The principle of the constant light speed was proposed by Einstein as a hypothesis in 1905. It is one of the cornerstones of the theory of special relativity. In the next 120 years, physicists have continuously discussed the reasons for the constant light speed, but their understanding of the causes of the constant light speed remains in Einstein’s initial hypothesis stage. From 2017 to 2022, Chinese scholar Song Guanyi, according to the analysis of the cosmic microwave background radiation data found by American radio astronomers Arnold Penzias and Robert Wilson in 1964, realized that the cosmic microwave background radiation is that the early strong radiation light quantum during the long distance traveling constantly loses energy (redshift), and evolves into a microwave (wavelength from 0.3 ~ 75cm). The observations prove that the light quantum is not previously understood as an independent, indivisible particle entity, and it should be composed of two parts: matter and energy. Based on the change of the structure of light quantum, this paper interprets the following concepts of physics related to light quantum.

a. The light quantum is composed of two parts: ground state matter (ground state photon) and energy (dynamic energy). When the ground state photon is excited by the dynamic energy, it turns into a light quantum. The light quantum is propagated in a continuous collision (elastic collision) manner between the light quantum and the ground state photon. The ground state photon is the medium particle of the light quantum propagation. A light quantum from any light source in the universe is new-born, and its propagation velocity (in a vacuum) has the same value C (whether it is emitted from a stationary or moving object).

b. Interpretation of wave-particle duality.

c. The existence state of ether (essentially the ground state photon) and its action.

d. The difference between light wave and electromagnetic wave.

e. The reason for the deviation when the starlight passes near the sun.

f. The cause of the redshift of the galaxy spectral lines observed from the earth.

g. The existence form and characteristics of dark matter (essentially ether).

h. The existence morphology and characteristics of dark energy (essentially it is the energy carried by the light quantum and formed after the ground state photon (dark matter) is excited by the limited (one share by one share) dynamic energy).