Question: In what year did a Soviet, Russian, and American theoretical physicist, whose main contributions are in the field of condensed matter physics, come up with his famous theory?
Sentence (from "Keith Brueckner"): Keith Allen Brueckner (March 19, 1924 – September 19, 2014) was an American theoretical physicist who made important contributions in several areas of physics, including many-body theory in condensed matter physics, and laser fusion.
Relevant evidence: No