Oppenheimer’s “Terrible Possibility” - Atmospheric Ignition

in the cold dark hours before the United States detonated the first nuclear bomb on July 16 1945 Manhattan Project physicist Edward Teller was making everybody nervous it was before 4am in the New Mexico desert the sun wasn't out yet but he was applying sunscreen teller was worried about a different kind of radiation trying to relieve the unbearable tension that years of Highly secretive work had led up to fellow physicist Enrico Fermi decided to take bets he reportedly said quote now let's make a bet let's make a bet whether or not the bomb will ignite the atmosphere and if so whether it will merely destroy New Mexico or destroy the world a few scientists took the bet he may have been joking at the time but only because a number of the world's top scientists convinced themselves that the first atomic explosion would not accidentally destroy the entire planet Los Alamos laboratory director J Robert Oppenheimer bet ten dollars against another physicist's entire month's pay that the bomb wouldn't work at all and waited silently in a hardened bunker for the milliseconds long transition to the nuclear age that his Gadget would soon usher in this is the true story of the day we almost set the world on fire for most of human history science has been comparatively tame Galileo dropping two spheres of different masses to interrogate gravity Newton angling a prism to unweave the rainbow but as the centuries passed technology allowed humans to press onwards into increasingly extreme energy regimes today experiments with kilometers wide particle accelerators Force us to at least entertain the possibility that for example smashing atoms together at just three meters below light speed could produce microscopic black holes in 1942 we had to ask a similar existentially imperative question would detonating the first nuclear weapon ignite the atmosphere and end all life on Earth a few years before the first nuclear detonation codenamed Trinity obliterated a bleak stretch of New Mexico desert one of the physicists on the project Edward Teller reportedly walked into an office with a few other scientists and asked bluntly what would happen to the air if an atomic bomb were exploded in the air this basic question apparently hadn't been fully considered and so it was taken to his superiors on the project one of them being J Robert Oppenheimer what they were worried about was the possibility of a nuclear explosion being so intense that the fission event would cause a fusion event where atoms in the air fuse together releasing many times more energy than if they were split and this would start a runaway chain reaction that would spread promptly through all of Earth's air emitting enough energy to vaporize everything some of the scientists were immediately skeptical of atmospheric ignition but no one had ever unleashed the atom like this before there's nitrogen in the air teller told Oppenheimer and you can have a nuclear reaction in which two nitrogen nuclei Collide and in this process you set free a lot of energy couldn't ignition happen that's a terrible possibility Oppenheimer responded and someone had to take oppenheimer's terrible possibility seriously Edward Teller Arthur Compton Oppenheimer and other Manhattan Project physicists now needed some calculations to address two possibilities when the gadget as they called it goes off its apocalyptic energy is going to expand outwards in a sphere if that energy causes additional Fusion to happen in air this sphere will pick up energy as it moves outwards eventually consuming everything that was one possibility the other possibility was that even if the bomb caused Fusion of air molecules as the blast expanded it could lose energy to the environment faster than it gained energy from Fusion to solve this dilemma some of the smartest men alive were tasked with calculating whether or not earth had an ignition point and so the analysis began the worst case scenario for energy gains the scientists figured would come from a single reaction involving nitrogen a fusion reaction between two nitrogen atoms will produce Fusion products like magnesium and alpha particle and 17 Mega electron volts of energy in the form of photons 17 Mev sounds like a lot but it's only around a trillionth of a joule a million times less energetic than a single snowflake striking the ground however the danger wasn't in a single reaction it was in all the possible reactions nitrogen makes up 78 of Earth's atmosphere if you were to cup your hands right now there are likely one million quadrillion nitrogen atoms in the air that you've captured if all those atoms underwent Fusion because of a nuclear blast just the energy in your hands would be in the gigajoule range as though you were Zeus himself grasping a lightning bolt knowing the worst case reaction the scientists then estimated how many nitrogen atoms would be in the air around the gadget How likely it would be for those particles to fuse with other particles near them and how energetic this hypothetical Chain Reaction would actually be they had the gains now they needed the other side of the equation the losses [Music] in the first milliseconds after a nuclear bomb explodes a spherical region of air is heated to star-like temperatures in this Ultra hot plasma products of fission and or Fusion are flying around with tremendous kinetic energy smacking into the air at the edge of the fireball giving it energy however while the nuclei of these Edge atoms protons and neutrons can hold on to this impact energy helping to maintain the temperature of the explosion the electrons flying about in this plasma cannot they let go of the energy imparted to them very quickly when electrons are accelerated or decelerated in the presence of an electric field like from a Charged particle in a nuclear plasma they can trade in some of their kinetic energy for electromagnetic radiation across the Spectrum this so-called breaking radiation was the main energy loss nuclear physicists considered when Imagining the Earth basically engulfed by a star knowing the main energy gains and losses in a catastrophe they did not intend Manhattan Project scientists working out of Los Alamos worked out what would eventually go into this paper in the April of 1946 it wasn't Declassified until the late 70s again the fear was that Earth's atmosphere could ignite if Fusion gains during the Trinity blast exceeded the energy losses divide these two values then and you get a ratio that tells you how close you are to that terrible possibility of ignition and so Trinity's safety Factor would be just how much larger the calculated losses were than the calculated gains any sane engineer would want the losses to be many many times larger than the gains for this ratio to be bigger than one but when the safety Factor was calculated it was just 1.6 in the complicated calculations you can read yourself the safety Factor could get as low as 1.6 your car's engine parts have a better factor of safety than that this value was low enough that if any of these scientists were off in their calculations by just a handful of percentage points they'd be flirting with human extinction no sane person would take a risk like this so why did nuclear testing proceed and proceed for decades 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 for Theory alone zero would be nice what this disturbing factor of safety was missing was the variable of temperature the fusion of atmospheric nitrogen and therefore civilization-ending World fire would require a trinity blast temperature of at least 100 billion Kelvin but at the time the highest temperatures that any bomb could even theoretically produce were a thousand times lower than this changing the safety factor from one to one thousand from this value the original report concludes that quote it is shown that whatever the temperature to which a section of the atmosphere may be heated no self-propagating chain of nuclear reactions is likely to be started end quote however though the Manhattan Project scientists didn't identify any bomb that could feasibly lead to the end of the world that doesn't mean they didn't calculate one just in case the huge safety Factor wasn't enough to quell private concerns the three scientists writing the original paper calculated the minimum volume of air that would have to be heated up to that 100 billion Kelvin temperature and the energy required to do so they figured out that not only would a nuclear blast have to create a sphere of air ten thousand times hotter than the core of the Sun in order to sustain a nitrogen Fusion chain that sphere of air would have to be over a hundred meters wide and to do all this it would require an amount of energy equivalent to 20 times more energy than is contained in the current world supply of nuclear weapons impossible when the little boy nuclear bomb was dropped on Hiroshima Japan just a few weeks after the Trinity test in the August of 1945 it contains 64 kilograms of uranium-235 but when it detonated less than one kilogram underwent fission the total amount of energy released that day was from just half a gram of mass turning directly into energy to set the whole world on fire the Los Alamos scientists reassuringly calculated would take roughly a million times more material than this a bomb with 1.5 million kilograms of uranium reacting with 100 efficiency again impossible the Manhattan Project also considered one final protection from atmospheric annihilation in a small volume of air radiation can easily Escape but in a much larger volume of bomb heated air there is a larger chance at the radiation and energy inside will interact with itself before leaving inside a glob of star temperature air photons of radiation and hot electrons bump into each other which robs the electrons of their energy energy needed to sustain potential Fusion reactions the end result of this inverse competence scattering is even more energy losses in the safety Factor equation increasing the safety Factor by up to 400 percent and making a very unlikely scenario even more unlikely to be clear Manhattan Project physicists were skeptical of atmospheric ignition even before the ink on the calculations was dry but in these numbers they found all the justification they needed to split the atom and therefore history in two 15 seconds before 5 30 am on Monday July 16 1945 half of the world's supply of plutonium was compressed by conventional explosives into a critical mass the resulting energy release vaporized the gadget disintegrated the tower it was hoisted up and melted the sand around the site into radioactive glass a mushroom cloud Rose into the morning Sky a second Sunrise as the scientists described it and instantly became the symbol of the nuclear age Manhattan Project scientist George kistikowski was reportedly knocked to the ground even though he was five miles away he got up and ran over to Robert Oppenheimer who was nearby Opie he said you owe me ten dollars in most of the reports you'll read the scientists doing these calculations were satisfied with their conclusions but fears about igniting the atmosphere have persisted in public Consciousness since the 40s obviously the world didn't end with Trinity but I'm struck by how just a few calculations were enough to dismiss a brand new existential risk and move forward headlong into the atomic age but it must be said that the gravity of what had happened there in the desert that day was not lost on Oppenheimer or his colleagues many of the scientists present were haunted for the rest of their lives few people laughed few people cried most people were silent I remembered the line from the Hindu scripture of the bhagavad-gita Vishnu [Music] is trying to persuade the prince that he should do his duty and to impress him takes on his multi-armed form and says now I am become death the destroyer of worlds I suppose we all thought that one way or another one way or another considering what happened to the people of Hiroshima and Nagasaki considering that nuclear Annihilation is more likely today than it was all those years ago destroyer of worlds is exactly what they became until next time foreign [Music] [Music] [Music]

Channel: Kyle Hill

Views: 1,698,887

Keywords: because science, engineering, kyle hill, learning, math, physics, science, stem, the facility, chernobyl, nuclear, oppenheimer, trinity, gadget, Oppenheimer, Openheimer, nuclear age, Manhattan project, half-life oppenheimer, trinity test, world war II, trinity bomb, los alamos, plutonium, trinity nuclear test, alamogordo, nuclear physics, J. Robert Oppenheimer, oppenheimer’s trinity test, igniting the atmosphere, atmospheric ignition

Id: 2QI88aLyaOs

Length: 15min 59sec (959 seconds)

Published: Fri Aug 11 2023