Witten Goes Anthropic

Multiverse mania started seriously among string theorists around 2003, with a defining event Susskind’s February 2003 The Anthropic Landscape of String Theory. At the time I was finishing up writing what became the book “Not Even Wrong”, and my reaction to Susskind’s paper was pretty much “This is great! Susskind’s argument implies that string theory can’t ever be used to predict anything. If people accept that, they’ll have to give up on string theory since it has come to the end of the line.” Over the next year or two it became clear that devotion to multiverse mania wasn’t just localized at Stanford (where Andrei Linde had always been pushing this, even before the string theorists climbed aboard). Other proponents of the string theory landscape were up and down the California coast, including Raphael Bousso at Berkeley and Joe Polchinski at UCSB. One West Coast holdout was David Gross, who that summer at Strings 2003 quoted Churchill’s words to his country during the Nazi bombardment of London: “Never, never, never, never, never give up”. On the East Coast, the center of the resistance was at the IAS in Princeton, where several people told me that Witten was privately strongly making the case that this was not physics.

I ended up adding an additional chapter to the book about this, and covering developments closely here on the blog. For many years I found it impossible to believe that this pseudo-scientific point of view would get any traction among most leaders of the particle theory community. How could some of the smartest scientists in the world decide that this was anything other than an obviously empty idea? After a while though, it became clear that this was getting traction and that there was a very real danger that particle theory would come to an end as a science, with most influential theorists giving up, justifying doing so by claiming they now had a solid argument for why there was no point in trying to go further. String theory is the answer, but the answer is inherently unpredictive and untestable.

It has become clear recently that we’ve now reached that end-point. From the new video of his discussion with Rovelli, it’s clear that David Gross has given up. No more complaints about the multiverse from him, and his vision of the future has string theory solving QCD 80 years from now, nothing about it ever telling us anything about where the Standard Model comes from. Today brought an extremely depressing piece of news in the form of a CERN Courier interview with Witten. Witten has also given up, dropping his complaints about the string theory landscape:

Reluctantly, I think we have to take seriously the anthropic alternative, according to which we live in a universe that has a “landscape”of possibilities, which are realised in different regions of space or maybe in different portions of the quantum mechanical wavefunction, and we inevitably live where we can. I have no idea if this interpretation is correct, but it provides a yardstick against which to measure other proposals. Twenty years ago, I used to find the anthropic interpretation of the universe upsetting, in part because of the difficulty it might present in understanding physics. Over the years I have mellowed. I suppose I reluctantly came to accept that the universe was not created for our convenience in understanding it.

I’ve never really understood the kind of argument he is making here, that the problem with the string theory multiverse is that it’s upsetting, but we just have to get control of our feelings. Feelings have nothing to do with it: the problem is not that the idea is upsetting, but that it’s vacuous.

The rest of the interview is also pretty depressing. At the high energy physics experimental frontier, Witten promotes “split supersymmetry”, something which does little more than try to keep on life support failed ideas about supersymmetry and “naturalness”:

There is also an intermediate possibility that I find fascinating. This is that the electroweak scale is not natural in the customary sense, but additional particles and forces that would help us understand what is going on exist at an energy not too much above LHC energies. A fascinating theory of this type is the “split supersymmetry” that has been proposed by Nima Arkani-Hamed and others.

On string theory, he follows Gross in referring to not “string theory” but “the string theory framework” and describes the situation as

We do not understand today in detail how to unify the forces and obtain the particles and interactions that we see in the real world. But we certainly do have a general idea of how it can work, and this is quite a change from where we were in 1973.

The situation with string theory unification is that it’s a failed idea, not that it’s a successful general idea just missing some details.

Finally, Merry Christmas and best wishes for the New Year. Fundamental physical theory may now be over, replaced with a pseudo-science, but at least that means that things in this subject can’t get any worse.

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41 Responses to Witten Goes Anthropic

  1. Jackiw–Teitelboim says:

    Interesting “developments” in less than a week: Gross’ demonstrating his degree of rudeness is unbounded, particularly with Rovelli’s (BTW I watched Penrose/Linde’s debate at same channel, maybe Penrose is too just much of a gentleman to compare with but… well, poor moderator!); Strominger’s story about Witten’s hope on electron/muon’s mass ratio; and, of course, Witten’s speaking about “different portions of the quantum mechanical wavefunction”.

    I am not going to start a debate about Everett’s interpretation, but mixing stringy/eternal-inflation multiverse cosmologies with a very debatable interpretation of quantum mechanics is bearing not in pseudo-science, but poor judgment.

    Let’s hope next year Ed can make another contribution at the same level as in 1994 with Seiberg.

  2. Paolo Bertozzini says:

    Dear Peter,
    as regards Witten’s interview, there might be some other reasons why the “multiverse mania” is no more the main center of discussion … when questioned about “Which current developments in theory are you most excited about?”, Witten clearly stated that the “It From Qbit” ideas connecting gravity and quantum theory, via the insight from “holographic duality” on the relation between gravity and gauge theory, is the new game in town. As far as I understand, this line of research is only very mildly related to the original string theoretic program (through the *original* AdS/CFT duality).

    As regards the discussion between Gross and Rovelli, personally I did not like it very much … maybe because the only sincere agreement that I could spot was on the common fashionable criticism of mathematical motivated investigations (“Lost in Math” in direct opposition to sound theoretical ideas describing the “true in natural reality”). So … for Rovelli, string theory is beautifully lost in sterile mathematics … and for Gross fundamental physics outside string theory is missing the true messages from the real world accumulated wisdom in the study of the standard model unification (that He seems to consider to be somehow a prediction of string theory). *Both* points above (that string theory is “mathematically elegant” or “clearly motivated by experimental insight”) are for me quite problematic.

    I find the pairing of “naturalism/realism” with “divorce from mathematical soundness” much more troublesome for theoretical physics investigation, compared to an anthropic/multiverse mania that, after all, has always been around in different philosophical shapes since Bruno, if not much earlier.

    Things might still get worse 😉
    Merry Christmas and Happy New Year 2022.

  3. anonymous says:

    Why is it that the likes of Gross and Witten never think that there is a third alternative, that one gives up string theory instead of giving up their critique of the multiverse/anthropics?

  4. Ron Martin says:

    The best case scenario I see now for theoretical physics is that as people move on from string theory to other hotter areas of study in theoretical physics (such as gauge/gravity duality and the It from Qubit program), string theory gradually fades into irrelevance as its current defenders die out and new research programs take over. Worst case scenario is that the current string theorists, despite moving on to other fields, still nevertheless manage to catechise a new generation with the belief that “string theory is the only way to fundamentally explain the universe”, who then go on to perpetuate this belief indefinitely far into the future making string theory into essentially a new religion.

  5. Johan Smit says:

    Paolo Bertozzini,

    Even worse than either the “multiverse”/anthropics or the disentanglement of “naturalness” and “mathematical soundness” is the redefinition of string theory to cover more and more of theoretical physics, like what Gross, Strominger, Witten and presumably other string theorists are saying in their interviews, lectures, and debates, i.e. quantum field theory (especially conformal field theories and their duals) is string theory, condensed matter physics is string theory, quantum information science is string theory, even parts of mathematics is string theory. At some point, the term “string theory” itself will become such a general term that “string theory is true” will become a tautology, which would make no sense to anybody even a decade ago.

  6. Sabine says:

    Contrary to what most particle physicists believe and will tell you (and have written), arguments from naturalness never worked as predictions. The one case where that isn’t obvious is the charm quark but what they called “naturalness” in that prediction is not what they call (technical) naturalness today* (it’s rather an argument from simplicity – pairing up the quarks increased predictive power). As Witten correctly notices, naturalness turned out to be just wrong: neither the CC nor the mass of the Higgs boson is technically natural.

    What particle physicists should do at this point is

    (a) abandon naturalness rather than trying to bring it back in modified fashion and
    (b) understand how it could possibly happen that so many particle physicists believed in a criterion that’s so obviously unscientific as this, and then
    ( c) prevent the same problem from happening again for other unscientific ideas

    As to the multiverse. This idea is promoted by people who mistake math for reality and who don’t understand what a scientific explanation is. Saying that all values of a constant “exist” if you can only ever observe one value is both scientific and philosophical nonsense, and if you, after you’ve said that, still have to assume the constant has that value which you actually observe, then you haven’t explained anything. Re-expressing a set of constants by the maximum of some probability distribution just adds a completely superfluous story.

    Also, I have noticed a few times that the title of my book “Lost in Math” has taken on a meaning on its own. I want to stress that the message of my book was NOT to criticize the use of mathematics in physics, but rather to say that physicists do not take math seriously enough.

    Merry Christmas everybody 🙂

    * Incidentally, I got this wrong in my book. I have regrets.

  7. Eric Weinstein says:

    Nice Dylan reference Peter.

    If I might try something a bit out of pure physics, it is worthwhile asking why stagnation issues are afflicting the most theoretical disciplines across different fields. Neo-classical theory also became the dominant paradigm in economic theory as did the neo-darwinian synthesis in evolutionary biology.

    In all these cases, it feels like there was something special about the particular time when the idea hardened into dogma. I didn’t get to watch biology or economics when this happened. But in physics it was clearer because it happened more recently. I don’t think we could have a new dogma now. No person on the scene is invested with sufficient power at this moment to create dogma the way String Theory became nearly religious in the devotion it inspired in its 1980s practitioners.

    My sense is that this phenomenon of a field becoming dogmatic is personality dependent. Arrow, Samuelson, Friedman etc were all very different titans of economics. In biology, Triver, Williams, Dawkins, Alexander etc. were similarly giants. In Physics, we have only had Witten at that level for a long time (1980-2000 ish) with support from Juan, Nima etc in physics and Atiyah, Singer, Quillen, Segal, Freed, etc in math. But it felt for a long time that, often enough, only Witten fullly understood the plot.

    So my thought is that this is a bit like Greenspan admiting that, as the former oracle, he didn’t know fully what he was doing with the economy after all. He was all alone in that. Likewise, I fear it’s not really about the leadership of Witten, Gross, Vafa, Strominger, Seiberg etc. It’s really about Ed. Many years ago Joe Polchinski said to me ‘You keep mentioning String Theory Eric, but I am never sure whether String Theory really exists as a proper discipline or community…or whether we are merely runnning sub-routines for Ed.’

    I don’t know what to make of this. But it seems like a pretty important moment for the health of the field to free your younger colleagues and do what Greenspan did: admit you made a serious error in leadership judgement.

    I honestly don’t know why this group of leaders isn’t more concerned with the story of their stewardship of this field. Were I in their shoes, I imagine I might be thinking like Eisenhower did before his ‘Military Industrial Complex’ farewell address. Why not turn over a field that doesn’t have to labor under your unjustified pronouncements about the divine nature of Strings from 40 years ago? Give your intellectual descedents a new lease on life. This isn’t learning to love the landscape or appreciating anthropics after all. It’s really about admitting a catastrophic error in leadership judgment. And I think highly enough of Ed and company to think that they should do it out of love and concern for the field at their ages. But, what do I know.

    “Those of us who have looked to the self-interest of lending institutions to protect shareholders’ equity, myself included, are in a state of shocked disbelief,…Yes, I’ve found a flaw. I don’t know how significant or permanent it is. But I’ve been very distressed by that fact.” -Alan Greenspan at 82

    Physics is a science….so we should be able to do as well as the economists and financiers I would imagine. No? Something to think about anyway.

  8. Alessandro Strumia says:

    Dear Paolo, is “It From Qbit” a politically-correct way of saying “From It to Qbit”? Seasonal Greetings.

  9. Andrew Thomas says:

    I agree with your positive initial feelings about string theorists accepting the multiverse. It’s an admission that string theory has come to the end of the line. I’m not saying string theory is wrong, but this is the clearest possible admission that “there’s nothing to see, here”, and there’s now no longer any expectation that much of interest is going to come from continued research in string theory. Hopefully new students will take this as a coded message that they would be better off working on something else instead. It’s definitely a positive thing.

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  11. Anonymous says:

    “Fundamental physical theory may now be over, replaced with a pseudo-science, but at least that means that things in this subject can’t get any worse”?

    That brings to mind the Soviet era distinction between an optimist and a pessimist: an optimist thinks that things are as bad as they could possibly get, while a pessimist thinks things could always be worse. I’m not sure your optimism is justified, Peter, but perhaps it was meant as seasonal cheer. In any case, enjoy the holidays.

  12. Peter Woit says:

    Anonymous,
    I was tempted to end the posting with “Merry Fucking Christmas”, but thought better of it…

  13. John says:

    The issue with the current state of string theory is that too many string theorists have for far too long been studying string theories that were supersymmetric, which is not true in our world, and then equated string theory with superstring theory. And then they discovered that there are at least 10^500 different superstring theories, and decided that the multiverse and anthropic reasoning was necessary to explain the 10^500 superstring theories, all while ignoring that none of the multiverse or anthropic reasoning is even necessary because our world isn’t supersymmetric so none of the 10^500 theories even matter. And this has become especially apparent after the LHC results showed the non-existence of supersymmetry in the real world.

    If string theorists were actually serious about string theory as a fundamental physical theory, they would admit that the past 40 years, since the first superstring revolution, has been a wrong turn in the string theory research program, and then start over and begin searching for a consistent and stable non-supersymmetric string theory that has all the Standard Model particles and a spin 2 particle for gravity. Instead, the previous string theory holdouts against this multiverse nonsense, especially Ed Witten, the leader of the first superstring revolution, have not only failed to admit that superstring theories are a failed idea and that people should pursue alternative non-supersymmetric string theory approaches, they also have accepted the multiverse and largely given up on the string theory research program entirely, moving on to other fields such as the gauge/gravity duality research program in quantum field theory. Ed Witten and David Gross may say that a century into the future and we might see a string theory develop that might explain the Standard Model or QCD, but if nobody is working on (non-supersymmetric) string theory due to the acceptance of the multiverse and anthropic reasoning in the string theory community, I don’t see how string theory would make any progress in a century from where it is today.

  14. Mitchell Porter says:

    I would ask the commenters on this blog, who so dislike multiverse ideas and the anthropic principle and especially their combination… Do you have any thoughts on the possibility that that is how nature is? Do you just think that’s impossible or unlikely; do you think it is possible, but if it is so, it is inherently beyond the reach of science; or what?

    I will add that I am not objecting to the pursuit of theories that still hope to explain reality in terms of something unique. I am just wondering how categorical the association between “anthropic multiverse” and “unscientific” is.

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  16. Peter Woit says:

    Mitchell Porter,
    Maybe there is a multiverse, maybe there isn’t. I have no idea and don’t really have any feelings about it one way or another. But multiverse theories are pseudo-science unless they come with some scientific way of finding evidence for whether they are true or not. The problem with the string theory anthropic landscape multiverse is that there is nothing of this kind, see

    https://www.math.columbia.edu/~woit/wordpress/?faq=why-do-you-describe-the-multiverse-as-pseudo-science

    What is going on here is that the “multiverse” is being used not as a scientific explanation of anything, but as an excuse for not admitting a theory is a failure. Calling this “pseudo-science” is actually being charitable (less charitable would be something like “dishonest bunch of crap”….).

  17. Peter Woit says:

    John,
    Over the years many string theorists have tried to get around problems with using the superstring in 10d by finding string theories that work in other space-time dimensions or are not supersymmetric. The problem is that no one sees any way to do this. The standard theory of a non-supersymmetric string seems to need 26 space-time dimensions and even in that case has a tachyon. From early on in the subject, trying to get around this is something many people have worked on, unsuccessfully.

  18. Michael McGuigan says:

    John,

    There was a small resurgence of interest in non supersymmetric string theory after the LHC failed to discover supersymmetry. Much of the work was based on the tachyon free SO(16)xSO(16)’ Model in 10d or non Supersymmetric orbifolds. See for example:

    https://arxiv.org/abs/1407.6362
    https://arxiv.org/abs/1502.03087
    https://arxiv.org/abs/1907.01944

    There should probably be a workshop bring interested people together to develop this idea further and see what the implications are for particle physics.

    Sent from my iPhone

  19. History observer says:

    It has been complained many times on this blog that the young generation of physicists is dangerously being indoctrinated by the string theory-multiverse-anthropic ideas by the senior leaders of the field and/or by media. However, I find Weinstein’s comment above particularly relevant for understanding the important difference between the mindset of the past century’s young generation of physicists and the present day young generation of physics. Even Einstein was not taken back then as a leader in fundamental physics by the young generation of physicists. Very few followed him in his quest for a unified theory the way he *envisioned* it. That young generation found for itself the right path for progress and did not fall into delusion because of a great figure. That the present day generation is easily indoctrinated by media and/or by any senior investigator in a field actually reveals the value such a generation could in any case bring to the said field, even if it were not indoctrinated in the first place.

  20. John Peacock says:

    I can understand your negative outlook on anthropic reasoning in the specific context of string theory – indeed it would be a shame to abandon the aim of deepening our understanding beyond the great success of the standard model, especially if there is a risk of giving up too soon and too easily. But I can’t see that this alone explains or justifies your apparent hostility to every aspect of the multiverse. The logic of using observer selection in an ensemble to explain apparent fine tuning works fine in some contexts: we certainly didn’t need modern observations of thousands of exoplanets to be completely sure that they were there. Outside religion, the idea of winning a cosmic lottery is the only way to explain how the Earth happens to be the right distance from the Sun to permit life. With the cosmological constant, Lambda, we have a much stranger coincidence to explain; and in the absence of any idea of how its value might be explained from first principles, it seems reasonable to me to consider observer selection as a possible explanation. That would be true even if we didn’t have strong-field inflation models as a worked example to show that it is possible to generate an ensemble of causally disconnected universes; and certainly the discussion of multiverse issues in cosmology should not be tied to the specifics of inflation or string theory. Weinberg showed us that we can still make progress without such assumptions in the case where only Lambda varies within the multiverse, and this is a testable model: it predicts the posterior for Lambda, which can be compared with the single datum of the observed value. This is hardly precision cosmology, but it’s something. The existence of this calculation encourages one to think about specific issues, namely how much the efficiency of galaxy formation is suppressed in counter-factual models with increased Lambda. If the suppression is not large, then this model is ruled out and we would conclude either that there is no multiverse, or that more than one parameter varies within the ensemble. In fact, the best existing calculations indicate that the suppression is just about sufficient, and Weinberg’s model survives (https://arxiv.org/abs/1801.08781). This isn’t exactly a great triumph, since the other members of any ensemble cannot be observed – so yes the situation in cosmology is very different from the one in exoplanets, even if the initial logic is the same. What we are talking about here represents reaching the end of the road for experimental science – but that hardly proves that this isn’t the way things are. Of course we should continue to search vigorously for unique physical explanations of the parameters in our current theories; but this has been going on with little success for long enough, and therefore it seems to me that cosmologists are entirely justified in pursuing the parallel route of seeing where multiverse reasoning can take us.

  21. Johan Smit says:

    John,

    People have discovered that any tachyon-free string theory has to have some remnant supersymmetry, even if it is a broken misaligned supersymmetry.

    https://arxiv.org/abs/hep-th/9402006

    So you are out of luck if you want to abandon supersymmetry completely but keep string theory.

  22. Peter Woit says:

    John Peacock,
    My objections to the cosmological multiverse are in the context of using it to justify empty or failed ideas about fundamental theory, and, even worse, to then use this as an argument against any attempt to better understand fundamental theory.

    I don’t have any objection to people positing a cosmological multiverse and seeing what they can get out of the idea. It is a problem though that people doing this often overhype what they are getting, and engage in misleading claims about implications for fundamental theory.

    The Weinberg argument is a good example: as far as fundamental theory goes, it’s based on assuming a roughly flat measure on the CC in the relevant region, any CC equally likely. This isn’t much different than saying we know nothing about what the fundamental physics of the CC is. Somehow this gets magically turned into an argument for the string theory landscape, or for assuming there is no point to even trying to understand the fundamental origin of the CC.

  23. shantanu says:

    Peter: Witten also doesn’t seem too excited about neutrino experiments and I am surprised that the interviewee did not ask anything about non-0 neutrino mass, which is “supposed” to be evidence of physics beyond the standard model

  24. Alessandro Strumia says:

    Michael, how do you get flavour from the SO(16)xSO(16)’ string where the Higgs is the extra-dimensional component of a vector (so, its Yukawas are gauge couplings)?

  25. Michael McGuigan says:

    Allessandro,

    Yes that’s correct, the SO(16)xSO(16)’ Model has no gauged scalars in 10d and Higgs type fields come from components of the higher dimensional gauge field in the simplest situation, with Yukawa interactions coming from higher dimensional gauge interactions, with the fermions and number of generations (flavors) related to the Euler characteristic. The other references talk about more complicated situations as well that can give rise to a Higgs type field. Like I said it would be nice to have a workshop to discuss these things.

  26. S says:

    John Peacock,

    You write that “Outside religion, the idea of winning a cosmic lottery is the only way to explain how the Earth happens to be the right distance from the Sun to permit life,” and also “What we are talking about here represents reaching the end of the road for experimental science – but that hardly proves that this isn’t the way things are.”

    It seems to me the juxtaposition of these two shows why it’s problematic for *physics* to go down this road. The fact that the alternate explanation(s) are religious also doesn’t prove that *that’s* not how things are — but religion isn’t physics. It’s perfectly possible, as you say, that there’s a multiverse or what have you, but surely it’s a relevant question to consider when the speculations of what might be have trailed into being equivalent to religious musings and are no longer physics?

    (That’s not to it’s fundamentally impossible to discuss predictions of the model, a la Weinberg. My point is just that “This might just be how things are” does not mean that whatever “this” is is physics.)

  27. Lars says:

    “I suppose I reluctantly came to accept that the universe was not created for our convenience in understanding it.” — Edward Witten

    I don’t understand what that is supposed to mean.

    How is it a justification for accepting the anthropic principle and multiverse?

    Is assuming that the physical constants, fundamental particles etc are what they are for some physical reason (ie, not just random variation of values in a multiverse that just happened to produce the conditions where humans came about) the same as assuming the universe was created for our convenience in understanding it?

    I don’t get it.

  28. DH says:

    Mitchell Porter,

    I for one don’t consider multiverse theories or anthropic reasoning to be inherently troubling/impossible/unscientific/etc. If it ultimately turns out that an inflationary multiverse seems to be a necessary implication of the best available evidence, then so be it–once again we become smaller, like we did with Copernicus and Hubble.

    However, I share the first commenter’s puzzlement that Witten seems to casually conflate this with the multiverse of Everettian QM–as though “the anthropic alternative” has any meaning/power as a concept in its own right, irrespective of the specific physical account of why a “landscape” exists & what it consists of. He says he “has no idea whether this interpretation is correct,” but what he posited there is not even AN interpretation, it’s a weird mishmash of completely different ideas that happen to share the (potential) necessity of embracing anthropic reasoning.

    So I don’t dislike multiverse ideas in general, but I also think it’s borderline meaningless to discuss/assess them “in general.” That there may be regions of spacetime that are wholly & permanently separate from ours, sufficiently so to consider them “different universes,” seems to me a perfectly sensible idea (though I lack the expertise to assess it). A mathematical multiverse that arises from philosophically reifying the Schrödinger equation is another matter entirely (probably you can tell I think it’s nonsense, but regardless, I think everyone should at least be able to agree that it’s another matter!).

    At times I think some of our most prominent theorists are essentially becoming Platonic idealists, while being too philosophically naive to even realize that that’s what they’re doing. Regardless of whether this is “unscientific,” it’s certainly…something.

  29. Anon says:

    I don’t see how the multiverse explanation can work if the basic theory has supersymmetry (such as superstring thy). Wouldn’t the landscape be dominated by the Minimal SUSY Std Model (MSSM) vacua as compared to the Standard Model vacua, precisely because of the hierarchy problem? Or are we imagining that in most other universes of the multiverse where there is galaxy formation/intelligent life, their Large Hadron Colliders (or even the LEP) will discover SUSY?

  30. Peter Woit says:

    Lars,
    I think the Witten quote gives away what’s really at issue. This is not about the multiverse but about whether one can claim to have a successful unified theory even if it is a theory that cannot be tested, with specific reference to the string theory and its purported landscape of vacua.

    Pre-LHC, whenever Witten and others were challenged about the testability of string theory they would point to the possibility of the LHC finding at least indirect evidence for string theory (via SUSY). With that possibility now closed off, Witten has been put in the situation of having to either give up on the theory or try to defend the concept of a theory that can’t possibly be tested. He’s taking the second option and that’s what the quoted argument is all about.

  31. Peter Woit says:

    DH (and others),
    I agree that it’s meaningless to discuss multiverse theories “in general”. To have a sensible discussion it needs to be about a specific set of models (or “framework” if you like). If your argument is not about the string theory landscape set of models, please, no more. On this specific issue I’ve devoted a huge amount of effort over the years to trying to understand exactly how such models work, and I don’t see anyway around the conclusion that this is a vacuous framework.

  32. Peter Woit says:

    Anon,

    The anthropic argument has nothing to say about SUSY: either SUSY or non-SUSY vacua are consistent with our existence. When the string landscape program got started 20 years ago Susskind and others argued that it was predictive, that it could predict whether the LHC would see SUSY: just count the number of vacua with TeV-scale SUSY and those without. If there were a lot more of one than the other, than you would have a statistical prediction for what the LHC would see.

    That never worked out, basically for the same reason the string theory landscape can never make predictions: it’s not well-defined enough to allow one to know what’s a string theory vacuum and what isn’t. You know far too little about what the theory is that you’re talking about to know how to characterize string theory vacua in general (much less count them).

  33. Johan Smit says:

    skydivephil has put a poll on Twitter asking who won the debate between Rovelli and Gross, and over two-thirds of the respondents said that Rovelli won:

    https://twitter.com/skydivephil/status/1472635458438021127

  34. The Big Red Scary says:

    “Things got a bit worrisome at the end, when he announced that he can’t understand Kevin Costello these days (if he can’t, who can?)”

    Presumably Kontsevich hasn’t really tried, or he has tried and he has understood, but doesn’t want to admit it since he’s not the king of that hill. Andre Weil claimed not to understand schemes, but I once heard a protege of his say that, upon being left alone in Weil’s office, he pulled Weil’s copy of Grothendieck’s EGA off the shelf and found every page full of carefully penciled remarks.

    I can well imagine that Costello is hard to read for almost all physicists, and I have no idea whether it is interesting as theoretical physics, but it’s fine mathematics and not so very hard to understand if you put the time into it.

  35. Steve Burton says:

    I believe that the correct Churchill quote is actually:
    “never give in, never give in, never, never, never, never-in nothing, great or small, large or petty — never give in except to convictions of honour and good sense. Never yield to force; never yield to the apparently overwhelming might of the enemy. . . ”

    Here’s a link to a reference:
    https://www.nationalchurchillmuseum.org/never-give-in-never-never-never.html

    IMO (1) the difference between “give up” and “give in” is subtle, but important, and
    (2) the entire document at the link is worth a read.

    Cheers!

  36. Peter Woit says:

    Steve Burton,
    When I wrote about the Gross quote in the last chapter of my book Not Even Wrong, I did discuss the Churchill quote and point out that Gross’s version was not accurate.

    What struck me at the time was that Gross was comparing the threat to science from the anthropic landscape with the threat to England of defeat and occupation by the Nazis. Nearly 20 years later, what I find striking about his not mentioning this now is that by his own comparison he has decided to give in and do something comparable to accepting Nazi occupation.

  37. Paolo Bertozzini says:

    @ Johan Smit

    I totally agree that the habit to “redefine as String Theory” whatever comes handy for “leading String Theorists” is ubiquitous and disgusting.

    On the other hand, I notice that this is unfortunately a characteristic of the current cultural supremacy of aggressive marketing over anything else (most of science today is de-facto reduced to a “branch of marketing”): creating an “influential marketing channel” is an extremely difficult (often random) and resource consuming task and hence it is more and more common to have ideas, techniques or area “rebranded” on-purpose, often forgetting the original motivations and history of that subjects.

    At the end of the day (if one is able to swallow His-Her own pride and ambition for recognition) the important is that certain crucial ideas achieve the attention they deserve (maybe with a different name and pursued by different groups of researchers) … the huge problem is that the hype implicit in this aggressive “marketing” often distorts the discussion, so that certain biases become almost impossible to discuss or correct: as a result, essential changes are hold back and might become effective only decades after their original inception.

    One example of such “rigidity” is the usage of ” (bad) excuses” to justify at all costs the validity of a research program that has otherwise failed some or all of its initial goals: this, as Peter said, is the real role of “multiverses” in this String theoretic context.

    On a more positive side (as I suggested in my original post), I personally see as promising that the real focus of interest is shifting to other nearby areas (and maybe people do not even bother to make opposition to previous questionable points). For example, I am very happy to see a revival of themes from Algebraic Quantum Field Theory (as explicit case, here are the last pre-prints from Witten: https://arxiv.org/abs/2112.11614, https://arxiv.org/abs/2112.12828) … although several of these ideas/techniques could have been explored decades ago 😉

    I would be very interested to know Peter’s opinion on these specific works.

    @ Alessandro Strumia

    As we all know, “It from Qbit” is just a quantum byproduct of the “If from Bit” originating from Wheeler. “Digital Physics” has an independent tradition significantly older than anything related to String Theory (and most of all the “Quantum hype” is today even more “influential”) so a “rebranding” in the above-mentioned sense might not be so easy in this case. I would completely agree that “From *It* to Qbit” sounds much more appropriate as a description of what has been actually happening 😉

    Sorry for the late reply (but here it is end of the academic semester and I was really submerged with work). Happy New Year 2022 🙂

  38. Roger says:

    Off-topic.
    RIP the Bogdanoffs. They played an entertaining and not insignificant role in the String Wars.
    https://www.bbc.com/news/world-europe-59867046

  39. In the CERN Courrier interview Witten says about string theory:

    This framework has turned out to be very powerful, even if one is not motivated by gravity and one is just searching for new understanding of ordinary quantum field theory.

    This reminds me of a remark by ‘t Hooft in

    … there is ample information in what we already know, but not fully understand, even when it sounds as boring as perturbative quantum field theory and perturbative gravity in the Schwarzschild background

    If “powerful” = “useful (for theoretical physicists)”, I find his comment relevant at least in the current context emphasized by Paolo Bertozzini. Algebraic quantum field theory in curved space-time might experience indeed a revival with particularly pedagogical efforts done by Witten in his recent preprints to explain to youngsters (engaged in solid theoretical research in natural geometric structures) the subtleties of type III von Neumann algebras & show them why these oldies but goldies are required in trying to make some sense from (not be fulled by?) the rare computable models available to “quantum gravity” explorers.

    The connection is loose but it would be funny if Leutheusser & Liu work “Emergent Times In Holographic Duality” under the scrutiny of Witten could help to make some progress in the thermal time hypothesis of Rovelli & Connes…
    I wonder if Paolo Bertozzini has an educated guess on this subject.

  40. Mark says:

    Interesting to see in Witten’s own words the devolution of the string theory research programme from a theory of unification of all the forces, to a theory of quantum gravity, to merely being a framework for providing tools to understand quantum field theory better. If so, then theoretical particle physics will have returned to the state it was before the first superstring revolution, where the dominant paradigm was quantum field theory, and everything else (including string theory) is studied for possible applications to quantum field theory.

  41. Paolo Bertozzini says:

    @ Cedric Bardot

    I agree that “old” (algebraic) quantum field theory will have several further surprises in store (also for quantum gravity); if they will find better reception by the theoretical physics community, it is probably because the current AdS/CFT and holography trends (coupled with the impasses in string theory) are forcing people in that direction.

    As regards the “thermal time hypothesis”: from a very approximate first reading of the work of Leutheusser Liu, the “emergent time” evolution, although not directly coinciding with a Tomita-Takesaki modular flow (used in the Connes-Rovelli thermal time case), is anyway obtained from the Borchers-Wiesbrock half sided modular inclusions (the generator has positive spectrum) and so the connection is not that far away.

    Elaborating on the deep interplay between modular theory and geometry is of course extremely tempting form me (and I would seriously risk of running out of topic). My suggestion has always been that modular theory provides a “thermal non-commutative space-time” (instead of just a classical “emergent thermal time”) – I think I have been pestering Carlo in many conferences with comments on this topic 🙂

    Leaving aside technical important points, the present wide consensus on the *emergent nature of space-time* in quantum gravity (that was recently mentioned by Peter on this blog) is probably the most serious obstacle for attempts in the above mentioned direction. In any case, the usage of methods from Tomita-Takesaki modular theory will continue to spread: the importance of modular theory is not related to specific models (and goes even beyond the area of von Neumann algebras) since it is an ubiquitous feature of complexification of ortho-symplectic spaces; it will likely lead to further intriguing links with *analytic continuation (Wick rotation / Osterwalder Schrader reflection positivity) and geometry* – see recent works by Longo and by Neeb Olafsson (that is another reason why I was asking Peter’s opinion on such developments).

    Sorry if I went a bit “tangential” 🙂

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