Conversation so far:
Who is Andrei Sakharov?
Andrei Dmitrievich Sakharov was a Russian nuclear physicist, dissident, Nobel laureate, and activist for disarmament, peace and human rights.
What happened to Andrei Sakharov in the 70s?
In 1972 Andrei Sakharov became the target of sustained pressure from his fellow scientists in the USSR Academy of Sciences, the Soviet press.
What else did you find interesting about Andrei Sakharov?
Andrei Sakharov was the first to propose proton decay and to consider CPT-symmetric events occurring before the Big Bang.

Question: What was the big bang?
Self-contained rewrite: What was the cosmological event called the big bang?