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I used to teach a class on the history of contemporary science (WW2-present) and I started the class with Trinity. There’s no other moment better. We know how

I used to teach a class on the history of contemporary science (WW2-present) and I started the class with Trinity. There’s no other moment better. We know how it turned out, but the people there waiting for the test did not know how it would turn out. The bomb might not have worked. Or it might have ignited a fusion reaction in the atmosphere and destroyed the world. Hans Bethe had sat down and done the calculations on that exact scenario and said it would not, but there was always the possibility of missing something. Enrico Fermi was offering bets on it on the day of the test, as a dark joke. In the end it worked as expected; one of the most successful and horrifying experiments in the history of science. Of all the photos from the test the one that struck me the most looking through them today was the photograph of the plutonium core being carried into the ranch house for assembly in a little heavy box. It’s a small thing, about the size of a grapefruit, although twice as dense as lead. It looked just like a sphere of any old metal, but it was something profoundly alien, made inside nuclear reactors. And it still is so strange to me that something that small has so much energy locked up inside and that, by imploding the little sphere just right, we can let the demon out. Trinity is one of the pivotal moments in the history of our species and eighty years on we still don’t know what the eventual consequences of it will be. The bombs are still here waiting for us and they still pose all sorts of terrifying questions for the future that most people prefer not to think about.

ronnier 4mo ago
Do you mind linking the photo you mentioned? I’d love to see it if you are able to find it
- marc_g 4mo ago
  It's in the TFA, there a photo of a fellow holding a small box thing that looks like a battery from a car or an old box torch.
  - ronnier 4mo ago
    I saw that but not a picture of the plutonium core which I thought the OP was referring to
  - libraryofbabel 4mo ago
    That’s the one I meant. It’s the core, but in a box, which makes it look even more innocuous, like he is indeed just lugging a piece of industrial equipment around. There’s lots of photos of the actual (unboxed) cores online if you search.
    - ronnier 4mo ago
      On flight WiFi so searching was a hard but I did find it. Thanks!
    - trhway 4mo ago
      >makes it look even more innocuous, like he is indeed just lugging a piece of industrial equipment around if i remember correctly what i read it was done intentionally for security reasons - instead of all the pomp-and-circumstance of a large strong security convoy the core was delivered by a driver in a simple inconspicuous truck.
SoftTalker 4mo ago
Was it a single solid core that was imploded? I thought it was at least two non-critical-mass hemispheres, or more, that were smashed together by the conventional explosives/detonators, to create a critical mass.
- libraryofbabel 4mo ago
  You’re thinking of the other bomb, the U-235 one, which they didn’t test at Trinity and which was dropped on Hiroshima. That is two separate pieces of Uranium that are slammed together to create a critical mass. The Pu-239 core was a single sphere of metal. It was subcritical until you compress it down with a spherical implosion from explosive charges all around it (from the size of a grapefruit to the size of a lime), at which point it reaches a high enough density to go critical.
  - wat10000 4mo ago
    The gun-type bomb (where a subcritical mass is shot into another subcritical mass) is very simple to build once you have the materials to do it. They didn't think it needed a test since it was pretty obvious that it would work. The implosion design is tricky. You need to arrange and detonate the explosives precisely to compress the core evenly from all sides, otherwise it shoots out the side or otherwise doesn't go bang the way you want it to. Hence the test. That trickiness can be a good thing. Almost all modern weapons use the implosion design, partly because it's much safer. With a gun-type design, an accident could easily cause the two pieces to contact each other, resulting in an unwanted detonation. With an implosion design, accidentally setting off the explosives is very unlikely to set them off with the correct timing, so you'll probably just lose the core. The implosion design is also a lot more efficient. Little Boy used 64kg of uranium. Fat Man used just 6.2kg of plutonium and even got a bigger bang out of it.
    - generuso 4mo ago
      It is all true, but one needs to take into account that because of the different properties of the materials, the critical mass for uranium-235 is intrinsically much greater than that for plutonium-239. For a bare sphere, it is about 10 kg for plutonium and 50 kg for uranium.
smcameron 4mo ago
Funny enough Adam Savage just posted a youtube video about building a replica of the demon core and the box to hold it. https://www.youtube.com/watch?v=V1Y4UR8xqxA https://www.youtube.com/watch?v=V1Y4UR8xqxA
ghaff 4mo ago
It was probably all pretty silly but there were a few probably-not-all-nutcases that were concerned about the LHC causing something horrible.
- fragmede 4mo ago
  I dunno, ever since that weasel got stuck in it in 2016, things haven't been super great.
gpm 4mo ago
> Or it might have ignited a fusion reaction in the atmosphere and destroyed the world Someone's got to explain to me how this was even remotely plausible. We've had orders of magnitude more energetic events in earth's history that they would be aware of (dinosaur slaying asteroid for instance). These didn't manage to destroy the earth by turning the atmosphere into a fusion reactor. Surely they were aware of this. So was the theory that neutrons are somehow special in a non-thermal way for causing fusion (not fission). And specifically that a concentrated neutron burst could somehow set off a chain reaction? And I guess that [edit: solar] neutrons weren't concentrated enough to cause this even at a detectable level?
- voidmain 4mo ago
  I think the tiny size of a nuclear weapon and very short interval of nuclear reaction before "disassembly" mean that even though the energy release is small compared to an asteroid impact the temperatures are probably much higher. (I'm not an expert, though, this is a guess)
- wnissen 4mo ago
  You might be surprised at how little we know about fusion. We can observe the sun, but the sun is already very hot, millions of degrees, so any unknown fusion reactions would have already happened. Nowadays we have high-powered lasers that can create laboratory-scale fusion reactions. E. O. Lawrence's 1930 cyclotron could generate protons at roughly a million degrees Celsius. But that's a single proton stream. Good for splitting atoms but not for fusing them. You really don't know what the cross section of a fusion reaction is until you do it. The properties of matter at that temperature are just super weird. If it had turned out that there was, e.g., a carbon-carbon fusion reaction with a lower initiation, that might be enough to "go critical" and kick off more fusions, and propagate around the world. According to estimates, the Chicxulub crater was 1-10,000 degrees C. Not even the same ballpark. https://www2.lbl.gov/abc/wallchart/chapters/11/4.html https://www2.lbl.gov/abc/wallchart/chapters/11/4.html
- queuebert 4mo ago
  We didn't know as much about possible nuclear reactions back then, so I think they thought there was a possibility that there was an exothermic chain involving N or O that could be ignited by the bomb and would be self sustaining. While an asteroid impact is very powerful over large scales, it doesn't create nuclear reactions, so Trinity was indeed a first at that scale. But, and I'm not sure how much of this they knew back then, we do get bombarded by high-energy cosmic rays, so chances are one of these hypothetical N or O reactions should've already randomly occurred at least in isolated events over the last few billion years if possible.
jstummbillig 4mo ago
Increasingly with more powerful and precise technology the relative danger of the bomb will decrease, to the point where the bombs will become meaningless. The stigma is too big, the blowback is too severe and we have countless other ways to pummel each other into oblivion with more finesse.
contubernio 4mo ago
My grandfather was a student of Kistiakowksy and worked on the simultaneity part of the firing unit and was present at the assembly of the bomb and to watch the detonation. He recounted being quite nervous that his contribution would fail (as it had a short while before the final test) and the test would be a dud, but no one involved seriously in the scientific and engineering part of the building of the bomb had serious doubts that it would work once the technical issues were overcome, and none of them worried that it would ignite the atmosphere, because they knew enough to know that was silly. They'd all been working on this and doing thousands (!) of tests for months or years at that point. During the test he was given what he called the "chicken switch" that could abort the test at the last moment, and he always said that his biggest worry had been that he would stupidly abort the test in a moment of panic (surely this was exactly why he was given the switch). He described the actual explosion as the most beautiful thing he saw in his life. When one looks at the history one needs to remember that these were scientists and engineers who behaved as such. My grandfather, for example, was the sort of person who always loved blowing things up. He'd nearly blown up the family home as a kid when given a chemistry set ... and he studied chemistry because he liked blowing things up ... and he wrote a PhD thesis about the shock waves generated by blowing up a really big (conventional) bomb. It all gets dressed up as studying shock waves and so forth, but it's really kids blowing things up. They get caught up in the challenge of it. The consequences, political, moral and otherwise, are not forefront in the thinking of most. None of them are innocent, but some have misgivings or second thoughts. Others are more cynical and ambitious and even sinister. There are Oppenheimers and there are Tellers.
- reedf1 4mo ago
  This very much overstates the certainty of the scientists in the outcome of the explosion. They could be pretty certain it would work - but they were not at all certain about the result of producing energy, pressures, temperature and forces that have never been tested on earthly reality before. There were many unexcepted outcomes of the explosion, we are just lucky (as we usually are with new science) that they weren't particularly bad.
leonidasrup 4mo ago
> Or it might have ignited a fusion reaction in the atmosphere and destroyed the world "The “near zero” chances Oppenheimer unnerves Groves with in-movie probably come from Manhattan Project physicist Arthur Compton, who told author Pearl S. Buck in a 1959 interview that they’d calculated the odds at “slightly less than one-in-three-million.” In 1975, Bethe denied that there had ever been a less-than-one-in-three-million chance of setting the atmosphere on fire, but the idea had already lodged itself in the public imagination." https://www.inverse.com/science/did-oppenheimer-really-worry-about-setting-the-atmosphere-on-fire https://www.inverse.com/science/did-oppenheimer-really-worry...

ronnier 4mo ago

Do you mind linking the photo you mentioned? I’d love to see it if you are able to find it

marc_g 4mo ago
It's in the TFA, there a photo of a fellow holding a small box thing that looks like a battery from a car or an old box torch.
- ronnier 4mo ago
  I saw that but not a picture of the plutonium core which I thought the OP was referring to
- libraryofbabel 4mo ago
  That’s the one I meant. It’s the core, but in a box, which makes it look even more innocuous, like he is indeed just lugging a piece of industrial equipment around. There’s lots of photos of the actual (unboxed) cores online if you search.
  - ronnier 4mo ago
    On flight WiFi so searching was a hard but I did find it. Thanks!
  - trhway 4mo ago
    >makes it look even more innocuous, like he is indeed just lugging a piece of industrial equipment around if i remember correctly what i read it was done intentionally for security reasons - instead of all the pomp-and-circumstance of a large strong security convoy the core was delivered by a driver in a simple inconspicuous truck.

SoftTalker 4mo ago

Was it a single solid core that was imploded? I thought it was at least two non-critical-mass hemispheres, or more, that were smashed together by the conventional explosives/detonators, to create a critical mass.

libraryofbabel 4mo ago
You’re thinking of the other bomb, the U-235 one, which they didn’t test at Trinity and which was dropped on Hiroshima. That is two separate pieces of Uranium that are slammed together to create a critical mass. The Pu-239 core was a single sphere of metal. It was subcritical until you compress it down with a spherical implosion from explosive charges all around it (from the size of a grapefruit to the size of a lime), at which point it reaches a high enough density to go critical.
- wat10000 4mo ago
  The gun-type bomb (where a subcritical mass is shot into another subcritical mass) is very simple to build once you have the materials to do it. They didn't think it needed a test since it was pretty obvious that it would work. The implosion design is tricky. You need to arrange and detonate the explosives precisely to compress the core evenly from all sides, otherwise it shoots out the side or otherwise doesn't go bang the way you want it to. Hence the test. That trickiness can be a good thing. Almost all modern weapons use the implosion design, partly because it's much safer. With a gun-type design, an accident could easily cause the two pieces to contact each other, resulting in an unwanted detonation. With an implosion design, accidentally setting off the explosives is very unlikely to set them off with the correct timing, so you'll probably just lose the core. The implosion design is also a lot more efficient. Little Boy used 64kg of uranium. Fat Man used just 6.2kg of plutonium and even got a bigger bang out of it.
  - generuso 4mo ago
    It is all true, but one needs to take into account that because of the different properties of the materials, the critical mass for uranium-235 is intrinsically much greater than that for plutonium-239. For a bare sphere, it is about 10 kg for plutonium and 50 kg for uranium.

smcameron 4mo ago

Funny enough Adam Savage just posted a youtube video about building a replica of the demon core and the box to hold it. https://www.youtube.com/watch?v=V1Y4UR8xqxA https://www.youtube.com/watch?v=V1Y4UR8xqxA

ghaff 4mo ago

It was probably all pretty silly but there were a few probably-not-all-nutcases that were concerned about the LHC causing something horrible.

fragmede 4mo ago
I dunno, ever since that weasel got stuck in it in 2016, things haven't been super great.

gpm 4mo ago

> Or it might have ignited a fusion reaction in the atmosphere and destroyed the world Someone's got to explain to me how this was even remotely plausible. We've had orders of magnitude more energetic events in earth's history that they would be aware of (dinosaur slaying asteroid for instance). These didn't manage to destroy the earth by turning the atmosphere into a fusion reactor. Surely they were aware of this. So was the theory that neutrons are somehow special in a non-thermal way for causing fusion (not fission). And specifically that a concentrated neutron burst could somehow set off a chain reaction? And I guess that [edit: solar] neutrons weren't concentrated enough to cause this even at a detectable level?

voidmain 4mo ago
I think the tiny size of a nuclear weapon and very short interval of nuclear reaction before "disassembly" mean that even though the energy release is small compared to an asteroid impact the temperatures are probably much higher. (I'm not an expert, though, this is a guess)
wnissen 4mo ago
You might be surprised at how little we know about fusion. We can observe the sun, but the sun is already very hot, millions of degrees, so any unknown fusion reactions would have already happened. Nowadays we have high-powered lasers that can create laboratory-scale fusion reactions. E. O. Lawrence's 1930 cyclotron could generate protons at roughly a million degrees Celsius. But that's a single proton stream. Good for splitting atoms but not for fusing them. You really don't know what the cross section of a fusion reaction is until you do it. The properties of matter at that temperature are just super weird. If it had turned out that there was, e.g., a carbon-carbon fusion reaction with a lower initiation, that might be enough to "go critical" and kick off more fusions, and propagate around the world. According to estimates, the Chicxulub crater was 1-10,000 degrees C. Not even the same ballpark. https://www2.lbl.gov/abc/wallchart/chapters/11/4.html https://www2.lbl.gov/abc/wallchart/chapters/11/4.html
queuebert 4mo ago
We didn't know as much about possible nuclear reactions back then, so I think they thought there was a possibility that there was an exothermic chain involving N or O that could be ignited by the bomb and would be self sustaining. While an asteroid impact is very powerful over large scales, it doesn't create nuclear reactions, so Trinity was indeed a first at that scale. But, and I'm not sure how much of this they knew back then, we do get bombarded by high-energy cosmic rays, so chances are one of these hypothetical N or O reactions should've already randomly occurred at least in isolated events over the last few billion years if possible.

jstummbillig 4mo ago

Increasingly with more powerful and precise technology the relative danger of the bomb will decrease, to the point where the bombs will become meaningless. The stigma is too big, the blowback is too severe and we have countless other ways to pummel each other into oblivion with more finesse.

contubernio 4mo ago

My grandfather was a student of Kistiakowksy and worked on the simultaneity part of the firing unit and was present at the assembly of the bomb and to watch the detonation. He recounted being quite nervous that his contribution would fail (as it had a short while before the final test) and the test would be a dud, but no one involved seriously in the scientific and engineering part of the building of the bomb had serious doubts that it would work once the technical issues were overcome, and none of them worried that it would ignite the atmosphere, because they knew enough to know that was silly. They'd all been working on this and doing thousands (!) of tests for months or years at that point. During the test he was given what he called the "chicken switch" that could abort the test at the last moment, and he always said that his biggest worry had been that he would stupidly abort the test in a moment of panic (surely this was exactly why he was given the switch). He described the actual explosion as the most beautiful thing he saw in his life. When one looks at the history one needs to remember that these were scientists and engineers who behaved as such. My grandfather, for example, was the sort of person who always loved blowing things up. He'd nearly blown up the family home as a kid when given a chemistry set ... and he studied chemistry because he liked blowing things up ... and he wrote a PhD thesis about the shock waves generated by blowing up a really big (conventional) bomb. It all gets dressed up as studying shock waves and so forth, but it's really kids blowing things up. They get caught up in the challenge of it. The consequences, political, moral and otherwise, are not forefront in the thinking of most. None of them are innocent, but some have misgivings or second thoughts. Others are more cynical and ambitious and even sinister. There are Oppenheimers and there are Tellers.

reedf1 4mo ago
This very much overstates the certainty of the scientists in the outcome of the explosion. They could be pretty certain it would work - but they were not at all certain about the result of producing energy, pressures, temperature and forces that have never been tested on earthly reality before. There were many unexcepted outcomes of the explosion, we are just lucky (as we usually are with new science) that they weren't particularly bad.

leonidasrup 4mo ago

> Or it might have ignited a fusion reaction in the atmosphere and destroyed the world "The “near zero” chances Oppenheimer unnerves Groves with in-movie probably come from Manhattan Project physicist Arthur Compton, who told author Pearl S. Buck in a 1959 interview that they’d calculated the odds at “slightly less than one-in-three-million.” In 1975, Bethe denied that there had ever been a less-than-one-in-three-million chance of setting the atmosphere on fire, but the idea had already lodged itself in the public imagination." https://www.inverse.com/science/did-oppenheimer-really-worry-about-setting-the-atmosphere-on-fire https://www.inverse.com/science/did-oppenheimer-really-worry...