Like the scientists first assumed in the movie ‘Oppenheimer’.
In: Physics
To understand why it *didn’t*, it’s helpful to understand why it *might have*.
Besides radioactive decay, there are two main types of nuclear reaction – fission (splitting a big nucleus into smaller ones) and fusion (joining small nuclei into bigger ones). The sun runs on fusion. Nuclear power and these early nuclear bombs run on fission.
Fusion requires very high temperatures and very high pressures. The scientists on the Manhattan Project were worried that an atomic bomb would briefly provide enough pressure and temperature to cause atmospheric gases to undergo fusion.
If the atomic bomb had caused fusion, and caused enough of it, then that fusion would have released more heat, expanding the zone of high temperature and pressure, creating still more fusion, and so on in a chain reaction that would encompass the whole globe.
When they calculated more carefully, they realised that the chance of this happening was miniscule, and it wasn’t a realistic worry.
That’s not to say fission bombs never cause fusion:
* Probably, in every atomic explosion, there are some fusion reactions happening nearby. Just nowhere near enough to cause a chain reaction.
* However, the way fusion bombs work is by redirecting all the energy of a fission bomb onto one specific spot, creating enough temperature and pressure to cause a large amount of fusion and therefore a bigger explosion. This doesn’t cause a runaway effect because the bomb is vaporised pretty quickly and the focusing mechanism is destroyed.
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