  The population dynamics underlying the diffusion of ideas hold many
qualitative similarities to those involved in the spread of infections. In
spite of much suggestive evidence this analogy is hardly ever quantified in
useful ways. The standard benefit of modeling epidemics is the ability to
estimate quantitatively population average parameters, such as interpersonal
contact rates, incubation times, duration of infectious periods, etc. In most
cases such quantities generalize naturally to the spread of ideas and provide a
simple means of quantifying sociological and behavioral patterns. Here we apply
several paradigmatic models of epidemics to empirical data on the advent and
spread of Feynman diagrams through the theoretical physics communities of the
USA, Japan, and the USSR in the period immediately after World War II. This
test case has the advantage of having been studied historically in great
detail, which allows validation of our results. We estimate the effectiveness
of adoption of the idea in the three communities and find values for parameters
reflecting both intentional social organization and long lifetimes for the
idea. These features are probably general characteristics of the spread of
ideas, but not of common epidemics.
