Parmenides made the ontological argument against nothingness, essentially denying the possible existence of a void. According to Aristotle, this led Leucippus to propose the atomic theory, which supposes that everything in the universe is either atoms or voids, specifically to contradict Parmenides' argument. Aristotle himself, proclaimed, in opposition to Leucippus, the dictum "nature abhors a vacuum". Aristotle reasoned that in a complete vacuum, motion would encounter no resistance, and thus infinite speed would be possible, something which Aristotle could not accept. There is a need for speed. The energy in a few grams of antimatter is enough to transport an unmanned spacecraft to Mars within few minutes. Aristotle did not think about antimatter at that time, but he was against the existence of absolute vacuum. He could not accept that in a complete vacuum infinite speed would be possible!