Skip to main content

Bright White Light

Sixty-five years ago a blinding flash of light leveled the city of Hiroshima Japan. The United States dropped the atomic bomb, dubbed "Little Boy," over the city's downtown. Three days later, the United States dropped "Fat Man" on the outskirts of Nagasaki. Japan surrendered six days later, ending the most devastating war the world had ever seen.

Hiroshima was completely destroyed. Before and after photos show that the buildings in the city were almost totally razed. Over 70,000 people died the first day, with roughly 70,000 more perishing from radiation poisoning in the following months.

But why was Hiroshima chosen in the first place? Its strategic importance was only part of the reason it was chosen. There were several military camps around the city including the headquarters of the Fifth Division and 2nd General Army. However up to that point, the U.S. Air Force hadn't deemed it as important enough to bomb in the preceding months of the war.

It sounds twisted, but in a way the city was chosen to be a massive science experiment. As far back as May, the bomb planning committee which included Manhattan Project leader Robert Oppenheimer chose Hiroshima as one of five potential sites because of its pristine state in order to cleanly study the bombs' effects on a metropolitan area. Dr. Joyce C. Stearns who was in charge of recommending targets to the air force, looked specifically for cities untouched by Allied bombing runs.

Hiroshima Before the Bomb

Hiroshima After the Bomb

Before Little Boy was dropped, the only nuclear explosion the world had ever seen up to that point was the Trinity test in the middle of the New Mexico desert. The test showed the bomb worked, and showcased its devastating effects over the desolate sands of the American Southwest. (To this day, large sections of ground are still covered in "Trinitite," a kind of glass formed when the intense heat and pressure of that fist mushroom cloud fused desert sand into glass.)

Nuclear weapons were a completely new weapon and no one knew for sure what kind of devastating effects it possessed. The scientists who created it knew the explosion would be huge and radiation would likely permeate itself around the area, though how much was anything but certain.

After the bombs fell, Japanese and U.S. researchers descended upon Hiroshima and Nagasaki to study its after effects. These researchers studied everything from the blast patterns of the bomb to the effects of radiation on human tissue. Much of what is known today about the effects of nuclear fallout came from the researchers studying the survivors of Hiroshima and Nagasaki.

The city of Hiroshima has long since been rebuilt; however the city still bears the marks of the bombing. Though almost the entire city was leveled, the ruins of the Hiroshima Prefectural Industrial Promotion Hall remained standing located almost directly below the detonation. Its ghostly shell still stands amidst the city today, as a reminder and a warning of the awesome power of nuclear weapons. It has been renamed the Hiroshima Peace Memorial or the Genbaku Dome, and is a part of the Hiroshima Peace Memorial Park.


  1. The phrasing of this article seems to single out Dr. Joyce Stearns for devising the twisted notion of dropping the bomb on a populous and previously undamaged area. Stearns was indeed in charge of submitting the list of potential target cities, in May of 1945, to the Committee that ultimately selected Hiroshima as the target for the first bomb dropped in August. (The minutes from that meeting can be found in the National Archives, and a transcription can be found here: However, Stearns was not responsible for the selection criteria that he applied in coming up with the list of specific cities, and he was not happy with the outcome of that committee meeting. A month later, he became a signatory of the Franck Report, which urged that these bombs not be used in warfare, especially on human beings. (See here: It therefore seems grossly unfair to single him out, among the many scientists and military personal and political leaders, who had a hand in this decision. He used what limited clout he had to try and avert the bombing of Hiroshima and Nagasaki.

  2. This is not true: "To this day, large sections of ground are still covered in "Trinitite," a kind of glass formed when the intense heat and pressure of that fist mushroom cloud fused desert sand into glass."

    This was true immediately after the Trinity explosion in 1945. However, the military realized that the Trinitite was radioactive and removed most of it not long afterwards.

    The Trinity site is open to the public one day a year. I was there in April 2014. I saw and photographed a few pieces of Trinitite here and there, but nowhere in that area is the ground "covered in Trinitite."

    Here is a close-up photo I took of a piece of Trinitite on the ground at Trinity site next to my radiation detector:


Post a Comment

Popular Posts

How 4,000 Physicists Gave a Vegas Casino its Worst Week Ever

What happens when several thousand distinguished physicists, researchers, and students descend on the nation’s gambling capital for a conference? The answer is "a bad week for the casino"—but you'd never guess why.

Ask a Physicist: Phone Flash Sharpie Shock!

Lexie and Xavier, from Orlando, FL want to know: "What's going on in this video ? Our science teacher claims that the pain comes from a small electrical shock, but we believe that this is due to the absorption of light. Please help us resolve this dispute!"

The Science of Ice Cream: Part One

Even though it's been a warm couple of months already, it's officially summer. A delicious, science-filled way to beat the heat? Making homemade ice cream. (We've since updated this article to include the science behind vegan ice cream. To learn more about ice cream science, check out The Science of Ice Cream, Redux ) Image Credit: St0rmz via Flickr Over at Physics@Home there's an easy recipe for homemade ice cream. But what kind of milk should you use to make ice cream? And do you really need to chill the ice cream base before making it? Why do ice cream recipes always call for salt on ice?