Classical physics In contrast to classical physics, "modern physics" is a slightly looser term which may refer to just quantum physics or to 20th and 21st century physics in general. Modern physics includes quantum theory and relativity, when applicable. A physical system can be described by classical physics when it satisfies conditions such that the laws of classical physics are approximately valid. In practice, physical objects ranging from those larger than atoms and molecules, to objects in the macroscopic and astronomical realm, can be well-described (understood) with classical mechanics. Beginning at the atomic level and lower, the laws of classical physics break
Molecules in stars don't allow atoms to form molecules. Stars have very high temperatures, primarily in their interior, and therefore there are few molecules formed in stars. For this reason, a chemist (who studies atoms and molecules) would not have much to study in a star, so stars are better explained by physicists. However, low abundance of molecules in stars is not equated with no molecules at all. Although the Sun is a star, its photosphere has a low enough temperature of 6,000 kelvins, and therefore molecules can form. Water has been found on the Sun, and there is evidence of H in