and the natural world back together. Because after all, physics—just ask any physicist—is the science of everything.
Historically, the physicist’s notion of everything has been a bit limited, though. For most of the past three centuries, physics concerned itself mostly with matter and the forces guiding its motion; eventually, the study of matter in motion incorporated energy and its transformations. In the century just gone by, Einstein added cosmic time and space to the mix. He even simplified reality’s recipe by combining matter with energy and space with time. Through the 20th-century physicist’s eyes, then, “everything” comprised mass-energy and space-time.
Toward the end of that century, a number of physicists began to realize that one ingredient was missing. Awakened by the metaphorical power of the digital computer, astute observers realized that information was the glue connecting the outside world to its scientific description. From the second law of thermodynamics to the weirdness of quantum mechanics to the murky milieu of a black hole’s interior, physicists found information to be an indispensable element in codifying and quantifying their understanding of nature.
Information opened physicists’ eyes to the rest of reality. Information encompassed biology. Biology included people. People created a new universe of realities for physics to contemplate—vast networks of economic, social, and cultural systems and institutions. So physicists began applying their favorite all-purpose tool—statistical mechanics—to everything from the stock market to flu epidemics. It was all very much in the spirit of Isaac Asimov’s fictional mathematician, Hari Seldon, who adopted the principles of statistical mechanics to forecast the future. By the dawn of the 21st century, real-life physicists were trying to do almost exactly the same thing that Seldon had done, using statistical mechanics to build mathematical models of society for the purpose of making predictions.