In the last few
years, physicists have learned that the different string theories discovered
and studied in different ways are limiting cases of a single, more powerful
theory, known as M theory. "M" stands for magic, mystery, or
matrix, according to taste. Some of these developments will be explained in
this lecture.

Edward Witten, professor
of physics at the Institute for Advanced Study in Princeton, N.J., is
arguably the premier theoretical physicist of our time. Renowned for his
many contributions to particle physics and string theory, Witten has almost
single-handedly constructed a new branch of mathematical physics For his
achievements, he has been awarded mathematics' highest prize, the 1990
Fields Medal. A member of the National Academy of Sciences, he is a
recipient of a MacArthur Prize, the Dirac Medal, and many other honors.

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