Jonathan Fetter-Vorm

“Only one facet of the atomic bomb was still missing: Criticality. “Criticality” is a term used to describe the ideal conditions for a chain reaction. A row of dominoes is “critical: if each domino that falls knocks over one other. Fermi assembled a “critical mass” of uranium in his reactor, and he achieved a linear chain reaction. Each atom that fissioned caused one other atom to fission. Theoretically, that sort of reaction can go on forever (given infinite atoms), but it’s not getting any bigger. A bomb, however, requires something more explosive: a chain reaction that grows exponentially. A bomb requires a super critical mass.

Imagine an area the size of an empty basketball court and a pile of dominoes. To make a super critical mass, line up the dominoes so that each one that falls will knock over two more dominoes. And each one of those knocks two more over, and so on… This is essentially what happens inside the core of an atomic bomb. The reactive material — uranium or plutonium — is packed together so tightly that when one atom fissions the released neutrons can’t help but hit two more atoms, causing them to fission as well. In other words, once a super-critical mass is assembled, an exponential chain reaction is practically inevitable.

Variations on this kind of super-critical mass happen often in nature. Avalanches. Epidemics. But it’s a lot harder for humans to re-create these sorts of complex systems. A super-critical reaction requires an astounding amount of work and organization just to get all the necessary pieces arranged in the right order. All this work, whether it’s lining up dominoes or enriching uranium, builds toward one single moment: the moment when what was once impossible becomes unavoidable. In that moment the logic of the chain reaction takes over. The fire will only stop when there is nothing left to burn.

The Trinity test was that moment. Once construction had finished on the factories, the laboratories, and the test sites… once the nation’s brightest minds had demonstrated the potential power of nuclear fission… and, finally, once the military had organized these many parts into a coherent plan to test a bomb… a chain reaction was about to be set in motion, making certain outcomes inevitable.

With all that momentum, if a bomb could indeed be built, was there any justification to not build it? And once a workable bomb was built, was there really any chance that it wouldn’t be used?”
― Jonathan Fetter-Vorm, Trinity: A Graphic History of the First Atomic Bomb

“The fire will only stop when there is nothing left to burn.”
― Jonathan Fetter-Vorm, Trinity: A Graphic History of the First Atomic Bomb