Planck and Wave Theory

With the approach of the twentieth century, the classical wave theory of radiation—a widely accepted theory in physics—began to encounter obstacles. This theory held that all electromagnetic radiation—the entire spectrum from gamma and X rays to radio frequencies, including heat and light—exists in the form of waves. One fundamental assumption of wave smoothly to any setting—and that any conceivable energy value could thus occur in nature.

The major challenge to wave theory was the behavior of thermal radiation, the radiation emitted by an object due to the object’s temperature, commonly called “blackbody” radiation because experiments aimed at measuring it require objects, such as black velvet or soot, with little or no reflective capability. Physicists can monitor the radiation they found almost none, a result that became known among wave theorists as the “ultraviolet catastrophe.”

Max Planck, a classical physicist who had made important contributions to wave theory, developed a hypothesis about atomic processes taking place in a blackbody object that broke with wave theory and accounted for the observed patterns of blackbody radiation. Planck discarded the assumption of radiation’s smooth energy continuum and took the then at first quite critical of Planck’s hypothesis, in part because he presented it without physical explanation.

Soon thereafter, however, Albert Einstein and other physicists provided theoretical justification for Planck’s hypothesis. They found that upon being hit with part of the radiation spectrum, metal surfaces give off energy at values that are discontinuous. Further, they noted a threshold along the spectrum beyond which no energy is emitted by the a catastrophe generated a new vision in physics that led to theories still in place today.