What if the Trinity test had failed?

>Everyone involved was confident the gun-type bomb would work.

Yes. That's why the design of the Little Boy bomb carried by the Enola Gay was only "unit tested." That's not what the Trinity test tested. The uranium gun-type bomb dropped on Hiroshima was basically a backup plan in case the plutonium-implosion design--which was the primary focus of Los Alamos during the later part of the Manhattan Project--couldn't be made to work.

And it was the plutonium-implosion design that was tested at Trinity. (And was the design dropped on Nagasaki.)

> They'd tested bringing two pieces of enriched uranium close together in criticality experiments. That experiment killed several people at Los Alamos.

I think the fatal criticality accidents at Los Alamos involved a single chunk of plutonium and neutron reflectors: https://en.wikipedia.org/wiki/Demon_core

> They'd tested bringing two pieces of enriched uranium close together in criticality experiments. That experiment killed several people at Los Alamos.

I thought the Los Alamos demon core was plutonium?

Did they switch to making plutonium bombs exclusively, after the war?

> There might have been some completely unexpected physics at scale. But given that nuclear reactors were already a thing, that would have been very surprising.

That sort of happened in a later test: https://en.wikipedia.org/wiki/Castle_Bravo

"Castle Bravo's yield was 15 megatons of TNT, 2.5 times the predicted 6.0 megatons, due to unforeseen additional reactions involving lithium-7"

Trinity was a plutonium device. Reactors were uranium devices. Nobody was really sure if the plutonium implosion device would work - that's why they did the test; they were very sure that the uranium bullet device, that was used on Hiroshima without testing, would work.

But some people expected that: "The observers set up a betting pool on the results of the test. Edward Teller was the most optimistic, predicting 45 kilotons of TNT (190 TJ). [...] Others were less optimistic. Ramsey chose zero (a complete dud), Robert Oppenheimer chose 0.3 kilotons of TNT (1.3 TJ) [...]" (Wikipedia)

If your time tolerance is nanoseconds, the engineering is everything.

I am not sure about this. There is a lot of physics other than nuclear going on (rad-hydro,hydrodynamics and atomic physics at HED, etc.)

I think the uncertainty had more to do with the implosion mechanism than nuclear physics. The ability to simulate the hydrodynamics of an imploding sphere was obviously pretty limited in 1945, and while Los Alamos devised a series of pretty ingenious experiments to test how symmetrical such implosions could be made, for obvious reasons they had to use mock setups with metals other than Plutonium. So there seems to have been a fair amount of skepticism that such a mechanism could be made to work right up until Trinity.

That's true, but if you think about today, there are lot of things that are well understood by scientists and yet disputed by many politicians and members of the public. If the Trinity test had failed, it's not inconceivable it would have colored the leadership's perceptions of the feasibility of atomic bombs in general.

> A lot of people would have been very surprised if it had failed.

How often does a radically new technology work the first time?

> bomb could have ignited the atmosphere

This appears to be a misunderstanding or myth. It was well understood prior to Trinity that such an occurrence was not possible. The issue was carefully studied by multiple top physicists affiliated with the Manhattan Project.

See here: https://blogs.scientificamerican.com/cross-check/bethe-telle...

You’re getting hammered for this, but you’re probably correct. One could imagine a parallel universe where our test didn’t go so favorably.

One could also imagine a future physics breakthrough that we’re fairly confident about, which turns out to be horribly wrong.

However, with each decade that the standard model turns out to be correct, one could also imagine that this chance will never happen again; that we’ll be forever confident in our predictions. (This seems the most arrogant statement of all, though.)

"They worried about this, and were fairly confident in their calculations. "

The problem with saying it this way, is that it's implied 'there was a risk but it was within threshold'.

There was no risk. It wasn't a thing.

It's not like putting 100lbs in the elevator and knowing it will 'be ok' because it's way below the 1000lb threshold.

It's not really 'safe' by calculation, it's mostly 'safe' by rationalisation.

"The bomb could have ignited the atmosphere,"

No, it could not have.

I'm not following. You're suggesting they had an exaggerated sense of their own abilities? It doesn't seem they did, given they accomplished what they set out to do. And their calculations turned out to be correct w/r/t the risk of igniting the atmosphere.

It seems odd to suggest they were arrogant because they didn't have physics knowledge that wasn't available to them - or anyone - at the time.

"In the twenty-two hundred recorded points of my conferences with Hitler, nuclear fission comes up only once, and then is mentioned with extreme brevity. Hitler did sometimes comment on its prospects, but what I told him of my conferences with the physicists confirmed his view that there was not much profit in the matter. Actually, Professor Heisenberg had not given any final answer to my question whether a successful nuclear fission could be kept under control with absolute certainty or might continue as a chain reaction. Hitler was plainly not delighted with the possibility that the earth under his rule might be transformed into a glowing star. Occasionally, however, he joked that the scientists in their unworldly urge to lay bare all the secrets under heaven might some day set the globe on fire. But undoubtedly a good deal of time would pass before that came about, Hitler said; he would certainly not live to see it. "

From the Making of the Atomic Bomb by Richard Rhodes. Such an amazing book, and required reading for any scientist IMO.

That's a bit too fearful of the unknown. Where would we be if our ancestors didn't play with fire?

They got the bit about nuclear power wrong though. Fission was discovered in Germany just before WWII, which is why Einstein (the real one) was concerned that the Germans might develop nuclear weapons first and advised the US to do it. At that point it wasn't obvious that a bomb was possible even if fission was, but even if it wasn't, the application of fission to power generation would still have been obvious.

If anything they'd have probably had more nuclear power generation, because the proliferation risk wouldn't have been a concern and the scary association with city-destroying weapons wouldn't have been such a PR problem.

I really enjoyed the Manhattan series, which covered similar ground. Some reasonably accurate but dramatised scenes about viability of the bomb types and exploring how to get there, both physically and in maths. https://en.m.wikipedia.org/wiki/Manhattan_(TV_series)

Sliders also predicted people going to bars without masks during a pandemic.

"One" I think. Probably was "ne" and got autocorrected to "me" instead of "one" (would make sense, "less than me" probably occurs more often than "less than one").

The mayor of Nagasaki reported that the bomb was a dud, and only then realized he'd heard nothing from the north half of the city. Same statistical paradox as the Brits reinforcing the parts of planes that returned with bullet holes, until someone said, "Um", ...

The Japanese surrendered before realizing that Nagasaki had been half destroyed.

The bomber crew was going to release on radar alone, against orders, realizing this made more sense than releasing over the ocean before landing. Then they saw an opening in the clouds. Not a good day for visibility; Nagasaki wasn't even the primary target.

>I think it's pretty clear ...

I don't think there is a clear consensus on any of the points you bring up:

>...a) the Japanese had been willing to surrender on one condition (keeping the emperor) for weeks,

https://en.wikipedia.org/wiki/Surrender_of_Japan

>...On June 9, the Emperor's confidant Marquis Kōichi Kido wrote a "Draft Plan for Controlling the Crisis Situation," warning that by the end of the year Japan's ability to wage modern war would be extinguished and the government would be unable to contain civil unrest.

>...Kido's proposal did not contemplate Allied occupation of Japan, prosecution of war criminals or substantial change in Japan's system of government, nor did Kido suggest that Japan might be willing to consider relinquishing territories acquired prior to 1937 including Formosa, Karafuto, Korea, the formerly German islands in the Pacific and even Manchukuo.

In July, Togo told the ambassador to the Soviet Union:

>...Although the directing powers, and the government as well, are convinced that our war strength still can deliver considerable blows to the enemy, we are unable to feel absolutely secure peace of mind ... Please bear particularly in mind, however, that we are not seeking the Russians' mediation for anything like an unconditional surrender.

>In reply, Satō clarified:

>It goes without saying that in my earlier message calling for unconditional surrender or closely equivalent terms, I made an exception of the question of preserving [the imperial family].[49]

>On July 21, speaking in the name of the cabinet, Tōgō repeated: With regard to unconditional surrender we are unable to consent to it under any circumstances whatever. ...

>...b) the U.S. was holding out for an unconditional surrender

It is more accurate to say they were holding out an acceptance of the Potsdam Declaration.

>...c) the USSR entering the war pushed Japan to make, and the U.S. to accept, a privately-conditional / publicly-unconditional surrender.

It is not like the US didn't know the Soviet Union was going to enter the war. When the Japanese government demanded that the emperor would remain in power, the reply simply was:

>...From the moment of surrender the authority of the Emperor and the Japanese government to rule the state shall be subject to the Supreme Commander of the Allied powers who will take such steps as he deems proper to effectuate the surrender terms. ... The ultimate form of government of Japan shall, in accordance with the Potsdam Declaration, be established by the freely expressed will of the Japanese people.

Eventually Japan agreed to the Potsdam Declaration.

>...From a Japanese perspective they destroyed nothing that hadn't already been firebombed to smithereens

That is basically true and had been true for months. The question is why did so many have to die in Okinawa? I think an argument can be made that the atomic bomb made it very clear to the emperor how ruinous the situation was and pointing at the bomb allowed him to save face:

>...In a meeting with the Emperor, Yonai spoke of his concerns about growing civil unrest:

>I think the term is inappropriate, but the atomic bombs and the Soviet entry into the war are, in a sense, divine gifts. This way we don't have to say that we have quit the war because of domestic circumstances.

Indeed the major reason that Hirohito publicly mentioned in his speech to the nation was:

>...Moreover, the enemy has begun to employ a new and most cruel bomb, the power of which to do damage is, indeed, incalculable, taking the toll of many innocent lives. Should we continue to fight, not only would it result in an ultimate collapse and obliteration of the Japanese nation, but also it would lead to the total extinction of human civilization.

https://en.wikipedia.org/wiki/Jewel_Voice_Broadcast

>...It's really hard to believe that the war with Japan would have had a different outcome if either or both bombs had not been dropped.

There is no way that Japan would have "won" the war at point, but if the surrender of Japan had been delayed and the invasion occurred, there would have been many more casualties on both sides. Both sides were preparing for a horrific battle:

>...Instead, everything was staked on the beachhead; more than 3,000 kamikazes would be sent to attack the amphibious transports before troops and cargo were disembarked on the beach.[8] If this did not drive the Allies away, they planned to send another 3,500 kamikazes along with 5,000 Shin'yō suicide motorboats and the remaining destroyers and submarines—"the last of the Navy's operating fleet"—to the beach.

On the other side:

>...Operation Olympic, the invasion of Kyūshū, was to begin on "X-Day", which was scheduled for 1 November 1945. The combined Allied naval armada would have been the largest ever assembled, including 42 aircraft carriers, 24 battleships, and 400 destroyers and destroyer escorts. Fourteen U.S. "division-equivalents" (13 divisions and two regimental combat teams)[28] were scheduled to take part in the initial landings.

and if that armada wasn't enough:

>...Ken Nichols, the District Engineer of the Manhattan Engineer District, wrote that at the beginning of August 1945, "[p]lanning for the invasion of the main Japanese home islands had reached its final stages, and if the landings actually took place, we might supply about fifteen atomic bombs to support the troops.

https://en.wikipedia.org/wiki/Operation_Downfall

The published article annotated modes of failure with respect to the desired operational objective of a 5kton blast, 500 ton, various component failures, and their implications. It's written from a operational impact perspective on the war, Potsdam, and cold war implications.

Read the article, but he's talking about failures as in not exploding (or exploding with significantly lower yield).

Perhaps setting the atmosphere ablaze would have been an exceptional success? I remember someone telling me that this possibility was still being discussed before the Trinity test and, again, after thermonuclear bombs entered the arena. This seems to be a nice summary: http://large.stanford.edu/courses/2015/ph241/chung1/

I think they refer to the failure mode where: Nothing happened for a day or two. All the experts travel to the location to try to understand what went wrong, in situ... and THEN the explosion occurs.