A Medieval Multiverse: Mathematical Modelling of the 13th Century
  Universe of Robert Grosseteste
  In his treatise on light, written in about 1225, Robert Grosseteste describes
a cosmological model in which the Universe is created in a big-bang like
explosion and subsequent condensation. He postulates that the fundamental
coupling of light and matter gives rises to the material body of the entire
cosmos. Expansion is arrested when matter reaches a minimum density and
subsequent emission of light from the outer region leads to compression and
rarefaction of the inner bodily mass so as to create nine celestial spheres,
with an imperfect residual core. In this paper we reformulate the Latin
description in terms of a modern mathematical model. The equations which
describe the coupling of light and matter are solved numerically, subject to
initial conditions and critical criteria consistent with the text. Formation of
a universe with a non-infinite number of perfected spheres is extremely
sensitive to the initial conditions, the intensity of the light and the
transparency of these spheres. In this "medieval multiverse", only a small
range of opacity and initial density profiles lead to a stable universe with
nine perfected spheres. As in current cosmological thinking, the existence of
Grosseteste's universe relies on a very special combination of fundamental
parameters.
