June 24: Fred Hoyle

Fred Hoyle

June 24, 1915 – August 20, 2001

Sir Fred Hoyle FRS was an English astronomer primarily remembered today for his contribution to the theory of stellar nucleosynthesis and his often controversial stance on other cosmological and scientific matters, in particular his rejection of the Big Bang theory. In addition to his work as an astronomer, Hoyle was a writer of science fiction, including a number of books co-authored with his son Geoffrey Hoyle. Hoyle spent most of his working life at the Institute of Astronomy at Cambridge and served as its director for a number of years.

An early paper of Hoyle's made an interesting use of the anthropic principle. In trying to work out the routes of stellar nucleosynthesis, he observed that one particular nuclear reaction, the triple-alpha process, which generated carbon, would require the carbon nucleus to have a very specific energy for it to work. The large amount of carbon in the universe, which makes it possible for carbon-based life-forms (e.g. humans) to exist, demonstrated that this nuclear reaction must work. Based on this notion, he made a prediction of the energy levels in the carbon nucleus that was later borne out by experiment.

While having no argument with the Lemaître theory, (later confirmed by Edwin Hubble's observations) that the universe was expanding, Hoyle disagreed on its interpretation. He found the idea that the universe had a beginning to be philosophically troubling, as many argued that a beginning implies a cause, and thus a creator. Instead, Hoyle, along with Thomas Gold and Hermann Bondi, argued for the universe as being in a "steady state". The theory tried to explain how the universe could be eternal and essentially unchanging while still having the galaxies we observe moving away from each other. The theory hinged on the creation of matter between galaxies over time, so that even though galaxies get further apart, new ones that develop between them fill the space they leave. The resulting universe is in a "steady state" in the same manner that a flowing river is - the individual water molecules are moving away but the overall river remains the same.

The theory was the only serious alternative to the Big Bang which agreed with key observations of the day, namely Hubble's red shift observations, and Hoyle was a strong critic of the Big Bang. Ironically, he is responsible for coining the term "Big Bang" on BBC radio's Third Programme broadcast at 1830 GMT on 28 March 1949. It is popularly reported that Hoyle intended this to be pejorative, but the script from which he read aloud clearly shows that he intended the expression to help his listeners. In addition, Hoyle explicitly denied that he was being insulting and said it was just a striking image meant to emphasize the difference between the two theories for radio listeners.

The evidence that resulted in the Big Bang's victory over the steady state model, at least in the minds of most cosmologists, included the discovery of the cosmic microwave background radiation in the 1960s, the distribution of "young galaxies" and quasars throughout the Universe in the 1980s, a more consistent age estimate of the universe and most recently the observations of the COBE satellite in the 1990s and the Wilkinson Microwave Anisotropy Probe launched in 2001, which showed unevenness in the microwave background in the early universe, which corresponds to currently observed distributions of galaxies.

Hoyle appeared in a series of radio talks on astronomy for the BBC in the 1950s; these were collected in the book The Nature of the Universe, and he went on to write a number of other popular science books. In 1957 he was elected a Fellow of the Royal Society, and he was knighted in 1972. He was jointly awarded the Crafoord Prize by the Royal Swedish Academy of Sciences.