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).
Dr. Woit remarked:
String theorists make an excellent point when they note that the laws of nature are not subject to a popular vote. We’re going to have to wait for the LHC and see. In that connection, new calculations taking into account the latest hadronic PVES experiments apparently place tighter constraints on physics beyond the Standard Model:
http://www.jlab.org/div_dept/theory/highlight/beyondSM.html
Of course if no exotica beyond the SM show up in the LHC it’s easy to predict that the string contingent will simply move their predictions to higher energies, as usual.
Let’s put quantum mechanics to a popular vote. If it fails we’ll discard it as a theory and replace it with something that gets more votes, like angels. That’s they way to do science – popularity contests.
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”.
I’d be curious to know what similar numbers would be if you asked not visitors to the Wired site, but Ph.D. physicists. My suspicion is that they wouldn’t be very different. About the only population where the results would go the other way would be if you asked string theorists. And even there, I’m not so sure, they seem pretty discouraged these days…
Maybe string theorists are a large part of the population competent to comment on the matter at all.
There’s no reason to expect an experimentalist working on optics to have any more of an idea about string theory than an algebraic geometer.
And because science is not a popularity contest, there is no reason to think that that the opinion of string theorists themselves have any bearing on the correctness of string theory either. And might even have LESS, to the degree that their jobs and reputations are built on string theory.
Hi Peter,
indeed I think this new delay of LHC schedule was greeted by string theorists as new breathing air…
Cheers,
T.
The “String Phenomenology” codology is an attempt at brand repositioning. When your consumers tell you they don’t want your product, instead of reworking the product you go for a re-branding exercise and try to find new applications and markets. New ad campaign, new logo, the works. The alternative is to shut down those factories and layoff all those highly trained workers. Unfortunately, when the product is fundamentally unfit for purpose, you’re onto a loser.
The lads at the IAS have been running their string theory show every second year since 2002. They try to attract students from the ICHEP conferences – also biennial. Now ICHEP is where all the action is in experimental HEP but string theory always gets short shrift there, presumably because these people are actually concerned with testing real theories, not mathematics masquerading as physics.
In place of gimmicks, string theorists should take a lead from Witten’s approach – use insights from mathematical physics to make new discoveries in pure mathematics – of which his latest paper on Geometric Langlands provides yet another eloquent example.
I think that Occam’s Razor has slit String Theory’s throat.
Hi Mclaren,
String theorists make an excellent point when they note that the laws of nature are not subject to a popular vote.
That’s ironic, given that so far the success of string theory has been measured mostly by its popularity. Doesn’t seem they are really against voting, but have concerns about who should be allowed to vote.
Or maybe the point is that instead of voting on poorly understood ideas, we should vote on people. Edward Witten is chosen “most likely to succeed.” A videotaped incident at the KITP comes to mind, where a string theorist proposes a vote on whether Lee Smolin is a crackpot.
For better of worse, public engagement in the issue has happened and is largely the result of yours and Lee’s spur.
As a particle physics experimentalist I have little real knowledge of string theory. Certainly, not enough to form anywhere near an informed opinion as to whether your arguments about string theory making little progress are valid. If I feel unqualified to judge – and I’m trained to a reasonably high level in particle physics theory – then the average politician certainly won’t have a clue.
This is what troubles me. I am persuaded by the idea that it is better to keep this debate out of the public arena. Politicians like simple messages. If the prevailing message is that theorists have wasted a lot of money doing stupid things (I know this isn’t your message but may be message they get) then it is conceivable that they will cut funding for theoretical physics, irrespective of the topics under study.
The LHC may well provide new directions for the theoretical community which would reduce the influence of string theory. I think it would have been better to wait for the data before starting this debate, especially now that the issue is getting its own momentum and will soon be out of the hands of you and Lee.
Maybe string theorists are a large part of the population competent to comment on the matter at all.
You don’t have to be a string theorist, or even a physicist, or even a scientist, to appreciate the scientific method. When you say you can make predictions, and then you don’t, your audience doesn’t have to be Wittens and Susskinds and Motls to know whether something is wrong.
Roger wrote:
“As a particle physics experimentalist I have little real knowledge of string theory. Certainly, not enough to form anywhere near an informed opinion as to whether your arguments about string theory making little progress are valid. If I feel unqualified to judge – and I’m trained to a reasonably high level in particle physics theory – then the average politician certainly won’t have a clue.”
It may be difficult for a non-string theorist to understand WHY so little progress in string theory has been made, but it does not take fine sense of discrimination to ESTABLISH lack of progress. It takes almost no brains to figure out that string theory keeps to promise a lot and delivers very little on the promises.
Yes, the average politician is well trained to sift the wheat from the chaff, even though he/she may be unable to tell one kind of wheat from another. Remember the cancellation of the superconducting supercollider? The project died largely because of delays and cost overruns, but also because of the associated hype (e.g., the promise of cure for cancer) and DOE’s deceptive claims.
“When your consumers tell you they don’t want your product, instead of reworking the product you go for a re-branding exercise and try to find new applications and markets. New ad campaign, new logo, the works.”
Of course:
Pre-owned – > Used
Private security contractors -> Mercenary
String Phenomenology -> String Theory
and many others…
Roger said:
“This is what troubles me. I am persuaded by the idea that it is better to keep this debate out of the public arena. Politicians like simple messages. If the prevailing message is that theorists have wasted a lot of money doing stupid things (I know this isn’t your message but may be message they get) then it is conceivable that they will cut funding for theoretical physics, irrespective of the topics under study.”
I strongly disagree. People shouldn’t shut up out of fear that some stupid politician misinterprets their words and cuts funding. Quite opposite. The duty of scientists is to educate laypeople and politicians. Open and honest debate is a part of that education.
Eugene.
Mo,
What do you think the promises made by string theorists are, and what do you think a reasonable time frame for delivery on these promises would be?
Dear Peter,
Briane Greene once said string theory is the only game in town.
In NEW you yourself pointed out that one reason string theory was popular in early 80s was there were few unresearch seemingly promising ideas left to address the shortcomings of the SM.
What do you think will happen to string theory and to string theorists should LHC fail to find evidence for SUSY? Or, in otherwords, what would most string theorists today (i.e Witten, Greene, Randall, Susskind) work on (both HEP and QG) in an era where LHC does not find evidence of SUSY in the next few years? Will those string theorists interested in QG continue to work on strings or would they switch to LQG?
Do you think those string theorists interested in HEP might jump on Smolin’s/Sundance preon braiding bandwagon? Or will string theorists continue to do stringy research ignoring a LHC null result.
Dan
If smart people genuinely think they can get something worthwhile out of this string phenomenology business then good luck to them. But they should have the same obligations to demonstrate interesting and important progress as the rest of us. If they are able to make such progresses, let them “prove it” by publishing them in PRL. And if they can’t get published there then the rest of us will draw the obvious conclusion. I’m not personally qualified to assess the worth of research on this topic, but I trust in the capability of the referees and editors of PRL to do so.
“There’s no reason to expect an experimentalist working on optics to have any more of an idea about string theory than an algebraic geometer.”
Wrong! An experimentalist working on optics would have to know the theory behind her experiments. And she’d therefore know if string theory had been formulated such that it could reduce, under certain conditions, to the those standard theories. And if it hasn’t been thus formulated, she knows string theory is far from complete and usable.
That is much more than an algebraic geometer knows, unless the algebraic geometer also happens to have a working knowledge o physics.
And another thing.
The public’s job is not to decide whether string theory is valuable or not. The public’s job is to decide whether or not string theorists should each be given over a hundred thousand dollars per year to sit around with paper and pencil thinking about string theory. And even an unintelligent uneducated member of the lay public can ask, “What’s in it for me?” And if no one can give him a satisfactory answer, he has the right to withdraw his tax money from the paychecks of the string theorists. And if that happens, it doesn’t mean string theorists have to stop working on string theory. They can get a day job and do string theory at night if they’re so convinced it’s a blockbuster.
dear roger,
let’s assume that someone to whom nonabelian gauge theories are a total mystery would need to be convinced of the correctness of qcd. do you have to carry that guy thru the proof of renormalizibility? does he need to know how to compute the beta function?
no. you show him the bjorken scaling plots in the pdb an that’s it.
how about the SU(2)xU(1) weak theory? do you need to understand the higgs mechanism for gauge boson mass generation? no. just look at that picture from UA1 and there is the W and the Z. and you can understand the higgs mechanism better than higgs himself and still there is this shadow of doubt if it is correct at all because we have not seen the particle yet.
every reasonable person is qualified to judge scientific theories, that’s the beauty. they make predictions that either get validated or not.there is a certain time lapse of course. in 1960 the big bang theory was fine even without direct experimental proof. it would be hard to defend today if no CMB would have been found yet. it is equally hard today for steady state fans to argue against the big bang – even if the hardcore ones still do so.
for string theory the clock is just ticking. and they are on the move.
when oh when, will you stop being so negative and grace us with your brilliant alternative so we can put that to a vote……
A.J. Says:
“Mo,
What do you think the promises made by string theorists are, and what do you think a reasonable time frame for delivery on these promises would be?”
Speaking in the simplest possible terms, it is better to point out past promises that became claims:
1) they claim they have a theory, but string theory (or more accurately M-theory that substituted it) doesn’t really exist yet;
2) they also claim string theory provides a unification of all of fundamental physics, but it doesn’t even predict the Standard Model parameters.
Re: time frame. Let’s look at comparable projects. It took Einstein about ten years to formulate general relativity. It took 16 years to complete the electroweak theory, from Yang-Mills (1955) to Glashow-Salam-Weinberg (1960s) to t’Hooft (1971). So I would expect that by now we should have had a complete formulation of string theory.
Interesting responses.
I stand by what I wrote that dragging this into the public arena at this stage is not sensible, especially with the LHC around the corner. Were there to be no LHC then it would be more appropriate to begin the debate now. As it is, should the LHC discover new physics then my money is on the theorists trying to understand the new phenomena quantitatively i.e. chasing the Nobel prize. If string theory is not fit for this purpose then it will naturally ebb away to an extent. Others may have different opinions of how future events will pan out. However, nobody knows anything for sure other than that we have experiments waiting to come on-line which stand a fighting chance of changing the direction of physics research. In this situation it is sensible to hold back – after all we’ve already waited twenty years.
Unless I missed it then nobody responded to my main point which is that sending the message that theoretical physicists are a useless bunch who can’t be trusted with the public’s money is a dangerous message to send. This is the message which is being sent. With every popular magasine picking up this debate, the qualified and carefully worded criticisms become more and more distorted.
As for string theory having made no progress, I’m not going to restate the string theorists arguments, which are well known.
The issue of hype was also mentioned. The LHC has probably been hyped as much as string theory. According to every popular science magasine I’m taking part in an experiment which will explain mass (well not really since most observable mass comes from the strong force), explain dark matter (let’s hope that the hierarchy problem is as serious as we think and we get new TeV physics), and also allow us to somehow unify the fundamental forces (such is the message getting through). The fact is that every science field hypes its work in order to get the public and policy makers on board.
I don’t have any particular love for string theory. My own opinion, for what its worth, is that theoretical physics research may have gone down a blind alley for the past twenty years and needs to learn lessons to avoid repeating this behaviour in the future. However, I’m not convinced that the current blog wars and bringing the fight into the public arena at this stage is the most sensible way to achieve continued funding and future excellence in research, which has to be the final aim.
Roger,
Your position resembles that of Gerhard ‘t Hooft, and is, I believe, the majority view held by physicists, whether they be theoreticians or experimentalists.
It is a traditional stance and can be summarised as “don’t wash your dirty linen in public”.
The problem, as has been repeatedly explained by Smolin and Woit, is that until recently very little debate has taken place either within or without the physics community, and string theorists have had free reign to hype their theories to the public while establishing hegemony over much of theoretical physics research in the US.
The fact that the physics community allowed this to happen shows that the ‘t Hooft approach doesn’t work. That much of the debate has had to be stirred by an outsider (Woit) only highlights a twenty year failure of the physics community to address this issue internally.
Your expectation that the LHC will further diminish string theory status exactly mirrors the prevailing view, i.e., that we can trust to experiments to sort the wheat from the chaff. There is no evidence that string theorists will take a blind bit of notice of any negative outcomes from the LHC.
The physics community’s ostrich mentality will have serious consequences for future physics funding when, not if, the string theory program collapses. Because we didn’t put our house in order when we had the chance to do so, outside forces will do it for us, and we only have ourselves to blame.
You say there is no evidence that there experimental data will sort the wheat from the chaff. This is a statement of the obvious – we haven’t taken data yet. Nobody knows what will happen. The only certainty is that we have experiments about to start which have a fighting chance of changing the face of physics. That hasn’t been the case for many years. Being hot-headed now is somewhat absurd given the risks of inflicting lasting damage to the reputation of the field.
I’m very sceptical that the damage created by this messy public debate is less than if string theory “internally” collapsed. Funding and the general health of science relies on public trust – with every magasine article this trust is being eroded. One has to be damn certain before opening a public debate and washing dirty linen in public. I’ve yet to see any evidence that the approach you’re advocating is any more constructive than my favoured option which is to wait several more years and see how the LHC influences the field before opening the can of worms.
Its very easy to start a public debate, its not so easy to control it. The end result of all of this may well be unsatisfactory for string and non-string enthusiasts alike.
Note, by the way, a lot of qualifications in my statements. I don’t know what will happen. This is why I strike a note of caution. I’m not convinced that any of the posters here have any more prescience than me and the certainty and, at times, fanaticism with which both sides push their view is very worrying.
Roger,
I did not write “there is no evidence that there experimental data will sort the wheat from the chaff”. I wrote “There is no evidence that string theorists will take a blind bit of notice of any negative outcomes from the LHC.” That is based on the assumption that they will continue to behave as they have to date when faced with inconvenient and unanticipated experimental outcomes, witness the use of anthropic arguments when faced with the lambda-CDM cosmology.
Proposing that public debate be closed down is just an argument for a restoration of the status quo pre Smolin and Woit. Well, that’s not going to happen. Either the community resolves this internally or funding authorities will do it, with knock-on implications for the reputation of all physicists, especially in the HEP sector.
Once again, I point out that it is this blind faith in experiment as the arbiter of string theory’s demise or success which is the Achilles heel of the community’s response to date. It’s cosy, convenient and a recipe for doing nothing. It ignores the fact that the LHC is incapable of falsifying string theory as things stand. So what if LHC doesn’t find supersymmetry? Not to worry, check higher up. Oh you can’t, well, build a bigger machine and in the meantime we’ll do some more calculations.
When string theory eventually collapses, its practitioners can go back to doing what many of them are eminently qualified to do, making fine contributions to pure mathematics, as Witten does, or diversifying into other areas of mathematical physics. The physics community will be left holding the baby.
You know nothing about what will happen in the theoretical community during the LHC era and nor does anyone.
Tell me, why does the community need the public debate *now* and not, for example, in 4-5 years time when the data could already have led to other promising approaches and a greater diversity emerging ?
«And even an unintelligent uneducated member of the lay public can ask, “What’s in it for me?”»
Please. The average joe is not qualified to judge the best clothes to wear on a rainy day and you want them to make these decisions about prospects that are anything but clear?
Some people’s faith in humanity never ceases to amaze me.
why does the community need the public debate *now*
Woit’s original evaluation, physics/0102051 appeared in 2001. Glashow’s (Nobel 1979) and Ginsparg’s attack on string theory, Desperately seeking superstrings, appeared in Physics Today in 1986. 2001 and 1986 are hardly “now”.
What is happening now is that string theorists no longer have the power to suppress critique. A generation of physicists has spent 20 years on the receiving end of unchallenged string theory propaganda can no longer be ignored.
I know that the LHC it will not be able to falsify string theory as things stand today, because no predictions are made that can eliminate the theory if they are not found. Phenomena may be discovered which are tough to reconcile with string theory, but that has never been an unsurmountable obstacle.
The HEP community needed this debate many years ago, and has crouched behind the bogus LHC “messiah” argument for long enough. It has painful lessons to learn.
Feynman blasted string theory publicly back in the mid-1980s, and was ignored. Twenty years on, do you believe we are better off?
Roger (and others),
Thanks for the thought-provoking comments. I have been thinking about these issues as this debate has become a public one over the last year or two.
There are two answers to “why now?”. One is that it’s already way too late. Much of this debate could have and should have taken place 20 years ago. I got involved in 2000, after many years of frustration that the obvious issues were not being addressed, attempting unsuccessfully to get something published in Physics Today, addressed not to the public, but to the physics community. That was stopped, and the piece ended up being published in American Scientist, getting an audience of not just physicists. The book was written a couple years later, and an editor at Cambridge University Press was interested in publishing it. Again, string theorists put a stop to that, which just delayed the publication and forced me to go to a publisher much more in the business of marketing to a wide public. All of this was going on at a time when LHC results were still quite a few years in the future.
The other answer to “why now?” is that much of this is already over: the “dirty linen” has already made its public appearance, with the heaviest public attention to this taking place last fall when my book and Smolin’s appeared in the US around the same time. At this point, the cat is out of the bag, with a widespread perception that string theory is a subject in trouble. If string theorists want to respond to this by saying “yes, things are not going well, let’s see what the LHC says”, there’s not much to debate. If they decide to go to the press claiming that Smolin/Woit are all wrong, everything is fine, and keep publicly fighting a debate they have so far been losing, that’s their choice, but I think not a smart one.
As far as the effects of this on funding of particle physics, it’s not so simple. People calling up their elected representatives to demand defunding of particle theory is not the way the world works. The FY2008 proposed DOE and NSF budgets contain quite healthy increased funding for HEP, both experimental and theoretical. I can see why string theorists are not happy to lose the status with the public that years of hype had bought them and have to live with a more realistic one, but funding questions are in the hands not of the public, but of a much smaller and better-informed group. It undoubtedly is a tougher sell these days to use string theory to get private funding from philanthropists, but I can’t say I think that’s a bad thing. Much of the funding and health of particle theory is based on the decisions of other physicists, who are making the decisions about whether to hire particle theorists in their departments and advising the NSF about how to allocate resources. The main problem for particle theorists is this possible loss of support not from the ill-informed public, but from their much-better informed colleagues.
As far as this danger goes, the main problem is just the too-obvious lack of progress in the subject. When people see nothing new coming out of a field for a long time, they start thinking that resources are better allocated elsewhere. As far as the effect of my book and Smolin’s, I think they gave many physicists a more realistic awareness of what the state of HEP theory is, and what the level of string theory hype has been. This is uncomfortable for many theorists, but I don’t see the argument that it’s a bad thing. From talking to many people, I actually think the worst damage to the interests of string theory has come from the behavior of string theorists themselves. Lubos Motl, aided by significant support from other string theorists, personally did a huge amount of damage to the perception of the subject. Lenny Susskind and others promoting the anthropic principle (through books and articles for the public) have done even more. When I talk about the problems of string theory with physicists and mathematicians who don’t know much about the subject, they generally have a prejudice in favor of the idea that things can’t be really that bad, given how smart some string theorists are and how many people work on it. When they see Susskind or others going on about the anthropic principle, I often see a strong reaction of visceral disgust and a lot of sympathy for the idea that there really is a big problem here.
So, as far as the “public debate” goes, particle theorists should be worrying not about the public, but about their colleagues and specifically about the damage that promotion by prominent theorists of pseudo-science is causing. Allowing this to go unchallenged is a huge mistake. As far as the wider debate about string theory goes, I think it would have been a lot smarter for string theorists to react in public the way many of them react privately: acknowledging that the problems of string theory are very real, and that the subject is in a difficult state. Instead of going to the public with claims that Smolin/Woit don’t know what they’re talking about, everything is fine, they would do a lot better by acknowledging problems, and telling the public that this is how science is done: much if not most of the time ideas don’t work out as hoped.
My own worry about HEP theory funding is a different one. I see physicists drawing the conclusion that what went wrong here was too much emphasis on mathematics, that if theorists had just stuck to “phenomenology” and not gone off into mathematically sophisticated formal investigations then there wouldn’t have been a problem. The problem with string theory is not that it’s too mathematical, it’s that it’s a wrong physical idea about unification. What I see happening now is not a defunding of particle theory in general, but an abandonment of the kind of deep, long-term investigation of difficult issues that is needed, in favor of often outrageous attempts to claim “real world” applications of string theory. To some extent this is being justified by the idea that the LHC is going to save the day, that all theorists need to do is get up to speed on how to analyze collider data. Maybe this will work out, but I don’t think the way all eggs are being put in that basket is wise.
David wrote: “when oh when, will you stop being so negative and grace us with your brilliant alternative so we can put that to a vote……”
Actually there are quite a few interesting alternative topics to ST in formal particle theory. Reasonable string theorists don’t seem to have any problem acknowledging this; Jacques Distler even listed some of them here. I suspect these alternatives would do quite well if put to a vote…
Regarding Roger’s points: I agree it is potentially damaging that the string theory punch-up has led to the public getting a negative impression of the state of physics in general. The solution imo should be to give the public a more accurate picture of present day physics research. Unfortunately they have been brainwashed into thinking that the only interesting problems are quantizing gravity and “unifying the forces”. Even the LHC is being partly sold to them as something that is supposed to give insights into these things. If the public realized that most of what goes on in physics (including much of HEP) takes place through conservative, uncontroversial, bottom-up approaches, and that these are generally doing fine and continue to produce important advances in physical knowledge, then I don’t think they will want to pull the plug on physics just because they hear about a relatively small segment of physicists getting bogged down in a metaphysical multiverse.
The seeds of the current public airing of dirty linen were sown a long time ago by string theorists who for some bizarre reason felt that the public absolutely had to know all about their speculative research program, extra dimensions and all, without it having a shred of experimental evidence or having reproduced the standard theories we already know are correct at low energies. If it hadn’t been for this the current airing of dirty linen probably wouldn’t be in the public domain (they wouldn’t know about it).
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?
Dear Peter and others,
One question that I would like to pose to you is, suppose that the string landscape is true and there are really 10^500 possible vacua. Do you claim that of these 10^500 vacua that there is not one which corresponds to our universe? If so, how would you know? Unless you can prove that there is no such vacuum, then your claim that string theory cannot make any predictions is baseless.
Essentially, the purpose of the field of string phenomonelogy is to find this vacuum from a ‘bottom up’ approach. Now, we may or may not be able to explain why this particular vacuum is chosen, but that is a seperate question.
Eric,
I’ve already gone on about what I think about this point far too many times, here and elsewhere. If “string phenomenologists” want to make the case for their subject by saying that they’re going to keep at it and not give up until every one of the 10^500 vacua has been investigated and carefully examined to make sure it doesn’t agree with experiment, they can do that, but this is just going to convince people that the criticisms of the subject are valid.
Well, Peter is no different that the state of particle physics in the 1950’s when there was an elementary particle zoo rather than a string landscape. I suppose it’s a good thing that the phenomenologist of the time ‘kept at it’.
Eric,
One minor difference: the “elementary particle zoo” was experimental data, the “string landscape” isn’t.
Peter,
The point is that there was no fundamental theory which could explain the plethora of elementary particles. There was no Standard Model and it was far from clear that QFT was the correct description of elementary particle physics.
Regarding the string landscape, the data that we hope to have soon is the superpartner spectrum from which it is hoped that the pattern of soft masses may be deduced. Since the soft masses are calculable in string models, as opposed to the MSSM where they must be put in by hand, it may then be possible to zero in on a particular class of vacua.
Eric,
what if LHC doesn’t find any SUSY partners?
Eric,
Your line of reasoning is very curious. You are trying to make an analogy between 1) complicated experimental data, and the need for a theory to simplify that data and 2) complicated possibilities from a theory, and picking out one of many possibilities with the aid of experiments.
These two situations are not analogous.
I’m no expert in string theory but I think the fact that no one has been able to get a string theory land scape based inflation model which produces gravity waves is a very important thing to keep in mind. Over the next few years cosmic microwave background polarization experiments should be able to detect gravity waves if the scale of inflation is not too low. If they do, my impression is that the landscape is going to be in big trouble. Another way cosmology could make life very difficult for the landscape is if the dark energy is shown to have a time varying equation of state. The landscape based solutions predict an equation of state equal to -1 (a cosmological constant).
mo,
I’m not sure I agree about the time frame, or about the statement that GR and Yang-Mills theory are comparable projects. Trying to simultaneously unify particle physics and construct a theory of quantum gravity strikes me as vastly more difficult than either of these. I suspect that a reasonable time frame might be something more like a century or two. (This is a somewhat pessimistic take on Witten’s comment that strings was a piece of 23rd-or-whatever century physics.)
How do you judge progress in a project on such a long time frame? I don’t really know. The best answer I have is that you look for spin-off, good ideas that are applicable elsewhere. There’s some precedent for this: many of the techniques used to study gauge theories were first developed in early attempts at quantum gravity.
A.J.,
I think the way you evaluate any ambitious project is whether, as you learn more, you are moving towards your goal. The problem with the idea of unification via string theory is that since 1984, as people learn more and more about it, they find more and more problems with it. Instead of producing even some minimal explanation about the standard model, it has instead led to the reductio ad absurdum of the landscape.
I think one can argue for continued research on string theory based on hopes for spin-offs, but it’s not a good idea to be pursuing a failed project purely based on such hopes. You’re more likely to get spin-offs from trying something different than from continuing to work on something that has already failed.
Crackpot. Noun: crackpot ‘krak`pót. … In physics: those who promote extravagant ideas before having accomplished the calculations necessary to check the validity of such ideas.
cosmologist: the Lyth bound suggests that measuring a large tensor-scalar ratio is problematic in field theory, not just in string theory…..
Peter O,
The situations are exactly analogous. Suppose it is 1959 and you have experimentally the elementary particle zoo and you have QFT. In this situation, would there not be a complicated set of possible QFT’s which you could construct in order to try to explain the data? There is no priniciple inherent in QFT which would uniquely lead you to the Standard Model. Thus, what was done is to construct phenomenlogical models which then can lead us to the correct description.
With string theory, we are looking to experimental data in the form of information about the supersymmetry breaking soft terms which will guide us to the correct string theory description.
Dan,
If no supersymmetric partners are discovered at LHC, then it’s still possible that string theory might be right. However, since in this case there is very little chance of ever making contact with experiment I would expect interest in the subject to dwindle. However, there must be some new physics at the TeV scale one way or the other. We shall see.
Eric wrote:
With string theory, we are looking to experimental data in the form of information about the supersymmetry breaking soft terms which will guide us to the correct string theory description
The situation with not analogous to 1959 because we don’t know that supersymmetry is real. Your example is, to put it crudely, we are waiting to find out the size of an angel, so that we can figure out how many can dance on the head of a pin.
Well, Arun we find out if supersymmetry is realized in nature very soon.
I would like to remind you that the idea of quarks were introduced to simplify the particle zoo, however there was no evidence for these for many years just like in the case of supersymmetry. In fact, most physicists did not accept their existence since they had never been observed.
I am dismayed by the attitude that various commenters of this Blog have. They are suggesting that all research in string theory should stop. In particular, there is this idea permeating various posts that string theorists are being payed enormous ammounts of money to do fluffy landscape metaphysics with no connections to reality.
It is important to remember the following:
Models of light strings at the TeV, or 10 TeV scale have not been ruled out experimentally. They might be diisfavoured by certain theoretical prejudice, but they are not ruled out. We have to wait for the LHC data before we say that strings are not relevant for the TeV scale.
String theory is not just about unification of the standard model with gravity and predicting the couplings of the standard model. That is just one of the goals that the program of string theory as a whole is trying to pursue.
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).
Via the AdS/CFT correspondence, string theory ideas offer a unique insight into strongly coupled phenomena of gauge theories. Considering that QCD was proposed over 30 years ago and that it has not been solved (even with the most powerful computers and the efforts of thousands of people in the lattice QCD program) it seems ridiculous to toss away a formalism that gives you some analytic handle on strong coupling phenomena just because some other aspects of the string program are not satisfactory at the current moment. This is like tossing away the Ising model for being unrealistic. As a matter of fact, calculations using black holes in higher dimensions are still the best theoretical match for certain measurements that have been done in the RHIC experiment. There is a lot of cross-talk between experimentalists, string theorists and QCD experts at the moment, and it is centered on data.
To all of you with this intense anti-string prejudice: get back to reality and research the field and its current status before you start making pejorative statements just because you have a grudge.
David B.:
“String theory is also (at the very least) a toy model of quantum gravity ….”. This I believe is a statement that no string theorist would support. What happen to the statement : “string theory is believed to be the only consistent theory of quantum gravity”?
Eric wrote:
Well, there’s one I’ve been wondering about, actually. Should we really expect supersymmetry to imply that supersymmetry will be found at the LHC? I mean, we apparently don’t see any supersymmetry under 1 TeV. Why must we see it under 15 TeV? Is there anything special about that particular factor of 15 that causes us to expect it to bring the superpartners into visibility range?
I’ve seen it expressed previously that if we don’t see SUSY at the LHC, then probably SUSY is false. Is this fair, and is there any particular reason for this argument? What is the constraint that makes it unreasonable that the lightest superpartner would be massed at greater than 15 TeV? Why should we expect that we’ll find out whether supersymmetry is realized in nature very soon?
Meanwhile, people seem to generally act as if they’re expecting the Higgs to be found before any superpartner. Let’s say this in fact happens. Should we then conclude that ALL the superpartners are heavier than the lightest Higgs? If it turns out that all superpartners are heavier than the lightest Higgs, does this tell us anything? Would this be viewed as unusual, predictable, mere coincidence?