Since the dawn of civilisation, invisible people, forces and objects have held a powerful appeal. Just as the ability to disappear from sight while remaining part of the action was key to mythology and magic, today many are fascinated by the physics of “invisibility cloaks” and the mysteries of the dark matter and dark energy that dominate our universe.
The history of invisibility provides a rich seam of stories and analysis for Philip Ball, one of the most engaging contemporary science writers. Despite the difference in subject matter, Invisible has parallels with his 2011 book Unnatural, which looked at the artificial creation of life over the ages. In both cases, ancient myths gave way to occult practices in the Middle Ages and Renaissance, with often gruesome spells and recipes that seem weirdly similar whether they are intended to achieve invisibility or breathe life into inanimate matter.
These ancient obsessions would later inspire novels such as Mary Shelley’s Frankenstein and HG Wells’s The Invisible Man. Now science has taken up the baton, with research in fields from synthetic biology and embryology to metamaterials and astrophysics faintly echoing the hopes and fears of a more superstitious age.
One of the first surviving accounts of invisibility appears in Plato’s Republic. A Lydian shepherd called Gyges discovers a gold ring that can make him vanish. Unfortunately, Gyges does not use his power for good; he manages to seduce the queen of Lydia, kill the king and establish a new dynasty. This sets the scene for many subsequent invisibility tales: invariably, they are about sex, wealth or death.
The sheer diversity of prescriptions for achieving invisibility – as Ball says, no grimoire was complete without one – makes their meaning almost impossible to grasp many centuries later. Ball asks whether the tradition of “natural magic” was a serious intellectual enterprise, a smokescreen for charlatans or superstition surviving from pre-Christian folk belief. “The truth”, he writes, “is that magic in the western world was all of these things and for that very reason has been able to permeate culture at so many different levels and to leave traces in the most unlikely of places: in theoretical physics and pulp novels, the cults of modern mystics and the glamorous veils of cinema.”
Although natural magic receded in the 17th century, the occult tradition survived the Enlightenment and was revived in the 19th century, when believers invoked a new range of invisible forces to channel communications with the spirit world. Ball gives wonderful accounts of seances and similar sessions in which mediums put gullible patrons in touch with the departed. Some even used the new technology of photography to give visible form to previously unseen ghosts and spirits.
When the book reaches the 20th century, it tackles the scientific meanings of invisibility. One is rooted in optics: either you become transparent and arrange for your refractive index to be the same as your surroundings, so that light passes through you without deviating (as imagined by Wells, though as yet unrealised); or you arrange for light waves to bend around you – the approach taken by contemporary physicists developing “metamaterials” for (still far from perfect) invisibility cloaks.
A more prosaic form of invisibility, which Ball also discusses entertainingly, is to blend into your surroundings. Some plants and animals achieve this through natural camouflage, though it is also possible to put off predators by confusing them – an approach exemplified by the zebra’s “dazzle” stripes.
One of the best passages in this excellent book concerns the quest for the most effective camouflages to apply to warships, aircraft and army equipment. The claims of competing schemes from dazzle to drab, multicolour to monotone – and the surprisingly colourful characters promoting them to the world’s armed forces – are every bit as entertaining as the spells and concoctions of those seeking true invisibility.
Invisible: The Dangerous Allure of the Unseen, by Philip Ball, Bodley Head, RRP£25, 320 pages
Clive Cookson is the FT’s science editor