Is String Theory About to Snap?

The August issue of Discover magazine is out, with a cover story entitled “Is String Theory About to Snap?”. The editors of the magazine describe how they recently became aware of the controversy over string theory when they organized a celebration of Einstein in Aspen last summer. They quote Lawrence Krauss as telling them “String theory may be in a worse position now regarding being testable than it has been at any time in the past 20 years.” To get a response to this, they asked Michio Kaku to write something for them. They refer to him as a “cofounder of string theory”, which I suspect some people might object to. Presumably they meant to repeat what is in their profile of him, which calls him a “cofounder of string field theory.”

Kaku’s article is entitled Testing String Theory, and is a thoroughly intellectually dishonest piece of writing, designed to mislead anyone without expertise in what is at issue here. He succeeded in misleading whoever wrote the blurb for the article which goes: “No experiment has ever allowed us to test whether any of the assumptions of string theory are true. That is about to change.” No it’s not. None of the experiments Kaku mentions will “allow us to test whether any of the assumptions of string theory are true”.

As I’ve explained in detail on other occasions, the simple fact of the matter is that string theory does not make any predictions, unless one adopts a definition of the word “prediction” different than that conventional among scientists. A scientific prediction is one that tells you specifically what the results of a given experiment will be. If the results of the experiment come out differently, the theory is wrong. String theory can’t do this, since it is not a well-defined theory, but rather a research program that some people hope will one day lead to a well-defined theory capable of making predictions.

At places in the article Kaku qualifies his claims of “predictions”, for instance saying near the beginning of the article that certain experiments “could provide significant evidence that would support string theory” (note all the qualifiers in this phrase: “could”, “significant evidence”, “support”) but that “the rub is that all the new evidence, no matter how compelling, will still provide only indirect proof.” He soon abandons his qualified language and starts talking about the following topics:

1. Gravitational waves: He says of gravitational waves created in the Big Bang: “String theory predicts the frequencies of such waves”, and that this prediction will be tested by LISA. I don’t know specifically what he has in mind here, but I know of no way to use string theory to make a specific prediction of the spectrum of gravitational waves that LISA will see. The only things he mentions are inflation and epkyrotic scenarios, the first of which has nothing to do with string theory, the second very little.

2. The LHC: Kaku discusses the possibility that superpartners exist, but does note that you don’t need string theory to have these. He also discusses possible Tev-scale particle physics effects of extra dimensions, without mentioning that string theory makes no predictions at all about what these extra dimensions are like, or even what their size is. There is absolutely no reason other than wishful thinking to expect extra dimensions in string theory of a size invisible until now, but visible at LHC energies.

3. Laboratory tests of the inverse-square law: Kaku claims: “according to string theory, at small scales like a millimeter, gravity might hop across higher dimensions and perhaps into other, parallel universes”. This is a load of nonsense. String theory predicts no such thing. It may be consistent with this, purely because it is consistent with anything. He does go on to say “Perhaps the additional dimensions would show up only on smaller scales — string theory is still somewhat vague about this prediction.” “Somewhat vague”??? As far as I know string theory makes no prediction about this at all, except that most string theorists expect effects to show up below 10-33cm, not 10-1cm.

4. Dark matter searches: according to Kaku “Once particles of dark matter are identified in the laboratory, their properties can be analyzed and compared with the predictions of string theory.” Only problem is string theory makes no such predictions. He’s talking about neutralinos, but in string theory the neutralino mass could be absolutely anything. After discussing these string theory”predictions” about dark matter, he goes on to speculate that maybe there is no dark matter anyway, just “huge clumps of shadow matter in a parallel universe, causing our galaxies to form in mirror-image locations”, then admits that such an idea is incapable of ever being experimentally tested.

After going through all this, he saves the real kicker for the end: “Some theorists, myself among them, believe that the final verdict on string theory will not come from experiments at all”. So he doesn’t even believe in any of the nonsense he has been spouting. He admits that “The principal reason predictions of string theory are not well-defined is that the theory is not finished.” So the earlier talk of “predictions” is now no longer operative. He goes on to invoke the pipe dream that someday someone will come up with a finished version of string theory that will predict precisely the standard model, neglecting to mention that there’s not the slightest evidence that this is a realistic possibility. On the contrary, all the evidence now points to the conclusion that, if string theory makes sense at all, it has an infinity of different vacuum states, and is probably a radically non-predictive theory. Impressive that Kaku could write a whole article about the prospects of string theory, and somehow neglect to mention the huge and very relevant controversy surrounding the idea of the landscape. Do you think he hasn’t heard about it?

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40 Responses to Is String Theory About to Snap?

  1. Anonymous says:

    Alejandro wrote: “Hmm, anonymous, could it be said that a fat graviton is something as a colored gluon, and then asymptotic freedom strikes? Or is it another mechanism?”

    I don’t think there’s *any* concrete model, really. From the Sundrum papers it seems one really wants to realize the graviton as an extended object on the scale of 20 microns, while the photon and other known particles remain pointlike. Needless to say, this is a strange picture that doesn’t look like any known field or string theory.

    I have wondered about the asymptotic freedom idea you suggest, but I don’t know how it could be realized.

    I think whoever first comes up with a good field theoretic or string theoretic framework in which a fat graviton seems plausible will have made major progress.

  2. Torbjorn Larsson says:

    Alejandro, thank you, I enjoyed the info.

    It seems like I have one or two years to read it all thoroughly. 🙂 It’s a pity if they want to sit on their results until they themselves can verify with differing experiments. Hopefully the other groups work faster…

  3. ks says:

    @Anonymous

    Are you shure that string theory is NOT a kind of ( nevertheless constrained ) meta-language of physics that is able to include/express anything? What is blurred at least to an outsider of string theory like me is the relationship between expressivity as a language and it’s own constraints and assumptions. As an analogy: in software development we distinguish between frameworks and applications. A framewok by itself is vacuos ( it can be useless or clumsy but it never maps an application domain in a falsifiable way ). It just defines how applications can be customized with few effort to run under the constraints of the framework. The applications ( ‘theories’ ) are performing the real stuff. In this sense ‘string theory’ may be a kind of doubling of theoretical physics within physics, creating a framework for particular theories to work with.

  4. Alejandro Rivero says:

    Torbjorn, the information is identical to a rumour started in Lubos blog one month ago, if you read it slowly.

    http://motls.blogspot.com/2005/06/deviations-from-newtons-law-seen.html

  5. Torbjorn Larsson says:

    I’m sorry about the confusement; I was reading too fast, I guess.

    The summary article was from April and with full references, so it didn’t contain the information you were privileged to have.

    Thanks for the info, it looks interesting!

  6. Alejandro Rivero says:

    Hmm, anonymous, could it be said that a fat graviton is something as a colored gluon, and then asymptotic freedom strikes? Or is it another mechanism?

  7. Anonymous says:

    Torbjorn, your repeated posts confuse me, but I’m sure what I said was right, so let me elaborate:

    — Down to 100 microns, the tests show no deviation.
    — Below 100 microns, they do begin to see some deviation. So far this is unpublished, and might go away. If it does not, it poses a serious problem for string theory. The reason is that string theory can easily explain gravity getting *stronger* at short distances (due to more dimensions being accessible), but not getting *weaker*. It doesn’t immediately invalidate the theory, but no one seems to have any model of how string theory could account for this.
    — The fat graviton, to be related to the cosmological constant, implies gravity will be modified below some scale that cannot be much larger than 20 microns. In other words, if the tests find no deviation below about 20 microns, the fat graviton is ruled out. But if the current deviation is confirmed, it’s provides a compelling reason to think about the fat graviton.

  8. Torbjorn Larsson says:

    I have a bad day; Anonymous said the reverse, and it fat gravitons aren’t ruled out.

  9. Torbjorn Larsson says:

    Oops, sorry; they seem also to have ruled out the fat graviton as Anonymous said.

  10. Torbjorn Larsson says:

    “I think it’s worth noting that tests of the inverse-square law stand to actually *invalidate* string theory,…”

    I’m no expert but I don’t think they invalidate ST; it has as usually covered all bases. According to http://physicsweb.org/articles/world/18/4/6/1 the inverse-square law is fine to small scales. What they started to rule out is some, but not all, brane-world scenarios.

  11. Anonymous says:

    dan mentions
    http://motls.blogspot.com/2004/12/ny-times-20-years-of-strings.html

    which is Lubos blog about the Overbye NYT article. There was a Notevenwrong blog too about the same article, if I remember right.
    It was an interesting article partly because of the anecdotes, and gems of triumphant rhetoric. I dont happen to have a subscription to the NYT so I used these alternative links

    http://www.iht.com/articles/2004/12/07/news/string.html

    http://pmbryant.typepad.com/b_and_b/2004/12/string_theory_d.html

    the second has a part of the original Overbye article that the first omits, namely the exchange between Brian Greene and Steve Shenker at the conclusion, about “If it’s wrong, don’t you want to know?”

    dan also quotes A. Garrett Lisi from earlier this thread, the comparison with microsoft, posted at July 14, 2005 01:05 PM.
    I would like a direct link to that. Has Garrett published that comparison somewhere else? it is too apt to lose. I don’t like having to hunt for it by scrolling down though the comments.

    A propos overblown rhetoric, there is Overbye’s final paragraph:


    String theory’s biggest triumph is still its first one, unifying Einstein’s lordly gravity, which curves the cosmos, and the quantum pinball game of chance, which lives inside it.
    “Whatever else it is or is not,” Harvey said in Aspen, “string theory is a theory of quantum gravity that gives sensible answers.”

    should be an anthology of grandiose string pronouncements. It would make entertaining reading now, and more so in a few years, I suspect.

  12. Anonymous says:

    I’ve always had the impression that string theorists roll their eyes upward at Kaku’s attempts to exaggerate his role in the development of string theory, but are loathe to diss him in public in fear of negative publicity for the field.

  13. dan says:

    Does Lubos Motl work for Microsoft?

    http://motls.blogspot.com/2004/12/ny-times-20-years-of-strings.html

    “The article also includes an appropriate portion of a text about loop quantum gravity – a few percent. The most relevant recent discovery in loop quantum gravity was done, according to the article, by Vafa, Neitzke, Gukov, and Dijkgraaf, and Cumrun explains that if loop quantum gravity is correct, it must be a part of string theory. I am sure that our loop quantum gravity colleagues will agree wholeheartedly. ;-)”

    as a response to

    “I see string theory as the microsoft of physics — all marketing, with technological “development” coming only from the principle of “embrace and extend” leveraged to succeed via its monopoly. If I use this model to speculate as to the future, I don’t think string theory will have a spectacular crash, as some might hope and as it certainly deserves. Rather, some non-string researcher, or research group, will make some real progress and the string theory mob will embrace it and claim it as their own. The resulting fun will depend on how adamantly the successful “confounders of string theory” protest that their stuff has nothing to do with strings — but my pessimistic view would be that this voice would be lost amid the torrent of stringy activity and papers tied to their work. Time will tell.”

  14. Anonymous says:

    I think it’s worth noting that tests of the inverse-square law stand to actually *invalidate* string theory, or at least force one to consider very different scenarios than the conventional ones, in the very near future. Eotwash apparently sees a weakening of gravity at around 20 microns, where Raman Sundrum predicted one would see this if a “fat graviton” explains the cosmological constant. This is exciting stuff, and I hope they are able to confirm the tentative evidence of a signal.

  15. Quantoken says:

    Kyle said:

    “In fact, I’ll go a step further. There are high school REU students out there who hold greater claim to having advanced physics than Kaku has in the past twenty years. If only they were doing work on things that sound suitably star-treky, then maybe they could join him in such grand publications as Discover.”

    Actually I will make the observation that any random walking soul on the streets would have a perfectly legitimate claim that he/she has advanced physics in the past year than what Kaku did in the past 20 years.

    Because even if the random soul has not worked in physics, he/she has very likely paid taxes and thus provided support by the public funding to support physics researches. So that’s a positive contribution. Whereas Mr. Kaku, if he had achieved nothing, he would have wasted 20 years worth of research funding and thus contributed negatively to science.

    But it’s even worse. By going to TVs and publish popular readings that utterly lie about and mislead the public about scientific facts and realities, Kaku not only wasted tax payer money, he also contributed negatively to the progress of real science.

    Quantoken

  16. Ben says:

    I’m no expert, but it boggles my mind that someone who has published the highly technical books that Kaku has, by major technical publishers (Springer, Oxford), could be incompetent, which seems to be the implication here. On the other hand, that seems to be the implication about all of string theory. I am not saying you are right or wrong, since as I said I don’t know. But something really weird is going on.

  17. A Scott Crawford says:

    How much did the LIGO facility down south cost? $600 million or something? And now we eagerly await a signal that’ll EITHER be a wrinkle in gravity, OR a car backfiring on a not so nearby highway! Just as Einstein predicted!

    Just to play the devil’s advocate… the LISA system is going to adjust the position of it’s three SV’s using the coronasphere model. This assumes there is ALWAYS solar weather, or varying degrees of both proton and photon density interacting in a particular volume of “euclidian” space (at one AU), &etc. (CQ Magazine has monthly solar weather charts for the curious)

    The first observation is that solar weather is, in practical terms, aether. One might almost want to look at chromatic aberrations, or (echm) other signal characteristics (like spherical aberrations or x) to see if an interferometer inside a spaceship can allow one to determine lots of stuff without looking out the windows. That’d be pretty cool, as it’d be nice to zoom up past ‘c’.

    The second observation is that the LISA SV’s beams aren’t traveling through a shielded vacuum or a stable magnetic fiield. The SV’s will tell us a lot of things about Sol. But how one distinguishes between a space jiggle due to cloud of charged dust from the sun and one due to a cosmic wave of gravity is beyond me.

    The last observation is actually a question. Is the scientific principle commonly referred to as Ockhams Razor, dead, or alive? If the former, what’s replaced it? If the latter, how well does String Theory (xyz) hold up if the Razor is applied?

  18. ks says:

    It is at least the mass audience who is willing to spend money into an enterprise without any practical use ( former generations may have believed in new high energy wappon systems as a side-product of accelerator research ). It will be sold as a part of “culture” starting with greek intellectuals speculating about the arché and ends up with string theorists doing the same thing collaboratively with more advanced mathematical tools. Maybe Kaku has understood better than the mainstream mathematical physicist that whatever theory will be finally accepted by the community it will end up in physics-actors like him and books about timetravel, wormholes and parallel universes i.e. pop-culture that justifies the luxury of HEP research. Therefore Kaku goes well beyond John Horgans claim that scientists practice ‘ironic science’ but deny this circumstance.

  19. I think Kaku is pop-scientist, that is what offends a great deal of his critics. Regardless of his position, lack thereof, and the liberties he’s taken, what he has managed to do is communicate to a mass audience — which is not such a bad thing — even if some say he’s delving into the realm of science fiction.

  20. D R Lunsford says:

    Kaku’s QFT book is not bad. In fact it’s very conservative, which is what you really want in a textbook. Of course there is no single tome that will do, since the theory is broken to begin with.

    Peter’s comment perplexes me. As I understood it, string theory emerged from an attempt to explain nuclear forces and in particular resonances, in the sense of literally banding together nucleons and using Hooke’s law (!). So how could Kaku have been an evangelist before there was anything to get really worked up about?

    -drl

  21. Kyle says:

    Why would that irk you? It doesn’t take much to pass up someone standing still. Spend a couple of years helping out in a good lab and you’ll have done more to increase the scope of physics’ predictive power than some others have in decades of mathematical meanderings.

    In fact, I’ll go a step further. There are high school REU students out there who hold greater claim to having advanced physics than Kaku has in the past twenty years. If only they were doing work on things that sound suitably star-treky, then maybe they could join him in such grand publications as Discover.

  22. ksh95 says:

    Hack said
    I seriously doubt it! What kind of demented instructor would choose Kaku as a primary text for a QFT course? Aside from Kaku himself, of course.

    Agreed. I think it’s a horrible introductory text. The quality of Kaku’s book, however, was not the point of my post.

    I just get irked by goofy statements like, “…I contributed more than Kaku when I was an undergrad…”.

  23. hack says:

    “Respect your elders young grasshopper. One day you may be taught QFT from Kaku’s books.”

    I seriously doubt it! What kind of demented instructor would choose Kaku as a primary text for a QFT course? Aside from Kaku himself, of course.

  24. Peter Woit says:

    Hi Garrett,

    I think you’re being unfair to Microsoft, their product actually works. But I think you’re right that what will happen in the future is that anything new and successful will be dubbed a “version of string theory”. In his Discover article, Kaku refers to all sorts of different things as “versions of string theory”.

  25. garrett says:

    I see string theory as the microsoft of physics — all marketing, with technological “development” coming only from the principle of “embrace and extend” leveraged to succeed via its monopoly. If I use this model to speculate as to the future, I don’t think string theory will have a spectacular crash, as some might hope and as it certainly deserves. Rather, some non-string researcher, or research group, will make some real progress and the string theory mob will embrace it and claim it as their own. The resulting fun will depend on how adamantly the successful “confounders of string theory” protest that their stuff has nothing to do with strings — but my pessimistic view would be that this voice would be lost amid the torrent of stringy activity and papers tied to their work. Time will tell.

  26. Anonymous says:

    A few years back I was at a conference where Kaku was a guest of honour. I was looking forward to meeting the guy and managed to pull strings to join him for dinner. He was not the person I expected. He was one of those annoying scientistic scientists – one of those who thinks that if it’s been published in a paper it must be “absolutely and scientifically proved”, even, surprisingly, from the ‘softer’ sciences like biology. He’d quote stuff on a wide variety of topics as if he were some kind of oracle with perfect knowledge of The Truth. Anyway, the next day he gave his talk. It was more of the same with him laying down The Law as to what was and wasn’t physically possible. He stated some ‘fundamental’ limit on computing: maybe it was a limit on switch size, something like that. Anyway, there was a bit of noise coming from the back of the auditorium. It got a bit louder. A bunch of people were conferring. And eventually they said something. This group had already exceeded his so called ‘fundamental’ limit in the lab. They had intended to make no announcement about it yet but after the arrogance of Kaku’s speech they couldn’t contain themselves any longer!

  27. ksh95 says:

    Kyle said
    I’m proud to say that by the time I graduated with a B.S., I had contributed more to physics than Kaku has before or since.

    Respect your elders young grasshopper. One day you may be taught QFT from Kaku’s books.

  28. Anonymous says:

    I found the statement “cofounder of string field theory” on his web site.

    That’s very clever, actually. The layman will not notice the difference between “string theory” and “string field theory”, so it practically reads “cofounder of string theory”. But to the expert, Kaku can always say “Hey, I said string FIELD theory”, which is a relatively obscure subject that very few people know or care about its history anyway. Very clever!

  29. Mike Crowley says:

    Peter,

    I found this entry very helpful in providing a more realistic context for Kaku’s book “Parallel Worlds”. The article you described is very similar to the arguments he sets out in this book.

    I reviewed the chapter where he discusses testing String Theory. He devotes a lot of space to gravity waves but I’m still unclear how they confirm String Theory; however, he writes “One important goal of LISA is to provide the smoking gun for the inflationary theory… Some, such as Kip Thorne of Cal Tech, believe that LISA may be able to tell whether some version of string theory is correct. As I explain in chapter 7, the inflationary universe theory predicts that gravity waves emerging from the big bang should be quite violent, corresponding to the rapid, exponential expansion of the early universe, accompanied by much smoother gravity waves. LISA should be able to rule out various rival theories of the big bang and make a crucial test of string theory.”

    At the end of the chapter he writes, “My own view is that verification of string theory might come entirely from pure mathematics, rather than from experiment. Since string theory is supposed to be a theory of everything, it should be a theory of everyday energies as well as cosmic ones. Thus, if we can finally solve the theory completely, we should b able to calculate the properties of ordinary objects, not just exotic ones found in outer space. For example, if string theory can calculate the masses of the proton, neutron, and electron from first principles, this would be an accomplishment of first magnitude.”

    He then quotes Einstein and concludes the chapter dramatically: “If true, then perhaps M-theory will make possible the final journey for all intelligent life in the universe, the escape from our dying universe trillions upon trillions of years from now to a new home.” (After learning what I’ve learned here, it’s no longer possible to read paragraphs like that with a straight face.)

    Yesterday morning on a local talk show in Phoenix I heard the anchor praise Kaku, describing him as “one of the fathers of String Theory” and also “like the rock star of theoretical physics–he has a huge following and a web page.”

  30. Peter Woit says:

    Kaku was one of the co-developers of string field theory, see his 1974 papers with Kikkawa. Of course there was little interest in this at the time, since a year earlier Gross et. al. had discovered asymptotic freedom and the best people in the field were all doing gauge theory.

  31. Anonymous says:

    It’s also a fact that there is (almost) no such thing as a (serious) “string field theory”, and if there is, then Witten is the founder (probably Warren Siegel should also be mentioned). I recall that Kaku wrote a paper or two on the subject in the 80’s (as so many other people), but nothing like a major contribution.

  32. Joe Bolte says:

    I would encourage you to write something similar to what is here as a letter to the editor of Discovery. No matter who owns it, or what its standards are, I think it’s important to point out to readers who may not have a sophisticated knowledge of what constitutes science that Mr Kaku is being extremely slippery here.

  33. Kyle says:

    I’m proud to say that by the time I graduated with a B.S., I had contributed more to physics than Kaku has before or since.

    I believe this is so because though he has done much work (of what quality?) in mathematics, I have never seen any evidence of Kaku having produced anything in physics at all.

  34. Anonymous says:

    Kakuphony!

  35. Alejandro Rivero says:

    I fail to find the updated version of “Comments On String Theory”, if it is http://arxiv.org/abs/hep-th/0212247

  36. Anonymous says:

    Peter,

    For pete’s sake, Discover Magazine is a rag owned by Disney which is far below the standards of Scientific American (which itself has been going downhill for the past two decades). Who cares what they have to say pro or con.

    Some of your concerns in your post can be put to rest by Witten himself in his paper entitled “COMMENTS ON STRING THEORY” which was updated as of June 2005.

    but no you keep chasing after kooks like kaku because you’re runnin a mockracy.

  37. M says:

    Maybe a fine-tuned version of your post would be an appropriate “letter to the editor” of Discover, or even a rebuttal to Kaku’s piece? Or do you think Discover would ignore it, preferring sensation over accuracy along the lines of “We are on the cusp of discovering great things; isn’t that really exciting?”

  38. Quantoken says:

    MICHIO KAKU. I wonder what kind of scientist this guy is and what kind mind he has. These days I can not turn on television without seeing the face of this big mouthed MICHIO KAKU, especially when I watch science related channels.

    Does any one know what kind of research he does? A search in ARXIV turned up just 6 of his papers. And nothing since 1999. Has he turned himself into a TV actor or SciFi novelist or sort of thing?

    Quantoken

  39. Anonymous says:

    Kaku, Kaku. What can I say! Where do I begin!

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