What Are The Odds We Destroy The World?

How should science deal with existential risks?

Credit to hipydeus. Shared under CC BY 2.0.

At first the terrifying prospect seemed plausible. Detonate an atom bomb in water, scientists had already realised, and you can trigger an even bigger explosion — a technique would later become the hydrogen bomb. But why, Edward Teller wondered, would water be needed? What would happen if you used air instead?

The concept was simple. When an atom bomb explodes in a tank of purified heavy water, the result is an explosive chain reaction. The energy of the bomb forces hydrogen atoms in the water to collide, and every time that happens a powerful pulse of energy is released. Each pulse adds a bit more energy to the explosion, until a nuclear inferno erupts.

That was fine, the scientists thought, and perfectly controllable, as long as your aim was to blow up a city. But Teller took things a step further. If heavy water could detonate a hydrogen bomb; why not sea water? The sea is full of hydrogen too, and thus susceptible to the same chain reaction. Unlike the hydrogen bomb, however, the sea is vast in size, and the potential chain reaction uncontrollable.

Could detonating an atom bomb in the sea trigger a chain reaction that would swallow the planet in a nuclear inferno? That idea was bad enough, but things could get worse. What if you detonated the bomb in air, as the scientists at Los Alamos planned to do in six months time?

Air doesn’t contain much hydrogen, but it does contain nitrogen, an atom that can undergo the same type of explosive chain reaction. When they set off the first atom bomb, Teller wondered, might they also ignite a nitrogen chain reaction throughout the atmosphere? Would the bomb destroy humanity and turn Earth into a miniature star?

The prospect was terrifying enough to make its way up the chain of command, attracting the attention of senior figures in the Manhattan Project. Scientists were ordered to study the risk. A wonderfully titled paper, “Ignition of the Atmosphere With Nuclear Bombs” was written, deeming the chances irrelevant.

The idea of burning the atmosphere, the physicists concluded, was impossible. The nitrogen in the air was too spread out, the heat of the bomb too low. Six months later the…