Karl Friston wanted me to know he had plenty of time. That wasn’t quite true. He just didn’t want our conversation—about his passion, the physics of mental life—to end. Once it did, he would have to step outside, have a cigarette, and get straight back to modeling COVID-19. I caught the University College London neuroscientist at 6 p.m., his time, just after he had sat on a panel at a COVID-related press conference. He apologized for still having on a tie and seemed grateful to me for supplying some “light relief and a distraction.”
A decade ago, Friston published a paper called “The Free-Energy Principle: A Unified Brain Theory?” It spells out the idea that the brain works as an editor, constantly minimizing, “squashing” input from the outside world, and in the process balancing internal models of the world with sensations and perceptions. Life, in Friston’s view, is about minimizing free energy. But it’s not just a view of the brain. It’s more like a theory of everything. Friston’s free-energy theory practically sets your brain on fire when you read it, and it has become one of the most-cited papers in the world of neuroscience. This May, Friston published a new paper, “Sentience and the Origins of Consciousness,” that takes his ideas into new intellectual territory.