Conversation so far:
Who is Andrei Sakharov?
He was a Russian nuclear physicist, dissident, Nobel laureate, and activist for disarmament, peace and human rights
What happened with Andrei Sakharov in the 70's?
In 1970 Sakharov was among the three founding members of the Committee on Human Rights in the USSR along with Valery Chalidze and Andrei Tverdokhlebov.

Question: What year did he return to fundamental science?
Self-contained rewrite: What year did Andrei Sakharov return to fundamental science?