A Beginner's Guide to Invisibility

Just what is invisibility?
Is it the condition of being transparent, so that all light passes through you undisturbed?
 Or of being cloaked in something all-concealing, like Harry Potter sneaking around Hogwarts?
Or does it mean to be incorporeal, so that you exist but are made, like a thought, of nothing?
Or does it simply mean to be overlooked? Is it always a property of whatever is unperceived, or can it be a limitation of the would-be perceiver? And why do we count as invisible the things that we do? Ghosts, gods, demons, superheroes, ether, X rays, amoebas, emotions, mathematical concepts, dark matter, Casper, Pete’s Dragon, the Cheshire Cat—what is all this stuff doing in the same category?
 And why have we ourselves expended so much imagination and energy in trying to join them?
 These questions are not so much answered as provoked by “Invisible: The Dangerous Allure of the Unseen” (Chicago), by the British science writer Philip Ball. A former editor of Nature and the author of nineteen previous books (he should write about that superpower), Ball leads us on a very fun, largely chronological journey through invisibility, beginning with myth and early magicians, ending with quantum physics, and stopping along the way at Newton, Leibniz, microscopy, photography, spiritualism, B movies, and science fiction. He is lucid and interesting on every topic he touches, from the ghost in “Hamlet” to those unseen extra dimensions posited by string theory. But he is more a tour guide than a theorist, and he never entirely succeeds at pulling the category together, or illuminating our own ambivalent relationship to the prospect of becoming invisible. Still, his book takes seriously a subject that, perhaps aptly, has heretofore been mostly disregarded. Invisibility looms large in the kingdom of childhood—in pretend play and imaginary friends, in fairy tales and comic books and other fictions for kids—but it seldom receives sustained adult scrutiny. And yet, once you get past the cloaks and the spells, invisibility is a consummately grownup matter. As a condition, a metaphor, a fantasy, and a technology, it helps us think about the composition of nature, the structure of society, and the deep weirdness of our human situation—about what it is like to be partly visible entities in a largely inscrutable universe. As such, the story of invisibility is not really about how to vanish at all.
Curiously enough, it is a story about how we see ourselves. continue