Oppenheimer's Apocalypse Math

References
Los Alamos Report 602: sgp.fas.org/othergov/doe/lanl...
The bomb - the end of the world? large.stanford.edu/courses/201...
Ultimate Catastrophe? www.tandfonline.com/doi/abs/1...
Welch Labs
/ welchlabs
/ welchlabs
www.welchlabs.com/

[@MomirViggwilv]

It's kind of reassuring, actually, to know just how much effort scientists put on calculating the potential remifications of their experiments.

[@ericrawson2909]

Well, they used to do that. Now they are told to follow "the science" which is dictated to them by people who want to make vast profits, or else they will get no funding and lose their job.

[@youssubernfissi5559]

I don't think it's assuring, the bad result here is everyone dies including them and their families so of course they'll go to great lengths to prevent that, don't expect such effort if the bad outcome only concerns you,like medicine, chemicals in day to day products, byproducts of various manufacturing lines.......

[@iberianrider5361]

put, but in past tense

[@AscendantStoic]

Not anymore sadly 😐

[@BAGELMENSK]

Not as many as you'd hope do this kind of due diligence.

[@jhonbus]

The fact the calculation starts with the assumption that every collision between nitrogen nuclei results in a fusion tells you exactly what you need to know about the actual possibility of this scenario occurring. This wasn't a serious concern after this calculation was done. It's a kind of "Is this vaguely plausible even given the worst possible case?" and the answer was no.

[@chyza2012]

Keep in mind this was brand new physics, nobody knew if there weren't any other factors at play.

[@joshuazelinsky5213]

@@chyza2012 Only up to a point. Actual fusion had already been discovered by Mark Oliphant before the war, involving tritium and He-3, and so they had empirical evidence that it was very rare in at least those cases. And since a nitrogen atom had a larger positive charge, at least one aspect would make one suspect it was even rarer. And Oliphant was one of the people working on the Manhatttan Project, so people had to have been aware of his work. Other work in the 1920s and 1930s got upper limits on fusion rates in the sun, and the CNO-cycle estimates for the sun would have probably been a good estimate also that a 100% collision rate was highly unrealistic.

[@benmaxwell115]

@@joshuazelinsky5213 Scientists literally did not know if they knew everything, their equation could have been wrong due to an unknown factor and they knew this. They could not predict the chance of themselves being wrong without any evidence, so the chance was "near zero" but until you've done the test you don't know for sure. Now we have done the test we know it's a load of tosh, but it was a genuine concern at the time.

[@nikolailevin2077]

@@joshuazelinsky5213 There was a lot of room for error. In the same days they were also discussing the fuels that could allow a thermonuclear fusion. They settled on the isotope lithium-6. In 1954 during Castle Bravo they tested a bomb 40% lithium-6 and the rest lithium-7, which was considered mostly inert. It wasn't. They expected a 6 megaton explosion and got a 15 megatons one (one of the worst radiological disasters). This to say that there were plenty of important things they did not know if they did not know.

[@user-ch4yf8kc9v]

@@chyza2012 nah not really they used fission to make the plutonium before hand and had a pretty solid model for how it all works nothings really changed in the models since the manhatten project

[@JayKayKay7]

The version I like best is during the first test in New Mexico, someone asked, "Are we going to set fire to the Earth's atmosphere? Enrico Fermi whips out a slide rule, does some quick calculations, puts the slide rule away, turns to the original questioner, and states flatly, "Probably not."

[@4Four_Studios]

Holy shit, that's hilarious.

[@Timmy-fk8uk]

man i wish they had this in the movie now

[@vedantganesh6923]

The slide rule - every 20th century physicist's famous weapon

[@thothheartmaat2833]

its literally just a big bomb.. jesus fucking christ.. everyone thinks theyve "become god" every time they do "literally anything" chill the fuck out humans youre not that important.. the number of times this movie suggests that this man or this movie is the most important thing in history.. youd all be dead if you took a shot every time.. holy fucking christ..

[@savant7288]

@@13eastxpharoh94 *Teller

[@dannymartial7997]

I like how in the movie, Einstein said that if they DID conclude that atmospheric ignition was a possibility, then the next step would be to release the information publicly, especially to the Nazis and they’d all agree not to use any nukes. The thinking being no matter how evil the other side of the war is, no one would risk human extinction.

[@taiyoqun]

A few years later, and people started to believe that was actually a good thing about nuclear bombs. Don't mind me, I'm just mad at MAD

[@ptdnxyz]

@@taiyoqun There hasn't been a war between great powers in almost 80 years now. MAD worked.

[@wawawuu1514]

If anybody, it would be the Nazis to explode the Earth if they could. They literally had a scorched Earth policy (even if the command hasn't heeded everywhere) when it became clear they were losing the war.

[@gorpand]

Would have been a perfect experiment for Mythbusters - first busting the myth and then creating conditions and seeing what does it take to make it work.

[@DWal32]

"Today on Mythbusters, we got a nuclear bomb, and we're gonna find out if it'll end the world!"

[@andrewjgrimm]

Don’t try this at home!

[@finnbraaten3264]

Aside from the joke, not really. The Oppenheimer estimate is an extreme best (or worst case-scenario) estimate. Given that 100% efficiency of fusing is a massive overestimate and the atmosphere has more than just nitrogen, they showed that it wasn't possible, even using extreme overestimation.

[@Nukestarmaster]

Yes, I'm sure the Mythbusters are the people to solve sustained thermonuclear fusion. Frankly we have literally been spending billions of dollars on trying to answer your question.

[@lyricalcarpenter]

Adam Savage Ends the World

[@lakshaymd]

Never knew that this was a possibility they were discussing. Wild to think about. Of course, if it is the first bomb of its kind, there might be consequences that no one has thought about. Terrifying.

[@drbeavis4211]

I do rememeber hearing about this concern when I was reading various pop-sci books. It was heavily studied with rigorous mathematics and physics to rule out the possibility. That said, things have gone wrong before and their was no guarentee. Good video, I learned a bit more then I did before it.

[@timb6558]

Feels like we're experiencing the same thing right now with A.I. Can only hope that in 100 years someone is making a friendly video explaining how we DIDN'T destroy ourselves!

[@lakshaymd]

Haha, hope so. Wonder what opinions people then will have about all the AI related fiction we have so far.

[@rphb5870]

imagine a scenario, not in which the lines crossed, but in one where Oppenheimer thought that they did due to a calculation error that wasn't discovered until a decade later, that resulted in the entire manhatten project being scrapped.

[@pmsteamrailroading]

Being a Michigander, I want to know what city and what lake.

[@beehard44]

how is this video only 5 minutes long? So much material presented concisely yet beautifully, it feels like I got more than 5 minutes' worth

[@WelchLabsVideo]

Felt this same way shooting it!

[@kingzcomparison3683]

Because this video is nearly 6 minutes long

[@Lavabug]

Cause it was scripted by a physicist. No frills or cheap thrills, just substance!

[@cmdrreggit]

"Shutup and calculate" 👍

[@RennieAsh]

Yes, it took him more than 5 minutes to create the video, so you sure did get more than 5 minute's worth! ;-)

[@Boodoo4You]

This 5 minute video felt like 15 minutes of information, and was still perfect. I love when a creator tries to make their videos succinct yet engaging enough to not feel short.

[@danielferrell1867]

“Edward (Teller) brought up the notorious question of igniting the atmosphere. Bethe went off in his usual way, put in the numbers, and showed that it couldn’t happen. It was a question that had to be answered, but it never was anything, it was a question only for a few hours. Oppy made the big mistake of mentioning it on the telephone in a conversation with Arthur Compton. Compton didn’t have enough sense to shut up about it. It somehow got into a document that went to Washington. So every once in a while after that, someone happened to notice it, and then back down the ladder came the question, and the thing never was laid to rest” - Robert Serber

[@Novastar.SaberCombat]

The weak-minded always latch onto the improbable but "impressive" possibilities. 🐲✨🐲✨🐲✨

[@fatfurry]

@@Novastar.SaberCombat 🐲🐲🐲🐲🐲🐲🐲

[@ImperativeGames]

Actually it was very, very smart to be concerned about self-sustaining fusion reaction that can end the world. Considering that back then it was all a theory and scientific theories are replacing previous ones (proven wrong) constantly.

[@Mystic_Void]

@@ImperativeGamesEspecially when you consider that self sustaining fusion is possible from the sun

[@wildliferox2]

@@Novastar.SaberCombat The possibility of extraordinary events does capture the Human imagination. Problem is we don't know everything, and its starts to get way more complex with interaction of compound issues. With any new technology there is a learning curve. Name calling 'weak-minded' because someone might have identified a concern. By all means allay their fears, but is it really necessary to demean that person simply for expressing it.

[@icybrain8943]

I think it's also worth pointing out that your perception of a small margin of safety may be a bit skewed if you don't take into account that you're looking at a logarithmic scale on the y-axis

[@fakestory1753]

It does, you should check again.

[@nabilfreeman]

Most people are not going to notice this

[@simeonlaplace6495]

He converts the difference from eV to temperature to show how big it is. So he got that covered implicitly.

[@SupGaillac]

Well spotted. Because margin is a matter of ratio, it does actually makes a lot of sense to use log scale for the y axis. (That is, in addition to the usual common reasons. )

[@lorenzodiambra5210]

4:58 *_it's better to all submit to the Nazis than to have a tiny chance of dying_* cit. Arthur Compton (That's the bravest sentence I've ever heard🥲💪👍).

[@dwurry1]

Please note that the graph in this video is logarithmic. This makes the lines appear to be converging when they actually are diverging. The more extreme the temperature gets, the further they diverge. The appearance of these lines become closer together because logarithmic graphs hide exponential growth by design! If you displayed thins information the bottom line would bearly come off the bottom of the graph and you would see zero (or near zero relationship between them. At 12 MeV (right side of graph) value of the green line at the end of the graph is 1,500,000 while the red line is 4,000,000. At 6 MeV the values are 700,000 and 2,000,000. So at 6MeV the values are 1,300,000 apart while at 12 they are 2,500,000 (almost twice as far apart). *Like all good physics my characteristics of values of lines are estimates. This is a great example of "how to lie with statistics". Want to make two things appear to converge? Use logarithmic charts.

[@shufflecat3334]

So what I'm hearing is that temperatures even higher than what were shown on the graph might be able to ignite the atmosphere, but I'm also hearing that a bomb capable of producing that amount of energy already destroyed the world, igniting the atmosphere is just an additional "and you're also dead this way too".

[@jasexavier]

Essentially the only way to get appreciable rates of N-N fusion is to be inside a star which is collapsing in the process of going supernova. You need insane temperatures and pressures. N-N is more than 10^100 times harder to ignite than D-T, which is already pretty tough. Even a bomb big enough to completely unbind the earth and turn it into a new asteroid belt wouldn't cause any kind of N-N chain reaction.

[@iamsick5204]

​@@jasexavierbut even then it wouldn't be a runaway reaction right?

[@Hadronikle]

You also need to keep in mind density, the density of nitrogen on earth is nowhere near enough to enable the fusion of nitrogen.

[@jasexavier]

@@iamsick5204 I'm not sure what you're referring to. A supernova is a runaway fusion reaction, consuming the vast majority of exothermic fusion fuels remaining in a star in about 1 second. If the earth were somehow deposited, whole and intact, into a star during that one second, the nitrogen in the atmosphere would become part of that runaway reaction. A huge bomb that turns the earth into pebbles would not cause any significant nitrogen fusion in the atmosphere, so no, no runaway reaction there.

[@iamsick5204]

@@jasexavier yes that what im referring too... Not the supernova part tho

[@MrAntiKnowledge]

Holy fuck. The stuff about igniting the atmosphere has been brought up a couple times in sci-fi. And I always thought it's a bit far fetched since the atmosphere can't "burn" on its own, being mostly nitrogen and oxygen. It never clicked until now that it meant a fusion chain reaction. Luckily for us that it isn't that easy to keep a fusion reaction going, I guess.

[@tyson31415]

We know how to make anti-matter, but we currently suck at storing it in any quantity. But eventually we'll sort that out, so we could still light the air on fire someday.

[@MCNarret]

@@tyson31415 it shouldn't be self-sustaining though

[@svenmorgenstern9506]

Same basic problem that Teller had with his original Super design - unless you squeeze the bejeezus out of the fuel (in this case, a chunk of Earth's atmosphere) getting the reaction to go just isn't going to happen. Which, incidentally, is why the Tsar Bomba didn't incinerate the planet when it was detonated in 1961.

[@johndododoe1411]

​@@svenmorgenstern9506Also Tsar Bomba was still less than 100.000 Trinity bombs in strength .

[@centralintelligenceagency9003]

if it was that easy to get a fusion chain reaction going, lightning, asteroid impacts and other such energetic events would have done it a long time ago.

[@Howtheheckarehandleswit]

I think a very important point that is often not made clear, is that the phrase "igniting the atmosphere" does not mean "setting the atmosphere on fire". In the context of nuclear physics, "ignition" refers to starting a self-sustaining fusion reaction. To "ignite the atmosphere" in this context means to cause the entire atmosphere to momentarily behave like the core of a star.

[@stevensteven3417]

Which is, setting it on fire.

[@Howtheheckarehandleswit]

@@stevensteven3417 That is not what fire is

[@CarrotConsumer]

You're one of those people that say you don't die from getting shot, but from the lack of oxygen to the brain, aren't you?

[@cmdrreggit]

A star is a bright ball of plasma held together by a large center of gravity. Fire is also a non-ionized plasma (at low temperatures), not a gas or a solid. It's a kind of transient state between being composed of the elements prior to ignition and the spent fumes. Different sure - but still plasma.

[@atata2000]

​@@cmdrreggit a combustion reaction is definetly not a nuclear reaction. So not even close

[@juango500]

"Ferb, I know what we're gonna do today!"

[@Optable]

The movie itself left so many of us questioning Nolan's decision to leave out such vital pieces to the remarkable work. The innerworld-building aspects, the highlights of the science itself. The math, the problems, the solutions, the designs, the inner structures of work at Los Alamos. No montage, no groundbreaking research, no frame of view. It's an absolute must in biopics/historical filmmaking. Take a scene in Scorcese's Casino: "The dealers watch the players, the floormen watch the dealers, the pit bosses watch the floormen, and..." while seamlessly keying the audience in to the systems in place. From the beginning to end, the big picture is answered by the little things with balanced structure, screenplay, and dialogue. This is done in Goodfellas and Wolf of Wall Street flawlessly as well. For these specifically, they simplify and engage us with timeline, complexity, shock, and gratification. Nolan crushed this aspect in Inception, The Prestige, The Dark Knight, and parts of so many others. Some less than others, and some more. Some like Catch Me if You Can by Spielberg, surround the entire plot in this notion: of world-building, a microscopic lens into the logic, steps, structure, and overall theme. While I'm not asking he remove the first third, and last third chapter of the film, by just giving us a decent 10-15 mins in each third, or a few montages per chapter; like the contributions of each bright scientist, the timeline of advance, the problems to overcome, the math itself, etc. - this would have done the trick and satisfied us all so much more. The communism and relationship stuff was far overdone. We could have gotten all of the themes and implications of each, from about 60% of that whole combined hour, fully replaced by scenes and clips surrounding better above decisions. These guys were the greatest scientists in the world, the brightest minds in history, among a revolutionary project of high level problem solving, mathematics, physics, chemistry, design, engineering, and fabrication. Let us in on that stuff- their determination, pursuit, and brilliance, but not in a bland, underwhelming general way (like with a single 2 second shot of the bomb construction)... All the impacts of the emotional struggle, success and turmoil, and mental struggle; the plot and theme itself, is enhanced so much further when we can grasp a better idea around: the back-end, the grit, the aptitude, the raw talent, structure and precision, etc. Let us in on THAT, not on sending me out of the theater, right to youtube, to find out how the bomb was assembled and engineered, or what brilliant math allowed that assembly to come to fruition. Even a taste of it! There was just warm alcohol for so much of the behind-the-scenes. So much of the film would have satisified us all so much better, had he highlighted these aspects with a purposeful zoomed in lens, then back and forth out into the big picture stuff.

[@LeftyScaevola]

Everything after "worst case scenario" for the probability of nitrogen fusion was essentially academic, since that assumption was WAY higher the the actual probability of nitrogen fusion, and with an actual figure there, the energy produce and and lost curves would be very far apart.

[@gnarthdarkanen7464]

The hell of it is that by the nature of pioneering the bomb in the first place, they couldn't possibly know what they didn't know. That assumption was made as a shortcut to TRY to compensate for every possibility that they weren't exploring stacking the odds against them, and adding to the chances of a runaway fusion reaction in the atmosphere... It seems easy to assume they'd theorize several alternatives, add a few functions on supposition of those theories, and run the calculations through a computer model, BUT the most sophisticated and powerful computer available at the time couldn't even power an 8-bit video game like Pac Man or Tik-Tak-Toe... These guys were engaged in a government funded mission to BUILD THE BOMB and on a schedule, using slide-rules and pens and paper for their calculations. They HAD to operate on the assumption that there WERE factors of fission that they did NOT know about. While they had some fissal processes ongoing, just for plutonium enrichment, NOBODY had produced a self sustaining fission reaction to the scale that was being attempted. Had even any of the earlier mathematical models been "off" for some reason, they had a very narrow margin before the earth being consumed in a fiery magnesium plasma would've become a terrifying reality for a very VERY short and awful time. ;o)

[@GijsvanDam]

I was left wondering what was the actual difference between the two curves after they had real data from detonations?

[@jasexavier]

@@GijsvanDam From measurements the lower curve would just be a flat line at 0. The cross section for N-N fusion, even at the temperatures and pressures in a nuclear explosion, is so low we can't measure it, only calculate it. For context, compared to the value they were using, 1, the cross sections of "easy" fusion reactions, such as D-T, are on the order of 10^-25. So if they'd been doing this in an atmosphere of deuterium and tritium, they still would have had a safety margin of 1.6x10^25 at least. The calculated maximum value for N-N is around 10^-141! So even at crazy high temperatures it takes 10^141 collisions to produce one fusion event. In addition, to produce the necessary temperatures to have any nitrogen fusion would require multi-gigaton weapons, and even then it would immediately fizzle out because of the low cross section. With even the largest weapons we've built and the most sensitive instruments you would not be able to measure a single N-N fusion event.

[@kuhluhOG]

well, you need to keep in mind that the probability of nitrogen fusion was not yet known in hindsight it was academic but with the knowledge available of that time it was a safety check

[@troybaxter]

@@kuhluhOG while it was not known, the possibility could never be worse than 100%.

[@guesswho2232]

The physics and mathematics of the Manhattan Project are absolutely stunning. It makes for such a crazy juxtaposition with what they were working towards.

[@andmos1001]

Science are leaning on giants in their respective fields to make future discoveries. You will be surprised how much impactprevious research have on todays modern research. A good example is antibiotics. There are actually several types of antibiotics that all of them have been found in the same time.The one we most know is penicillin. But there are two others ground breaking discoveries: the synthetic antibacterial compound that use sulfur, and viruses that their sole purpose is to attack the bacteria. We are beginning to understand the virus aspect as an antibacterial treatment, with Georgia being the leading country in this field

[@leonidfro8302]

What's so stunning here? Physics and mathematics of internals of modern cellphones are match more complex.

[@andmos1001]

@@leonidfro8302 true, but can you calculate this math by hand?

[@leonidfro8302]

@@andmos1001 You don’t need math, that’s my point.

[@mrfahrenheit677]

@@leonidfro8302 "you dont need math"...buddy you have no idea the genius it took to do this stuff. saying "oh we have cell phones now" doesnt detract from that...at all

[@lidarman2]

One of the best lines in the movie was "What do you expect from theory alone?!" -Oppenheimer (Movie version). A running joke in my quantum mechanics class and education was "In theory, there is a small, but very small, chance you could tunnel through the door instead of opening it."

[@wowzers94]

I love your new set of videos. Great presentation and explanations! Keep up the good work!

[@kappascopezz5122]

this reminds me of how some people seem to be scared that particle accelerators cause black holes

[@DendrocnideMoroides]

or that particle accelerators will cause vacuum decay

[@andrewpacifico8193]

this reminds me of how crazy it would be if the universe started from a singularity! :P

[@m73m95]

It's a pretty good example of just how far away the average person is from real science. Through propaganda, politics, and TikTok, a real understanding of the scientific method is all but lost on most people (I don't discount myself in that). Some amazing discoveries, and proof of theories written a hundred years ago, have been done at the CERN Laboratory... meanwhile flat earthers still walk among us

[@SevenTheMisgiven]

They do cause black holes. The issue was if they would be sustainable black holes but they are too small and evaporate too quickly.

[@Klaux]

​@@m73m95when the impostor is

[@tanchienhao]

Thanks for covering this part of the movie! Your series came out just at the right time for Oppenheimer movie release!

[@Ka-zl7fi]

This video is everything I wish the rest of KZbin was - your delivery is so succinct and concise - really well made I loved it

[@theironraven5502]

I mean, if the whole atmosphere turned into plasma, I'm pretty sure that would end the war in an instant.

[@jmackmcneill]

Not a math guy, but that was clear enough that even I understood it! Good Job! I've always wondered what the details of this particular calculation were. No matter how confident you are, there is always the nagging doubt at the back of your mind that literally everyone forgot to "carry the two" at the same time on this one calculation.

[@clarkelliott5389]

I remember reading about Arthur Compton's concerns perhaps 40 years ago. The whole Manhattan Project was a very interesting time in this country. (If the Tsar Bomba did not set the atmosphere off, I think we are pretty safe.)

[@MartinH81]

I think there's a huge miconception about the power of nuclear weapons relative to each other. Not saying you're thinking this, but the vast majority of people think a 10x more powerful nuclear bomb is 10x more destructive or 10x more whatever... That's simply not true. Not only because of non-linear scaling of the efficiency of the bomb and other technical factors, but mostly because of the simple reason that an explosion takes place in 3 dimensions. For a 2x 'stronger' bomb in all 3 dimensions you need a 2-cubed = 8x higher yield.

[@DigitalWolverine]

Edward (Teller) brought up the notorious question of igniting the atmosphere. Bethe went off in his usual way, put in the numbers, and showed that it couldn’t happen. It was a question that had to be answered, but it never was anything, it was a question only for a few hours. Oppy made the big mistake of mentioning it on the telephone in a conversation with Arthur Compton. Compton didn’t have enough sense to shut up about it. It somehow got into a document that went to Washington. So every once in a while after that, someone happened to notice it, and then back down the ladder came the question, and the thing never was laid to rest” - Robert Serber

[@paulkurilecz4209]

Thank you. I have always wondered about the back story to this. It does point out that a variate analysis is needed when assumptions are made about values for given phenomena.

[@curtisdaniel9294]

I read Richard Rhodes book when it first came out. This atmosphere on fire is mentioned but not greatly explained. Your short vid is Great at explaining how they did these calculations. Thanks for this! This is my third or fourth time I have watched one of your videos. This one sparked me to become a subscriber.

[@mariostudio7]

This video is so good, but it was too short it almost felt incomplete in a way... it is cut off when the viewer is engaged the most.

[@maskettaman1488]

Nah screw off. We don't need 5 minutes of well produced video stretched in to 15 minutes for no reason

[@cakcakcak]

maybe it was a matter of probability, but not in the sense that “three in every million atom bombs ignite the atmosphere.” more like “there is a 3/1MM chance that our determinations of the key variables are incorrect enough to ignite the atmosphere”

[@jhonbus]

That's exactly what it means, yes.

[@JonWilsonPhysics]

Systematic uncertainty.

[@Nukestarmaster]

Eh, they massively overestimated in every way possible and the best they got was a 1.6x input to output ratio. There was a 0% chance that the bomb would fuse the atmosphere.

[@That_Awesome_Guy1]

@@Nukestarmaster We know that now.

[@Nukestarmaster]

@@That_Awesome_Guy1 They knew it then, too. That's why the project got a green light.

[@Josh-qm7fl]

2:57 the temperature unit of Kelvin is just Kelvin [K] not degree Kelvin [°K]

[@boi_howdy]

dude i just got this video recommended in my feed watched it and then all of your other recent videos THEN i realised you’re the guy who made the video series on complex numbers! Those videos, and the shot of you pulling the complex plane out of the paper in particular, inspired me to go to college. Here we are roughly five years later and i just got excepted into my universities masters program, with the goal of writing my masters in, fittingly, nuclear physics. You, among a few other educational youtubers, have undeniably changed my path in life, thank you for that mate! p.s. the video is really good!

[@papasmurf7944]

excepted

[@nahuel3256]

You're such a good communicator and teacher!! The only bad thing is that bittersweet taste that leaves me wanting more

[@nogodiggydie]

I always thought it was interesting that they can only use steel from sunken pre WW2 battleships to make radiation-detecting equipment. I never considered that possibility.

[@jwstolk]

There are alternative solutions, using very old steel is just the cheapest solution. The (very small) radioactivity in not in the iron ore, it is added from oxygen, used in the steel reduction process. Alternative solutions are based on creating steel without using oxygen from the air, to avoid adding traces of radiation resulting from nuclear testing. Lead has similar issues when used to shield very sensitive equipment.

[@jhonbus]

@@jwstolk The lead is really interesting, the isotope that causes a problem for sensitive equipment is Pb-210, which is pretty radioactive at a half life of about 22 years. Nukes aren't the problem here, lead-210 is constantly replenished and kept at a stable level in the environment because of the steady decay of radon, so lead has always had a small amount of this isotope whenever collected and smelted. This means if you want very low radioactivity lead, you need to mine and smelt the lead down into a chunk of metal, and then wait a couple thousand years for all the lead-210 to decay to the stable lead-208. Not very convenient. But hey! Those Romans have us covered, since they did indeed smelt down a load of lead 2000 years ago and now it's nicely depleted in radioisotopes! So yes, if you need to shield very sensitive equipment, you use Roman lead.

[@jhonbus]

Also radiocarbon dating doesn't work on anything newer than 1945 and never will. There has been a steady level of carbon-14 in the atmosphere for thousands of years due to cosmic ray capture, but we completely f'ed that level by exploding nukes.

[@DrDeuteron]

ultra sensitive detectors...signals with 10's of counts per month.

[@crowe6961]

Enough time has passed that increasing amounts of postwar steel are becoming available as well, now.

[@deilusi]

The amount of stress those guys had is absurd. If you mishandle that small ball, demon core, everyone in the room is goner. If you missed a digit in that superbly complicated math you did by hand, the world is gone. Be careful not to accidentally explode it or we will have city sized hole here.

[@CheeseLordAlmightytheOneGod]

No they multiply the equation by nearly 1 trillion just to be safe in case of the worst scenario

[@akiskarorimakis741]

I've read in a book by Paul Virilio that there was a danger for something like that to happen and I though at the time that those were exaggerations of interesting points that he made. I couldn't imagine that this was such a serious discussion at the time. Thank you very much for your work!

[@landonkryger]

I'd be curious what conditions would be necessary for the reaction to run away. Could there be aliens on another planet, with a different atmosphere, where the math works out that they would be annihilated?

[@richard_d_bird]

mohr power faster hotter

[@neopalm2050]

Fusion research says "we wish. If we could make fusion happen with _every_ collision then we'd have all the energy we could ever dream of."

[@theterminaldave]

They mentioned the temp/power needed for a runaway on this planet. I wonder if humanity is capable of creating a weapon with that potential now? (Though not even the tsar bomba produced that effect.) As for your second question, there are all sorts of atmospheres out there, so i guess it would really come down to the question of what type of atmospheres are capable of supporting life, then work the problem back from that.

[@Muonium1]

Probably not on any planets, but the possibility of igniting the "atmosphere" rises to a complete certainty on, say, a white dwarf star just below the Chandrasekhar mass in orbit around and cannibalizing a red giant. There will unquestionably be a time when the dwarf is highly unstable and a fusion burn wave ready to initiate at any moment. It's easy to imagine a nuclear bomb detonation setting off a type 1A supernova on a star in such a precarious state.

[@lukasstaar6860]

The only reason this figure was only 1.6x is because they assumed a gargantuan cross sectional area of 2 barn for a nitrogen nucleus fusion reaction due to lack of experimental data. In practice, something like a microbarn is probably more accurate.

[@aidanwarren4980]

This gives a lot of context to Vonnegut’s novel Cat’s Cradle, in which a scientist creates a crystalline structure of water that freezes below room temperature, which threatens to destroy all life on earth by freezing the oceans if released. It always seemed like a silly but creative idea to me. The fact that it may have been written in the context of “we might’ve triggered a fusion chain-reaction that would turn the atmosphere into molten metal” adds a lot to my understanding.

[@masonga1995]

If you want to know more, the general concept is actually found in many places across physics. In that example the solid phase is a lower energy state than the liquid phase, but quite often matter needs an "example" to copy or start building off of, which leads to weird phenomena where an entire body of water could be still liquid at below zero (supercooled), but snap freeze once an impurity is added (nucleation). Vonnegut’s theoretical "more stable than ice" crystal may seem fantastical, but is a real concept and similar ideas exist in other areas such as the strange matter or false vacuum hypothesis, except in relation to all matter or space-time itself respectively. The strange matter hypothesis is considered quite unlikely still, but the false vacuum hypothesis has managed to remain stubbornly probable despite continuing research.

[@albertohart5334]

Excellent video, extremely concise, well made, informative and entertaining 👍

[@NoriMori1992]

I learned about this concern over a decade ago from Freeman's Mind of all things. But he characterized it as them trying it despite still being worried! Glad to learn the real story.

[@que_93]

Extremely interesting subject matter and an equally coherent explanation. Thank you!

[@tronpauli1475]

If fusion were that easy to do... there wouldn't be nitrogen to fuse because it would have fused already. Ex. because it wouldn't have survived production in a supernova (which they may not have known about then). In general though... if it were possible to do in a self-sustaining way, some random event would have kicked it off already. Same reason we don't find large amounts of free hydrocarbons on the surface. In any case where they would build up, a process like forest fires exists to remove them.

[@varno]

But we do know that nitrogen fuses within stars, (which is where it is produced). However the conditions are not possible in the atmosphere.

[@DrDeuteron]

Hans Bethe figured out solar fusion in 1936, iirc. He solved core-collapse supernova in the 1990s.

[@realdragon]

Fusion and fission are different things

[@HopelessBromantic]

Thank you for this video I’ve been searching everywhere for an explanation to that

[@Magnasium038]

I always wonder what kind of precautionary calculations scientists do to check for safety concerns. It's neat that the check is simple enough in concept that I can understand it and agree that it makes sense to perform, even if I can't calculate it myself. As a side note, graphs are a wonderful way of translating equations which are way too complicated for a casual observer for me to understand, into something I can.

[@francescozani9488]

Fermi and Szilard already ruled out way before the experiment. And they were well prepared for this, since the use of A bomb to ignite fusion was already investigate in Manhattan project.

[@raphpopozz4495]

Very interesting video that explains those lines we hear in the teaser, thank you. Interesting to know they are not just Hollywood fantasy but that it had been a real concern that had been assessed. The scale of the graph is logarithmic, right? Makes it look more dramatic.

[@jaymorf7374]

Excellent, excellent presentation, accessible to all. You've gained a subscriber.

[@YolandaPlayne]

Wow, such a great video. Very informative I watch all the time.

[@1495978707]

The real reason that there was still some uncertainty here is that they were under no illusions of fully understanding the nuclei. They used what they knew at the time and calculated the worst possible scenario, but there was still a chance that there was something yet to be discovered at that point

[@HistoryfortheAges]

As a History professor I am looking forward to this movie. I hope it is historically accurate. I made a short 5 minute video for anyone who wants to learn a bit more about the actual history before you see the movie.

[@theterminaldave]

You should make a short or two from your video, and link back to the full video in the comments, as that movie will be getting a lot of searches over the coming days and weeks.

[@HistoryfortheAges]

@theterminaldave I have. Made a few in fact!

[@HistoryfortheAges]

@@theterminaldave kzbin.infot46AyCQLNNg?feature=share3

[@Android480]

Their marketing materials have been less than accurate so far. But I’m hoping that’s just the marketing department, and Nolan cares more about the history.

[@HistoryfortheAges]

@Android480 always hard to tell from the trailer. We will see

[@vincentcausey8498]

I recall a similar concern before the switching on of the large hadron collider, although the threat was the creation of a mini black hole. Nice to know that neither event came to pass.

[@magicrubinny5764]

I absolutely love the format of this video

[@WelchLabsVideo]

Thank you!

[@jackn4853]

It's Kelvin not degrees Kelvin! My physics teacher was so strict about this, and drumming into us the importance of units, units units.

[@SevenTheMisgiven]

What a waste of educational time lol. But teachers are very good at not actually teaching students important things. Any 4 year old understands this concept.

[@Pablo360able]

It's not a unit error, lol. It's an unimportant misstating of the *name* of the unit.]

[@lenidragovich1471]

you sound insufferable like your physics teacher

[@mayfield3314]

Getting psyched for the movie!!! By the way, Kelvin is a unit by itself. You cannot say "degrees Kelvin".

[@SlenderSmurf]

​@@retiredbore378😂 this is such a goofy joke

[@my3dviews]

They used to use "degrees" on the Kelvin scale up until 1968. So, often you would hear older scientists still saying degrees Kelvin. Not sure what this guy's excuse is though, since he probably wasn't even born yet when it was dropped.

[@DrDeuteron]

@@my3dviews ppl still use it, and no-one cares in the business, unless its's a peer reviewed publication. Ofc, ppl also say "one mega hurt" for 1 MHz. Ppl also say "electron volts" when they mean eV/c^2....and again, no one cares.

[@my3dviews]

@@DrDeuteron Obviously someone cares, or it wouldn't have been brought up in this thread. Listing other things that people say wrong, doesn't make this one right. Most people who have a scientific background know the difference. Never heard anyone say mega hurt. Maybe a child or someone who never had any science education. As far as "electron volt or volts", that is an actual unit of energy, vs. mass when using eV/c^2. So, it is not always wrong depending on what they are referring to, as degrees Kelvin is now considered to be. If you or other people don't care, that's fine, but usually people who make science videos try to get things correct, or at least they should.

[@DrDeuteron]

@@my3dviews I'm talking about people who split atoms, land on Mars, and build black space stuff, so: the real world. No. One. Cares.

[@jg54cule]

Really good video. Thanks for visualizing the math.

[@inccrosby]

You’ve done and amazing job with this video.

[@johanfuhri]

Imagine having to do the math, knowing that a mistake could literally set the atmosphere on fire...

[@juliaclaire42]

Kelvin is Kelvin and not ° Kelvin.

[@Sirsoyuz]

Imagine the sense of responsibility they must have felt when their calculations being wrong even had the smallest chance of triggering an apocalyptic event. The physics they dealt with weren't entirely new but the application of those physics completely untested. I wonder if scientists currently working on AI or genetical manipulations for example have similar ethical considerations we are unaware of...

[@realdragon]

Physics might not be new but the thing about it is that we didn't discover everything. We don't know what physics might do if we didn't test something before. For example Newton's gravity is great, observing Mercury shows that's not how exactly it works

[@arfyness]

gotta love the satie for this video 💗 so dark and melancholy yet eccentric and somehow energetic

[@2Oldcoots]

Simple, understandable, and thorough ='s an outstanding presentation! Thank you sir.

[@humbledb4jesus]

love your formula breakdowns...if i had these 30yrs ago, i would have scored higher than a B for my astro degree...

[@yayhandles]

"Inverse Compton Effect" Is this just a weird way of referring to Beverly Hills?

[@joesilverbliss1721]

Love that Rockwell calculator. I still have mine and it still works! Great video.

[@gregwarner3753]

I have wondered about that concern. Thank you for the enlightenment.

[@phred196]

When any atoms split or fuse, a huge amount of energy is released which in turn drives surrounding matter apart (the kaboom). Atoms must be packed closely together to split or fuse. that's why the core is a nice solid lump of plutonium or some such. Vaporizing the core causes it to spread apart and become less dense. And when density drops, the reaction stops. That's why most bombs only consume a fraction of their core. In essence, the bomb turns itself off during the explosion. Now, air is way less dense than solid plutonium or for that matter any solid. But heat air to 10k degrees or more and it really spreads out (explodes) thereby reducing density substantially. Even if there was sufficient energy to fuse a few oxygen atoms (or whatever) at atmospheric pressure the blast would blow itself out in exactly the same way as the metal core blows itself out. Any atomic blast which gets totally out of hand is therefore self limiting. Now, I would be willing to consider that perhaps in a super high density environment like perhaps the earth's core where temperatures are already thousands of degrees and pressures are way over 100+ atmospheres maybe you could get something going. maybe. But if you can drill three thousand miles down and drop a nuke into that then I think your tech is of a level sufficient to run accurate simulations to figure our the risks. Short answer, it can't happen on this planet in this life. Try Jupiter?

[@realdragon]

Not true, some atoms require energy to split and some atoms release energy when they split. Otherwise you could just split and fuse atoms indefinitely and get infinite energy

[@ddopson]

If it were that easy to ignite a Nitrogen atmosphere at merely 1 bar to self-sustaining fusion, then it would have happened already. Meteor collisions create insane temperatures and pressures, and Earth is constantly bombarded by exotic high energy cosmic particles. One of these would have tripped the ignition conditions and that would have been it. No, the reason this doesn't happen is that fusion isn't self-sustaining without the incomprehensible pressures and temperatures achieved inside stellar cores. They already knew this and the math was just a sanity check.

[@donaldhobson8873]

Meteor collisions get hot, but not nuclear hot. Cosmic rays are small. You really do need the math and nuclear physics theory.

[@DrDeuteron]

what he said, but a 6 mile 40 mile per second meteor dumps its gigatons into a 500 cubic mile volume in 150 milliseconds, while a fission devices dumps 20 kT into a few cubic inches in 10-100 ns. The power density of the later is insane, while for the former...it's just the total energy that is nuts.

[@timothymoralez]

Thank you for this content, well done

[@userNULL]

The production on this video is super nice. love the aesthetic of it, the cool calculator is a nice touch as well. the lack of the standard jarring-outro-channel-plug is very refreshing.

[@philipstuckey4922]

There's something weirdly compelling about math typeset and then annotated by hand

[@niwaka273]

It might be helpful to cite the music source as well. The piano piece starting at 4:31 is called "Gnossiennes 1" composed by Erik Satie published in 1893. kzbin.info/www/bejne/hn2ph3qtfLaWeJI The description of the link above includes interesting info on the piece and the composer. If anyone is interested to know how I found out the name of the piece, here are the steps: 1) Type in a general description of the piece (in this case "creepy piano classical". I knew the piece isn't classical but including the last one would filter out cover videos and similar false leads). 2) To save time, pick a long youtube video with timestamps. 3) Listen in to the pieces while ruling out obvious misleads (since the piece in question is relatively simplistic, I was quite certain that it couldn't be Chopin, Beethoven or other classical composers) 4) Continue the search while analysing and remembering the songs found during the search. Gathering new knowledge makes future searches easier, see step 3 (knowing styles and trends make it easier to rule out false leads). If persistent enough, most searches succeed. I mean the best case scenario is if the title is included in the video description but going down a rabbit hole is also quite nice.

[@Cookster997]

If you like this music, definitely check out more compositions by Satie. Lots of very similar works, and very playable for lower skill pianists too.

[@furTron]

The song is sooooo odd familiar to me. I am 100% sure Ive heard it many times, but I cannot remember where. Like if from some long forgotten dream

[@tuff_lover]

@@furTron spam bots, be gone

[@forsaken841]

I just taught my self this song on the piano.

[@Kazuyaa3]

It's like you read my mind! thank you

[@EdgarGuevara-yn6ux]

Thank u so much for ur work! Excellent explanation.

[@chrism3790]

There were plenty of other fuck ups due to incomplete knowledge during the development of nuclear weapons, like the massively underestimated yield in the Castle Bravo test, which involved an incorrect assumption that the Li-7 isotope would be inert during the fusion reaction. I'm glad they got this one right.

[@PalmettoGD]

I like your funny words magic man

[@SlimThrull]

Thank you. I've heard various "explanations" of this over the years. Yours is far more detailed and explains most of the questions I had. However, it strikes me is that it would be possible to ignite the atmosphere if the density of nitrogen were significantly higher. If the 57 meters was instead say 10 meters? 5 meters? Would that be enough to do it? Eyeballing the numbers it looks like we'd need an atmosphere significantly more dense than anything on Earth. However, it just might be possible to do on the gas giants. Any idea what the actually density would have to be?

[@jimsagubigula7337]

It's not about the density of the gas, but how hot it gets. You need about 160 billion kelvin to fuse nitrogen 14, a temperature much higher than any nuke can achieve.

[@samorgan5361]

Beautifully made and explained!

[@KevinZ.000]

It's been a minute since I studied upper-level college physics but was glad to know the meaning of the equations presented. I guess studying calculus is like riding a bike to some degree.

[@mage1over137]

It was never really a fear, just like black holes out of the LHC were never really a fear. The assumption that every Nitrogen collision results in a fusion is obviously an overestimate by many orders of magnitude. So when Bethe said it was impossible he wasn't being dismissive. There would have to be some crazy physics mechanism to even make that basically already 0 probability even valid.

[@josh34578]

I wonder how analogous calculations turn out for other planets with their different atmospheres.

[@KingdaToro]

For it to actually work, you'd need something on the verge of becoming a star on its own. Think Jupiter, but 79 times more massive.

[@reubenm.d.5218]

Beautifully produced video

[@dingo8babym20]

The document you displayed shows Si 14 - Al13 - Mg12 - 08 + C6. So, was the final product of their calculations thought to be oxygen and carbon, instead of magnesium? Fascinating vid. Subbed.

[@jackassrower]

Would be interesting to know how high the concentration of nitrogen would need to be in the atmosphere to make this actually happen.

[@zoomer9686]

high enough to be non-breathable for humans, so we won't be around for it anyways

[@szkoclaw]

"Look how close those lines come" No, they don't come close. This is logarithmic scale. There's a factor of 2 between them at the narrow point. And then the assumption of every collision reacting, which is completely off the scale.

[@jaspervermeer659]

They didn't know enough to say that was completely off the scale

[@aidanfarrell1926]

thank you so much for not making a 30 minute long dragged out video like 90% of youtubers would

[@kellymoses8566]

Typing all those equations on old typewriters must have been hell.

[@alltheclovers266]

As they made ever bigger bombs, did the math get worryingly closer?

[@nekopop8159]

The Tsar Bomba certainly brought those chances even closer, but the rest of the atmosphere didn’t blow up right?

[@MrCelaneous]

It occurs to me that if the atmosphere _could_ have been ignited in that way, asteroid impacts would've already done it a long time ago, they're energetic enough. I wonder if that argument occurred to anyone at the time.

[@MarkoLomovic]

They knew much more then that. Whole Manhattan project isn't about discovery of science behind how bomb would work but how to make the damn thing and developing those processes. You just need to see insane scale of whole project to apricate it Just looking at Y-12 and k-25 facility and those two together made only 50kg of material needed.

[@Drelcoz]

Insanely good video!

[@VideoMakesMeHappy]

Amazing video! Instantly subscribing

[@knightrider585]

Turns out self-generating fusion reactions are way more difficult to create that this. We still can't do it even when we want to.

[@jovanovicoliver]

media.tenor.co/sjsnwJuDRGkAAAAC/no.gif?t=AAYAu_kJ9uQKZldIQA-MeA&c=VjFfZmFjZWJvb2s&itemid=26066475

[@gameonyolo1]

😿(fusion scientist)

[@sirelkir]

I was curious about this claim of "igniting the atmosphere" so I looked it up and found this exact document two days ago! Well it's just a testament to how well both Openheimer and you make that particular history and physics interesting!

[@mrchejov4993]

Great content !

[@nena73]

absolutely fascinating video. makes me wish i was good at physics so i could fully comprehend this

[@sigmundfreude4088]

I am not a Supervillian or anything but just for curiosity: Is it possible by todays standards to build a single atomic bomb that would cause such a thing as a fusion reaction in the whole atmosphere? To build a single bomb that could destroy the world?

[@1088lol]

try it for science and not villainry of course

[@AlcyonEldara]

No. The "every collision is a fusion reaction" is off by several orders of magnitude. You'd need to reach a temperature and density only found in a supernova, and the Earth would be destroyed before that.

[@FridayFroths]

I will never understand how anybody can truly understand any of this. It is beyond incredible that some humans understand math and physics, things you cannot see, and determine the results of experiments on this scale. It is mind blowing. Salute to all scientists man!

[@thomaswomack3888]

theoretical physics is heady stuff and its good that there are people who are forward thinking enough to actually crank thru the 'what ifs' before testing something with this many unknowns. Responsible science is what I would call it.

[@RabbitEngineering]

Daniel Ellsberg mentioned in an interview that Fermi thought there was a 10% chance that they had missed something in their model, and then gave odds of Trinity burning the entire state of New Mexico, and the entire world. You can listen to that in the 80,000 Hours podcast episode featuring Ellsberg.

[@formerctgovernordannelmall1452]

(Me, Watching a well researched physics video that is thoroughly explaining itself in every way possible and that there is literally no issue with) (2:52 Narrator says “degrees Kelvin”) “Clearly this is objectively the worst video to have ever existed, and I believe the creator to be personally responsible for 2.8 thousand unrecognized war crimes. I’ve called the police.”

[@fraizie6815]

According to some sources, someone (I forgot the name) said, when observing the first nuclear explosion, it looked to him as if the sky is burning and wouldn't stop. That their worst fear actually became a reality. But thankfully that didn't happen.

[@realdragon]

Yea I would shit my pants looking at it

[@anaelbogoss8022]

Thanks for your work

[@WelchLabsVideo]

Thank you!!

[@esterhudson5104]

Excellent! Well presented!!