On this day in 1900, Max Planck presented his derivation of black-body radiation. This followed off the ultraviolet catastrophe. According to classical physics, if you were to heat iron up to higher and higher temperatures, it should radiate light at higher and higher frequencies. But it doesn’t. Instead, it radiates according what we now call Planck’s law.
What Planck found was that energy was quantized. We tend to think of energy as a continuum. But it is actually made up of little packets that are equal to the frequency of the energy times the Planck constant. Based upon this, Planck was able to derive the black-body radiation function.
What still boggles my mind is that Planck could develop all this stuff and yet never accept quantum mechanics. He never even accepted Einstein’s work on the photoelectric effect, even though it is little more than an application of what Planck did. Some day I will have to read a biography about Planck and try to figure this out. He must have had his reasons.