What didn’t happen

What didn’t happen

A self-sustaining fusion reaction taking place 93 million miles from Earth • Photo by Oscar Ävalos on Unsplash

Originally published 16 October 2005

Albert Ein­stein once said: “The most incom­pre­hen­si­ble thing about the world is that it is comprehensible.”

And when you think about it, it is indeed remark­able that a mass of nerve fibers the size of a can­taloupe can com­pre­hend the cos­mos — a vast geog­ra­phy of hun­dreds of bil­lions of galax­ies — at least! — with a 14 bil­lion year history.

Some can­taloupe-sized mass­es of nerve fibers are more remark­able than oth­ers. This year [in 2005] we cel­e­brate the 100th anniver­sary of Ein­stein’s “year of mir­a­cles,” when he pub­lished five papers on physics any one of which might have won him a Nobel Prize. One of the papers helped lay the foun­da­tions of quan­tum physics; two con­firmed the nature and dimen­sions of mol­e­cules; one estab­lished his the­o­ry of spe­cial rel­a­tiv­i­ty; and one debuted his famous equa­tion E=mc2, the equiv­a­lence of mat­ter and energy.

Ein­stein’s genius was being able to imag­ine what no one had imag­ined before — or saw any rea­son to imag­ine. He was able to imag­ine, for exam­ple, that a can­taloupe-sized ball of ura­ni­um or plu­to­ni­um might yield enough ener­gy to blow up a city. And if that was­n’t incom­pre­hen­si­ble, what is?

The idea was giv­en the ulti­mate test in the New Mex­i­co desert on the morn­ing of July 16, 1945. We’ve heard plen­ty about the test called Trin­i­ty, but few peo­ple know that what what was most impor­tant about the explo­sion was not what hap­pened, but 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. 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 tried before.

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-sized “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. 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.

When the bomb explod­ed, the con­fi­dence of at least one physi­cist was briefly test­ed. Emilio Seg­re, 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 three hun­dred years of exper­i­ments. Cal­cu­la­tions based on the incom­pre­hen­si­ble premise that the human mind can com­pre­hend the fun­da­men­tal archi­tec­ture of the universe.

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