In my opinion, the focal point of Lee Smolin's book comes down to this:
The issue is not whether string theory is worth doing or should be supported, but why
string theory, in spite of a dearth of experimental predictions, has monopolized the
resources available to advance fundamental physics, thus choking off the investigation
of equally promising alternative approaches.
The Trouble With Physics: The Rise of String Theory, the Fall of Science, and What Comes next
Lee Smolin, Houghton Mifflin 2006, pages 267-268.
I don't trust Smolin's judgement. For one thing, he is himself the principle author of one of the "equally promising alternative approaches" which is apparently suffering from the monopolization of resources by string theory. John Schwarz
gave a talk on string theory to the Los Angeles Astronomical Society a year or so ago, and he made the observation that "scientists vote with their feet". They work on what interests them, like anybody else, and string theory is a fascinating topic to work on for theoretical physicists.
There is another book of similar ilk by Peter Woit.
Much theoretical activity by scientists is speculative, in the sense that it consists of
asking questions of the kind, “What if I assume X is true? Could I then construct a
real theory using this assumption?” This is certainly the kind of thing that scientists
spend a lot of time doing, and one presumably doesn’t want to label it unscientific.
Superstring theory is very much a speculative endeavor of this kind. Theorists involved
in this area are considering a very speculative assumption: that one should replace the
notion of elementary particles with strings or more exotic objects, and trying to see
whether a scientific theory capable of making falsifiable predictions can be built on this
assumption. Generalizing the notion of “scientific” to include speculation of this kind
would definitely make superstring theory a science. But does one really want to say
that all such speculative activity is scientific?
Not Even Wrong: The Failure of String Theory & the Continuing Challenge to Unify the Laws of Physics
Peter Woit, Basic Books 2006, page 208
Woit concludes that the answer to the last question here is no. But I would ask instead, “But does one really want to say that any such speculative activity is science”? Replace “all” with “any”. I see no reason why speculative activity that is integral to the process of scientific discovery must necessarily be labeled unscientific.
Furthermore, both Smolin & Woit take the opinion that because the problems of string theory are not already solved now, then we should stop trying altogether. My response is to note that Isaac Newton published his theory of gravity in 1687 (Philosophiae Naturalis Principia Mathematica
), at which time he was already aware of the basic problem of general relativity, for which Albert Einstein published the (or at least a
) solution in 1915, a mere 228 years later. String theory was conceived from the dual resonance model published by Veneziano in 1968, and born in 1970 from the combined efforts of Yoichiro Nambu, Leonard Susskind & Holger Bech Neilsen (Nambu shared the 2008 Nobel Prize in Physics
, though not for string theory). So we have had about 40 years to figure out string theory, which is arguably a harder problem to solve than was general relativity. We have 188 years left, if we follow the "228 year rule", that I just made up. I have to say I am unimpressed by the observation that the problem of string theory is not yet solved.
Also, as Sol Invictus
has already noted, there are testable predictions made based on string theory, but one should also note that some of those predictions can be and in fact are being tested, even now. One prediction is the presence of spatially compact extra dimensions (covered in some detail in Elegant Universe
). Those dimensions can reveal themselves in high energy accelerator experiments if they are spatially very small, or in short range experiments on the inverse square law of gravity. Supersymmetry is a prediction of string theory, and laboratory searches for supersymmetric partners of known particles are something we can do now, even if the results may be hard to interpret.
I see no reason to think that string theory is on the way out, or anything close to that. And so I will close with an interesting quote from Stephen Weinberg ...
String theory is very demanding; few of the theorists who work on other problems have
the background to understand technical articles on string theory, and few of the string
theorists have time to keep up with anything else in physics, least of all with high energy
experiments. Some of my colleagues have reacted to this unhappy predicament with
hostility to string theory. I do not share this feeling. String theory provides our only
present source of candidates for a final theory - how could anyone expect that many of
the brightest young theorists would not work on it? It is a pity that it has not been more
successful, but string theorists like everyone else are trying to make the best in a very
difficult moment in the history of physics. We simply have to hope that string theory will
become more successful, or that new experiments will open up progress in new
Dreams of a Final Theory: The Scientists Search for the Ultimate Laws of Nature
Steven Weinberg, Pantheon Books 1992, pages 218-219