Editing Epicureanism (section)

===Physics===
In his letter to [[Herodotus]] (not the historian), Epicurus presented three principles as to the nature of the physical world, i.e. that that which exists cannot come into being from that which does not exist, that which is destroyed does not cease to exist, and all that exists now always did exist and always will.<ref>Epicurus, Letter to Herodotus 38-39</ref> The object of these principles was to establish the fact that all that constitutes the world is permanent and unchanging.<ref>Long, A.A.; Sedley, D.N. (1987). The Hellenistic Philosophers. Vol. 1. New York: Cambridge University Press. p. 26.</ref> Epicurean physics held that the entire universe consisted of two things: matter and void.<ref>{{harvnb|O'Keefe|2010|pp=11–13}}</ref> Matter is made up of atoms, which are tiny bodies that have only the unchanging qualities of shape, size, and weight.<ref name="Wilson-2015a">{{harvnb|Wilson|2015|p=page=9}}</ref><ref>{{harvnb|O'Keefe|2010|p=21}}</ref> The Epicureans believed that atoms were unchanging because 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 the same species,<ref name="O'Keefe-2010j" /><ref name="Sharples-1998">{{Cite book|title=Stoics, Epicureans, and Sceptics: An Introduction to Hellenistic Philosophy|last=Sharples|first=R. W.| publisher=Routledge| year=1998| location=New York, NY| pages=34–35}}</ref> but 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.<ref name="Sharples-1996b" /><ref name="O'Keefe-2010j" />

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.<ref name="Wilson-2015a" /> Epicurus explains this position in his letter to Herodotus:

<blockquote>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.<ref>{{Cite book|url=https://www.loebclassics.com/view/diogenes_laertius-lives_eminent_philosophers_book_x_epicurus/1925/pb_LCL185.573.xml|title=Lives of Eminent Philosophers: Volume II: Books 6-10|last=Diogenes|first=Laertius|publisher=Harvard University Press|year=1925|location=Cambridge, Mass|pages=573–575|translator-last=Hicks|translator-first=R. D.|url-access=subscription }}</ref></blockquote> Because of the infinite supply of atoms, there are an infinite number of worlds, or ''cosmoi''.<ref name="Wilson-2015a" /> Some of these worlds could be vastly different from our own, some quite similar, and all of the worlds were separated from each other by vast areas of void (''metakosmia'').<ref name="Wilson-2015a" />

Epicureanism states that atoms are unable to be broken down into any smaller parts<ref name="Sharples-1996b">{{Cite book|title=Stoics, Epicureans, and Sceptics: An introduction to Hellenistic Philosophy|url=https://archive.org/details/stoicsepicureans0000shar|url-access=limited|last=Sharples|first=R. W.|publisher=Routledge|year=1996|location=New York, NY|pages=[https://archive.org/details/stoicsepicureans0000shar/page/n48 35]–37}}</ref> 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.<ref name="O'Keefe-2010j">{{harvnb|O'Keefe|2010|pp=18–20}}</ref> Atoms are constantly moving in one of four different ways.<ref name="Wilson-2015b">{{harvnb|Wilson|2015|p==11}}</ref> Atoms can simply collide with each other and then bounce off of each other.<ref name="Wilson-2015b" /> When joined with each other and forming a larger object, atoms can vibrate as they collide into each other while still maintaining the overall shape of the larger object.<ref name="Wilson-2015b" />

When not prevented by other atoms, all atoms move at the same speed naturally downwards in relation to the rest of the world.<ref name="Wilson-2015b" /><ref name="O'Keefe-2010k">{{harvnb|O'Keefe|2010|pp=25–28}}</ref> 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.<ref name="O'Keefe-2010k" /> 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.<ref name="Wilson-2015b" /><ref name="O'Keefe-2010k" /> Epicurus also felt that the swerve was what accounted for humanity's free will.<ref name="Sharples-1996e">{{Cite book|title=Stoics, Epicurus, and Sceptics: An Introduction to Hellenistic Philosophy|url=https://archive.org/details/stoicsepicureans0000shar|url-access=limited|last=Sharples|first=R. W.|publisher=Routledge|year=1996|location=New York, NY|pages=[https://archive.org/details/stoicsepicureans0000shar/page/n78 64]–66}}</ref> If it were not for the swerve, humans would be subject to a never-ending chain of cause and effect.<ref name="Sharples-1996e" /> This was a point which Epicureans often used to criticize [[Democritus]]' [[Democritean theory of atoms|atomic theory]].<ref name="Sharples-1996e" />