Plenary lecture: Philip Ball

What does invisibility really mean?
The history of a metaphor from Plato to metamaterials

In his 1895 novel The Invisible Man, H. G. Wells drew on the latest in physics - X-rays and refractive optics - to update a fantastical idea that can be traced to antiquity. As Wells admitted, his book recast for the late Victorian era a story of invisibility told by Plato in his Republic. It is common now for scientists to return the compliment, invoking fantasy and science fiction to popularize their research. Work on transformation optics and metamaterial-based cloaking technologies in the early 2000s invoked imagery from the Harry Potter books, even seeking to show how such “unnatural” optics might be harnessed to create hidden portals like the one at London’s King’s Cross station through which pupils reach the wizardry school of Hogwarts. Related work in metamaterials has invoked science-fictional “tractor beams” and levitation. I will argue that these cultural allusions are more complex than is often recognized. From Plato to Wells, invisibility has carried moral connotations, being depicted as a corrupting influence because of its liberation from of social accountability. As invisibility became a theme of nineteenth-century physics, for example via the discovery of X-rays and other “occult” aspects of the physical world, it was enlisted (even by some prominent scientists) as a medium that connected the tangible to “hidden” spiritual layers of reality. Using invisibility as an example, I suggest that scientists will do well to pay heed to the deep cultural roots of the metaphors they use to talk about their work, not just to the braoder public but within science itself.