Alexander Dalgarno FRS[1] (5 January 1928 – 9 April 2015) was a British physicist who was a Phillips Professor of Astronomy at Harvard University.

[4] He was an academic at the Queen's University, Belfast from 1951 to 1967 where he worked with Sir David Bates and rose from assistant lecturer to professor.

In the 1950s, he laid the foundations for long-range atomic interaction studies which are of critical importance for today's interest in Bose–Einstein condensates.

Dalgarno's research covered three main areas: theoretical atomic and molecular physics, astrophysics and aeronomy (the study of the upper atmosphere).

Sir David Bates wrote in 1988 that "There is no greater figure than Alex in the history of atomic physics and its applications."