inserted its multiple detonators, and connected them through a harness of cables to a bank of battery-powered capacitors that would charge them. Oppenheimer gave his offspring a final inspection Sunday evening; it crouched in the high cab ugly as Caliban.

The test was scheduled for Monday morning, July 16, just before dawn. Los Alamos scientists, project leaders flown down from Washington, and Army men gathered to watch it. A front off the Gulf of Mexico had blown in. Thunderstorms began lashing the Jornada at about 0200 hours. “It was raining cats and dogs, lightning and thunder,” the Columbia University physicist I. I. Rabi remembered, and everyone was “really scared [that] this object there in the tower might be set off accidentally.” But, by 0315, the clouds had begun to open and a few stars were shining. The countdown started in the control bunker ten thousand yards south of ground zero. At 0529:45, the firing circuit closed.

Detonators at thirty-two detonation points simultaneously fired, igniting concentric shells of shaped charges that directed the explosion inward. A shock wave moved through the heavy uranium tamper shell that surrounded the core, liquefied it, squeezed the core itself to a critical mass less than half its former diameter, and smashed the little initiator at the very center of the arrangement, kicking free a few neutrons to start the chain reaction. And then nuclear fission multiplied its prodigious energy release exponentially through eighty generations in millionths of a second, heating the core to a fireball hotter than the center of the sun that began ferociously expanding.

It was too hot to see, but as it expanded, it cooled to visibility. Rabi at base camp felt menaced: “We were lying there, very tense, in the early dawn, and there were just a few streaks of gold in the east; you could see your neighbor very dimly. Those ten seconds were the longest ten seconds that I ever experienced. Suddenly, there was an enormous flash of light, the brightest light I have ever seen. ... It blasted; it pounced; it bored its way right through you. It was a vision which was seen with more than the eye. It was seen to last forever. You would wish it would stop; altogether it lasted about two seconds. Finally it was over, diminishing, and we looked toward the place where the bomb had been; there was an enormous ball of fire which grew and grew and it rolled as it grew; it went up into the air, in yellow flashes and into scarlet and green. It looked menacing. It seemed to come toward one.

“A new thing had just been born,” Rabi adds, “a new control; a new understanding of man, which man had acquired over nature.”

What was that new control, that new understanding? Military men imagined at first that the scientists had

delivered to them a decisive new weapon of war, but the scientists had done the numbers and knew better. Nuclear weapons were too destructive to be decisive. So long as one nation held a monopoly on them, it would still be possible to use them, as the United States demonstrated at Hiroshima and Nagasaki. But the knowledge required to build such weapons was no secret; it was physics. And once other nations applied it, as they soon would do, so much destructive force would become available to them that conflict between nuclear powers would be rendered suicidal.

Nuclear weapons would not put an end to all war, since wars could still be fought below the nuclear threshold. But they would raise a bar against unlimited wars like the two world wars that scarred the twentieth century. After Trinity the choice would no longer be war or peace. The choice would be limited war or general destruction. National leaders saw the futility of nuclear war almost immediately despite their desperate stockpiles and their occasional displays of brinkmanship. McGeorge Bundy, John Kennedy’s and Lyndon Johnson’s national security adviser, confirmed the transformation retroactively as early as 1969, writing that “in the light of the certain prospect of retaliation, there has been literally no chance at all that any sane political authority, in either the United States or the Soviet Union, would consciously choose to start a nuclear war. This proposition is true for the past, the present and the foreseeable future.”

The experiment at Trinity thus marked the historic moment when science as an institution, going about its open, democratic, and peaceful business of trying to understand how the world really works (rather than how we would like it to work), surpassed in power and authority the belligerent system of nation-states that had dominated the world since the eighteenth century. Niels Bohr, the great Danish physicist, who had worked on the bomb at Los Alamos, explained the change most simply. “We are in a completely new situation,” he said in 1957, “that cannot be resolved by war.” But war is the ultimate determinant of national sovereignty. Science, by discovering how to release the energy locked in the atomic nucleus, had discovered a limit to war, which forced national leaders to limit their most destructive expression of national sovereignty. In the long history of human slaughter, that is no small achievement.

Some experiment.