The universe tends toward chaos. Things fall apart, structures dissolve, energy disperses. And yet some systems persist—cells, minds, institutions, civilizations—for millions and even billions of years. How? In The Physics of Identity, Boris Kriger reveals that the answer lies not in any mysterious life force but in two structural necessities that every persistent system must satisfy: it must conserve what defines it, and it must be able to transform its own structures when the world demands it.

These principles—familiar from the conservation of energy and the equivalence of mass and energy in physics—turn out to govern everything from the temperature regulation of a living cell to the institutional resilience of a constitutional democracy. But the story does not end there. Kriger shows that the classical guarantee of statistical knowledge—the law of large numbers—breaks down precisely in the systems that matter most to us.

When it fails, systems must build internal models of the world, compressing the wisdom of vast numbers of past trials into representations that guide action under uncertainty. The cognitive biases that psychologists have cataloged for decades are not failures of rationality but structural consequences of this compression—the price of being an agent too valuable to waste.

Drawing on physics, evolutionary biology, cognitive science, robotics, and institutional theory, The Physics of Identity offers a unified account of why complex systems are organized the way they are—and a new way of seeing the conservation laws, conversion factors, and compressed models that operate silently in every domain of organized complexity, including your own life.