High Life

Posted on October 3, 2018 by woit

I spent yesterday night at the New York Film Festival, watching Claire Denis’s new film High Life. For a detailed and accurate review of the film, see the one at Variety.

This film is about a voyage to a black hole, in some sense an anti-Interstellar. Where the scientific plot of Interstellar was inspirational and made no sense at all, in High Life you get a plot that is all too plausible, and completely depressing. There’s a spaceship headed on a mission to a black hole, but this one doesn’t have brilliant scientists, traveling in a clean and shiny environment, and out to save the world. Instead, the crew is a bunch of ex-Death Row inmates, stuck on a dead-end trip in a filthy spacecraft swarming with recycled excrement, being subjected to grotesque sexual experiments, with periodic violent assaults, murders, and screaming babies to liven things up.

The supposed mission of the spacecraft is to travel to a nearby black hole and test whether energy can be extracted by the Penrose process. Because of all the murdering and such, that doesn’t work out too well. The ending involves another trip into a black hole, with discussion of whether they’re going to hit a “firewall”. One character thinks not, but that sure looks like one to me at the end. Theorist Aurélien Barrau is listed as “Cosmic Companion” or some such, and must have been responsible for providing the higher level of scientific verisimilitude than that of Interstellar (one of the images of a black hole does look like the famous one Kip Thorne provided for the earlier film).

I can’t really recommend this film to the average viewer seeking enlightenment or entertainment. On the other hand, if you’re looking for something unrelievedly grim, grotesque and disturbing, and really like black holes, maybe you should check it out.

Posted in Film Reviews | 15 Comments

Various and Sundry

Posted on September 28, 2018 by woit

First, news related in some way to Australia:

  • This summer the Sydney Morning Herald published a nice profile of Geordie Williamson.
  • By the way, the ICM plenary lectures are finally available on video, with Williamson’s among those worth watching.
  • The Sydney Morning Herald also recently had an article on quantum computing, motivated by a public talk by Patrick Hayden. The opening lines of the piece contain a classical superposition of quantum hype:

    Quantum computing will be so advanced that it will make your desktop computer look like an abacus, says Stanford University professor Patrick Hayden.

    However Professor Hayden, who will present a public lecture in Sydney on Wednesday, is keenly aware that “the hype is just out of control at the moment”.

Among talks I wish I’d gotten to see or am sorry I won’t be able to attend, there’s

If you just can’t get enough of the debate over string theory:

On politics and quantum theory:

  • I learned today from the Economist that the President of Armenia, Armen Sarkissian, is a theoretical physicist. Early in his career he worked in general relativity, see here. The Economist has Sarkissian promoting the idea of “quantum politics”:

    In his view, our interpretation of how politics traditionally works should be updated to reflect the way that physics has been reimagined. The classical world of post-Newtonian physics was linear, predictable, even deterministic. By contrast, the quantum world is highly uncertain and interconnected and can change depending on the position of the observer.

    “A lot of things in our lives have quantum behaviour. We are living through a dynamic process of change,” he says. “I think we have to look at our world in a completely different way.”

    I have no idea what’s going on in Armenian politics and whether quantum theory is the way to understand it. As for the current horror-show that is US politics, one thing that doesn’t deserve the blame for it is quantum theory.

A very quick mini-book review:

  • I just got a copy of Alvaro de Rújula’s Enjoy Our Universe, which is a short and entertaining, colorfully illustrated, overview of the current state of of high energy physics and the universe. The book brings back fond memories of a late-seventies course on particle physics that I took from de Rújula, whose humorous and lively character comes through in the book. For instance, about credit for discoveries:

    There is increasingly convincing evidence that the Vikings set foot in America as early as the tenth century. There is no question that the Amerindians were there much before that. And yet, the glory of “discovering” America goes to Columbus. Thus, the point is not being the first to discover something, but the last.

    About the relation of theory and experiment (this comes with a hand drawn illustration):

    In particle physics, discoveries – serendipitous or not – are generally made by experimentalists, in astrophysics and cosmology by observers. In both cases there are also the theorists. High time to explain the distinctions. This is done in Figure 53. The question is what the similarities between the two sets are. One set consists of a farmer, his pig, and the truffles, the other of the theorist, the experimentalist (or the observer), and the discoveries. The farmer takes his pig to the woods. The pig sniffs around and discovers a truffle. The farmer hits the pig with his bat and takes the truffle away. These are the similarities. The difference is that the theorist scarcely ever directs the experimentalist to woods where there are truffles.

    Beside the humor, the book is mostly succinct, clear and profusely illustrated explanations of important physics and astrophysics. The author early on explains that he plans to avoid discussing the sort of speculation popular in many other books, with a footnote justifying this:

    There is nothing wrong in discussing these subjects, except, in my opinion, doing it without a very clearcut distinction between facts, reasonable conjectures, and outright fantasies.

Update: Some news and views on an open access development, courtesy of Mark Hillery:

  • “Plan S has been put forward by a consortium of European funding agencies, including those of the UK, France, and the Netherlands, though not, as of now Germany, and it would require recipients of their funding to publish in gold open-access journals or vaguely defined compliant open access platforms by 2020. Hybrid journals, such as the Physical Review, will not be allowed. Gold open access requires that authors pay to have their papers published. The claim is that a cap on article processing charges (APC’s) will be mandated, but the details have not been spelled out yet. More information can be found here.

    http://www.sciencemag.org/news/2018/09/european-science-funders-ban-grantees-publishing-paywalled-journals

    A good discussion of open access can be found here.

    https://otwartanauka.pl/in-english/experts-on-open-access/open-access-will-remain-a-half-revolution-interview-with-richard-poynder

    This is an attempt to force the gold open access model on all of scientific publishing. In a rebuttal to Plan S,

    Response to Plan S from Academic Researchers: Unethical, Too Risky!

    a group of young European researchers has pointed out that it would prohibit them from publishing in 85% of existing journals. They also point out a number of additional problems with Plan S.
    1. While anyone can read an article in a gold open access journal without charge, publishing in one is a different story. APC’s, or what used to be known as page charges, are typically several thousand dollars per article. This seriously restricts the pool of people who can publish is such journals.
    2. What happens if the rest of the world does not go along with Plan S? Collaborations between EU and non-EU researchers would not be able to publish their results in many high-impact journals (Physical Review Letters, for example), and this could discourage such collaborations. It should be noted that Robert-Jan Smits, the Open Access Envoy of the European Commission, is tying to persuade funding agencies in North America to join in Plan S.
    3. Telling people where they can publish violates academic freedom.
    4. In a gold open access journal, the financial incentives favor publishing lots of papers; the more papers published, the greater the income of the journal. This could lead to quality problems.
    The rebuttal also points to possible alternatives to Plan S, such as green open access, which would allow a researcher to deposit a version of their paper in an online depository, such as the arXiv, at the time of submission and then submit the paper to a journal of their choice.

    While I am not a fan of commercial scientific publishers, whose profit margins are ridiculous, I am a fan of society journals (I work part time for one, Physical Review A). These journals are reasonably priced, and income from them helps support societies, such as the American Physical Society, and their activities. Plan S is a bureaucratic attempt to impose, from the top, a publishing model on the world with which many people disagree or have grave reservations.”

Posted in Book Reviews, Uncategorized | 30 Comments

Scholze and Stix on the Mochizuki Proof

Posted on September 20, 2018 by woit

As discussed here a couple months ago, Peter Scholze and Jakob Stix believe they have found a serious problem with Mochizuki’s claimed proof of the abc conjecture, and traveled to Kyoto in March to discuss it with him. Their write-up is now available here. Mochizuki has made public his response to this, creating a web-page available here. There’s also an updated version of Ivan Fesenko’s take on the story, as well as a possibly relevant FAQ on IUTeich from Go Yamashita.

Erica Klarreich has an excellent long and detailed article about this story at Quanta.

Update: Looking through these Scholze/Stix/Mochizuki documents, my non-expert opinion is that Mochizuki does not seem to effectively address the Scholze-Stix objections, which are aimed at a very specific piece of his argument. Unfortunately, he also does his own credibility a huge amount of damage by including over-the-top attacks on the competence of Scholze and Stix, in typefaces that make him look unserious. For instance, there’s

I can only say that it is a very challenging task to document the depth of my astonishment when I first read this Remark! This Remark may be described as a breath-takingly (melo?)dramatic self-declaration, on the part of SS, of their profound ignorance of the elementary theory of heights, at the advanced undergraduate/beginning graduate level.

or the last couple pages of his report.

Update: More of the same about IUT from Fesenko available here. His argument is that the overwhelming majority of leading experts in arithmetic geometry who are skeptical of the purported abc proof should be ignored, since they haven’t put in the two years of continuous study of IUT necessary. I don’t think this collection of ad hominem arguments will do anything to change anyone’s mind. I also don’t see why he doesn’t instead produce what could change minds: a clear and convincing technical refutation of the Scholze-Stix argument.

Posted in abc Conjecture | 37 Comments

This Week’s Hype

Posted on September 10, 2018 by woit

The Stanford string theory group is not taking the attack by Harvard’s Cumrun Vafa lying down. After an arXiv barrage of papers defending KKLT (see here), they’ve now enlisted the Stanford press office, which has produced a five part promotional series about the scientific glories of the string theory landscape. The first part of the series is online today, the rest to come soon.

The great thing about having your university press office write stories like this for you is that they will just print whatever you want, unlike journalists, who might ask your critics what they think and even quote them. Even better than not having to hear from your critics, you can try and discredit them as close-minded reactionaries unethically thwarting the search for truth, by misrepresenting their arguments:

“One dominant view in the community is that believing in the Landscape might have the negative effect of leading people away from fundamental physics, so we shouldn’t even discuss it,” said Shamit Kachru, who holds the Wells Family Directorship of the Stanford Institute for Theoretical Physics (SITP).

I’ve never heard anyone argue that “we shouldn’t even discuss it”. There is a dominant view in the field that what the theorists at Stanford are doing is not science, but the arguments for this are scientific, not arguments about what is or what isn’t good PR. Will we see any of these arguments in the rest of the series?

Update: All five parts of this are now on-line. No critics of the string landscape are named and their serious arguments are ignored (they are described as “hating” the idea, creatures of their out-of-control emotions). In the context of the old arguments of the string wars, two things to note are

  • This could be accurately described as a campaign by people who are losing in the scientific marketplace of ideas to, instead of doing science, start a PR effort aimed at the public.
  • It’s once of the best examples of the kind of extreme tribalism and “group-think” Lee Smolin was pointing to that I’ve ever seen. Stanford is portrayed as uniformly of one opinion about this, other opinions are wrong and only held elsewhere. If you are (or want to be) at Stanford and have a different opinion, especially if you’re a postdoc or grad student, it’s being made very clear that you best keep this to yourself.

Update: For those who want to follow the latest on the “Swampland” challenge to the Stanford/KKLT landscape program being promoted by the Stanford press office, there’s a conference later this week in Madrid, talks here. Among the roughly 100 participants at the conference, no one from Stanford. Not invited? Invited, but refuse to participate in any scientific discussion critical of their program? Inquiring minds want to know…

Update: Nima Arkani-Hamed gave the colloquium talk ending the Madrid conference. At the end (1:30), he had these mystifying comments about the landscape, somehow relating this posting to the previous one:

The raises the possibility that we are misinterpreting the string landscape – the different regions aren’t “out there” but are different APPROXIMATE “System/Observer” splits of A SINGLE OBJECT.

I have absolutely no idea what this is supposed to mean.

Posted in Multiverse Mania, This Week's Hype | 19 Comments

Is Quantum Mechanics a Probabilistic Theory?

Posted on September 7, 2018 by woit

There is a simple question about quantum theory that has been increasingly bothering me. I keep hoping that my reading about interpretational issues will turn up a discussion of this point, but that hasn’t happened. I’m hoping someone expert in such issues can provide an answer and/or pointers to places where this question is discussed.

In the last posting I commented that I’m not sympathetic to recent attempts to “reconstruct” the foundations of quantum theory along some sort of probabilistic principles. To explain why, note that I wrote a long book about quantum mechanics, one that delved deeply into a range of topics at the fundamentals of the subject. Probability made no appearance at all, other than in comments at the beginning that it appeared when you had to come up with a “measurement theory” and relate elements of the quantum theory to expected measurement results. What happens when you make a “measurement” is clearly an extremely complex topic, involving large numbers of degrees of freedom, the phenomenon of decoherence and interaction with a very complicated environment, as well as the emergence of classical behavior in some particular limits of quantum mechanics. It has always seemed to me that the hard thing to understand is not quantum mechanics, but where classical mechanics comes from (in the sense of how it emerges from a “measurement”).

A central question of the interpretation of quantum mechanics is that of “where exactly does probability enter the theory?”. The simple question that has been bothering me is that of why one can’t just take as answer the same place as in the classical theory: in one’s lack of precise knowledge about the initial state. If you do a measurement by bringing in a “measuring apparatus”, and taking into account the environment, you don’t know exactly what your initial state is, so have to proceed probabilistically.

One event that made me think more seriously about this was watching Weinberg’s talk about QM at the SM at 50 conference. At the end of this talk Weinberg gets into a long discussion with ‘t Hooft about this issue, although I think ‘t Hooft is starting from some unconventional point of view about something underlying QM. Weinberg ends by saying that Tom Banks has made this argument to him, but that he thinks the problem is you need to independently assume the Born rule.

One difficulty here is that you need to precisely define what a “measurement” is, before you can think about “deriving” the Born rule for results of measurements, and I seem to have difficulty finding such a precise definition. What I wonder about is whether it is possible to argue that, given that your result is going to be probabilistic, and given some list of properties a “measurement” should satisfy, can you show that the Born rule is the only possibility?

So, my question for experts is whether they can point to good discussions of this topic. If this is a well-known possibility for “interpreting” QM, what is the name of this interpretation?

Update: I noticed that in 2011 Tom Banks wrote a detailed account of his views on the interpretation of quantum mechanics, posted at Sean Carroll’s blog, with an interesting discussion in the comment section. This makes somewhat clearer the views Weinberg was referring to. To clarify the question I’m asking, a better version might be: “is the source of probability in quantum mechanics the same as in classical mechanics: uncertainty in the initial state of the measurement apparatus + environment?”. I need to read Banks more carefully, together with his discussion with others, to understand if his answer to this would be “yes”, which I think is what Weinberg was saying.

Update: My naive questions here have attracted comments pointing to very interesting work I wasn’t aware of that is along the lines of what I’ve been looking for (a quantum model of what actually happens in a measurement that leads to the sort of classical outcomes expected, such that one could trace the role of probability to the characterization of the initial state and its decomposition into a system + apparatus). What I learned about was

In these last references the implications for the measurement problem are discussed in great detail, but I’m still trying to absorb the subtleties of this story.

I’d be curious to hear what experts think of Landsman’s claim that there’s a possible distinct “instability” approach to the measurement problem that may be promising.

Update: From the comments, an explanation of the current state of my confusion about this.

The state of the world is described at a fixed time by a state vector, which evolves unitarily by the Schrodinger equation. No probability here.

If I pick a suitable operator, e.g. the momentum operator, then if the state is an eigenstate, the world has a well-defined momentum, the eigenvalue. If I couple the state to an experimental apparatus designed to measure momenta, it produces a macroscopic, classically describable, readout of this number. No probability here.

If I decide I want to know the position of my state, one thing the basic formalism of QM says is “a momentum eigenstate just doesn’t have a well-defined position, that’s a meaningless question. If you look carefully at how position and momentum work, if you know the momentum, you can’t know the position”. No probability here.

If I decide that, even though my state has no position, I want to couple it to an experimental apparatus designed to measure the position (i.e. one that gives the right answer for position eigenstates), then the Born rule tells me what will happen. In this case the “position” pointer is equally likely to give any value. Probability has appeared.

So, probability appeared when I introduced a macroscopic apparatus of a special sort: one with emergent classical behavior (the pointer) specially designed to behave in a certain way when presented with position eigenstates. This makes me tempted to say that probability has no fundamental role in quantum theory, it’s a subtle feature of the emergence of classical behavior from the more fundamental quantum behavior, that will appear in certain circumstances, governed by the Born rule. Everyone tells me the Born rule itself is easily explicable (it’s the only possibility) once you assume you will only get a probabilistic answer to your question (e.g. what is the position?)

A macroscopic experimental apparatus never has a known pure state. If I want to carefully analyze such a setup, I need to describe it by quantum statistical mechanics, using a mixed state. Balian and collaborators claim that if they do this for a specific realistic model of an experimental apparatus, they get as output not the problematic superposition of states of the measurement problem, but definite outcomes, with probabilities given by the Born rule. When I try and follow their argument, I get confused, realize I am confused by the whole concept: tracking a mixed quantum state as it evolves through the apparatus, until at some point one wants to talk about what is going on in classical terms. How do you match your classical language to the mixed quantum state? The whole thing makes me appreciate Bohr and the Copenhagen interpretation (in the form “better not to try and think about this”) a lot more…

Posted in Quantum Mechanics | 74 Comments

Beyond Weird

Posted on September 5, 2018 by woit

Philip Ball’s Beyond Weird is the best popular survey I’ve seen of the contemporary state of discussions about the “interpretation” of quantum mechanics. It appeared earlier this year in a British edition (which I just read a copy of), with the US edition scheduled to come out next month. Since it’s already out in Britain, there are several reviews you can take a look at, an insightful one is Natalie Wolchover’s at Nature.

The topic of the “weirdness” of quantum mechanics is one receiving a lot of attention these days, with two other books also appearing this year: Adam Becker’s What is Real? (which I wrote about here), and Anil Ananthaswamy’s Through Two Doors at Once. Lack of time as well as not having much of interest to say about the book has kept me from writing about Through Two Doors at Once. It’s much more focused than the other two, giving close attention to the two-slit experiment and surprising variants of it that have actually been performed in recent years.

Some of what I very much liked about Beyond Weird is the way Ball avoids getting into the usual ruts that books on this topic often end up in (with the Becker book one example). He avoids the temptation to follow a historical treatment, something that is almost irresistible given the great story of the history of quantum mechanics. The problem is that the early history of quantum mechanics and the struggles of Bohr, Einstein and Heisenberg to understand what it was saying is a fascinating story, perhaps the most compelling in the history of physics, but it is one that has been well-told many times in many places. Books that cover the later history have found it hard to resist the temptation of revisionism, caricaturing Bohr, Heisenberg and the dominant “Copenhagen interpretation” while making heroes instead of David Bohm, John Bell and Hugh Everett.

Ball has little to say about the personalities involved, but instead seriously engages with the central troublesome issues of the quantum mechanical picture of the world. The Copenhagen interpretation is given a fair treatment, as a warning about the limits one runs up against trying to reconcile the quantum mechanical and classical pictures of reality.

Instead of spending a lot of time in the rut of Bohmian mechanics, Ball dismisses it quickly as

But it is hard to see where the gain lies… Even Einstein, who was certainly keen to win back objective reality from quantum theory’s apparent denial of it, found Bohm’s idea ‘too cheap.”

Dynamical collapse models like GRW also get short shrift:

It’s a bodge, really: the researchers just figured out what kind of mathematical function was needed to do this job, and grafted it on… What’s more of a problem is that there is absolutely no evidence that such an effect exists.

As for the “Many-Worlds Interpretation”, which in recent years has been promoted in many popular books, Ball devotes a full chapter to it, not because he thinks it solves any problem, but because he thinks it’s a misleading and empty idea:

My own view is that the problems with the MWI are overwhelming – not because they show it must be wrong, but because they render it incoherent. It simply cannot be articulated meaningfully… The MWI is an exuberant attempt to rescue the ‘yes/no’, albeit at the cost of admitting both of them at once. This results in an inchoate view of macroscopic reality suggests we really can’t make our macroscopic instincts the arbiter of the situation…
Where Copenhagen seems to keep insisting ‘no,no and no’, the MWI says ‘yes, yes and yes’. And in the end, if you say everything is true, you have said nothing.

There’s a lot of material about serious efforts to go beyond Copenhagen, by understanding the role that decoherence and the environment play in the emergence of classical phenomena out of the underlying quantum world. This discussion includes a good explanation of the work of Zurek and collaborators on this topic, including the concept of “Quantum Darwinism”.

The last part of the book is up to date on what seem to be some currently popular ideas about the foundations of quantum mechanics. One aspect of this goes under the name “Quantum Reconstruction”, the attempt to derive the supposedly hodge-podge axioms of quantum theory from some more compelling fundamental ideas, hopefully the kind your grandmother can understand. These ideas are conjectured to somehow have to do with “information” and limits on it. I’m not sympathetic to these, since the axioms seem to me not “hodge-podge”, but connected to the deepest unifying ideas of modern mathematics. At the same time, I remain confused about what “information” is supposed to be and how these new foundations are supposed to work. And, as far as I’ve ever been able to tell, these are not things your grandmother is likely to understand, unless your grandmother is Scott Aaronson…

Posted in Book Reviews | 14 Comments

Quick Links

Posted on August 31, 2018 by woit

A collection of links that may be of interest:

  • Talks from the SM at 50 conference held earlier this summer are available here.
  • A detailed expose of the “Fake Science Factory” is here, a related Nature story is here.
  • For those wondering what came out of this story, you might be interested in this.
  • If you want to know what happens to string theorists who leave the field, one answer is that they perform as Ninja Sex Party.
  • Burt Richter passed away last month at the age of 87, some obituaries are here, here and here. Blog postings here discussing talks or papers by him can be found with this search.
  • Terry Tao has come up with his own take on arithmetic geometry, available here.
  • A Capella Science is really too wonderful for words. For an example, check out William Rowan Hamilton. Tommaso Dorigo explains here that Tim Blais will be at CERN on Sept. 19.
  • October 10 there will be a program at the New York Academy of Science about The Mystery of our Mathematical Universe. I can’t help noticing something about discussions of the deep role of mathematics in physics: they rarely involve mathematicians.
  • I’ll do an online web interview on September 6, as part of the Festivalettura in Mantua.


Update: Frank Wilczek has an insightful review of Lost in Math at Physics Today.

Posted in Uncategorized | 7 Comments

Quantum Supremacy

Posted on August 26, 2018 by woit

Hasn’t been much that I’ve heard about worth discussing here recently. Presumably everyone is on vacation. I’ll try and gather some things that may be of interest, starting first with the hot topic of “quantum computation”. It looks like this will be drawing an increasing amount of attention and resources in the field of physics research. For instance:

  • Slides and videos from the summer IAS program From Qubits to Spacetime are available here.
  • There will be a graduate seminar at Harvard this fall, blog post about it here.
  • In a few weeks Fermilab will host a workshop on Next steps in Quantum Science for HEP.
  • Moving through the US Congress is a National Quantum Initiative Act, which would provide over a billion dollars in funding for things related to quantum computation.
  • At the NSF MPS (Mathematics and Physical Sciences) they’re promoting NSF’s Quantum Leap. This is the first of four “Big Ideas” (discussed here) which will influence what gets funded. The other three are multi-messenger astrophysics, big data, and things related to biology.
  • Launching this week is The NSF 2026 Idea Machine, which is a competition for suggesting research questions, more “Big Ideas” for the NSF to fund. If you want to enter the competition that opens Friday, I’m guessing that invoking the word “Quantum” will help.
Posted in Uncategorized | 11 Comments

On Status of KKLT

Posted on August 16, 2018 by woit

(Warning, this is just more about the topic of the last posting, which for most people will be a good reason to stop reading now. On the other hand, if you’re obsessed with the controversy over string theory, you might find this interesting).

I finally got around to watching some more of the Simons Center Workshop on the Swampland talks, and noticed a remarkable exchange at the end of Thomas Van Riet’s talk On Status of KKLT (starting at 1:30). The first commenter (a German, Arthur Hebecker?) starts off saying “I think you are doing something that is very dangerous”, with the danger being that KKLT will get thrown out and people will think that it is a “theorem” that string theory has no dS vacua. He is interrupted by Vafa who tells him that “your statement is defamatory, let’s calm down”. The German goes on to explain to Vafa the significance of the danger he is concerned about:

Maybe for you in the US it’s fine at Harvard, for me it will be a pain because people will turn against me. The little standing that string theory and new physics at all has in Germany will be harmed by a backlash on us that we have been talking nonsense all the time, which is not true.

Van Riet after a while interjects that there is an even worse danger:

The opposite happened and actually back-reacted very badly. We had the books by Woit and Smolin and it was based on the existence of the multiverse as a correct statement, right? And that’s when the criticism of string theory took off, right?

Someone else in the audience (Iosif Bena?) comes in on the Vafa/Van Riet side of the argument, criticizing multiverse mania:

I think the main problem was that at the beginning people in the KKLT camp, they came up with, “OK string theory has the multiverse, we’re not going to do physics anymore, the anthropic principle…” They came up with all these ideas that hurt string theory much much worse, at least in Europe, at least in my part of Europe. And you know, essentially hurt us heavily… Then there were these books by Woit and Smolin that were very popular…

It’s remarkable to see publicly acknowledged by string theorists just how damaging to their subject multiverse mania has been, and rather bizarre to see that they attribute the problem to my book and Lee Smolin’s. The source of the damage is actually different books, the ones promoting the multiverse, for example this one. A large group of prominent theorists, especially many from the West Coast, including the group at Stanford and the late Joe Polchinski at Santa Barbara, used the existence of the KKLT construction to push very hard a pseudo-scientific excuse for why string theory wasn’t working out. I’ve often point this out, and I do think this has been very damaging to the public perception of string theory. But the underlying problem is the takeover of string theory by multiverse pseudo-science, not that I and Lee Smolin criticized it.

A striking fact about the Stony Brook workshop is that none of the participants were from Stanford, and none of the many prominent figures responsible for promoting KKLT were there. It looks like there is now a dramatic split going on, with Vafa leading the charge to try and fight back against what in recent years has been a seeming dominance of string theory by the pro-multiverse faction. I think such a split is long overdue, that most string theorists for years now have been making a terrible mistake by going along with multiverse pseudo-science. As Hebecker(?) explained though, fighting back publicly at this point carries its own dangers. In particular, many observers will be asking: “for years you told us about the 10500 vacua”, now you say that maybe there aren’t any. Which is it? Why can’t you tell? And do you really have a serious alternative for how to connect string theory to the real world?

Vafa tries to not take sides, to portray this as a simple technical question that will yield to further calculations by theorists. Where I disagree with him is that I’m very skeptical that this is a technical question with a well-defined answer. This is not a new controversy: theorists have been arguing about moduli stabilization and this de Sitter/no de Sitter issue for twenty years or so, without coming to any firm conclusions. If you watch the technical talks at the Stony Brook workshop, the degree of technical complexity of the arguments is striking, as is their often rather vague nature. What you don’t see is a specific set of equations that everyone agrees on. We’ll see what happens in coming months and years, there are likely to be a large number of papers written on this subject. Also to look out for, likely the efforts of Vafa and others to throw doubt on KKLT will not be taken lying down. The West Coast Empire will strike back…

Update: At CNN, Don Lincoln has an article about this, which ends with:

It’s not quite a WWE cage match, but it’s going to be fun to watch these theories fight it out.

Update: Tonight the West Coast Empire has struck back, defending here and here their dS vacua against the Swampland attack, and going on the offensive, accusing the conjecture of their attackers as being “ruled out by cosmological observations, at least at the 3 sigma level”.

Posted in Multiverse Mania, Swampland | 15 Comments

Theorists with a Swamp, not a Theory

Posted on August 13, 2018 by woit

In recent weeks string theory has been again getting a lot of press attention, because of claims that new progress is being made in the study of the relation of string theory and the real world, via the study of the “swampland”. This is a very old story, and I’ve often written about it here. I just added a new category, so anyone who wants to can go follow it by clicking on the Swampland category of posts.

Recent press coverage of this includes an article by Clara Moskowitz at Scientific American, entitled String Theory May Create Far Fewer Universes Than Thought. This motivated Avi Loeb to write his own Scientific American piece highlighting the dangers of string theory speculation unmoored to any possible experimental test, which appeared as Theoretical Physics is Pointless without Experimental Tests. Loeb reports:

There is a funny anecdote related to the content of this commentary. In my concluding remarks at the BHI conference we held at Harvard in May 2018, I recommended boarding a futuristic spacecraft directed at the nearest black hole to experimentally test the validity of string theory near the singularity. Nima Arkani-Hamed commented that he suspects I have an ulterior motive for sending string theorists into a black hole. For the video of this exchange, see

https://www.youtube.com/watch?v=WdFkbsPFQi0

Last week Natalie Wolchover reported on this controversy, with an article that appeared at Quanta magazine as Dark Energy May Be Incompatible With String Theory and at the Atlantic as The Universe as We Understand It May Be Impossible (the Atlantic headline writer misidentifies “we” as “string theorists”).

Wolchover accurately explains part of this story as a conflict between string theorists over whether certain solutions (such as the KKLT solution and the rest of the so-called “string theory landscape”) to string theory really exist. Vafa argues they may not exist, since the proposed solutions are complicated and “Usually in physics, we have simple examples of general phenomena.” In response Eva Silverstein argues:

They [Vafa and others] essentially just speculate that those things don’t exist, citing very limited and in some cases highly dubious analyses.

On Twitter, Jim Baggott explains the problem

Let’s be clear. This is not a ‘test’ of string theory. There is no ‘evidence’ here. This is yet another conjecture that ‘might be true’, on which there is no consensus in the string theory community.

and in a retweet, Will Kinney accurately notes that

The landscape is a conjecture. The “swampland” is a conjecture built on a conjecture.

and points to an earlier tweet thread of his about this. Sabine Hossenfelder replies with the comment that

The landscape itself is already a conjecture build on a conjecture, the latter being strings to begin with. So: conjecture strings, then conjecture the landscape (so you don’t have to admit the theory isn’t unique), then conjecture the swampland because it’s still not working.

The Simons Center summer workshop this year has been devoted to Recent Developments in the Swampland, videos are here (this was also the case in 2006, see here). Next month in Madrid a conference will be devoted to Vistas over the Swampland, and I’m sure many more such gatherings are planned.

Unfortunately I think the fundamental problem here somehow never gets clearly explained: String theorists don’t actually have a theory, what they have is an approximation to an unknown theory supposed to be valid in certain limits, and a list of properties they would like the unknown theory to have. If this is all you have, there’s no way to distinguish when you’re on dry land (a solution to string theory) from when you’re in the swamp (a non-solution to string theory). Different string theorists can generate different opinions, conjectures and speculations about whether some location is swamp or dry land, but in the absence of an actual theory, no one can tell who is right and who is wrong. I don’t know why Vafa back in 2005 chose “Swampland” as the metaphor for this subject, but it’s an unfortunately apt one: string theorists are stuck in a swamp, with no way of getting out since they can’t tell what’s dry land and what isn’t.

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