent controversy over attempts to excuse the failure of string theory by invoking the multiverse. The article (unfortunately behind a paywall) does a good job of describing the nature of the controversy: what do you do when it becomes clear your theory can’t be tested? Do you follow the conventional scientific norms, give up on it and work on something else, or do you try and find some kind of excuse, even if it means abandoning those norms?

Much of the article deals with the issues raised at the recent Munich conference (discussed here). Two of those quoted (Dawid and Gross) are not multiverse partisans, instead argue that the motivations that got people interested in string unification more than 30 years ago are good enough to justify indefinitely pursuing the theory, no matter how bad things look for prospects of connection to experiment. On the other hand:

Their enthusiasm is far from universal, and some physicists are downright alarmed. Woit warns that the need for empirical vindication could be pushed so far into the background as to be invisible. Carlo Rovelli, a theorist at the University of Aix-Marseille in France, believes that this scenario has already come to pass. Rovelli … argues that the last thing we need is a system that legitimises failed theories. “A theory is interesting when it teaches us something new about the real world,” he says. “Not when it becomes a house of cards that delivers nothing but university positions.”

On the question of the string theory multiverse as science, those gathered at the Munich conference were pretty uniformly hostile. As a proponent of this, the article quotes only one person, who wasn’t there:

Sean Carroll, a theorist at the Caltech Institute of Technology at Pasadena and a leading advocate of the multiverse, insists that if anyone is being unscientific, it is those physicists who seek to enforce outmoded philosophical principles and impossibly high standards. “People support these theories because they offer the best chance of providing a useful account of the data we actually do collect here in our universe.”

I’m not sure how the string theory multiverse provides an account of data we have collected that is “useful”, except in the sense of “useful to those who don’t want to give up on string theory.”

Carroll has explained his views in more detail here, arguing that falsifiability is an idea that needs to be retired, to be replaced by “empiricism”. “Empiricism” seems to mean “ability to account for the data”, with “the multiverse did it” an acceptable way to account for data, even if not falsifiable. He’ll be giving a talk on this at the American Astronomical Society meeting in San Diego this summer, with abstract:

A number of theories in contemporary physics and cosmology place an emphasis on features that are hard, and arguably impossible, to test. These include the cosmological multiverse as well as some approaches to quantum gravity. Worries have been raised that these models attempt to sidestep the purportedly crucial principle of falsifiability. Proponents of these theories sometimes suggest that we are seeing a new approach to science, while opponents fear that we are abandoning science altogether. I will argue that in fact these theories are straightforwardly scientific and can be evaluated in absolutely conventional ways, based on empiricism, abduction (inference to the best explanation), and Bayesian reasoning. The integrity of science remains intact.

Carroll’s argument seems to be that the conventional understanding of how science works that we teach students and use to explain the power of science has always been wrong. Falsifiability by experiment isn’t necessary, instead, what is the “absolutely conventional” way to do science is “empiricism, abduction (inference to the best explanation), and Bayesian reasoning”. I’d never heard of abduction as a basis of science before. If you believe Wikipedia, this goes back to Charles Sanders Peirce, whose view in later years was:

Abduction is guessing. It is “very little hampered” by rules of logic. Even a well-prepared mind’s individual guesses are more frequently wrong than right. But the success of our guesses far exceeds that of random luck and seems born of attunement to nature by instinct (some speak of intuition in such contexts).

As for “Bayesian reasoning”, I would have thought that Polchinski’s Bayesian calculation of an “94% chance” of a multiverse would have conclusively shown the absurdity of that.

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Various and Sundry

  • The online magazine Smashpipe has the first part of a two-part article written by Gerald Alper, who recently came up here to Columbia to talk to me about string theory/etc. It was an interesting conversation, so I’m curious to see what he makes of the more substantive part, which is in part two, planned for next week.
  • If instead you’d like to read about a conversation with my colleague Brian Greene, there’s a piece at Cosmos Magazine. Brian is taking his World Science Festival to Australia next month and will be on tour there.
  • In other Columbia news, LHC experimentalist Emlyn Hughes has evidently
    baffled the students in Frontiers of Science again. Three years ago he undressed for the students, this year the performance somehow involved a student mistress (see here and here). No, I don’t understand any of this either.
  • As a last Columbia story, this semester in the physics department Bill Zajc is teaching a string theory course for undergraduates, Physics W4012, based on the Zwiebach book. While Zajc isn’t a string theorist, he is a frequent commenter at Lubos Motl’s blog.
  • There’s a new issue out of Inference, which has some interesting articles, including an essay by Pierre Schapira on category theory (French version here). Also there’s Jean-Pierre Luminet on holography.

    Inference is a bit of a mystery, unclear who is editing it (some speculation here). Whoever it is though, it’s quite worth paying attention to.

  • The HEP Postdoc Project is collecting anonymously information aimed at helping potential postdocs (or even Ph.D students) find out more about what it’s like to work with various senior HEP theorists. No, like Inference, I have no idea who is behind this.
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Yet More About Grothendieck

Since Grothendieck’s death somewhat more than a year ago, quite a lot of new material about him and his mathematics has become available. Visit the Grothendieck Circle to find a lot of this, with just one example some new chapters of the English translation of the third volume of Scharlau’s biography.

This month’s AMS Notices has the first of two parts of a long article with contributions from many mathematicians discussing Grothendieck’s work and their memories of him and his influence on their careers. Colin McLarty has an excellent expository article, maybe the best of attempts I’ve seen to explain some of the themes of Grothendieck’s mathematics in a relatively accessible manner.

While you’re there, this latest issue of the Notices has quite a bit else worth reading, from my colleague Ivan Corwin on KPZ universality to Beilinson on Gelfand’s seminar, and an amusing attempt by Jeremy Gray to guess not the next Fields medalist, but who would have gotten one in 1866.

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This Week’s Hype

This week’s dramatic announcement of the discovery of gravitational waves was a major milestone for the fields of physics and astrophysics. The LIGO observation validates a lot of previously untested aspects of our understanding of general relativity, and promises the imminent opening up of a new field of observational astronomy, as LIGO sees other astrophysical sources of gravitational waves. Watching the announcement, the lead up to it, and the press stories that came out, many immediately as the embargo was lifted, I was struck by the general high quality of the stories in the press (I linked to a few of them in the last posting, but there are many more). Congratulations to whoever organized this, and to all the science writers who have done a great job producing enthusiastic but generally hype-free coverage of the story.

Unfortunately, those physicists brought in by major news organizations to tell the public what the significance of this is often can’t resist the temptation to indulge in the usual hype. At the Wall Street Journal today, Michio Kaku’s commentary is labeled Riding Gravity Waves to the Big Bang and Beyond, and subtitled “Once again, Einstein’s theory of relativity is confirmed by scientists. Next stop: Creation.”

There’s nothing in his piece about what else LIGO might observe and what we might learn from it about the universe. Instead, it’s all about the big bang, Creation, and before the big bang, things which as far as I can tell, LIGO data is highly unlikely to tell us anything about:

Now we are witnessing the third great revolution in telescopes, the use of gravity waves to open a new chapter in astronomy. For the first time, waves from the very instant of creation might be observed, giving us “baby pictures” of the universe as it was born. High-school textbooks may have to be rewritten to incorporate the new discoveries coming from this third generation of telescopes.

This may also have philosophical implications. Right now the big-bang theory doesn’t tell us what banged, why it banged, and what caused it to bang. It only tells us that there was a bang. But if space-based gravity-wave detectors similar to LIGO’s detectors can measure the radiation emitted an instant after the big bang, then, using mathematics, one can run the equations backward to determine what set off the big bang in the first place, in effect answering the biggest question of all: What banged and why?

When Einstein postulated gravity waves a century ago, he not only opened up an entirely new chapter in astronomy, he also opened the door to answering the most important philosophical questions of all time, including the creation of the universe.

Over at the New York Times, in the Sunday Review, Lawrence Krauss has a more sensible piece, entitled Finding Beauty in the Darkness. Multiverse mania seems though to be irresistible, as he ends up with this summary of the physics significance:

Ultimately, by exploring processes near the event horizon, or by observing gravitational waves from the early universe, we may learn more about the beginning of the universe itself, or even the possible existence of other universes.

Posted in Multiverse Mania, This Week's Hype | 30 Comments

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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