The Only Game in Town

Posted on May 1, 2009 by woit

This week’s New Scientist has an article promoting the string theory multiverse, starting off with positive comments from Brian Greene, and continuing with a claim that the majority of physicists now embrace the idea:

Greene’s transformation is emblematic of a profound change among the majority of physicists. Until recently, many were reluctant to accept this idea of the “multiverse”, or were even belligerent towards it. However, recent progress in both cosmology and string theory is bringing about a major shift in thinking. Gone is the grudging acceptance or outright loathing of the multiverse. Instead, physicists are starting to look at ways of working with it, and maybe even trying to prove its existence.

In his promotional book on the subject, Susskind is able to come up with exactly one bit of information that the string theory multiverse hypothesis provides, a prediction of the sign of the spatial curvature of the universe (others don’t think that even this bit is there, see this by Steve Hsu). The New Scientist article ends:

…says Susskind. “If it turns out to be positively curved, we’d be very confused. That would be a setback for these ideas, no question about it.”

Until any such setback the smart money will remain with the multiverse and string theory. “It has the best chance of anything we know to be right,” Weinberg says of string theory. “There’s an old joke about a gambler playing a game of poker,” he adds. “His friend says, ‘Don’t you know this game is crooked, and you are bound to lose?’ The gambler says, ‘Yes, but what can I do, it’s the only game in town.’ We don’t know if we are bound to lose, but even if we suspect we may, it is the only game in town.”

The arguments for string theory have evolved over the years, with the “it’s the only game in town” one being made starting fairly early on. Weinberg seems to be willing to go for a new variant of this, that not only is it the only game in town, but it’s probably crooked (i.e. can’t possibly work, is obvious pseudo-science…), and this doesn’t matter, one should continue anyway.

It has become increasingly clear to me in recent years that there is a large cohort of people who have so much invested in string theory that they will never, ever give up on the idea of string theory unification, no matter how clear it becomes that the game is crooked and not legitimate science. They will be active and with us for a long time, but the idea that there has been “recent progress in both cosmology and string theory … bringing about a major shift in thinking”, causing the majority of physicists to sign on to this is nonsense. Quite the opposite is true, with the increasingly obvious problems with string theory causing non-string theorists to shun the subject and avoid hiring anyone who works on it.

The New Scientist article is also available here, and if you want more recent multiverse promotional material, there’s this. Finally, a panel discussion on this was held at the Origins symposium at ASU recently, and is now available on-line.

Update: The torrent of string theory hype seems to continue unabated, with claims that the Planck satellite will tell us something about string theory (see here):

The results could also offer insights into the much vaunted string theory – science’s big hope for a unified theory of everything. The idea involves a complex 11-dimensional universe, with seven ‘hidden’ dimensions on top of the four observable dimensions of space and time.

Professor Efstathiou said: “The potential for fundamental new discoveries that will change our understanding of physics is very important and that is what I’m really hoping for with Planck.

“We might find signatures of pre-Big Bang physics. We might find evidence of cosmic defects – superstrings in the sky.

“Unravelling the physical information may tell us something about the warped geometry of the hidden dimensions.”

Posted in Multiverse Mania, This Week's Hype | 42 Comments

The Strangest Man

Posted on April 29, 2009 by woit

When I was in Edinburgh I picked up a copy of Graham Farmelo’s new biography of Dirac. It’s entitled The Strangest Man: The Hidden Life of Paul Dirac, Quantum Genius, and is not yet available in the US. I read the book on the plane trip back to New York and very much enjoyed it. While I’ve read a large number of treatments of the history and personalities involved in the birth of quantum mechanics, this one is definitely the best in terms of detail and insight into the remarkable character of Paul Dirac. I gather that Farmelo had access to many of Dirac’s personal papers, and he uses these well to provide a sensitive, in-depth portrait of a man who often is reduced to a bit of a caricature.

The book is less of a scientific biography than the other book about Dirac I know of, Helge Kragh’s 1990 Dirac, A Scientific Biography, and emphasizes more the development of Dirac’s personality and the story of his relations with others, especially with his father, his mother, and his wife (who was Wigner’s sister). I learned quite a lot about Dirac that I’d never known before, including for instance the story of his work on the atomic bomb project during WWII.

Dirac is responsible for several of the great breakthroughs in 20th century physics. At the age of 23, while still a graduate student, he took Heisenberg’s ideas and found the fundamental insight into what it means to “quantize” a classical mechanical system: functions on phase space become operators, with the Poisson bracket becoming the commutator. This remains at the basis of our understanding of quantum mechanics, and Dirac’s textbook on the subject remains a rigorously clear explanation of the fundamental ideas of quantum theory. Two years later he found the correct relativistic generalization of the Schrodinger equation, the Dirac equation, which to this day is at the basis of our modern understanding of particle physics. This equation also turns out to play a fundamental role in mathematics, linking analysis, geometry and topology through the Atiyah-Singer index theorem. Around the same time, Dirac was one of the people responsible for developing quantum field theory and quantum electrodynamics, as well as coming up with an understanding of the role of magnetic monopoles in electromagnetism.

The period of Dirac’s most impressive work was relatively short, ending around 1933. By 1937, the year he married, Farmelo reports Bohr’s reaction to reading Dirac’s latest paper (on the “large numbers hypothesis”):

Look what happens to people when they get married

Farmelo discusses a bit the question of why Dirac never later achieved the same sort of success after the dramatic initial period of his career. There may be a variety of reasons: the open problems got a lot more difficult, marriage and celebrity changed the way he lived and work, the war intervened, etc. For the rest of his career, Dirac took the attitude that there was something fundamentally wrong with QFT, and this may be why he stopped making fundamental contributions to it. He believed that a different sort of dynamics was needed, one that would get rid of the problems of infinities. He never was happy with renormalization, either in the form used to do calculations in QED after the war, or the more sophisticated modern point of view of Wilson and the renormalization group.

Unfortunately, some of the later parts of Farmelo’s book are marred by an attempt to enlist Dirac in the cause of string theory. This starts with the claim that Dirac’s work on “strings” during the fifties should be seen as a precursor of present-day string theory. These “strings” occur in the context of QED and magnetic monopoles, where they are unphysical artifacts of a choice of gauge, and have very little to do with the modern-day interest in physical strings as a basis for a unified theory.

Farmelo sees string theory as a resolution of the problem of infinities that Dirac would have approved of:

What would surely have impressed Dirac is that modern string theory has none of the infinities he abhorred.

I don’t see any reason at all to believe that Dirac would have been impressed with the idea of resolving the problems of QFT that bothered him by replacing it with a 10-dimensional theory that, despite the endless hype, has its own consistency problems (its perturbation expansion diverges, just like that of QFTs, and, unlike QFT, a 4d non-perturbative theory remains unknown). String theory was around for at least a dozen years before Dirac’s death, I’m sure he had heard about it, and there is no evidence he took any interest in the idea. Farmelo reports the reaction Pierre Ramond got from Dirac in 1983 when he tried to sell him on the idea of replacing 4d QFT with a higher-dimensional theory:

So he asked Dirac directly whether it would be a good idea to explore high-dimensional field theories, like the ones he had presented in his lecture. Ramond braced himself for a long pause, but Dirac shot back with an emphatic ‘No!’ and stared anxiously into the distance

The book ends with long discussion of Dirac and string theory that I think is seriously misguided, but it does include a mention of the fact that many physicists are unconvinced by the idea of string theory unification. Veltman is quoted, and the last footnote in the book refers the reader to Not Even Wrong.

Dirac is famous among physicists for his views on the importance of the criterion of mathematical beauty in fundamental physical law, once writing:

if one is working from the point of view of getting beauty in one’s equation, and if one has really sound insights, one is on a sure line of progress.

Farmelo believes that Dirac “would have revelled in the mathematical beauty” of string theory, but this is based on an uncritical acceptance of the hype surrounding the question of the “beauty” of string theory. “String theory” is a huge subject, and one can point to some mathematically beautiful discoveries associated with it, but the attempts to use it to unify physics have led not to anything at all beautiful, but instead to the landscape and its monstrously complex and ugly constructions of “string vacua” that are supposed to give the Standard Model at low energies.

I very much share Dirac’s belief that fundamental physics laws and mathematical beauty go hand in hand, seeing this as a lesson one learns both from history and from any sustained study of mathematics and physics and how the subjects are intertwined. As it become harder and harder to get experimental data relevant to the questions we want to answer, the guiding principle of pursuing mathematical beauty becomes more important. It’s quite unfortunate that this kind of pursuit is becoming discredited by string theory, with its claims of seeing “mathematical beauty” when what is really there is mathematical ugliness and scientific failure.

Ignoring the last few pages, Farmelo’s book is quite wonderful, by far the best thing written about Dirac as a person and scientist, and it’s likely to remain so for quite a while. Definitely a recommended read for anyone interested in the history of the subject, or some insight into the personality of one of the greatest physicists of all time.

Posted in Book Reviews | 27 Comments

Atiyah80

Posted on April 27, 2009 by woit

Last week I was in Edinburgh for a few days and managed to attend the last two days of the conference in honor of Sir Michael Atiyah’s 80th birthday. Atiyah is now retired, but he was one of the dominant figures in mathematics during the second half of the twentieth century, as well as perhaps the person most responsible for bringing together mathematicians and physicists around issues of common interest in geometry and physics. His interactions with Witten played an important role in several major developments, including the whole idea of “topological quantum field theory”. One major part of my mathematical education was spending quite a lot of time for a few years reading through Atiyah’s collected papers. He is at all times a very lucid writer, with his expository writings quite marvelous and uniformly worth reading.

The biggest news at the conference was the announcement by Mike Hopkins of his solution (with Mike Hill and Doug Ravenel) of most of an old problem in topology that goes back to the sixties, known as the Kervaire invariant problem. Hopkins in his talk labeled the new theorem a “Doomsday Theorem”, because it nearly finishes off the subject it deals with, by ruling out the existence of a certain class of possible interesting topological invariants in all the remaining open cases except one. I wasn’t looking forward to trying to explain this here on the blog, since what is involved are issues in stable homotopy far beyond my expertise, so I was pleased to find this morning that others have beat me to it with explanations. The slides from his talk are here, John Baez has a posting here (including a comment from Hopkins here), and the news was spread to the ALGTOP mailing list here.

Another report of impressive progress on a problem was Simon Donaldson’s talk on the problem of showing that a Fano manifold has a Kahler-Einstein metric if and only if it is stable. This is one of the big open problems in complex geometry, and Donaldson discussed the appropriate notion of stability and outlined a strategy for getting a proof. He is not claiming a proof, with significant work still to be done, but experts seem to believe that the goal is now within sight and the next few years will see a resolution of this problem.

Unfortunately I arrived too late at the conference to hear Witten’s talk, the slides of which are available here. He is continuing his work of the past few years on Geometric Langlands. Dijkgraaf gave a nice talk reviewing a wide range of topics connected in one way or another with topological strings. Perhaps his slides will soon become available, but the topics covered were similar to those of his talks at UCSB last spring (see here). Vafa gave a rather clear explanation of his program to try and get particle physics out of local F-theory models. I’m not convinced this does more than reinterpret GUT extensions of the standard model using quite complicated constructions, but you can see for yourself here. He didn’t talk about the crucial question of whether this approach makes distinctive predictions about supersymmetry breaking testable at the LHC.

One evening was devoted to a public program about the Higgs particle, with a panel discussion featuring Higgs himself. It was not clear to me how much got through to the public about the electroweak symmetry breaking issue and what we hope to learn at the LHC. As always, some of the public wanted to know about what string theory has to do with this question. Unfortunately they were not given the simple, accurate and easy to understand answer “nothing at all.”

Update: The web-site for the conference is here, and conference organizer Andrew Ranicki has set up another web-site here for various materials associated with the conference.

Update: Videos of the talks at Atiyah80 are now available at the web-site linked to above.

Posted in Uncategorized | 16 Comments

Atiyah-Singer String Index Theorem

Posted on April 21, 2009 by woit

Just made it to Edinburgh for the Atiyah conference. It seems that someone at a local newspaper really wants to get my goat. See the story headlined World’s Great Minds Gather to Celebrate Atiyah’s Birthday.

Update: Will try and write more about the conference soon. At least one string theorist argues for the new name for the index theorem, on the grounds that it is used in string theory. When I get back to Columbia I think I’ll tell my Calculus students about the Taylor string series….

Posted in This Week's Hype | 23 Comments

Quantum tunnelling of a new, third kind could finally put string theory to the test

Posted on April 20, 2009 by woit

The whole “finally, a way is found to test string theory” business is starting to become a complete joke. See the latest such nonsense:

Quantum tunnelling of a new, third kind could finally put string theory to the test

which is based on this preprint.

Note: I’ll be traveling this week, first to Edinburgh, where a celebration of Sir Michael Atiyah’s 80th birthday is going on, then stopping in Dublin on the way back to New York.

Update: As usual, Slashdot can be relied upon to promote the latest “predictions from string theory” hype.

Posted in This Week's Hype | 7 Comments

Strings Strike Back

Posted on April 14, 2009 by woit

The February AAAS press event (discussed here) designed to get out the word that the critics are wrong and string theory is making predictions about physics that are getting tested has finally made it to Slashdot, via an article in Science News by Tom Siegfried.

Siegfried has been making his living selling string theory hype since at least the mid-nineties when he wrote quite a few articles for the Dallas Morning News with titles like “Physicists sing praises of magical mystery theory”. In 2000 he published The Bit and the Pendulum: From Quantum Computing to M-theory, which somehow manages to put together quantum computing, consciousness, and string/M-theory. His next book, in 2002, was Strange Matters: Undiscovered Ideas at the Frontiers of Space and Time, 300 pages of solid hype for problematic speculative ideas, with branes and superstrings playing a leading role. More recently, he has been at work hyping cosmic superstrings in the pages of Science magazine (see here) and trashing me and my book for claiming that string theory doesn’t make predictions (see here).

Most of the Science News article actually gives a reasonably sensible description of the story of attempts to use string duals and holography to study strongly coupled systems in 3 and 4 dimensions. But in the concluding paragraphs this story is shanghaied into service in the string wars, in a section entitled “Strings strike back” which begins:

In recent years it has become popular to criticize string theory as out of touch with reality. Popular books have been written by scientists, some prominent and others not so prominent, arguing that string theory makes no predictions that experiment can test, that its fundamental objects can’t be observed, that physicists have wasted their time on an enterprise that isn’t even scientific to begin with.

Such arguments leave an impression of utter unfamiliarity with the history of science. In times past, the same kinds of aspersions were cast against quarks, neutrinos, even the very existence of atoms. Superstrings are in good company.

You see, some critics of string theory are such ignorant idiots that they question the existence of superstrings even though any student of history knows that they are no more problematic than quarks, neutrinos and atoms. And experiments at RHIC show that string theory does make predictions, ones that have been successfully tested by experiment….

Update: I just read through some of the comments by Slashdot readers. The level of hostility towards string theory and string theory hype is remarkable.

Update: Commenter Hendrik points to a new piece from New Scientist where they have helpfully gathered together in one place all the outrageous string theory hype that has appeared in their pages in recent years.

Posted in This Week's Hype | 27 Comments

First Principles

Posted on April 10, 2009 by woit

I learned recently from Sabine Hossenfelder’s blog that there’s a new book out by Howard Burton, entitled First Principles: The Crazy Business of Doing Serious Science (she has some comments on the book here). It’s a fascinating and entertaining book. I couldn’t put it down this morning, so took a very long breakfast during which I finished reading it.

Burton got a Ph.D. in theoretical physics at the University of Waterloo, which led him (like most Ph.D.’s in theoretical physics) to need to find some sort of employment doing something else. He was saved from getting wealthy in the financial industry by Mike Lazaridis of RIM, who was on a list of people that Burton wrote to asking if they had any job openings. It turned out that Lazaridis was starting to think about the idea of funding a theoretical physics institute, and decided that Burton was just the person to hire to look into the idea.

One of the most interesting parts of the book is Burton’s description of the process he went through of talking to a large number of theorists around the world to get their ideas about the state of theoretical physics, and about what sort of well-funded new institute would be viable and make sense. An interesting problem to have, and one that he got a lot of good advice about from many people.

One of the main motivating ideas behind the founding of Perimeter was to support work on foundational issues that normally don’t get funded because they are considered “too hard” to make progress on. The other was to encourage openness and communication between groups that normally don’t talk to each other. Burton was quite struck by the situation with superstring theory (this was back in the late 1990s, long before the recent “string wars”):

…what did shock me was my growing awareness that the field was rife with dissention and sociological barriers. Superstring theorists, for example, did not interact in any meaningful way with people pursuing other approaches to the problem, and vice versa. Worse still, the groups were downright hostile to one another, lobbing ad hominem and defamatory attacks across one another’s bows, condemning mountains of work with a dismissive (and often ignorant) wave of the the hand while trumping up the claims of their own theories well beyond any defensible level… they were simply refusing to engage with one another, separating off into rival sects like high school gangs…

My first, albeit indirect, encounter with superstring theory was a perfect case in point. As a PhD student, I spent a good deal of time talking with Nemanja Kaloper… Actually Nemanja did most of the talking, particularly once he discovered that I had gone over to “the dark side” by opting to spend time learning various non-superstring approaches to quantum gravity instead of his beloved superstring theory. For Nemanja, this was nothing more than a time-wasting combination of obstinacy and simple-mindedness: superstring theory simply was quantum gravity; trying to learn quantum gravity without string theory made about as much sense as writing music without notes…

The more I kept my eyes open the more I realized that Nemanja’s behaviour was hardly unusual: indeed such counterproductive squabbling and rampant dogmatism existed on all sides of the issue, making it hard to see how any genuine progress in any direction might be attained in the near future…

The Olympian heights of pure reason, when examined in more detail, turned out to be reducible to a furiously contested form of highly esoteric tribal warfare.

The story of how Perimeter grew out of these ideas and came into being is a fascinating one, and Burton tells it with a sense of humor in a very entertaining way. He became executive director of the institute, all the while lacking the usual sort of credentials as an eminent researcher that would be expected for such a position. The book ends with a short epilogue discussing the fact that he was forced out of this position in June 2007:

The official reason given for my departure was that contract negotiations broke down, but I think it’s fair to say that such a justification hinges on a particularly loose interpretation of the world “negotiations”.

He speculates that the reason for this was the book he was writing:

So what on earth happened?

What happened, so far as I can determine, is the book you hold in your very hands. Bizarre as it may seem, it appears that a major preoccupation of the institute’s board of directors for the first six months of 2007 was what to do about this pernicious book, followed closely, presumably, by how to get rid of its author who had the brazen temerity to once again bring the dark story forward publicly.

I know nothing about what really happened, but if Burton is right that the book played such a role, that’s extremely odd. The book makes a wonderful case for Perimeter and what it has been doing, portraying it (accurately I think) as a big success. It does so in a way far more effective than the kind of PR materials such institutions usually hire professionals to produce.

Perimeter does seem to have become quite a success, playing an increasingly large role in the theoretical physics community. It now has a new director (cosmologist Neil Turok), plans to expand, and nine prominent members of the theoretical physics establishment have recently signed on as “Distinguished Research Chairs”. If anything, one might worry that the institution is in danger of too much conventional success, merging with the establishment that it was set up to provide somewhat of a challenge to. Their advertisements for new faculty specify that they are looking for people in “Cosmology and Quantum Information”. I don’t know much about the quantum information business, where they seem to be leaders, but these days the idea of a well-funded institute for cosmology isn’t exactly revolutionary (see here).

I’m curious to see what happens with Perimeter now that it’s entering adulthood, and glad to have read Burton’s book which does a great job of telling the story of its birth and infancy.

Update: Lubos has a posting about this, although it’s clear he hasn’t read the book. According to him Burton “managed to write a public text that exposes pretty much all the business (and personal) secrets of the Perimeter Institute. He wants to earn money by publishing this sensitive stuff.”

If you buy the book hoping to find out the “business (and personal) secrets” of PI, I think you’re going to be very disappointed.

Posted in Book Reviews | 15 Comments

Various News

Posted on April 6, 2009 by woit

The CERN Bulletin has been providing weekly updates about the progress of LHC repairs, with the latest one here. One thing they don’t seem to have mentioned is that it looks like the schedule has recently slipped by nearly a month. The schedule approved in early February had checkout of the machine in week 38 (week of Sept. 14) and first beam week 39 (week of Sept. 21). The latest draft of the schedule (see page 42 of this presentation) has checkout in week 42 and beam in week 43. So, it looks like the latest plan calls for injection of a beam around October 19th, collisions sometime in November.

I today heard an odd rumor about a problem this past weekend with the on-going repairs in sector 34, but there may be nothing to it, so I’ll try to stick to only mongering confirmed rumors.

The blogging world continues to expand with new institutional initiatives to set up blogs. There’s a new version of Quantum Diaries out, along the same lines as a similar site set up back in 2005. That’s the one that Tommaso Dorigo survived, along with some other physicists who have kept blogging, including Gordon Watts and Peter Steinberg. Unlike the 2005 incarnation, this version seems to be restricted to experimentalists, no theorists allowed. It also uses the same address as the old site, which unfortunately seems to no longer be accessible. Whether it is possible or desirable to set up a mechanism to ensure the availability in the future of blog content is an interesting question.

The AMS has set up a blog for mathematics graduate students, which so far mostly consists of professional advice.

One piece of news that might be interesting to some of these graduate students is that the NSF has just announced a plan to use some of the stimulus money to provide 30 two-year postdocs aimed at students on the job market this spring who have not yet found employment. The money is being funneled through the various institutes supported by the NSF, with the idea that the jobs will generally be hosted at other institutions, which will provide a mentor and possibly teaching opportunities. The deadline to apply for these jobs is very soon (April 10), there’s more here, here, here and here.

One unusual thing about these postdocs (compared to usual NSF postdocs) is that it appears they are available to anyone who is getting their degree from a US university, not just US citizens or green-card holders. It also seems to be possible to hold the postdoc outside the US, at some MSRI-affiliated institutions such as the University of Toronto. Adding up the cost of the 30 postdocs comes to maybe $3 million or so, leaving open the question on everyone’s mind in academia: what about the other %99.9 percent of the $3 billion in NSF stimulus money? Where’s that going to go?

I always wondered who the Pupin building housing the physics department here at Columbia was named after. Here’s the scoop.

The Origins symposium at ASU is finishing up today. It was webcast, but if you missed it archived video is starting to appear here. The Science Friday segment featured Michael Turner responding to Steven Weinberg’s claim that some anthropic argument is just common-sense with the remark that “some of us chafe at using anthropic and commonsense in the same sentence”. I haven’t yet seen the full multiverse discussion from later last Friday, but presumably that will be available soon.

Update: One more. Today at CERN they’re celebrating Carlo Rubbia’s 75th birthday. Webcast going on right now, slides here.

Update: Hamish Johnston at Physics World asked CERN spokesman James Gillies about the delay in the draft schedule:

He also said that CERN is now looking for ways to make up the extra time identified by Bailey and he said that the repair team are confident of having the LHC running towards the end of September as planned.

Update: Yet one more: New Scientist has an interview of Witten by Matthew Chalmers here.

Posted in Experimental HEP News, Multiverse Mania, Uncategorized | 15 Comments

Origin of the World

Posted on April 1, 2009 by woit

Arizona State University’s new Origins Initiative is starting off this year with some mind-expanding programs, including an Origins Symposium that will start tomorrow. The number and quality of speakers who will be making the trip to Tempe is remarkably high. The event will be webcast, so the rest of the world can get the inside dope by following along here.

Cosmology will be the main topic on the first full day of the Symposium, with Science Friday broadcasting live at 11am a panel discussion on “Physicists and the Origin of the Universe”. The afternoon program will be in three parts, with the last part about new observational methods. The first two deal more with the chronic heady topics and pipe dreams of theorists (“How Far Back Can We Go?” and “Is our Universe Unique, and how can we find out”), and will have a break for tea and brownies, finishing up at 4:20 with Glashow (whose title is the blunt “Is Particle Physics Over?”) and Vilenkin (“Mediocrity as a principle”).

I hear that refreshments will be provided by Tempe’s own ChebaHut and there will be an exhibit featuring work of local artists. Arizona is putting on quite a show, with a major effort to attract cutting-edge researchers in physics to the state, including the recent announcement of proposed new legislation.

Update: The final paragraph above was inspired by the posting date, and is pure fantasy. In addition, I have no idea whether brownies will be served during the break tomorrow, or what might or might not be in them. I do look forward to seeing what the various speakers will have to say, and am sure they will be addressing the multiverse/pre-big-bang topic without the aid of any mind-altering substances, difficult as that may be to believe.

Posted in Multiverse Mania | 10 Comments

Anything Goes

Posted on March 26, 2009 by woit

Yesterday at the KITP Wati Taylor gave a talk entitled Freedom and Constraints in the Landscape of Intersecting/Magnetized Branes. During the talk he explained in detail the problem of lack of predictivity caused by the landscape. As far as anyone knows, to the extent you can calculate anything, you can get whatever you want: “Anything Goes”, and string theory is useless for ever predicting anything. He was looking at some particular classes of vacua, chosen for their computational tractability, and hoping to find some constraints among the quantities one can compute. There’s no known reason to expect this, but one can compute anyway and hope. The end result was the expected one: you can get whatever you want. Here are some quotes from the talk:

So, We’re really in a very challenging situation where we don’t really know how to define the theory, we don’t know what the set of solutions are, and even if we did we would have a very hard time making a sensible statement about what that means for predictions…

Every piece of data we have so far I would say is consistent with the notion that everything is pretty much uniformly and randomly distributed in the landscape.

There was extensive discussion of the predictivity problems and overwhelming evidence string theory can’t ever predict anything below the Planck scale (this wasn’t discussed, but I don’t see how it predicts much above the Planck scale either). For some reason there was no drawing of the obvious conclusion that one should just give up on the idea and try something else.

Posted in Multiverse Mania | 26 Comments