Alpher, Ralph Asher

(1921– ) US physicist: (with Robert Herman) predicted microwave background radiation in space; and synthesis of elements in early universe.
A civilian physicist in the Second World War, Alpher afterwards worked in US universities and in industry. He is best known for his theoretical work concerning the origin and evolution of the universe. In 1948, Alpher, together with and , suggested for the first time the possibility of explaining the abundances of the chemical elements as the result of thermonuclear processes in the early stages of a hot, evolving universe. This work became known as the ‘alpha, beta, gamma’ theory. As further developed in a number of collaborative papers with R Herman (1914–97) over the years, and in another important paper with Herman and J W Follin Jr, this concept of cosmological element synthesis has become an integral part of the standard ‘Big Bang’ model of the universe, particularly as it explains the universal abundance of helium. The successful explanation of helium abundance is regarded as major evidence of the validity of the model. While this early work on forming the elements has been superseded by later detailed studies involving better nuclear reaction data, the ideas had a profound effect on later developments.

Again in 1948, Alpher and Herman suggested that if the universe began with a ‘hot Big Bang’, then the early universe was dominated by intense electromagnetic radiation, which would gradually have ‘cooled’ (or red-shifted) as the universe expanded, and today this radiation should be observed as having a spectral distribution characteristic of a black body at a temperature of about 5 K (based on then-current astronomical data). At that time radio astronomy was not thought capable of detecting such weak radiation. It was not until 1964 that and finally observed the background radiation. It was realized later that evidence for this radiation had been available in 1942 in the form of observed temperatures of certain interstellar molecules. The existence of this background radiation (current observed value 2.73 K), whose peak intensity is in the microwave region of the spectrum, is widely regarded as a major cosmological discovery and strong evidence for the validity of the ‘Big Bang’ model, to which Alpher, Gamow and Herman contributed the pioneering ideas.