B2FH Paper - Physics Before Hoyle

Physics Before Hoyle

Prior to Hoyle's theory of nucleosynthesis in stars and to the B2FH paper, George Gamow advocated a theory of the universe according to which virtually all elements, or atomic nuclei, were synthesized during the big bang. The implications of Gamow's nucleosynthesis theory (not to be confused with present-day nucleosynthesis theory) is that nuclear abundances in the universe would necessarily be largely static. Thus, it was not known by Gamow and others that the abundances of chemical elements heavier than hydrogen and helium were not perfectly static. However, at the time, stellar fusion theories did not show how to create any elements heavier than helium, and so Gamow advocated the theory that all elements were residual from the big bang. Nuclear fusion in stars began when Hans Bethe and Charles L. Critchfield had together derived the pp-chain in 1938, and Carl von Weizsäcker and Hans Bethe had independently derived the CNO cycle in 1938 and 1939, respectively, to show that the conversion of hydrogen to helium by nuclear fusion could account for stellar energy production. This great insight by Bethe calculated how the sun is able to stay hot while it radiates heat for five billion years, but it did not extend to formation of the chemical elements in stars. The helium produced might simply remain in the core of the evolved stars. Then helium burning in stars was introduced in 1952 by Salpeter, and he extended that paper to show that fusion of carbon with itself might occur when the carbon products of helium burning became heated. Hoyle in 1954 saw how the excited 0+ state of carbon was required for it to burn and how the subsequent carbon burning process enabled almost the entirety of nucleosynthesis in stars. B2FH reviewed these pictures, suggesting that all atomic nuclei heavier than lithium must have been synthesized in stars and not during the big bang.