There’s a new philosophy of science book out, Richard Dawid’s String Theory and the Scientific Method (available online here if your institution is paying Cambridge University Press appropriately or if you have a credit card). It comes with endorsements from string theorists David Gross and John Schwarz, with Schwarz writing:
Richard Dawid argues that string theory plays a novel role in the scientific process that has been neglected by philosophers of science. I believe that this book is a valuable contribution to the philosophy of science, which should interest practicing scientists as well as those who are more interested in the methodology of science.
Dawid is a particle theorist turned philosopher, and as you might guess from the endorsement, he approaches string theory from an enthusiast’s point of view. The fundamental question addressed is how one can reconcile string theory’s failure in terms of conventional methodology of science with its continuing hold on at least part of the physics community. He explains how the book came about as follows:
This book has been on my mind ever since I left physics and turned to philosophy in the year 2000. A core motivation for making that step at the time was my feeling that something philosophically interesting was going on in fundamental physics but remained largely unappreciated by the world outside the departments of theoretical physics – and underappreciated even within. Twelve years of grappling with the specification of that general idea have considerably changed my perspective on the issue but left the overall idea intact. This book is the attempt to present it in a coherent form.
Reading the book in an odd way reminded me of my recent experience reading Gordon Kane’s reissued book on supersymmetry and string theory written in 2000, especially Witten’s essentially unchanged introduction. The degree of self-confidence of string theorists at that time was much different than now: AdS/CFT was a new idea, with a solution to QCD on its way, SUSY a sure thing at the LHC if not at the Tevatron or LEP, and at least half of the new jobs in the field going to string theorists. No landscape or multiverse pseudo-science was around to sow dissension in the ranks. No failure of SUSY to show up anywhere. No discouraging numbers like those for the last two years which show, in the US at least, 9% of jobs going to string theorists, with more jobs going to lattice gauge theorists in 2011 than to string theorists. And of course, a uniformly positive press, with no naysayers like Smolin and Woit causing trouble.
In Dawid’s description, string theorists are still partying like it’s 1999:
String theory has attained a pivotal role in fundamental physics and has been treated as a well-established and authoritative theory for quite some time by the community of string theorists and by physicists in related fields. As we have described above, large parts of fundamental physics are influenced by string theoretical analysis. The string community is one of the largest communities in all of theoretical physics and for many years has produced the majority of the field’s top-cited papers. Moreover, many string theorists express a remarkably strong trust in their theory’s viability.
For the actual list of last year’s top-cited papers in HEP, see here, and “remarkably strong trust in their theory’s viability” seems to me more 2000 than 2013. He does go on to mention skeptics, but to him a majority of the field is behind string theory, with the skeptics only coming from outside particle theory:
On one side of the divide stand most of those physicists who work on string physics and in fields like inflationary cosmology or high energy particle physics model building, which are strongly influenced by string physics. That group represents a slight majority of physicists in theoretical high energy physics today. Based on an internal assessment of string theory and the history of its development, they are convinced that string theory constitutes a crucial step towards a better and more genuine understanding of the world we observe. On the other side stand many theoretical physicists of other fields, most experimental physicists and most philosophers of physics. They consider string theory a vastly overrated speculation.
Dawid’s main thesis is that string theory critics fail to recognize that a new paradigm of scientific methodology is now needed:
String theory thus should not be taken to announce an end of science but rather to represent a new phase of scientific progress. In this new phase, progress in fundamental physics is no longer carried by a sequence of limited, internally fully developed theories, but rather by the discovery of new aspects of one overall theoretical scheme whose general
characteristics identify it as a candidate for a final theory, yet whose enormous complexity bars any hope of a full understanding in the foreseeable future.
What is the reason you should accept this final theory that no one can understand? Obviously the lack of any empirical support is a problem, so Dawid turns his attention to a detailed study of the subject of “non-empirical theory assessment”: how do you assess scientific progress absent connection to experiment? This is a real and serious problem, which Dawid studies in detail, although from a point of view which just naively accepts all arguments made by string theorists. He considers three main reasons for studying a theory with no empirical support:
- The No Alternatives Argument. This is the best argument for string theory: there aren’t a lot of viable unified theories out there. Of course, the way science progresses is that there always are unsuccessful ideas with no good alternatives, until the day someone come up with a better idea.
- The Unexpected Explanatory Coherence Argument. This is the idea that if a theory holds together better after you start studying it and understand it better, that’s a good thing. Dawid repeats uncritically claims of some string theorists that this is the case for string theory. I think you could make an equally good case for string theory unification becoming a more and more dubious idea as it became better understood (see, the Landscape).
- The Meta-Inductive Argument. Here the idea is that if a theoretical research program worked before, so will a similar later one. Dawid claims that the string theory research program is just like the research program that led to the Standard Model:
Given the entirely theoretical motives for its creation, the lack of satisfactory alternatives and the emergence of unexpected explanatory inter-connections, the standard model can be called a direct precursor of string theory.
Honestly, this I just find bizarre, and have no idea what he’s talking about, with the history of the Standard Model and the history of string theory two radically different subjects.
In one crucial respect, this book is very different though than Kane’s. Kane is well aware that the idea of an inherently experimentally untestable theory is something he can’t sell to his colleagues and the public, so he devotes his book and its argument for string theory to supposed experimental tests. More savvy string theorists than Kane though are seeing the writing on the wall: no SUSY at 8 TeV means almost surely no SUSY at 13 TeV, and thus no prospects for experimental evidence for SUSY during any of our lifetimes. To prop up the string theory unification program past SUSY null results from the 13 TeV LHC in 2016 is going to require relying on Dawid’s “non-empirical theory assessment” and convincing people that string theory and the multiverse represent a new paradigm for how to pursue fundamental science. This book will be welcomed by those pursuing such a goal.
Update: For a different take on the book you can see Lubos Motl’s review (as you might expect, he’s a big fan). The case of the most prominent string theorist blogger reminds me of one of the funnier things in the Dawid book that I forgot to mention, this footnote:
It should be emphasized that physicists on both sides of the divide are aware of the slightly precarious character of the “non-physical” arguments deployed in the debate. Lee Smolin has applied the concept of groupthink to the community of string physicists (which, incidentally, seems a quite accurate representation of what many critics of string physics do think about string physicists) but is careful not to present it as a core argument. String theorists, when entering a discussion with their critics (see e.g. Polchinski in his reasoning against Smolin), try to keep the debate at an entirely physical level.