| Apart from two books devoted to his autobiography,
two short stories and a novel, Norbert Wiener's works concern mainly
logic and mathematics, cybernetics, mathematical physics and philosophical
issues.
His papers on logic, written mainly at the beginning
of his career, show a philosophical interest in mathematical thinking
and its possible limitations. His contributions to mathematics and
probability theory started in the early twenties with a mathematical
modelling of Brownian motion introducing what was later to be called
Wiener Measure. It gave rise to his concept of "differential space",
which is akin to Banach space. These researches culminated in 1930
with his "generalized harmonic analysis" which allows the Fourier
transform to be used for a large class of very irregular functions
(of which periodic and almost periodic functions are special cases),
also introducing their "covariance function" and "spectral distribution.
He was inspired in that field both by J.Willard Gibbs as regards
statistical physics, and by Henri Lebesgue, who propounded a famous
generalization of the notion of integral. In a way, generalized
harmonic analysis introduced what Wiener later (1938) called "homogeneous
chaos", a notion not so far removed from what Jean Bass presented
as "pseudo-aleatory functions" (1974, 1984).
The idea of "cybernetics" came to Wiener at the
beginning of the forties, prompted by his work on anti-aircraft
defence and by contacts with colleagues in Mexico ("Behavior, purpose
and teleology" with A. Rosenblueth and J. Bigelow, Philos.Sci 1943).
lt was made known to the world by the book Cybernetics or Control
and Communication in the Animal and the Machine, published in l948
after contacts in l946 with M. Freymann of Hermann et Cie (Paris).
Coined from the Greek "kubernetike" (the art of the steersman),
cybernetics involves the theory of regulation and of signal transmission
applied to technical devices, living beings and even societies.
It may also concern the art of government, or "cybernetique" as
Ampere conceived it in 1843, which Plato, using the already existent
Greek word, compared to that of the captain of a ship. Two main
ideas play a part in cybernetics: negative feedback with its stabilizing
properties, and transmission of information, which helps to make
a whole of the many parts of a complex system, whether living or
not. The metaphor of the computer, with the role of Boolean logic,
is also present in cybernetics. It is of interest to note that Wiener,
remembering Leibniz's "calculus ratiocinator" and his construction,
after Pascal, of a mechanical computer, considered him a patron
saint of cybernetics, whereas Warren S. McCulloch favoured Descartes.
Research into the transmission of information
is greatly indebted, as Wiener emphasized, to Claude E. Shannon's
information theory (1948,1949), introducing the concept of quantity
of information which involves a degree of formalism close to that
of entropy in statistical mechanics. It is also linked to the theory
of signal transmission in the presence of a perturbative noise,
as developed by Wiener in 1942 in a classified monograph (nicknamed
"the yellow peril" because of the color of the cover and the difficulty
of the subject) and then in Extrapolation, Interpolation and Smoothing
of Stationary Time Series with Engineering Applications (1949).
In this book Wiener applies generalized harmonic analysis to stationary
aleatory signals and solves the problem of optimal elimination of
the perturbative noise and of optimal prediction of the signal itself,
with the help of a filtering operator. Quite independently, A.N.
Kolmogoroff had announced results in the same domain at a time (1941)
when scientific communications were interrupted. Improvements regarding
prediction were published by Wiener in collaboration with Pier Masani
in 1959.
Norbert Wiener was also deeply attracted to mathematical
physics. His interest originated in a collaboration with Max Born
in 1926 on quantization and developed (1927,1928) in the direction
of relativistic quantum theory and the use of a fifth dimension
as proposed by Kaluza and Klein. Einstein's attempt to unify gravitation
and electromagnetism also aroused his interest (1929). Later, Wiener
returned to quantum mechanics with a theory of statistical hidden
variables using his differential space and aiming at explaining
the principles of quantum measurement. These researches were published,
in collaboration with Armand Siegel, from 1953 to 1956and presented,
along with other considerations, in a posthumous book (1966).
Wiener's interests were not limited to logic,
mathematics, cybernetics or mathematical physics. He was also familiar
with all the aspects of philosophy, from epistemology and metaphysics
to morals. . With The Human Use of Human Beings (1950) he gives
a presentation of cybernetics underlining its social aspects with
some emphasis on the role of randomness and entropy. Another book,
entitled God, Golem, Inc. A Comment on Certain Points where Cybernetics
Impinges on Religion, published in the year of Wiener's death, shows,
although he was a skeptic, his interest in theology. In a very different
field, he wrote two short stories and a novel (The Tempter,1959).
Wiener also published an autobiography in two parts: Ex-Prodigy:
My Childhood and Youth (1953) and I Am a Mathematician (1956).
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