Planck and quantum physics around 1900

1900, Planck, a professor at the University of Berlin, Germany, first put forward the "quantum theory".

The fuse of quantum revolution is not the study of matter, but the radiation problem. The specific challenge is to understand the spectrum of blackbody (that is, some hot objects) radiation. People who bake too much are familiar with the phenomenon that a hot object will glow, and the hotter it is, the brighter it will be. The spectral range is very wide. When the temperature rises, the peak of the spectrum moves from the red line to the yellow line and then to the blue line (which we can't see directly). It seems that combining the concepts of thermodynamics and electromagnetism can explain the shape of the spectrum, but all attempts have ended in failure. But Planck assumes that the energy of light radiated by vibrating electrons is quantized, and thus an expression is obtained, which is completely consistent with the experiment. Planck applied his quantum hypothesis to the oscillator energy on the surface of radiator. In 1905, he did not hesitate to conclude that if the energy of the oscillator is quantized, then the energy of the electromagnetic field that produces light should also be quantized. The photoelectric effect experiments in the following ten years show that light energy can only be absorbed if it reaches a certain discrete order of magnitude, just like being carried by particles.