Not Even Wrong

John Brockman at his “Edge” web-site has put up an exchange between Smolin and Susskind about the “multiverse” and the anthropic principle. This includes the page and a half paper by Susskind that was rejected by the arXiv. Susskind seems quite willing to give up the idea that a physical theory should be falsifiable, so his response to Smolin’s argument that his use of the anthropic principle is not falsifiable is basically “Yeah, and so what?”.

To Smolin’s claim that non-falsifiable theories aren’t really science, Susskind answers by listing several prominent physicists (Weinberg, Polchinski, Linde, Rees), their titles, affiliations and prizes they have won. He then announces that since these prominent people agree with him and think the anthropic principle is science, Smolin should just shut up. I don’t know about other people, but one reason I went into physics was that it was supposed to be a subject where issues could be decided by rational argumentation, not appeals to authority. That doesn’t seem to be the case anymore.

Jeff Harvey sent in a comment correcting me on a point of history in my last posting. I’d read somewhere about Green and Schwarz fed-exing their paper to Witten, and had assumed this was their idea. Harvey, who was at Princeton at the time, recalls that it was Larry Yaffe who brought news of Green and Schwarz’s result from the Aspen Workshop to Witten at Princeton, and Witten was the one who asked Green and Schwarz to fed-ex him the paper.

Harvey also strongly disagrees with the statement that people were not impressed by the work independently of Witten. He was at Princeton at the time, so knows far more about what attitudes there were. For those who weren’t at Princeton or at Aspen, news of Green and Schwarz’s paper and Witten’s arrived more or less at the same time (they were published in the 13 and 20 December issues of Physics Letters B, the preprints were circulating in October). At that time any new paper by Witten was a major event, especially one in which he took up a new topic. I stand by my recollection that for people I was talking to at the time, the fact that Witten was working on the subject overshadowed the Green-Schwarz result itself.

Update:

This morning I tracked down my original source for what happened at Aspen. It is John Schwarz’s article entitled “Superstrings – a Brief History”, published in the proceedings of a conference on the history of particle physics held at Erice in 1994. The volume is entitled “History of Original Ideas and Basic Discoveries in Particle Physics” and contains many things very much worth reading. Schwarz describes in detail what happened at Aspen, ending with the following remarks:

“But still, given our previous experiences, neither of us had any idea of how sudden and enthusiastic the response of the physics world would be. In my opinion this was largely due to the influence of Edward Witten, who immediately grasped the implications of our result. Without that, string theory would probably have emerged much more gradually. As soon as our letter came off the printer we sent Witten a copy by Federal Express. (This was before the days of TeX and email!). I am told that the next day everyone in Princeton was studying it. Our letter on anomaly cancellation was submitted September 10, 1984. The deluge began 18 days later with Witten’s letter suggesting ways to compactify SO(32) superstrings to get anomaly-free theories in four dimensions.”

This is what led me to believe that it was Schwarz and Green’s idea to Fed Ex Witten their paper. Presumably Harvey is right that he had asked them to do this. But that’s about the only thing that I think I got wrong in the original posting.

Today a symposium is being held in Aspen to celebrate the twentieth anniversary of the “First Superstring Revolution”. The canonical story of this “Revolution” is that twenty years ago this month, on a dark and stormy night at a workshop in Aspen, Michael Green and John Schwarz completed a calculation showing that gauge anomalies canceled in a specific superstring theory, thus changing physics forever. The more complete story of what happened at that time goes more or less as follows:

By 1984 Witten had been taking some interest in superstring theory for a while, giving a talk on the subject in April 1983 at a conference on Grand Unified Theories, but not publishing anything about it himself. In 1983 at the Shelter Island conference he had shown that the popular unification idea of the time, using supergravity on higher-dimensional spaces and the Kaluza-Klein mechanism, could not give the kind of asymmetry between left and right handed particles that occurs in the standard model (this has had a revival in M-theory, which these days invokes singular compactification spaces to get around Witten’s no-go theorem). The failure of supergravity ideas had gotten him interested in superstring theory, but he was concerned about the issue of gauge and gravitational anomalies in the theory, anomalies that he worried would render the theory inconsistent. In his 1983 paper about gravitational anomalies with Luis Alvarez-Gaume, they noted at the end that these anomalies canceled in the supergravity theory in ten dimensions that is the low energy limit of the type II superstring. This theory didn’t allow for low-energy gauge theories so wasn’t useful for unification. Witten suspected that the type I superstring (which could be used for unification) would have insurmountable problems with anomalies, but the Green-Schwarz calculation showed that these anomalies could be canceled for a specific choice of gauge group.

Evidently Green and Schwarz talked to others about their new result at the 1984 Aspen workshop, but I would suspect that no one was very impressed (if anyone who was there knows differerently, I’d be interested to hear about it), since superstring theory was generally considered pretty much a far-out, highly unlikely idea. Green and Schwarz were well aware that their only real hope for getting attention was to get Witten interested, so on September 10th they sent him a copy of their paper via Fed Ex (this was before e-mail) at the same time they sent it off to Physics Letters B. Witten immediately went to work full time on superstring theory, with his first paper on the subject arriving at Physics Letters B on September 28th. I think this is really the point at which one should date the First Superstring Revolution.

Witten was at the height of his influence, and the news that he was now working on superstring theory spread very quickly through the particle theory community. I had just finished my graduate work at Princeton and was starting a post-doc at the Institute for Theoretical Physics at Stony Brook when I heard the news. Over the next six months to a year I remember hearing from a couple colleagues who had gone down to Princeton to talk about their work with Witten, only to hear from him that, while what they were doing was all well and good, the future was in superstring theory, so they should drop what they were doing and start working on that.

My own attitude was that it didn’t look like a very promising idea. It was a complicated theory and didn’t really explain anything at all about the standard model. I figured that there would be a lot of smart people working on it for a while and within a year or two either they would get somewhere with the idea and it would be clear I had been wrong, or they wouldn’t, and everyone would lose interest. Neither I nor anyone else could conceivably have guessed that 20 years later superstring theory would still not explain anything about the standard model, but would completely dominate particle theory.

One reason for this is the string theory hype machine continues in high gear. The University of Chicago has issued a press release telling us that “growing numbers of physicists see superstring theory as their best chance” to formulate a theory of everything. Jeff Harvey is quoted as saying that “It’s an intellectual enterprise that’s extremely exciting and vigorous and full of ideas”, which is very different than what I hear string theorists telling me in private.

A couple conferences going on this week have already put some of the talks online.

SLAC has a summer school each year, aimed more at experimentalists than theorists. This year’s topic is “Nature’s Greatest Puzzles” and there are quite a few interesting talks already online there.

The Michigan Center for Theoretical Physics is hosting this year’s String Phenomenology 2004 conference. The “Landscape” seems to be a big topic; two online talks are Michael Douglas’s, which is more or less the same as his one at Strings 2004 a few weeks ago, and Michael Dine’s. Dine seems optimistic that the Landscape will lead to predictions, saying

“If we adopt the anthropic viewpoint, we may be lead to predictions – perhaps the first predictive framework for string theory”

Before taking this too seriously, one should note that Dine has been giving review talks about “superstring phenomenology” and claiming that predictions are right around the corner since before most of our incoming students at Columbia were born (see his 1986 Erice lectures, no, they’re not online, this was way before the arXiv).

And I’m headed off soon for a short vacation out of the range of the internet, back late next week.

Roger Penrose has a new book out in England, called “The Road to Reality”. It is 1000 pages long and is now ranked number 17 on Amazon’s UK site. There’s a review of the book here.

It sounds like the book contains all sorts of things, including some of the material about string theory that Penrose has presented in public talks various places about “Fashion, Faith and Fantasy in Modern Physical Theories”. One version of these talks is available online from Princeton. By “Fashion” Penrose is referring to string theory, and he considers the question of why it is so fashionable. String theory has been heavily sold as “beautiful” and to some extent Penrose seems to go along with this, but his invoking of the term “fashion” indicates an awareness of how problematic notions of “beauty” can be. The latest fashionable clothes are heavily promoted for their beauty, although after a few years, when they become unfashionable, this beauty is no longer so obvious.”Beauty” is very often a social construct, with many people willing to agree that something is “beautiful” if everyone around them is saying so. Recall the story of the emperor and his fashionable outfit.

I’ve never understood these claims that string theory is “beautiful”, and was again struck by this when I got ahold of a copy of Barton Zwiebach’s new book on string theory aimed at undergraduates called A First Course in String Theory. Most of the first 270 pages of the book are devoted to working out in detail the quantization of the bosonic string in light-cone gauge, and I find it hard to believe that anyone finds this a beautiful subject. It is mathematically rather complicated and not that interesting, and has no real connection to any observable physics.

Later on in the book Zwiebach does devote a fair amount of space to trying to connect string theory to the standard model, mainly using the construction of intersecting D6 branes. At the end of this section, he acknowledges that this construction is truly hideous and looks all too much like a Ptolemaic use of epicycles on epicycles to explain planetary motion, saying “the models seem contrived, at least in the sense that they are engineered to give the physics that we observe, rather than obtained naturally as the simplest solutions of string theory”. He quotes Alfonso the Wise (1221-1284) as having said the following about Ptolemaic epicycles:

“Had I been present at the creation, I would have given some useful hints for the better ordering of the universe.”

He tries to end on a more optimistic note, hoping that some deeper meaning of string theory will emerge with more work, quoting Maimonides as follows:

“In the realm of Nature, there is nothing purposeless, trivial or unnecessary”

which begs the question of whether string theory is part of the “realm of Nature”.

Susskind has posted a new preprint entitled “Cosmic Natural Selection”. It’s just two pages of various attacks on Lee Smolin’s theory of cosmological (not cosmic) natural selection. Smolin’s theory is described in detail in his book “The Life of the Cosmos”, published seven years ago. As far as I know the terminology of “Landscape” entered physics in this book, where Smolin adopts the term “fitness landscape” from evolutionary biology.

Why is Susskind all of a sudden taking an interest in Smolin’s old theory? Well, last Tuesday a preprint by Smolin appeared entitled “Scientific Alternatives to the Anthropic Principle” in which he gives a detailed criticism of the anthropic principle as unscientific. The next day Susskind tried to post a response to Smolin, consisting of a 3 page paper, half of which was just a quote from a summary of his argument that Smolin had sent to him. The one and a half pages that Susskind himself wrote were pretty much incoherent, and showed no sign that he had bothered to actually read Smolin’s article.

This was such a bizarre document that someone responsible for the arXiv actually refused to accept it. I’ve heard of several non-mainstream physicists who have had problems getting their articles accepted, but this is the first time I’ve heard of this happening to a well-known mainstream physicist. Whoever did this was doing Susskind a huge favor, but he then immediately forwarded a copy of the paper via e-mail to a long distribution list.

So that’s why Susskind’s latest begins “In an unpublished note I criticized Smolin’s theory of cosmological selection…” Note that he is not addressing any of Smolin’s criticism of his own work as unscientific, instead he is attacking Smolin’s own speculative ideas. I’ve personally experienced this kind of thing from more than one string theory fanatic. They don’t respond to criticism of what they are doing (because they don’t have much of a response), and instead forcefully and incoherently attack one for any speculative comments one may have made.

This just gets weirder and weirder all the time….

Now string theory is being used to peddle Verizon DSL service (courtesy of Lubos Motl). According to the writers of the advertising copy :

“String Theory: The so-called unified theory is gaining credibility among young scientists”

Right.

Gregg Easterbrook is a senior editor at the New Republic, and gives every indication of being a complete moron. His column about Hawking’s recent talk on black hole information loss is a masterpiece of anti-intellectualism. He appears to believe that the problem with physics is that, in trying to understand the big bang, ideas have been invoked that “don’t do especially well on the common-sense test”.

Only someone with zero common-sense would think that common-sense is going to explain the state and dynamics of the universe billions of years ago when conditions were utterly unlike those in which humans evolved and continue to exist.

Jacques Distler has something interesting about the prospects for producing black holes at the LHC. This has often been promoted as one of the most exciting possibilities for new physics from the LHC. Evidently it turns out that cosmic-ray experiments currently in progress also are sensitive to this kind of hypothetical black hole prediction. Depending on one’s assumptions about the minimal mass of a black hole that can be cleanly distinguished, either all or almost all of the range of new fundamental gravity scales accessible to the LHC will have been covered by the cosmic-ray experiments. So, if there is a new unexpected gravity scale in the range of a few Tev, this is very likely to first be seen in cosmic-rays, not at the LHC.

These Tev-scale gravity models have gotten a lot of attention in recent years, much of it in the form of claims of string-theory “predictions” that could be tested at the LHC. A few days ago I was talking to one of my colleagues, who believed, based on hearing a talk by Nima Arkani-Hamed, that string theory made predictions about what would happen at the LHC. Of course this is nonsense. There are lots of models you can construct involving string theory and any gravity scale you want. Past experiments rule out the possibility of a gravity scale up to the range of 100’s of Gev-1 Tev, but there is no reason other than wishful thinking and a desire to have something to say to people who point out that string theory makes no predictions, to believe that there is a gravity scale just a bit too high to have been seen at the Tevatron, but observable at the LHC. Such an assumption actually ruins what string theorists consider the major success of the whole string theory/supersymmetry picture, the fact that the 3 coupling constants in the standard model nearly come together at an energy somewhat below the Planck mass.

Personally I’ve always found the current “Large Extra Dimensions” Tev-scale gravity models to be just hideous and completely unmotivated. On the other hand, the one thing we know is that the electroweak-breaking scale is in this region, and since we don’t yet know what is causing this breaking, it is not completely inconceivable that it has something to do with gravity. The argument that the scale of quantum gravity is the Planck scale is not water-tight. It is based on the assumption that whatever generates the Einstein-Hilbert action as the effective low-energy action for gravity produces it with a magnitude of order one. If instead it comes with an exponential factor, the underlying gravity scale could be quite different than the Planck scale.

Besides some enthusiasts whose talks give the impression that Tev-scale gravity is a prediction of string theory, most string theorists believe that this is something unlikely to occur (Distler is one of these). One of the weirder things I’ve encountered in arguing with prominent string theorists is that they like to say that the Tev-scale gravity models are one of the major achievements in string theory in recent years, while at the same time saying they don’t believe in these models. What’s up with claiming as a point in favor of your theory that it “predicts” something you don’t believe?

Lee Smolin has a new preprint discussing the “anthropic principle”. He argues that one standard form of the anthropic principle that has been invoked by proponents of the “Landscape” is not falsifiable and he gives an eloquent explanation of the importance of falsifiability for a shared scientific enterprise. He also discusses the “prediction” of the rough magnitude of the cosmological constant that supposedly uses the anthropic principle and is due to Weinberg. He points out that this argument really isn’t an anthropic one, since it is independent of the existence of intelligent life. It just relies on showing that there is a relation between the cosmological constant and the existence of gravitationally bound structures. Then, since we see galaxies, we know something about the cosmological constant.

One of Smolin’s concerns is to show that his theory of “cosmological natural selection” (discussed in his book “The Life of the Cosmos”), while being a theory of a “multiverse” just like the string theory Landscape, is different in that it is potentially falsifiable, unlike some recent anthropic arguments.

He states well the predicament that theoretical physics finds itself in, with the tactic that worked so well throughout the 20th century, that of searching for unification by exploiting symmetry, no longer having much success. While I agree with most of what he has to say in this preprint, I’m more optimistic than him that future progress through new ideas about unification and the exploitation of symmetry is still possible. My point of view is more that the reason the last twenty years have seen no progress of this kind is that virtually all the field’s effort has gone into pursuing one very speculative and not very promising idea about unification, ignoring other possible lines of research.