The Day We Almost Set the World on Fire

moments before the United States conducted the world's first test of Anton mcbomb on July 16 1945 legendary physicist Enrico Fermi was taking bets perhaps trying to relieve some of the tension at the time he is quoted as saying now let's take a bet whether the atmosphere will be set on fire by this test he may have been joking at the time but many of the world's top scientists at one point worked very hard to make sure that joke would indeed be funny that the world wouldn't accidentally be destroyed by the first atomic blast let's get technical [Music] for most of human history the science that we've been doing has been pretty tame like Galileo dropping spheres of different masses from different heights to interrogate gravity or Newton recreating the Dark Side of the Moon album cover none of this was ever going to destroy the planet but now today as we experiment in more epic energy regimes we are forced to at least consider the possibility of an existential threat from the science that we are doing for example smashing together atoms at the LHC and creating mini black holes that might destroy the earth but why would you be able to see it in 1942 we asked ourselves one of these existentially imperative questions with the science that we were doing would the first nuclear blast accidentally ignite the Earth's atmosphere and vaporize the entire planet scientists working on the Manhattan Project took this question seriously for some amount of time so knowing how often this question still pops up in popular consciousness we're gonna take it seriously too first a bit of context a few years before the first nuclear bomb exploded one of the physicists working on the Manhattan Project Edward Teller reportedly walked into an office with all the other scientists in it and he said bluntly wait what would happen to the air if a nuclear bomb exploded in the air apparently this question hadn't been fully considered and it was so serious that it was taken to his superiors what they were worried about was the possibility that a nuclear blast would be so intense that it would literally fuse atoms in the air together and this fusion event would release energy will profuse other nearby atoms in the air and this would spread to all of the Earth's air eventually releasing so much energy that everything would be this wouldn't be fine teller Compton Oppenheimer and other legendary physicists working on the project now needed some calculations to address a relatively simple dilemma when a nuclear bomb explodes its energy expands outwards in more or less a sphere if that energy causes additional fusion events to happen that sphere will get bigger and bigger more energetic as it goes along until the sphere of doom gets so big that it consumes everything that's one possibility the other possibility is that when a nuclear blast goes off even if it is creating fusion events in the air around it it actually starts losing energy to the environment more energy than it's gaining and so eventually this sphere will just dissipate away harmlessly like every explosion you've ever seen and not propagate through the air based on this analysis gains vs. losses than Manhattan Project scientists were tasked with finding out whether or not earth had an ignition point the majority of the energy gains the scientists figured out would come from a single reaction the air that you're breathing right now is 78% nitrogen and aside from being relatively abundant nitrogen is relatively less stable compared to other atmospheric gases a fusion reaction between two nitrogen nuclei will produce some fusion products like magnesium here an alpha particle and a good amount of energy 17.7 mega electron volt sounds like a lot but if you do the conversion it's only one trillionth of a Joule which would be something like a million times less energetic than a single snowflake softly striking the ground the danger here is in that relative abundance of nitrogen in the air for example if you were to cup air in between your hands like this right now it's likely that you have captured a million quadrillion nitrogen nuclei in your hands now if all of these nuclei underwent this same fusion reaction you multiply these two numbers together you find that you're suddenly just with this amount air in the gigajoule range in terms of energy effectively a Kamehameha and you don't want the Earth's atmosphere to go super safe knowing the main reaction the Manhattan Project scientists then estimated how many nitrogen atoms would be in the air how likely it would be for them to fuse with nearby nitrogen atoms and just how energetic this chain reaction would be they had one side of the equation now they needed the other the losses in the first milliseconds after a nuclear bomb explodes some region of air is heated up to enormous temperature inside of this ultra hot plasma the products of fission and/or fusion reactions are flying all around with tremendous kinetic energy slamming into the air as this explosion expands and giving it energy however while the nuclei of these atoms the protons and the neutrons being impacted are relatively good at hanging on to the energy they are given thereby maintaining the temperature of this plasma the electrons flying all around are not and they radiate the energy they are given away pretty quickly when you give energy to an electron and you accelerate it or decelerate it in the presence of an electric field a field like from the charged particles in a nuclear plasma it will trade off some of its kinetic energy for electromagnetic energy across the e/m spectrum and slowed down because it's losing kinetic energy this so-called braking radiation or bremsstrahlung is the main energy loss that these nuclear physicists considered when they thought about the earth turning into a star for a hot second now knowing the main energy gains and energy losses in this potential catastrophe the scientists working out of Los Alamos published this paper in the April of 1946 it wasn't Declassified until the late 70s again our atmosphere could theoretically ignite if the energy gained during the event was larger than the energy lost to the environment and so if you divide these two values you can see how close you would come to that terribly consequential ignition point our safety factor then would be how much bigger the losses are than the gains and you'd want that number to be a lot bigger than one a lot bigger one point six from the complicated calculations that you can read in the report yourself the safety factor could get as low as one point six the engine parts in your car have a higher factor of safety than this this is so low that if any one was off by a few percentage points in their calculations here we'd be flirting with human extinction no sane person would take a risk as big as this with numbers as low as this so why did nuclear testing proceed and proceeded for decades what is our math missing temperature it was missing temperature where the safety factor got close to one in these calculations and close to a civilization ending world fire brought on by our own need to constantly innovate regardless of - sorry I was just thinking about kittens our scary low safety factor didn't exist in a vacuum it required in these calculations a nuclear blast temperature upwards of a hundred billion Kelvin and at the time the highest temperature that even a theoretical fishing or fusion bomb could produce was in the neighborhood of a hundred million Kelvin a thousand times less and so for a more realistic temperature that would occur during the world's first nuclear blast it pushes the safety factor from one to over a thousand and given this enhanced safety factor the original report concludes the present calculations indicate that no ignition point exists no bomb the scientists considered could feasibly lead to the end of the world but that doesn't mean they didn't think of one just to be thorough in case the huge safety factor wasn't enough to quell concerns the three scientists writing the original report then calculated the minimum volume of air that would have to be heated to this ludicrous billion Kelvin temperature they figured out that a sphere of uber hot air over a hundred meters wide would need to be created by a nuclear blast in order to sustain a world ending chain reaction through the atmosphere and this is a lot of crispy air it's as though an Empire State building's worth of air suddenly and violently became a hundred million times hotter than the Sun oh oh my people my peepers and if that wasn't ridiculous enough they calculated how much energy it would take to create this sphere of world-ending air and they got twenty twenty times the energy currently contained in the entire world's arsenal of nuclear weapons and we're not even done with the near impossibility of igniting the atmosphere just yet the nuclear bomb that was dropped on Hiroshima Japan in the August of 1945 was filled with 64 kilograms of your 2:35 but when it detonated less than a single kilogram actually underwent fission the total amount of energy released on the city that day was equivalent to just half a gram of matter converting directly into energy the weight of a butterfly to set the whole world on fire the Los Alamos scientists reassuringly calculated would take roughly a million times more material a nuclear bomb with 1,500 tonnes of uranium reacting with a hundred percent efficiency which is impossible this would be a nuclear bomb heavier than the International Space Station I'm really strong and on top of all of this there was one final protection that the scientists of the Manhattan Project considered that would theoretically protect us from atmospheric disintegration let's consider a small volume of air radiation or energy produced inside this small sphere would have an easy time escaping however in a much larger volume of bomb heated air there is a greater chance that before escaping this radiation and energy will interact with itself inside of a glob of star temperature air like this there are hot electrons and photons of radiation smacking into each other and sometimes when they collide the photon can gain energy and the electron can lose energy energy that was needed to sustain this catastrophic chain reaction the end result is more energy losses in our equation factoring in this phenomenon the scientists calculated that the safety factor might increase by up to 400% and so partly justified by these calculations that you and I just went through on the morning of July 16th 1945 at 5:29 in the morning the world's first nuclear detonation happened the world was forever changed by this but the earth remained in most of the reports you'll read the scientists doing these calculations were satisfied enough that this situation was basically impossible but fears persisted in public consciousness through the 40s 70s and up to today especially on the internet obviously the world didn't end with the first nuclear test but just think for a second on how we were able to use just a few calculations to dismiss an existential threat it speaks to the power of science and perhaps to our maybe dangerous unstoppable curiosity after witnessing the first atomic blast robert Oppenheimer gave a now famous quote from Hindu scripture I am become death the destroyer of worlds he could have been right good thing we checked because science [Music] the kind of thing that keeps me up at night is that what if the variables were different it could have been the case that the nitrogen in the air was a lot easier to fuse than they thought or that the propagation of the chain reaction just happened in a different way or they didn't consider a different energy gain or energy loss and one variable could have been missed and then the entire earth could have exploded during this test what we've gotten lucky up until this point but there will be a day when the luck will run out if we don't really do a lot of math that's why you need math kids thank you so much for watching Sydney if you like this video you will probably like some of our other nuclear inspired videos like what actually happened during the Chernobyl meltdown and how fallouts mini nukes actually exist if you want to suggest ideas for future episodes or stay up-to-date with me in the show you can follow us here at these social media handles thanks [Music]

Channel: Because Science

Views: 2,129,391

Keywords: Nerdist, Because Science, Kyle Hill, Nuclear Science, Nuclear Energy, Trinity Tests, Castle Bravo, Nuclear Atmospher Ignition

Id: NFjVUSOnPzo

Length: 14min 11sec (851 seconds)

Published: Thu Aug 15 2019