Walking in London, Szilard conceives of a self-sustaining nuclear chain reaction capable of releasing vast destructive energy.

Chadwick discovers the long-sought neutron at Cambridge, providing a charge-neutral particle that can penetrate atomic nuclei directly.

Hahn's Berlin laboratory proves that neutron bombardment of uranium produces barium, confirming the uranium atom can be split in two.

Nazi racial laws force one quarter of Germany's physicists from their university posts, triggering a mass flight to Allied nations.

Einstein co-signs a letter drafted by Szilard warning President Roosevelt that Germany may soon develop an atomic weapon.

Roosevelt orders the Advisory Committee on Uranium to convene, officially beginning America's first government nuclear research program.

Segrè and Seaborg at Berkeley separate element 94 from uranium decay products and name the new material plutonium.

Japan's surprise attack on Pearl Harbor kills more than 3,500 Americans and pulls the United States into World War II.

Fermi's team achieves the first controlled nuclear chain reaction in a graphite-and-uranium pile under the University of Chicago's stadium.

Oppenheimer is appointed director of the Los Alamos laboratory, a secret research city built for scientists on a New Mexico mesa.

The Trinity test detonates the first nuclear device in the New Mexico desert, producing a blast equal to 19,000 tons of TNT.

The Enola Gay drops Little Boy on Hiroshima, instantly leveling most of the city and killing tens of thousands of people.

Days after the Hiroshima blast, seemingly uninjured survivors develop radiation sickness, suffering bleeding, hair loss, and fatal tissue destruction.

A B-29 named Bock's Car drops Fat Man, a plutonium implosion bomb, on Nagasaki after clouds obscure the primary target.

Emperor Hirohito announces Japan's surrender on radio, telling his people the enemy has used a new and most cruel bomb.

Richard Rhodes traces the atomic bomb from Leo Szilard's chain reaction insight in London to its devastating use on Japan in 1945. Nazi persecution of European Jews paradoxically accelerated Allied progress, as the continent's finest physicists fled to Britain and America and placed their knowledge in Allied hands. Einstein's letter to Roosevelt convinced the United States to launch a formal nuclear program, which grew into the massive Manhattan Project under Oppenheimer at Los Alamos. Fermi's controlled chain reaction in Chicago proved the bomb was scientifically achievable, and the Trinity test in the New Mexico desert confirmed its terrible power. Within weeks, Little Boy leveled Hiroshima and Fat Man destroyed Nagasaki, producing radiation sickness that continued killing survivors for months. Emperor Hirohito's radio surrender announcement marked both the end of World War II and the dawn of the nuclear age.

The race to build and deploy the world's first atomic bomb.

Thomson discovers the electron using cathode ray tubes at Cambridge, proving that atoms contain smaller internal particles.

Rutherford wins the Nobel Prize in chemistry for his work on radioactive decay, alpha particles, and the structure of the atomic nucleus.

Fritz Haber's chlorine gas is deployed against British forces at Ypres, killing five thousand soldiers and wounding ten thousand more.

Young physicist Harry Moseley is killed at Gallipoli, prompting an American scientist to call his loss one of history's most irreparable crimes.

Seven extraordinarily gifted Hungarian-Jewish scientists, dubbed the Men from Mars, scatter from their homeland to research posts across Europe and America.

Fermi's team in Rome systematically bombards each element with neutrons, creating artificial radioactive isotopes of twenty different materials.

Fermi accepts the Nobel Prize in Stockholm and immediately uses the prize money to escape Fascist Italy with his Jewish family.

Meitner flees to Sweden after Austria's annexation by Germany makes her subject to Nazi anti-Jewish racial laws.

Britain's secret MAUD committee issues a report concluding that an atomic bomb is feasible and recommending immediate industrial-scale development.

Heisenberg meets Bohr in Nazi-occupied Copenhagen to discuss nuclear weapons, and the encounter ends in permanent estrangement between the two men.

General Groves, who just finished overseeing construction of the Pentagon, is appointed to manage the Manhattan Project and immediately accelerates the work.

Norwegian commandos raid and destroy Germany's only heavy-water production plant, setting back Nazi nuclear weapons development by up to a year.

Seaborg's Chicago team successfully extracts the first tiny visible speck of plutonium from two tons of irradiated uranium.

Bohr escapes Denmark with his family and persuades the Swedish government to publicly offer sanctuary to Denmark's seven thousand Jews.

Allied intelligence teams advancing through Germany seize a large uranium cache and capture nuclear scientists including Hahn and Heisenberg.

This pool follows the crucial figures and events that built the foundation for the atomic bomb, from the earliest experimental discoveries in nuclear physics to the final days of the war. Thomson and Rutherford laid the experimental groundwork for understanding the atom, while World War I claimed brilliant young talent like Moseley and demonstrated how industrial technology could be weaponized on a massive scale. A remarkable cohort of Hungarian-Jewish scientists fled persecution to fuel Allied research, joining Fermi and Meitner whose own escapes brought critical expertise to the West. Britain's secret MAUD report and the failed Heisenberg-Bohr meeting in Copenhagen illustrated both the Allied edge and the tragic rupture between science and nationalist politics. Allied sabotage of Germany's heavy-water plant and the eventual capture of German nuclear scientists confirmed that the Nazis had never come close to winning the bomb race.

The scientists and supporting events that shaped the bomb's creation.

Szilard moves to Berlin, solves a major problem in thermodynamics, and begins collaborating with Einstein on scientific inventions.

Heisenberg publishes his uncertainty principle, showing that the position and momentum of a subatomic particle cannot both be precisely known.

Einstein derives his equation E=MC2 while working at the patent office, revealing the vast energy stored dormant within all matter.

Szilard files secret patents on his chain reaction research, hoping to prevent German scientists from independently accessing the method.

Irene and Frederic Joliot-Curie announce at the Solvay Conference the creation of the first artificially generated radioactive element.

Bohr realizes that the rare U235 isotope, unlike common U238, is far more capable of sustaining a nuclear chain reaction.

The Columbia University team proves that U235 emits twice as many neutrons during fission as it absorbs, confirming a chain reaction is feasible.

Frisch calculates that an atomic bomb made of pure U235 would require only eleven pounds of material and would definitely explode.

Fermi offhandedly suggests to Teller that the heat of an atom bomb might ignite a far more powerful hydrogen fusion weapon.

Bethe calculates that a hydrogen bomb would not accidentally ignite Earth's oceans or atmosphere, clearing the path for thermonuclear weapons research.

Scientists discover that reactor-bred plutonium contains a rogue isotope causing premature detonation, forcing a complete switch from gun-type to implosion design.

Bohr arrives at Los Alamos carrying a sketch from Heisenberg that suggests Germany's nuclear program may be far behind the Allies.

The Hanford reactor mysteriously shuts down repeatedly until Fermi and Wheeler identify xenon gas as the cause of neutron absorption.

The Interim Committee decides against warning Japan or staging a demonstration, opting instead for a surprise nuclear strike on an undamaged city.

Japan's military government offers conditional surrender after Nagasaki, and Truman chooses not to authorize a ready third atomic bomb.

This pool traces the critical intellectual breakthroughs and moral crossroads that transformed nuclear physics from pure science into history's most destructive weapon. From Einstein's E=MC2 and Heisenberg's uncertainty principle to Szilard's secret patents and Bohr's identification of U235's unique fission properties, each revelation narrowed the path toward the bomb. Frisch's calculation that a bomb could be built from eleven pounds of material made the weapon feel suddenly real, while Fermi's casual suggestion to Teller about a hydrogen bomb opened an even darker door. The discovery that reactor-bred plutonium made a gun-type design impossible forced a complete engineering pivot to the complex implosion approach, nearly derailing the project. The Interim Committee's decision to bomb Japan without warning or demonstration, and Truman's choice not to authorize a third strike after Japan's conditional offer, mark the moral endpoints at which the nuclear age truly began.