Compactifying means “curling up” extra dimensions of the theory to a very small size. ×īut compactifying this eleven-dimensional theory down to four dimensions has been challenging. Pierre / University of California at Santa Barbara Compactifying a doughnut into a circular wire. M theory lacks precise equations of motion, but in 1996, Tom Banks, of Rutgers University in Piscataway, NJ, and his colleagues proposed that M theory might be described by ” matrix theory,” whose basic variables are matrices. There is no consensus on the meaning of the “M,” but many string theorists take it to stand for “membrane,” since the theory contains vibrating surfaces of several different dimensions. Three years ago it was discovered that the five distinct types of string theory were actually different limits of “M theory,” an eleven-dimensional theory that includes supergravity. String theory posits that the world is made of incredibly small strings vibrating in a ten-dimensional spacetime. In the 6 April PRL, a team of string theorists makes a leap toward solving the compactification problem for matrix theory. Compactification also specifies most of the interesting properties of such a theory. Its proponents have struggled with the most vexing problem of all such theories: explaining exactly how the extra dimensions are “compactified” to make them unobservable in our four-dimensional world. Matrix theory, the latest formulation of string theory, has eleven spacetime dimensions. The ultimate goal of string theory is not only to unify quantum mechanics with general relativity, but also to explain the spectrum of particles and forces observed in nature. Pierre / University of California at Santa Barbara String theories as limits of M theory.
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