The Ultraviolet myth

Abstract

It is very common to introduce quantum physics in an historical context. Though there are advantages to this, it is a problem that many of the stories that have become central to the physics lore are mere pseudo-histories far detached from the real events. It is about time that we stop uncritically copying these stories and instead make an effort to present the development of quantum physics as it actually was. This paper deals with one of the most common myths in quantum history, the one about the ultraviolet catastrophe and how it motivated Planck's introduction of quantum physics. On closer inspection it turns out this story has the time-line completely turned on its head. The ultraviolet catastrophe was first discussed several years after Planck published his radiation law so it played no role in his motivation. Instead Planck was concerned with finding a theoretical derivation of the law for blackbody radiation. This law was first thought to be Wien's radiation law, but when new data disagreed, Planck came up with his own law that fitted the data. Planck's radiation law first came about as an elaborate fit to data and to derive it he found no other way than to use statistical mechanics and divide the energy that was to be distributed on the atomic oscillators into packages $hf$ so that he could count the number of ways to distribute this energy. Planck did not consider this a quantization, but merely a mathematical trick to be able to calculate the entropy of the oscillators.