Physicist John Baez has some interesting observations about string theorists who become defensive when their theory is questioned that’s relevant to our debate:
. . . [S]ome people have tried to refute the claim that string theory makes no testable predictions by arguing that it predicts the existence of gravity! This is better known as a “retrodiction”.
Others say that since string theory requires extra assumptions to make definite predictions about our universe, we should – instead of making some assumptions and using them to predict something – study the space of all possible extra assumptions. For example, there are lots of Calabi-Yau manifolds that could serve as the little curled-up dimensions of spacetime, and lots of ways we could stick D-branes here or there, etcetera.
This space of all possible extra assumptions is called the “Landscape”. Since it’s vaguely defined, the main things we know about it are:
a) it’s big,
b) it keeps growing as string theorists come up with new ideas,
c) nobody has yet found a point in it that matches our universe.
Despite this, or perhaps because of it, the Landscape has been the subject of many discussions. Often these devolve into arguments about the “anthropic principle”. Roughly, this says that if the universe were really different, we wouldn’t be having this argument – so it must be like it is!
One can in fact draw some conclusions from the anthropic principle. But it’s really just the low-budget limit of experimental physics. You can always get more conclusions from doing more experiments. The experiment where you just check to see if you’re alive is really cheap – but you don’t learn much from it.
(Of course I’m oversimplifying things for comic effect, but usually people take the opposite approach, overcomplicating this stuff to make it sound more profound than it is.)
Serious string theorists are mostly able to work around this tomfoolery, but it exerts a demoralizing effect. So, when Woit and Smolin came out with their books, a lot of tempers snapped, and a lot of strange arguments were applied against them.
For example, one popular argument was “Okay, buster – can you do better?” The idea here seems to be that until you know a solution to the problems faced by string theory, you shouldn’t point out these problems – at least not publicly. This goes against my experience: hard problems tend to get solved only after lots of people openly admit they exist.
Another closely related argument was “String theory is the only game in town.” Until some obviously better theory shows up, we should keep working on string theory.
It’s true there’s no obviously better theory than string theory. Loop quantum gravity, in particular, has problems that are just as serious as string theory.
But, the “only game in town” argument is still flawed.
Once I drove through Las Vegas, where there really is just one game in town: gambling. I stopped and took a look. I saw the big fancy casinos. I saw the glazed-eyed grannies feeding quarters into slot machines, hoping to strike it rich someday. It was clear: the odds were stacked against me. But, I didn’t respond by saying “Oh well – it’s the only game in town” and starting to play.
Instead, I left that town.
It’s no good to work on string theory with a glum attitude like “it’s the only game in town.” There are lots of other wonderful things for theoretical physicists to do. Things where your work has a good chance of matching experiment… or things where you take a huge risk by going out on your own and trying something new. . . .