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 ("metakosmia").