UNCERTAINTY

Science writer Lindley (Degrees Kelvin, 2004, etc.) chronicles the early days of quantum theory.

Around 1825, Scottish botanist Robert Brown, a friend of young Charles Darwin, was observing small particles under a microscope and saw them jiggling about erratically. Eighty years later, Albert Einstein showed that this “Brownian motion” originated in the random movement of molecules in the suspending fluid. Einstein’s paper was only one indication that the orderly Victorian scientific worldview was breaking down. The Curies’ investigation of radium revealed energy that seemingly came from within atoms, and Max Planck had tentatively offered a theory treating light as a collection of particles of discrete sizes: quanta, he called them. Explaining these phenomena required new models of the atom and of light. Around 1914, Danish physicist Niels Bohr imagined the atom as a miniature solar system, with electrons orbiting the nucleus and changing orbits as they absorbed or emitted quanta of light. A younger generation of physicists, led by Wolfgang Pauli and Werner Heisenberg, developed Bohr’s atomic model into a new, mathematically rigorous discipline, quantum mechanics. But this model raised a fundamental question: How does an electron “decide” when to change orbits? Bohr’s substitution of probability for cause and effect deeply bothered Einstein, who spent much of the rest of his career sniping at Bohr and trying to devise a theory that would remove the evident discrepancy between quantum randomness and the causality of classical physics. In the midst of this controversy, Heisenberg stated his famous uncertainty principle, perhaps better understood as a “blurriness” principle. Oddly, although Einstein tried to refute uncertainty, he apparently found it less irrational than the inherent randomness of quantum processes. Lindley smoothly recapitulates the scientific developments, the careers and characters of the key players and the cultural context of the era in which they operated.

A good overview of a historic scientific debate.