I have a long-percolating post that I hope to finish soon (when everything else is finished!) on “Why String Theory Must Be Right.” Not because it actually must be right, of course; it’s an hypothesis that will ultimately have to be tested against data. But there are very good reasons to think that something like string theory is going to be part of the ultimate understanding of quantum gravity, and it would be nice if more people knew what those reasons were.
Of course, it would be even nicer if those reasons were explained (to interested non-physicists as well as other physicists who are not specialists) by string theorists themselves. Unfortunately, they’re not. Most string theorists (not all, obviously; there are laudable exceptions) seem to not deem it worth their time to make much of an effort to explain why this theory with no empirical support whatsoever is nevertheless so promising. (Which it is.) Meanwhile, people who think that string theory has hit a dead end and should admit defeat — who are a tiny minority of those who are well-informed about the subject — are getting their message out with devastating effectiveness.
The latest manifestation of this trend is this video dialogue on Bloggingheads.tv, featuring science writers John Horgan and George Johnson. (Via Not Even Wrong.) Horgan is explicitly anti-string theory, while Johnson is more willing to admit that it might be worthwhile, and he’s not really qualified to pass judgment. But you’ll hear things like “string theory is just not a serious enterprise,” and see it compared to pseudoscience, postmodernism, and theology. (Pick the boogeyman of your choice!)
One of their pieces of evidence for the decline of string theory is a recent public debate between Brian Greene and Lawrence Krauss about the status of string theory. They seemed to take the very existence of such a debate as evidence that string theory isn’t really science any more — as if serious scientific subjects were never to be debated in public. Peter Woit agrees that “things are not looking good for a physical theory when there start being public debates on the subject”; indeed, I’m just about ready to give up on evolution for just that reason.
In their rush to find evidence for the conclusion they want to reach, everyone seems to be ignoring the fact that having public debates is actually a good thing, whatever the state of health of a particular field might be. The existence of a public debate isn’t evidence that a field is in trouble; it’s evidence that there is an unresolved scientific question about which many people are interested, which is wonderful. Science writers, of all people, should understand this. It’s not our job as researchers to hide away from the rest of the world until we’re absolutely sure that we’ve figured it all out, and only then share what we’ve learned; science is a process, and it needn’t be an especially esoteric one. There’s nothing illegitimate or unsavory about allowing the hoi-polloi the occasional glimpse at how the sausage is made.
What is illegitimate is when the view thereby provided is highly distorted. I’ve long supported the rights of stringy skeptics to get their arguments out to a wide audience, even if I don’t agree with them myself. The correct response on the part of those of us who appreciate the promise of string theory is to come back with our (vastly superior, of course) counter-arguments. The free market of ideas, I’m sure you’ve heard it all before.
Come on, string theorists! Make some effort to explain to everyone why this set of lofty speculations is as promising as you know it to be. It won’t hurt too much, really.
Update: Just to clarify the background of the above-mentioned debate. The original idea did not come from Brian or Lawrence; it was organized (they’ve told me) by the Smithsonian to generate interest and excitement for the adventure of particle physics, especially in the DC area, and they agreed to participate to help achieve this laudable purpose. The fact, as mentioned on Bloggingheads, that the participants were joking and enjoying themselves is evidence that they are friends who respect each other and understand that they are ultimately on the same side; not evidence that string theory itself is a joke.
It would be a shame if leading scientists were discouraged from participating in such events out of fear that discussing controversies in public gave people the wrong impression about the health of their field.
Peter Woit wrote ” … the people who have made the big breakthroughs in this subject often do so at a relatively young age, so if you want to think about how to maximize the chances of such a breakthrough, you need to think about how to encourage young people to try and do something new and ambitious. I’ve made some suggestions on my blog and in the book (e.g. instead of many short postdocs, guarantee people support for longer terms, “birth control” to bring the number of people and the number of jobs into better balance). Unfortunately I think it may also be necessary to not just provide incentives to original ideas, but disincentives to unoriginal ones. As long as people see that the most likely path to a permanent position is to keep their head down and work on the most conventionally accepted topics, that’s why many if not most people are going to do. I’d love to see some discussion and debate of these issues.”
This can be very easy, Peter: Devote on your blog a special post just to this issue (and not to string theory); explain your ideas on the matter, perhaps Lee Smolin who devoted large portions of his book to these issues will present his ideas and then open it to discussion and debate (which will not be about string theory.)
I read carefully Smolin’s suggestions on these issues and while very very original, for most parts they are also very problematic and unconvincing. Taking originality as the ultimate parameter in scientific quality is one serious problem with your approach.
Trying to juggle together “pure” scientific issues and these serious issues regarding sociology of science is by itself very problematic.
If you want to have an informed opinion about the question of whether my claims about string theory’s failure are correct or not, you need to try and follow that argument.
So if I have not read your book, I am not informed and do not have the right to comment? I note that here you are again telling me what I “need” to do, and have cast your own role in the debate as central. I am in fact trying to follow the larger argument, including your part in it.
However – and it’s worth mentioning again that I’m utterly undecided on the merits of either “side” here – your particular rhetorical style is one that I frankly do not want to force myself through a whole book’s worth of. But, I will probably still give it a shot, and if I have any truly well-developed skill at all it’s the ability to keep an open mind, so I’ll try to focus on the merits of what you say rather than how you say it. Right now I’m trying to do the same thing with Susskind’s book on the landscape, in which he constantly claims that String Theory (with caps like that) is the ONLY valid approach to practically any topic worth discussing. I don’t like his style, but I’m trying to get past that to the meat of his argument.
If you want to decide who is right about this based on your dislike of people’s “arrogance”, I think you’ll find plenty of it on all sides of this debate, so it’s not a criterion that will help you very much.
Ah, the Straw Man. I don’t want to decide “who is right” based on arrogance, flatulence, cromulence or any other such quality. It’s not for me to say who’s right, in fact I am highly suspect of any notion of final “rightness” in as primal and complex a subject as this. I am interested in the quality of the debate.
Intellectual arrogance abounds in this field, no doubt. I’m well aware of it, given that I read nearly every popular-level book written by a physicist. I tend to let it slide since I’m not qualified to judge between competing claims. But rhetorical arrogance is a different story, and I can’t remember I had this kind of negative reaction (outside of the political arena, or perhaps the pseudoscience wars) to what I perceived as an attempt to manipulate the debate with the purpose of moving the Overton Window in your desired direction via reframing techniques.
When I read some of your posts I find myself deconstructing them, which is the trained mind’s defensive response to manipulative, salesman-esque language. I have to force myself to go back through and read these for content in a value-neutral state.
And, to be fair, when I do that, you do seem to have something to add to the conversation; perhaps you even deserve to be a driving force. I would contrast your very interesting reply #175 with the tone of post #130 which drove my initial comment. My point is that your tone is not equivalent, and that, in my case anyway, it hurts your case.
This future is going to be determined largely by who gets hired into permanent jobs, and who doesn’t, and everyone in the subject is well aware of that.
It’s certainly true that there are resource allocation issues that are valid, and the bruising realpolitik of tenure is well known. I simply think that for the physics community to hold this particular part of the debate in public is highly unwise.
The capitalist social-darwinian competition/survival aspect of modern science has been critiqued enough without my adding much to the hot air. Clearly the system is poorly thought out. And certainly problems arise when any one subfield becomes dominant, yes, this is an obvious problem: the research equivalent of a monoculture subsistence economy, very well, let us deplore it.
However, from the perspective of the non-working-physicist, it’s easy to think (incorrectly, but this will be the perception) that you all are less interested in the validity of the science and more interested in shoring up your own professional situations. I do not think this is true. But it is how you will all be perceived if you continue talking about this part of it in public.
To be quite blunt, we don’t care who gets the good job at Caltech and who gets stuck at East Podunk U for their fifth postdoc; and when the debate turns that way, people will glaze over or become wary of their tax dollars. We want to know: are you making progress? Does it mean anything to me, either technologically or, I suppose, epistemologically?
Work calls. Peter, I will read your book, and consider what you have to say. Meanwhile, please consider what I am saying: your strident tone and potent, skillful rhetoric can work against you. In the age of the All-Spin Zone many of us have become very finely attuned to this type of language; it sets off BS detectors, in many cases unfairly, because the content of the message may be entirely valid., but the messenger becomes distrusted.
Peter, what would you think about automatic postdocs for all new physical science Ph.D.s? You get a Ph.D., the NSF gives you a five-year postdoc, no need for applications. In the NSF budget, this would actually be a fair small amount. Five years would let you dive into a topic, maybe one very different from your dissertation, and give you several years before having to turn your attention to your next career move.
The NAS report on science competitiveness, “Rising Above the Gathering Storm”, proposed expanding the early-career grant program, but their plan would still help only a few hundred people.
George
Dear Peter:
String theory is widely believed to be a theory of beyond the standard model physics, if anything because it includes gravity. As such, one would need a complete description of how the standard model arises, and on how to calculate the various coupling constants of the standard model itself. If that turns to be an ill-defined problem (which it can), then one should try to predict new particles that are accessible to an experimenter from the data that has been already collected.
There are various models based on strings that get some qualitative agreement with the standard model (3 generations, non-zero Yukawa couplings, etc). The devil is in the details and the standard one should meet is to get things to a level where one can compare with precision experiments in particle physics. The best data available at the moment is in precsion electroweak data. That is why I mentioned it.
There is a possibility that a dual string theory of just the standard model exists (without gravity in 4d). This possibility is not discussed very often. At this level, that dual description should be just as good at calculating various standard model corrections as doing loop calculations in the standard model itself. Otherwise, its just a curiosity.
In this vein, it is believed that strings have a good chance at being able to reproduce the spectrum of just QCD in the strong coupling (confinement) regime. Again, we don’t know for certain. But it is interesting to find out.
The point I was making above (without trying to go into the details) is that all of these are questions one can address with string theory ideas and that is why one studies string theory. Indeed, some of these questions are considered to be fundamental questions in physics. String theory gives you a toolset that is in principle able to answer them (all evidence of our understanding points in that direction). In practice, we don’t know if it will for sure. That is part of the reasons research in string theory is exciting.
Tyler, you don’t want the debate to be held in public?
Sure, that subsection of theorists that don’t ever take public money are welcome to form some supersecret cabal to discuss Weighty Matters. The guys that are taking public money, though, are answerable to the public. Indeed, the openness, across the board, of modern science makes a great fit with public money being provided to support it.
George,
I’m a bit dubious about the “postdoc for all physical science Ph. D.s” idea, partly because it seems unrealistic that such a thing would be funded, partly because there are a significant number of people getting Ph.Ds who for whom the offer to with no effort spend the next five years of their life being badly paid to do research they’re not really cut out for would not be a good idea. Either for them or for the field.
I do think the idea of setting a standard of making all postdocs five year or longer term is a good one, at least in the field of particle theory, given the current situation. Also, some way should be found to fund postdocs not for everyone, but for those who have impressed people around them with their intelligence and promise, even if they have little to show for themselves in terms of results because they’re trying to do something overly ambitious and haven’t managed yet to get anywhere with it.
David B.,
OK, I take it that your reference to “precision electroweak physics” is to the idea of string theory describing beyond the standard model physics and that you see this as something string theory promises to give us an understanding of (since you write “String theory is widely believed to be a theory of beyond the standard model physics”).
I really don’t understand this invocation of “precision electroweak physics”. The problem with “string phenomenology” is that no one has any idea how to make any predictions with it at all, much less precise predictions about electroweak physics. String theory can’t predict even the crudest things about the standard model, such as the number of generations.
“all of these are questions one can address with string theory ideas and that is why one studies string theory. Indeed, some of these questions are considered to be fundamental questions in physics. String theory gives you a toolset that is in principle able to answer them (all evidence of our understanding points in that direction).”
It seems to me that, as far as the standard model is concerned, all recent evidence points in exactly the opposite direction. The lesson of the landscape is that string theory inherently can’t address any of the questions about the standard model that we’d like answers to (except for possibly how to do certain QCD calculations).
tyler,
My only point about informing yourself was that there is a serious and extended argument behind the claims about “failure” that I’m making, I’m not just saying that I think something so you should believe me. Up to you whether you want to spend your time looking into this, there are good reasons not to, most people have better ways to spend their time.
I’m actually not trying to sell anything to the public here, if I were I’d adopt a different tone and discuss different issues, in a different way. For better or worse, this blog has a mixed audience: both scientists in this area and interested on-lookers. My interest has always been in starting what I see as an important discussion among the people in this field. The book was always aimed more at such people than at the general public, and the fact that it was published by a commercial publisher and promoted widely was not my choice (I intended it for an academic press and a smaller audience).
Particle theory does need to have a serious debate about what to do about the problematic situation it is in. Maybe it would be better if this were somehow conducted less publicly, but the past history is that of an unwillingness to confront these problems, coupled with a seriously misleading publicity campaign aimed at the public, designed to convince them that all was well with string theory. This publicity campaign now shows signs of being derailed, and I can’t say I don’t think that is a good thing.
Peter:
Just like Einstein’s gravity predicts black holes, that does not mean that every solution of gravity has black holes in it. By the same token, some solutions of string theory have three generations, therefore string theory PREDICTS three generations in one of its solutions.
The problem with string phenomenology is not that ” no one has any idea how to make any predictions with it at all”, but rather that the typical prediction is for new particles at about the GUT scale, well beyond what we can accomplish technologically.
That seems to be a general omission of this whole discussion. Absent an accelerator that can probe that scale directly, one has to look at small deviations from ordinary standard model physics. This means one needs to have a setup that permits one to calculate with the same precission as in the standard model to find a new efffect.
You’re also wrong about the landscape. It makes predictions: in principle it gives a discrete description of vacua. This means that certain values of the fundamental constants are just not allowed. This is a route to falsifying the theory.
In practice it’s too large to explore effectively, and we don’t know how to get the numbers in sufficient detail to compare to experiment. This is a motivation to try to do better.
There is another thing: some models based on strings seem to be able to access fundamental strings near the TeV scale. These are not ruled out experimentally yet. If we are lucky, they will be seen at LHC. Some of those models can make very precise predictions for various coupling constants of new particles to the standard model. By that standard, they are just as good as usual phenomenology models of physics beyond the standard model: not ruled out yet, and with some new particles at the TeV scale.
There is no unique preddiction from string theory for what will happen at LHC.
I guess that’s too bad for us, but it is not as hopeless as you portray it.
David B.,
You are using “prediction” in a non-standard way. Saying that string theory PREDICTS 3 generations because it has a solution with 3 generations is kind of misleading if you don’t also tell people that it has solutions with 1, 2, 4, 5, 6…., or basically any number of generations you want. String theory doesn’t determine the number of generations at all. As far as the string theory framework is concerned, this number could be anything.
The problem with the landscape, and with the string theory framework in general if you believe that it includes the landscape, is that the nature of the vacua is so varied and complex that, as far as anyone can tell, you can get just about anything you want. You can get virtually any number of generations, any gauge group, any fermion representations, any Yukawa couplings, etc. You also can get any energy scales you want: electroweak and supersymmetry breaking scales can be anything you choose. In brief, nothing about the Standard Model Lagrangian is explained by string theory.
It’s not just that there isn’t a “unique” prediction about LHC physics. Other than a few very conjectural “swampland” arguments that certain very exotic things can’t happen, as far as anyone knows, string theory has solutions with essentially any possible effective field theory at LHC scales. And this is not just a problem about the LHC scale. The situation wouldn’t change even slightly if physicists were given the funds to build an accelerator as large as the orbit of the moon. There are no real predictions, not just at the LHC scale, but even at the GUT scale (and very little if anything in the way of predictions even at the Planck scale). Whether experimentalists figure out how to make accelerators a billion times higher in energy, or do precision experiments to a billion times accurately, string theory can’t say what they are going to see.
I don’t understand why you claim that the “typical prediction” is for new particle physics at the GUT scale, but not at other scales. You can write down string models with new physics at any scale you want, as long as it’s above scales visible to the Tevatron so you avoid conflict with experiment.
As far as anyone can tell, the Landscape is so extensive that, within experimental accuracy, you can get any values of the standard model parameters you want. There also are good arguments that, if the landscape exists, you can’t ever hope to calculate these parameters, for computational reasons. This conjectured discreteness is not a viable route to falsifiability.
Sure, maybe when the LHC is turned on, it will turn out that the fundamental string scale is such that we haven’t seen its effects at the Tevatron, but will at 7 times higher energy. After all, the string scale could be anything. There’s just not a shred of evidence for this, it’s pure wishful thinking.
Pingback: Sharp Sand » The Culture Wars Have Moved into Physics
Peter:
You’re acting as a bully: Every time someone writes something that tries to capture why we do what we are doing, trying to capture some of the excitement about the work we do, you come and try to stomp over our arguments to show why your opinion counts so much. I don’t buy that.
You just believe that if you heckle enough, you win. Well, you don’t. I won’t asnwer any more of your questions on this thread, so don’t bother asking.
The whole issue of the GUT scale, is that the most conservative models of string theory have the string scale close to the Planck scale.
The universal prediction of strings (if they are sufficiently weakly coupled, and the indication from the standard model is that particle physics is weakly coupled at high scales) is an infinite (or very long) tower of states of very high spin, with approximate Regge behavior, and the Regge slope is governed by the string scale.
The big question is if that scale is near or far. If it is near, we are in luck. If it is far, we have to content ourselves with low energy approximations. People have built many models of string physics that resembles the standard model, but does not get all the details right.
You don’t like the landscape, well, I don’t either. That does not mean that string ideas are worthless and that we are all wasting our time. We have good reasons to do what we do. I was posting what some of those reasons are. You have all the right not like them for yourself, but some of us find them very interesting. You seem to be incapable of understanding this one point: that we do what we do because we believe that what we are doing is important, and your argumenst are not convincing for peple who have studied the subject and are working on it.
Have a good day.
Dear George,
Thanks for persisting in raising the issue, “I long for a debate where we roll up our sleeves and solve problems rather than snipe. For instance, I think we can find common ground on the fact that the system of science funding in this country is broken; the grant process devours too much productive time and discourages out-of-the-box thinking of the sort Peter thinks is neglected.”
This is the discussion I hoped to stimulate by writing my book. This is why the discussion of string theory takes only one of four parts, and why the last of the parts is devoted to raising this question and making some concrete suggestions to address it.
I have lots of evidence that senior people in a wide range of fields worry about these same issues. I quoted from some of them in my book, such as a biologist who was formerly the president of the NAS, and since writing it I have heard from other senior people across the sciences who worry about these issues in their fields.
I like your suggestion of universal 5 year postdocs, there are risks of course, but in my view greater benefits. It is very important that you emphasize that compared to the overall US science budget (or even just the NSF budget) such a program would be cheap. Other suggestions I made are equally cheap such as mimic the system of Royal Society Fellowships that can identify very independent original thinkers and jump start them into faculty positions. If we fund every recent Phd in science with the rare capacity to formulate while a postdoc a novel and ambitious research program, that also would be cheap, because such people are a small percentage of the people who do get funded.
Certainly some of these people would find that their ideas, when explored, lead nowhere. But it is an easy bet that much progress would result in science coming from the development of ideas that are going to have trouble getting supported in the present environment because they don’t fit into any decades old research program led by senior scientists.
Given that many prominent and experienced people agree with your and my estimation of the problem, what I want to spend time discussing is how to fix the problem by getting proposals like this implemented. As you emphasize, what is required is not that expensive, nor is it that experimental given that there are good models to study in the policies of other countries and fields. So while blog discussions are a useful starting point, and I look forward to seeing if others answer your challenge, this duscussion can only be a prelude to discussing how to get proposals concretely implemented by public and private foundations and universities.
Thanks,
Lee
David B.,
I’m not heckling you, bullying you, or “stomping over your arguments”, or trying to “show why my opinion counts so much”. I’m making objective statements about what the problems with the “Landscape”, and thus with string theory are. If something I write is inaccurate, all you have to do is point out where the inaccuracy lies. If you don’t want to take the time to do this, don’t. But attacking me in personal terms is not an answer to the scientific issues I am raising.
In the end, your answer to the arguments about fundamental problems with the research program you’re involved with is that you’re “excited” about what you’re doing and you think it is “important”. That’s fine, every scientist should be excited about what they are doing and think it is important, but that’s not enough. The people at the Discovery Institute are excited and think they’re doing something important. Scientists are supposed to have something more: solid answers to the question of how their work is someday going to be experimentally testable and may lead to a deeper understanding of nature. Right now, string theorists are able to give some reasonable answers to this question for part of their research program, that concerned with using string theory to understand QCD. But as far as using string theory to explain anything about the standard model Lagrangian, the landscape has made this impossible.
Folks might want to check out my discussion of justifications for why space needs to have three large dimesnions in classical terms – no string theory etc. needed. It’s based on comparing EM interactions in model universes of different space dimensionalities. Check the blog (May 05, 2006). I know I have been remiss on keeping it up, but if I get some new comments I’ll try to put up some new posts.
Peter:
You admit that string theory might be useful for QCD. But then you turn around and say that research in string theory is useless and that we should give up, mainly because you don’t like the landscape. You say your arguments are technically accurate. The arguments I gave you are also technically accurate, so then what? String theory is not just about the landscape. It is much richer than that.
When I wrote my piece, I said that it was my personal opinion and then you went straight for trying to argue about the landscape and had all kinds of technical objections. I felt that you were getting personal so I said so. I said that you are acting like a bully and are a heckler. I did not insult you. I was making what I believe is an objective observation on your behavior. This pattern has repeated itself many times: there are many instances of other people getting tired of your style. I’m not particularly tactful sometimes. I try to be direct. Sorry you got hurt. I get frustrated, just like the next guy.
I don’t see the relevance of the existence of a large number of string vacua that look nothing like the real world, particularly since the Standard Model iitself has a landscape of vacua that look nothing like the real world.
Endless repetition does not make it true. Your “objective statements about what the problems with the ‘Landscape'” (#) are nothing more than a guess at an answer to a question that is still very much open
Perhaps your guess is correct. Most likely, it isn’t. No one knows (though everyone seems to have a strong opinion).
I should point you to comment 39 (and countless posts on my blog) where I argue the contrary position.
But, in all likelihood, that would be futile. I hold no particular hope of convincing you of anything. But it would be a grave disservice to the non-expert readers (assuming there are any left) of this comment thread to allow you, unchallenged, to pass off your opinions on the subject as established facts.
David B.,
I don’t claim “string theory is useless”, I do try and be careful to say that it seems likely to be useful for some purposes (a dual to QCD, mirror symmetry in mathematics), just not others (understanding where the standard model comes from}. Maybe someday someone will come up with a very different form of string theory that will give insight into the standard model, but what I see now is just a massive effort to study complicated backgrounds and justify why they can’t be used to make any conventional predictions.
I’ll take your comments about my style of argumentation into consideration. On the whole, I’d rmuch rather be convincing people than pissing them off…
Jacques,
Not much point in trying to convince you of the untestability of string theory, since you’re the only string theorist I know of who has recently issued a press release claiming to have a way to test string theory next year at the LHC. There is the minor fact that no one seems to believe this except you (including the referee of the paper….).
George wrote: “Peter, what would you think about automatic postdocs for all new physical science Ph.D.s? You get a Ph.D., the NSF gives you a five-year postdoc, no need for applications. In the NSF budget, this would actually be a fair small amount. Five years would let you dive into a topic, maybe one very different from your dissertation, and give you several years before having to turn your attention to your next career move.”
and Lee wrote: “I like your suggestion of universal 5 year postdocs, there are risks of course, but in my view greater benefits. It is very important that you emphasize that compared to the overall US science budget (or even just the NSF budget) such a program would be cheap. Other suggestions I made are equally cheap such as mimic the system of Royal Society Fellowships that can identify very independent original thinkers and jump start them into faculty positions.”
Automatic five-years postdocs for all new Ph. Ds in physical sciences is problematic. For one thing, getting a postdoctoral position is an important step in the academic selection of the better Ph. D graduates towards academic positions. Delaying the time when people will know if they can get into academic life or have to quit can be bad for the researchers themselves as well as for the universities.
Such a move will probably increase the overall number of people getting Ph. D in physical sciences. I am not sure if it is desirable and it can only magnify the problems it meant to solve. Of course, like in everything else we discuss the details are quite important.
Similarly, Lee’s suggestion for special programs for original researchers is problematic and may give the opposite incentives regarding such researchers. (I tried to analyze in some details this specific suggestion in a comment to Asymptotia tea cup VI.)
Yes, your unshakable conviction that String Theory is inherently untestable is every bit as solidly grounded as your speculations about the refereeing process on that paper.
In a way, I’m kinda glad that you immediately tried to change the subject, and didn’t even attempt to respond the scientific points raised.
That, in its own way, is progress…
Jacques, a few years ago a possible outcome of strings seemed
(a) a failure (this often happens even when doing good research)
(b) masked as a success by propaganda.
For example, somebody might have claimed that strings have been tested because WW scattering at LHC obeys causality, or that the string landscape exists because after compactifying the Standard Model one gets a few vacua, or …
Now (b) seems avoided.
If you or anybody else will avoid (a) by getting real physics out of strings, it will be great. Nobody wants to prevent it.
I am really hoping comments #192, #193 and #195 do not signal the start of yet another cat-and-dog fight between apparently implacable foes…
Hi Peter,
You say and have said several times that string theory/phenomenology is a failure because it can never say anything about low energy physics; the landscape renders this impossible. In particular, you say that `as far as anyone knows, string theory has solutions with any possible effective field theory at LHC scales.’
If you think that, then no wonder you think string phenomenology has failed as a research program. Indeed, if that were true, it would have.
The problem is the statement isn’t true, or rather that there is no evidence it is true. For example, consider the IIB flux landscape. Maybe if all scales in the compactification are Planck-scale you can get almost anything. I don’t know. But now put the hierarchy in, specifically low-scale supersymmetry and a TeV-scale gravitino mass. When do this, you then start getting relations among the low-energy scales. For example, the soft terms are suppressed compared to m_{3/2} by a factor ln(M_P/m_{3/2}) and moduli masses rise by the same fashion. This holds in both the ways used to study TeV-scale supersymmetry in this framework, namely the mirage mediation models where W is fine-tuned small and the large-volume models I have worked on.
So, rather than vague musings about the swampland, here’s a concrete question: can you give a IIB flux landscape model, with a low-scale gravitino mass, such that the soft terms are suppressed by ln(M_P/m_{3/2})^2 compared to m_{3/2} and moduli masses enhanced by this factor?
While this post has focused on the narrow issue of light gravitationally coupled particles, you can extend this to the more interesting question of soft terms: what soft terms do you get from what string construction/moduli stabilisation mechanism? Again, there isn’t any evidence to suggest that the answer to this question is simply arbitrary, and indeed this is what lots of current research is on.
To summarise: I don’t think anyone expects to go uniquely from zero free parameters to the Standard Model. But once you start putting scales and hierarchies in the compactification, then all the evidence is that you get non-trivial relations between the low-scale `observables’. If you wish to argue the contrary, I think the burden is on you to show that this does not hold.
All best wishes
Joe Conlon
That would, indeed, be tiresome (and none would find it more tiresome than I).
But there’s an important scientific point at stake — one which cuts to the heart of Woit’s “untestability” argument. Lots of people (Clifford Johnson, most notably) have tried to challenge Peter on his blithe assertions on the subject, with little success.
I doubt that I will succeed either.
But, as David B discovered, one can’t discuss any of the positive reasons for studying string theory, without Peter butting in to repeat his assertion that the Landscape makes string theory untestable (and hence, not even wrong).
The best that I, realistically, hope to achieve is that ‘interested bystanders’ (such as yourself) will realize that Peter’s assertions are, at least, questionable.
Hopefully, that won’t require another 300-comment thread that seems to go absolutely nowhere.
Marty,
I’m not even trying to respond to Jacques’s repetition of his usual attacks on me for the obvious reason you mention. Anyone who wants to know my argument for why string theory is untestable can find it at
http://www.math.columbia.edu/~woit/testable.pdf.
Anyone who wants to know why I think it would be a mistake to try and have a serious discussion with Jacques can take a look at the result of any of my large number of attempts in the past and see where they went. Or, for entertainment, take a look at his press release claiming to show that string theory is testable at the LHC, and compare it to the preprint and published versions of the paper it is based on. Other theorists have publicly characterized this as “hilarious”.
Joe,
In any particular class of models, I don’t doubt that once you make certain choices you get certain constraints. I’m not claiming that these models are infinitely malleable. If you set the scales of the theory in a specific way, you’ll presumably get certain relations. But the scales could be anything: we don’t know what the supersymmetry breaking scale is. The anthropic landscape people, on some days, say that they may statistically “predict” that it will be high, not low, in which case your relations won’t hold.
The set of compactifications string phenomenologists look at is extremely complicated, and getting more and more complicated as time goes on and people find new constructions. I’m not claiming to know what the ultimate end-point of the structure of that set would be if people spend the next millenium investigating it, following the vision that many string theorists seem to have for the future of particle physics.
What I am claiming is that enough is now known about it that no one is able to use the string theory framework to explain why any of numbers that characterize the standard model have the values they do, or to predict what new physics will be seen at the LHC, or at any future higher energy collider. The theory really is untestable.
This kind of untestability is precisely the conventional kind you often end up with when you pursue a wrong idea. Simple versions of the idea disagree with experiment, so you have to make things more and more complicated in order to avoid contradiction with experiment. Introducing branes and fluxes can stabilize moduli and avoid predictions of unobserved long-range forces, but the cost of avoiding these predictions you don’t want is that your framework becomes not rigid enough to make solid predictions. I just don’t think it’s a controversial statement to note that there are no such predictions from string theory about LHC physics, or that we’ve been led to this situation by having to abandon simple string theory compactifications because they disagree with experiment.