Max Planck

The Black Box

Summary The Black Box

In this equation, E stands for the total energy of the light source, v is the frequency of the light, and h was a mathematical constant that came to be known as "Planck's constant." If Planck was right, then energy could only be emitted in certain units–multiples of hv. Planck called these units "quanta," Latin for "how much." This equation challenged everything that had been previously thought about energy. But no one, not even Planck, realized this at the time.

Planck's equation worked, and by 1908, everyone in the field had accepted it, but even the best physicists of the time failed to see its implications. Like Planck, they considered the quantum assumption to be nothing more than a convenience, a mathematical abstraction with no consequences for the real world.

Despite this oversight, Planck's work was impressive enough to draw the attention and admiration of his peers. The new equation would, in itself, have been enough to make Planck's career. Planck's theory yielded two new universal constants that related mechanical measures of energy to temperature measures: h and K. Planck called K "Boltzmann's constant", a gesture of appreciation to Ludwig Boltzmann, whose theories had led Planck to his own grand solution. In 1900, the value of h meant little to physicists, but K meant a great deal.

Knowing that such a constant as K existed, physicists had composed the equation LKT = pressure of a standard unit of gas. In this equation, L stands for the number of molecules in a standard unit of gas and T stands for the absolute temperature of the gas. They knew that the number of molecules and the temperature of a gas were directly related to the pressure it exerted, but they didn't know how, since the values of both L and K were a mystery.

Thanks to Planck, physicists could finally derive a value for L. And knowing L eventually led to even more discoveries, including a theoretical confirmation of the charge of a single electron. This was one of the earliest connections physicists were able to make between electrodynamics and atomic theory, and bridging the gap between these two fields had been one of Planck's highest goals.

He wasn't the only one with this goal. As the impact of Planck's work grew and grew, his peers sat up and took notice. In 1908, Planck was nominated for the Nobel Prize in physics for the discovery of his two constants and the E = hv formula itself. But Planck's nomination was voted down, not because his work wasn't significant enough, but because someone had finally realized it had even more significant implications. It was pointed out to the Nobel committee that Planck's equation implied that energy did not come in a continuum, and, horrified by the thought, the committee declined to award Planck the prize. Instead, the 1908 Nobel Prize went to Gabriel Lippman, for his work in the new field of color photography.

Max Planck: Popular pages