Stoic physics is the
natural philosophy adopted by the
Stoic philosophers of
ancient Greece and
Rome used to explain the natural processes at work in the
universe. To the Stoics the universe is a single
pantheistic God, but one which is also a
material substance. The primitive substance of the universe is a divine essence (
pneuma) which is the basis of everything which exists. The separation of
force from
matter produces a divine fire (
aether) which, as the basis of all matter, is differentiated into elements and shaped by the tension caused by the
pneuma working according to the divine reason (
logos) of the universe. These processes are responsible for the formation, the development, and ultimately, the destruction of the universe in a never-ending cycle (
palingenesis). The human
soul is an emanation from the fiery
aether which permeates the universe, and sensation is transmission of
pneuma-currents from objects, which interact with the substance of the
mind, which is the soul's ruling part. The Stoics also recognised the existence of other gods and divine agents as manifestations of the one primitive God-substance.