Three Roads To Quantum Gravity

182 THREE ROADS TO QUANTUM GRAVITY
theory could succeed that did not incorporate the deep
principle discovered by Galileo that objects fall with a
constant acceleration. They would be unconcerned with the
motion of planets, because they would see nothing to disagree
with the old and profoundly beautiful idea that planets move
in circular orbits.
Two ¯oors above them there would be a larger room where
the ellipse theorists met. They would spend their time
studying the orbits of planets, both in the real solar system
and in imagined worlds of various dimensions. For them the
key principle would be the great discovery by Kepler that
planets move on elliptical orbits. They would be quite
unconcerned with how bodies fall on Earth because they
would share the view that only in the heavens could one see
the true symmetries behind the world, uncontaminated by the
complexities of the Earth, where so many bodies pushed on
one another as they sought the centre. In any case they would
be convinced that all motion, including that on Earth, must in
the end reduce to complicated combinations of ellipses. They
would assure sceptics that it was not yet time to study such
problems, but when the time came they would have no
problem explaining falling bodies in terms of the theory of
ellipses.
Instead, they would focus their attention on the recent
discovery of D-planets, which would have been found to
follow parabolas rather than ellipses. So the de®nition of
ellipse theory would be extended to include parabolas and
other such curves such as hyperbolas. There would even be a
conjecture that all the different orbits could be uni®ed under
one common theory, called C-theory. However, there was no
agreed set of principles for C-theory, and most work on the
subject required new mathematics that most physicists could
not follow.
Meanwhile, another new form of mathematics was being
invented by a brilliant mathematician and philosopher in
Paris, Rene Descartes. He propounded a third theory, in
which planetary orbits have to do with vortices.
It is true that while Galileo and Kepler did correspond, each
seemed to show little interest in the key discoveries of the