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.
Eric,
If dimension were an operator, then why would it necessarily take integer eigenvalues? There should be a physical reason for that, right? Let me know if I’m wrong, but I don’t think string theory provides an answer (at least at present).
The basic idea of String theory, that of replacing a particle by a string, seems too simple to be true.
One of the commentators above is correct in saying that there is nothing really new in String theory (except the above idea). There is no awe one feels on learning it (unlike GR and QM). This of course, is nothing against the theory. It may be that we have already discovered all the mind-bending ideas that nature has to offer.
Obviously, its most serious failure is that it predicts nothing at this point. It also does not connect in a satisfactory way with Quantum Field theory.
The fact that it is consistent, in not really a big point in its favor, because all the consistency is really coming from the two dimensional conformal field theory of the worldsheet.
Its biggest success till today seems to be that one of the string states is a massless spin two particle. Sean mentions black hole entropy and field dualities above, but I personally have’nt looked into them.
However, since String theory is not a finished product, hope is not dead. There are still enough loose ends in it, that people can work on. Having done so much work, I don’t think researchers will be ready to give up until they have followed every lead to its bitter end. Or insightful turn, that leads to predictions, and maybe even awe (Are’nt we all in physics for the thrills?).
The string army, may be losing the battle, but its resources are not exhausted yet.
Ellipsis,
Every bosonic degree of freedom corresponds to one dimension. If you like, you can look at the spin as being the eigenvalue, so that in some sense fermionic degrees of freedom give us half-dimensions.
Need to grade problem sets, so I’m going to have to leave this productive discussion — it’s been fun…
Rather, the two-dimensional conformal field theory which they are studying is a part of pure mathematics, and therefore the assertions they make about it are true.
Former string theorist, if you anytime get bored with being stuck in 2D, maybe you are interested in some post-stringy mathematics. A nice thing is that this is pretty much virgin territory, which hasn’t been beaten to death by Witten & Co for the past 25 years.
Eric Mayes:
In your comment 22 you announced that after your complete derivation of neutrino masses and mixings anti-string people should sit down and be quiet. In your paper I find: “Moreover, the suitable neutrino masses and mixings can be generated via the seesaw mechanism by choosing suitable Majorana mass matrix for the right-handed neutrinos”. Is this a 1 Aprile joke or hironic science?
In the conclusions you write: “We have calculated the supersymmetry breaking soft terms, and obtained the low energy supersymmetric particle spectrum within the reach of the LHC”. Maybe “We have fixed by hand m_3/2 = 1100 GeV and other 26 free parameters such that sparticles are within the reach of LHC” is a more precise summary of what you did? (Unless kostya is right and you will have to increase m_3/2 by 16 orders of magnitude).
What is really depressing is not that you have many free parameters, but that you do not even try to see if, despite the many free parameters, your construction gives some acceptable prediction.
“… You’re right that the crucial question is how such work gets evaluated. It’s not true that working on something speculative that isn’t successful will destroy one’s career. Lots of people doing this have tenure. The people participating in these public debates all have tenure, and aren’t going to lose their jobs if they lose the debate (my situation is somewhat special: I don’t have tenure, but do have a pretty secure permanent position). The problem is mainly for junior people, where the reward structure is such that getting another job and getting tenure requires that they either work on certain widely accepted speculative ideas, or, if they decide to do something else, are both lucky and brilliant enough to make a big breakthrough. …” – Peter Woit
There’s a contradiction in Lee Smolin’s sociological arguments about this in The Trouble with Physics. In the text, he writes on p. 309 (US ed.):
“The prime example is Einstein, who … was slow in argument, easily confused; others were much better at mathematics. Einstein himself is said to have remarked, ‘It’s not that I’m so smark. It’s just that I stay with problems longer.’ Niels Bohr was an even more extreme case. … there is not a single calculation in his research notebooks, which were all verbal argument and pictures.”
He adds that de Broglie’s 1924 PhD thesis on particle-wave duality was only saved from being failed by the examiners when Einstein stepped in with praise. (Einstein himself published 4 major papers, including his future PhD thesis, as papers before his PhD was accepted.) However, Smolin in endnote 9 on p. 370 writes of his defence of free-thinkers:
“I have here to again emphasize that I am talking only about people with a good training all the way through to a PhD. This is not a discussion about quacks …”
So you have to get a PhD, and today (unlike the case in Einstein’s time) that isn’t just a case of submittting a thesis on what you are interested in, but of being conformist and doing what you are told in some mainstream area.
The contradiction is, Smolin’s prime case studies, Einstein and de Broglie, didn’t have PhD’s when they published their first papers with crucial new ideas, yet Smolin implies that such people are ignorant quacks in his endnote…
Rob in #97- thanks for the reply! I like it and admit I’m a touch tactless myself, so I may use it. People only take college students as seriously as they want to, anyway. 😉
My concern is that some proponents of string theory, who have worked to popularize it, have misrepresented string theory as nearly finished and/or already known to be correct, rather than simply as promising. I see the new counterarguments, and their effectiveness, as a backlash against these overstated claims.
Either I forgot to submit my post on (I think) Saturday, or else it was deleted for making mention of a Certain String Theorist at Harvard.
Anyhow, the point I was trying to make (and apologies if someone else has made the same point in the subsequent 100ish posts) is that a fair amount of money that goes into research comes from the taxpaying public. Additionally, many research institutions are tax-exempt. The public, therefore, has an entirely legitimate interest in what’s happening with that money and if there is a debate as to the worth of a particular area of research (and I think that there really is; many of the other physicists that I’ve spoken to aren’t at all enthused with string theory either) then string theorists do have to make their case, both to their fellow physicists and to the general public. It’ll work best if it’s not done with a “you’re just too stupid to understand” sort of sneer, too (I don’t think that most string theorists are guilty of that but it’s not something I’ve been devotedly studying). If researchers don’t like that, well, stop taking the public dime.
Of course, it would be possible to agree with the string theorists that there is great promise in string theory and still want, say, to cut funding for research in string theory down to 20% of whatever the current level is. Money is finite and subject to competition, after all.
Just a remark somewhat aside of the issue. It is a bit strange that people choose to focus some much effort in a single-minded pursuit of theoretical physics problems which are so remote and so far from the experimental/observational world. It is not that is wrong to do it – either following the mainstream, or following a more original set of hypotheses -, but that it is strange that they do not choose to also work in problems from areas of physics where the confrontation with the experimental phenomena is possible. After all, working in string theory should create a lot of frustration due to the lack of experimental input, and it would be natural to diversify the research.
The great heroes of the early 20th worked on a wide range of subjects. Am I wrong to have the impression that this is not the case nowadays?
The great heroes of the early 20th worked on a wide range of subjects. Am I wrong to have the impression that this is not the case nowadays?
Yes, you are wrong. String theory does not equal theoretical physics. In fact, open an arbitrary physics magazine, like e.g. Physics Today and you’ll notice that we are talking about a sub-field of a sub-field which just currently happens to be subject of open-heart surgery in the public domain. Even by reading nothing else than CV you will notice that the range of subjects is wider than a single-minded pursuit of theoretical physics problems which are so remote and so far from the experimental/observational world.
Best,
B.
If one cannot see “the mechanism being used” then of course it won’t make sense.
String Theory Landscape
Quantum Effect, however allow a manifold to change state abruptly at some point-to tunnel through the intervening ridge to a nearby lower valley.
Some maybe happy with the propagation of the species 🙂 but one would have to draw their attention to the geometrical basis of these two differing views on the landscape brought forward?
I am invoking “Boltzmann’s brain” here. 🙂 While it may ensue from “first principles” I am still referring to quantum gravity in both regards.
If this is not done, then the debate will continue, “in the land of babble” and “Pink Elephants.” Us lay people are not happy about this.
Here at Scientific American, I can say that the perception that string theory has lost the debate has definitely been filtering into our staff discussions, and I bet the same is true at other magazines, too. That said, I have seen the theory go through too many ups and downs (real and perceived) to get too excited about the current trough.
I long for a debate where we roll up our sleeves and solve problems rather than snipe. For instance, I think we can find common ground on the fact that the system of science funding in this country is broken; the grant process devours too much productive time and discourages out-of-the-box thinking of the sort Peter thinks is neglected. Let’s work that problem rather than turn on one another.
George
B, I am affraid I didn’t state my point/question clearly. I know that theoretical physics is much, much more than string theory. My question is: do string theorists work on other areas of physics closer to experimentation – just like as many other famous theor. physicists of the past have worked in more than one sub-field of physics. If not, why?
Hi MP-S,
My question is: do string theorists work on other areas of physics closer to experimentation – just like as many other famous theor. physicists of the past have worked in more than one sub-field of physics. If not, why?
Because theoretical physics today has gotten significantly more involved, there are many areas that require a rather long phase of learning, and to work at the front of research it has become necessary to specialize at some point. (I should add though that I don’t think it has to be as extreme as it is today, and I don’t think the present situation is good for progress, but that’s a different issue. Right now, this is just the fact. )
I don’t know many theorists that work on other areas besides their main interest, regardless of whether they are string theorists. I know several cases where theorists have changed their research topics, but also that is an exception. I think it would be beneficiary for the whole community if all ‘areas of physics’ were kept closer together. I sometimes feel like working on the tower of Babel. Again, I don’t understand why all these problems are exercised on the example of string theory since there are many other areas that suffer from similar problems.
Best,
B.
Hi B.,
“I think it would be beneficiary for the whole community if all ‘areas of physics’ were kept closer together. I sometimes feel like working on the tower of Babel.”
Yes, I agree.
” Again, I don’t understand why all these problems are exercised on the example of string theory since there are many other areas that suffer from similar problems.”
Absolutely, this applies to the other areas too. My impression is that the over-specialization may also be caused by the tenure and grant processes mentioned in some comments.
B said: “I don’t know many theorists that work on other areas besides their main interest, regardless of whether they are string theorists. ”
Interestingly, I know many experimentalists who DO work in different areas, and its not just a case of doing Raman Spectroscopy on whofnium, whafnium, etc. and counting those as different fields. Look at the career of Sid Nagel at the University of Chicago and you’ll see a common theme (complex systems) but no one experimental technique nor material system. I myself work in amorphous semiconductors, granular media and neuroscience, and the experimental techniques are all over the map, and the shifting of gears is a challenge, I can assure you. I may not understand the mathematics of M-Branes, but I’d put Sid’s intellectual chops against anyones.
And George Musser: I agree wholeheartedly that the real funding crisis is the ever increasing amount of the work day that the search for research support has been demanding, as more and more scientists chase relatively fewer dollars (the NSF’s budget could be doubled with what is spent in three weeks in Iraq, but that’s another topic). I’ve been doing my part to speak to the general public (nine public lectures scheduled for the first six months of this year alone). In every talk I point out how the work of a few physicists, developing Quantum Mechanics, directly led to the lifestyle we enjoy today. Moreoever, at no other point in our history have so many people been so wealthy, directly owing to their education! (That is, not owning land, serfs or mineral rights). These points seem to register with high school students and their parents. I’d like to see more of this along the lines of Yvette’s work described above.
Hi Ellipsis, dimension, properly defined is an observable in several background independent approaches to quantum gravity including causal dynamical triagulations and causal sets. You can find papers on these subjects where the haussdorf or scaling dimensions are measured. Indeed, in these kinds of theories, the effective dimension matter degrees of freedom see as they propagate can depend on scale, and these can be fractional. See recent works of Ambjorn, Loll and collaborators for calculations where the dimension, as a function of scale, is an output rather than an input. Indeed, a good feature of their model is that at large scales their measurements are consistent with 3+1 dimensions, and at short distances at 1+1,
Thanks,
Lee
Lee,
Just want to say I have enjoyed your books. I don’t know that much about Loop Quantum Gravity, but I do think that in the end, it will probably be part of the solution and more people should probably be working to connect it with string theory.
Lee,
Any possibility that the worldsheet bosons and fermions of string theory are related to the spin networks of LQG?
Getting String Theory funded to the levels that Theology is funded would probably be a good thing for String Theory.
The most salient comment thus far, in my opinion, is that of the Count:
The fact that it requires 6/7 extra space dimensions that are not observed, and that time seems to be emergent, implying that physics must somehow be done without time, is enough to give serious thinkers pause. Not about string theory per se, which is only the symptom of the trouble, but about our understanding of the true nature of space and time.
We know that something very fundamental in our understanding in this regard is wrong, so Peter’s thesis that string theory is not even wrong really implies that our physical theory in general can’t be argued cogently. Of course it’s wrong and for the very same reasons that the Count points out: As many are now coming to realize, it’s an extension of a more fundamental idea that is wrong. Therefore, the broader implication is that all current physical theory is not even wrong; that is, current theories can’t be defended logically from the point of view of what is right and what is wrong, because they are all founded on the same wrong assumptions, and thus are not capable of even being evaluated in the context of right or wrong.
All that can be said of them is that they are successful to some degree or another, but not that they are right or wrong.
Well, I don’t think it would be a good thing for ANY sub-field of physics to be funded at THAT level. But, speaking of which, from this week’s Newsweek poll:
Nearly half (48 percent) of the public rejects the scientific theory of evolution; one-third (34 percent) of college graduates say they accept the Biblical account of creation as fact. Seventy-three percent of Evangelical Protestants say they believe that God created humans in their present form within the last 10,000 years; 39 percent of non-Evangelical Protestants and 41 percent of Catholics agree with that view.
The 10,000 years part gets me. We didn’t pull the agoe fo the Earth out of a hat. It’s based upon radioactive isotope dating. It’s been 60+ years since the atomic bomb was developed. At this point, we understand radioactivity (at least for applications like dating the Earth or the Shroud of Turin). If you don’t believe that we understand radioactivity, then we must also not understand Quantum Mechanics. And if you don’t accept quantum mechanics, that’s fine, just please, put the cell phone down!
Sean coaxingly requested,
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.
It seems remarkable to me, 120+ comments later, how few people have responded in this vein. Over at Clifford’s blog there have been some angry discussions (e.g., this and this) about the merits of Lee’s and Peter’s books, and some string theorists and partisans were quite vocal in their usually unfavorable opinions about the books (often without having read either of them), jumping at the chance to trash Lee and Peter or repeat common assertions like “string theory is the only game in town.” But now, when Sean has offered an excellent opportunity in a widely read forum to make a case in favor of string theory (rather than just another opportunity to trash its opponents), it seems most proponents have little to say:
1. Moshe (comment #5), a string theorist, seems to view Sean’s request as an invitation to continue a debate, which he is not inclined to do, apparently believing it is unproductive;
2. Wolfgang (comment #12) pointed to a blog post by Jacques Distler that he felt did a good job of addressing Sean’s request;
3. Sean (comment #16) asked Moshe to reconsider his inclination, arguing that it is very worthwhile to try to educate the non-experts about the primary merits of the string program, but Moshe (comment #94) later says he doesn’t mind losing a debate among those scientists who are willing to judge the string program without understanding it at a technical level;
4. Eric Mayes (comment #22 and others later) claims to have a phenomenological construction of much of the standard model from string theory, which if true and is not too ad hoc could be a step forward;
5. Haelfix (comment #30) refers to Distler’s blog as a good place to look for reasons why string theory should be taken seriously;
6. Sean tries to very briefly answer his own call in comment #55.
That seems to be about the extent of “why string theory is compelling” from string theorists and partisans! A couple of references to Jacques’ blog and Sean partly answering his own request!
If one needed a better understanding of why string theory may be losing the public debate, this pathetic response by its proponents speaks loudly. Given that Cosmicvariance is a popular blog that is read widely by the lay public and journalists as well as scientists, it is especially hard for me to understand why the string theory community should be content to put the onus of looking for reasons why the string program is worthwhile onto the public that funds most of the effort. A reference to Jacques Distler’s blog is not a substitute for a coherent, concise argument, especially because the level of discussion at Jacques’ blog is not what the typical lay reader would find comfortable. One could easily come away from the above discussion assuming that either string theorists are spending time on it because it is “the only game in town” or that they really could care less whether anyone knows why it is worth doing as long as the dollars keep flowing.
This is the observation of a physics grad student who doesn’t currently count himself among the string theory partisans.