(May 1998)

Ajay Sathyanath

SCO, Murray Hill

- Back Ground Information
- Theory
- Other Sources of Information
- The Official String Theory Web Site
- String Theory and the Unification of Forces
- General relativity: a very weird world

The two main theories that have dominated theoretical physics this century are quantum theory and general relativity. Quantum theory is able to describe the electromagnetic, strong nuclear and weak nuclear forces through packets of energy or quanta. General relativity is able to describe gravity, with the basis of the warping of space-time. However, the two theories are incompatible. Gravity will not unite with any of the other forces.

This is where superstrings come in. In string theory, all the four forces are united into a single theory. Of course, this has not happened yet, as there is much work to be done. Some physicists predict another "superstring revolution", a revolution that will fully unite the four forces into a Theory of Everything.

One problem with string theory is that it only works in ten or twenty-six dimensions. This is because if there are any other number of dimensions, mathematical anomalies appear. The question then has to be asked, where are the other six dimensions? In normal life there are only four. However, the Kaluza-Klein Theory shows that it is possible for a dimension to be "curled" up into an extremely tiny ball (10-31 cm long), which we could obviously not detect. In string theory, this is what has happened to the other six dimensions. It is theorised that they curled up just after the Big Bang. It is possible that if some variables in the Big Bang were different to what they turned out to be, some or all of these extra dimensions would have expanded. What would such a universe look like? Obviously, our 4-dimensional perceptions cannot imagine what it would be like, but the possibility of it happening remains.

String theory states that the electroweak and strong forces have the same strength at an energy of 1016GeV, and that gravity as well will have the same strength at 1019GeV. If all the forces have the same strength, an equation can be written to describe them. (At least, that's the theory.) At this stage, no-one knows what will happen if a particle accelerator could produce the required energies. We are certainly going to have to wait a while for the results, as the US Congress has blocked moves to build an accelerator powerful enough.

Originally there were five separate string theories, each one of them working in different situations. These, in 1994, were unified into a single "M-theory". M-theory may only holds true in eleven dimensions, which is different from the original ten.

The theory has not been fully fleshed out. There are many advancements still to make. It may be that and "F-Theory" (F for father) will emerge, a string theory that involves strings being present in either ten, eleven or twelve dimensions. We are still far from the utimate Theory of Everything.

- The Official String Theory Web Site.
- String Theory and the Unification of Forces.
- General relativity: a very weird world