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.
Sean,
My comment about debates did explicitly refer to “physical theories”, and I think it’s true that it’s highly unusual for abstract theories about physics to become the topic of this kind of public debate (by the way, on the whole I think such debates are a good thing, modulo obvious problems with dealing with technical issues in this kind of forum). Johnson did try and come up with an example of such a debate from earlier periods in physics (he thought maybe there had been some about relativity). I’m quite curious to know if anyone can point to such an example.
Horgan enjoys being extreme and provocative, so some of his over-the-top comments weren’t surprising and one would be justified in not taking them completely seriously, but I do find it striking that string theorists are losing people like George Johnson, who traditionally have been quite sympathetic to what they are doing. I think one important reason is the way they have reacted to the challenge posed by my book and Smolin’s. Johnson makes it pretty clear that he was strongly struck (and not positively), by the way people at the KITP behaved in the discussion he held on the topic there.
I’ve also been kind of amazed by what a terrible job string theorists are doing of responding to criticism. The most sensible ones are pretty much keeping quiet, letting the response (at least on the web and in blogs) be dominated by some of their colleagues with less than good judgement, especially ones who think that ad hominem attacks are an appropriate response to criticism of a scientific theory.
Peter, if you look closely you’ll see that I actually linked to such an example in my post. (Today, the question of whether nebulae are galaxies or just gas clouds doesn’t seem that abstract, but in the 1920’s it was.) That’s just the most famous one; I don’t think examples are that hard to come by. The Bohr-Einstein debates about quantum mechanics weren’t carried out in front of public audiences, but they easily could have been, and it might have been a good thing.
I agree with you that the most sensible string theorists are (pretty much) keeping quiet — this post was in part an attempt to tweak them into speaking up!
You know, I promised myself I’d give up Lee Smolin for Lent (when is that, anyways?), and now you try to pull me back in.
So, I’ll just suffice with self-promotion and refer back to my review of Peter’s book where I try to do just what you say.
On the other hand, I think is is part of a natural media cycle of promotion and backlash. Once people are through proving their iconoclasm bona fides, I tend to think things will even out to a reasonably sober equilibrium.
I am not a scientist, (I don’t speak math, so that kills any scientific aspirations), but love reading and learning about what’s going on in different scientific fields. I guess you could say I’m the audience that consumes scientific dialog “for dummies”.
I could never write a paper on string theory or quantum-loop gravity, but I can certainly discuss the benefits of funding programs of discovery. So to read a statement such as “things are not looking good for a physical theory when there start being public debates on the subject”, stuns me. Did these words actually come from a scientific mind? Does discussion of scientific theory constitute valid data that the theory is flawed? Or is public discussion viewed as evidence that the subject matter is too accessible to the minds of little people, and therefore not worthy of attention by great minds?
I doubt such an (ego-driven?) attitude will get real legs…at least I would hope not. The backlash from the public for such thinking would likely be similarly childish; “If you’re are unwilling to discuss it, we’re unwilling to fund it.”
As for me, I think these are heady times for scientific observers. It seems to me that we, (by which I mean you science types), have really begun to learn how to learn. That may seem offensive, but when I read about all the various data points supporting global warming and consider that “connecting the dots” has really only come together in earnest over the past ten years, you can see my pov.
In fact, it is only by taking scientific dialog out of the lab and making it available to a broader audience that allows the “dots” to be connected. My understanding is that cosmic microwave background radiation was discovered (when it was) because a guy who knew the scientists at both Princeton and Bell Labs learned what each were working on and introduced them, thereby literally connecting the “dots”.
So I support your view that public discussion of scientific developments is a good thing. And not just because I am personally interested. Rather, I feel such dialog will bring closer the day that a room full of politicians can publicly laugh Intelligent Design right back under the rock from which it crawled. But until the public can discern between science and philosophy, (ok, string theory isn’t helping there YET), politicians will play ball with both crowds. And they make the appropriations decisions so discuss, discuss, discuss!
Sorry Sean, but I came with time to precisely the opposite conclusion. At least as far as the public blogosphere is concerned, I have no evidence of anyone ever changing their minds, or even changing any of the details of their arguments. More generally, this is a highly technical subject, inevitably any public debate will come down to who is the nice guy and who sounds more reasonable. Personally, if I had any intention of engaging in marketing I would want to get paid more for it…
Luckily, as you note, among quantum gravity experts there is a near consensus on the merits of this approach, this ought to be the important thing. Of course, technical debates among experts are going on all the time, let’s just say they have a slightly different flavor than the public debates.
(not to say that string theory should not be explained to the public, and to our colleagues, but debate and explanation are two separate issues).
Sean, thanks for your thoughtful post on my conversation with George Johnson. Just let me clarify my view of the debate between Greene and Krauss over strings. Contrary to what you imply, I don’t think a scientific theory loses credibility just because it’s debated publicly. It was the jokey tone of the Krauss-Greene debate–at least as described in one online report–that struck me as yet more evidence that strings are in big trouble. Neither Krauss nor Greene seemed to be even attempting to be serious about strings. They were just posturing, performing, for fun. In other words, they seem to tacitly agree with my description of string theory in The End of Science as “ironic science,” which is more akin to philosophy or even literature than real science and should not be taken literally. Sean, jump off the sinking ship while you still can!
God forbid scientists should have a sense of humor.
“Johnson did try and come up with an example of such a debate from earlier periods in physics (he thought maybe there had been some about relativity).” – Peter Woit
Einstein debated general relativity on 25 September 1920 with his Nobel Laureate Philipp Lenard:
“On September 25, the day of the debate on relativity, Born and Einstein walked out of the train station to face a changed scene: guards armed with fixed bayonets. Not trusting the scientists’ sangfroid, the government prepared for trouble, unnecessarily, as it turned out.
“In Bathhouse 8, five to six hundred eager listeners “squeezed together on seats, stood along the walls, filled the balcony … .” First came hours of invited papers, until session chair Max Planck finally opened the floor to discussion. Lenard spoke first. When Einstein followed, Planck was forced to silence heckling, perhaps orchestrated. Lenard and Einstein rebutted each other’s comments, as others in the audience asked questions and offered opinions, including Born. Then Planck, who had maintained a more dignified proceeding than many had considered possible, observed that relativity theory still had not made it possible to extend the time for the meeting and ended the discussion.
“Einstein was disappointed in his performance. “I will … not allow myself to get excited again, as in Nauheim,” he wrote Born. “It is quite inconceivable to me how I could have lost my sense of humour to such an extent through being in bad company.” Born knew that Einstein suffered under the attacks and worried that he might leave Germany. This was all the more reason for the Borns to react strongly to the swirl of publicity that surrounded Einstein and, in their opinion, made him more vulnerable to attack – publicity that the Borns and other friends such as Max Wertheimer attributed to Einstein’s good nature and Elsa’s enjoyment of the attention.”
– http://www.maxborn.net/index.php?page=excerpts
Relativity was an ad hoc explanation for existing physical concepts such as the FitzGerald-Lorentz transformation (including length contraction, time dilation, and mass increase after 1897 when J.J. Thomson showed that the mass of a charge is inversely proportional to its radius), so it’s not a good analogy to string theory. Relativity was a working theory, addressing data, straight off. String theory isn’t even a model of anything already known to exist.
A better anology to string theory is the debates concerning the Bohr-Heisenberg Copenhagen, particularly during the 1927 and 1930 Solvay Congresses, which led to the EPR paradox published in the Physics Review (1935), “Is the quantum description of physical reality complete?” In turn, this first led to Bell’s inequality and then to Aspect’s tests in 1982, so although interpretational difficulties still abound the foundations of quantum mechanics, at least the subject isn’t hyped up so much now as ending with Copenhagen. There was eventually interesting physics generated from the arguments: it wasn’t a waste of time.
Rob,
“Did these words actually come from a scientific mind?”
Yes, these words did come from a scientific mind, mine. Do you really think it’s necessary to make insulting comments like this to make your argument? The point I was making (as were Horgan and Johnson) is not that there is anything wrong with these debates, just that they are an unusual phenomenon in this particular science and thus indicate something unusual is going on. Sean has helpfully pointed to another example, from astrophysics, but it’s one from nearly a century ago. I don’t think it is in any way unreasonable to suggest that the existence of these debates suggests that something unusual is going on in this subject.
One thing that struck me in reading the transcript of the recent Smolin/Duff debate were Chris Isham’s remarks that quantum gravity is not like other subfields of physics because theoretical claims can’t at all be confronted with experiment, and scientific disagreements adjudicated through this means. This has a lot to do with the unusual current situation. Nobody was holding public debates in the early seventies about the Weinberg-Salam model and whether there were weak neutral currents. They were making models that made distinct predictions about this and evaluating them as the data came in. Maybe they should have been having public debates, and that would have been fine, but the debates would have had a different nature, with everyone looking to experimental results to sustain their points.
Again, I don’t think there’s anything at all “wrong” with these debates, actually I think their existence is great. I’m a big fan of the free marketplace of ideas, whenever it’s a free marketplace…
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John and Aaron,
One of the things that most struck me about some of the KITP on-line videos of talks on the Landscape is the amount of nervous laughter involved. People seemed to be very much aware of the kind of ludicrous nature of some of the arguments being presented. Nothing wrong with a sense of humor, but this seemed to me something different. There’s a difference between making jokes about one’s ideas and the ideas being a joke.
I think Jacques Distler did a very good job, explaining the Motivation(s) for string theory in this blog post.
I’m noticing that everyone here is being careful to describe the debate about string theory as a debate about its merits as a theory of quantum gravity. As someone who has always been most concerned with its merits as a supposed theory that explains things we can actually hope to observe (e.g. particle physics), I’m just wondering: is the debate on that point over?
Sean,
> The Bohr-Einstein debates
Actually, I find comparisons of the recent debate about string theory and the Bohr-Einstein debate (and other historical debates) very painful.
The contrast between the high level of discourse in the past and the low level now, often quickly degenerating into name-calling, is perhaps a major reason why string theory might be ‘loosing the public debate’.
Bohr did not call Einstein a ‘crackpot’, but tried to convince him…
Wolfgang, many string theorists can’t respond directly to criticisms because M-theory originator Ed Witten has stated in a letter to Nature that responding to criticisms may add fuel to controversies:
‘The critics feel passionately that they are right, and that their viewpoints have been unfairly neglected by the establishment. … They bring into the public arena technical claims that few can properly evaluate. … Responding to this kind of criticism can be very difficult. It is hard to answer unfair charges of élitism without sounding élitist to non-experts. A direct response may just add fuel to controversies.’ – Dr Edward Witten, M-theory originator, Nature, Vol 444, 16 November 2006.
For those who aren’t aware of Dr Witten’s view:
‘String theory has the remarkable property of predicting gravity.’ – Dr Edward Witten, M-theory originator, Physics Today, April 1996.
Wonder why he won’t respond directly to criticisms?
Moshe, it’s a shame you feel that way. I was talking, of course, about “explanation” more than “debate,” and in a broader context than just the blogosphere. But I think that too many sensible people read some pointless name-calling on blogs, and conclude that it’s a waste of time to talk to non-specialists in general. Which is a mistake.
And I should say specifically that the “it’s a technical subject” argument is missing the point in an important way. Of course, non-experts (whether they are non-scientists or other physicists) aren’t going to be adjudicate the role of polymer representations of non-seperable Hilbert spaces, or the difficulty of stabilizing moduli in a controlled large-volume approximation. But they certainly can understand the basic reasons why an approach might be promising even in the absence of direct experimental support. It’s worth making an effort to make those reasons clear. (Which I know that you, as one of the good guys, appreciate.)
It might be nice if the academic system allowed young folks to just spend 7 years in their attic — a la Andrew Wiles & Fermat’s Last Theorem — to actually work out an actual mathematically-consistent alternative to string theory… But this is fundamentally not possible with the present system (due to publication, tenure, and career pressures), thus all we get is a Soviet-style single (and untestable) choice in the matter of a quantum mechanical theory of gravity. (I don’t think many people would consider quantum loop gravity to be an alternative, at least at this point.)
Dimension is actually an operator that acts on a state.
Minkowski space is its vacuum expectation. Complete those two sentences… 🙂
What happens if one were to promote dimension to an operator? Many people have wondered about that — note that one would need to establish its commutation relations, for one thing — but no one has been able to do the resulting mathematics. So maybe that line _might_ even end up resulting in an alternative to string theory — but no one has been able to take the plunge, mostly because of academic pressures.
I think that’s unfortunate.
Peter — I was responding to the fact that Mr. Horgan seems to think of it as an indictment of a theory that people are willing and able to debate it in good humor.
As for the landscape, you know as well as I do that the debate about the landscape within the string theory community has been at least as vehement as that without, if not nearly as public.
As for the other, no attempt at a theory of quantum gravity has been able to produce a falsifiable prediction. There are various things that might be confirmatory, however. As is well-known, there are effective field theory arguments that make it extremely difficult to directly observe quantum gravitational effects. Nonetheless, there are conjectural restrictions on the sort of effective field theories that might arise out of string theory. If these could be more firmly established, they would constitute falsifiable predictions and/or retrodictions.
It seems to me that Horgan’s attack is really on theoretical high-energy physics, not on string theory. His arguments are against the whole idea of unifying quantum mechanics and relativity. The idea is that physics has gotten as far as it possibly can, and that from now on it is bound to be theology. Johnson’s praises a “pragmatic” approach of… just giving up. Why do we need a single, unified theory anyway?
That’s the saddest thing about today’s “public debate”: the people who brought string theory to the court of public opinion don’t realize that what they are sinking is their ship too. If tomorrow LQG were to become the new darling of high energy physicists, people like Horgan would be bashing it just like today they are doing with string theory, on precisely the same grounds.
I don’t suppose I will be the one who will convince these critics that they’re being short-sighted. I’ll just add that it is rarely mentioned that string theory has _already_ led to very nice progress in mathematics. Oh yea, but maybe not even geometry is a “serious enterprise”.
Peter, about your comment #13: I find it hard to understand how you can totally separate debating string theory’s promise in understanding quantum gravity from a larger debate of it’s viability. I agree that string theory seems unlikely to tell us anything about electroweak scale particle physics(except perhaps through gauge/gravitational duality as applied to QCD). But it isn’t really fair to claim that it is thus dead in water. String theory excited many theorists by providing a quantum gravity candidate and, in the end, exploring that regime will be what determines if it sinks or swims. Admittedly, that doesn’t appear like it will happen soon. But does the fact that one doesn’t know when one can test an idea make the idea unscientific?
I see my previous comment strayed a bit from what you were saying, Peter. I can’t speak for every string theorist(many will disagree with me probably), but I don’t think there’s much chance of string theory saying much about “particle physics”. I use the quotes since what is usually meant by that term is electroweak scale collider physics, where QCD is weakly coupled. But I do think string theory may provide insight into hadron physics, strongly coupled QCD etc. through dual gravitational models. This would be very different from string theory as the “theory of everything” since such a thing would be an effective model which may only apply in a certain regime.
As a string phenomenologists, I find the comments by the anti-string people that string theory cannot be tested to be somewhat insulting and completely wrong. We can now competely derive the MSSM from string theory, including the quark, tau lepton, and neutrino mass matrices and mixings (see our paper on Monday), so these people should sit down and be quiet.
I would like to see a semi-popular debate on the issues. The landscape, extra dimensions, branes/strings/particles, Maldacena conjecture would all be covered. With most pop physics books, the assumption is that the reader is a complete idiot. Yet there are plenty of pop math books that include a “lite” version of various concepts and equations. Books like Superstrings (edited by Davies) were a step in the right direction.
The ad hominem attacks are degrading the signal to noise ratio, but they do have a point. String theory is a technical field, thus it’s fair to question the credentials of the critics.
Easy to read papers like “A Laymen’s Guide to M-theory” (hep-th/9805177) are good idea too.
Eric,
Your paper sounds very exciting. How about a hint. What is the mass of the Higgs and the what particle is the LSP?
Eric: “derive” (i.e. “predict”) … or “construct”.
An important logical distinction…
If it’s really the former, then what is the value of delta (the Dirac CP phase)?
If you can actually predict that, and you are proven to be correct, then clearly you will have a Nobel prize waiting for you.