Leaving the Realm of the Visualizable: Waves, Quanta, and the Rise of Quantum Theory

Abstract

Toward the end of the nineteenth century, Lord Kelvin, one of the best known and most respected physicists at that time, commented that “only two small clouds” remained on the horizon of knowledge in physics. In other words, there were, in Kelvin’s view, only two sources of confusion in our otherwise complete understanding of material reality—the results of the Michelson-Morley experiment, which failed to detect the existence of a hypothetical substance called the ether, and the inability of electromagnetic theory to predict the distribution of radiant energy at different frequencies emitted by an idealized “radiator” called the black body. These problems seemed so “small” that some established physicists were encouraging those contemplating graduate study in physics to select other fields of scientific study where there was better opportunity to make original contributions to scientific knowledge. What Lord Kelvin could not have anticipated was that efforts to resolve these two anomalies would lead to relativity theory and quantum theory, or to what came to be called the “new” physics.

Some physicists would prefer to come back to the idea of an objective real world whose smallest parts exist objectively in the same sense as stones or trees exist independently of whether we observe them. That, however, is impossible.

—Werner Heisenberg