Tuesday, January 18, 2005

String theory quotes

I'm on record as not being a fan of string theory. My objection is not that it is necessarily wrong, but that we probably won't know one way or another for a very long time.

Recently I've been looking at the blog of Peter Woit, a Columbia math professor who was originally trained as a particle theorist, and a very outspoken critic of string theory. Try his Jan. 11, 2005 post (for some reason the trackback URL doesn't work) for some juicy comments on the current state of string theory. In the interest of fairness, you can also have a look at the blogs of string theorists Lubos Motl or Jacques Distler.

I thought I would list, just for fun, some comments by famous physicists about string theory (all are Nobelists except Woit :-):

Woit: "... string theory ... has given up any claims to being a legitimate science and has taken on the characteristics of a cult. ...I just can't believe the way essentially the entire particle theory establishment, including many people I have the highest respect for, continue to allow this situation to go on without public comment. ..."

Richard Feynman: in Davies and Brown, Superstrings, Cambridge 1988, pp. 194-195:"... I do feel strongly that this is nonsense! ...I think all this superstring stuff is crazy and is in the wrong direction. ... I don't like it that they're not calculating anything. ...why are the masses of the various particles such as quarks what they are? All these numbers ... have no explanations in these string theories - absolutely none! ... "

Sheldon Glashow: "... superstring theory ... is, so far as I can see, totally divorced from experiment or observation. ...string theorists ... will say, "We predicted the existence of gravity." Well, I knew a lot about gravity before there were any string theorists, so I don't take that as a prediction. ... there ain't no experiment that could be done nor is there any observation that could be made that would say, "You guys are wrong." The theory is safe, permanently safe. I ask you, is that a theory of physics or a philosophy? ..."

Phil Anderson:"Is string theory a futile exercise as physics, as I believe it to be? It is an interesting mathematical specialty and has produced and will produce mathematics useful in other contexts, but it seems no more vital as mathematics than other areas of very abstract or specialized math, and doesn't on that basis justify the incredible amount of effort expended on it.

My belief is based on the fact that string theory is the first science in hundreds of years to be pursued in pre-Baconian fashion, without any adequate experimental guidance. It proposes that Nature is the way we would like it to be rather than the way we see it to be; and it is improbable that Nature thinks the same way we do."


Anonymous said...

I agree with your view.

The "positive" aspects of string theory approach:

* One should explore all options. Well, for the recent landscape business, maybe at least testable, though, of course, it will not rule out string theory.
* String theory is useful for those with paticle physics background to pick up good mathematics.

Some other comments (my particle physics is rusty):

* I think the "Theory of Everything" mindset in particle physics started with Grand Unified Theories. Granted, unlike string theory it is testable (proton decay) and falsifiable (original Georgi-Glashow SU(5) dead?). But it had the audacity to relate physics several orders of magintude (10^{17} GeV to 10^3 GeV). Of course, the incredible success of standard models did not help.

* I do not see any way string theory in any more "unique" than QFT. For instance, with the intersecting brane models, pretty much any QFT gauge group and fermion content can be achieved. So where is the uniqueness? The proponents claim UV completion is the big difference. Maybe (I am not sure), but it is no guide to particle physics model building.

* Also, the large order of magnitude makes it unlikely string theory, even if correct, can ever be definitive. The standard model details are irrelavant for condensed matter physics (except for general properties like charge conservatiuon from U(1) gauge invariance). Would it make any difference if QCD gauge group was SU(5) (with AF fermion content)?

The best I can think of is nuclear physics-QCD relationship: meson properties follow from simple approximate flavour symmetry of QCD. And success of the large N approximation probably means that effective physics insensitive to details like gauge group...

So I remain unconvinced. And 20+ years of work has not yielded much for particle theory. The bottom line is that flavour problem is hard, as evidenced by tight constraints from precision electroweak measurements.

The fun hopefully begins in 2008!


Anonymous said...

This is fun; as was the PBS series on string theory. Think on :)


Steve Hsu said...

We are living through a very bad time in particle theory. Without significant experimental guidance all we are left with is speculation and social dynamics driving the field. I hope things will get better when LHC data starts coming in - at least, most of the models currrently under consideration will be ruled out (although, of course, not string theory :-)

I will probably write a post at some point about how scientific fields which run through fallow experimental periods longer than 20 years (the length of a person's academic career) are in danger of falling into the traps which beset the humanities and social sciences. These were all discussed by Bordieu long ago.

Steve Hsu said...

Oops - Bourdieu not Bordieu!

Anonymous said...

"I will probably write a post at some point about how scientific fields which run through fallow experimental periods longer than 20 years (the length of a person's academic career) are in danger of falling into the traps which beset the humanities and social sciences."

This will be welcome, but why include the humanities? Is there a theory of painting or poetry that you have in mind, or are you thinking of history in the humanities? Is there a theory of history, other than Tolstoy's theory that history is our collective individual histories, which means that history is always anecdotal? Intertesting. Write away.


Calculated Risk said...

Steve - great site. I've always felt that string theory fails the Karl Popper test of falsifiability ... at least so far. And the common mantra, "String theory predicts gravity", is for obvious reasons not very satisfying. I'm glad to see that FAR more qualified individuals (than me) hold that same view.

Carson C. Chow said...

Hi Steve,

For us low energy folks, it doesn't matter if it's strings or branes or any high energy theory. I don't commpletely discount its importance but "The theory of everything" may not be able to explain everything. In a shameless promotion of my new blog on the block - sciencehouse.blogspot.com, I just posted an entry on this topic.


Anonymous said...

When you think about it, the arguments string theorists have in favor of string theory boil down to

1. It's like really beautiful and elegant.

2. We've tried really hard, but we just can't think of anything else it could be.

Now that's a pretty open and shut case. I mean historically, when the preeminent scientists of the day had an (to their eyes) elegant theory, and there were no compelling alternatives, have they ever been wrong?

Anonymous said...

have any of you idiots heard of a particle accelerator? string theorists are getting close to discovering super symmetry of sparticles and the disappearance of a graviton from one universe to another parrellel one right on the other side of a brane. so how are these two close to being proven evidences any less scientific than your views, and god, alot of you believe in god but the very mention is nonsense. if the universe is expo-infinite as well as into-infinite than god is impossible.

Anonymous said...

AND i would like to add a quote

I wouldn't have thought that a wrong theory should lead us to understand better the ordinary quantum field theories or to have new insights about the quantum states of black holes.

qoute by Ed Witten who made M-theory

Anonymous said...

Try this way of differentiating intellectual activity: All human ideas are supernatural until proven to describe physical reality. Some content is permanently supernatural (gods, philosophy, politics); other ideas must wait for experimental proof; other ideas remain supernatural due to our inability to accept them (sun centered planetary system). Others, like evolution, are accepted as proven by most people, but remain heresy to supernaturally-minded people who find it impossible to believe in reality, even when confronted with evidence. String Theory (why theory - isn't it a hypotheses?) needs to be classified as supernatural like every other idea that has yet to be proven to describe physical reality: to deny that evidence is necessary to the description of nature/reality is supernatural thought, so retreating to the cover of philosophical argument is not valid. "Show me the evidence," applies to the world of "strings" as it does to all of our ideas. (I am using the standard defintions of natural / supernatural, but would qualify supernatural as a product of the human brain.)

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