WWII Science & Technology: The Race That Changed Everything - Part 2: The Scientists Who Refused: When Genius Said No to War

The Most Consequential Failure in History

In the summer of 1942, Werner Heisenberg—one of the greatest physicists who ever lived, Nobel laureate, father of quantum mechanics—made a calculation that would determine the fate of millions.

He got it spectacularly wrong.

The question that has haunted historians for eight decades: Was it a mistake, or a choice?

The Uranverein: Germany’s Forgotten Manhattan Project

When World War II began, Germany had every advantage in the nuclear race. They had:

• The discoverers of fission: Otto Hahn and Lise Meitner (before she fled)
• The best theoretical physicists: Heisenberg, Carl Friedrich von Weizsäcker
• A head start: The Uranverein (Uranium Club) began in April 1939
• Heavy water: Control of Norway’s Norsk Hydro plant

The Americans, by contrast, were late to the game. Einstein’s famous letter to Roosevelt wasn’t sent until August 1939. The Manhattan Project didn’t truly begin until 1942.

Yet Germany never came close to building a bomb. Why?

The Official Explanation: Resources and Priorities

The conventional historical narrative is straightforward:

1. Hitler didn’t understand physics and preferred “wonder weapons” he could visualize
2. German industry was overstretched fighting on multiple fronts
3. Allied bombing disrupted research facilities
4. The heavy water raids at Norsk Hydro set the program back years

All true. All insufficient.

Because the deeper you dig, the stranger the story becomes.

The Heisenberg Calculation Problem

Here’s where it gets interesting.

To build an atomic bomb, you need to know the “critical mass”—the minimum amount of fissile material needed for a self-sustaining chain reaction. Get this wrong, and you’re either building a dud or wasting years acquiring unnecessary material.

The Manhattan Project, through painstaking experimentation and theoretical work, determined that roughly 52 kilograms of highly enriched uranium-235 would be sufficient.

Heisenberg’s estimate? Several tons.

“It would require tons of U-235, making a bomb practically impossible.”
— Heisenberg’s report to German Army Ordnance, 1942

This wasn’t a minor error. This was the difference between “difficult but achievable” and “forget it, focus on rockets.”

The Copenhagen Meeting: History’s Most Mysterious Conversation

In September 1941, Heisenberg traveled to Nazi-occupied Copenhagen to meet with Niels Bohr, his former mentor and one of the founders of quantum physics.

What they discussed has been debated ever since.

Bohr left the meeting convinced Heisenberg was working enthusiastically on a German bomb. Heisenberg later claimed he was trying to establish a mutual agreement among physicists not to build nuclear weapons.

The truth died with both men. But the meeting’s aftermath is telling:

• Bohr immediately began cooperating with Allied intelligence
• The information contributed to Allied fears and accelerated the Manhattan Project
• Heisenberg returned to Germany and… slowed down

The Farm Hall Transcripts: Caught on Tape

After Germany’s surrender, ten German nuclear scientists—including Heisenberg—were detained at Farm Hall, an English country house.

What they didn’t know: every room was bugged.

The transcripts of their conversations, declassified in 1992, are extraordinary documents. When news of Hiroshima reached them on August 6, 1945, the recordings captured their reactions in real-time.

Heisenberg’s immediate reaction: Disbelief. He insisted it must be propaganda, that a bomb was impossible.

Then, over the following days: He rapidly recalculated and arrived at roughly the correct critical mass—within 48 hours.

This raises an uncomfortable question: If he could solve it in two days under pressure, why couldn’t he solve it in five years with a staff and resources?

The Passive Resisters

Heisenberg wasn’t alone in his apparent… lack of urgency.

Carl Friedrich von Weizsäcker steered the program toward reactor research—useful for power generation, but a dead end for weapons. He later claimed this was deliberate.

Max von Laue, Nobel laureate, refused to participate at all and spent the war years quietly undermining the program.

Otto Hahn, who had discovered fission, was reportedly “shattered” when he learned his discovery had killed 80,000 people at Hiroshima. The Farm Hall recordings show him in genuine anguish.

“I was completely shocked. I felt responsible for the deaths of a large number of people.”
— Otto Hahn, Farm Hall, August 1945

The Conscience Hypothesis

There’s a reading of history that goes like this:

German physicists, many of whom had Jewish friends and colleagues, many of whom despised the Nazi regime, found themselves conscripted into weapons research. They couldn’t openly refuse—that would mean death. But they could:

• Overestimate difficulties
• Underestimate urgency
• Pursue “promising” dead ends
• Fail to solve problems they could have solved
• Provide pessimistic reports to leadership

In other words: they could lose on purpose.

The Counter-Argument: Incompetence and Chaos

But there’s another reading, equally supported by evidence:

1. German physics had been hollowed out. The “Aryan Physics” movement had driven out Jewish scientists—who happened to include most of the best nuclear physicists.

2. The program was fragmented. Multiple competing groups with poor coordination, unlike the centralized Manhattan Project.

3. Heisenberg was a theorist, not an engineer. His genius was in abstract physics. He may have simply been bad at practical weapons development.

4. Overconfidence bred complacency. German scientists assumed they were ahead and didn’t need to rush.

The scientists Germany drove out included Edward Teller, Leo Szilard, Hans Bethe, Enrico Fermi’s wife (which prompted his departure), and of course, Einstein.

Germany’s greatest contribution to the Allied bomb may have been its persecution.

The Heisenberg Uncertainty (of History)

Here’s the uncomfortable truth: we will never know.

Heisenberg spent the rest of his life crafting a narrative of passive resistance. His critics point out that he accepted honors from the Nazi regime, never openly opposed it, and continued his work throughout the war.

His defenders note that open opposition would have been suicidal, that he protected Jewish colleagues when he could, and that his “errors” were suspiciously convenient.

The man who gave us the uncertainty principle left us with the ultimate historical uncertainty.

What It Means for Us Today

The story of the German atomic program isn’t just historical curiosity. It raises questions that haunt every scientist working on dual-use technology today:

When does working on a project make you complicit in its use?

The German physicists worked on “reactor research” that could theoretically lead to weapons. Today’s AI researchers work on “beneficial AI” that could theoretically enable autonomous weapons. The line is never clear.

Can you sabotage from within, or does participation legitimize?

Some German scientists believed they could control the outcome by staying involved. Others, like Einstein and Leo Szilard, concluded that only non-participation was moral.

Does motive matter if outcomes are the same?

Whether Heisenberg failed through conscience or incompetence, millions of lives were saved. Does his intention change our moral evaluation?

The Final Irony

The Manhattan Project was driven, in large part, by fear of German progress. Allied scientists worked in desperate haste, convinced they were in a race.

They weren’t.

The Germans had effectively given up by 1942. The race was only in American minds—created by Heisenberg’s carefully leaked (or carelessly estimated) reports of “progress.”

If Heisenberg was sabotaging the German program, he was simultaneously accelerating the American one. The bomb was built faster because scientists feared what Heisenberg was doing.

History’s greatest irony: the same man may have prevented a Nazi bomb while ensuring an American one.

The Lesson

The scientists who refused—whether through calculation, conscience, or incompetence—remind us that individuals can shape history in ways that remain invisible.

Every scientist faces a version of Heisenberg’s choice: What am I willing to build? For whom? At what cost?

The uncertainty principle of history is that we may never know what choices were made in those German laboratories. But the outcome speaks for itself: the most scientifically advanced nation in the world, with a head start and the discoverers of fission on its team, never built the bomb.

Sometimes the most important discoveries are the ones that never happen.

This post is part of the WWII Science series, exploring how wartime pressures transformed technology and ethics forever.