Things are not going well for string theory on the public relations front. Someone just pointed me to the poll at Wired magazine they call String Theory Smackdown, where the side arguing for string theory is losing the voting by more than 3 to 1.
The argument that seems to be carrying the day with the public is the simple one that a supposedly unified theory that can’t make a single testable prediction, despite more than twenty years of work, must have something really wrong with it. Many string theorists acknowledge that this is the situation the theory is in, but make the case for what they see as promising aspects of the theory that justify continued work on it.
Unfortunately, some string theory partisans have chosen to react to recent criticism not by acknowledging the fact that string theory can’t be tested, but by making misleading claims that the theory does make predictions and is testable. On Monday here at Columbia, Gordon Kane gave a colloquium talk of this kind, with the title String Theory and the Real World — a “new” subfield, string phenomenology. Kane began by quoting David Gross as being highly skeptical about the whole idea of string phenomenology, arguing “we don’t know what string theory is, how can it have a phenomenology?”. Kane’s claim that “string phenomenology” is a new field is rather peculiar, since it was an active subject back in the early 1990s. It is however true that, for better or worse, it has become a more active one the past few years, as string theorists have reacted to their colleague’s complaints that they do mathematics, not physics, by trying to sell themselves as “phenomenologists”.
Kane mostly actually ignored string theory, concentrating on supersymmetry, which he has been promoting for more than 20 years (he had an article about “Is Nature Supersymmetric” in Scientific American back in 1986). He described seeing supersymmetry as essential, pretty much the only way of getting a “window to the Planck scale”. There was some mention of the idea that string theory makes predictions about cosmology, but the “prediction” was just that in “most” string theories, the size of B-mode polarization in the CMB is unobservably small. He put up plots from this recent paper, claiming that one could distinguish different string “backgrounds”, by their “footprints” on LHC data. Looking at the paper, it appears to be based upon a large number of assumptions (e.g. that one just gets the MSSM), designed to provide enough constraints so that one could not get absolutely anything, but not so many as to be forced into contradiction with experiment.
For another exercise of this kind, take a look at Kane’s 1997 Physics Today article entitled String theory is testable, even supertestable. This included an impressive looking detailed, specific spectrum of the masses of superpartners, implying that it was the sort of thing “predicted” by string theory. Only problem is that by now it looks to me as if these “predictions” are almost all in disagreement with experiment. Back in 1997 Kane was arguing against John Horgan that string theory really was testable, that it “would predict a specific spectrum of particles and superpartners that can be compared with experimental data”. He seems to have backed off on that claim, there were no such spectra mentioned in his talk this week. About the landscape and its exponentially large number of possibilities, he had little to say except that we “have to learn how to think about this”.
He repeatedly made the claim that “String theories DO give predictions” and “String theory is falsifiable”, giving as an example work by 3 graduate students of Mary Gaillard that showed that one specific heterotic string compactification scheme gave no light neutrino masses and thus led to models incompatible with experiment. Another repeated point was that the problem with string phenomenology was just a lack of manpower. If more people (especially graduate students) were doing these calculations, great progress would be made. In the question session, asked about the CC, he said that there were lots of ideas about how to solve it, what was needed was just more people doing calculations.
Evidently many agree with him, since the IAS has just announced that next year’s summer program for graduate students and postdocs will be on Strings and Phenomenology.
I decided not to ask any question in the question session, having the overwhelming feeling that arguing with “string phenomenologists” is now just wasting one’s breath. They have made it clear that, no matter how dubious the arguments needed, they’re going to keep promoting this field as predictive and highly relevant to the LHC. The intellectual “dead zone” of “string phenomenology” will be with us no matter what and perhaps even come to dominate particle theory until LHC results are in. May they stay as close as possible to schedule! (Kane estimates first physics collisions next September).
Cecil,
We except supersymmetric partners of the TeV scale because this is required for SUSY to solve the gauge hierarchy problem. Since the Higgs is a fundamental scalar, it’s mass should recieve corrections which diverge quadratically. Introducing a fermion which is the partner to the Higgs cancels these divergences and stabilizes the Higgs mass.
As far as your statement that SUSY hasn’t been yet been seen up to the TeV scale, this is wrong because this energy has yet to be probed by any experiments. LHC will be able to probe this regime, and if LHC doesn’t find SUSY then SUSY must not be the solution to the hierarchy problem.
“This I believe is a statement that no string theorist would support…”
Pretty funny statement in context, I love the confidence…kind of puts in perspective the idea of trying to reason with those aforementioned commenters.
Eric, thanks for the clarification.
I’m a bit surprised to see PW still saying that the Landscape is pseudo-science. Jacques D explained why that is not so over in the “infinte thread” on CV:
“I’ve explained why I think it is likely that, when we manage to find a family of vacua which bear more than a passing resemblance to the Standard Model (so far, we haven’t), they will have a sparse distribution of values for the parameters — both those which have already been measured (which can, if you want, be used to further prune the vacua which bear looking at) and, more importantly, of the parameters we have not yet measured.
Since we haven’t yet found the family of vacua we are looking for, my argument can hardly be called ironclad*. But it is a good deal more persuasive than the mere assertion than “You can get anything you want on the Landscape.”
In any case, if you’re going to go around repeatedly making the latter assertion, then you have to explain why the above argument is wrong. ”
Well, I have to admit that I don’t like his attitude any more than you do, and I did have a good laugh at your jibes at his weird obsession with typesetting. Rising above all that, however, the man has made a point — not every flux on a CY manifold contributes to renormalizable SM couplings; in fact, generically, very few do. So it is just not true that “anything goes” except for a few things like the cosmological constant.
What is your response? I’m not trying to score points here, I just thought it was an interesting point that certainly bears further discussion.
I thought it was clear that string theory as THE theory of everything, the one and only game in town, the language in which God wrote the universe, etc., has so far gone nowhere; and is the one that is being derided; there are other much less grand, but more scientific, uses of string methods; by all means pursue them. And maybe one day, string theorists may even have the last laugh.
Jock,
I’ve already responded to this multiple times elsewhere, explaining exactly what my argument about the landscape is. Jacques and others typically ignore my actual detailed argument, take one phrase out of it like “you can get anything you want” and insist on just arguing with that. I’m not claiming that the landscape can be disproved with 6 words, and I don’t know whether zero, a finite number or an infinite number of supposed vacuum states of string theory will match to experimental accuracy all the standard model parameters. I am claiming that all hopes to get real predictions out of it are based on massive amounts of wishful thinking, and wishful thinking is not science. It’s up to people like Jacques who claim the landscape is science to come up with the standard sort of scientific evidence for this, which is something more than “if we could just do certain computations which are now completely hopeless, the results would be certain very complex constraints on real world data which might be true”. You can’t just assert this, but have to come up with some evidence for it.
David B.,
If you read blogs regularly I’m surprised that you’re “appalled” to find that some blog commenters are not extremely well-informed about some topics. Funny that you only seem concerned by ill-informed commenters who aren’t happy with string theory. What about ill-informed commenters like Eric who are promoting string theory, do you think they’re also a problem?
I notice you’ve completely ignored the content of my posting.
Dear Peter,
I think I know a thing or two more about both particle physics and string theory than you, so I think I would be careful about who you are calling ill-informed. So please go back to studying representation theory or whatever it is you pretend to study in order to create the impression that you’re a scientist and not just some computer administrator.
Eric,
And David and Moshe wonder why so many people have acquired a low opinion of string theorists…
David B,
“I am dismayed by the attitude that various commenters of this Blog have. They are suggesting that all research in string theory should stop.”
Well, that’s not my suggestion. And I don’t think it is Peter Woit’s suggestion either.
“String theory is also (at the very least) a toy model of quantum gravity where many questions about the nature of black holes and geometry can be answered. This alone is sufficient justification to keep the program runing in the eyes of many scientists (not just string theorists).”
I agree completely. Not obviously inconsistent theories of quantum gravity are few and far between, so when one comes along then of course people should study it and learn all they can about it, within reason.
I have to take exception to your comments about AdS/CFT and QCD though. I think what irks many people about this is the way string theorists present it as a dramatic great breakthough that revolutionizes our understanding of QCD. That’s simply not the case at the moment. Firstly, AdS/CFT gives at most an effective theory description for QCD in certain regimes. And as far as I’m aware it isn’t even clear at present whether, and to what extent, this really is a valid effective theory for QCD. Secondly, and more importantly, the impact of this on QCD theory research as a whole is not very big. (One way to quantify this would be to count the number of PRL publications on QCD theory in recent years and see what fraction of them involve AdS/CFT.) Afaik it has made no impact on central topics such as understanding the QCD dynamics responsible for confinement, realistic calculations of hadronic mass spectra, and calculations of the various operator matrix elements relevant for studying the weak interactions and thereby testing the Standard Model. Contrast this, e.g., with the large impact that the theoretical breakthough in formulation of chirality on the lattice has made. It is of course very welcome that AdS/CFT is able to say something about regimes of QCD where lattice methods fail (e.g. at high density, due to the sign problem at nonzero chemical potential), assuming that the effective theory description it provides really is valid. But this hardly justifies the hype. There has been much progress in nonperturbative QCD theory in recent years. AdS/CFT is just one of a number of interesting developments. Despite the impression that you and other string theorists try to give, it does not tower above the others in it’s significance and impact. If anything it is of lesser significance so far, especially considering that its status as an effective description of QCD is still up in the air.
Finally, since you emphasized that the AdS/CFT approach is analytic, let me just mention that the lattice approach can also be done analytically in certain limits, most notably the strong coupling limit where Wilson’s original (analytic) derivation of the area law was carried out. Analytic studies of QCD in the lattice and other formulations continue to this day; you shouldn’t imagine that the AdS/CFT approach is at all special in that regard.
I just can’t wait until LHC turns on.
Amused –
Finally, a question for Roger: What do you think about string theorists continuing to put out misleading press releases about “tests of string theory”? Is it really best to just ignore these for the time being, to avoid letting the public get a bad impression?
Its a very difficult question to answer. In an ideal world the string theorists would desist from their extraordinary claims. However, it looks like the opposite is happening. Whether the right response *at this time* is for another group of scientists to stand up in public and say “they’re talking nonsense, are fools, and have wasted money” – the message absorbed by the public – is the right one is something history will judge.
We shouldn’t forget we’re in unchartered territory here, both in terms of the physics under debate and the power of mass media. The only equivalent major spat over science which I can think of which has spilled into the public area is over global warming. I don’t think for one moment that this issue will get anywhere near the level of hysteria and press-coverage as the greenhouse effect. However, it is a salutory warning of what can happen given a mix of genuine, concerned scientists, scientifically illiiterate journalists and crackpots with websites.
THE ONLY LOGICALLY POSSIBLE PROPOSALS I HAVE SEEN FOR LANDSCAPE PREDICTIONS ARE STATISTICAL ONES. I PERSONALLY DON’T BELIEVE THESE MAKE SENSE (YOU CAN NEVER KNOW THE MEASURE).
–PW
David B.,
I have not now, nor have I ever suggested work in string
theory should stop (I’d conceivably be working on it myself, were
I not occupied with other matters). Nor has Peter W., I think.
Nor did some of the other commenters on this thread.
Eric,
I am looking at your response to my comment from yesterday
and some of your further remarks. I am still not persuaded
(if anything, even less so) that your analogy is right.
As I understand it, you are trying to make the following analogies:
1. the space of field theories is analogous to the landscape.
2. the standard model is analogous to one string theory solution.
These are not analogous. Nobody claimed in the sixties that
the SPACE of ALL field theories was something emerging from fundamental theory of nature. The Holy Grail (except to the
large community of S-matrix advocates) was ONE correct field
theory. People searched for one theory which would explain the
data. They did not search for a solution of what they wished
would be the correct theory consistent with data. There is a
difference between a scientific theory and a particular solution.
They aren’t the same – think about it.
On another matter, trying to pull rank on Peter W., by saying you
know more than he does, undermines anything valid you might
have to say.
Anon,
If you want to discuss what I actually think you need to respond to what I write here. The tactic of ignoring what I write in favor of pulling out of context phrases from some other discussion is a tedious one.
..since some commenters demanded to go ‘back to reality’: not anybody in this blog seemingly denied the mere possibility the landscape could bare at least a family of solutions which could match a given set of known parameters of the ‘real world’, the subtle point is exactly the interpretation whether the situation is analogous and is being transported to be analogous to the situation of QFT in ‘1959’, I would agree to Eric if the landscape wouldn’t reach the measure of confidence with which it seems to be correlated: a parameterized model made to be constrained by experimental data which could eventually fail.
So, as someone whose physical interests remain that of a mathematical observer: why do physicists, i.e. Suesskind et al. claim, a set of mathematically ‘valid’ models could represent a set of ‘possible universes’, which mathematical concepts, as it is obvious not to rely on experimental data, force this interpretation? Is it possible to prove strong belief in the possible validity of a constrained set of models without any sufficient constraint data? Did someone, and Lubos at least seemingly could not deny this possibilty, exclude the perspective that for any given energy scale there will be, if at all, a family of models which matches the given data, but can only be distinguished beyond the given scale, implying any predictions beyond a given, experimentally observed, scale would be impossible, as long it wouldn’t be the Planck scale?
a.k.
There are a lot of possibilities which I can’t deny out of hand. I’d
like evidence, however, or at least a solid motivation for a possibility before seriously considering it. That’s the problem with the landscape
– there is nothing simple or compelling about it. So why launch a
research program to attempt to parametrize the world with it? After
all, there are plenty of other ways to parametrize the world (say, by using the particle data table).
I wasn’t suggesting that the results of a vote like this have anything to do with the validity of a theory. But the fact that string theorists have been losing the public debate does explain some of the tactics they are now adopting in this debate. You don’t hear any more the argument for string theory that “it has triumphed in the market of ideas”. – PW
The latest issue of Physics Today has a free, excellent letter (“American physics implosion”), discussing NEW and TTWP, in which this notion of “market of ideas” is refuted and points out a disturbing trend in American physics. For anybody interested, the letter URL is:
http://ptonline.aip.org/journals/doc/PHTOAD-ft/vol_60/iss_10/16_2.shtml
Nature does not shop at our market place of ideas…she is the way she is — and only reveals herself through honest inquiry and experiment, rather than hype.
So please go back to studying representation theory or whatever it is you pretend to study in order to create the impression that you’re a scientist and not just some computer administrator.
Oh yeah? Yeah?…Well…you’re…you’re just a DUM-DUM HEAD! So THERE!! :P:P:P
Don’t be so rude!
Wikipedia
Dear amused (and others)
I’m not saying that lattice QCD has not solved many problems in the theory of the strong interactions. I’m actually very supportive of using whatever it takes to solve a theory of nature.
Even if with lattice one can see the area law, there are various things that are beyond computation because we do not have infinite resources. For example, getting the Regge behavior observed in nature and the unstable resonances in the meson spectra is beyond what can be done
on the lattice. If there has been a recent development that solves this problem I will be very glad to see it.
Regarding confinement, in toy models based on strings this can be understood as a geometric transition (topology change). This gives you an easily identifiable order parameter in the AdS realization. A lot of the papers where this was understood have about 500 citations and I would claim that that is a successful set of ideas.
You should also read the recent papers by Alday and Maldacena on scattering of gluons in conformal field theories. This is a very interesting new development.
My point of not tossing the Ising model for being unrealistic is exactly that: there are many situations where string models provide a lot of insight into strong coupling phenomena, even if not directly on QCD yet. One has to keep things in perspective.
I also don’t see what the number of PRL’s has to do with success in high energy theory. If you present a very long computation, it is hard to reduce it to four pages. I’ve gotten a few papers published in PRL, and it is usually a lot more work than what it is worth (I’ve had situations where the paper goes back and forth with the editors and reviewers five times and the whole process took over 8 months). If instead your result is a number with an error bar, that is a lot easier to package in the required format.
Regarding my coment of strings as a toy model of quantum gravity, I subscribe to that point of view and I am considered a string theorist.
We (as a string community) do not all agree on the various merits of various phenomenological approaches to the standard model. I am less optimistic than some others regarding predictivity, but I’m not going to tell people who are trying very hard to match with known experimental data to stop working on what they are doing because I’m prejudiced against some set of ideas.
I hope this has clarified my (very personal) point of view.
“If you want to discuss what I actually think you need to respond to what I write here. The tactic of ignoring what I write in favor of pulling out of context phrases from some other discussion is a tedious one.”
So we’re not allowed to examine individual propositions in your argument, and decide whether they are true or false? Or to see whether one statement follows logically from the others?
Anon,
You can do whatever you want. But if you just take something I wrote on another blog out of context, try and make some point here with it, ignoring the fact that I already responded to that same point already on that blog, and ignore what I actually write here in response to you, it’s really hard for me to believe that what you’re interested in is a serious discussion. Somehow I get the idea that any time I decide to spend responding to you is just wasted. The fact that you are doing this under multiple anonymous pseudonyms, some juvenile, means that I have no idea who you are, why you are doing this, or any indication of seriousness on your part.
LDM,
Thanks. The same issue also has
http://ptonline.aip.org/journals/doc/PHTOAD-ft/vol_60/iss_10/12_1.shtml
which features anectdotal evidence about what is happening to students doing theoretical phds these days.
Dear David B,
I’m certainly not suggesting that AdS/CFT isn’t interesting and should be tossed, and I agree that it would be akin to tossing the Ising model. My beef is with with the impression that you and other string theorists seem to be trying to create that AdS/CFT towers above other QCD theory developments in its significance and impact.
I’m aware that it provides an interesting model with a deconfining transition that might be related or similar to the one in finite temperature QCD. But does it have anything to say about the specific confinement mechanism in QCD and features of the QCD vacuum that give rise to it? E.g., does it give any insight into whether the picture of confinement based on dual Meissner effect is correct? Or why the deconfinement and chiral symmetry restoration transitions occur at more or less the same critical temperature? My impression, maybe wrong, is that AdS/CFT doesn’t have much at all to say about these central issues in QCD theory.
“You should also read the recent papers by Alday and Maldacena on scattering of gluons in conformal field theories. This is a very interesting new development.”
Ok, I’ll try to find time to take a look. And while I’m doing that you should read Lellouch and Luescher’s paper hep-lat/0003023 on weak transition matrix elements from finite volume correlation functions, which was also a very interesting development of continuing importance as well as a technical tour de force. And if you have some more spare time you should think about how to develop a Hamiltonian formulation for overlap/Ginsparg-Wilson lattice fermions, resolve the apparent difficulty with CP symmetry (see hep-lat/0501010), and prove Osterwalder-Schrader positivity for this formulation so as to put it on a secure theoretical foundation. These are very important issues that deserve your attention.
“A lot of the papers where this was understood have about 500 citations and I would claim that that is a successful set of ideas..[…]..I also don’t see what the number of PRL’s has to do with success in high energy theory….”
It’s kind of amusing that our views on the significance of citations vs PRL publications are diametrically opposite… But I think your insinuation that it’s easier to publish papers whose “result is a number with an error bar” is no less silly than the view of people who say that the real reason string theorists reject PRL publication as a measure of value is because if they accepted it then it would be possible to measure the value of ST work against the value of work on other topics and that comparison would lead to a conclusion that was uncomfortable for string theorists’ egos. At any rate, my experience and impression of PRL is quite different from yours. My papers in there are all on formal theory topics; the results were not “numbers”, in fact none of the papers contained a single physical unit. Moreover, the results in several of the papers were based on lengthy calculations that would have exceeded the PRL page limit n times over if written out in full. But as with all letter publications, as I’m sure you know, the thing to do in these situations is simply sketch the main steps in the calculations and state and explain the result. (And there is nothing unique about my PRL experiences; it’s been the same in quite a few other cases that I know of.) I can’t believe there should be any special difficulty for string theorists in this, especially considering the apparent ease which they summarize their work in press releases and press articles for the general public.
Dear amused:
Unfortunately I don’t know your name. You can on the other hand probably figure out who I am rather easily as I don’t hide behind a pseudonim.
When I have an idea that I think fits in the PRL format I make an effort to publish there. Also, when I spoke about numbers with error bars, it was not meant in any derogatory sense. I know very well how hard it is to produce a number with an error bar, as I have been recently doing exactly that and it has taken me over eight months of work to learn how to do it properly. I’m stating that it is a lot easier to put that type of calculation in a PRL format than other theoretical speculations. Don’t take it personally.
I feel that you are extrapolating assumptions about my personna and stereotyping me without bothering to know me or my scientific output.
I have never said that the string community has a compete handle on QCD, nor have I ever stated that the other developments in QCD are not important. I was trying to put the work of some segment of our community in perspective. It is very hard to get the point across that many of us actually care very deeply about real physical phenomena, to then be accused of making claims of the type “my field is better than yours”.
In fact, I am very glad for all the effort that has gone into the lattice QCD program and I think that some of the results in that field are outstanding. I’m also very glad that you pointed me to the work of Lellouch and Luscher on Weak transition matrix elements. This still does not explan the Regge behavior nor the strong decay matrix elements of unstable resonances which is the point I was trying to make. I hope this clears this apparent confusion.
Now, regarding citations versus publishing in PRL, that is a question of objective criteria to determine the quality of a paper and will certainly satisfy various bureaucratic bean-counters.
What counts as having made more impact on physics? A paper with 500 citations (which is a huger number by any measure), or managing to put a paper in PRL format?
I think you are over-reading the tea-leaves regarding my opinions in this matter.
I certainly hope this has clarified things a bit.
Dear David B,
I’m sorry if you are bothered by my anonymity but there are good reasons why someone might prefer to remain anonymous in blog discussions…I have no idea who you are either.
Regarding publishing in PRL, from what I’ve seen the main consideration that people make in deciding whether to aim for it is whether or not their results satisfy the interest and importance criteria. That’s where the real challenge lies. I don’t think it’s at all difficult to put a more formal theory paper into PRL format (it can be a pain, but I wouldn’t say it’s hard).
“It is very hard to get the point across that many of us actually care very deeply about real physical phenomena, to then be accused of making claims of the type “my field is better than yours”.”
I don’t doubt your sincerity, but the way string theorists present the potential application of AdS/CFT to QCD often comes across as aggrandizement and misleading advertising (e.g. the lack of caveat about whether it really gives a valid effective theory for QCD in some regimes, which isn’t known yet). Maybe there’s a clash of cultures here.
Regarding citations, having a huge number of them is no doubt a sign of good work, as is a large number of papers in PRL. But beyond that I can’t really take it seriously as a measure of anything. It seems that papers that catch a wave of research activity at an early point can ride it to become highly cited without necessarily having made a major contribution. This happened (on a lesser scale) for one of my papers once, through dumb luck. There was nothing particularly great about it, and others which I consider to be much better have hardly any cites.
Anyway, thanks for taking the time for this discussion, hopefully we understand each others viewpoints better as a result.
Eric,
let us assume angels do really exist. then, how do you calculate how many of them will have room to stand on a needle’s tip? 🙂
dear david b.,
i would like to point out that a) there is no effective string description of QCD yet and b) that the sheer viscosity is a quantity that every model – no matter how crude – seems to get correct. i see it more of an interesting question as to why this quantity is so insensitive to the underlying theory or approximation methods than anything else. and by the way, there are accurate lattice predictions of this quantity as well.
regarding the lattice QCD results i am willing to make the following bet: we will have the complete meson and baryon specrum calculated with 3% precision before you will even have a dual string description of QCD.
oh, and of course these papers will hardly be topcite 500. our community is just that much smaller. but we have learned to live with this renormalization factor. it is also not too bad when you think about it. today a paper that does a rough order of magnitude estimation in a toy model does get 5 times more citations than the actual ab initio calculation. but in 50 years, i wonder which of these 2 numbers will end up in a textbook about qcd.
One thing I find troubling is the suggestion that “a computer programmer or an analytical chemist or a forklift operator” can not do or think about theoretical physics (or anything else for that matter). One does not need an advanced degree (or even a degree) to be able to pick up books, read information, work out the math, draw their own conclusions, and maybe provide some insights into a topic. Lets not forget the gentleman (and gentlewomen) scientists of an earlier era who did important work.