The equation E = hv explains the relationship between the energy of a blackbody and the frequency of the emitted life. In the equation, E stands for energy, v stands for frequency, and h is a constant, now known as Planck's constant. Planck made his equation work only by making the radical assumption that energy was emitted not in a continuous wave, as had always been assumed, but in discrete packets–multiples of hv. Planck and his colleagues accepted this bizarre assumption as nothing more than a mathematical tool to make the numbers work out. But a few years after Planck introduced the equation, Albert Einstein published a paper giving E = hv a new twist. Einstein proposed that the equation actually described reality and that light energy actually came in finite packages called "quanta." The upheaval caused by this suggestion spurred a physics revolution, resulting in the creation of a new field, quantum physics. The quantum physicists struggled with the contradictory results of their experiments, some of which proved without a doubt that light came in waves, other which proved with equal certainty that light was a particle. They eventually resolved the question by declaring that light was both a particle (or quanta) and a wave, depending on how it was measured.

As he espoused all over the world in the early twentieth century, Planck firmly believed that the purpose of science, particularly physics, was to uncover the fundamental truths of the natural world. He believed that it was possible for physicists to discover universal constants and laws that would remain true for any observers anywhere in the universe. Planck set out his views in direct contrast with the advocates of positivism, who argued that all science is subjective. According to the positivists, science can teach us nothing about the world beyond the human senses–if a scientist does not have direct experience with something, then he shouldn't be making any scientific claims about it. Planck thought this was ridiculous and that such thinking hindered scientific progress from producing useful results. Perhaps this is why he was particularly disturbed by the formulation of quantum physics that was advanced in the 1920s. The quantum physicists concluded that light could be either a particle or a wave, depending how it was measured–thus, all experiments were subjective, and all information about the universe was dependent on the person who measured it. Planck could no longer claim that positivist thinking was useless, for it was thinking in this vain that formed the backbone of the new physics.

Planck loved his country–this may have advanced his career, but it also led him into several difficult situations. His nationalism proved particularly problematic during World War I. At the beginning of the war, Planck believed that Germany was in the right and assumed it would soon triumph in its noble struggle. He signed his name to the Appeal of the Ninety-Three Intellectuals, a jingoistic support of the German military that horrified his colleagues in other European countries. It was only when Planck began to realize that Germany might actually lose the war that he began to scale back his nationalism. However, his new moderation came too late. The war ended, and German science was isolated by the rest of Europe, due in part to the attitudes of Planck and his colleagues. But Planck continued to love Germany and was distressed by its new inferior position on the international stage. So, Plancl channeled his nationalism into a new outlet. Planck decided that the way to win back the respect that Germany deserved was to drive German scientists to excel. If they once again emerged as the best scientific community in the world, Germany's neighbors would have to take notice and their respect for German science would expand to encompass Germany as a whole. As a leader of several large scientific organizations, he was in place to put his grand plan into action, in parts by handing out grants to promising researchers. And, within a few years, Planck and his colleagues had succeeded in putting German science back on the map. However, they suffered another soon to be more damaging setback with the arrival of the Nazi party. German science was once again marginalized as the rest of the world shrank back from Germany's alarming governmental policies. Many fled the country, either in fear or disgust. But Planck's nationalism kicked in again, and he stayed, working desperately to find a way to save German science from destruction. Over the years, Planck came to identify the scientific community with the country as a whole, and he felt that if German science died, the rest of the country would soon follow.