EARLY in Oppenheimer, the protagonist, who led the US atomic bomb development programme during WWII, attempts half-heartedly to poison one of his supervisors by injecting an apple with poisonous chemicals.

As a science student in an experimental lab, he has easy access to these chemicals. As the film explores, these poisonous materials are not the most deadly things that Oppenheimer works with in his life. The Manhattan Project that Oppenheimer and many thousands of others worked on in strict secrecy culminated in the first atomic weapons: two bombs that killed at least 130,000 people in Hiroshima and Nagasaki. 

The rationale behind the secrecy was obvious. They were designing the deadliest bomb anyone had ever seen, and trying to do so before the Nazis. Since then, there have been no further uses of atomic bombs in war, although how to build an atomic weapon is no longer secret.