If you want to get an understanding of the ideology that many string theorists subscribe to, you should check out Lubos Motl’s latest posting. Besides the usual dismissal of non-believers as idiots, incompetents and crackpots (an attitude that unfortunately seems to be all too common among string theorists), Lubos does actually address some scientific issues.
There’s nothing at all in what he has to say that actually makes any connection between string theory and the real world. The effort to find such a connection is completely ignored, including the work of the large part of the string theory community that continues to unsuccesfully work on this. No mention of “string phenomenology”, the landscape, or anything of this kind. He chooses instead to address scientific issues in a resolutely unscientific way, basing everything upon faith and ideology, beginning with the opening part of his argument:
I will treat the “whole Universe” and “all of string theory” as synonyma because I am not aware of any controllable framework that would allow me to separate them sharply.
Most of the rest of the posting is a series of criticisms of other ideas that people have advanced as alternatives to string theory. At one, point, after criticizing John Baez and Urs Schreiber for their interest in 2-groups and gerbes, he makes clear what he sees as the proper way to approach new ideas about fundamental physics that one is not familiar with:
The previous paragraph also clarifies my style of reading these papers. The abstract has so far been always enough to see that these fundamental gerbes papers make no quantitative comparison with the known physics – i.e. physics of string theory – and for me, it is enough to be 99.99% certain (I apologize for this Bayesian number whose precise value has no physical meaning) that the paper won’t contain new interesting physics insights.
This attitude makes life very simple. You don’t have to bother doing the hard work of trying to understand what non-string theorists are doing. All you need to do is to read the abstracts of their papers, note that they aren’t doing string theory, and then you can be sure you don’t need to read any farther, because if it isn’t string theory, it can’t provide any interesting new insights into physics.
Lubos dismisses various ideas about string theory one after the other. Much of this is devoted to dismissing the idea that has led particle physics to many of it’s biggest successes: that of looking for new symmetries or new ways of exploiting ones that are already known. He insists that:
we have learned that the gauge symmetries are not fundamental in physics.
with the idea being that because of dualities, the character of gauge symmetries is not fundamental but what he calls “social scientific”. This argument doesn’t make any sense to me. An equivalence of two different gauge theories is very interesting, but it in no way tells you that gauge symmetry is not fundamental. Making such an argument is like arguing that representations of Galois groups in number theory are not fundamentally important because of Langlands duality.
More seriously, Lubos does mention the philosophically trickiest aspect of gauge theories: the physical degrees of freedom are not parametrized explicitly, but as quotients by the gauge group action of a larger space of degrees of freedom. It’s certainly true that this is how gauge theory works, and one can try and argue that one should just ignore gauge symmetry and work directly with gauge invariant degrees of freedom. In terms of representation theory, physical states are gauge-invariant ones, so one could hope to just work with these physical states. The problem is that in most interesting cases this isn’t possible. The space of connections modulo gauge transformations is non-linear and in general can’t be parametrized in a useful way. Working with the linear space of connections, which can be easily parametrized and understood, and then taking into account the action of the gauge group, is the method that actually works and has been hugely successful. All experience shows that fundamental theories are best understood using an extended space of states, together with a method for picking out the physical subspace.
After dismissing alternatives to string theory, Lubos finally gets around to explaining what he sees as the fundamental principle of string theory. Amazingly, it’s the bootstrap philosophy, the failed idea that guided much of particle theory during the sixties and early seventies, before the advent of gauge theories and the standard model. The bootstrap philosophy is that symmetries are nothing fundamental, what is really fundamental are certain kinds of consistency conditions. All you need to do is impose these consistency conditions, and miraculously a unique solution will appear, one which describes the real world. In the sixties the hope was that the strong interactions could be understood simply by imposing things like unitarity and analyticity conditions, and that this would lead to a unique solution of the problem. It turned out that this can’t work. While unitarity and analyticity properties are very useful and tell you a lot about the implications of a theory, they in no way pick out any particular theory. There are lots and lots (a whole landscape of them, even) of QFTs that satisfy the consistency conditions. There never was evidence for uniqueness, and the bootstrap philosophy was from the beginning built on a pipe dream and large helpings of wishful thinking.
The new version of the bootstrap that Lubos wants to promote goes as follows:
In the context of quantum gravity, many of us more or less secretly believe another version of the bootstrap. I think that most of the real big shots in string theory are convinced that all of string theory is exactly the same thing as all consistent backgrounds of quantum gravity. By a consistent quantum theory of gravity, we mean e.g. a unitary S-matrix with some analytical conditions implied by locality or approximate locality, with gravitons in the spectrum that reproduce low-energy semiclassical general relativity, and with black hole microstates that protect the correct high-energy behavior of the scattering that can also be derived from a semi-classical description of general relativity, especially from the black hole physics.
So, the idea is that, at its most fundamental level, physics does not involve simple laws or symmetry principles, just some consistency conditions (of a much more obscure kind than the analyticity ones of the original bootstrap). Lubos avoids the crucial question of how big the space of solutions to these consistency conditions is. All the evidence so far is that it is so large that one can’t hope to ever get any predictions about physics out of it, and the string theory community is now divided between those who hope this problem will magically go away, and those who want to give up and stop doing science as it has traditionally been understood.
In 1973 the theory of strong interactions was heavily dominated by string theory and the bootstrap philosophy. The willingness of Veltman and ‘t Hooft to do the hard work of understanding how to properly quantize and renormalize non-abelian gauge theories ultimately led to asymptotic freedom and QCD. This pulled the plug conclusively on that era’s version of the bootstrap. Perhaps sometime in the future, new hard work on gauge theories will lead to insights that will pull the plug on this latest version, which thrives despite conclusive failure due to the kind of unscientific ideological fervor that Lubos so perfectly embodies.