In 1964 he demonstrated that quantum mechanics is nonlocal and in some ways appears to require supraluminal signaling. He showed that von Neumannís proof against deterministic quantum mechanics lacked rigor and that Bohmís work got around von Neumannís objections through the use of supraluminal signaling. He later defended his work against those distorting its meaning to favor indeterministic quantum theories. He became a supporter of Bohmís work and called its suppression a "scandal" within physics.
He died in Belfast.