Matrix theory, M-Theory..

Matrix theory is the theory (idea) of all the different known universes coming together into one 4 dimensional world.
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M-theory
In 1995, Edward Witten started what has been called the Second Superstring Revolution by introducing M-theory to the world. This theory combines the 5 different string theories (along with a previously abandoned attempt to unify General Relativity and Quantum Mechanics called 11D-Supergravity) into one theory. What Witten actually did was to predict that the fact that all these different theories were connected was a result of there being some underlying theory to which they were all approximations of. This theory is somewhat vague in nature and has not yet been pinned down.

Additionally, it was found that the equations that required string theory to exist in 10 dimensions were actually approximations as well. The proposed M-theory would need one extra dimension and instead be a theory that takes place in 11 dimensions. Witten has himself described this idea in simple terms as the general taking position on a hill-top, the extra space-coordinate, to get a better view of the battlefield's two other dimensions.

The combination is accomplished by knitting together a web of relationships between each of the string theories called dualities (specifically, S-duality, T-duality, and U-duality). Each of these dualities provides a way of converting one of the string theories into another. T-duality is probably the most easily explained of the dualities. It has to do with the size, denoted by R, of the curled up dimensions of the string theories. It was discovered that by taking a Type IIA string theory that has a size R and changing the radius to 1/R the result will end up being what is equivalent to a Type IIB theory of size R. This duality, along with the others, creates connections between all 5 (or 6, if supergravity is counted) theories. The fact that these dualities existed had been known before Witten came up with the idea of M-theory.

Additional amusement has come for many in guessing what the M might stand for (possibilities include Matrix, Muffin, Mystery, Mother and Membrane). Regardless of what the M might possibly mean, M-theory has become one of the most interesting and active areas of research in theoretical physics today.

For a more technical explanation, see w:M-theory (simplified explanation).

quelle : wikipedia , en