I’ve generally had a view of String Theory well-encompassed by this fabulous XKCD strip. However, Cosmic Variance has a couple of really interesting posts defending String Theory that I find, if not entirely convincing, at least intriguing enough to warrant a second thought.
Let’s start with this one, the oldest of the three articles I read there. It gives a pretty good summary of how string theory came about and why it’s the most promising theory in advanced physics right now. More importantly for me, it answers the “What does that imply?” question from XKCD:
Once you set off down this road, you are are inevitably led to a remarkably rich structure: extra dimensions, gauge theories, supersymmetry, new extended objects, dualities, holography, and who knows what else. Most impressively of all, you are led to gravity: one of the modes of a vibrating string corresponds to a massless spin-two particle, whose properties turn out to be that of a graviton. Itâ€™s really this feature that separates string theory from any other route to quantum gravity.
Hey, neat! Granted, we didn’t need string theory to infer the existence of gravity, but the interesting bit is that we can derive a string that looks exactly like a graviton from a more fundamental basis. Sean points out that most other theories for quantum gravity start with the gravity as we know it and work down from there, trying to force it to quantise. String theory, by Sean’s description, derives gravity from the bottom up, already quantised.
Ok, I’m listening. Do go on.
The next article I saw was this one. It reiterates the gravity-prediction quality above, but gives more of a historical background on how exactly string theory got to its current position of dominance. There’s not the “Oh, duh” moment of the previous one, but there’s good information for anyone interested, arguments for both pro and con, as well as links to some current (as of last summer) research.
And then there’s this more recent post, where Sean responds to a recent Bloggingheads dialogue that trashed string theory. He also brings up some points that get lost in the transition from academia to the public. The fact that scientists have vocal disagreements over theories says nothing about the theories themselves. That’s just how science works, and we shouldn’t want it any other way.
I do have to take a small exception, however. Sean mentions evolution as a response to Peter Woit’s statement that â€œthings are not looking good for a physical theory when there start being public debates on the subjectâ€. The substance of Sean’s criticism of that statement is quite correct — whether or not there’s a public debate has little to do with the scientific accuracy of a theory — but I personally wouldn’t be so quick to equate debates over string theory with debates over evolution. The fact is that string theory has not yet reached a significant level of acceptance among scientists, and is still in its infancy, whereas evolution is a theory with roots 150 years old confirmed by myriad strands of evidence that has withstood several field-shaking discoveries since its conception, including the early genetic revolution that led to the Neo-Darwinian synthesis.
String theory has yet to experience such a trial by fire, but that’s not a bad sign. Only time will tell whether it ends up like Lamarck’s theory, viewed historically as an important but ultimately incorrect first step, or like Darwin’s, a vital unifying theory that spawns hundreds of years of fruitful new research.
Either way, Sean’s arguments have convinced me that string theory probably deserves some more time to work itself out before we start passing judgement on it. Especially those of us in the general public.