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.
For some mysterious reason my prevous comment disappeared! I’ll try again:
Should we not already count the popular books written by ‘string people’ which, without specifically addressing the vocal critics, do attempt to give a good picture of the current state of research? For example those by Brian Greene, Lisa Randall, Lenny Susskind. I think this kind of book is a much better use of time and effort than pursuing “the intestine shock and furious close of civil butchery” which the public debate currently resembles.
Is it worthwhile for any ‘string person’ to write a book and go on a long publicity campaign *purely* in order to provide a counterweight to Woit, Smolin, Horgan etc. There are a few factors coming in here. First, that would take several months, and few string-ers want to take such a time off from actually doing research. It seems to me the books and publicity blitzes are coming from people whose research field is rather less crowded and busy than strings, who therefore, on average, have more free time… Second, if the arguments being offered against string theory are sociological or irrelevant or highly subjective, and it seems that many (I don’t say all) of them are – judging a theory by the amount of nervous laughter? – is it worth anyone’s time and effort to go into detail rebutting them? Who on earth would read a book specifically devoted to answering or debunking everything said by Woit and Smolin?
T
PS on ‘testability’: gauge theory per se is, by the same standards, untestable, since you can construct a lot of strongly-coupled nonperturbative models in gauge theory that simply can’t be calculated. (Technicolor, anyone?) Electromagnetism, electroweak theory and QCD in certain regimes have turned out to be testable because, mainly, of sheer luck: we happened to encounter them in a regime where they can both be calculated and experimentally probed.
T
As a lay person following the debate on the issue of Finiteness in String Theory landscape was the point technically reached that I was referring too.
David has been careful to lead us through this and as a layman I am watching the way he is describing, so I am learning, as I learnt in other debates.
I hope Jacques that you would encourage David instead of express the futility of such an debate, I have learnt as so many others that you have to “talk past a certain point” if you can no longer get the subject moving beyond the ole rhetoric.
So while learning the difference between the “Fitness landscape” and the “String theory landscape, I learnt the difference is the “finiteness issue in the String theory Landscape?” This then been carried to the issue of Mandelstam and the triple torus?
So this in itself was what allowed us to say that the string theory landscape was indeed working toward the issue of Finiteness with which many have found to be a problem.
Moshe #149 (and Gina #168), my experience of ST is quite the opposite to
your very lyrical description of an effortlessly unfolding string theory.
(Mine is a clunkier mathematical physics point of view.)
“quantizing a relativistic string”:-
First, quantization is not an algorithm, there are serious mathematical
obstructions (cf. http://arxiv.org/abs/dg-ga/9605001 ).
Full quantization maps generally only exist on small subalgebras of the full Poisson algebra, and if they do, they need not be unique.
OK, but let’s say you have decided for the string what your quantum observables, their algebraic relations and gauge transformations/constraints are by some method.Then you need to realize (represent) them as operators on a suitable Hilbert space, but here you find that you need to do it on a Fock-Krein space, and so the usual spectral theory is not accessible to you. (You require the spectral theory to integrate up your generators of symmetries, evolution etc, since after all we need finite transformations in real life).
OK, so let us say you have managed to integrate up the generators of your symmetries (and it can be done, but it is hard cf. Comm. Math. Phys. Volume 156, No. 3 (1993), 435) then you need to encode your unbounded operators into an algebra of bounded operators (C*-algebra), so you can have access to different representations, and this can be done too, at least for the open bosonic string (cf. Comm. Math. Phys. Volume 156, No. 3 (1993), 435). [You need these other representations since even mild interactions move you out of your given representation, cf. J. Math. Phys., Vol. 26, No. 6 p1280, 1985, and constraint conditions can be insoluble in your original representation, but soluble in others cf. Lett. Math. Phys. 15, 205 (1988)]
OK, so now you need to enforce your constraints, and immediately
you see that in your initial representation there is no solution
except in dimension 26. However, this is a representation dependent
phenomenon and you can avoid it by going to other representations,
but that is not the usual way…. So, you decide perversely to accept that the
universe is 26 dimensional and forge on. The method by which you choose
to enforce the constraints (BRST) is known to give different results
from the usual Dirac method (for some quantum constraints),
and it often needs to have ad hoc additions to work (I have a PhD student
working on the maths of quantum BRST), but you forge on.
Next, you decide that you need fermions associated to your string, so you make it supersymmetric (despite the fact that no supersymmetry has ever been seen in nature). Mathematically this seems almost impossible, due to the obstruction theorem in Commun. Math. Phys. 159, 15-27 (1994), but only very recently someone did manage to set up mathematically a supersymmetric toy model in QFT, http://arxiv.org/abs/math-ph/0604044 so maybe if you work very hard, you can at least define an open bosonic supersymmetric string properly. But your perverse choice above (to stay in the original representation) created a problem, of what to do with the extra dimensions….
So to me, the very start of the string enterprise seems very ad hoc with
a lot of nonphysical components. You may say that for usual QFT we do not
demand mathematical consistency from the start, but the point is that
we do have it, and the initial (free) quantum fields are very easily
defined at a mathematical level with a minimum of fuss.
(Of course, once you add in interaction, it is a different story.)
A larger issue than the elegance of the string, is the justification question,
– the subject of fiery debate above. I think that ultimately, there can only be
two justifications for a physical theory
1) direct experimental confirmation of central predictions not obtainable by existing theory,
2) a logically consistent extrapolation of experimentally well-established
theory.
Criteria of elegance, beauty etc. can only be a guidance for discovery, but
definitely not an ultimate justification for a theory.
ST at present is not justified in the sense of (2), and I think it is timely to ask for a justification in the sense of (1), given the large amount of effort, funds and jobs that has gone into it at a time when we have sufferred many cutbacks worldwide. Of course these points have been made and argued well in the books of Peter Woit and Lee Smolin.
Peter,
> 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
what do you think about the two papers discussed here ?
The claim is that “F-theory with all matter coming from an isolated E8 singularity predicts three generations of fermions because of purely group-theoretical reasons!”
Do you find such results at least interesting?
“Electromagnetism, electroweak theory and QCD in certain regimes have turned out to be testable because, mainly, of sheer luck…” – Thomas Dent
There’s no luck here: these theories were based on experimental data analysed by hard work, so they made predictions automatically by extrapolation of data. You find a model to represent data, and after development the model predicts things, which allows it to be tested. There is experimental data at each end, both in the input to the theory and in other tests of the theory.
Light was predicted by unifying electricity and magnetism, both experimentally based sciences. The velocity of light is a combination of the electric and magnetic constants put into the theory from experiment. The prediction of neutrinos was based on experimental data for beta decay plus the experimentally based principle of conservation of energy. (Some string theorists defend themselves by pretending that the neutrino is a bit like stringy predictions because it was hard to test: but it was experimentally known that 2/3rds of the energy in beta decays was disappearing, and by conservation laws the neutrino was predicted from this experimental data.)
#205
>
hmmm….. is “theoretics” a valid research area without experimental verification? 🙂
wolfgang,
I haven’t read the relevant paper, and Lubos’s blog entries aren’t exactly reliable sources of information, so I don’t know exactly what that particular model achieves that others don’t. There’s a huge and ever increasing number of string theory models, keeping up with the details of all of them would be a full-time job. There are already vast numbers of string theory models that have three generations, so if getting that integer right is the main reason to pay attention to this particular model, no I don’t find it interesting. It doesn’t change at all the underlying fact that you can get any number of generations you want out of string theory.
Personally I think it’s best to take a `live and let live’ approach to these things. In physics we all place our bets by the topics we chose to work on, and then the onus is on each of us to show that our bets are working out by making demonstratable progress in research. If a research program is doing poorly, this will manifest itself in a lack of papers making major advances in it. Conversely, if the program is doing well, people will be able to say “Look, major advances on this topic have recently been made in papers X, Y and Z…” This is where the focus should be when discussing the merits of string theory (or any other research program). Without knowing the full details of how nature works and what surprises it might have in store for us I don’t think it makes sense to say that research program X has failed for reasons A, B and C. Instead, the argument should be: researchers on program X are no longer making major advances – cut their funding until such a time that they start making major advances again. People should of course be free to work on whatever they think is most interesting and promising, but in the knowledge that the onus is on them to make advances in their chosen topic (which will be compared against advances in other topics) and that if they don’t make sufficient progress then they will pay the price.
It might seem that the question of whether some work constitutes a `major advance’ will often be controversial and not something that people can agree on. But I expect this will be less of a problem than people might imagine. The maths community seems to be at least as specialized and fragmented researchwise as physics, but they manage to reach agreement on such questions so I’m sure people in physics can as well if they put their minds to it. One important thing that I think is currently missing in physics though is a proper accreditation system for major advances. The mathematicians have this – the accreditation there comes through publication of the paper in a top maths journal. We could really do with something like that in physics as well and I hope people will consider it.
Gina makes a good point that automatic postdocs might merely put off the day of reckoning:
This might be addressed by combining the automatic postdocs with graduate “birth control”, i.e. fewer graduate-school admissions. To be sure, birth control has its own tradeoffs. Every system does; the question is whether it would be better than what we have now.
One beneficiary of automatic postdocs would be lab heads. It would take off some of the pressure on them to bring in grants and maybe even let them do some research again.
George
‘Light was predicted’? I thought light was already known of before Maxwell.
Anyway, I wasn’t comparing EW theory or QCD to string theory; I was comparing *gauge theory*, in complete generality, to string theory.
The gauge principle was first thought of by Weyl, and he used a real exponential transformation rather than an imaginary phase. Effectively, conformal transformations. Is this really a fundamentally useful thing to describe nature? We don’t know yet.
Or take Yang and Mills. They invented a theory that, for several decades, seemed to be a total crock in terms of any relation to data – nonabelian gauge theory. They were lucky!
T
Dear George,
It does not look that this modified idea is particularly good either. What is wrong with the current system?
Dear Herbert
I was impressed by your thoughtful and detailed comment. If I understand you correctly some of the smooth and inspiring steps that Moshe talked about are not so smooth for you as a mathematician. And you regard some of the steps (like the extra-dimensions and maybe also supersymmetry) as ad hoc and artificial. (Of course, different people may well have different tastes/point of view/etc.)
I wonder if some of these difficulties or similar do not arise already for established physics theories like the standard model. (The usual interpretation of these difficulties is that mathematics is not quick enough to catch up with progress in physics.)
You wrote:
“I think that ultimately, there can only be two justifications for a physical theory
1) direct experimental confirmation of central predictions not obtainable by existing theory,
2) a logically consistent extrapolation of experimentally well-established theory.”
It looks to me that ST is mainly aiming at item 2) (although not in a mathematics-rigor level) and there are also some (highly debated) thoughts in the direction of 1). There are also claims that any quantum gravity theory will have similar difficulties for item 1) as ST.
Gina asks: “What is wrong with the current system?”
Lee and Peter have argued that string theory is a case of an instability in the system that overallocates resources to one field and starves others. Whether or not that’s the case, people do spend an inordinate amount of time writing proposals or postdoc applications. Hiring committees and grant review panels, faced with a huge oversubscription, tend to choose more conservative proposals from name researchers. The grant proposals themselves are sometimes written in a less-than-entirely-frank way. The whole system has a certain “prisoner’s dilemma” effect whereby individuals’ incentive is to submit as many proposals as they can, heightening the competition for each grant, even if collectively everyone would be better off with fewer proposals.
Anyway, if anyone wants to continue this discussion with me offline, please send me email at gmusser@sciam.com. I’m really looking for viable alternatives to the present system.
George
George:
I think that it really has to come down to a pit-fight. The younger, and often better physically conditioned, researchers will be able to use their youthful vigour to counteract the wilier street-fighting techniques of the more experienced rivals.
Alternatively, a limited version of the ‘Quickening’ scenario from Highlander might be pursued, where everyone interested in a particular grant or position chases the others around the world with swords with the aim of beheading their rivals. There can be only one.
Gina:It looks to me that ST is mainly aiming at item 2) (although not in a mathematics-rigor level)
I am not sure how you can write that knowing some technical issues presented.
George from following the discussions, it seems to me to be a smoke screen that’s been put up by Peter and Lee that leads away from the issues. Knowing one’s perspective views on “another area” let’s say one’s version of the landscape” seem to me to indicate that such decisions based on that position would also develop from that point of view. Look to support that position. See all the “injustices” in the world?
If you can show that the position Peter has adopted was just as flimsy as he purports of string theory and his forgone conclusion, then that has to be taken out of the equation?
The merits of the landscape issues are still being worked out? String theorist have confronted Peter on the technical issues?
No interest here in other approaches to the question of space dimensionality, despite the theme of skepticism about string theory? I hope some could at least check my blog, Tyrannogenius, for curiosity’s sake. I discuss how comparisons of E&M interactions in different spaces show preferability of three large space dimensions. This is not a rehash of existing facts of the specialness of 3-D space, but points to novel inconsistencies found in other spaces.
Dear Gina,
No doubt selection has to be done at some point, based on some criteria. The question is when it is best done, and what the criteria should be. There are basic requirements like, mastery of the material and tools of the subject, ability to do the research, produce correct results, write them up etc, all of which should be the criteria to get a Ph.D. Once you get past that stage and consider the group of people who are in fact contributing to research during their Ph.d. my view is that the most important predictors of future impact on science are intellectual independence, creativity, originality and originality. How many original ideas do they come up with which are aimed to solve key problems? How willing are they to take risks on their own ideas rather than follow others and do “me too science”? I once asked Stu Kauffman how you tell which scientists will have the original ideas that lead to breakthroughs, he said, “its easy, by the time they are a few years out from the Ph.D they have already had and published several highly original, in some cases, surprising ideas.” Some will work, some won’t but the ambition, creativity and originality will be clear. My observations after many years in research centers and institutes hiring postdocs is that this is correct.
Here is one thing that gives me pause. The great generation that made American science dominant in the world, hired from the late 40’s to the 60’s faced a very different situation than we do. Before the early 70s there were in many fields more open faculty positions than new Ph.d.s. There was consequently selection for who went to the elite places, but much less overall selection for which Ph.D’s got to have a career in science at some university or college. Many people in this generation I’ve spoken to never applied for a job-even for a first job after their Ph.D.
Now this generation did great science which dominated the world. Since the 70s we have faced a situation of vast over production of physics Phd’s relative to faculty jobs in research universities and institutes. So we spend a lot of time and effort on selection. My question is, do we do this well? Do we use the best methods and criteria, in the interests of the progress of science, or do we use methods and criteria that disadvantage the kind of people I described above in favor of people with less originality and independence? My thesis, which is defended in the book, and supported by many statements quoted there and elsewhere by senior scientists in different fields, is that we do not do a good job of this and that we make it too easy for careerists with lots of competitivity and little originality and too hard for those who are really original and independent.
When there was little selection we naturally got a wide diversity of types of scientists, which was good for science. My view is that we need that diversity, we need both the hill climbers and the valley crossers, the technical masters and the seers full of questions and ideas. My worry is that having to institute narrow selection, we have done it badly, in a way that narrows the diversity of types of scientists we need for the progress of science. My conviction, however, is that this is easily fixed, by changing the criteria and methods of selection to ensure we get the full range of types and characters we need for science.
Thanks,
Lee
@ Count Iblis #92
I don’t think (at least I don’t hope as far as I am concerned), that string theory is loosing credit in the public, just because it
was “overhyped” in the past. After all, this is about science and I never get bored by electromagnetism or general relativity. I rather agree with what you say in the second paragraph. To me loop quantum gravity looks more interesting than string theory, is because it addresses the question “what is space” in a fundamental way, whereas string theory just puts strings in the same old Minkowski space, where the point particles of field theory are sitting in. Out of the approach of loop quantum gravity naturally comes the question, to what accuracy Lorentz invariance describes nature. These are the kind of good experimental questions then, which bring science forward even in the case of a negative experimental result (Lorentz invariance confirmed in the experimental bounds). Admittedly string theory has a similiar merit by encouring experiments to check for the strength of gravity in the low distance regime and thus looking for extra dimensions. This is, why I perfectly agree with Smolin to have a diversity of theoretical approaches, especially in the present time, when nobody can clearly claim to know the way ahead.
What also somebody from the public can do (and what every person does in his daily life, when he has to rely on “experts”), is to judge those experts from their social behaviour. And here I can’t see, why a person like Smolin is not invited as a speaker on the strings main conference. He can’t be such a bad scientist, that it is not worth for the string theorists to listen to him and therefore abandon one of the many talks on the “landscape” problem.
Jacques (#199),
You wrote,
That is reassuring, but I don’t understand why you would invite a pointed response by an unnecessarily antagonistic “aside” to Peter in your otherwise reasonable comment #192:
Back to comment #199, you say
Good. And most of the rest of us would get a lot more out of your commentary and not be left a bad taste in our mouth if you and others just addressed those points and left the personal jabs and innuendo completely out of the discussion.
I’ll get off my soapbox now.
Dear Lee,
Many thanks for your kind comment.
One clear advantage of the American system (compared e.g. to continental Europe) is that scientists are becoming academically independent at an early stage. When a young scientist has a solid tenure track or tenured position she can pursue science in the way that suits her best. (Whether to solve hard problems by others or pursue her own agenda or one of many other possible ways to practice science.) Indeed, few years out of Ph. D. is often a good time to make the call.
Probably nobody disagree that originality is an important merit of a scientist and an important ingredient in hiring decisions at all levels. Different scientists and different departments may have different weights on various criteria for hiring, (and this diversity is good) but I am quite sure that originality is always considered as important.
I do not see a need for administrative measures giving extra incentives (say, for originality or risk taking) on top of the usual methods departments use in their hiring decisions. Moreover, understanding the precise incentives administrative methods like the ones proposed here (automatic 5-years post-docs), or in your book (and maybe also in Peter’s book, I do not recall right now) is often a tricky business. In the few examples I looked at, the specific proposals you and others suggested may well lead to an outcome opposite to the intended one.
(BTW, the new terminology of valley-crossers and hill climbers is very nice.)
OK … so, from your perspective, what more do I need to say?
(If you want formulæ, perhaps we could move this over to my blog, where technical discussions are possible. Tell me what you want to know and, if need be, I’ll craft a blog post in response.)
Peter,
In #146 you responded to my question.
Since we have no consistent model of SM and gravity at present, I’d be happy to see one even if it is as ugly as you describe. It would be a huge accomplishment, in my opinion, to have a single theory that is consistent with every piece of data that we have.
Certainly, I will be happiest if that model is natural, mathematically beautiful, and unique so that it predicts the result of every future particle experiment and future cosmological observation as well. Do you see any avenues for achieving such a special theory? I don’t.
I saw a long physics documentary that continuously adressed string theory, so at least someone has done his job.
I speak as someone who has not the mathematical knowledge to understand the coherences they claim they have discovered through string theory. If you say you’ve made the mathematical demonstration, that the numbers fit nicely, so it must be, but I still cannot tell for myself.
So much enthusiasm in physics around this is important, I know many brilliant minds have pursued ST.
Sometimes scientific movements like this end up “intellectually bankrupt” (for instance, haeckel’s fundamental biogenetic law). Some scientific movements use a basic idea or argument, a “truth” that can outshine the insufficiencies (which are eventually unavoidable).
At least I am sure that has been a problem with some movements within the history of biology (look up the “dogmatic hardening” of the neodarwinians in the 50’s in Gould’s fat book)
A diversity of points of view is most desirable. String theory will exist as long as it remains capable of attracting the minds of brilliant people.
Dear Jacques,
There was an exciting post on the Reference frame about these papers
which came out today:
http://arxiv.org/abs/0704.0445
http://arxiv.org/abs/0704.0444
Could you please comment on this work?
Thank you!
BK