  Aristotle has split physics at the sphere of the moon; above this sphere
there is no change except eternal spherical motion, below are two different
kinds of motion: Natural motion (without specific cause) and enforced motion.
In modern view motion is caused by gravity and by other forces. The split at
the sphere of the moon has been definitely overcome through the observation of
a supernova and several comets by Tycho Brahe. The second distinction was
eradicated by Isaak Newton who showed that gravitational motion was caused by a
force proportional to the inverse square of the distance. By the theory of
General Relativity, Albert Einstein showed that there is no gravitational force
but motion under gravity (i.e. Aristotles <natural motion>) is caused by the
curved geometry of spacetime. In this way, the Aristotelian distinction between
natural motion and enforced motion has come back in the form of two great
theories: General Relativity and Quantum Field Theory which are today
incompatible. To find a way out of this dilemma is the challenge of modern
physics.
