Twentieth Anniversary of the First Superstring Revolution

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 “Its an intellectual enterprise thats extremely exciting and vigorous and full of ideas”, which is very different than what I hear string theorists telling me in private.

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69 Responses to Twentieth Anniversary of the First Superstring Revolution

  1. JC says:

    Danny, Chris,

    The only TV shows and documentaries I remember seeing on PBS when I was a kid, were mostly space and/or NASA oriented ones. I guess I missed all the shows that were on particle physics, as well as many of the biology related ones.

    The only other science related documentary from that time I really remembered were ones about the Manhattan Project and the making of the nuclear bomb. At the time I didn’t really know what the significance of the Manhattan Project was in the context of World War 2, but I had a “morbid” fascination of the pictures and footage of the mushroom cloud explosion and the subsequent shock waves at the Trinity test site. It was many years later when I started to understand what the destructive power and significance of the nuclear bombs were really all about.

  2. D R Lunsford says:

    JC – as a kid (teen) I well remember the NOVA episodes about the gauge revolution – interviews with Feynman, Glashow, Weinberg etc. etc. Compared to today’s pabulum (did you see that abortion by Greene?) they were outstanding shows.

    I also remember “The Ascent of Man” and “America”, miniseries on PBS. I think these shaped my whole intellectual outlook way before college. So there was good stuff on the TV back in the day.

    The awful “Cosmos” series was a watershed. Since then it’s been mostly downhill for “hard” science.

    -drl

  3. Chris Oakley says:

    Maybe that’s the advantage of having fewer channels in the U.K.: if the BBC decides that it wants to try to educate you then there are fewer alternatives to switch to. The most prominent science/medicine documentary series was/is a BBC one called “Horizon”. This was much the best (the commercial channel ITV had a series called “World in Action” but the brow was significantly lower both in choice of topic & presentation). Horizon programs were and probably still are “must see” for A-level (16-18 yr old) science students. They were generally topical and informative, although were structured like investigative journalism and would not normally provide the level of technical detail that one would find in a “Scientific American” article.

  4. JC says:

    Chris,

    How common were science type of shows on British television in the 1970’s?

    I guess where I grew up in north america, I hardly ever saw any science shows when I was kid, largely because my folks didn’t have cable TV for a long time and when they finally did get cable TV, they were always watching crap TV and seemed to have very little to no interest in science type of TV shows. The only channel from that time which had science type of shows every once in a while, was mainly the publicly funded PBS affiliate. Even then most of the shows on PBS were crap for the most part too.

    The only way I found out about science in those days was mainly from reading Scientific American, which my father had a subscription to and he left them laying around on the coffee table in the living room. Sometimes I would go to the local public library and borrow books about physics or science in general, where most of these books were largely descriptive with very little to no math.

  5. Chris Oakley says:

    What sparked your interest in particle physics originally?

    Simple really: the popular science programs on TV. It seemed like a happening area and I liked the idea of it being the most fundamental of sciences. There really was a lot of coverage in the media and the main players (Feynman, Gell Mann, etc.) came across as interesting and entertaining people.

  6. JC says:

    Chris,

    What sparked your interest in particle physics originally?

    If I didn’t know any better, the 1970’s looked like it was the heyday for experimental particle physics and the Standard Model. If I was around your age or Peter’s age, my interest would have probably been sparked from seeing the successes of particle physics in those days.

    In my case I came across several Scientific American articles on particle physics when I was in high school. At the time I thought it was fascinating that most of matter and the forces of nature could be explained by a small number of fundamental particles. It sure looked a lot better and more “compact” than the periodic table, which I was learning at the time in my high school science and chemistry classes. Not knowing any better at the time, I thought Feynman diagrams looked really cool and was fascinated by how one could calculate a lot of physics by just writing down a bunch of squiggly looking diagrams. It sure seemed a lot more interesting than the science class experiments I was doing at the time, like masses hanging on springs, measuring pendulums, concave & convex mirrors and lenses, etc …

    In fact in high school, I actually hated math and science for the most part. When I was a freshman in college, I also hated physics! All those freshman and sophomore introductory physics courses seemed so boring and tedious at the time, that I thought about quitting and not returning to college after the term was over. I thought it seemed like a waste of money at the time, in paying tuition for a bunch of boring and tedious classes which I had very little to no interest in. It felt like I was a sucker and/or a glutton for punishment at the time.

    During that summer when I was thinking about not going back to university in the fall, I actually went to a nearby college library and tried to find some books about particle physics and how to do Feynman diagram calculations. (I was bored that summer and didn’t have much else to do). Besides reading the first two or three chapters (usually some qualitative discussions of the elementary particles, interactions, and/or hadrons, with very little math) of several graduate level particle physics books, I got lost very quickly afterwards mainly from the mathematics level being way beyond my ability at the time. Though by skipping over most of the math I didn’t really understand at the time, I was amazed at how the final answers for many Feynmann diagram calculations looked kind of simple and had close agreement with the quoted experimental data. Not knowing any better at the time, I thought the form of many of those final answers for cross sections and decay rates could be guessed by just naively looking at the dimensional units of the possible quantities involved, and getting the final expressions to have the same units as a cross section or decay rate. At the time I was wondering why it involved a lot of tedious nasty looking math just to eventually get a numerical coefficient, for the final expressions with forms which could otherwise be guessed from dimensional analysis and semi-intuitive arguments.

    With some advice from my parents and ignoring my misgivings and gut feelings at the time about the tedium and boredom of college, I decided to go back to college that fall, hoping that I would one day be able to understand how to do Feynman diagram calculations. It took another few years of undergraduate physics before I was able to understand how Feynmann diagram calculations were actually done.

    Years later I heard about string theory also from reading some Scientific American, and thought the idea looked neat at the time. I guess I fell for the propaganda and hoopla surrounding it at the time, to the point of literally being “converted” overnight on the spot and becoming a “true believer” in string theory. I was definitely quite naive and clueless at the time. I even bought a copy of the Green, Schwarz, and Witten (GSW) book on superstring theory, despite not knowing a thing about string theory. This may sound kind of silly today in hindsight, but at that time I literally thought that GSW’s “superstring theory” book was like “the Holy Bible”.

  7. Chris Oakley says:

    I think that this goes back to Peter’s earlier point that in the 1970’s elementary particle physics really looked like it was motoring, whereas now it looks like it is sputtering. Brian Greene’s efforts to get the public excited about the subject are heroic and commendable but it really would make all the difference if the experimentalists were part of the journey. If I were 25 years younger I would probably be looking to get into molecular biology or computer science and not particle physics.

  8. JC says:

    Thomas, Chris,

    I wonder how much the ratio of “genius” to “non-genius” in the population has changed over the years, or whether it’s a ratio that remains more or less constant with time. Except maybe in another time, place, and circumstances, the “genius” may not be recognized as easily and/or is squandered and wasted away.

    One ominous example in the 1900-1902 period would be the case of Heinrich Himmler who was born on Oct 7, 1900, and later became the head of the Nazi SS, Gestapo, and was the main architect behind the “final solution” holocaust. Whether this was a satanic-like “genius” for “evil” is debatable, but arguably this could be the classic textbook case of a “genius” that was squandered and wasted away.

    In more recent times, other cases of “genius” being squandered and wasted away would perhaps be the case of hardcore computer hackers who like breaking into computers and/or stealing data, such as Kevin Mitnick or Kevin Poulsen when they were younger.

    If there’s less kids going into science and engineering these days, perhaps some of the future “geniuses” will end up in non-science areas like business, law, high finance, etc … instead of physics areas like quantum gravity and string theory.

  9. JC says:

    Chris,

    I remember going through several old books and papers on analytic S-Matrix theory from the 1960’s, when I was bored one afternoon.

    In one approach, it turned out they took the approach of “extracting” some results from quantum field theory (QFT), and then throwing away the QFT afterwards. At the time it sure seemed like they were “cheating” when they were trying to do analytic S-Matrix theory which didn’t believe in QFT, but they were using the very same QFT to “extract” results from!

    I spoke to several older particle theory professors who were around when analytic S-Matrix theory was at its peak heyday during the late 1950’s and 60’s. They all mentioned that Geoff Chew’s “axioms” for the analytic S-Matrix were just “too general” to get any useful results from. Since nobody was really getting any useful results from just looking at Chew’s axioms alone, many folks ended up going back to QFT in an attempt to “extract” some useful results, literally as an act of desperation towards the end in the late 1960’s. That was probably the breaking point which marked the beginning of the end for analytic S-Matrix theory as a viable framework for particle physics.

    This sort of thing reminds me of the attitude many economists had towards math when economics was first starting to use “advanced math” extensively. At the time, economists had the mentality of using the math to “extract” useful results and then throwing away and “burning” the math afterwards.

    At times I wonder if string theory has reached its “breaking point” yet, and whether there is a single event when could be marked as the “beginning of the end” of string theory as a viable framework for a quantum theory of gravity. If I didn’t know any better, the anthropic junk sure looks like it could be something which may mark the “breaking point”. The point if and/or when Witten abdicates from string theory would perhaps be the “beginning of the end” for string theory. The earliest possible date I can envision would perhaps be shortly after the LHC is producing data, and there’s no supersymmetric partner particles and/or there’s no “light Higgs” found in the data.

  10. Chris Oakley says:

    I can well believe that Landau might have made that proposal. Of course the whole “S-matrix” phenomenon of the sixties was based on the notion that quantum field theory did not really exist.

    As for renormalization, my views are (hopefully, by now) well known although I might post more detailed stuff on my web site about what I think of “effective field theories with an unknown ultraviolet completion”, and why. BTW this is a great phrase, but I think “arbitrary set of rules inspired by but not derived from quantum field theory” is more accurate.

  11. JC says:

    Chris,

    Didn’t Landau make the proposal of burying quantum field theory forever?

    I think it was in some paper where Landau did some calculation which showed that if you tried to eliminate the scale dependence in the coupling constant of quantum electrodynamics after using the renormalization trick, the only way possible he found was to make the coupling constant zero?

  12. Chris Oakley says:

    …infinity problems which held up progress in quantum field theory for almost 20 years, until Feynman and Schwinger came along with the renormalization “crutch”.

    It is very likely that banging your head vigorously and repeatedly against a brick wall is likely to lead to brain damage. People were looking to create quantum field theory in the image of quantum mechanics, and it does not seem to have occurred to them that the reason that they were unable to do it was because it was not possible!

    Take this, for example:

    H = H_0 + V

    This is a tremendous equation for quantum mechanics, but a diabolical one for anything relativistic. If we were being relativistic we ought to write

    P_\mu = P^0_\mu + V_\mu

    … but the the idea of a “free” and “interaction” three-momentum seems to be singularly unhelpful, so we carry on with the original equation, using the interaction picture derived from it that is horribly unrelativistic and just block our ears when the mathematical mines start to go off.

    The lesson? Don’t get too hung up on formalism. Symmetry and consistency are more important. The formalism can be adjusted to fit.

    IMHO, the same considerations apply to quantising gravity: it could just be that no-one has been able to do this simply because it cannot be done! Formal quantisation simply does not work. What would make much more sense would be to be a little more practical. Do we really need all that much anyway? After all, in the absence of any experimental knowledge about quantum gravity all we require is the classical limit, which need not even be GR – an SR gravity theory that reproduces the experiments would do just as well.

  13. JC says:

    Thomas, Chris,

    Perhaps some people’s genius becomes forgotten by history largely because they were born in a different time and place, and/or it was squandered and wasted away?

    Maybe if folks like Witten, Polyakov, etc … were born in Germany or Austria around the same time as Pauli, Wigner, Heisenberg, etc … their genius could have been recognized if they worked on the foundations of quantum mechanics during the mid 1920’s?

    On the other hand, if folks like Pauli, Heisenberg, Wigner, Dirac, etc … were born around the same time as Witten, Polyakov, Schwarz, Gross, etc … (ie. around the 1940’s and 50’s), perhaps they would have become just “another face” in the large crowd of particle and/or string theorists during the 1970’s and 80’s? Maybe the competition in the 70’s and 80’s was a lot more intense than in the 1920’s?

    If Hitler was assasinated before 1933 or shortly after he became chancellor of Germany, perhaps Germany would have remained as the “Weimar Republic” well into the 1940’s with no war, no Nuremberg race laws, no holocaust, etc ..? If this would have happened, perhaps there would have been no mass defection of scientists to America, while Germany would have possibly remained the world’s powerhouse in physics and math, as well as no nuclear or hydrogen bombs being built?

    If there’s a wholesale abandonment of string theory from Witten abdicating from it, how many folks will still be actively working on it other than perhaps Schwarz, Green, and maybe Lubos Motl and a few other unnamed “string fanatics”?

    On a silly note, if Lubos Motl was born in Austria (ie. Czechoslovakia was still a part of Austria in 1901) around the same time as Pauli, Dirac, Wigner, etc … perhaps he would have became a “quantum theory fanatic”, or even a “quantum field theory fanatic” despite all the infinity problems which held up progress in quantum field theory for almost 20 years, until Feynman and Schwinger came along with the renormalization “crutch”. In this case his “quantum fanaticism” would have largely been right for most of the rest of his life.

  14. Chris Oakley says:

    To be precise –

    Pauli: born 24 April 1900
    Fermi: born 29 September 1901
    Heisenberg: born 5 December 1901
    Dirac: born 8 August 1902
    Wigner: born 17 November 1902

    I saw Dirac in person once, in 1981, where he gave a talk at Edinburgh University while I was at a summer school there. He wrote down his equation, in components, using alphas and betas – no gammas, of course (you can’t teach an old dog new tricks) and talked about how he arrived at this equation through considerations of beauty and symmetry. Considering the bluntness of some of the things he is famous for saying, he struck me as a delightful man. Wigner I saw at a conference on Group Theory at ICTP in Trieste in 1983, but did not speak to him as I could not think of a particularly intelligent question to ask or intelligent comment to make.

    Thus Quantum Mechanics, being developed between 1925 and 1928 by three of these men, plus the relative “old man” Schroedinger (he was in his late thirties) was mostly a children’s crusade. There is no denying their brilliance, but nonetheless this still does say to me that (i) they were lucky to be born at this time and (ii) it is time that our society acknowledged that young people are, or at least should be, the driving force behind frontier research.

  15. Thomas Larsson says:

    JC,

    Re people who are born at the right time. Arguably almost half of the top ten theorists of the twentieth century (Dirac, Heisenberg, Pauli, Fermi, with runners-up like Wigner and von Neumann) were born in 1901 or 1902. Nobody doubts of course that they were among the smartest people of their generation, but anyway. What are the odds that such brilliance would be concentrated to 2% of the century?

  16. Chris Oakley says:

    On second thoughts the scepticism/credulity scale ought to be dimensionless (a bit like probability). We’ll call the quantity C (=Credulity).

    C = 0 – You believe nothing
    C = 1 – You believe everything

    These are obviously the limits to the allowed values.

    However, as a matter of convenience in representing extremes of scepticism and credulity without having to use very small numbers or numbers very close to one, one could define a transformation

    C = atan(WM)/pi + 1/2

    The quantity WM (the Woit-Motl index) then is unbounded. Negative values are known as “Woit” values and positive values are known as “Motl” values.

  17. D R Lunsford says:

    Leading to “Boil’s Law”

    WM = const

    so a nanoMotl is the same thing as a gigaWoit.

    -drl

  18. JC says:

    The “Motl” becoming the unit for scientific fanaticism!

    1000 Motls = 1 kiloMotl

    😉

  19. Chris Oakley says:

    Yes – the “Woit” could be a unit of scientific scepticism

    1,000 Woits = 1 KiloWoit

  20. D R Lunsford says:

    JC,

    IOW the times make the men? This is the “misanthropic principle” 🙂

    I don’t think we should project the failures of current efforts onto the past. In any case we don’t need even 1 more Pauli – at this point we need 1000 Woits.

  21. JC says:

    Chris,

    Perhaps there’s a lot to be said that being in the right place at the right time, makes a huge difference. If somebody like Sir Issac Newton was born a hundred years earlier, perhaps today all the physics and math with Newton’s “name” would have somebody else’s name in place of Newton. I suspect the same thing if Einstein, Schroedinger , Heisenberg, Dirac, Pauli, etc … were born in a different time and place. If Einstein never wrote the letter to president Franklin D. Roosevelt and/or Hitler created a nuclear bomb before the Americans, the world of physics may very have become “Nazified” with the names Einstein, Pauli, etc … purged away from physics history in a Nazi revisionistic rewrite of physics history?

    Just to be silly, if Lubos Motl was born 100 years earlier perhaps he would have been an Austrian “aether” fanatic?

  22. D R Lunsford says:

    Chris –

    Much more important to the US gov’t in that time frame were radar, sonar, and aeronautical technology. The US still imagined it had the atomic genic bottled and there were no plans or funding as yet for the “super”. That needed a few more years to develop.

    -drl

  23. Chris Oakley says:

    JC,

    If you want my honest opinion, the thing that caused the increase in government funding after WW2 was the fact that people were impressed by the achievements of physicists during the war. My apologies to any Japanese people who might be reading this who have some connection to the horrendous and unforgivable events of August 1945, but however destructive this episode may have been, it clearly impressed everyone, turning the likes of Oppenheimer, Fermi and Feynman into minor celebrities. I seriously doubt that governments would have been prepared to commit billions of dollars to particle physics twenty years later had not these events taken place. I know that there have been a few practical things that have come out of the study, but it would be foolish to pretend that these would justify such enormous expenditure.

    My earlier point, although somewhat flippantly made, was not about government funding per se, but about how the money is spent. It is a very simple truth that one is more mentally agile when one is younger and I maintain that this agility would generally be better deployed in doing research in the ways that one sees fit rather than in devising especially ingenious ways of grovelling to the establishment. Having a more rapid turnover of research staff, however it is achieved, would help a lot in preventing ossification. Power and influence needs to be shifted to younger people. I do not have all the answers about how this can be done, but it certainly needs to be done in some way.

  24. JC says:

    Chris,

    The only other thing I can think of if there’s no tenure for professors, would perhaps be a lot more competition amongst folks fighting for various lecturer/researcher jobs. The immedidate consequence perhaps would be a lot more “resume padding” type of research papers being produced.

    I think it would also be highly dependent on how the selection process for new faculty worked. If the selection committee consisted of people who were around for a long time (ie. after several consecutive re-appointments), then these “old timers” may have a conflict of interest where they would prefer to hire a crappy or crackpot researcher who wouldn’t be able to compete against them, and hence less of a threat to the old timers’ job re-appointment prospects. I can’t really see an easy way out of this conflict of interest, unless there’s some sort of “outside” independent selection committee making the selections, with no conflicts of interest.

    It seems like when many folks get tenure, some slow down and don’t publish as many papers. In fact some folks seem like they fell off a cliff after getting tenure, and hardly published anything afterwards. Seems like many folks have less motivation afterwards and/or have different priorities, when they are not “under the gun” any longer after getting tenure. Some folks seem like they “burned out” by the time they got tenure, and hardly produced anything of significance afterwards.

    Perhaps it’s not so surprising as to why there’s some tenured folks who end up as “deadwood”, who look like they had all the passion and soul beaten out of them. I knew many folks over the years who were computer whiz kids in the past (ie. programming stuff since they were 12 years old) who ended up going into the computer/hi-tech profession as adults. After a many years, a large number of them seemed to really dislike and started to really hate computers. It seems like for many “dream job” type of professions, a lot of folks become “deadwood” after many years where they have less interest and very little to no passion left for the job, while just “going through the motions” to get things done. (ie. “dream job” professions like music, sports, acting, writing, etc …). Maybe this is a sign of job “burnout” for many folks?

  25. JC says:

    Chris,

    Do you think progress in particle physics and quantum field theory would have progressed as fast as it did over the last 50+ years (ie. after Sputnik), if there was no tenure and/or very little to no government funding for physics?

    Looking at the pre world war 2 generation, there didn’t seem to much extensive government funding of physics at the time either in America or Europe. It seems like many universities were focused more around teaching than the heavy research focus after Sputnik.

    When the center of extensive physics activies was still in Germany and central Europe before Hitler took power, the Privatdozent (ie. sort of like a postdoc with some assistant professor duties) were frequently unpaid academic jobs, where they usually had to find other sources of income like teaching courses or family support. It seems like the generation of quantum theory pioneers in the 1920’s could come up with groundbreaking research work, with many folks being an unpaid or a lowly paid Privatdozent with very little to no direct government funding. At times I wonder if the German Privatdozen system was implemented in America along with no post-war boom in science funding after world war 2, would particle physics have progressed as fast as it did?

  26. Thomas Larsson says:

    I would say this though: I went to a talk by Chris Isham about 20 years ago where he wrote down the algebra of GL(4,R) and the transformation law of a vector in the fundamental representation. He then announced that he had just quantised gravity. I could not see it, but maybe there were fifty steps missing that were obvious only to him.

    It is the full diffeomorphism group – general covariance – that is relevant to general relativity. GL(4,R) is a subgroup, whose algebra is generated by vector fields of the form x^i d/dx^j. Many properties can be deduced from this subgroup, but not all; e.g., GL(4,R) cannot distinguish a connection from a tensor field of type (1,2), symmetric in the lower indices.

    I don’t understand the import of the Virasaro algebras, or the Kac-Moody algebras. I don’t think that I’m incapable of learning this, but I can’t find any coherent presentation of why these things are physically important and interesting.

    The physically most important application, in the sense that it makes predictions that are in agreement with observation, is in 2D statistical mechanics. Lowest-weight irreps of the Virasoro algebra with L_0 eigenvalue = h (i.e. L_0 |vac> = h |vac>) correspond to fields whose correlation functions decay as G(x,y) ~ |x-y|^-2h. There are standard ways to relate these h’s to other critical exponents, which have been intensely investigated, both theoretically and experimentally. The discrete spectrum of critical exponents predicted by CFT has been perfectly confirmed. If you compare with exact solutions of integrable lattice models, there are infinitely many numbers which agree exactly.

    A good online presentation was written by Ginsparg.

  27. Peter says:

    Thanks for the correction about the circumstances under which Greene and Schwarz sent Witten their paper. I was hoping if I had any of this wrong someone who knew more about what happened at Aspen would correct it, and said so in the posting. If I’ve gotten anything else wrong about this, I’d be interested to know it.

  28. Jeff Harvey says:

    The statement that Green and Schwarz knew they
    had to get Witten interested and so sent their
    paper to him is simply false. I was at Princeton
    when Witten heard about their work, through Larry
    Yaffe who was at the Aspen Center for Physics during
    the summer of ’84. After hearing about anomaly
    cancellation, Witten asked G&S for a copy of their
    paper by FedEx. I also disagree strongly with the
    statement that people were not impressed by this
    work independently of Witten. Dislike string theory
    all you want, but please don’t try to rewrite history.

  29. JC says:

    Chris,

    At this point I’ll remain anonymous. I can’t have any of my colleagues (both present and former) knowing that I read and post to this blog.

  30. Chris Oakley says:

    JC,

    How do we know that you are not an “insider” making maximum use of your anonymity here (Sheldon Glashow, maybe?)

    Incidentally, I would dearly love it if low-ranking academic staff did not feel constrained by career considerations in their choice of research. My dream is a Utopia like the world of “Logan’s Run” (great film, by the way, apart from that annoying silver robot) where everyone over the age of thirty is eliminated. People would not then have to worry about getting a tenured job because there wouldn’t be any tenured jobs. They would be forced to leave and do something useful with their lives instead.

  31. JC says:

    Chris,

    Perhaps folks who are still “insiders” in academic physics/math, are more likely to say the “party line”?

    Repeating the same “status quo” dogma over and over again like a broken record, hoping one day it will eventually be perceived as “the truth”. It seems like in any large cohesive group of people, conformity to a particular “ideology” is the biggest factor which keeps it together.

    On the other hand, former “insiders” and/or “outsiders” are more likely to “speak their minds” with very little to no self-censorship?

    You just have to read books written by former politicians after when they were ousted, in how they show their displeasure at how things were done and/or the gross incompetence of the folks running the government. Perfect example of this is former US treasury secretary Paul O’Neill’s memoirs of his two years in the Bush administration, after he was fired at the end of 2002. His book was talking about all the stupidity and incompetence that went on behind closed doors with Bush and his cabinet. I would be almost willing to bet that one of the big reasons why US defence secretary Donald Rumsfeld hasn’t been fired yet for the Iraqi postwar disasters, is largely because the Bush administration doesn’t want Rumsfeld yet to write his memoirs and/or to go on television criticising Bush and his cabinet, in a style similar to the memoirs of former US defense secretary Robert McNamara (who oversaw the Bay of Pigs, and Vietnam War disasters), especially before the upcoming presidential elections this November.

    I can imagine for “insider” folks who have very little to no political power in academia (ie. grad students, postdocs, faculty who don’t have tenure yet, etc …), they don’t want to say anything which may compromise their future prospects in academia. For people who are no longer “insiders” or who were never “insiders” at all, there probably won’t be any major consequences for yelling “the emperor has no clothes on” in public, or being branded as a heretic or traitor by their former colleagues.

    Perhaps there’s a lot of truth to the Machiavellian notion of “keep your friends close, but keep your enemies even closer to you”. Former “insiders” and/or “outsiders” can become loose cannons.

  32. D R Lunsford says:

    I’m unemployed and have been for more than a year – all my posts are out-of-pocket 🙂

    Yes, that was exactly what he was doing as far as I can tell. But physics seems to be post-modernized, where simply saying “there exists an N-bein formulation” is not good enough or important-sounding enough.

    -drl

  33. Chris Oakley says:

    Danny,

    I am sorry, but once again I have to plead ignorance on all counts. This sounds a lot like treating gravity as a gauge theory with a gauge group of GL(4,R) – similar to the vierbein formalism – but that is as far as I go.

    By the by, how many of us commentators are actually professional (as opposed to wannabe) physicists/mathematicians?

    Me: Programmer/quantitative analyst working for a Japanese bank in London.

    You: Software developer working in the U.S.

    JC: Obviously an old-timer like us. Background in particle physics but otherwise unidentified – something to do with the Second Coming, perhaps?

    Thomas Larsson: Working for a Swedish company that makes motors, by the look of it, but obviously with a very strong mathematical/physics background.

    And why do our employers allow us to spend a significant portion of the day doing stuff that is clearly not work related?

  34. D R Lunsford says:

    Chris, check out this post from SPR:

    A thought just occured it me. Isn’t it possible to eliminate the metric field g in general relativity in a simple way? Just introduce a
    GL(4,R) connection with the tangent bundle TM acted upon by GL(4,R) and insist every point has at most an SO(3,1) holonomy. For generic connections, this would determine g up to a global rescaling factor. In fact, since we’re making restrictions on the holonomy, this formulation would suggest we work directly with Wilson loops and lines instead. Also, generic connections would give rise to torsion.

    ..stifles cough..

    Perhaps you should have paid attention to Isham, you blighter!

    (Serious note: Math is dangerous in the wrong hands. Don’t do this at home. Save it for the office.)

    -drl

  35. Chris Oakley says:

    Thomas,

    At the moment I can only manage silence. The scorn will have to wait until I have learned more about Virasoro algebras.

    I would say this though: I went to a talk by Chris Isham about 20 years ago where he wrote down the algebra of GL(4,R) and the transformation law of a vector in the fundamental representation. He then announced that he had just quantised gravity. I could not see it, but maybe there were fifty steps missing that were obvious only to him.

  36. D R Lunsford says:

    I don’t understand the import of the Virasaro algebras, or the Kac-Moody algebras. I don’t think that I’m incapable of learning this, but I can’t find any coherent presentation of why these things are physically important and interesting.

    I would not be too concerned over silence out of SPR – it’s mostly struggling students I think. I have always enjoyed your posts, when I could understand them.

    -drl

  37. Thomas Larsson says:

    Tell us more.

    OK, although I have become reluctant to do so. I have tried to make the point on spr for the past three years, and so far only met with silence and scorn.

    We know that the groups of diffeomorphisms and gauge transformations play an important role in general relativity and the standard model, respectively. We also know that the representations that are relevant in quantum theory are projective and of lowest-energy type. So unification of the symmetry principles would amount to the construction of projective, lowest-energy representations of the diffeomorphism and gauge groups.

    On the Lie algebra level, this means that one must generalize the Virasoro and affine Kac-Moody algebras to several dimensions, and construct interesting classes of representations. On the surface this looks impossible, in view of two no-go theorems:

    1. The diffeomorphism algebra has no central extensions except in 1D.

    2. In field theory, there are no diff anomalies in 4D.

    These two theorems are correct, but the axioms are unnecessarily strong; the keywords are “central” and “in field theory”.

    The standard objection is that diffeomorphisms and gauge transformations are gauge symmetries, which are not genuine symmetries but rather redundancies of the description. Perhaps so, but I believe that in order to understand what is described, it helps to understand the description. Moreover, even if the total diff anomaly should cancel (which I don’t believe), subsystems must have a non-zero anomaly. Ironically, the prototype model here is first-quantized string theory, which can be regarded as quantum gravity in 2D. The ghost sector has central charge c = -26, so the requirement that the total central charge vanishes leads to bosonic strings living in 26D. Hence the coordinate subsystem has a non-zero central charge c = 26.

    Alas, unification of the symmetry principles is not the same thing as unification of the theories themselves, and I am stuck at this point. Nevertheless, I believe that the study of mathematical objects which naturally arise in experimentally proven physics has a physical value, even if no specific predictions have yet come out of it. At any rate, what can you demand from a theory which is 20,000 man-years younger than string theory?

    Here are some references. The last one is an attempt (and only that) to apply the formalism to physics.

    physics/9705040
    math-ph/9810003
    math-ph/0101007
    math.QA/0101094
    math-ph/0210023

  38. JC says:

    I always wondered when did this “mentality” of adding in zillions of new particles and forces into a theory, become an “acceptable” practice in particle theory research?

    Back in the days of Pauli, he jokingly thought that creating a new particle (the neutrino) which could not be observed, was the ultimate “cardinal sin” in physics.

    In other physics fields outside of particle theory, I get the sense that objects and/or entities which have very little to no experimental basis are generally NOT taken seriously at all. Folks in many of these other physics fields seem to be a lot more skeptical of speculative ideas and theories, compared to particle and gravity folks.

  39. Chris Oakley says:

    Having discovered the correct unification of the symmetry principles underlying GR and QM, I think that I have strong reason for this position.

    Tell us more.

  40. Thomas Larsson says:

    JC,

    Going back to the original topic of this thread, what are your thoughts on what would have happened if Witten had never advocated nor worked on string theory in the first place. (This is sort of a “what if” scenario in an alternate world).

    One non-obvious scenario I can think of in this “alternate world”, would be perhaps a faster decline of particle theory due to a lack of many interesting problems to work on.

    Maybe people would be taking general relativity and the standard model more seriously. Not only phenomenologically, but as something which might be quite close to the final answer. After all, there is no clear experimental evidence that anything more is needed. For sure, there are a few question marks, like dark matter and dark energy, but no clearcut disagreement with experiments. Besides, the standard model have shown an extraordinary ability to mend its cracks before.

    There are of course two strong theoretical reasons against this idea: GR and QM are mutually inconsistent, and the SM is somewhat ugly, with 25 free parameters (used to be 19) and a totally ad hoc gauge group. This indicates (to me) that we need a chunk of new mathematics, which would make the combination of GR and QM consistent and beautify the SM, rather that loads of new physics for which there is zero experimental support. Having discovered the correct unification of the symmetry principles underlying GR and QM, I think that I have strong reason for this position.

    The standard objection is of course that people thought that the end of physics was at sight already a century ago. But the situation was really different then, with many unexplained phenomena already at low energies. The impressive experimental agreement of GR and SM is true magic and mystery.

    – Perhaps nobody would have even heard the word “GUT” (grand unified theory) being used after the experimental proton decay result ruled out SU(5)?

    Other GUTs, especially SO(10), were quite popular already around 1980.

  41. Chris Oakley says:

    What would have happened if Witten had never advocated nor worked on string theory in the first place.

    I think that in this scenario the Berlin Wall would never have come down, and Lubos Motl would have been a Czech Freedom Fighter. He would have been captured by now and would be doing Supergravity calculations in his prison cell to pass the time, no doubt advocating, with his familiar unwavering certainty, that Supergravity is the language in which God wrote the world.

    One non-obvious scenario I can think of in this “alternate world”, would be perhaps a faster decline of particle theory due to a lack of many interesting problems to work on.

    There is no shortage of interesting problems to work on, and I doubt that there will ever be. But if particle physicists are so content to break the basic rules of mathematics then of course they will soon end up with something that is not worth bothering with.

  42. D R Lunsford says:

    Peter – a friend told me that the really hard part of PhD Princeton was making and firing the minature brass cannon 🙂

    BTW I asked my advisor in 1984 what he thought of string theory. He was in a position to know.

    “It’s horseshit.”

    “I agree.”

    That was the extent of our discussion of string theory 🙂

  43. JC says:

    Going back to the original topic of this thread, what are your thoughts on what would have happened if Witten had never advocated nor worked on string theory in the first place. (This is sort of a “what if” scenario in an alternate world).

    The obvious answer would be only a small minority of folks around John Schwarz and Michael Green working on string theory. A silly case would be Lubos Motl never being a string fanatic, but perhaps being a fanatic in something else.

    One non-obvious scenario I can think of in this “alternate world”, would be perhaps a faster decline of particle theory due to a lack of many interesting problems to work on.

    – SUSY possibly could have been a non-mainstream topic in particle theory, if string theory wasn’t there to give support to its advocates?

    – The non-renormalizable 2-loop pure quantum gravity result of Sagnotti in 1985, along with the non-renormalizable divergences in higher loop supergravity could have brought a lot of “quantum gravity” research to an eventual flatlining? Perhaps supergravity would have then faded away quickly into the dustbins of physics history shortly thereafter as another failed attempt at a “unified field theory”?

    – Perhaps nobody would have even heard the word “GUT” (grand unified theory) being used after the experimental proton decay result ruled out SU(5)? There would be very little motivation to look at more complicated GUTs, if there were no string theory results of SO(32) or E_8 x E_8 gauge groups to motivate further inquiries into the GUTs which were the low energy effective theories from string theory?

    Can anybody else think of anything that would have either faded away and/or would have never been that popular if string theory was never popular in the first place?

    On the surface, it seemed like string theory opened up a huge “treasure trove” of new exciting problems to work on at the time, while stuff like GUTs, supergravity, etc … were falling out of favor.

  44. JC says:

    The book “Disciplined Minds” reads like a semi-serious study of “Dilbert-ism”, with some reactionary “Marxist” sounding overtones.

  45. Thomas Paine says:

    Sorry, forgot to give the URL of the book mentioned in the previous post:

    http://disciplined-minds.com/

  46. Anonymous says:

    Since the discussion here steered towards the qualification exams in Physics, thought I would recommend the book “Disciplined Minds”, by Jeff Schmidt, who got his Ph.D. in physics from UC Irvine. He devotes considerable number of pages to the physics quals in the states. Has some thoughts similar to ones discussed here.

  47. Thomas Larsson says:

    I can boast that I made an attempt to learn string theory before the revolution. In the summer of 1984, I spent some time in the library doing leasurly reading, trying to learn about things that seemed cool. Among other things, I spent some time with John Schwartz’ 1982 Physics Report. Alas, this stuff was way above my head at the time. Besides, I was specializing in statistical physics, and particle physics and gravity were only side interests.

    Instead I spent most of the summer reading Mandelbrot’s Fractal geometry of nature, which was at a more appropriate level. What I didn’t realize at the time was that many interesting fractal dimensions can be computed with string theory methods. The catch is that it only works for planar graphs, essentially because you can regard the plane as a string worldsheet.

  48. Chris Oakley says:

    Maybe Mrs. Thatcher got to hear of Salam’s comment (as you can imagine, a complete anathema to a grocer’s daughter) as 1984 was about the time that she drastically reorganised the way in which the UK contributes to CERN, treating it as a standard part of the science budget rather than a special case.

  49. Thomas Larsson says:

    I remember that Weinberg was in Stockholm in December 1984 (as a former Nobel laureate, he has a permanent invitation to the Nobel party, and he usually shows up when one of his old buddies gets the Prize, which makes him a rather frequent visitor; in 1984 it was Rubbia and van der Meer). Anyway, I remember him predicting that one of the young bright string stars would win the Prize in 1991. Well, 1991 came and went, and the leading string theorists are perhaps still bright but definitely no longer young, and their Nobel prizes seem more distant than ever.

    Btw., Salam was also in the panel, and he said something which struck me as one of the most foolish things I ever heard. He said that society should be grateful to its big spenders, like experimental particle physics, because as society becomes richer it will run out of things to spend its wealth upon. I’m still waiting for a politician to complain about resources being too plentiful.

  50. Maynard Handley says:

    Chris,

    Seems a lot of the sociology behind physics research is along the lines of “monkey see, monkey do” or a “pied piper” luring away kids. Arguably one can see that in many other activities in the world, as in the “copycat” syndrome when something very popular and/or profitable comes up.

    At times I wonder how much of the string and particle community is exactly that of “monkey see Witten’s work, monkey tries to do Witten’s work”.

    …………………………….

    Especially pertinent to this is this
    http://www.johnkay.com/society/348
    which reviews a new book by J K Galbraith on the nature of conventional wisdom in finance.
    Physics likes to believe that its practitioners operate outside the rules of normal human psychology and sociology, something that I’ve not noticed as especially true.

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