HERMANN BONDI, mathematician, astronomer, physicist and cosmologist, was best known for proposing, with Thomas Gold and Fred Hoyle, the steady-state theory of the Universe in 1948. It is a cosmological theory that the Universe has always existed in a steady state with no beginning and that it will have no end. It says that the mean density of the Universe is constant. But because the Universe is known to be expanding the theory states that matter is being continuously created as a property of space.
It was discovered in 1965, however, that there is a cosmic background of radiation of microwave frequencies. The steady-state theory cannot account for this microwave background radiation and so it was supplanted with another cosmological theory, called the big-bang theory, now favoured by cosmologists. According to the big-bang theory, all the matter and energy in the Universe were created from a minute particle of unimaginable density and temperature (a sort of primeval atom) that exploded at a definite moment in the past.
But by this time, Bondi had lost interest in the steady-state theory and focused his attention on the theory of relativity and black holes. In particular, he worked on the theory of accretion by which the gravitational pull of a black hole, or a star, accretes gas in its vicinity.
Bondi, the son of Samuel Bondi, a medical heart specialist, was born in Vienna.
His early education was at the Realgymnasium in Vienna and he then became an undergraduate at Trinity College, Cambridge, completing a degree in mathematics in 1940. The Second World War had started by then and, being Austrian, he was interned and sent, with Gold, from a camp in England to Canada.
In 1942, the British Government realised Bondi's potential and he was allowed to return to Britain to work as an experimental officer in the Admiralty. He worked for three years on radio installations, particularly the theory of aerials. This brought him together with Gold and Hoyle and started the collaboration that led to the steady-state theory.
In 1943, Bondi was elected to a research fellowship at Trinity, a post he held until 1949. In 1945, on his return from the Admiralty, he became an assistant lecturer in mathematics and, in 1948, he was promoted to university lecturer. In 1954, Bondi left Cambridge to become Professor of Mathematics at King's College London, remaining there until 1971.
Bondi made considerable contributions to public affairs and greatly influenced public life. Between 1967 and 1971, he was director-general of the European Space Research Organisation (ESRO). Founded in 1962 by ten European countries and Australia (which made available the rocket-firing range at Woomera), ESRO launched seven satellites between 1968 and 1972 using American rockets. In 1975, ESRO merged with its sister organisation ELDO (the European Launcher Development Organisation) to form the European Space Agency (ESA).
In 1971, Bondi became the chief scientific adviser to the Ministry of Defence, a post he held until 1977. Between 1977 and 1980, he was the scientific adviser to the Department of Energy. He was appointed to this post by Tony Benn, then Secretary of State for Energy, replacing Walter Marshall, of the United Kingdom Atomic Energy Authority, with whom Benn had found difficult to work.
In 1980, Bondi became the chairman and chief executive of the Natural Environment Research Council (NERC), remaining there until 1984. NERC does independent research into, and gathers knowledge about, the Earth from deep oceans to the upper atmosphere and from the poles to the equator. Between 1983 and 1990, Bondi was the Master of Churchill College, Cambridge, remaining a Fellow until his death. It was an appropriate appointment: Bondi was a great admirer of Winston Churchill, regarding him as a champion of liberty and the saviour of the free world.
In 1982, Bondi became president of the British Humanist Association, which promotes humanism and represents people who seek to live their lives without religious or superstitious beliefs, and remained so until 1990. In the same year, he became president of the Rationalist Press Association. Although a non believer, he had considerable respect for those with religious beliefs.
After the 1953 floods that overwhelmed London, Bondi wrote a major report that eventually resulted in the Thames Barrier. He regarded this as one of his greatest achievements.
Bondi was a great and influential scientist with a worldwide reputation. Good university students were inspired and encouraged by him. The less good ones found his blunt manner rather difficult to cope with.
Bondi had a strong sense of the responsibility of scientists. He played an active part in the Pugwash movement, organised by Professor Sir Joseph Rotblat (obituary, September 2), and attended a number of Pugwash conferences on science and world affairs.
Bondi was very keen on public education in science. He wrote many popular articles on science and, like Jacob Bronowski, was one of the first to popularise science on TV. Between 1981 and 1997, he was president of the Society for Research into Higher Education, and between 1981 and 1985 he was president of the British Association of Science Writers.
Bondi was elected Fellow of the Royal Society in 1959 and was knighted in 1973. He wrote many scientific papers and a number of books, including Cosmology (1952), The Universe at Large (1961), Relativity and Common Sense (1964), and his autobiography Science, Churchill and Me (1990). His many honours included the Gold Medal of the Einstein Society (1983), Decoration of Honour for Science and Art, Austria (1997), and the Gold Medal of the Royal Astronomical Society (2001). He was awarded honorary doctorates by the universities of Sussex, Bath, Surrey, York, Southampton, Salford, Birmingham, St Andrews, Portsmouth and Vienna.
His wife, two sons and three daughters survive him.