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# Matrix Theory

Matrix theory is constructed in terms of *N* "points" (called
"D0-branes"--for zero-dimensional membranes that act as Dirichlet
boundaries for strings) which live in an eleven-dimensional spacetime.
Their spatial positions are determined by the eigenvalues of
nine *N*×*N* matrices, where *N* is eventually
taken to infinity. The tenth dimension depends upon *N*, the
number of points, and the page eleventh dimension is taken to lie
on the light cone-- leaving only nine dimensions to be specified
by matrix eigenvalues. This light-cone construction has its roots
in the idea of Leonard Susskind, of Stanford University, and
Gerard 't Hooft, of the University of Utrecht, in the Netherlands,
that the three-dimensional space in which we live can be completely
described by its two-dimensional boundary. Thus, the third dimension
is not independent of the other two, and the world is, in a sense, a
hologram.