Kuhn, Paradigm shifts, String Theory and Observations

Venturing onto thin ground for me, and giving the stringy folk a chance to patronise me in return. So... I've been reading Kuhn, the structure of scientific revolutions. An interesting book, which I shall blog about in a bit. In some ways its a bit like reading Leviathan, but in reverse.

So: the basic point is: that scientists do "normal" science for most of the time, until enough observations pile up that simply cannot be explained under the current theory, or until complications in the theory needed to explain obs piles up, and eventually someone comes up with a blindingly novel viewpoint, the "paradigm" shifts, and everyone hares off down a new track, except for the old fogeys stuck in their ways.

And the obvious examples are Newtonian gravity/mechanics; SR/GR; and QM. Fair enough.

Now, stop me if you've heard this before, but are we, today, with String Theory for the very first time desperately *searching* for a paradigm shift? Its as if they've all read the book, said "sod all this normal science, we're off on a new track" and deliberately set off to do so, *despite* a total lack of observations that contradict relativity or QM. Although of course ST is by now normal science. But ignore that.

The catalyst for this post is "The List" by Steinn; which again supports my contention that the current attempt-at-shift is unusual in being not driven by *any* inexplicable obs (let alone lots of them piling up; OK there is a possible pioneer effect but thats pretty marginal). Of course, what it is driven by is GR and QM not being compatible as theories; however this is really a rather different thing.


More like this

*despite* a total lack of observations that contradict relativity or QM.

Is the observation that relativity and QM contradict each other neither an observation that contradicts relativity nor an observation that contradicts QM?

[If it is, I'm sure Lubos would have pointed it out! Perhaps saying GR and QM contradict each other is a bit imprecise: they exist in different realms and don't touch much. If you extrapolate them all the way so they do touch, then they contradict, but thats not an observational matter -W]

One of the things Kuhn notes about the crises that precede paradigm shifts is that not everyone in the normal science community necessarily feels the crisis with the same urgency. So, perhaps the string theory folks are responding to anomalies that really haven't gotten under the skin of other physicists (so far). Maybe they're a "leading edge" that recognizes that the (still dominant) old paradigm is played out.

Alternatively, maybe Structure of Scientific Revolutions has made it fashionable (perhaps not the right word, but I think you know what I mean) to foment scientific revolutions even before all the juice is sucked out of the paradigm you're in.

I am officially agnostic about what the deal is with string theory, but I'm always happy to kibbitz about Kuhn!

There was an error in the papers connecting us - a paper with a fictitious double Nelson.

The best Motl number I can give you right now is 8 (distance) - via Edward Witten as a safe choice. See my blog.

Otherwise your text about physics is complete rubbish. String theory is not studied because we want a paradigm shift but because we know that the previous theories, the Standard Model plus General Relativity, cannot be the complete answer, for example because they are not compatible with each other. The Standard Model breaks down at the Planck scale and probably much earlier. It is a deep problem, as deep as similar problems in the past that led to new important insights, and we have exactly one known solution how to solve the problem. The solution simultaneously brings a lot of fascinating mathematics with it [deleted -W]

[Hi Lubos. I must say I expected something more interesting from you; you appear to have essentially conceeded my main point - that this is an entirely theory-driven "revolution". Perhaps thats whats wrong: if you have anomalous observations that gives you some clue as to how to proceed; when you only have incompatible theories it is less clear. Or then again, it may be that my observations on ST are as valuable as yours on Climate. I hope not -W]

Of course that the string theoretical revolution is entirely a theory-driven revolution. Is it the first time you learned it?

We know theoretically that we would have to obtain anomalous observations if we could increase energies in our experiments etc. by many orders of magnitude or if we could make other improvements - we know it by using the so-called brain [deleted - W]

Your Motl number is 7 after all, see my updated blog for details.


[I'm not sure I've ever seen it explicity written down that ST is entirely theory driven. This could easily be because I haven't studied it though: could you point me to a "canonical" source?

Glad to know your Connolley number is now 7. BTW, thats your second comment in a row I've had to edit for incivility. You'll get stuffed into a moderation queue if you keep it up - W]

The whole blog "Not Even Wrong" is dedicated to the fact that there is no experimental proof of string theory.

What you call incivility is normally called "important truth". ;-)

[Maybe it is, but http://www.math.columbia.edu/~woit/wordpress/ is a big place. Can you point to a definite statement of this. What I'm looking for is something that makes my entire post obviously redundant. I wouldn't be too surprised to find it, but I'd like to see it.

Rude words: you need to adopt the UK parliamentary practice: no rude words; be inventive instead - W]

My impression is that Einstein's work on general relativity wasn't really motivated by anomalous observations at all. There were one or two anomalous observations out there that it turned out to explain (Mercury's perihelion shift) and others that were motivated early on as tests of the theory (eclipse aberration of starlight), which led to its being generally accepted. But Einstein himself, with his small number of collaborators and correspondents, was just trying to theoretically reconcile gravitation with special relativity, since obviously Newton's theory wouldn't do the job.

[This is an interesting point, and may well be correct. Its hard to know how much the perihelion stuff matters; I'm inclined to agree that it wasn't the main thrust; but perhaps it helped to decide if the version produced was reasonable -W]

If you want to see sentences on Not Even Wrong that there is no experimental evidence for string theory, here are 100+ articles:


I could give you similar links to more trustworthy places, too. Woit's conclusions are of course not right, but the observation that string theory is not driven by particular experiments that have been done, is correct.

As Matt McIrvin points out - and I described in my blog article - it is certainly not the first big purely theoretically-driven enterprise in physics, and both theories of relativity were previous examples.

[No exp evidence *for* ST is not the same thing as whether there are obs inconsistent with QM/GR *driving* ST. And whether SR or GR were *purely* theory driven... no -W]

Surprisingly, it IS the same thing, William. If there were *observable* evidence of inconsistency of GR and QM, then there would also be observable evidence for physics beyond these theories, which would also be observable evidence for string theory (if it were going in the right direction). And vice versa.

Einstein had almost purely theoretical motivation to discover both special relativity as well as general relativity, in the very same sense as string theory today. For example, Michelson-Morley experiments did not play any substantial role for Einstein's reasoning, and at some moment, it was even questioned whether Einstein knew these experiments when he was working on special relativity. General relativity was even more theoretical enterprise. No particular anomaly was driving him. The new effects predicted by GR were appreciated as GR-related anomalies only after GR was fully developed - Mercury perihelion precession calculation, bending light (1919), gravitational red shift, and many others only came after 1915.


About your point that string theory is the first revolution entirely by theory, with no anomalous observations to guide it.

First of all, it's not clear what's a "revolution" and what isn't. String theorists like to talk about their multiple "revolutions", but the larger physics community and scientific consensus in general is not likely to accept the idea that string theory has revolutionized our understanding of physics until there is some experimental evidence for it. So, the first problem is that string theory is not a "revolution" in the same sense as other "revolutions" in the history of physics.

String theory is a highly speculative idea for how to unify physics. It's not a well-defined theory, but a research program, one that by now has clearly failed. There was no experimental anomaly motivating it; the motivation was the hope that it could resolve the conceptual incompatibility of QM and GR. The history of GR is a reasonable analogy: Einstein was trying to resolve the conceptual incompatibility of Newtonian mechanics and special relativity. The difference with GR is that, after a decade or so of work, Einstein had a very simple theory that explained previous anomalies (the precession of the perihelion of Mercury), even if doing this was not a main motivation. His theory also made new, testable predictions, which were soon checked (deflection of light, observed at a solar eclipse).

There have been many other speculative ideas guided by purely mathematical or conceptual considerations. Gauge theory was invented first by Weyl, then extended to a non-abelian group by Yang-Mills in 1954. Both of these were false starts, with the initial version of these theories turning out to be misguided, but close to something that did turn out to work spectacularly well, revolutionizing physics.

I do think the current situation of particle physics is historically unparalleled: there are no experimental anomalies to guide where to look for a better theory. Maybe this will change with the LHC, but if it doesn't, the only way a new revolution in our understanding will come about any time soon will be by a purely conceptual advance like that of Einstein's work on GR.

I'm not especially optimistic about this, but at this point the best case scenario for string theory is that it is a false start like Weyl's, that some quite different version of it will be found that really is revolutionary.

[Peter - thanks for your comments. The point about GR has now been made my enough people that I think I'm obliged to accept it: ST isn't the first motivated-by-theory-only attempt at revolution; OTOH your point about the difference to GR is good -W]

Dear William,

your way of reasoning is often very far from mine. I am baffled by your sentence "The point about GR has now been made my (or by) enough people that I think I'm obliged to accept it". Should not you try to understand all necessary data that one needs to answer the question whether GR was experimentally driven, and try to answer the question yourself without relying on obligations?

If everyone feels obliged to accept a point that has been made by many people, we would probably also have to accept creationism or a looming global warming disaster, among many other examples.


[On GR, its pretty clear that I don't have the time to understand the theory fully. Its on the stack for retirement, or perhaps when I get sacked :-). As to what *drove* theory, thats yet another question, and although there are some facts it must be a matter of judgement - W]

I think your account of experimental anomalies causing people to search for a new theory, followed by a novel new theory being found, followed by a paradigm shift is simplistic. The new theory may not be novel at all but an old out of favor theory that new experimental evidence vindicates. Consider continental drift (plate tectonics) for example.

And if in fact GR and QM are incompatible in some fundamental way that is in my opinion far more serious than a few anomalous experiments.

[Its not my account, its my paraphrase of Kuhn. And the continental drift stuff is historically compex. The coming and going of orbital forcing on climate is another.

I'm not really talking about how *serious* it is, but about what gives you guidance as to where to go next. Having anomalous obs is clearly useful. Having anomalous theories may be less so -W]

By James B. Shearer (not verified) on 05 Mar 2006 #permalink

speaking of paradigm shifts, I notice that stoat has been conspicuously silent about the recent NAS hearings...

clearly, there won't be any paradigm shifts coming. What is your view on MBH'98, william ? Unimpeachable ?
per :)

[If you have a link to the NAS hearings, do post it. I haven't heard anything yet -W]

Actually, there is a whole set of stuff from astronomy that is awaiting a good physics explanation. For instance, we don't know what makes up most of the matter in the universe, except that it isn't likely to be like the stuff we're familiar with, and that we know it only by its gravitational effects. However, this observational guidance is not sufficient to lead us to the new and better theory.

[True. But thats not incompatibale with any theories, just a bit puzzling - W]

In zeroth order quantum mechanics is a non-local theory in which information can be instantaneously transmitted, this is not compatible with relativity which limits information transmission to the speed of light. Experimentally this has been tested by a series of experiments (often called Aspect experiments because the first good ones were done by Alan Aspect). Theoretically this was first pointed out by Einstein in his EPR paper, and developed by John Bell. (You can wiki this using "EPR")

String theory, and the standard model before it are attempts to understand the structure of matter (e.g. the universe) as a unified thing from basic principles. Unfortunately, the fleas have fleas to bite 'em--. And so on ad infinitum,. which in the case of string theory is currently ~ 10^500 possible fleas.

Well I think it is pretty obvious where you go next, you look for a theory which has GR as one limit case and QM as another limit case. You can also look for feasible experiments for which GR and QM make different predictions. Most anomalous experiments have mundane explanations and nobody wants to waste years developing a theory to explain faulty observations. Incompatibility of GR and QM is obviously important and significant.

By James B. Shearer (not verified) on 06 Mar 2006 #permalink

Nice one.
As I mentioned in e-mail, I think a case can be made that the two conflicting theories of light in the 18th C were not observationally driven. There was a philosophical driver for both the particle and wave theories, and as I recall not really conflicting experimental evidence until turn of the 19th C, and no real resolution until early 20th C...
And then of course there's Goethe's "theory", which is not really physical, but interestingly relevant when you want to worry about psychological perception of colour and contrasts and model the biophysics.

On GR - Clark's biography of Einstein explicitly notes (p. 205) that he was conscious of the anomalous precession of Mercury, and of Hall's proposal that it could be modeled by a change in the effective potential, and he explicitly wondered if relativistic corrections to gravity would provide an explanation.
So, some observational evidence motivating the effort to derive a fully relativistic theory for gravity.