Epicureanism | epicurean physics
Epicurean physics held that the entire universe consisted of two things: matter and void. Matter is made up of atoms, which are tiny bodies that have only the unchanging qualities of shape, size, and weight. Atoms were felt to be unchanging because the Epicureans believed that the world was ordered and that changes had to have specific and consistent sources, e.g. a plant species only grows from a seed of that the same species.
Epicurus holds that there must be an infinite supply of atoms, although only a finite number of types of atoms, as well as an infinite amount of void. Epicurus explains this position in his letter to Herodotus:
“Moreover, the sum of things is unlimited both by reason of the multitude of the atoms and the extent of the void. For if the void were infinite and bodies finite, the bodies would not have stayed anywhere but would have been dispersed in their course through the infinite void, not having any supports or counterchecks to send them back on their upward rebound. Again, if the void were finite, the infinity of bodies would not have anywhere to be."
Because of the infinite supply of atoms, there are an infinite amount of worlds, or cosmoi. Some of these worlds could be vastly different than our own, some quite similar, and all of the worlds were separated from each other by vast areas of void (
Epicureanism states that atoms are unable to be broken down into any smaller parts, and Epicureans offered multiple arguments to support this position. Epicureans argue that because void is necessary for matter to move, anything which consists of both void and matter can be broken down, while if something contains no void then it has no way to break apart because no part of the substance could be broken down into a smaller subsection of the substance. They also argued that in order for the universe to persist, what it is ultimately made up of must not be able to be changed or else the universe would be essentially destroyed.
Atoms are constantly moving in one of four different ways. Atoms can simply collide with each other and then bounce off of each other. When joined with each other and forming a larger object, atoms can vibrate as they into each other while still maintaining the overall shape of the larger object. When not prevented by other atoms, all atoms move at the same speed naturally downwards in relation to the rest world. This downwards motion is natural for atoms; however, as their fourth means of motion, atoms can at times randomly swerve out of their usual downwards path. This swerving motion is what allowed for the creation of the universe, since as more and more atoms swerved and collided with each other, objects were able to take shape as the atoms joined together. Without the swerve, the atoms would never have interacted with each other, and simply continued to move downwards at the same speed.
Epicurus also felt that the swerve was what accounted for humanity's free will. If it were not for the swerve, humans would be subject to a never-ending chain of cause and effect. This was a point which Epicureans often used to criticize
Epicureans believed that senses also relied on atoms. Every object was continually emitting particles from itself that would then interact with the observer. All sensations, such as sight, smell, or sound, relied on these particles. While the atoms that were emitted did not have the qualities that the senses were perceiving, the manner in which they were emitted caused the observer to experience those sensations, e.g. red particles were not themselves red but were emitted in a manner that caused the viewer to experience the color red. The atoms are not perceived individually, but rather as a continuous sensation because of how quickly they move.