Why some aspects of physical reality must be experienced to be known

We will never fully know what pain, colour and love are really like for other people – never mind other animals. That means we may never know if we have created sentient AI

By Clare Wilson

Imagine a woman who has somehow been brought up from birth inside a black, white and grey room, so everything she sees is in monochrome. Yet imagine also that she has spent her life studying the science of colour. She learns how different wavelengths of light are perceived by the eye, how a prism separates white light into a spectrum and so on – but has never personally seen anything other than shades of black or white. Now, imagine that she leaves the room for the first time and sees the vibrant palette of the real world. Most of us would agree that, at that moment, the woman learns something new about colour.

This thought experiment, proposed by philosopher Frank Jackson in 1982, was intended to argue against physicalism, the belief that there is nothing over and above the physical universe. But it also suggests that there are types of knowledge that can’t be gained by reading, measuring or deducing. They have to be learned through direct experience.

The impossibility of sharing someone else’s subjective experiences has consequences for the world of medicine. It makes it harder to know …