The free energy principle (FEP) is one of those ideas that looks deceptively technical on the surface, yet underneath it’s really a story about how living systems manage to stay themselves in a world that’s constantly trying to tug them into disorder.
The core intuition
Any organism—microbe, mouse, or mind—has to keep its internal states within a narrow set of viable conditions. To do that, it must anticipate what’s happening in the world well enough to counteract surprises. The FEP formalizes this by saying:
A living system persists by minimizing the “surprise” of its sensory inputs.
But “surprise,” in this context, isn’t the emotional sort; it’s a technical quantity from information theory. Since organisms can’t compute surprise directly, the theory says they minimize a proxy called free energy—a mathematically tractable upper bound on surprise. | Chalk