This is a summary of the Science News article by Tom Siegfried.
The geopolitical instability that followed the bombing of Hiroshima 75 years ago is often discussed, but we seldom hear about the science that precipitated it.
It is no trivial exercise to pinpoint the moment when the course of events that led to the atomic bomb started. Nuclear fission? E = mc2? The discovery of radioactivity? Regardless of which discovery started it all, no force could stop the revelation of atomic power once the search started.
At first it was unclear whether non-radioactive atoms could split and release their atomic energy, but the discovery of the neutron provided a tool to split the nucleus. The first nucleus split went unnoticed, however, mistaken for the formation of a heavier atom. With their understanding of the laws of atomic physics at the time, physicists thought the splitting of the nucleus impossible.
In an experiment, the radium produced by fission was even believed to be barium. It turns out the barium atoms were produced by bombarding a uranium nucleus with neutrons until it split. The discovery of fission caught scientists by surprise. Then more scientists confirmed that bombarding nuclei with neutrons could release their tremendous stores of energy.
Near the start of World War II, the idea of a fission bomb emerged, but it was found to require a chain reaction. Work on the bomb started even though some physicists first thought developing the bomb would take too long to be of any use in the war. However, the lack of unforeseen difficulties allowed the bomb design path to be ready by 1943. The bomb prototype exploded in July 1945.
This unprecedented understanding of nature brought about the unprecedented destructive power of the bomb. Once discovered, it became inevitable. Heisenberg retrospectively figured out how the bomb could be possible once it had been proven so.
Like the nuclear chain reaction, the chain reaction of new knowledge was impossible to stop once started.
