What would you do if you had the power to render yourself invisible? Plato, as it happens, explored this question two millennia ago. He tells of a shepherd named Gyges, who one day finds a gold ring. He discovers that when he twists the ring toward his palm, he disappears from sight; turning it the other way, he reappears. Soon, Plato tells us, he seduces the Queen, murders the King and takes over the kingdom – all with the help of the magical ring and the power that invisibility bestows on those who tame it. He who wields such power, Plato assures us, would be "a god among men."
No wonder the quest for invisibility beckons, from H.G. Wells's The Invisible Man to Harry Potter's invisibility cloak. And yes, there are real-life scientists working on making Harry's cloak a reality (sort of). But Invisible, by veteran British science writer Philip Ball, is more than just a history of an ancient, exotic (and perhaps hopeless) quest. The book is full of insights drawn from a broad survey of history, literature and philosophy; wherever the invisible is being contemplated, Ball is there to select the juiciest anecdotes. Along the way, we discover just how uneasily the unseen fits into our understanding of the world. Do invisible entities fall within the domain of the magician? Of the scientist? Of the imaginative writer?
Often, it seems, the boundary between science and magic is itself invisible – especially in the 19th and early 20th centuries, when discoveries in physics and chemistry were coming fast and furious, but mystical thinking still held enormous appeal. Arthur Conan Doyle, best known for creating the hyperlogical Sherlock Holmes, believed that psychics could really read minds, sought evidence for life beyond the grave, may have believed in fairies and elves and was convinced that Harry Houdini was a real magician. The Lincolns, meanwhile, held séances in the White House. But this was also the age of the telegraph, the telephone, wireless radio, X-rays and radioactivity – all of which would have seemed miraculous only a few decades earlier. Who could have imagined that invisible waves could carry voices across the ocean, or that invisible beams of particles could reveal the bones within our bodies? (Many of the first dabblers in radio, Ball points out, wondered if they might make contact with the dead.) Science and spiritualism, he says, "fed one another."
One of the more intriguing figures from this period was a man named William Crookes. Both a respected chemist and an enthusiastic spiritualist, Crookes, like Conan Doyle, was in awe of psychics and mediums. The gadgets he tinkered with in his laboratory were real enough – but their effects were often less tangible. Matter and force, he told a scientific conference in 1879, "seem to merge into one another, the shadowy realm between the known and the unknown. … I venture to think that the greatest scientific problems of the future will find their solutions in this borderland, and even beyond; here, it seems to me, lie ultimate realities, subtle, far reaching, wonderful." Crookes invented, among other things, the cathode ray tube; decades later, it would form the heart of a new technology known as television – "the vehicle," writes Ball, "that allowed glowing dreams to be plucked out of the invisible ether and brought into the domestic hearth."
(I'm not sure if Ball was partly inspired by David Kaiser's terrific book from a few years ago, How the Hippies Saved Physics, which showed how a few of the crazy ideas of the 1960s and 70s were not so crazy after all. Ball's new book could perhaps have been called How the Spiritualists Saved Science.)
Science slowly untangled itself from the supernatural. But even as science became "scientific," the unseen continued to tease. Today, Ball reminds us, physicists speak of superstrings, extra dimensions, dark matter and dark energy. Their existence is suggested by indirect observations and by mathematical analysis – but they are quite impossible to see or touch. (Ball saves his harshest words for those, such as physicists Brian Greene and Max Tegmark, who write earnestly about an infinite array of unseen, parallel universes.)
And the quest to actually render objects – or people – invisible? Don't hold your breath. Ball details the latest experiments with "metamaterials" – materials whose electrical properties force light to bend in peculiar ways – as well as systems involving millions of tiny video cameras and LEDs. Physicists have, in fact, managed to build a clever microwave-invisibility apparatus; if you shine microwaves at it, they appear to pass right through. It's impressive – as are the stealth warplanes that can elude detection by radar – but as Ball admits, we're still very far from Harry Potter territory.
Invisible is most compelling when Ball shines a light (so to speak) on forgotten episodes in the history of science. His discussion of present-day issues is sometimes less captivating. (Does the anonymity provided by the Internet make you "invisible"? Perhaps, but this seems like a topic for a different book.) But for anyone interested in the interplay between science and spirit over the centuries, and especially in the Victorian world, Ball is a lucid, witty and highly entertaining guide.
Dan Falk is a science journalist based in Toronto. His most recent book is The Science of Shakespeare: A New Look at the Playwright's Universe.