Why did J Robert Oppenheimer study physics?

Answer 1

Like most of the scientists on the Manhattan Project, the threat (or fear) that the Nazi's were developing an atomic weapon, basically compelled them (and the Army) to proceed with the development.

Answer 2

J. Robert Oppenheimer studied physics because he was fascinated by the fundamental workings of the universe and sought to uncover the secrets of nature through scientific research. His interest in physics led him to become a prominent theoretical physicist and eventually play a key role in the development of the atomic bomb during World War II.