The little-known story of how two of history's greatest physicists waged a war over the existence of the atom and the nature of reality itself

Nearly 2,500 years ago, the Greek philosopher Democritus argued presciently, but without evidence, that all matter is made of tiny indivisible entities called atoms. Other sages, similarly lacking proof, suggested that nature is continuous. By the later nineteenth century, though science progressed, the question of nature's basic ingredients remained elusive. Two extraordinarily brilliant, incredibly stubborn Austrian physicists of that era-Ernst Mach and Ludwig Boltzmann-fought to determine whether flowing energy or discrete matter was the chief component of the universe. Mach treated atoms as useful fictions. Boltzmann, however, insisted atoms were a physical necessity. The titanic struggle rattled Boltzmann's nerves, and he eventually descended into madness and suicide. Extraordinary experiments soon thereafter vindicated his lonely plea for atoms. Despite their differences, both thinkers influenced the young Albert Einstein, paving the way for relativity and quantum theory. Mach is best known today for his groundbreaking work on supersonic speed and shock waves.

By connecting the clash of Boltzmann and Mach to today's debates over what is fundamental, The Great Atom Debate does more than help us understand physics' past. It helps us make sense of the unseen entities that loom over physics' future.