 First, he distinguished between the atom, which by its nature cannot be broken apart, and the minimum conceivable expanse of matter: atoms have such minima as parts, but are not minima themselves — there can be no free-standing entity one minimum expanse in size. This resolves the problem of atomic edges, and also that of how atoms can come in different shapes and sizes (though never large enough to be seen): to have the hooks and crevices needed to form compounds, they can scarcely be theoretically partless. Second, Epicurus agreed that time too is discontinuous, as is motion: Simplicius (p. 934.23–30 Diels; translation in Konstan 1989) quotes him as affirming that it is untrue to say that an atom is moving over a minimum interval, but only that it has moved (some scholars maintain that this is a later innovation in the school; see especially Verde 2013). What is more, as Aristotle had argued must be the case, atoms all move at the same velocity (the principle of isotakheia). This last claim entailed difficulties of its own, such as how atoms ever overtake each other, if they are moving in the same direction. (Lucretius invoked the idea of a random swerve to solve this one; see below.) But it also provided a solution to another problem, that of entropy: for since atoms can never slow down, the universe can never come to a halt (in modern terms, there is no loss of energy). As for gravity, Epicurus may have had a solution to this too, and in a novel form. If an atom just on its own cannot slow down or alter its direction of motion, then an atom that is rising or moving in an oblique direction cannot at some point begin to tilt or fall, unless something blocks its progress and forces it to do so. If, however, after a collision atoms tended to emerge in a statistically favored direction — that is, if the motions of all atoms after collisions did not cancel each other out but on average produced a vector, however small, in a given direction, then that direction would by definition be down. The absence of a global orientation in the universe was thus immaterial. Due to this vector, any given world will, like our own, be similarly oriented in respect to the direction “down.” (Given the infinite expanse of the universe on Epicurean theory — see below — we must expect there to be a plurality of worlds, some like ours, some — within limits — different.)