After last month’s posting at Cosmic Variance about how String Theory is Losing the Public Debate, Sean Carroll seems to have decided to go on the offensive (or defensive…), with a piece in New Scientist entitled String theory: it’s not dead yet, which he reproduces and has a posting about here.
I can’t really disagree with Sean about either title. Yes, string theory is losing the public debate, and no, it’s not dead yet. Some of Sean’s claims in the New Scientist piece are descriptive claims about the behavior of theoretical physicists:
String theorists are still being hired by universities in substantial numbers; new graduate students are still flocking to string theory to do their Ph.D. work…
Ideas about higher-dimensional branes have re-invigorated model-building in more conventional particle physics… Cosmologists thinking about the early universe increasingly turn to ideas from string theory.
All of these are true enough (although the word “re-invigorated” might not be the most appropriate one), but don’t address the value judgment of whether any of this activity is a good thing or not. One could also come up with other evidence for continuing activity in string theory, such as the large number of press releases being issued claiming to have found new ways to “test string theory”, but the fact that these have all been bogus is relevant to evaluating whether this activity is a good thing or not.
Sean’s positive case for string theory is mostly about its role as a quantum gravity theory, acknowledging that the Landscape is a problem, and that progress has slowed since the mid-90s (although more accurate would be “come to a dead halt, now moving backwards..”). He describes that period as “it seemed as if there was a revolution every month”, displaying the predilection for over-the-top hype that has characterized much string theory salesmanship over the years. His claims about the achievements of string theory vary from relatively modest exaggerations (“The theory has provided numerous deep insights into pure mathematics”) to standard misleading propaganda:
“a promising new approach has connected string theory to the dynamics of the quark-gluon plasma observed at particle accelerators” (connected? wonder how strong the connection is…)
“it is compatible with everything we know about particle physics” (and also compatible with just about everything we know to not be true about particle physics…)
“Michael Green and John Schwarz demonstrated that string theory was a consistent framework” (there’s a lot more to consistency than canceling that anomaly…)
“It was realized that those five versions of the theory were different manifestations of a single underlying structure, M-theory” (would be nice if we knew what M-theory actually was…)
In the comment section Sean explains how string theorists have no intention of standing behind what used to be considered the main “prediction” of the theory, TeV-scale supersymmetry:
If the LHC discovers supersymmetry, string theorists will be happy, but if it doesn’t there’s no reason to give up on string theory — the superpartners might just be too heavy.
So, prospects for string theory remain bright, since with each new experiment the situation is: heads they win, tails doesn’t count.
Also at Cosmic Variance is the latest in an exchange between Joe Polchinski and Lee Smolin, entitled Science or Sociology? (some earlier parts of the exchange are here). I’m mostly resisting the impulse to get involved in various parts of that argument since Smolin doesn’t need my help: the points at issue don’t seem to me central to the claims of his book, and his positions and what he wrote in the book are perfectly defensible.
While I don’t see the point of arguing about things like how conjectural the AdS/CFT duality conjecture is (pretty damn conjectural I’d think though, since no one even knows what the definition of one side of the duality is…), it is interesting to see what it is that Polchinski finds most objectionable about Smolin’s criticisms. In the context of an argument about how much of a problem the positive CC was considered to be by string theorists in the late 90s, he strong objects to Smolin’s description of “a group of experts doing what they can to save a cherished theory in the face of data that seem to contradict it”, going on to describe the work on moduli stabilization that led to the landscape as “a major success” which Smolin is trying to paint as a “crisis”. Ignoring the argument about who thought what back then (although if you really care about this, for some relevant evidence, see the Witten quote), in a larger sense “a group of experts doing what they can to save a cherished theory in the face of data that seem to contradict it” describes precisely the behavior of Polchinski, Susskind, Arkani-Hamed, and many others in the face of the disastrous situation created by the “major success” of moduli stabilization.
The “anthropic landscape” philosophy is nothing more than an attempt to evade failure, and it is an failure of scientific ethics of a dramatic kind. Once one understands a speculative idea dear to one’s heart well enough to see that one can’t make any conventional scientific predictions using it, ethics demands that one admit failure. Instead we’ve seen scientists announcing a new way of doing science, even writing popular books and magazine articles promoting this. Most physicists (including even a sizable fraction of string theorists) are appalled by this behavior. If you don’t believe me, consult a random sampling of the faculty in your nearest physics department, or watch Susskind’s recent talk in Israel where he describes himself as at the center of a circular firing squad.
Polchinski ends by claiming that Smolin’s case for “group-think” and for a “sociological” problem with string theory is “quite weak”. This problem is obviously hard to quantify and a matter of perspective. While I don’t doubt that Polchinski sees himself as not suffering from “group-think”, if he were, he obviously wouldn’t think so. One thing I think is undeniable about the “sociology” of all this is that the blog phenomenon has put a lot of evidence out there for any unbiased observer to judge for themselves, and this is one of the main reasons for what even a fervent string theory proponent like Sean Carroll has noticed: string theorists are losing this debate.
Anyone who regularly follows the most well-known blogs run by string theorists pretty soon becomes convinced that they have a real problem. Lubos Motl is the Id of string theory on uncensored display. The fact that his colleagues promoted him and show signs of only having a problem with his politics, not his behavior as a scientist (if they have any problem with his calls for my death or other attacks on me, I’ve never seen evidence of it) is truly remarkable. Two out of three recent string theory textbooks prominently carry his endorsement. All another prominent string theorist blogger, Clifford Johnson, has to say about Lubos is “I thank him for his physics contributions and for widening the discussion.” This was in the context of an eight-part personal attack on Lee Smolin and me for having written books that Clifford steadfastly refuses to read. The other of the three prominent string theory bloggers is renowned for his sneering attacks on the competence of anyone who dares to criticize string theory, issues press releases claiming tests for string theory that other physicists describe as “hilarious”, while misusing his position of responsibility at the arXiv to stop links to criticism of string theory articles from appearing there. Among those string theorists without their own blogs who choose to participate in the comment sections of others, a surprising number seem to think that it is an ethical thing to do to post often personal attacks on string theory critics from behind the cover of anonymity. Less anonymously, a large group of string theorists at the KITP seem to have thought it was an intelligent idea to act like a bunch of jeering baboons, on video, for distribution on the web.
This kind of public behavior and the lack of any condemnation of it by other string theorists is what has convinced many physicists and others that, yes, string theory does have a “sociological” problem. I have to confess that my experience over the last couple years has caused me to come to the conclusion that the string theory community has a much greater problem with personal and professional ethics than I thought when I wrote my book. The fact that so many string theorists have decided to respond to my book and Smolin’s not with scientific arguments, but with unprofessional behavior I think speaks volumes for the strength of their scientific case, and this has been noticed by their colleagues, science journalists, and the general public. While I applaud Polchinski for behaving professionally in his response to the two books, I suggest that he should take a look at the behavior of many of his colleagues and ask himself again whether or not there might be a sociological problem here.
Dear Peter,
Who cares, if we physicists are losing the (public) debate?
At some points it has seemed, that real scientists are also
losing the debate in the US over the Intelligent Design movement.
Progress will not — in the end — be driven by sociology, or superstition.
But instead by something completely different. This something is what is usually called “truth”….
-Kasper
relatively modest exaggerations (”The theory has provided numerous deep insights into pure mathematics”)
Do you disagree with that statement as written then?
This was quite a polarizing post. And yet from what I’ve seen, I can’t really disagree with any of it.
Coin, re: pure mathematics: I think the issue may be one of degree. I don’t know if “numerous” and “deep” are the appropriate qualifiers here. Although I’m not knowledgeable enough to say for sure, I think that string theory really hasn’t contributed all that much to mathematics, at least from the perspective of mathematicians who are actively working toward “numerous deep insights” instead of developing new tools mathematical tools as needed.
Kasper,
What’s going on is not “physicists losing the public debate”, but string theorists losing the debate among physicists. You might try asking your non-string theorists colleagues their opinion of string theory these days…
Coin,
While string theory has contributed to mathematics in various ways, as I wrote, I do think that saying it has provided numerous deep mathematical insights is an exaggeration.
Peter,
The problem here is that lots of non-string theorists know very little about string theory and just follow the trend of “hating” string theory. At least I konw many people of this type. Nevertheless, I agree with you that string theory is in big trouble and some string theorists are too biased about it.
J,
Sure, few people actually understand much about string theory. In the past the hype surrounding the subject led to a lot of people being very impressed by it. As it has become clear that much of this was hype, and the problematic “sociology” becomes more manifest, this is leading to a backlash and to people “hating” string theory. “Hating” isn’t a reasonable reaction to a scientific theory, but it is a reaction to the hype and to the behavior of some string theorists.
…how conjectural the AdS/CFT duality conjecture is (pretty damn conjectural I’d think though, since no one even knows what the definition of one side of the duality is…)…
How can they talk about this duality if they don’t know both sides? What do string theorists say if they explain the duality??
Peter….
*wheeze-exhale*
I ..am ..your ..father!
*wheeze-exhale*
More seriously, I agree with you on the fact that the statement that string theory “is a fundamental theory of physics” is “not even wrong”, but to suggest that string theory is completely useless (I don’t know, maybe I am taking you out of context here) is perhaps a bit of an over exaggeration. I am sure that there are many stringy inspired pieces of mathematics that will be of great interest to mathematicians for years to come, and potentially many more reserves of mathematical complexity that have yet to be tapped. Though I must admit that I could be wrong here, I think certainly one has to acknowledge that there is a whole community of theorists working in the area that think that there is definitely SOMETHING there, so, maybe there is! Just maybe not the fundamental “theory of everything” that has been (dishonestly?) hyped in the media. Something to think about anyway.
As someone who knows little about the physics involved, but a lot about the math (I’m finishing my Ph.D. in representation theory & algebraic geometry this summer), I can say that from my point of view Peter is completely right about physicists losing the argument from a sociological standpoint. I’m a long-time reader of this blog as well as other physics blogs and it has been amazing to see Peter (as well as Lee Smolin elsewhere) being unflappably polite while being subject to the most absurd ad hominem and personal attacks. I can’t speak to the substance of the posts arguing physics, but when string theorists claim that Peter has no authority since he isn’t publishing academic papers (as though this has any bearing at all on his arguments) or call him a crackpot or worse, it only makes them look bad. Add to this the vicious postings by string theorists on their own sites that don’t address the substance of Peter’s arguments but only hurl insults in his direction, and consider Lubos’ quite unhinged nature — my own personal favorite post of his is the one where he claims women can’t do physics or math — and it’s no surprise string theorists are losing on the public relations front.
As for the claims of physicists that string theory has greatly enhanced mathematics, I can only say that I am unaware of this impact in my field. I know that string theory has had an impact on enumerative algebraic geometry (eg work of Kontsevich on curve counting) but it’s not valid to claim that the impact has been huge. In fact it seems like string theorists are taking the shiniest new baubles from mathematics and claiming them as part of string theory. A case in point is new claims that geometric Langlands has import in string theory — maybe I’m off base here, but can anybody tell me how the hell, say, Hecke eigensheaves on a moduli stack have anything to do with string theory? Undoubtedly QFT has had an impact on representation theory, especially the infinite-dimensional flavor, but string theory? Color me unconvinced.
Aged String Theorist,
I’m quite sure I’ve never claimed string theory is “completely useless”. It’s a huge subject, many parts of which remain worth pursuing. But the idea of unifying physics with 10/11 d string/M-theory really has pretty conclusively failed, and string theorists should start publicly acknowledging this instead of allowing Landscape pseudo-science to flourish and continuing to promote misleading hype about the theory.
The relation of string theory to mathematics is a really complicated subject, with one reason for this being that a big part of the story is 2d conformal field theory, which is an independent subject. Just as it would be a really good idea for physicists to think clearly about what string theory ideas have failed and which have led somewhere, the same is true about the interaction of string theory and mathematics. Hype about “numerous deep insights into pure mathematics” isn’t really helpful.
I think it’s a pretty silly exercise to bicker about the extent to which string theory has influenced mathematics. In certain fields (Gromov-Witten theory, for example), string theory has inspired many results; in others not so much.
To answer the specific question, the moduli stack can be approximated by the Hitchin moduli space which arises when placing the equations of a particular 4D TQFT on a Riemann surface. (It’s been argued that working on the stack is equivalent to working in the full 4D context, but I don’t think that’s been made precise.) One then gets a 2D model of maps into this moduli space. Using ideas from topological string theory, we can identify boundary states of this field theory with objects in the derived category. There are specific operators in the 4D theory called ‘t Hooft loops which operate on boundary states and thus give functors on the derived category. The Hecke eigensheaves are the same things as “eigenbranes”.
Peter,
As far as I can tell, the only people who believe that string theory has failed are you and your accolytes. This certainly is not the opinion of most high-energy physicists and you should stop misrepresenting this fact. Basically, this a pseuodo-controversy created by you and others, just as creationists try to give the impression that there is a controversy over evolution. It’s irritating, but in the end irrelevant.
Aaron,
Referring to the 2d sigma model involved as a “string theory” seems to me to be rather gratuitous. You’re not summing over surfaces, you’re not summing over metrics, it’s an interesting TQFT with little relation to physical string theory. As I wrote in the previous comment, it really would be useful to keep straight what is what, and not try and muddy the waters. The QFT/Langlands story is about gauge theory and TQFT, not about string theory.
Eric,
You really should get out more…
Referring to the 2d sigma model involved as a “string theory” seems to me to be rather gratuitous.
I wasn’t aware I did that.
Aaron,
“Using ideas from topological string theory, we can identify boundary states of this field theory”
It requires fairly close reading of this to realize that there’s no string theory here, just a use of “ideas from topological string theory”, which aren’t about string theory.
Ok, Peter, say that in a few years when you’ve been completely forgotten, and all of the emnity you’ve created comes home to roost.
Ummm, yeah. Ok.
. . . so am I understanding this correctly, that geometric Langlands really pertains to QFT and less to string theory? I’m already aware that there are connections to QFT (cf Edward Frenkel’s notes on the topic).
As for Eric Mayes’ comments, they are a classic example of what Peter is talking about — even though I don’t know a lot about evolutionary theory it’s patently obvious that intelligent design and arguments against evolution by religious nuts are unscientific. However, although I don’t know the physics involved, it is NOT patently obvious that Peter is being unscientific; in fact it doesn’t seem like that’s the case at all. It’s pretty great that Eric has come along to underline precisely the point that Peter makes, which is that ad hominem attacks have taken the place of reasoned conversation, and that this is making string theorists look pretty bad to those of us who don’t know physics on a deep level.
Math Grad Student,
Witten (with Kapustin and Gukov), over the last few years has been exploring the relation between certain 4d topological QFTs and geometric Langlands. He relates the 4d TQFT to 2d TQFT based on maps from a 2d space with boundary (such as the upper half plane) to the Hitchin moduli space of bundles over a Riemann surface. Langlands duality then is related to mirror symmetry between two such TQFTs.
This is one sort of relation of QFT to Geometric Langlands, but there’s another quite different one, that is explained in many of Edward Frenkel’s articles and lectures. There use is being made of ideas from conformal field theory (and especially vertex operator algebras) to do explicit constructions in geometric Langlands. As far as I know the relationship between these ideas and Witten’s newer ones is not understood, but maybe someone better informed than me knows something about this. If so, I’d love to hear about it…
so am I understanding this correctly, that geometric Langlands really pertains to QFT and less to string theory?
Yes. As I said (which apparently Peter thought was deeply hidden in my opaque prose), some ideas that had their origin in string theory have gone into the analysis, but all the theories are topological QFTs. Strangely enough, these do not seem obviously related to the CFT stuff that Frenkel discusses in his notes.
In regards to the increasingly tiresome string PR wars, I’d suggest reading various more formal reviews of the relevant books as opposed blog comment threads which involve a vanishingly small fraction of the community.
One question which keeps coming to my mind is if physicists believe that you have to fully understand (or even partially understand) their theory to discuss certain grand ideas in scientific thought.
One is Occam’s razor. One arm of this principle is that a new theory must fully describe the same results as another theory, with less assumptions or somehow more simply.
Another principle is the ability to predict results prior to experiment. This seems important because if the theory doesn’t predict results, it is impossible to argue that the theory even applies to the experiment.
Underlying both of these principles is the bedrock assumption: physical experiments are required, and any theory, or any part of any theory, which does not deal directly with the observable world is by definition un-necessary, it is dead weight, and must be discarded using Occam’s razer.
What I’m getting from the string theorist’s side of the debate is that their theory is more important than these principles, so the principles themselves must be incorrect. It’s a neat trick.
I see. Thanks for the information on TQFTs — I have Frenkel’s paper and I’m planning on reading through it. It’s good to have some sort of rough overview of the picture when reading about the interface between mathematics & physics, which I often find confusing. Frenkel’s book on geometric Langlands & loop groups comes out in a month also, and I’m hoping it’ll be readable — the preprint version of the book from his website included a forward in which he said that the book should be accessible to a bright undergraduate or beginning graduate student, which made me feel kind of dumb.
Math Grad Student,
Frenkel’s comment about that book being accessible to someone with an undergrad math background is one of the funniest things I’ve seen in the math literature. That he might be serious about it is one of the scarier things…
The deal is this:
1) Quantum mechanics and general relativity are incompatible
2) There are currently no experiments that probe regimes where this incompatibility is important.
Given (2), there are two options. The first is just to not work on number one. This applies to string theory, loop quantum gravity, causal dynamic triangulations and any other theory you can think of. None of them had made anything remotely resembling a falsifiable prediction.
The thing is, people don’t having a problem in front of them and not working on it. So people have their favorite ideas for working on (1). Most people who have thought about these questions think that string theory is the best of the various ideas out there. And so they work on it.
In the end, none of this matters. The LHC will turn on and either end the debate or end particle physics. If we find something, it will clarify the direction theory needs to head. If we find nothing, we will all be working at hedge funds. Personally, I’m hoping for the latter. I’ve always wanted a sailboat.
Math Grad Student wrote:
“it’s patently obvious that intelligent design and arguments against evolution by religious nuts are unscientific.”
While it is true that some arguments by some ‘religious nuts’ are unscientific, it is not true that intelligent design and (all) arguments against evolution are unscientific. There are plenty of reputable scientists who believe that the universe was designed and created, and whose reasons against the evolution theory are based on scientific facts. See here for a list.
At any rate, I thought the comment was irrelevant to the current discussion and sounded like a ‘cheap shot’ coming from certain string theorists :-), which was out of character of your other posts. (Your first one, for example, was fair, unbiased, and well-argued.)
Any further attempt to use this blog to carry on the ID vs. evolution debate will be ruthlessly suppressed. Don’t even think of it…
Frenkel’s book on geometric Langlands & loop groups comes out in a month also, and I’m hoping it’ll be readable
Does “loop groups” in this context mean the same thing as holonomy groups?
No,
a loop group is just the group of maps from the circle into a group, with point-wise multiplication.
The holonomy group is something different. Given a connection, it’s the group generated by parallel transport around a loop.
I see, thank you.
It’s interesting that while string researchers themselves have the strong impression that trememdous progress has been made at various times (e.g., “it seemed as if there was a revolution every month” in the mid 90s), from an outsider’s perspective there appears to have been no progress or change at all, at least for the past 20 years or so. I base this largely on the popular book “Superstrings, A Theory of Everything”, edited by Davies and Brown, published in 1988. The book (in case anyone here hasn’t read it) is a fascinating collection of interviews with prominent string researchers, conducted in 1987, exactly twenty years ago. Those interviewed were Schwarz, Witten, Green, Gross, Ellis, Salam, Glashow, Feynman, and Weinberg.
Re-reading this book recently, the overwhelming impression I got was that absolutely nothing has changed in the past twenty years. In fact, it seems to me that the popular chronology of string theory (first revolution, second revolution, etc.) is wrong, or at best misleading, because already in 1987 we find every aspect of the present discussion, including the unification of the various versions into a single over-arching theory, the idea of invoking higher-dimensional surfaces (instead of just one-dimensional strings), the huge number of possible vacuum states due to the various ways of curling up the extra dimensions, the prospect of needing to appeal to the anthropic principle as a way of choosing between them, the possibility of formulating the theory in four dimensions from the start, the issue of “background independence”, the difficulty with the cosmological constant and the fact that we don’t know how to break supersymmetry without producing an excessively large CC, acknowledgement of uncertainty about whether it has really been fully proven that string theory will be completely finite in every sense and to all orders, and the over-riding lament that “we don’t understand what string theory is”, and we seem to be missing some fundamental principle. And so on.
There was also a discussion of the sociological issues, noting the “totalitarian” aspects of the string research community, and questioning whether it’s a good idea to focus so much one speculative idea. The book even contains a tinge of “flame war”: The interviewer mentioned that Feynman was quite critical of string research, and Green began his response by saying “I would not have thought that this was the kind of approach to physics that Feynman would favor”. (How did that get past the editors? It’s the only ad hominen comment in the book.)
It may be that experts in string research could “date” those interviews, but my guess is that most people would find them indistinguishable from blog discussions typed this morning. (Just about the only give-away is that they say “the LEP stands a good chance of detecting the Higgs”, whereas now one says “the LHC stands a good chance of detecting the Higgs”.) And yet, as I said, the string researchers themselves have the impression that they have been progressing (at various times since 1987) at breakneck speed. I can only assume that the research has generated several internal problems that have been tackled and resolved, giving workers in the field the impression of progress, despite the fact that, in overall terms, the program hasn’t budged since 1987.
Here’s a nice succinct question and answer.
Interviewer: It seems at the moment that this must be a rather major obstacle to further progress in the theory – not knowing how the higher dimensions curl up.
Witten: We would be much happier if we understood how the higher dimensions curl up and therefore what the vacuum state of the theory is.
Amos Dettonville,
Thanks for the pointer to that 1987 book. It was recently republished in an attractive-looking paperback edition, I see.
http://www.amazon.com/Superstrings-Everything-P-C-Davies/dp/052143775X
It is available new for $20 or so, (not counting shipping) and I see that used copies are for sale for $0. 47 on the same basis. How can anybody resist an up-to-date book on string theory for 47 cents?
Though others may have missed your reference to 1986 anticipation of M-theory, I think that must be what was meant here:
…the popular chronology of string theory (first revolution, second revolution, etc.) is wrong, or at best misleading, because already in 1987 we find every aspect of the present discussion, including the unification of the various versions into a single over-arching theory, the idea of invoking higher-dimensional surfaces (instead of just one-dimensional strings), the huge number of possible vacuum states due to the various ways of curling up the extra dimensions, the prospect of needing to appeal to the anthropic principle as a way of choosing between them,…
Hi Peter,
I have a kind of off-topic question. Do you have any idea why DARPA is funding geometric langlands program? I mean, it is a military agency and I cannot see the motivation behind it. I am not in this field but this is pure math as far as I can see
If Sean’s claim
String theorists are still being hired by universities in substantial numbers; new graduate students are still flocking to string theory to do their Ph.D. work…
is true, then the perceived loss of the public debate is moot -it would still appear to be business as usual. I only care about the public opinion in this debate to the extent it can influence the allocation of academic and research funding…
If somebody wants to study string theory on their own — fine, just don’t ask the tax payers to support their delusion under the guise of conducting physics research. Get a philosophy grant instead.
.
I would like to second Amos. I have had the book in question for several years as well as other string theory books (sorry Peter I have NOT yet bought your book but intend to). I can maybe see why some researchers would really be interested in ST, but how to get rid of all those extra dimensions!!!
Aaron:
It maybe the “only game in town” but could it just be a suckers game? Just asking.
String theory could certainly not be the correct theory of quantum gravity. It’s lucky, then, that it has inspired many new ideas in the field of phenomenology and mathematics. In addition, the AdS/CFT conjecture gives us a new way to understand gauge theories. It might be disappointing if gauge/geometry duality is the only connection between string theory and more traditional physics, but it is still a remarkable discovery that deserves further investigation.
ali,
From the DARPA web-site:
http://www.arpa.mil/dso/thrust/math/fathm.htm
I think DARPA has traditionally been willing to sometimes fund basic research whose possible military applications are pretty far-fetched. This seems to be a pretty extreme example.
Peter,
There are certainly relations between the CFT type
approach to geometric Langlands and the 4d TFT one –
I think most of the fundamental structures in geometric
Langlands can (or will) be seen from this POV.
I think the key to this is understanding the Kapustin-Witten
TFT in codimension three, i.e. on the circle, but sadly I think
neither the algebra nor the TFT (I self-censored after saying “math” and “physics” 🙂 ) is sufficiently developed to make such statements precise. I’ll just say that both sides are pretty definitely about loop groups.
In fact I think 2d gravity/topological strings will soon
become relevant to the geometric Langlands story —
at the very least the “space of string states” seems to appear when you try to relate representation theory of loop groups to that of groups..
Peter and Ali,
DARPA of course has zero interest in string theory as a physical theory…It is only interested in any mathematics that string theory may have influenced and whether or not such mathematics can be used in defense:
“The fundamental mathematics developed in this program is expected to have broad significance in basic science and several avenues of possible long-term defense impact, including quantum algorithms and devices; cryptography; fast structured algorithms for signal/image processing and other DoD-critical applications; and high-density data coding”
Public key encryption as a secure cryptosystem relies on the mathematical assumption of the difficulty of factoring large numbers — a difficulty which apparently has never been proved. Hence the DARPA interest in number theory and Langlands.
Quantum algorithms and devices (mentioned by the DARPA link) refer to quantum computers (and also quantum key distribution)—the development of quantum computers would give an exponential increase in factoring speed , rendering public key encryption broken.
On the other hand, a successful development of quantum key distribution would solve the problem of secure distrubition of encryption keys, which would immediately make the one time pad cryptosystem (known to be secure) practical.
The DARPA funding looks reasonable.
LDM, thanks for the insight. I know NSA is also very interested in quantum computers too for obvious reasons. I just did not know geometric langlands program could have any such practical realization. I am not in this field
Galileo lost the public debate.
In much of the US so did Darwin.
Not sure the public debate is very relevant for sciencitific questions.
What I don’t like about military funding of science is that if anything interesting comes up, it will be classified secret to stop enemies knowing about it. This probably won’t stop the enemies finding it, because you always get leaks from the Dr Klaus Fuchs sort, but it will prevent the interesting applications being known widely.
“…but it will prevent the interesting applications being known widely.’ Perhaps, but only for a little while…
String theorists are still being hired by universities in substantial numbers; new graduate students are still flocking to string theory to do their Ph.D. work…
Ideas about higher-dimensional branes have re-invigorated model-building in more conventional particle physics… Cosmologists thinking about the early universe increasingly turn to ideas from string theory. — Sean Carroll
All of these are true enough (although the word “re-invigorated” might not be the most appropriate one), but don’t address the value judgment of whether any of this activity is a good thing or not. One could also come up with other evidence for continuing activity in string theory, such as the large number of press releases being issued claiming to have found new ways to “test string theory”, but the fact that these have all been bogus is relevant to evaluating whether this activity is a good thing or not. — Peter Woit
Fascinating. When I made essentially the identical point in a comment on the Cosmic Variance blog, Sean Carroll deleted my post.
In particular, I went on to make a further point in the comment which Carroll deleted. Namely, that there’s nothing radically new about the peculiar properties of string theory as science. Irving Langmuir called this kind of activity “pathological science,” and he gave a famous lecture on the subject:
http://www.cs.princeton.edu/~ken/Langmuir/langmuir.htm
Examples of pathological science include Blondlot’s N-rays, mitogenetic rays, the Davis-Barnes effect, and the Allison effect. I would add to that list phlogiston, alchemy, hard AI, and the luminiferous aether. (Some will doubtless disagree about hard or GOFAI, but the evidence there seems pretty clear after 50 years. Look at the CYC project for a classic example.)
Sean Carroll claimed that string theory is unique because it has gone on so long without getting experimentally tested in such a way as to definitely disconfirm it, but that’s actually not correct. Each of the above examples of pathological science never got an experimental disconfirmation which proponents of the theory accepted as definitive. The supporters of N-rays, for example, tried to wriggle out of Wood’s report by claiming that N-rays don’t operate according to Snell’s law, that Wood didn’t know how to read the scintillations properly, that Blondlot was tired during that particular experiment, etc.
We hear exactly the same kinds of excuses today whenever new data places a lower bound on the possible mass of the superpartners. I.e., the string supporters simply move the bar.
There’s nothing new about any of this. We see this in pathological science for at least the last 100 years, and if you count phlogiston, going back several hundred years.
The scientists who came up with phlogiston weren’t stupid. There were superificially convincing reasons to believe in it — metals lost weight when heated, gained weight when heated. It seemed credible. (Turned out to be oxides, not phlogiston.)
There are likewise some superficially convincing reasons to believe in string theory, particularly the mathematical ones. The problem is that regardless of how convincing it might seem, string theory hasn’t generated testable falsifiable experimental predictions.
One of the biggest problems with string theory is that (like all patholgoical science) it has not been fertile in a scientific sense. It has proven mathematically fertile. Lots of new and wonderfully fascinating math has come out of it. But after 30 years, no new areas of physics have been opened up to investigation by string theory and explored with experiments. This is very different from the case with, say, quantum theory. Initially, quantum theory merely offered a way of explaining the absorption lines of the simpler elements like hydrogen and helium, in particular the Ballmer series. But then quantum theory got applied to crystalline solids and you got band-gap theory of semiconductors, and that led all sorts of fascinating research and a wealth of new experimental results. Likewise, LInus Pauling applied quantum mechanics to organic chemistry, and that led to incredibly productive areas of research, including X-ray crystallography and eventually the decoding of the structure of DNA. Again, quantum theory was applied theoretically by Dirac to predict negative energy states, leading to the prediction and soon the discovery of the postiron, and antimatter, which opened the door to a vast new realm of experimental research in particle physics. Dirac certainly did not imagine Gell-Mann’s “eightfold way” when he made the prediction about negative energy states, but Dirac’s work proved incredibly fertile.
All these cases involved experimental predictions which led to further epxierments, and opened up huge new areas of active and productive research.
What huge new areas of productive research has string theory led to in 30 years?
Where are the experimentally testable falsifiable predictions from string theory? Where are the experiments based on string theory predictions which have opened up vast new areas of active productive research, and led to new technologies and new realms of applied science?
There are none. String theory has not been fertile.
That’s a big warning sign.
Another big problems is string theory’s prediction of 10, or, possibly, 11 dimensions (depending whether you adhere to M-theory or not). Every scintilla of experimental evidence we have amassed in the entire history of physics so far converges on the conclusion that we live in a 4-dimensional world — 3 dimensional of space, one dimension of time. There is not a single shred of experimental evidence pointing to the physical existence of more than 4 dimensions in our universe.
There’s no reason why compactificaiton couldn’t be theoretically correct, mind you — it’s just that there’s absolutely no experimental evidence to support it. And, if compactification occurs anywhere near the Planck length, the energies required for an experimental test lie far beyond anything anyone can hope to reasonably produce in any possible particle accelerator. That makes compactification unfalsifiable. And that’s yet another big problem for string theory.
The parallels between string theory and other types of pathological science, like N-rays or mitogenetic rays, run even closer. Drs. Woit and Smolin seem to have played a similar role to the physicist Robert Wood in the N-ray affair — except that Wood pointed out that Blondlot’s experimental results were incorrect, whereas Woit and Smolin are pointing out that the string theorists aren’t even making any predictions that anyone can provide experimental results to test. (That’s even worse than the case with Blondlot’s N-Rays.) And we’re getting much the same kinds of responses from string theorists that the N-ray proponents gave back in the early 1900s.
Viz., critics of the theory “don’t really understand it and thus are not qualified to comment.” (Rejoinder: I don’t need to understand the mathematical details of a theory to know whether it has produced an experimentally testable falsifiable prediction. This is the same faulty argument as claiming “You can’t judge who won the Olympic sprint, since you’re not a world-class runner.” Yes I can. I don’t need to be a world-class runner to see who crossed the finish line. )
And again, proponents of the pathological science claim to have tests of the theory — except that the tests turn out to be phoney. We’re seeing this now with string theory. Each time a new “test” of string theory gets announced, it turns out to be pure twaddle.
And again, proponents of pathological science resort to censorship of critics.
None of these tactics ever works. Eventually a scientific theory must produce experimentally testable falsifiable predictions, or it dies. This is why it’s hard to see how string theory can be accurately described as “alive and kicking.” Its proponents continue to flail around in search of some way of generating testable falsifiable predictions from their theory. Jacques Distler’s swampland approach with statistics on the vacua represents one approach, Ed Witten’s latest toy model represents another. These are all valiant efforts, and there’s certainly a great deal of furious activity going on…but the simple fact remain that all this furious activity on the part of string theory never seems to lead anywhere. We never get a unique falsifiable hard number out of string theory for, say, the mass of the Higgs — a number that’s solid and unique and can be disconfirmed by experiment. We never get a single hard testable fasifiable number for the compactification length. Maybe Ed Witten’s new 2d + 1 approach will finally give hard testable numbers. But I can tell you this…I’m not going to hold my breath, based on past experience.
The acid test of a theory of physics remains: What does it take to disconfirm it? What experimental results will disconfirm your theory? String theorists have never been able to answer this crucial question.
That’s the sign of what Hubert Dreyfus called “a degenerating research program.” It seems clear to most unbiased observers that the string theory reserach program is degenerating badly. Despite all the furious activity by string theorists, no falsifiable testable numbers are coming out of the equations.
Some string theory proponents have made an analogy with the early days of quantum chromodynamics. Initially, those equations blew up and produced infinities — then renormalization was discovered, and things settled down. However, it’s important to remember that renormalization was invented and applied within a very short time. The gap between QCD and hard testable numbers was only a handful of years. (Gell-Man and Low actually invented the renormalization group in 1954, though Fisher typically gets the credit for it.)
It’s now been three decades for string theory. Still no hard testable numbers. That doesn’t seem analogous to the QCD situation. In fact, it’s not analagous to any case in theoretical physics that comes to mind, other than pathological science.
That’s my take on why string theory is losing the battle for credibility. As for the continued hiring of string theorists, institutional inertia is the simplest explanation. Linda Rosa’s critique of the “therapeutic touch” studies appeared in 1996 and to sensible skeptical observers, that closed the case.
http://www.quackwatch.org/01QuackeryRelatedTopics/tt.html
But hospitals still hire therapeutic touch “experts” 11 years later.
Hubert Dreyfus’ book What Computers Still Can’t Do appeared in 1979…but universities continue to hire and grant tenure to researchers pursuing “hard” AI. In economics, Rational Choice theory is currently on the outs, and its record of failed predictions (Martin Luther King’s voting marches in the deep south couldn’t have occurred because of the low utility function) is leading to a widespread abandonment of that particular theoretical framework. But, once again, some universities do continue to hire and grant tenure to Rational Choice theorists in their economics departments.
This is human nature. People aren’t perfect. It takes time for groups of people to absorb information and reach conclusions, even more time for institutions to form a consensus.
A consensus about string theory apepars to be forming within the HEP community. I would be surprised if string theory is still around in any significant way in another generation.
‘… Eventually a scientific theory must produce experimentally testable falsifiable predictions, or it dies. …’ – mclaren
In order to debunk string, you need to bring a new game to town, or the gamblers will only play at strings. You seem to be assuming that the field is competitive. The only competitions are those inside mainstream string theory, because it’s the only game in town.
anon.:
In order to debunk string, you need to bring a new game to town, or the gamblers will only play at strings. You seem to be assuming that the field is competitive. The only competitions are those inside mainstream string theory, because it’s the only game in town.
In my humble opinion, entire post-Standard-model theoretical physics looks like one big casino. People throw around outrageous ideas hoping to hit the jackpot. For some reason, the “string table” attracted more gamblers than other equally destructive games. The only solution is to stop gamble and to switch to some constructive work. It may be slow and boring, but that’s the only way forward… in my humble opinion.
Apodictically wrong. If a scientific theory persistently fails to produce testable falsifiable predictions, it debunks itself.
In order to debunk string, you need to bring a new game to town…
Apodictically wrong. If a scientific theory persistently fails to produce testable falsifiable predictions, it debunks itself.
These two quotes demonstrate the difference between the theoretical conception of the practice of science and science as actually practiced. Since science is a human enterprise, there will always be a disconnect between the two. The practice of string theory shows this disconnect. Science as practiced will continue to have these problems. You might define the problem away by saying that what they are doing is not science, but that does not correct the actual practice issue.
I don’t know that string theorists are behaving that differently from scientists in other fields. It is (and should be) very difficult to dethrone an established scientific theory. The problem in this case is that string theory somehow became an “established scientific theory” with what many people consider only the flimsiest circumstantial evidence in favor of it.
How did this happen? There were several decades with no experimental evidence for anything beyond the Standard Model, and during the 80’s and 90’s, string theory looked very promising, so it got established as the leading contender to unify gravity and quantum mechanics during this time. Now, even if somebody comes up with a promising alternative theory at this point, sociology means that it will be very hard to battle the particle physics establishment.
‘… Now, even if somebody comes up with a promising alternative theory at this point, sociology means that it will be very hard to battle the particle physics establishment.’ – Peter Shor
String theorists say that the problem of alternatives being starved of funds and prestige is the same sociological issue that always arises in all the sciences, and string theory is therefore not a special problem. But in other mainstream theories (e.g., the big bang, evolution, etc.) there is plenty of evidence for the theory.
String, despite lacking evidence, must be defended using aesthetic (‘beautiful ideas’) and romantic (‘all the real geniuses believe in string theory’) arguments, backed up with serious-sounding assertions that nobody has any other serious ideas.
This seems to be the reason why string is preventing the development of alternatives. Who can develop a theory to rival strings which will be taken seriously by anybody? Will an alternative need to be developed secretly for decades to accumulate as many results as string, before being published with an expensive fanfare of hype, press conferences, advertising, etc? How on earth can any conceivable alternative capture the limelight from a 10/11-d multiverse theory? Who will pay the slightest attention? Alternatives to rival string theory may require as much effort as has gone into string theory. How can that ever happen in the current high energy physics climate?