A curiosity piece: about the most expensive shortage in the history of science — fifty percent of the mass.
If in 1945 someone had been asked to describe the most important ménage à trois in the history of physics, they probably wouldn't have described Los Alamos — Los Alamos was monogamous. They would have described Germany: three groups, three leaders, one goal, and an utterly phenomenal inability of these groups to talk to each other. That's where the answer to the main "what if" of the twentieth century lies.
Let's start at the end, because good stories always start at the end. Summer 2013, physicist Tim Koeth, a collector of nuclear artifacts, drives to a parking lot for a "package." In a blue bag, wrapped in paper towels — a uranium cube about 5 centimeters on a side, weighing around 2.4 kilograms. Wrapped with a sheet of paper "like a ransom note on a rock": "Taken from the reactor that Hitler tried to build. Gift of Ninninger."
Koeth immediately understood he was looking at an artifact from the German wartime reactor. There was no mistaking it: the nature of the uranium, bubbles on the surface from primitive 1940s metallurgy, and most importantly — the note with the misspelled surname Nininger, a man who worked on the Manhattan Project. Nininger's wife would later confirm: yes, there was such a cube, yes, her husband gave it to a friend. But the question locked in that laboratory drawer was far more interesting than authenticity: where did the other 658 go?
Let's go back twenty years, to the winter of 1944. The German atomic program wasn't a monolith but three competing islands: Berlin (Werner Heisenberg), Gottow (Kurt Diebner), and Leipzig. This is crucial to understand: Germany didn't have "its own Manhattan" — it had an internal English Channel, and physicists were drowning in it one by one.
Heisenberg — author of the uncertainty principle, 1932 Nobel laureate, absolute star of German theoretical physics — by that point was finalizing his design for reactor B-VIII. The project was being built in a cave under a rock in the small town of Haigerloch in southern Germany — beneath a church, in a former beer cellar (now the Atomkeller Museum). Contemporaries described the B-VIII construction as a "sinister chandelier": 664 cubes of natural uranium, each weighing five pounds, suspended on aircraft cables in a tank of heavy water, with graphite shielding around.
Outwardly — a Gothic nightmare. Technologically — close to a breakthrough. According to a 2009 reconstruction, to achieve a self-sustaining chain reaction, they needed fifty percent more cubes. Germany didn't have them — or rather, they had them in the wrong place. More on that below, in the arithmetic chapter.
The choice of shape wasn't a detail. Geometry determines how neutrons travel through the lattice. Fermi in Chicago in 1942 built a stack of blocks and rods convenient for assembly-line production; the Germans bet on cubes in heavy water. And small-batch production — hundreds of identical castings for cottage-scale manufacturing — became their Achilles' heel.
Spring 1945. The Allies enter Germany, and Operation Alsos under General Leslie Groves plays out its role — it had been on the trail of German physics since 1943. The name is a brilliant joke born of boredom: "alsos" in Greek means "grove." That is, Groves's mission, signed by Groves, in Greek. There's more wit in that signature than in the entire German program.
Alsos digs up uranium from a field near Haigerloch — of 664 cubes they collect 659, five remain lost in the earth — and Heisenberg's documents have to be fished out of a cesspit: poor Samuel Goudsmit, scientific director of Alsos, got stuck with that particular job. The cubes are shipped to the United States. No official documented trail of this delivery exists. There was no need: by April 1945 Oak Ridge was doing just fine without German uranium.
The cubes literally dissolve into America — no invoices, no list, no trail. By 2019, searches by Koeth and his colleague Miriam Hiebert turn up ten specimens across the entire country: one at the Smithsonian, one at Harvard, several in private collections, one at Pacific Northwest National Laboratory (PNNL). And one — in that 2013 parking lot.
Heisenberg himself at this time leaves on a bicycle, with a couple of cubes in his backpack — away from American troops toward his family. Later, as a key intellectual resource, he's interned in England, at Farm Hall estate, along with other physicists from the program. This is the most crucial turning point of the entire story, and we'll return to it.
The cube isn't a criminal object, but the opposite of Hiroshima: all the physics of the era is in it, just without consequences. Natural uranium — a "natural product" — is weakly radioactive: 99.3% U-238, 0.7% U-235. In a 2.4 kg cube — self-shielding: the metal is so dense that radiation is almost entirely born and dies inside, emission comes only from the surface. You can walk around the kitchen with such a cube and set down a cup of coffee.
Within the first week Koeth constructed a gamma spectrometer and obtained an energy emission graph. An authentic natural uranium cube gives characteristic peaks; depleted uranium (a byproduct of enrichment for reactors) looks different. Result: Koeth's cube is genuine natural raw material, never operated in a reactor. No signs of cesium-137, which accumulates in irradiated material. The cube is a witness to failure, not its accomplice.
Now for the main dramatic knot. In July 1945, German physicists — Heisenberg, Otto Hahn (co-discoverer of nuclear fission, 1944 Nobel laureate in chemistry), Weizsäcker, Diebner, Wirtz, and others — are sitting at Farm Hall estate in England. Interned. Rooms bugged, transcripts of Operation Epsilon later declassified.
August 6, 1945, an officer enters the room and announces: an atomic bomb has been dropped on Hiroshima. Uranium. The reaction from the transcripts is Shakespearean-level:
Hahn (co-discoverer of fission): I don't believe it... They are 50 years ahead of us.
Heisenberg: I don't believe a word of it. They would have had to spend all their 500 million pounds on isotope separation — and then, perhaps...
Heisenberg made a mistake at the most painful point: he was looking for the answer in the wrong place. Manhattan indeed spent about $2 billion, but Hiroshima's "Little Boy" was a gun-type design: two pieces of uranium accelerated toward each other by conventional explosives. It required neither a reactor nor plutonium — only highly enriched uranium, which by August 1945 Oak Ridge was already churning out. The plutonium "Fat Man" detonated over Nagasaki — now that one required a reactor: the reactor in this scheme serves as a plutonium-239 factory. But the German path to either branch lay through their own reactor reaching criticality — and their reactor didn't make it.
Wirtz: I'm glad we didn't have it.
Weizsäcker: It's dreadful that the Americans did it. It's madness on their part.
Heisenberg: One can't say that. One might equally well say: "That's the quickest way of ending the war."
Hahn: That's what consoles me.
And then — classic: "We didn't make it because we didn't want to." Weizsäcker: "I think the reason is that all physicists didn't want to, on principle. If we'd all wanted Germany to win, we would have succeeded." Hahn: "I don't believe it, but I'm glad we didn't succeed."
This was renting moral comfort. A legend of purity that German physics would rent from itself for decades: we were too decent to make the bomb. The Farm Hall transcripts show something else: the program was killed not by morality but by fragmentation — three groups, zero cooperation, different departments and personal ambitions. Heisenberg himself later lets it slip: "we wouldn't have had the moral courage to ask the government in spring 1942 for 120,000 people to build it" — meaning Manhattan's manpower. That is, not "didn't want to" but "didn't dare."
A few days after Hiroshima, Heisenberg gives his colleagues a lecture on the physics of the uranium bomb — and his calculation turns out surprisingly adequate. The real nightmare for the Allies would have been if Germany had learned the truth about itself: only fifty percent more mass remained to the critical point — and no one in the game knew how close that was. In that gap lives the entire story.
Back to the number that deserves a bold "what if." The 2009 model says: B-VIII fell short of a self-sustaining chain reaction by roughly 50% in uranium mass. Not ten times more was needed — half. Now pay attention: Diebner in Gottow had about four hundred more cubes sitting idle. Rough strategic arithmetic: 664 + 400 — that's already over the needed ~1,000. All materials for breakthrough existed, but lay in two different cabinets of two different departments, and no one decided to combine them. Of course, two designs don't bolt together — this isn't a blueprint, it's a diagnosis. But it's a harsh diagnosis: had these cubes come together in one basement, Germany would have had a working reactor. A reactor — the path to plutonium. Plutonium in 1946 — a bomb.
This isn't fantasy. This is the geometry of failure: three groups standing in the same building don't share materials or data. A slap in the face to the idea that "brilliant physicist = powerful program." A program requires not genius but operational coherence. The US had one general who kept asking "why isn't it done yet," and one hard timeline dictator named Leslie Groves. Germany had three Nobel egos.
Here's where history stops being history and becomes pure detective work. In 2021, PNNL takes three cubes (including Koeth's Cube) and runs radioisotope forensics on them. Question: which cube belonged to Heisenberg and which to Diebner?
The evidence — coating. The Berlin group preserved cubes with cyanide lacquer, Gottow — with styrene. Brittany Robertson, a PNNL graduate student, took on a measurement everyone thought impossible: finding traces of organic coating that had spent eight decades next to uranium metal. "I honestly thought it was a shot in the dark," she admits. "I didn't believe organic material would survive next to uranium for decades and remain detectable." The shot in the dark hit the bullseye.
Result — a twist in the entire detective story. On Koeth's cube, which documents traced to Berlin, styrene coating was found — meaning the cube was from Gottow. But then the archives do a turnaround: Diebner sent some of his cubes to Heisenberg in Berlin when he needed more fuel. Koeth's cube may have worked in both reactors. One piece of metal, two groups, three cities, eighty years.
Practical bonus: PNNL uses its cube to train border guards from more than 73 countries — as a radiation sample for training in intercepting nuclear material smuggling. An artifact of the Nazi program became a sentinel of nonproliferation. Irony worthy of Vonnegut.
Of the 664 cubes dismantled at Haigerloch and 400 cubes from Gottow, the majority — that is, tons of natural uranium — are officially unaccounted for anywhere. Hiebert in 2023 published a book about this, "The Uranium Club." Koeth and Hiebert have an email open for "I have something similar in my garage." The club of people, accidental possessors of a cube — small, mysterious, scattered across the world.
The German program is the most fascinating scientific failure, and that's its value. It shows: science is driven not by intellect in a vacuum but by infrastructure of cooperation. Koeth's cube weighs two and a half kilograms — and behind it trails the entire subsequent world. A world where the reactor in a beer cellar beneath a church never reached the only thing "that one," the Chicago one, achieved back on December 2, 1942 — a self-sustaining chain reaction.
And somewhere out there, in a garage, in an attic, in a forgotten box, a cube may still lie. That very one. Weighing two and a half kilograms and fifty percent of history.
Sources: Koeth & Hiebert, "Tracking the journey of a uranium cube," Physics Today, May 2019 (doi:10.1063/PT.3.4202); Miriam Hiebert, "The Uranium Club: Unearthing the Lost Relics of the Nazi Nuclear Program," 2023; PNNL press feature, June 2019; Operation Epsilon / Farm Hall transcripts (ten physicists, 1945); ACS Fall 2021 (Robertson & Schwantes, radiochronometry); Atomkeller Museum, Haigerloch.