Video: https://www.tiktok.com/@distilledscience/video/7543340030144630046
Transcript
Are we saying there's a chance that when we push that button, we destroy the world. Chances are near zero. Near zero. What do you want from theory alone? Zero would be nice. How near was near zero? This declassified document shows the original calculations that Oppenheimer and his team used to check if their bomb would cause a chain reaction in the atmosphere and destroy the world. Give me three minutes and I'll make you an expert on nukes. If you can't handle it, scroll now. Ready? Let's go. That near-zero phrase was likely based on an interview with Arthur Compton back in 1959, where when discussing this ultimate catastrophe, he says, better to accept the slavery of the Nazis than to run the chance of drawing the final curtain on mankind, but also that they calculated the odds to be just below the threshold of three parts and one million. And so they went ahead with it. Would you have if that number was accurate? Thankfully, it probably wasn't. Compton and Oppenheimer first spoke on this topic before they did most of the detailed math Now for some science. Nuclear fission is when the nucleus of an atom splits into smaller parts, releasing all the energy from the bonds that held them together. It's like cutting apart a rubber band ball and watching all the bands snap. The original atom bomb did this with uranium, a very large atom that's easy to break up, and when you do, it also releases a few neutrons that can hit nearby uranium atoms and split them open, causing a chain reaction. Big boom. Fusion is what happens in the sun. It's when you smash two atoms together hard enough to combine them, and in the process, straight into energy. That E equals MC squared amount is way more than you get out of fission, but making fusion happen is like trying to take the two positive sides of a magnet and force them together. It's really hard, and so can only happen at super high temperatures and pressures, like in the sun. Or the heart of a nuclear bomb explosion. Now we're ready to look at this document, declassified back in 1973. This is the reaction that they were worried about happening in our atmosphere, that the force of the bomb would slam together two nitrogen atoms and create these possible byproducts. The most worried about the output being magnesium, which would produce 17.7 MEV of excess energy per reaction. To put that in perspective, using one gram of nitrogen would be like blowing up 4,000 pounds of TNT. And the hotter the air, the more frequent these reactions are. And the more energy is produced. Some of the energy produced goes into heat and radiation, and some goes into fueling more reactions, which produce more energy. For a chain reaction to happen, the amount of energy produced in a given region of air has to be more than the amount of energy lost through heat and radiation. for energy produced and lost at different temperatures. At 11 billion degrees, the amount of energy lost is still around 7 times more than what would be produced, making a chain reaction impossible. But a factor of 7 is still a bit risky, so there's a lot more involved. In order to sustain the reaction, they calculated that the bomb would have to heat up a sphere of air equal to 57 meters and radius. And less than 1% of the energy that a bomb produces actually gets converted into heat, the rest goes into radiation, more so as it gets hotter. to 11 billion degrees, it would take 150 million kilograms of radioactive material. Uranium. Try dropping that from a plane. The bomb they used at that Trinity test was six kilograms. Bit of a difference. Hans Beth, shown in the movie as this guy, published an updated analysis of all of this back in 1976, partially in response to some new press around the Compton interview. He concluded that there was never any possibility of causing a thermonuclear chain reaction in the atmosphere. Not even three parts in one million.
Additional notes
Reading through declassified physics documents has got to be one of my nerdiest guilty pleasures! What did you guys think about Oppenheimer? And what other movies would you want to see science breakdowns of? #science #moviescience #oppenheimer #stem #TikTokSceneStealerContest
References
- Declassified 1973 atmospheric ignition calculations document discussed in transcript; direct URL not listed in workbook.
- Arthur Compton 1959 interview discussed in transcript; direct source not listed in workbook.
- Hans Bethe updated 1976 analysis mentioned in transcript; title/source URL/DOI not listed in workbook.