Friday, April 20, 2007

Why I stopped worrying and learned to love string theory

I learned about superstrings when I was 12. But it was in university that I first started to really learn about what they were and the mathematics behind them. The phrase that came to mind was EPICYCLES (see above). It could be a natural bias of mine but I wouldn't characterize string theory as elegant. Aside from the fact that dimensions spring out of the theory like grasshoppers out of an open box and that the theory predicts an inordinately high number of possible universes and that just about nothing in string theory is testable, it lacks any sort of unified set of principles. It still treats space-time as a stage where strings are the actors. Fast forward to today.
String theory has become M theory and the lack of testability is beginning to worry some physicists (and the fact that all the best talent is being sucked up by this monster). Two good books address this Lee Smolin's The Trouble with Physics and Peter Woit's Not Even Wrong. And some recent developments such as the accelerating universe seem to cause problems for string theory. Of course anything can be explained by string theory, just as the positions of the planets could be explained by epicycles if you added enough epicycles.
So what are the alternatives to string theory? Well there are a few:
  • Abhay Ashtekar's and Lee Smolin's Loop Quantum Gravity which quantizes space-time and worries about unification later (makes sense as one of the biggest problems is that gravity and quantum theory are incompatible).
  • Then there is Alain Connes's noncommutative geometry which looks at a geometry linked to the noncommutativity of quantum phase space (position and momentum). Unlike ordinary numbers where 2x3=6=3x2, certain operations are noncommutative (ex. moving on the surface of Earth - if you start on the equator and move 200km north and 200km west, this will put you in a different position on earth then first travelling 200km west and then 200km north).
  • Twistor String theory, which is based on Roger Penrose's Twistor Theory, which relates real 4 dimensional Minkowsky space to 4 dimensional complex space.
I suspect that all of the theories (including M)are orbiting some common theory that they don't see yet. There are some striking similarities sometimes in the mathematics of the theories that suggest this is the case. Problem is that M Theory is getting all the limelight and funding to the detriment of the other theories and to science.

But I do like string theory and it is mathematically quite splendid.

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