Joe Polchinski’s contribution to the ongoing Munich meeting has now appeared on the arXiv, with the title String Theory to the Rescue. Evidently he’s not actually to be at the meeting, I’m not sure how his paper will be presented.
It’s pretty much the usual hype about the string theory and the multiverse, with untestable ideas about quantum gravity the only topic. The one innovation is that it contains a calculation: the probability of a multiverse is 94%:
To conclude this section, I will make a quasi-Bayesian estimate of the likelihood that there is a multiverse. To establish a prior, I note that a multiverse is easy to make: it requires quantum mechanics and general relativity, and it requires that the building blocks of spacetime can exist in many metastable states. We do not know if this last is true. It is true for the building blocks of ordinary matter, and it seems to be a natural corollary to getting physics from geometry. So I will start with a prior of 50%. I will first update this with the fact that the observed cosmological constant is small. Now, if I consider only known theories, this pushes the odds of a multiverse close to 100%. But I have to allow for the possibility that the correct theory is still undiscovered, so I will be conservative and reduce the no-multiverse probability by a factor of two, to 25%. The second update is that the vacuum energy is nonzero. By the same (conservative) logic, I reduce the no-multiverse probability to 12%. The final update is the fact that our outstanding candidate for a theory of quantum gravity, string theory, most likely predicts a multiverse. But again I will be conservative and take only a factor of two. So this is my estimate for the likelihood that the multiverse exists: 94%.
This is not to say that the multiverse is on the same footing as the Higgs, or the Big Bang. Probability 94% is two sigma; two sigma effects do go away (though I factored in the look-elsewhere effect, else I would get a number much closer to 1). The standard for the Higgs discovery was five sigma, 99.9999%.
My problem with a lot of the West Coast theorists is that I don’t seem to have the same sense of humor, so often I have trouble telling when they’re joking (does anyone know when Andrei Linde is joking?). Here though it seems quite clear that Polchinski is pulling the leg of the philosophers gathered to hear him speak. My calculations show that the chance the above text could be a serious contribution to a philosophy of science conference cannot be above .1%.
The other evidence that something comical is going on here comes from some of the over-the-top claims about the virtues of string theory. In particular, we’re told
A remarkable feature of string theory is that the dynamics, the equation of motion, is completely fixed by general principle. This is consistent with the overall direction of fundamental theory, describing the vast range of phenomena that we see in terms of fewer and fewer underlying principles. Uniqueness would seem to be the natural endpoint to this process, but such theories are truly rare…
Indeed, when I assert that the equations of string theory are fully determined by general principle, I must admit that we do not yet know the full form of the equations, or the ultimate principle.
Polchinski is quite right that it is “remarkable” to know that you have a unique theory, with unique equations, fixed by a general, ultimate principle, but you don’t know what the theory is, what the equations are, or what the principle is. I’m curious to hear from people at the conference what gets the bigger laughs: this or Kane’s argument that the unknown theory predicts a 1.5 TeV gluino (unless it’s not found, in which case it doesn’t).
Update: See here for the latest coverage of the meeting from Massimo Pigliucci, who comments at one point:
[Yet another string theorist. I must say, there does seem to be a stacking of them at this conference, and no experimentalists have been invited either]
Update: For more on Polchinski’s paper there’s Sean Carroll on Twitter, here and here, who tells us
So strange how the public perception of string theory has been warped by a few contrarian voices. Good topic for some future PhD thesis.
and that Polchinski’s new paper
lays out the case for string theory, and how unexpectedly successful it’s been.
I’m assuming by “contrarian voices” he’s referring to Polchinski. That string theory has been “unexpectedly successful” and the multiverse is a 94% sure thing is a highly contrarian point of view among physicists.
Update: More coverage of the workshop is available from Sabine Hossenfelder and Massimo Pigliucci.
We are told Joe’s paper will be presented by David Gross instead.
Peter, David is presenting his talk. But he said he will disagree with Polchinski.
the above comments are correct, David Gross will present Polchinski’s intervention (apparently, he is sick). This may turn out to be an unfortunate choice, for two reasons: i) Gross has had (far) more than his fair share of commentary already at the conference (he rarely actually asks questions of other speakers, he just gives his extended opinion on whatever they said); ii) it is going to be difficult for us to tell how much Gross will present Polchinski’s actual paper and how much editorializing he will do. I’ll report on today’s session at my platofootnote.org blog tomorrow, while my report on yesterday’s session will come out in about three hours. Cheers.
For some reason Polchinski’s words remind me of Cumrun Vafa’s argument (footnote 2 here: http://arxiv.org/pdf/physics/0308078v4.pdf) that the reason we do not see hyper-advanced aliens around is that they will have migrated to a more happening part of the multiverse. This in a supposedly-serious scientific paper. I wonder whether the whole String Theory phenomenon is just a huge wind-up. I suppose that I have always assumed that it was, but still …
Polchinski emphasises the string understanding of black hole issues. At the conference Dvali presented his ideas about black hole issues, which are sensible and make any UV understanding (such as strings) irrelevant. What was the reaction by string theorists?
Polchinski gave a talk which looks very similar to that arXiv post last week at the Einstein Centennial Conference in Berlin. He made the same comment about have unique equations following from a unique principle. He meant it seriously, although he also told us we were “allowed to laugh.” Ashtekar pressed him on what it might mean, and the response was essentially that this was a property of certain approximate results which he expected to persist in the full theory (whatever that might be).
We were told later in the conference that Polchinski was taken to the hospital with what sounded like rather serious symptoms. I don’t know any details, but this would explain why he’s not giving his talk in Munich.
I’ve deleted some later comments about Polchinski’s health. I hope that his health problems are not serious.
Gross presented Polchinski’s talk, basically read it from the paper, with very few comments of his own. No questions were asked since Joe is not here to answer (and because we were overtime). The 94% estimate for the multiverse produced a good laugh in the audience. 🙂
In your last post on this conference, I suggested Bayesian confirmation theory ought to be discussed, especially its relation to post-empirical confirmation (PEC), as I suspect PEC amounts to arguments for high prior probability in a particular theory.
How sad I am read Polchinki’s utterly fatous “calculation” in Bayesian probability.
David did a pretty good job. (Except for running badly over time.) I’ll have a summary of the workshop at Starts With a Bang, but not sure how quickly Ethan will be able to get it out, today or tomorrow.
Lies, damned lies and Bayesian statistics.
Sounds like there was also some comedy from David Gross, who today was reading Polchinski’s paper about the 94% probability of the multiverse, and string theory’s ultimate unknown unique principle, but then explained that
“The public is confused because there are a host of ppl who write blogs or books who attack string theory”
Under further probing by Sabine at the beginning of her presentation on cognitive and social bias in theory assessment ( which was excellent btw) Gross said he wasn’t referring to you. Heaven knows who he was referring to then…
Polchinski’s parody of Bayesian argumentation is interesting not least because Dawid’s main argument for the “no alternatives argument” is Bayesian. One wonders if the parody is aimed at Dawid himself, which would be curious coming from someone like Polchinski.
I’d guess that the intent of Polchinski’s parody is to say, in effect, “we don’t need no stinkin’ Bayesian argumentation”.
The spurious Bayesian argumentation aside, Polchinski seems to be reiterating what has been the standard line for at least a decade. Remember when Susskind was declaring that the grumbling was to no avail, and it was time to stop worrying and love the Landscape?
Indeed, Polchinski is arguing (yet again) that based on very general considerations about the prevalence of metastable states in more familiar physical contexts (accessible to experiment) we should have expected to end up here. That sounds to me rather like asserting in 1890 that the existence of an aether is inevitable, given everything we know about classical mechanics and electromagnetism, but it will sound convincing to many until a shift in perspective makes it seem otherwise, regardless of the problems of aether theory.
Dr. Woit – Sean Carroll seems to be on the offensive with String Theory today. Check out his Facebook page: https://www.facebook.com/seanmcarroll?fref=nf
“So strange how the public perception of string theory has been warped by a few contrarian voices. Good topic for some future PhD thesis.”
Earlier in the day he posted: “Joe Polchinski lays out the case for string theory, and how unexpectedly successful it’s been.” http://arxiv.org/abs/1512.02477
Wondering if he caught wind of your recent post about Einstein spinning in his grave after the PBS NewsHour interview?
I saw those on twitter, added a mention as an update to the posting.
The Polchinski piece itself is clearly part of a PR offensive for string theory, and Carroll seems to feel the need to join in on the side of his tribe. I get the impression string theorists are feeling somewhat embattled these days, as the LHC no-SUSY results shut off the last hope for vindication from experiment, and the public perception that the theory has not been successful hardens. Not sure that going on twitter and saying it’s all the fault of some blogger who has “warped” public perceptions is really going to do anything other than convince people that you’re a sore loser.
It’s funny to think of the situation 10 years ago when the argument was that string theory critics such as Lee Smolin and myself were just losers in the marketplace of ideas. Now that things haven’t been going so well for them in this marketplace, they start complaining about market distortions…
Maybe they feel embattled in part because of this conference. Despite the dominant presence of ST-related people, and the supportive opinions on ST by some philosophers, the unanimous conclusion of the participants today was that multiverse is nonsense. And yes, I mean unanimous, unless somebody silently lied when Gross initiated an opinion vote/poll.
The day started with an excellent lecture by George Ellis, who did a thorough analysis and the rebuttal of virtually all versions of the multiverse (save for the many-worlds interpretation of QM which is a different ballgame and was never really even mentioned seriously). There was no bashing or anything — Ellis presented in turn each multiverse idea as a legitimate scientific hypothesis, tried his best to take it seriously and interpret it charitably, and then mounted a fatal counterargument, rendering it either false or irrational. A textbook example of serious and proper scientific argument.
After Gross read/presented Polchinski’s paper (and IMO did a fairly good job at that), there were several very nice lectures both on philosophy and physics. The panel discussion was “regular”, basically what you would expect of any normal panel discussion, with a nice Q&A session at the end. All in all, a very nice conclusion to the event, if somewhat less vigorous than previous days. No serious controversies, only a couple of friction sparks here and there that are maybe better left unmentioned.
In the end, everybody I asked had a very positive overall opinion of the whole three-day event, myself included. Despite a few lectures that included some ST hype (the Polchinski lecture being by far the worst in that regard), most of the people expressed a very reasonable overall opinion both on ST itself and on the related philosophical issues. The conference was actually educational in the positive sense, IMO.
Too bad Polchinski wasn’t there to be the lone voice for the multiverse. It really is an odd situation now, especially in the US. Here some of the most prominent theorists (either not invited to Munich or not willing to travel there), and many of the ones who most often appear in the media, act as if the multiverse is a done (or 94% done) deal. On the other hand, from your account of the conference, and my impressions from people I talk to, an overwhelming proportion of professional physicists don’t think it’s science (or, not successful science).
I agree that the situation in the U.S. is particularly odd. If an overwhelming proportion of professional physicists don’t think ST/multiverse passes for legitimate science, then the fact that some prominent theorists in America would go so far as to consider it a “done deal” demands explanation. It’s one thing to see a wide range of opinions regarding some theory or idea. It’s another thing altogether to see opinions sharply divided between strongly convinced, and strongly unconvinced… especially if one of these camps is a clear minority. It seems to me that in cases like this something other than science is driving things. If ST/multiverse really is a “done deal” why aren’t there more than just a few American theorists who think so, no matter how prominent they are? I think it’s fair to ask whether personal beliefs, agendas, or anything else having nothing to do with science might be contributing to the certainty these folks have. Thoughts?
Scott, I think all the multiverse love comes from a desire to think that the ultimate theory had been discovered in their lifetime. We all want to know the answer to life, the universe, and everything – we just don’t want the answer to be found after we are dead.
First of all, I think it’s too bad there wasn’t a wider range of view represented at this conference, the deck was kind of stacked in favor of string theory and against the multiverse, reflecting the point of view of the organizers. So, even if Marko is right and the consensus there was that the multiverse is nonsense, that doesn’t necessarily reflect what is going on in theory groups, especially in the US.
My view is certainly that the side that sees the multiverse as not science has by far the better scientific case, so no need to invoke other reasons. As for what is driving multiverse mania among some theorists, I think it’s a combination of factors:
1. If your interest is in having a high media profile, communicating to the public an inspiring tale of current scientific progress, then the multiverse works well: it’s easy to explain, it sounds impressive, and it explains away uncomfortable questions about why the ideas you were promoting a few years back didn’t work out. This is going to work much better on TV than “we’re kind of stuck, haven’t been making much progress…”.
2. The string theory unification really has conclusively failed, and this puts people who have invested a lot of their lives in the subject in an uncomfortable position. Most of them (except for a few outliers like Kane) have given up on explaining anything about particle physics via string theory, and are concentrating on quantum gravity or connections to condensed matter, or quantum information theory, or anything else. Adopting the multiverse as an excuse in this situation is tempting: it gives you an argument for why the problem was insoluble. People then struggle with this temptation vs. knowing that this is an abandonment of science.
3. I think John has a point. Those who convince themselves of the multiverse can feel that, while they may not see a final theory, the framework they have devoted their life to working in is close to one.
(Rumor about Polchinski’s health removed).
David said he wasn’t referring to you, but not who he had in mind. Either way, as one of the few bloggers who write about quantum gravity I felt offended enough to defend the integrity of science bloggers. It is debatable who is to blame for much of the hype in the media, whether it’s the scientists themselves, institutional press offices, or science writers. But the problem clearly doesn’t have its origin in the bloggers, who most of the time just try to sort out fact from fiction. (I suspect David doesn’t actually read blogs.)
I came away thinking that the conference had been a helpful meeting of minds, a chance for philosophers to set the record straight on the use of falsifiability criteria and help get past the slogans. But it was also a missed opportunity. Ellis and Silk made points in their Nature article last year that were simply not addressed. Instead, the conference was broadly configured as a way to defend string theory against the charge that it is untestable and so unscientific. Despite Kane’s attempt to shoot the counsel for the defence in the foot with his absurd claims, I suspect the string theorists will be broadly satisfied with the outcome. Shifting attention to the multiverse was a clever ploy, as even astrology would look vaguely scientific in comparison (and it was indeed a great pity that Polchinski couldn’t attend).
This was just an opening skirmish, I think. The success of a series of best-selling popular science books, a continuing stream of popular science articles and television documentaries, and the award of prestigious “breakthrough” prizes valued at $3 million have all helped to create the impression in the public consciousness that string theory is a valid or even “true” description of nature. This is surely not a good thing.
I was really struck by the consensus in the room that string theory is NOT confirmed or validated. In his opening presentation Gross explained that it’s actually not even a theory, of the kind that can be put into a single equation and printed on a t-shirt. It is rather a “framework”, a set of ideas, concepts and mathematical relationships. To become a theory it has to be set up in the right way. Gross admitted that we can test theories but it’s really hard to test a framework. The trouble is that string theorists don’t yet know how to set up the string framework in precisely the right way.
Setting aside the question of whether they will ever be able to figure this out, it seems to me that it would be really refreshing to see one or two leading string theorists make an honest appraisal of the status of the theory in a couple of popular science vehicles, much as Gross did at this conference. I think this would really help to set the record straight. People have all sorts of different reasons for wanting to invest belief in stuff like this, but making the position on string theory clear would in my view restore some sense of integrity.
For those who attended the meeting, does anyone know the name of the gentleman
who in the opening talk by David Gross mentioned that “my theory can be written on a t-shirt” after Gross said that you cannot write down the equations of string theory on a T-shirt. one thing no one brought up in the meeting is the disproportionate amount of funding given to string theorists and those who work on landscape and its very hard for people who don’t work on this or LQG to earn a living. I was too tired by the panel debate,
but would have raised this issue, if I was there.
After reading the last 2 comments, I’m wondering whether agencies that fund HEP theory should change their application process. “Send us a T-shirt with your proposed theory written on it…”
Report of the meeting from Sabine Hossenfelder (in SWaB):
Near the end:
‘But Gross has his worries: “The public is confused because there are a host of people who write blogs or books who attack string theory.” As one of the few bloggers who regularity writes about quantum gravity, this remark offends me. The reality is that the biggest task of science bloggers – like Peter Woit, Ethan Siegel and myself – has become to clean up after sloppy science journalism. Hype is a real problem. But it’s not the bloggers who are to blame for this.’
In case some of the commenters above really don’t know: the reason that there is not an equation defining perturbative string theory is that it is an S-matrix theory, so it isn’t defined by an equation that constrains states, but by a prescription for how to compute the S-matrix elements: the string perturbation series.
Jim: Regarding your last paragraph, I feel obliged to point out I have just written a book Why String Theory? on precisely this topic, with 250 pages on what string theory is today in 2015, what it means in 2015, and what are the various reasons people actually spend time working on it 😉 And indeed, it was published all of 2 weeks ago.
You might want to explain that point about not needing equations because it’s S-matrix theory to David Gross. He was a student of Chew’s doing S-matrix theory in the mid-60s. For his account of his 1966 realization that this “was less of a theory than a tautology”, see here
I suspect he’d say the same about your claim to explain non-perturbative string theory this way.
Upon re-reading Urs’s comment I realized I misread it as about non-perturbative string theory. As he wrote it, I really don’t understand at all what he means. You can write down equations for perturbative string theory as a sum over worldsheets, and this isn’t an S-matrix theory (or, you can compute the S-matrix, but not just the S-matrix).
Looking forward to seeing your book. If it addresses the criticisms of string theory that for some reason got very little attention at the Munich workshop, and gives an honest appraisal of what the state of the subject is (not just hype a la Polchinski), that would be really great.
You’ll be pleased to know your book was mentioned several times (by Fernando Quevedo during his presentation and personally to me by Graham Farmelo), and it’s on my Christmas wish list. However, I’d still like to see some of the leading figures in the string theory community – Gross himself, perhaps, or Brian Greene or Lenny Susskind – make more effort to provide an honest appraisal of the current status of the theory, in much the way that Gross did at this conference.
@PeterWoit Some coverage of the Munich Conference: https://www.quantamagazine.org/20151216-physicists-and-philosophers-debate-the-boundaries-of-science/ You seem to have gotten some press too!
Pingback: Fundamental physics may be merging back into Philosophy due to untestable ideas | Daily Hackers News
Pingback: Theories Don’t Have Probabilities: Or, Is The Multiverse Real? |
In the version of the multi-verse I live in the probability is only 0.001%
Is there a good Bayesian estimate of the probability that Bayesian inference is an adequate replacement for the empirical verification of scientific theories?
David H. Bailey & Jonathon M. Borwein weigh in on the Munich meeting in this Huffington Post article, http://www.huffingtonpost.com/david-h-bailey/data-vs-theory-the-mathem_b_8886292.html. Most of the article is a rehash of what has been said here, and the article quotes you, Peter. It is the last paragraph that stands out. “This does not mean that all research in string theory and the multiverse must stop. But the practitioners of these fields should recognize that the chips are down: they cannot exist much longer as science if they cannot at least establish some crisp, testable connections with the real world of scientific data and analysis. They should not be given a free pass for all time.”
Pingback: a Luta pela Alma da Ciência | Universo Racionalista
Pingback: Beyond Experiment: Why the scientific method may be old hat | Not Even Wrong