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An Introduction to Super String Theory

(May 1998)
Ajay Sathyanath
SCO, Murray Hill


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Background on the Superstring Theory.

For many years now, scientists have tried to find a Theory of Everything - a theory that unites the four forces.
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.

String Theory

The basis of the theory is that all matter is composed of strings. The strings themselves are the smallest possible particles, with a length of 10-33 cm, and no width or height. Strings can be open or closed. Closed strings have the shape of a circle or oval, and open strings have ends. A string occupies one single point in space-time at any one time. Its path through time can be shown in a space vs time graph, and is called a worldsheet. The superstring theory can describe the three forces (electroweak, strong nuclear, and gravitational) if the tension in the string is 1039 tons. The predictions of this theory are identical to general relativity in most cases. However, at a distance of 10-33cm (the quantum level), the two theories differ.

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.

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