Greg Peshkov was with the scientists watching from ten thousand yards away. He had two hopes: first, that the bomb would work; and second, that ten thousand yards was far enough.

The countdown started at nine minutes past five in the morning, Mountain War Time, on Monday 16 July. It was dawn, and there were streaks of gold in the sky to the east.

The test was codenamed Trinity. When Greg had asked why, the senior scientist, the pointy-eared Jewish New Yorker J. Robert Oppenheimer, had quoted a poem by John Donne: ‘Batter my heart, three-person’d God.’

‘Oppie’ was the cleverest person Greg had ever met. The most brilliant physicist of his generation, he also spoke six languages. He had read Karl Marx’s Capital in the original German. The kind of thing he did for fun was learn Sanskrit. Greg liked and admired him. Most physicists were geeks but Oppie, like Greg himself, was an exception: tall, handsome, charming, and a real ladykiller.

In the middle of the desert, Oppie had instructed the Army Corps of Engineers to build a one-hundred-foot tower of steel struts in concrete footings. On top was an oak platform. The bomb had been winched up to the platform on Saturday.

The scientists never used the word ‘bomb’. They called it ‘the gadget’. At its heart was a ball of plutonium, a metal that did not exist in nature but was created as a by-product in nuclear piles. The ball weighed ten pounds and contained all the plutonium in the world. Someone had calculated that it was worth a billion dollars.

Thirty-two detonators on the surface of the ball would go off simultaneously, creating such powerful inward pressure that the plutonium would become more dense and go critical.

No one really knew what would happen next.

The scientists were running a betting pool, dollar a ticket, on the force of the explosion measured in equivalent tons of TNT. Edward Teller bet 45,000 tons. Oppie bet 300 tons. The official forecast was 20,000 tons. The night before, Enrico Fermi had offered to take side bets on whether the blast would wipe out the entire state of New Mexico. General Groves had not found it funny.

The scientists had had a perfectly serious discussion about whether the explosion would ignite the atmosphere of the entire earth, and destroy the planet; but they had come to the conclusion that it would not. If they were wrong, Greg just hoped it would happen fast.

The trial had originally been scheduled for 4 July. However, every time they tested a component, it failed; so the big day had been postponed several times. Back at Los Alamos, on Saturday, a mock-up they called the Chinese Copy had refused to ignite. In the betting pool, Norman Ramsey had picked zero, gambling that the bomb would be a dud.

Today detonation had been scheduled for 2 a.m., but at that time there had been a thunderstorm – in the desert! Rain would bring the radioactive fallout down on the heads of the watching scientists, so the blast was postponed.