Fermi’s conclusion that carbon and heavier elements could not be produced in the big bang combined with Bethe’s assertion that these elements could not be produced in stars such as the Sun created a perplexing mystery: Where and how were the heavy elements synthesized? This was the point at which Fred Hoyle entered the picture.

In the late fall of 1944, Hoyle’s wartime activities in naval radar took him to the United States, where he used the opportunity to meet with one of the most influential astronomers of the time, Walter Baade, at the Mount Wilson Observatory in California. At the time, this observatory contained the largest telescope in the world. From Baade, Hoyle learned how enormously dense and hot the cores of massive stars can become during the late stages in their lives. Examining those extreme conditions, he realized that at temperatures approaching a billion degrees, protons and helium nuclei could easily penetrate the Coulomb barriers of other nuclei, resulting in such a high frequency of nuclear reactions and back-and-forth exchanges that the entire ensemble of particles could reach a state known as statistical equilibrium.

In nuclear statistical equilibrium, while nuclear reactions continue to occur, each reaction and its inverse occur at the same rate, so that there is no further overall net change in the abundances of the elements. Consequently, Hoyle argued, he could use the powerful methods of the branch of physics known as statistical mechanics to estimate the relative abundances of the various chemical elements. To actually perform the calculations, however, he needed to know the masses of all the nuclei involved, and that information was not available to him during the war years. Hoyle had to wait until the spring of 1945 to obtain a table of the masses from nuclear physicist Otto Frisch. The result of the ensuing calculation was an epoch-making paper published in 1946, in which Hoyle delineated the framework of a theory for the formation of the elements from carbon and higher in stellar interiors. The idea was mind boggling: Carbon, oxygen, and iron did not always exist (in the sense of having been formed in the big bang). Rather, these atoms, all of which are essential for life, were forged inside the nuclear furnaces of stars. Think about this for a moment: The individual atoms that currently form the two strands of our DNA may have originated billions of years ago in the cores of different stars. Our entire solar system was assembled some 4.5 billion years ago from a mixture of ingredients cooked inside previous generations of stars. Astronomer Margaret Burbidge, who was to collaborate with Hoyle a decade later, gave a wonderful description of her experience of listening to Hoyle at a meeting of the Royal Astronomical Society in 1946: “I sat in the RAS auditorium in wonder, experiencing that marvelous feeling of the lifting of a veil of ignorance as a bright light illuminates a great discovery.”

Scrutinizing the consequences of his embryonic theory, Hoyle was gratified to discover a marked peak in the abundances of the elements neighboring iron in the periodic table, just as the observations seemed to indicate. This consistency of the “iron peak,” as it came to be known, indicated to Hoyle that he was doing something right. However, those missing rungs in the ladder—the absence of stable nuclei at atomic masses 5 and 8—continued to beleaguer any attempt to construct a detailed (as opposed to a skeletal) network of nuclear reactions that would produce all the elements.

To circumvent the mass-gap problem, Hoyle decided in 1949 to reexamine the possibility (previously aborted by Bethe) of fusing three helium nuclei to create the carbon nucleus, and he assigned this problem to one of his PhD students. Since helium nuclei are also known as alpha particles, the reaction is usually referred to as the triple alpha (3α) process. As it so happened, that particular student decided to ditch his PhD work before completing it (he was Hoyle’s only student to ever do so), but he failed to cancel his formal registration. The rules of academic etiquette set for such cases by the University of Cambridge were clear: Hoyle was not allowed even to touch the problem until either the student or an independent researcher published the results. Eventually, two astrophysicists published results, although the work of one of them went almost entirely unnoticed.