But if this rationalist assumption seems natural these days, it is not necessarily permanent. The educated class of Victorian England went wild for fairies and spirits in the heyday of scientistic optimism, and both Vallée and von Däniken offered up their books amid the Age of Aquarius’s similar craze. (Just read Sally Quinn’s tales of murderous hexes in her recent memoir to recall how old-fashioned in their magical thinking the New Age’s devotees could become.)

Sometimes our own elite opinion seems to be shopping for a new religion: I have read books in the last year pitching versions of Buddhism, pantheism and paganism to the post-Christian educated set. For such shoppers, the striking overlap between U.F.O.s and fairy stories might eventually become an advertisement for an updated spiritualist cosmology, not a strike against it — especially if woven together with multiverse and universe-as-simulation hypotheses that imply a kind of metaphysics of caprice.