The atmosphere itself is colorless. The blue of the sky is a picture created by atmospheric molecules, ice crystals, water droplets and sunlight.

19 10 years, Einstein finally solved this problem. Einstein proved that even the purest air will fluctuate with the newly developed statistical thermodynamic theory of entropy (a measure of chaos). The density fluctuation of air itself can also be scattered, and blue light is easily scattered. The scattering of density fluctuation, neither too much nor too little, can just produce the blue sky we see. If air is an ideal gas, Einstein's result is the same as Rayleigh's. So, to put it simply, the blue sky is caused by:

"There are indelible impurities in the air, which is the fluctuation of the air itself. The scattering of solar light by density fluctuations forms a blue sky. "

The physics of the origin of "sky blue" was not initiated by Einstein, but the most complete theory was laid by Einstein. So the physics of "Sky Blue" was completed in 19 10.

Rayleigh and Einstein's "sky blue" theory is universally applicable. It can be used to explain the "blue sky" phenomenon in pure air, and it can also be used to explain the "blue sky" phenomenon in pure water, pure glass and other liquids or solids.