Brandon Carter

British physicist (1942–)

Born in Sydney, Australia, Carter was educated at the University of St. Andrews and at Cambridge University, where he completed his PhD in 1968. He remained in Cambridge as a research fellow at the Institute of Astronomy until 1973. Carter then moved to France to join the Centre National de la Recherche Scientifique (CNRS), working from 1986 as director of research at the Paris-Meudon Observatory.

In 1974 Carter formulated what is known as the anthropic principle. The argument began with Copernicus whose heliocentric system is often thought to have removed man from any special privileged position in the universe. Carter, however, insisted that it is privileged to the extent that our location in the universe must be compatible with our existence as observers. That is, if the universe had differed significantly in its size, age, and character then intelligent life would not now be present to observe it. If, for example, the strength of the gravitational force differed by just one part in 10⁴⁰ all stars would be either blue giants or red dwarves; with no Sun-like stars to nourish life, the universe would be without observers. The fact that it has observers, therefore, presupposes that the nuclear, gravitational, and electromagnetic forces all fall within some very narrow limits.

This is sometimes known as the ‘weak form’ of the anthropic principle. Carter advanced from this to the strong version with his claim that “The universe must have those properties which allow life to develop within it at some stage in its history.” While some physicists have seen in the anthropic principle a profound key to the secrets of nature, others have dismissed it on the grounds that it is immune to falsification, makes no significant predictions, and offers all its explanations after the event.