The discussion centers on the implications of the universe's expansion and the associated redshift of radiation, which indicates energy loss. According to relativity, this energy loss raises questions about conservation. From a Newtonian perspective, the energy loss is compensated by the work done through radiation pressure during the universe's expansion. In contrast, the General Relativity (GR) viewpoint posits that energy conservation is not applicable due to the absence of a time-like Killing vector in the Friedmann-Robertson-Walker (FRW) metric.
PREREQUISITESAstronomers, physicists, and students of cosmology interested in the dynamics of the universe's expansion and the interplay between energy and radiation in a relativistic framework.