Now back from a trip to the West Coast, here are some accumulated things that may be of interest:
One thing I didn’t do while there was attend the 2020 Breakthrough Prize symposium. For videos of three talks about supergravity, see here. At the time of the award I wrote here about why a \$3 million prize for a failed idea about particle theory was a bad idea. Listening to the talks, I think an even worse idea is telling the public that this is a great example of why they should trust science.
For another dubious idea from the West Coast, in January the KITP is bringing high school teachers to Santa Barbara to teach them about Spacetime, Holography, and Entanglement. Most of the programs the KITP has run for teachers (see here) have been devoted to explaining important, solid science. Back in 2001 when they promoted string theory I thought that was a bad idea, this latest one isn’t much better. Again, when the credibility of science is under attack, why go to the public (or, in this case high school teachers) to promote a highly speculative research program? Is it really a good idea for high school teachers to be exposed to this kind of hype, presumably with the hope that they’ll somehow transmit it to their students?
On the evergreen topic of bad multiverse science, Scott Alexander here defends multiverse speculation, responding to Jim Baggott’s article. He and the authors of the more than four hundred comments debate at length a red-herring issue. Alexander writes:
My understanding of the multiverse debate is that it works the same way [as respectable paleontology]. Scientists observe the behavior of particles, and find that a multiverse explains that behavior more simply and elegantly than not-a-multiverse.
Yes, if theorists had a simple, elegant multiverse theory with lots of explanatory power, you could get into interesting arguments about its testability and whether the idea was solid science or not. The problem is that no such multiverse theory exists. If you want to talk about the MWI multiverse, your problem is that solving the measurement theory problem by just saying “the multiverse did it” may be “simple” and “elegant”, but it’s also completely empty. If instead you want to talk about the cosmological multiverse, the problem is that you don’t have a theory at all (and the actual fragments of a theory you do have are complicated and ugly). For more about this, see my posting and article on Theorists Without a Theory.
For something more positive, while traveling I noticed two quite interesting articles which explain in a detailed technical way approaches to two of the great unsolved problems of our time, while carefully discussing why the approaches have not (yet?) worked, leaving the great problems unsolved.
For mathematics and the Riemann Hypothesis, see Alain Connes and Caterina Consani’s article The Scaling Hamiltonian, about the attempt to understand the zeros of the Riemann zeta function in terms of the properties of a specific Hamiltonian operator, which in some sense is a generator of a group of scaling transformations.
For physics and quantum gravity, see Donoghue’s A Critique of the Asymptotic Safety Program, which has a detailed discussion of the problems with making sense of both quadratic gravity Lagrangians and the idea of a non-trivial fixed point gravity theory theory. I was interested to see that he has a lot to say about the Lorentzian vs. Euclidean signature issue, something often ignored.
Hype about string theory and fundamental physics seemed to have been dying down recently, with only three editions here so far in 2019 of This Week’s Hype. Today however brings a bumper crop of the highest quality, with new examples from a few of the world’s most prominent theoretical physicists. Today’s hype neatly exemplifies the two main current genres of hype about string theory and supposed new fundamental physics. The first is the old-school genre of string theory hype we’ve now been seeing for 35 years: “string theory makes a testable prediction” (no, it doesn’t). The second is the new, post-modern variety: no actual theory, just a grandiose claim that space and time have been replaced, although it’s unclear by what.
In the subtitle of this APS Physics piece from Cumrun Vafa, we learn that the string swampland has “led to testable predictions about dark energy.” If you read the article trying to find the testable predictions of string theory, you’ll get to Figure 3, where the caption says “The colored curves are string theory predictions for dark energy for different values of c.”
The problems with this include:
This is based not on a theory or calculation, but on a conjecture (see e.g. here) that consistent string vacua have certain properties.
Many experts disagree with this conjecture. In particular it would imply that the well-known supposed metastable string vacua of KKLT are inconsistent, and that is a matter of controversy.
This conjecture is not the sort of thing that can be proved one way or another, since it is not about something well-defined. The non-perturbative formulation of string/M-theory necessary to get a well-defined answer to such questions about string vacua remains unknown. You can make various conjectures about the behavior of this unknown theory, but then your swampland conjecture is a conjecture about a conjecture.
The conjecture involves an unknown constant “c”. Unless you know what “c” is, you don’t actually have a prediction.
In his conclusion, Vafa writes:
In the next 5–10 years, we may know, for example, whether dark energy is constant or not. If it is, that could pose a serious blow to string theory. But if dark energy is found to be changing, could that observation be the first experimental evidence for ideas emanating from string theory?
The most likely possibility over the next 5-10 years is that measurements continue to be compatible with constant dark energy. I don’t believe for a minute that 10 years from now after that result is in you will see Vafa or anyone else giving up on string theory or even admitting it has suffered a “serious blow”. On the other hand, if there is any evidence for a varying dark energy, Vafa or others will surely claim it as “evidence for string theory”, which it will not actually be.
Over the last 15 years I’ve often written here about this “Swampland philosophy”, which never made much sense to me. I didn’t understand back in 2005 and still don’t understand now why conjectures that behavior you don’t observe in the real world might be inconsistent with some other conjectures about an unknown M-theory are supposed to be of interest. The sociological motivation here is rather clear though: the KKLT-based “anthropic landscape” philosophy has not worked out well for the field, and the hope is to disentangle the subject from that morass. A good explanation of what is going on is provided by this (stolen from Will Kinney, who also has a lot to say about the whole swampland business):
This is a different sort of hype, with no direct relation to string theory. In this genre of hype, you don’t have any connection between your calculation and either experiment or a fundamental theory, but this doesn’t stop you from making grandiose claims. What’s behind this particular article is this paper, which develops a nice calculational method exploiting conformal symmetry. What’s not made clear in the Quanta article is that this has no connection to anything measurable. As the authors of the article explain:
In this paper, we have worked under the lamppost of weakly broken conformal symmetry. This has allowed us to derive particularly clean insights into the analytic structure of inflationary correlators. However, it also restricts the strength of the couplings between the inflaton and additional massive fields. This makes the observational challenge to detect these effects enormous.
In other words, this is about speculative models in which the observable effects described at length in the Quanta article would be unmeasurably small.
The post-modern hype come into play with the argument that these conformal-symmetry based calculations somehow tell us how to replace space and time.
This suggests that the temporal version of the cosmological origin story may be an illusion. Time can be seen as an “emergent” dimension, a kind of hologram springing from the universe’s spatial correlations, which themselves seem to come from basic symmetries. In short, the approach has the potential to help explain why time began, and why it might end. As Arkani-Hamed put it, “The thing that we’re bootstrapping is time itself.”
If you’re trying to understand the origin of this particular dollop of hype, it’s a good idea to keep in mind something Arkani-Hamed said at a talk about Lance Dixon’s work back in 2013:
… I AM an ideologue. In my defense at least I can say that I’m a serial ideologue, in the sense that I’ll take totally different ideologies and drop the last one without thinking about it, but it’s very important for me personally to be an ideologue when I’m working on something…
So, usually I’ll get up when I talk about scattering amplitudes and give a long introduction about how spacetime is doomed, we have to find some way of thinking about quantum field theory without local evolution in space time and maybe even without a Hilbert space and blah-blah-blah. This is all very high-falutin stuff, this is stuff that Lance wouldn’t be get caught dead saying. I think none of these guys would ever say something that sounds so pretentious, but I have to say it, you know I have to say it, because this is the only way I can get up in the morning, and like “I suck again, OK, here we go, I’m doing it because spacetime is doomed, I swear to God, right”.
I’m actually rather sympathetic to the “bootstrap” philosophy in some general sense, which I’d interpret as “all is unitary representation theory of the conformal group”, i.e. that constraints of conformal symmetry, analyticity and unitarity are almost enough to determine a fundamental theory. The 1960s version of this, trying to get strong interaction physics purely from such general principles, didn’t work out, but I’ve become more and more convinced that representation theory and fundamental quantum field theory are very deeply intertwined. I do think though that to get anywhere you’re going to need to either work top-down (i.e have an actual fundamental theory and derive its implications) or bottom up (i.e. use observations to find the route to better theory).
Update: Those interested in KKLT vs. Swampland debates might be interested in the latest from Tom Banks. He makes a detailed case against KKLT/eternal inflation/Landscape models, which string theory Swampland enthusiasts may find appealing. They should however note what he has to say about string theory itself:
A more sensible attitude, which I share, is to accept that string theory defines some models of quantum gravity, but obviously not the one that corresponds to the real world.
John Tate, who was responsible for some of the most important developments in number theory and arithmetic geometry during the second half of the twentieth century, has passed away at the age of 94. Tate was a faculty member in the Harvard math department when I was an undergraduate there, moving on to UT Austin in 1990, then retiring from there in 2009.
The work that Tate is famous for includes “Tate’s thesis”, his 1950 doctoral thesis, which may be the most influential doctoral thesis of modern mathematics. For a book-length explanation of Tate’s thesis, see Ramakrishnan and Valenza’s Fourier Analysis on Number Fields. The later generalization of the GL(1) case of Tate’s thesis to the non-abelian GL(n) case is one of the founding pillars of the Langlands program.
Tate was the Abel Prize laureate in 2009, and one can learn a lot more about him from an interview conducted around the time of the award. For an extensive discussion of Tate’s mathematical work, see this article from James Milne, or this review by Milne of Tate’s Collected Works.
A mathematician was explaining his work to Tate, who looked bored. Eventually the mathematician asked “You don’t find this interesting?” “No, no” said Tate, “I think it is very interesting, but I don’t have time to be interested in everything that’s interesting”.
As a thesis topic, Tate gave me the problem of proving a formula that he and Mike Artin had conjectured concerning algebraic surfaces over finite fields. One day he ran into me in the corridors of 2 Divinity Avenue and asked how it was going. “Not well” I said, “In one example, I computed the left hand side and got p13; for the other side, I got p17; 13 is not equal to 17, and so the conjecture is false.” For a moment, Tate was taken aback, but then he broke into a grin and said “That’s great! That’s really great! Mike and I must have overlooked some small factor which you have discovered.” He took me off to his office to show him. In writing it out in front of him, I discovered a mistake in my work, which in fact proved that the conjecture was correct in the example I considered. So I apologized to Tate for my carelessness. But Tate responded: “Your error was not that you made a mistake — we all make mistakes. Your error was not realizing that you must have made a mistake. This stuff is too beautiful not to be true.”
During a seminar at Harvard, a conjecture of Lichtenbaum’s was mentioned. Someone scornfully said that for the only case that anyone had been able to test it, the powers of 2 occurring in the conjectured formula had been computed and they turned out to be wrong; thus the conjecture is false. “Only for 2” responded Tate from the audience. [And, in fact, I think the conjecture turned out to be correct except for the power of 2.]
Tate’s father, John Torrence Tate Sr., was a physicist, editor of the Physical Review between 1926 and 1950. In one famous story, Tate Sr. stood up to Einstein by insisting that one of his papers be refereed in the usual way. Einstein was outraged (but it turned out the paper was incorrect). A few years ago I was at a talk here in New York at the Simons Foundation, during which the speaker put up a slide referring to Tate (Jr.)’s work, with a picture of Tate. After a moment, from the back of the room we heard “that’s not me, that’s my father!”.
Some links related to the foundations of math and physics:
Kevin Hartnett at Quanta has a long article on Jacob Lurie and his work on infinity categories. Unfortunately Lurie didn’t participate in the article himself, so comments are only from others. The article does a good job of giving at least a vague sense of what these very abstract foundational ideas are about, as well as examining the math community’s struggle to absorb them. Lurie’s work on this is spread out over more than 900 pages here and more than 1500 pages here. Recently he has been putting together an online textbook/reference version of this material as Kerodon, which is modeled after and uses much of the same software as Johan de Jong’s Stacks project.
In the new (November) issue of the AMS Notices John Baez has a review of a recent collection of articles about the foundations of mathematics and physics. The book, Foundations of Mathematics and Physics One Century After Hilbert, contains contributions about both math and physics, although in his review Baez concentrates on issues related to physics. He notes “The elephant in the room is string theory.”
The same issue of the Notices contains an informative long article about Michael Atiyah and his career, written by Alain Connes and Joseph Kouneiher (Kouneiher is the editor of the book reviewed by Baez).
The 2019 Physics Nobel Prizes were announced this morning, half going to Jim Peebles for his work on big bang cosmology, half to Michel Mayor and Didier Queloz for discovery of an exoplanet.
You can read elsewhere more details about the prize winners and their work, but I do want to point out that this announcement means (since there will be no further Physics Nobel Prize awards before the start of 2020) that John Horgan has won his 2002 bet with Michio Kaku, with \$2000 going to the Nature Conservancy. The winning prediction from Horgan was:
By 2020, no one will have won a Nobel Prize for work on superstring theory, membrane theory, or some other unified theory describing all the forces of nature.
If one looks at the comments back then, Gordon Kane signs on to an even stronger variant of the Horgan/Kaku bet:
By 2020 there will be a Nobel Prize for a string- or unification- or supersymmetry-based theory or explanation or experimental discovery.
Luckily for him he doesn’t seem to have put up any money for this, since he has now lost this bet.
For my own comments at the time, see here (this was a couple years before this blog was started). As I explained there, I was willing to sign up on Horgan’s side of the bet if the “other unified theory” clause was eliminated. Unlike Horgan, I’m not a sceptic at all of the existence of a unified theory, or of humanity’s ability to find it. My argument (which I think has held up well) was that we’re not going to get there by pursuing superstring theory or anything like it. In a better world, the LHC would have found not a vanilla Higgs, but something unexpected that gave us a new idea about electroweak unification, one that pointed to a successful new idea about a fully unified theory. I didn’t think this was likely, but I thought it was possible, and I wasn’t interested in betting against the possibility I would most like to have seen.
What shocks me about where we are now that Kaku and Kane have lost their bets is not that they lost, which was to be expected, but that this loss seems to have had zero effect on their behavior. Kane’s endless replacement of failed predictions by new ones is a well-known story. For Kaku, one can get some idea of his current point of view from this interview:
Yahoo News: So tell us about your work in string field theory. You’re trying to finish Einstein’s equation?
Michio Kaku: That’s right. We want to find the “God Equation” — the ultimate theory that explains the entire universe. We want an equation that’s maybe 1 inch long that would allow us to “read the mind of God” — those are Einstein’s words.
Yahoo News: And how’s it going?
Michio Kaku: We think we have it! It’s called string theory. It’s not in its final form, and it’s not testable yet, [but] we have the Large Hadron Collider outside Geneva.
We’re testing the periphery of the theory, but the theory itself is a theory of the universe — so it’s very hard to test. But we physicists are optimistic. We think we will be able to test the theory. And we think it is the final theory. So physics ends at that point. Another era opens up, but one era ends when we finally prove this is the Theory of Everything….
If string theory is correct, it means that all the subatomic particles — the electrons, the protons — are nothing but musical notes on a tiny vibrating rubber band. So that physics is nothing but the harmonies of the vibrating rubber bands. Chemistry is nothing but the melodies you can create from the vibrating strings. The universe is a symphony of strings.
And the mind of God is cosmic music resonated through hyperspace.
I don’t know of other bets on string theory, but there were quite a few bets about SUSY. I assume David Gross has now paid off his lost bets on SUSY, haven’t heard though anything about that. At the Copenhagen SUSY bet event, the losers (Arkani-Hamed, Gross and Shih) showed no signs that losing a bet on a scientific outcome had any effect at all on these scientist’s views on the issue they were willing to bet on.
Update: Horgan has posted his own take on this here.
The physics briefing book for the ongoing update to the European Strategy for Particle Physics is now available, for more see here. This describes the physics that one might hope to do with various proposed new machines. The hard part comes in the next few months: coming up with a proposal that has some chance of getting funded.
There’s an ongoing Cosmic Controversies conference in Chicago this week, which tonight will feature a panel discussion on “Do we need the Multiverse and can it made turned into a scientific theory?”. Tomorrow the panel topics will be more promising: “What more can we learn from particle physics about cosmology?“ and “Convergence or Disruption”. You can find video posted from the conference here including a live stream.
This evening I noticed that a recent documentary about Abdus Salam, entitled Salam: The First ****** Nobel Laureate, has just appeared on Netflix, and I spent some time watching it. The title is a reference to Salam’s membership in the Ahmadiyya sect of Islam, which in Pakistan has been declared heretical, and thus Salam not Muslim.
I enjoyed watching the film, and learned a lot I didn’t know about Salam, but there’s not a great deal in the film about his actual work in theoretical physics. While starting to write more here about the film based on some notes I took while watching it, I noticed that Matin Durrani last year at Physics World wrote an excellent detailed review of the film, and I recommend you consult that for more details.
Among those interviewed are Chris Isham and Michael Duff, who have interesting comments on what it was like to work with him. I was pleased to see that one old photograph had him standing in front of a blackboard that prominently featured “Unitary G-reps”.
Update: For another detailed review of the film, see here.
Photographer Jessica Wynne has been taking photographs of mathematician’s blackboards, and there’s a story about this in the New York Times. Many of her photographs have been taken here at Columbia, where we happen to have, besides some excellent mathematicians, also some excellent blackboards.
A non-Columbia excellent mathematician I’ve sometimes written about here is Bonn’s Peter Scholze. If you want to get some idea of the field he works in (arithmetic geometry) and what he has been able to accomplish, a good place to learn is Torsten Wedhorn’s new survey article On the work of Peter Scholze.
On the string theory front:
Arguments about the failure of string theory as a unified theory have been going on so long that they are now a topic in the history of science. For detailed coverage of many events in the long history of these arguments, you can consult historian of science Sophie Ritson’s 2016 University of Sydney doctoral dissertation. It and some of her other work is available at her academia.edu website.
For the latest in content-free argumentation about the failure of string theory unification, Steve Mirsky has a podcast discussion with string theory fan Graham Farmelo (see discussion of his recent book here), in which Mirsky challenges Farmelo about the problems of string theory. Farmelo has spent a lot of time at the IAS and basically takes the attitude that the point of view of certain unnamed string theorists there is what should be followed. I’d describe it as basically “we’ve given up working on string theory unification, but will keep insisting it is the best way forward until someone proves us wrong by coming up with a completely successful alternate idea.”
For the absolute latest attempt to extract some sort of “prediction” from string theory, see this week’s Navigating the Swampland conference in Madrid. Today there was a discussion session, with results shown of a survey of the views of those attending the conference. Note that, on the contentious topic of the reliability of supposed metastable de Sitter solutions of string theory, the Stanford group defending this reliability does not seem to be represented at the conference. I’ve been trying to understand what picture of physics this research has in mind, given that one main goal is to torpedo the metastable de Sitter solutions, and thus the usual “anthropic string landscape” picture. Looking at page seven, most participants seem to want to replace single field inflation models with more complicated quintessence or multi-field inflation models.
In Hirosi Ooguri’s talk he gives a supposed “unparalleled opportunity for string theory to be falsified”, I gather by claiming string theory somehow implies a small value of r. He quotes Arkani-Hamed as saying that string theorists should have reacted to the bogus BICEP2 measurement of r=.2 by saying “if this is true string theory is falsified.” They didn’t do that. When the topic came up at the time, what they had to say was:
Theoretical physicist Eva Silverstein of Stanford says she disagrees that string theory-based models of inflation are in any sort of trouble. “There is no sense in which we are forced to start over,” she says. She adds that in fact a separate class of theories that involve both axions and strings now look promising.
Linde agrees. “There is no need to discard string theory, it is just a normal process of learning which versions of the theory are better,” he says.
Several physicists now have pieces up explaining why Sean Carroll’s claim that “the Multiverse did it” (i.e. all you have to do is believe in multiple worlds) isn’t a real solution to the measurement problem. Beside the previously mentioned Chad Orzel, there’s also Sabine Hossenfelder and Philip Ball. I agree with Ball’s conclusion:
Here, then, is the key point: you are not obliged to accept the “other worlds” of the MWI, but I believe you are obliged to reject its claims to economy of postulates. Anything can look simple and elegant if you sweep all the complications under the rug.
Update: A video of the discussion session at the Swampland conference is here. It seems that I’m not the only one confused about what assumptions people working on this are making and what they are or are not accomplishing.
I’ve often added material to recent posts as “updates”, while aware that some who might be interested would likely not realize the added material was there. To improve the situation, I’ve just added a “Recently Modified Posts” widget on the right. The ordering is by modification time. I’ll try and figure out how to avoid having the modification time change when I do something like fix a typo (right now some old film reviews are appearing on the list because I recently added a “Film Reviews” category).
Among recent updates, I recommend the updates to this posting. Someone pointed me to a quite remarkable exchange earlier this week between Mike Peskin and Nima Arkani-Hamed.
Multiverse mania seems to have been dying down recently, with this only the third entry in that category here so far this year, after 10 in 2018, 13 in 2017, 10 in 2016, 17 in 2015, 18 in 2014, 12 in 2013, 9 in 2012, 15 in 2011. Bringing up the rear (hopefully…) is The Number of the Heavens, Tom Siegfried’s new book out today from Harvard University Press.
Siegfried is about the worst of the many journalists covering fundamental physics that I’ve run into over the years (only real competition is K.C. Cole). For some of his efforts as a journalist over the years, see here, here, here, here, here, and here. It’s not surprising that his multiverse book is an atrocious piece of propaganda.
It’s basically a compendium of arguments for string theory and the multiverse, with a bit of extra history tacked on. You get to read long sections of all the usual pro-string landscape and multiverse arguments from the usual suspects: Carroll, Deutsch, Guth, Greene, Linde, Polchinski, Rees, Susskind, Tegmark, and Weinberg. There’s the usual chapter on the MWI, ending with the acknowledgement that this has nothing at all to do with what the rest of the book is about. There’s a chapter about the glories of supersymmetry, brane-world scenarios, nothing about negative results from the LHC.
The way Siegfried handles criticism of string theory, etc. is very simple: pretend it doesn’t exist. As far as I can tell, there’s nothing anywhere in the book that even acknowledges that there’s another side to this story: for instance, no Baggott, Hossenfelder, Smolin, Penrose, or any reference to any book at all critical of string theory or multiverse hype. While there’s zero criticism of string theory, there are, as far as I can tell, just two appearances of multiverse critics:
On pages 223-8, remarks by Burt Richter at a panel discussion in 2006 get two paragraphs, followed by four pages of arguments from Linde, Susskind, Polchinski and Carroll explaining why he’s wrong. The prominent multiverse critic David Gross makes a brief appearance in these pages, with no mention of the fact that he is a multiverse critic.
Pages 262-9 are labeled a section on “Multiverse Deniers”, but there’s only one multiverse denialist quoted, George Ellis, with the only source given for his arguments this paper. In these pages short excerpts of his arguments are interleaved with long explanations from the author (as well as Weinberg, Wilczek, Carroll, Donoghue and Rees) about why Ellis is wrong.
Th one thing I can’t figure out about this book is how it got to be published by a reputable university press. My understanding has always been that university presses have some commitment to ensuring scholarly excellence in what they publish, for instance by having a manuscript about a controversy reviewed by experts from both sides. That obviously can’t have happened in this case, so I must be mistaken about how places like Harvard University Press now operate.