Originally published 2 November 1992
It was the most fateful physics experiment of all time.
The experiment was called Trinity, and it took place in the New Mexico desert on the morning of July 16, 1945.
Detonation of the world’s first atomic bomb proved that an explosive nuclear chain reaction was possible. What made the experiment even more important was what didn’t happen.
The chain reaction did not get out of control. The atmosphere and oceans did not ignite. The world did not end in a planet-enveloping blaze of light.
The Trinity bomb was not just an experiment in the application of atomic energy. It was a test of physics itself. It was a test of the power of the human mind to comprehend the laws of nature.
And the stakes were overwhelming.
A few dozen physicists bet everything — all life on the planet! — on their ability to calculate in advance the result of an experiment that had never been performed before. It was a wager of cosmic proportions.
Even Hitler blanched at the stakes.
Early in the war — the spring of 1942 — German physicists apprised Hitler, through his minister for armaments and war production, Albert Speer, of the possibility of constructing a nuclear bomb. Speer asked Werner Heisenberg, spokesman for the German nuclear scientists, whether a successful nuclear explosion could be kept under control with absolute certainty, or whether it might continue through the atmosphere as a chain reaction. According to Speer, Heisenberg hedged.
Speer wrote in his memoirs: “Hitler was plainly not delighted with the possibility that the earth under his rule might be transformed into a glowing star.”
A few months later, in the summer of 1942, American physicists considered the same awesome possibility. By then they knew that a fission bomb was possible. Atoms of uranium 235 are inherently unstable. When one breaks apart (fissions) spontaneously, a tiny amount of energy is released — along with an average of two subatomic particles called neutrons. The neutrons can collide with other uranium 235 atoms and cause them to break apart. With the right amount of uranium — a cantaloupe-size “critical mass” — a chain reaction of fissioning atoms will release a staggering amount of energy in a tiny fraction of a second.
Physicist Edward Teller considered another possibility. The huge temperature of a fission explosion — tens of millions of degrees — could fuse together nuclei of light elements, such as hydrogen, a process that also releases energy (later, this insight would be the basis for hydrogen bombs). If the temperature of a detonation was high enough, nitrogen atoms in the atmosphere would fuse, releasing energy. Ignition of atmospheric nitrogen might cause hydrogen in the oceans to fuse. The Trinity experiment might inadvertently turn the entire planet into a chain-reaction fusion bomb.
Robert Oppenheimer, chief of the American atomic scientists, took Teller’s suggestion seriously. He discussed it with Arthur Compton, another leading physicist. “This would be the ultimate catastrophe,” wrote Compton. “Better to accept the slavery of the Nazis than run a chance of drawing the final curtain on mankind!”
Oppenheimer asked Hans Bethe and other physicists to check their calculations of the ignition temperature of nitrogen and the cooling effects expected in the fireball of a nuclear bomb. The new calculations indicated that an atmospheric conflagration was impossible.
Later, Teller wrote of those heady days: “The discussions were fascinating and intense. Facts were questioned and the questions were answered by still more facts…A spirit of spontaneity, adventure, and surprise prevailed during those weeks…and each member of the group helped move the discussion toward a positive conclusion.”
Three years later, in the New Mexico desert, there was enough uncertainty about the outcome of the experiment to make a betting pool interesting. Richard Rhodes describes what happened in his award-winning book The Making of the Atomic Bomb. Senior scientists each put a dollar in the kitty. Edward Teller bet the bomb would pack the explosive equivalent of 45,000 tons of TNT. Hans Bethe picked 8,000 tons. Oppenheimer chose a modest 300 tons. All of the scientists were utterly convinced that even the most optimistic estimate of the bomb’s power would not produce temperatures high enough to ignite the atmosphere.
Nevertheless, the terrible possibility was on people’s minds. Enrico Fermi, one of the most brilliant of the atomic scientists, offered to take bets on whether or not the bomb would ignite the atmosphere, and if so, whether it would merely destroy New Mexico or the entire world. His macabre humor was not appreciated by everyone.
When the bomb actually exploded, the confidence of at least one physicist was briefly tested. Emilio Segrè, an eyewitness and nuclear scientist, wrote: “We saw the whole sky flash with unbelievable brightness in spite of the very dark glasses we wore…I believe that for a moment I thought the explosion might set fire to the atmosphere and thus finish the Earth, even though I knew that this was not possible.”
Not possible. Why?
Because the calculations said so. Calculations scribbled on blackboards and countless pads of paper. Calculations based on mathematical theories of the atom, of gas mechanics, of thermodynamics, of electromagnetism. Calculations based on 300 years of experiments. All of physics was riding on the bet.
The fate of the world was riding on the bet.
And the physicists won.
