Okay, okay, I know it's all now called M-theory. And any number of books and blogs are out there that say it is all just bullshit. You've got Peter Woit's ongoing blog: "Not Even Wrong", and his book: "Not Even Wrong: The Failure of String Theory and the Search for Unity in Physical Law". You've got Lee Smolin and the Perimeter Institute investigating loop quantum gravity. Smolin has written a critical book as well: "The Trouble With Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next".
There is still, to this day, absolutely no empirical proof that string theory is correct, or even that it can predict anything worthwhile. The theories have produced what is known as "The Landscape", which consists of perhaps 10 to the 100th power various predicted universes 9although probably more like 10 to the 10500th power). One wag, I think one of the actual theorists, perhaps Susskind, has apocryphally been quoted that "it predicts every possible universe --- except ours".
String theory apologists, such as Brian Green, have attempted to rationalize its failures by invoking the childish excuse that "no other theory does any better", or worse, invoke the multiverse in a bit of hand-waving to suggest that it somehow all works out.
But still there is that troubling lack of empirical evidence.
Science, at this stage of the game, consists of a foundational triad. The earliest, and still best foundation, is empiricism. If your beautiful theory contradicted by ugly facts, it's bullshit. This goes all the way back to Francis Bacon, and of anything, it separates the practitioners from the cranks.
The second foundation is theoretical physics, which is where string theory resides. There have been many cases where theories derived "from pure thought" (as Albert Einstein once put it, and I had trouble understanding that remark until I realized he actually meant an argument built up as the medieval scholastics did, as in "derived logically from prior inputs"). This has, in almost cases, after the fact, been every successful at explaining mysteries. But one must always, always, resort to empiricism as a verifier.
The third, most recent, and extremely promising, foundation is the Monte Carlo simulation, first automated back in the 1940s at Los Alamos, and today, built up into impressive computational models. Again, there have been successes where the mathematical theory becomes far too complicated for a general solution. But simulation seems to help. We run into (as it turns the same or similar problem theory runs into, which is, even with a watertight logical consistency, your model is only as good as the assumptions. Or in the hep parlance of today "GIGO: Garbage In, Garbage Out".
So again, I ask, why are string theorists not considered cranks? I'm not the only one asking this question. Margaret Wertheim, in turn, has a book out called "Physics on the Fringe", which delves into the world of Outsider Science. I've not read it, but I don't think she interviewed Brian Green. She should have.
I would note the defensive comment in the American Scholar article, by one Pavel Nadolsky, who notes that:
"Many difficult calculations that particle theorists have been doing are greatly simplified by organizing them along the lines suggested by string theory. These calculations are tested experimentally at the Large Hadron Collider and Tevatron, and the experimental data agree with what the string-inspired theoretical methods predict! In this sense, some implications of string theory are experimentally testable".True enough Pavel, in the same sense that the explanation of the origin of the universe is not directly testable, one can only build up a evidentiary case for it, one that is mutually consistent. And, as such, the evidence for a Big Bang gets an A minus. One cannot say the same thing for string theory, which, particle colliders or no, still comes in at around a solid D, perhaps even a high F (if there is such as thing). You need a lot more evidence, Pavel!
Or, as Richard W Hamming once said "Many a theoretical physicist has gotten the right number with the wrong equation".