Humans are made of atoms too, including our souls. If gods exist at all, they are uninterested in us. We are free, liberated by the unpredictability of the swerve, as are all living things. We are all connected, and when we die, our atoms go off to join other atoms elsewhere. Death is only dispersal; there is no need to fear any afterlife, or mutter spells and prayers to absent deities. We do better to live by the simple Epicurean law: Seek pleasure, avoid pain. This does not mean indulging ourselves gluttonously, but cultivating tranquillity while avoiding the two greatest human delusions: fear of what we cannot avoid, and desire for what we cannot have. One extraordinary section describes the frenzies of lovers, who exhaust themselves futilely trying to possess one another. The beloved always slips away. Instead, we should step off the wheel and contemplate the universe as it is — which brings a deep sense of wonder, rather than mere resignation or gloom. “What human beings can and should do,” as Greenblatt summarizes it, “is to conquer their fears, accept the fact that they themselves and all the things they encounter are transitory, and embrace the beauty and the pleasure of the world.”

It was an attractive philosophy, exquisitely expressed, and a few decades later Ovid enthused that “the verses of sublime Lucretius are destined to perish only when a single day will consign the world to destruction.” A world without Lucretius seemed unimaginable — yet that was just what nearly ensued. All ancient copies vanished, except for a few charred scraps in a library at Herculaneum. Some medieval copies circulated, but these too mostly expired from neglect or deliberate destruction, for Epicurean philosophies were uncongenial to Christianity. At last, in 1417, probably in the southern German Benedictine abbey of Fulda, one stray ninth-century copy caught the eye of a Renaissance book hunter from Italy, ­Poggio Bracciolini.

Poggio saw the manuscript’s significance at once, presumably knowing of Lucretius from Jerome and Ovid. He had a copy made and sent to a friend in Florence, who copied it anew. (That copy survives; both Poggio’s and the original have gone down Didymus Gulch.) Two more copies would turn up in Leiden 200 years later, but for now Poggio’s was alone, and it spawned more copies. With the advent of printing, it spread even farther and won more admirers. Among 16th-century readers was the French essayist Michel de Montaigne, who filled his copy with annotations, including one suffused with obvious delight: “Since the movements of the atoms are so varied, it is not unbelievable that the atoms once came together in this way, or that in the future they will come together like this again, giving birth to another Montaigne.” It was one of those “rare and powerful” moments, as Greenblatt writes, when a long-dead author seems to reach directly through time to a particular reader, as if bearing a message meant only for that person.

Another such magical moment would occur some 400 years later, when the young Stephen Greenblatt himself picked up a 10-cent copy of Lucretius for vacation reading. He too was amazed by how personally it spoke to him. Such encounters have become central to the philosophy Greenblatt has elaborated in several decades of work as a literary historian and theorist of the “new historicism” in literary studies. It combines hardheaded investigations of historical context with a profound feeling for the way writers somehow pull free from time, to enter the minds of readers. “I am constantly struck,” Greenblatt told The Harvard Gazette in 2000, when he was named a university professor, “by the strangeness of reading works that seem addressed, personally and intimately, to me, and yet were written by people who crumbled to dust long ago.” It is a rich literary paradox: authors are embedded in history, yet they slip away; they time-travel.