In their spare moments at the naval radar research facility, the trio of Hoyle, Bondi, and Gold started to discuss astrophysics, and these collaborative exchanges continued after the war. In 1945 all three returned to Cambridge, and until 1949 they spent a few hours together every day at Bondi’s place. It was during that period that they started thinking about cosmology—the study of the entire observable universe, all treated as one entity. The Royal Astronomical Society asked Bondi to write what was then called a note, which was really a review article that would bring together an extensive body of knowledge. Hoyle suggested cosmology as the topic, since in his view “the subject had been in abeyance for a long time.” To bring himself up to speed on the subject, Bondi immersed himself in the existing literature, including a sweeping 1933 article entitled “Relativistic Cosmology” by physicist Howard Percy Robertson. Hoyle, who had previously read the article, also decided to go through it again in more detail. They both realized that the almost encyclopedic essay rather dispassionately covered various possibilities for cosmic evolution without offering an opinion. In his typical nonconformist fashion, Hoyle immediately started thinking, “Has he [Robertson] really thrown his net wide enough? Are there any other possibilities?” At the same time, Gold was thrusting himself into more philosophical ideas about the universe. These were the seeds for the theory of steady state cosmology, which was put forward in 1948. As we shall soon discover, the theory had been a serious contender to the big bang for more than fifteen years before it became the focus of often-acrimonious controversy.

Bold ideas, unjustified anticipations, and speculative thought are our only means of interpreting nature . . . Those among us who are unwilling to expose their ideas to the hazard of refutation do not take part in the scientific game.

—KARL POPPER

Fred Hoyle’s most enduring works were in the areas of nuclear astrophysics and stellar evolution. Yet most of those who remember him from his popular books and prominent radio programs know him as a cosmologist and co-originator of the idea of a steady state universe. What does being a cosmologist really mean?