Lucretius is a hard character to figure out. He says the gods don’t care anything about us, but he starts his great poem, De rerum natura, by invoking the aid of Venus. He explains moon phases and eclipses in the right way, and then he turns around and proposes alternative theories that fly in the face of the evidence – evidence that was abundantly clear to any person from the first century B. C. with at least one good eye. His speculations about sight seem ludicrous, yet his speculations about the atomic nature of matter are astonishingly prescient.
Lucretius states his purpose several times in his verses: to show that every phenomenon has a material explanation so readers can be free from fear of the gods. Lightning is caused by particles of heat crashing in the clouds, not by Jupiter’s anger. If lightning were a punishment for human crimes and impieties, then why does lightning happen sometimes in the open sea? To make his point, Lucretius has to explain the material nature of everything – everything. Where the science doesn’t exist, he makes it up. All he has to do, after all, is show that materialism is plausible.
Somewhere between his explanations of the origins of dreams and the origins of earthquakes, Lucretius tackles astronomical events. He starts his discussion of lunar phases with the very sensible theory that, as the moon makes its way around the earth, the sun lights different parts of it. But then he indulges the urge to propose theories B and C: (B) that one half of the moon shines by its own light and spins as it revolves around the earth, and (C) that for some unknown reason the moon’s natural light fades and grows again in a continuous pattern. Now Lucretius could see as well as I (better probably) that the same dark spots sit in the same places on the moon’s surface and that the bourne between lunar day and lunar night moves across those dark spots. So obviously the moon doesn’t spin its supposedly stationary bright half away from the earth once a month. And Lucretius could see where the sun was (or figure where it would be when it rose) and note that the moon’s bright half always points toward the sun’s location. I think he knew perfectly well that the solar reflection theory was the correct one: he puts it first and spends longer on it than on the other two. And again, it accords with observation where the other two don’t. But then why did he offer the others?
Similarly with eclipses, Lucretius first says that the moon travels through the earth’s shadow (he even knows the umbra has the shape of a cone), causing a lunar eclipse, and then passes between the earth and the sun, causing a solar eclipse. But then – why? for some sense of false humility? – he says that he may be wrong and proceeds to give other possible explanations. Maybe the moon’s light just fades every now and then. Perhaps the sun’s fires run out of fuel and then start up again. Or maybe some other dark celestial object rushes in ahead of the moon and blocks the sun’s rays. Seriously? He knows where the moon is. He can see it morning by morning creeping its way toward the sun, its crescent growing thinner and thinner. So does he think the sun’s flames just happen to die exactly when the moon is right in front of it?
His view (hah!) of sight is so close, and yet so far! Every object, he says, constantly puts off tiny bits off stuff without any discernible loss. If this were not so, we’d never smell anything. So every physical object, every table for instance, must constantly shed tiny images of itself, a stream of “idols” cast off as a snake sheds skin. These idols fly through openings in the air, and, if light is shining on them, we see them. So he knows we see the idol because light shines on it, but he can’t fathom that we see the table itself because light shines on it? Lucretius likes his idol theory, though, because it gives the mind something material to see later when it remembers or imagines or dreams of tables. But watch out when the table idol and the leg idol crash into one another up there! We might start dreaming about walking tables.
While I smile through all these parts of De rerum natura, I find myself picking up my jaw while reading about “first-beginnings.” In a passage reminiscent of Aristotle’s argument for underlying matter, Lucretius points out that when the cold, gray, solid metal turns into something hot, red, and pliable, some kind of stuff must occupy that place through all the changes of appearance and quality. That stuff cannot absolutely fill the space; without void in the stuff, nothing could ever move. And the stuff must be in the form of tiny particles, since it is unimaginable that we could divide physical matter interminably. He calls these indivisible particles “first-beginnings” or “seeds.” There must be several different kinds of seeds, he argues, because there are so many kinds of material in the world: bone, wood, stone, water, iron, heat, smells, visible idols, etc. Each kind of substance must be made out of a different combination of seed types. Finally, each variety of seed must have a different shape, and those shapes must involve hooks to keep the combinations together in normal situations.
Substitute electromagnetic valence for Lucretius’ hooks, and you have our basic chemistry. Lucretius provides no details to be sure: he doesn't name Helium or Lithium. But he reasoned himself to a numerous set of atomic elements – more than the four traditional but fewer than the types of substance in the material world – and a molecular theory. The brilliant scientist and philosopher Aristotle muddles around trying to imagine all the world made out of just four elements and has no good hypothesis for how they stay grouped together until forced apart. And yet this poet sees through to an idea sixteen-hundred years ahead of its time. What may be even more amazing is that he doesn’t offer a ridiculous theory as a second option.