Larger matrices offered glimpses of larger windows in time. We then have to take an average over the matrices to get the physical information as to how the universe evolves in time," Nishimura explained. "What we do in this simulation is to generate hundreds or thousands of matrices, each of which describes the whole history of the universe during some finite time interval. "This was not possible with the conventional formulation of superstring theory," Nishimura wrote. Matrices, on the other hand, can be numerically simulated by supercomputers, and so the reformulation of string theory into a matrix model is enabling physicists to calculate how events would unfold at extremely high energies, such as those at the moment of the Big Bang. But the equations describing string interactions are so complicated that this method only works when all the possible interactions between strings are very weak - small perturbations rather than the high-energy collisions and compactifications that would have happened in the early universe. The usual method of doing string theory calculations is to use perturbation theory, in which all possible interactions between strings are considered together in a calculation of a single interaction. Infinitely large matrices being unwieldy, the physicists approximated the structure of the universe by working with finite matrices, the largest of which had 32 rows and 32 columns. "In the matrix model formulation for superstring theory, matrices are supposed to be the fundamental degrees of freedom, and the string picture emerges when one takes the limit of infinitely large matrix size," Nishimura wrote in an email. Nonetheless, the string theory framework is compelling because it gracefully explains most aspects of the universe that we do observe, from electromagnetism to gravity to the thermodynamics of black holes. And if it does, physicists wonder why three of those dimensions would be enormous and the other six extremely small. Like many other underlying aspects of string theory, there's no feasible experiment that could verify that these manifolds exist, and thus that the universe really does have a 9-dimensional spatial structure.
Our universe only appears to have three spatial dimensions, string theorists say, because the other six are curled up in undetectably tiny bundles called Calabi-Yau manifolds, which are a minuscule 10^-33 centimeters across. In order for the math to work, string theory requires that there be 10 dimensions: nine of space and one of time. String theory - a proposed "theory of everything" that unites quantum mechanics and general relativity together in one complete picture - models elementary particles as oscillating lines ("strings") rather than dimensionless points.
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