Invisibility – the power not to be seen – has captured the fascination and fantasies of people for literally thousands of years. In the earliest imaginings, invisibility was a power bestowed by the gods. In the 1st or 2nd century CE, for example, a Greek author now known as Pseudo-Apollodorus wrote about Perseus’ quest to kill the gorgon Medusa, aided by the Cap of Hades: ‘Wearing it, he saw whom he pleased, but was not seen by others.’ With the aid of the cap, Perseus was able to claim the head of Medusa and escape unseen from her sisters Stheno and Euryale. Stories of invisibility have been told ever since. One of the most recent tales is the movie The Invisible Man (2020), a reimagining of H G Wells’s classic novel. In this film version, a man uses invisibility technology to stalk and control his ex-girlfriend.

Invisibility, then, is sometimes seen as a blessing, sometimes as a curse. Until recently, it remained a complete fantasy. In 2006, the scientific journal Nature published a pair of papers by researchers from the University of St Andrews, Duke University and Imperial College London that demonstrated, theoretically, how to make an invisibility cloak – an object that guides light around a central region and leaves that region undetected. Since then, physicists have been captivated by the possibility of invisibility, proposing a variety of theoretical and experimental techniques for making something hard to see. Though there has not been anything created yet that could be described as ‘invisible’ in the colloquial sense (and there may never be), the attention that physicists have given invisibility shows how deeply intriguing the concept can be.

What is it about invisibility that is so timeless and compelling to the human imagination? We can turn to one of the earliest fables about invisibility to partly answer this question. In the Republic, Plato’s grand philosophical work, a character named Glaucon has a conversation with Socrates in which he shares a story about a powerful ring. In this story, the shepherd Gyges finds a rift in the ground. In the ruins that lie beneath it, he discovers a corpse wearing a gold ring, which he takes to wear for himself. The story continues:

Now the shepherds met together, according to custom, that they might send their monthly report about the flocks to the king; into their assembly he came having the ring on his finger, and as he was sitting among them he chanced to turn the collet of the ring inside his hand, when instantly he became invisible to the rest of the company and they began to speak of him as if he were no longer present.

Discovering that he has acquired the power of invisibility, Gyges immediately conspires to be sent to the royal court and, using his power, he seduces the queen, slays the king and steals the kingdom.

One reason that invisibility as a concept is so compelling: it represents power itself

The story of Gyges is introduced in the Republic to ask whether virtue exists only due to the fear of being punished. Socrates argues that a man who succumbs to the temptation for ultimate power will have, effectively, punished himself, by becoming enslaved to his own base desires. Whether one find