Max Planck, the Messiah of quantum physics

If physicists wrote history, we would now be in the second century of our era, specifically the year 116 of Planck, the German physicist who changed our view of the world when he laid the cornerstone of quantum theory in the year 1900 (of the Christian era.) And incredibly, some of his professors had recommended that he devote himself to mathematics, as physics had no future.

When Max Planck (1858-1947) entered university, it seemed that in the field of physics everything had already been discovered. By the end of the nineteenth century physicists understood movement, matter, energy, heat, electromagnetism and light very well when they were considered separately, but how they related to each other was less clear. For example, physicists had trouble explaining the way in which hot bodies radiate energy.


Max Planck portrait, circa 1930. Credit: Smithsonian Libraries

Although the human body emits infrared radiation, it is not hot enough to emit visible light; however, the Sun or a red-hot nail certainly is. If the nail is heated even more, its light will be predominantly orange, yellow, green, blue and violet. This was no way to fit this observation with any formula constructed according to the rules of classical physics, and thus, at age 42, Planck decided to skip over these rules and pulled from his sleeve a fixed number containing 34 zeros, which he introduced between the unknowns in his equations. At the beginning, he used this tiny number only because it enabled him to solve the problem, but months later he realized what it meant. He had discovered that radiation was not a steady stream of energy, but rather that energy is radiated and absorbed in small indivisible portions, which he called quanta. That sounded as ridiculous as if someone pressing a key on an organ keyboard heard an intermittent, choppy sound

Planck was a good musician. The concerts that he gave at his home in Berlin served as a peaceful meeting place for dedicated scientists, theologians, philosophers and linguists. Turning this intellectual world upside down was the furthest thing from his mind; in fact, Planck was the first to distrust his quantum theory and he tried very hard to rid himself of that tiny number (and from its revolutionary implications), which we now call Planck’s constant. But he failed and his theory changed physics forever, for which he received the Nobel Prize in 1918. Nor could he stop the Nazis, who came to power in the 1930s, from controlling and using the German Society of Science for their bellicose interests, an organization chaired by Planck. Therefore he resigned. He endured living in Germany until the end of World War II, despite losing all his scientific notes in a bombing and having his son executed, accused of plotting to assassinate Hitler.


Nernst, Einstein, Planck, Millikan and von Laue at a dinner in Berlin in 1931. Author: Unknown

Despite some initial resistance, first Einstein and then many other scientists adopted Planck’s quantum ideas to explain that light waves sometimes behave like a stream of particles, and that the electrons that revolve around atoms are simultaneously particles and waves; or to discover that there are more ways to produce light than by burning something or heating a metal. The benefits were enormous: fluorescent tubes, lasers, electronics…

Thanks to Planck and his quantum theory, physics could now be applied to the infinitely small, but in exchange it became something beyond our imagination; an electron occupies all points of its orbit simultaneously, can jump to another orbit without passing through any intermediate point and its path is unpredictable, unlike that of a moving object, such as a bullet. At least classical physics continued to be useful for the things we can see with our own eyes. As Niels Bohr, the first to use quantum theory to describe the atom, famously said: “If none of this seems shocking to you, then you have not understood it.

By Francisco Doménech for Ventana al Conocimiento