I would argue that string theory isn’t science because it can’t make predictions (I say “string theory is bobbins” as a joke 🙂

I did do a three lecture course in it years ago – I remember there are lines in spacetime that can either be closed loops or open strings, and when those lines move through spacetime they sweep out a 2d surface. You then do all of the field-theory maths on that 2-d co-ordinate system – the x,y,z,t of normal spacetime becomes a field on that 2-d “world sheet.”

What really confused me is that string theory introduces 26 space-time dimensions because the sum of all the positive integers should be -1/12 . This is not as mad as it sounds if you remove the infinities from that sum using renormalisation.

So string theory doesn’t have a lot to do with experimental particle physics right now. I’m *told* that if you supersymmeterise string theory then you get gravity, which is why people think it might be a candidate for a grand unified theory.

There was a (now not so well known) theory in the 19th century that different atoms were different types of knots. It had some nice features, but ultimately turned out to be wrong.

There some truth in James’s criticism. In principle string theory makes predictions, but most of them are extremely difficult to test. Some obvious predictions, for example that spacetime must have 10 dimensions, are clearly wrong, and therefore one needs to modify the theory to make it compatible with nature. However, it is the only even remotely feasible theory of everything we have, meaning a theory that describes all known interactions: electromagnetic, weak, strong and gravitational. Of course, that does not mean that it is true, but at least it allows us to see how that kind of unification could work.

String theory is a strange theory in many ways. It is often described as a theory of little pieces of strings, but that is actually just an approximation of the full theory, which we call M-theory. In fact, there are several different ways in which M-theory can be approximated by different types of little strings. The problem is that we don’t really know what M-theory is (and some would say we don’t even know if it exists), so we cannot actually write it down, but we know that in M-theory spacetime is 11-dimensional.

The “M” in M-theory actually originally stood for membrane, because it was thought that the full theory could be a theory of two-dimensional membranes. Now we know that that picture, too, is only an approximation of the same complete theory.

## Comments

strangenesscommented on :What about membrane theory, James? Is that any better, and how is it different to the “normal” string theory?

Arttucommented on :The “M” in M-theory actually originally stood for membrane, because it was thought that the full theory could be a theory of two-dimensional membranes. Now we know that that picture, too, is only an approximation of the same complete theory.

strangenesscommented on :A theory which we don’t even know exists? I can see why people say string theory is mad now! 😀