what was the feared runaway nuclear reaction from Oppenheimer?

Question

Can someone explain the feared runaway nuclear reaction that Oppenheimer presented Einstein in the film? The one where detonating a nuke would’ve exploded the whole world?

Wouldn’t that scenario require many orders of magnitude more energy than the output of the what the first (or current) nuclear weapons were capable of?

In: Physics

Answer 1

Two things:

1. A real but theoretical and highly unlikely chance that the detonation of an atomic bomb could result in a runaway fusion reaction that would destroy the world. It wasn’t true (nitrogen can fuse of course and this happens in very large stars at the end of their life – but at immense temperatures and pressures that far exceed any conditions that could be produced by a mere atomic detonation), but they ran the numbers to make sure.
2. A clever narrative device to create a second climax in the movie.

The challenge of telling Oppenheimer’s story is he has the mid-career climax of all climaxes at Trinity. You really can’t top that. But the second half of his career is kind of a long denouement in which not much dramatic happens. There’s the dispute over nuclear secrets and the development of The Super (H Bomb) and ultimately the security clearance issues and ultimate rehabilitation of Oppenheimer before an early cancer death. But it’s all. . .a big of a let down after Trinity.

But the use of the concern about the atmosphere burning was a very clever way to use a minor concern the scientists had to create a second climax which revolves around Oppenheimer’s fictionalized conversation with Einstein at Princeton. And I can’t remember the line, but we see it once early without the dialog and then at the end of the movie we see the scene play out again with the dialog and Oppenheimer says something like, do you remember when we ask you about the possibility of starting a chain reaction that would destroy the world? What if we did? And we see cuts to missiles launching presumably with thermonuclear warheads on them. And it creates this wonderful second climax as a way to tie in Oppenheimer’s career, his interest in the paradoxes of quantum mechanics, and the heightened concerns over an increasingly dangerous world.