Hayashi, Chushiro (1920– )

Japanese physicist whose research in 1950 exposed a fallacy in the ‘hot Big Bang’ theory proposed two years earlier by Ralph Alpher and others. Hayashi has published many papers on the origin of the chemical elements in stellar evolution and on the composition of primordial matter in an expanding universe.

Hayashi was born and educated in Kyoto, where he became professor of physics 1957.

Hayashi pointed out that in the Big Bang earlier than the first two seconds, the temperature would have been greater than 1010K, which is above the threshold for the making of electron–positron pairs. This radically altered the timescale proposed in the ‘hot Big Bang’ theory. He also showed that the abundance of neutrons at the heart of the Big Bang did not depend on the material density but on the temperature and the properties of the weak interreactions. Provided the density is great enough for the reaction between neutrons and protons to combine at a rate faster than the expansion rate, a fixed concentration of neutrons will be incorporated into helium nuclei, however great the material density is – producing a plateau in the relationship between helium abundance and material density.