Tuesday, May 2, 2017

Why String Theory Is Still Not Even Wrong

At its best, physics is the most potent and precise of all scientific fields, and yet it surpasses even psychology in its capacity for bullshit. To keep physics honest, we need watchdogs like Peter Woit. He is renowned for asserting that string theory, which for decades has been the leading candidate for a unified theory of physics, is so flawed that it is “not even wrong.” That phrase (credited to Wolfgang Pauli) is the title of Woit’s widely discussed 2006 book (see my review here) and of his popular blog, which he launched in 2004. Woit, who has degrees in physics from Harvard and Princeton and has taught mathematics at Columbia since 1989, tracks mathematics as well as physics on his blog, and some of his riffs (like a recent one on the difference between Lie groups and Lie algebras) are strictly for experts. But he provides plenty of clear, non-technical explanations for non-experts like me. Woit, whom I’ve known for more than a dozen years, is a good guy. He can be blunt, but he is always fair, and he does not indulge in cheap shots, snark or grandstanding. The next time the media tout an alleged breakthrough in physics or mathematics, check out Not Even Wrong to get the real scoop. Woit and I recently had the following email exchange. —John Horgan (...)

Horgan: You've recently denounced “fake physics.” What is it? Are journalists mostly to blame for it?

Woit: By "fake physics" I mean pseudo-scientific claims about physics that share some of the characteristics of "fake news", in particular misleading, overhyped stories about fundamental physics promoting empty or unsuccessful theoretical ideas, with a clickbait headline. Those most to blame for this are the physicists involved, who should know better and be aware that the way they are promoting their work is going to mislead people. Journalists need to be skeptical about what they're being told by scientists, but often they're more or less accurately reporting impressive sounding claims being made by physicists with impeccable credentials, and not in a good position to evaluate these.

Horgan: Do you still think string theory is “not even wrong”?

Woit: Yes. My book on the subject was written in 2003-4 and I think that its point of view about string theory has been vindicated by what has happened since then. Experimental results from the Large Hadron Collider show no evidence of the extra dimensions or supersymmetry that string theorists had argued for as "predictions" of string theory. The internal problems of the theory are even more serious after another decade of research. These include the complexity, ugliness and lack of explanatory power of models designed to connect string theory with known phenomena, as well as the continuing failure to come up with a consistent formulation of the theory.

Horgan: Why do you think Edward Witten told me in 2014 that string theory is “on the right track”?

Woit: I think the conjectural picture of how string theory would unite gravity and the standard model that Witten came up with in 1984-5 (in collaboration with others) had a huge influence on him, and he's reluctant to accept the idea that the models developed back then were a red herring. Like many prominent string theorists, for a long time now he no longer actively has worked on such models but, absent a convincing alternative, he is unlikely to give up on the hope that the vision of this period points the way forward, even as progress has stalled.

Horgan: Are multiverse theories not even wrong?

Woit: Yes, but that's not the main problem with them. Many ideas that are "not even wrong", in the sense of having no way to test them, can still be fruitful, for instance by opening up avenues of investigation that will lead to something conventionally testable. Most good ideas start off "not even wrong", with their implications too poorly understood to know where they will lead. The problem with such things as string-theory multiverse theories is that "the multiverse did it" is not just untestable, but an excuse for failure. Instead of opening up scientific progress in a new direction, such theories are designed to shut down scientific progress by justifying a failed research program.

Horgan: What’s your take on the proposal of Nick Bostrom and others that we are living in a simulation?

Woit: I like quite a bit this comment from Moshe Rozali (at URL http://www.scottaaronson.com/blog/?p=3208#comment-1733601): "As far as metaphysical speculation goes it is remarkably unromantic. I mean, your best attempt at a creation myth involves someone sitting in front of a computer running code? What else do those omnipotent gods do, eat pizza?"

Horgan: Sean Carroll has written that falsifiability is overrated as a criterion for distinguishing science from pseudo-science? Your response?

Woit: No one thinks that the subtle "demarcation problem" of deciding what is science and what isn't can simply be dealt with by invoking falsifiability. Carroll's critique of naive ideas about falsifiability should be seen in context: he's trying to justify multiverse research programs whose models fail naive criteria of direct testability (since you can't see other universes). This is however a straw man argument: the problem with such research programs isn't that of direct testability, but that there is no indirect evidence for them, nor any plausible way of getting any. Carroll and others with similar interests have a serious problem on their hands: they appear to be making empty claims and engaging in pseudo-science, with "the multiverse did it" no more of a testable explanation than "the Jolly Green Giant did it". To convince people this is science they need to start showing that such claims have non-empty testable consequences, and I don't see that happening.

Horgan: Is it possible that the whole push for unification of physics is misguided?

Woit: In principle it's of course possible that the sort of unification present in our best current theory is all there is. There are however no good arguments for why this should be, other than that it's proving hard to do better. The lesson of history is not to give up, that seemingly hard problems of this sort often find solutions. Looking in depth into the technical issues, I don't see anything inherently intractable, rather a set of puzzling problems with a lot of structure, where it looks like we're missing one or two good ideas about how things should fit together.

Horgan: Is physics in danger of ending, as Harry Cliff has warned?

Woit: One should be wary of claims about "physics" in general since it has many subfields, facing different issues. High-energy particle physics is a subfield that is in danger of ending. On the experimental front, it faces fundamental technological obstacles. Any next generation accelerator able to explore even modestly higher energies than the LHC will be far off in the future and very expensive. Whether there's the will to finance and build such a thing is now unclear. On the theoretical front, the field is now in crisis, due to the absence of experimental results that point to a better theory, as well as a refusal to abandon failed theoretical ideas.

Horgan: Is mathematics healthier than theoretical physics?

Woit: Mathematics is in a much healthier state than theoretical physics. One reason for this is that it has never been driven by experiment, so is immune to the problem of technological experimental barriers. Absent experiment to point the way forward and keep everyone honest, mathematics has developed a different culture than theoretical physics, one that emphasizes rigorous clarity about the dividing line between what one understands and what one doesn't. This clarity makes possible agreement on what is progress: that which moves the dividing line in the right direction. I believe that in its current crisis, theoretical physics could benefit a lot from behaving more like mathematicians. (I've had no luck though in getting physicists to agree with me).

by John Horgan, Scientific American |  Read more:
Image: Michael Blann/Getty