John Trevor Lewis, a mathematical physicist of considerable international repute, has died aged 71. He was principal investigator at the Communications Network Research Institute in the Dublin Institute of Technology (DIT), founder and chief scientist of Corvil Ltd and former director of the School of Theoretical Physics in the Dublin Institute for Advanced Studies (DIAS).
In the words of an old Oxford colleague, "John was a lovely man and a perfect fit to my ideal of an academic: a man of great learning, lightly worn, and no conceit of himself."
Lewis was born in Swansea in 1932 to Tegwyn and Trevor, a ship broker. He was educated at Cardiff High School and, when the family moved to Belfast after the second World War, the Royal Belfast Academical Institution.
He studied in Queen's, Belfast, where he met Maureen MacEntee, an organic chemist. They were married in September 1959 and have four children, of whom he often spoke with quiet pride.
In 1955 he was awarded his doctorate in applied mathematics by Queen's. He became a research lecturer at Christ Church, Oxford, in 1956 and a tutorial fellow in mathematics in Brasenose College in 1959. He was appointed to a university lectureship at the Mathematical Institute, Oxford, in 1965. While at Oxford he supervised 15 successful doctorate candidates, many of whom have become renowned academics in their own right.
He came to Dublin in 1972 to take up a senior professorship in the School of Theoretical Physics of DIAS and served as director of the school from 1975 until his retirement in 2001. It was characteristic of Lewis's generosity that one of his first acts as director was to introduce an open-access policy to its facilities, enabling scientists from all over Dublin to further their research.
His doctoral thesis introduced a method now known in most texts on quantum mechanics as the Dalgarno-Lewis method. In 1969 he spent a year at the Institute for Advanced Study in Princeton, New Jersey, and Rockefeller University, New York. His research ambitions were strongly influenced by his interactions there with the late Prof Mark Kac, who introduced him to two key topics. One was the study of noise in quantum mechanical systems, which brought him into a long-term collaboration with Profs Bill Ford and Bob O'Connell.
The other topic was boson condensation, the phenomenon that gives rise to superconductivity, which he continued to pursue in Dublin with Dr Joe Pule and others. Their work took a crucial turn in 1984 when they started using Large Deviation Theory to great effect.
This branch of probability theory underpins our understanding of areas as diverse as the mathematics of insurance and Shannon's theory of information. With Prof Charles Pfister and Dr Wayne Sullivan he used it to prove an elegant result known as the equivalence of ensembles.
In 1988, having reversed a Government decision to close DIAS, John set about broadening the scope of its research. On visits to Moscow he met leading researchers in the Institute for Problems in Information Transmission. They supported their research in pure mathematics with applications to telecommunications.
Inspired by this, he launched a programme investigating the applications of Large Deviation Theory to the Internet. After a revolutionary insight on how to measure Internet traffic, Lewis persuaded visionaries from the Computer Laboratory in Cambridge and the Swedish operator Telia to join him in a three-year research contract funded by the European Commission.
Starting in 1996, the project supported nearly a dozen students in pursuit of higher degrees in mathematics. After its successful conclusion, he led several of the researchers in commercialising the research.
The thriving company he founded, Corvil Ltd, was recognised this year as a "Technology Pioneer" by the World Economic Forum. Lewis also sought to complement his commercial success in networks with fundamental research. He bid successfully for a prestigious principal investigator award from Science Foundation Ireland, and in 2001 he and his team established the Communication Networks Research Institute (CNRI) in DIT.
He was a gifted teacher with a rare ability to present clearly the essential principles of a difficult subject without compromising its complexity. In Dublin, although his position was free of teaching duties, his passion for teaching mathematics led him to offer his talents to the School of Mathematics in Trinity College. For 24 years he taught statistical mechanics and probability theory to undergraduates.
He took his responsibilities as a physicist seriously and in 1971 helped found the Irish branch of the Pugwash Conferences on Science and World Affairs. Pugwash shared the 1995 Nobel Peace Prize with its president, Joseph Rotblat.
Lewis was elected president of the Irish Federation of University Teachers (IFUT) just before the Government announced its 1987 decision to close Carysfort Training College. He rose to the challenge and heartened IFUT members with rousing speeches while tirelessly engaging with the Government to find a solution, in which he succeeded.
It is a measure of the respect that he commanded that universities and governmental bodies in different countries sought his guidance on research standards and policies.
His close relationship with Trinity was marked by an honorary professorship and patronship of the Hamilton Mathematics Institute. He held honorary professorships at the Universities of Swansea and Cardiff. He was very pleased to accept many awards, including the Senior Vice-Presidency of the Royal Irish Academy in 1998, and one of the first honorary doctorates from DIT in 1999.
A keen sportsman throughout his life, he captained Queen's University Boat Club, with which he won the national senior championship for eights in 1953. He later rowed for Christ Church, reaching the final of the Ladies' Plate at Henley in 1957.
John Lewis is survived by his wife Maureen, children Caitriona, Michael, Roisin and Ciaran, brother Arthur, and five grandchildren.
John Lewis: born, April 15th, 1932; died, January 21st, 2004