I saw new worlds beneath the water lie,
New people, and another sky.

— Thomas Traherne, On Leaping over the Moon (NAEL 8, 1.1772)

Human beings have always dreamed about other worlds, but in the seventeenth century many writers and artists began to see them. An age of exploration helped bring about this giant leap in perspective. Since 1492, the New World had become an established fact, and the encounter of Europeans with other peoples and cultures revealed that other ways of life were possible, perhaps even satisfying. More and more well-defined places filled the empty stretches on the map of the earth. Jonathan Swift's Gulliver's Travels (1726) reflects — and mocks — this interest in distant regions and outlandish customs, alternatives or mirror images of Old World civilization. But the most amazing discoveries came from those who stayed at home and looked through novel instruments, the microscope and telescope. There, in a drop of water or the endless reach of the heavens, they found what human beings had never seen before: innumerable, incredible new worlds.

These vistas changed humanity's view of itself, as a species at the center of the universe, with all other things and beings proportioned to the visible, inhabited world — a comfortable human scale of values. Perhaps we were not so important after all; perhaps these new microscopic and cosmic worlds had their own inhabitants and justifications. This thought could be terrifying. Imagining himself engulfed between infinity and nothingness, the great French scientist and theologian Blaise Pascal expressed the terror of the interstellar spaces. Yet other writers enjoyed their contemplation of the infinite plurality of worlds within us and around us. The possibility of traveling there, at least in imagination, could liberate the mind from its dull rounds, from custom and authority; science could be as exciting as science fiction. To Margaret Cavendish, the duchess of Newcastle, the multiplication of worlds was second nature — not least because women as well as men could imagine worlds that were better suited to what they desired.

The fascination of seeing strange creatures and patterns beneath the microscope — "To see a World in a Grain of Sand," as William Blake recommended — or of looking deeper into the sky also made science accessible to the public. Knowledge was charming; it could provide new sources of pleasure. One of the most popular books of the age, in England as well as France, was Fontenelle's Conversations on the Plurality of Worlds (1686), in which a philosopher explains the universe to a beautiful and intelligent, though uninformed, marquise. The line between the professional scientist (or "natural philosopher") and the amateur enthusiast was not yet firm. Some writers argued that women, because of their natural curiosity and detachment from the business of making a living, could be better than men at scientific pursuits. Hence The Female Spectator encouraged ladies to take an active interest in peering through the microscope and telescope.

What was the significance of these new worlds? One common reaction, epitomized by Joseph Addison, was to celebrate the plenitude of God's creation, which crammed each bit of space, both great and small, with spirit and life and being. Alexander Pope's Essay on Man (NAEL 8, 1.2541–48) and Christopher Smart's Song to David both glory in the fruitfulness and generosity of the divine. Similarly, James Thomson's Seasons (NAEL 8, 1.2860–62) describe an English day from every perspective, whether vast or minute. Extraterrestrial life became an article of faith for many scientists, like the great Dutch physicist Christiaan Huygens. But other writers took a more skeptical view of the new philosophy. Samuel Butler, Cavendish, and Swift all ridiculed the scientific establishment embodied by the Royal Society; in one of Butler's poems, an elephant spied in the moon turns out to be a mouse caught in the telescope. More down to earth, the thresher poet Stephen Duck related mites to men.

Investigations of the worlds of the microbe and atom, the solar system and the Milky Way, eventually changed the conditions of life on earth. In literature, however, perhaps the most lasting effect was a new sense that reality has many different faces, that each of us might inhabit a different world. When the novelist Laurence Sterne recounted A Dream of the plurality of worlds, the hope and panic of his dream expressed the feelings of his century and those of centuries to come.