posted on Jun, 25 2013 @ 02:40 AM
Originally posted by Phage
reply to post by Moduli
Is string theory actually a theory? My impression is that it is more of a math construct.
Does it make testable predictions? Have any of those predictions been demonstrated?
It's a theory as much as anything else in physics is. And it makes plenty of predictions--you can't be physics without making predictions! And,
necessarily, any prediction must be testable, otherwise it's not a prediction!
The difficulty with string theory is that it is capable of making way too many predictions, and it's not always clear what the right way to set up a
problem is. But that's not a problem with the theory, that's a problem with us being too inexperienced at it. But complaining about that is kind of
like complaining that programming is hard, because you can write any possible program, when you really only want to write the one program you're
Of course, any good theory must make lots of predictions. For example, when Newtonian mechanics was written down, it was criticized for being hard to
make predictions with. How are you supposed to know in advance what all the forces acting on something are! It's very hard to deduce the equations of
motion that describe something without understanding how to set problems up in general. Now-a-days, we can do that for Mechanics, but outside of a few
special cases, we don't know how for string theory.
But it's easy enough to make general predictions with it. For example, the mass of the recently detected Higgs is in the range that many string
theory models predict. It makes general predictions about things like supersymmetry, and the relationships between normal standard model particles,
such as masses, CKM matrix elements, etc. Although it's still not known which model exactly corresponds to the Standard Model.
There are other predictions it makes outside of Standard Model like things. Gauge/Gravity duality is an obvious one, where a particular string theory
can be shown to be exactly equivalent to an ordinary quantum field theory that at first sight looks very different, and lives in one fewer dimension.
This is particularly interesting because some of these theories look just like the ones that condensed matter physicists study. So it's possible
there could be applications of string theory in things like solid state devices in the next 5 or 10 years.