If there is no energy loss in light propagation, will it continue to spread?

Theoretically, the propagation of light will continue without energy loss. For example, a lot of starlight we saw spread tens of thousands of light years, or even more light years, but eventually disappeared. On the inner wall of vacuum mirror, the process of light wave collision reflected by the inner wall should be bright in theory, but it is impossible to see. 300,000 kilometers per hour. In an instant, the loss of heat is converted into kinetic energy. This process is similar to laser generation, and the surface must be very hot.