On the surface, the propagation of

On the surface, the propagation of light in the universe is long-lasting, but the essence is that the light waves are declining, and the photons will be scattered in the cosmic space. The light away from the observer will also encounter the same light as the observer. The situation, which causes the photons to be continuously lost outside the light wave and become dark matter with a static mass of zero; the extension of the light wave shows a red-shifted state, and the near-to-far light wave is extending toward a longer spectrum. For the observer The extension of the wavelength is that the light wave moves towards the red end. When the light wave extends to infinity, the light wave will be obliterated in the universe, which is called dark energy. In short, a photon with a resting mass of zero, when it stops, becomes dark matter in the universe; when the light wave extends to infinity, it will be obliterated in the universe and become dark energy, which is the final destination of light.