# 2015 Dirac medal

Professor John David Barrow, University of Cambridge, for his combination of mathematical and physical reasoning to increase our understanding of the evolution of the universe, and his use of cosmology to increase our understanding of fundamental physics.

John Barrow is a highly original scientist whose work is concerned with fundamental questions about the origin and nature of the universe. He has been at the forefront of theoretical cosmology for more than 35 years. His book, The Anthropic Cosmological Principle, co-written with Frank Tipler, has been highly influential and unusually, uses physics to address philosophical issues. It is now a major part of cosmological thought.

Barrow’s research in cosmology is extraordinarily far ranging and he has made important contributions across many areas of gravitation, astrophysics and cosmology. It spans work of a mathematical nature, particle physics, mathematical statistics and observation. An example of his creativity coupled with ability to seek unconventional solutions to longstanding problems is his work on anisotropic cosmological models. He resurrected these from mathematical abstraction to develop challenging confrontations with data on primordial nucleosynthesis and the cosmological microwave background. He performed ever more intriguing comparisons with data in his papers on non-trivial topologies in cosmology.

His work on fundamental constants is of key importance, in particular his work on astronomical probes of the constancy of physical constants. He helped to pioneer new astronomical probes of the constancy of physical constants that are far more sensitive than laboratory experiments. They provided the first evidence for a time variation in the fine structure constant and the best upper bound on varying gravitational constant (G). He extended and solved Einstein’s equations to include a varying fine structure “constant” and predicted a detectable violation of the weak equivalence principle. He also found powerful new bounds on the spatial variations of many constants of Nature and was the first to show how galaxy formation leads to an anthropic upper bound on the magnitude of the cosmological constant.

Barrow is also a distinguished writer and lecturer for non-specialist audiences. His work in this area has made a huge contribution to public engagement with science.