In real life and in Christopher Nolan’s forthcoming film Oppenheimer, the engineers working closest to the Manhattan Project knew there was a chance that the atomic bomb might ignite the entire planet’s atmosphere. That fear’s very palpable in the movie’s latest trailer but isn’t nearly enough to stop anyone from racing toward the invention of a bomb that shaped the arc of history.

Though it’s full of artful explosions and the deeply unsettling crackle of a Geiger counter, Oppenheimer’s latest trailer mainly focuses on J. Robert Oppenheimer (Cillian Murphy) — the theoretical physicist and Los Alamos Laboratory director who oversaw the design of the atomic bomb — grappling with the gravity of what he and his colleagues are creating.

With Nazi Germany already being months into development on a bomb of its own, Oppenheimer, his wife Kitty (Emily Blunt), and Lieutenant General Leslie Richard Groves (Matt Damon) know that time isn’t on their side as they set out to recruit numerous scientists to become part of the Manhattan Project without their understanding what they’re becoming a part of. Oppenheimer fully understands, though, and the trailer emphasizes how his insight into what the bomb is and what it can do was both a source of deep hope and abject fear.

Oppenheimer hits theaters on June 21st.