The present work is the first volume of a substantially enlarged version
of the mimeographed notes of a course of lectures first given by me in
the Indian Statistical Institute, Calcutta, India, during 1964-65. When
it was suggested that these lectures be developed into a book, I readily
agreed and took the opportunity to extend the scope of the material
covered. No background in physics is in principle necessary for
understand- ing the essential ideas in this work. However, a high degree
of mathematical maturity is certainly indispensable. It is safe to say
that I aim at an audience composed of professional mathematicians,
advanced graduate students, and, hopefully, the rapidly increasing group
of mathematical physicists who are attracted to fundamental mathematical
questions. Over the years, the mathematics of quantum theory has become
more abstract and, consequently, simpler. Hilbert spaces have been used
from the very beginning and, after Weyl and Wigner, group
representations have come in conclusively. Recent discoveries seem to
indicate that the role of group representations is destined for further
expansion, not to speak of the impact of the theory of several complex
variables and function-space analysis. But all of this pertains to the
world of interacting subatomic particles; the more modest view of the
microscopic world presented in this book requires somewhat less. The
reader with a knowledge of abstract integration, Hilbert space theory,
and topological groups will find the going easy.