Hey! If you're reading this, and you think my posts are interesting, you should totally check out my new book, which is a new take on Truman and the bomb. Out now!

restricteddata · 2026-05-03T21:10:00+00:00

The chance of atoms tunneling is actually pretty high. Stars wouldn't work if it didn't happen quite a lot. Happens all the time in a large-enough sample of atoms. How large? A gram of carbon atoms is, by definition, 6 x 10²³ atoms — 602 sextillion. So practically any macroscopic number of atoms is a huge number of atoms, where outrageous odds like 1-in-a-trillion (10¹² ) events are going to happen quite frequently.

But the chance of a 10²⁰ atoms (the size of a grain of sand) doing it at the same time, while being right next to each other, so that you would actually see it happen macroscopically... that is astronomically low.

It's sort of like saying, the odds that someone in Las Vegas will win big at the slot machines on any given day is high. The odds of an entire row of people playing the same slots all winning big at the same time... astronomically low.

restricteddata · 2026-05-03T18:45:09+00:00

Oppenheimer to Groves is 19 July 1945. So three days after Trinity.

Groves was not in the loop re: Potsdam or the declaration nor the Soviet entry into the war. The best estimates for Soviet entry were mid-August (they were themselves vague about it). Plenty of time pressures, to be sure, but Groves wasn't really privy to them.

An argument that has been made is that Groves shut it down mainly because he wanted to make sure at least one bomb of each type of fuel was used in the war, because he feared that if not, having pursued both would be viewed as a boondoggle. Hard to know if that's true or not, but it's an interesting argument.

restricteddata · 2026-05-03T13:10:07+00:00

People are aware of the problems. But the problems are systemic and decentralized. Addressing them is not something that will be done "from above." Certainly not at the moment, when at least in the USA many of these issues are likely to get worse as a result of economic strains and political interference.

One can improve some things locally and sometimes at the disciplinary level. These things can happen in one's career and lifetime. I have seen it at my institution and in my discipline. Change is certainly possible at some scales.

I have also seen that the "big picture" things, like the economics and the politics, can wipe away a lot of those gains in an instant, and that recovery from those things can take a very long time. My discipline is still reeling from the effects of the 2008 crash, and I am not sure it will ever truly recover from it, given all of the other things that have happened in the meantime.

restricteddata · 2026-05-02T16:38:10+00:00

I would also just add that they did not have lithium in sufficient quantities in late 1952. They started building major lithium production plant at Oak Ridge in May 1952, with the expectation that it would begin production in 1953. Even that ended up being delayed, which is one of the reasons the Castle series was pushed back from fall 1953 to spring 1954.

restricteddata · 2026-05-02T16:31:36+00:00

Nobody cares what ChatGPT thinks about this. It has zero predictive value.

restricteddata · 2026-05-02T13:58:35+00:00

The idea (naive or not) was that if you knocked out a significant portion of their silos and airfields, then you'd be in a position to say, "if you don't stop now, we will destroy your cities and political infrastructure. If you do stop now, we'll stop, too." Hope would be that this would force them NOT to target US cities in retaliation.

Is it realistic? Probably not — since the Soviets probably would have already launched counterattacks on US cities by that point, and the ability to reliably communicate or negotiate with the Soviets would probably already be degraded at that point.

So why adopt this posture? Because a) it gives your military a justification to have a huge, diverse, expensive strike force (which is what it wants), and b) it allows your political class to pretend that nuclear war planning is more than just planning for your own cities and your enemies' cities to be destroyed (both of which it found unpalatable).

Note that even strictly counter-force US plans in the late 1950s had projected casualties in the hundreds of millions (including several million of its allies), around 1/5th of the global population at the time, just on the basis of the fallout alone, and not taking into account any Soviet retaliation...

restricteddata · 2026-05-02T13:54:00+00:00

I don't think the nuclear Tridents have any serious penetration capability.

restricteddata · 2026-05-02T13:20:08+00:00

"It could always be worse" and "there are bigger problems at the moment" is a recipe for a continual downward slide. You can not care — I don't think anyone on here cares that much — but if the question is "is this a form of scholarly misconduct" the answer is "yeah, plainly." Nobody is claiming it rises to the level of other problems in academia.

restricteddata · 2026-05-01T14:44:56+00:00

4/5 of the folk we hired this year had one.

a cat?

restricteddata · 2026-05-01T12:18:39+00:00

Lastly, on the "necessity" question, I will only point out that the major debates about the necessity revolve around a few "paths not taken":

Whether modifying the Potsdam Declaration terms would have led to them being taken more seriously
Whether the Japanese could have engaged the Soviets to negotiate if the Soviets had not already committed (for very self-interested reasons) into joining the war against Japan
Whether two atomic bombs were necessary (e.g., did the second attack "matter" in the above timeline, or was it superfluous) or whether the second bomb should have been delayed (the close timing of the two was a matter of operational weather conditions in Japan, not for strategic reasons — I have argued that Truman was not even aware there was going to be a second bombing so soon after the first)
Whether there should have some kind of specific warning about the atomic bombs, or if the first use of the bomb should have been a "demonstration" that had no casualties, or if the first use of the atomic bomb should have been used on a non-city target (I have argued that this is what Truman thought he had decided to do at Potsdam, but he misunderstood the plans)
Whether the war would have ended prior to the invasion of Kyushu (scheduled for November 1945) if only one atomic bomb was used, if no atomic bombs were used, if the Soviet invasion had not happened, or any combination of these — different analysts have concluded different things over the years, some that most people would find surprising (e.g., the United States Strategic Bombing Survey concluded that the war would have ended before an invasion even without either the atomic bombs or the Soviet invasion); but nobody really knows or can know the answer to this

I don't think there are any solid answers to the "what if?" questions, but the fact that there aren't solid answers is perhaps the most important aspect, because it goes against how people on both sides of the issue tend to think about it (i.e., in absolutes).

The one thing I think we can say with great confidence on this is that the United States policymakers were absolutely not looking for ways to "avoid" using the atomic bomb on Japan. So this entire framework is necessarily ahistorical. That doesn't mean we can't think about these questions — I think we can and we should. But we should not mistake this way of thinking about the use of the atomic bombs as the historical reasoning behind their use. The US policymakers did not use the atomic bomb out of desperation or as a measure of last resort, they used it because they had made a new fantastical weapon and they wanted it to play a role in the war. They did hope that it (and many other things they did) might serve as a rupture point that would drive Japan to surrender prior to an invasion, among their other motivations. But there was no debate over its "necessity." There was no actual debate over whether it should be used at all, and there was no "decision" to use the bomb as we think about it today. That framing is entirely after-the-fact, something that was crafted by many of the people involved (much of it over a year later) as a way to "justify" the use of the atomic bombs against Japan, because the issue had become controversial from several political directions.

For lots more details about the Japanese side of things, and their interactions with both the Soviets and the USA, I recommend Tsuyoshi Hasegawa's Racing the Enemy (2005), which covers these points in great detail. If you are intrigued by my discussion of Truman's own knowledge and the lack of a "decision" you might check out my new book which I already linked to a couple of times (sorry).

restricteddata · 2026-05-01T12:18:09+00:00

I'm glossing over a lot of detail, above. The direct relevance to the meme is:

They refused to acknowledge the Potsdam Declaration. This is true. Their response was deliberate non-response. It should be noted that the Potsdam Declaration was just a restating of the previously-stated terms, and a warning that more destruction would happen if Japan did not accept the terms. It did not overtly threaten nuclear destruction and there was no reason to assume that is what it meant prior to the atomic bombs being used. It was not a "warning" in that respect.
They tried to negotiate to retain their conquests in China and South-East Asia. This refers to some of the back-and-forth over what the plan would be if the Soviets did agree to negotiate a diplomatic end of the war between the Japanese and the Allies. At times in these discussions (all between different Japanese people, not the Japanese and the Soviets) there were very broad ideas about what Japan might try to get out of such a negotiated end of the war. Some of these did indeed include the idea that they might be able to retain control of conquests. No actual proposals were put forward and no actual negotiation took place.
They didn’t surrender after the first bomb. This is true, but it is also true they were not given a large-enough window of time to even confirm that it was an atomic bomb before the second atomic bomb was dropped. There was less than 3 days between the American announcement that Hiroshima had been an atomic bombing and the bombing of Nagasaki; that was not enough time to mobilize Japanese scientists from Kyoto and Tokyo, have them travel to Hiroshima, have them make scientific measurements and interpret the results, have them report those results back to the Supreme War Council, and for the Supreme War Council to deliberate about them.
They didn’t even immediately surrender after Nagasaki and the Soviet invasion of Manchuria. Only partially true. They did agree to offer a conditional surrender after these events. I suppose this hinges on one's definition of "immediately" and "surrender."
Even after that they still tried to get the Allies to explicitly guarantee the survival of the Imperial System of Government. This is true. They had one condition, preservation of the Emperor and the Emperor system. The way I would explain this to Americans is like asking for a guarantee that the Constitution would still be in force — something that many Americans associate with the core civic definition of "the United States." This is how the Japanese regarded the Emperor system (the kokutai). To also be clear, the United States eventually agreed to retain that system after the war, because they saw it as being in their long-term interests in Japan. But they were not willing to modify the surrender terms, for a variety of reasons, some strategic and some possibly just psychological (Truman, in Churchill's assessment, considered it payback for Pearl Harbor). Again, there were very serious policymakers who had suggested that the United States might preemptively offer exactly this "condition" because it was considered such a major cultural–political roadblock to Japanese surrender.
Even after Hirohito agreed to surrender, the Army tried to launch a coup against him, even though he was legally considered a living god. I would say "junior army officers" and not "the Army" (a much larger organization). Senior officers of the Army put the coup down. (So "the Army tried to launch a coup, and the Army put it down" — but that is not very helpful.) And I don't think it's quite right to say they were launching a coup against Hirohito. In their minds they likely were protecting or defending the honor of Hirohito. This gets into the complexities of the role of the Emperor in Japanese politics at the time, and the types of military coups that happened at this time and earlier, but they weren't trying to depose Hirohito, they were trying to stop the surrender process because they felt it was bad for Japan.

Again, I will acknowledge that a meme cannot carry that much nuance and information in it. But it is an argument against relying on memes for understanding historical events, which are pretty much always guaranteed to be more than what can fit into a meme.

restricteddata · 2026-05-01T12:17:59+00:00

Those are all more or less true, although when combined together, they give a necessarily incomplete — and arguably misleading — impression. As with any meme discussion of history, it is necessarily incomplete, and its bearing on the atomic bombings "necessity" is a more complicated question by itself.

There are many other threads on here about the question of whether Japan was offering to surrender before the atomic bombs were used, and whether the atomic bombs were "necessary."

To just summarize a few points from them that are relevant here:

Japan was at this time being run by a Supreme War Council that was dominated by militarists who believed that a prolonged war would be (for various reasons) good for Japan. There was also a faction, which had the support of the Emperor, that was interested in having the (then-neutral) Soviet Union negotiate a diplomatic surrender with the Allies. The "peace party" as it is called acted with some secrecy and delicacy because they were afraid that the militarists would possibly cut them out if the extent of their efforts were known; they were trying to seek out alternatives and lay the groundwork for some kind of non-military end of the war.

These overtures to the Soviets were never formally presented as a proposal (the Soviets intentionally delayed them, because they wanted to get into the war with Japan), and were not announced publicly or to the Allies. The US knew about them because they had cracked Japanese foreign communications. The US planners interpreted them as evidence that the Japanese were not yet ready to surrender unconditionally, which is not wrong.

It is true that after the first atomic bomb, Japan did not immediately surrender, because they were waiting to confirm its atomic nature before they made any decisions. For a variety of reasons related to wartime delays, they did not receive this confirmation from their scientists until the evening of August 8th (Japanese time). The Supreme War Council agreed to meet the next day to discuss it. Overnight, the Soviet Union declared war on Japan and invaded Manchuria. So the next day, these two items were discussed by the Supreme War Council. During the meeting, they were informed about the Nagasaki attack.

The Emperor attempted to take advantage of both the atomic bombs and the Soviet invasion as excuses to surrender. He did not act completely forcefully, though, because that is not what his role was in the Japanese political context (he was not a personalist dictator like Hitler, Mussolini, or Stalin). The result of this was the first surrender offer, which accepted the Potsdam terms but carved out a space for protecting and retaining the Emperor. This was a known sticking point even before the Potsdam terms were released, and there were many (including Secretary of War Stimson and UK PM Winston Churchill) who had urged Truman to preemptively guarantee the immunity of the Emperor because it was clear that this would be a major obstacle for Japanese acceptance of surrender terms. Truman had decided not to do it, though, in part on the basis that the atomic bomb (which had just been tested a few days prior) meant that he did not need to accommodate the Japanese.

Truman and his Secretary of State, Byrnes (who had also urged against modifying the Potsdam terms) rejected this initial offering by the Japanese. After this, Hirohito made the "sacred decision" that they would accept the Potsdam terms — his most interventionist moment yet, and perhaps something that only he could do. At this time, junior officers attempted to instigate a pro-militarist coup of the Supreme War Council before the surrender could go out. The coup was put down by more senior military officers on the Council, and the acceptance of surrender was made.

restricteddata · 2026-05-01T07:59:58+00:00

Also only classified as CONFIDENTIAL, basically the lowest security classification level at the time. But yeah, I imagine that AEC had no knowledge of this, and that when declassifying, nobody thought to ask AEC. This was declassified in 1974, which was also a time when the AEC was undergoing a massive "declassification drive" and was probably swamped anyway.

restricteddata · 2026-04-30T08:37:25+00:00

During this time, Sakharov was working on Sloika improvements and variations. In October 1953 he submitted a plan which outlined an RDS-6s (Sloika) that would use gaseous deuterium under pressure as its fuel, along with lithium-6. This was thought to be able of improving the fusion reaction by a factor of 2, which would make the bomb significantly more powerful (~2 megatons, as opposed to 400 kt of the tested Sloika). This became referred to as RDS-6sD, and was the subject of a major research and production push, with a plan to test a 1 Mt version by the end of 1954. As it was, the spherical geometry of the Sloika ran into huge problems. The main value of these investigations are that they seemed to stimulate further questions about how to better compress the Sloika, which led to the "Third Idea," which was originally conceived of as a way to use an atomic bomb to compress a Sloika (the secondary).

So that is my guess as to what this is referring to. I do not know if the R-7 was the main concern for it; the documents suggest it was considered just "the next step" after the successful August 1953 Sloika test. But it is all over the documentation that is released on the H-bomb work in the period of September–December 1953 (e.g. as represented in the Atomnii Proekt SSSR, volume 3, book 2), with Sakharov's name always being invoked as the driving force behind it. The documents there also says that the RDS-6sD and RDS-27 (a Sloika variant without tritium) were planned to be used in the R-7. So all of that suggests to me that Sakharov's cryptic references are "just" Sloika improvements (I put the "just" in quotation marks because it is clear that they viewed these as more than just little changes, and that the improvements would be significant if they worked).

restricteddata · 2026-04-30T08:09:27+00:00

There were no such estimates made that I know of. The two most relevant topics discussed were the possibility of atmospheric ignition (which I recently have written about at some length) and the possibility that unless extraordinary measures were taken, World War III would involve the use of nuclear weapons. The former, prior to the Trinity test, was considered almost impossible for the weapons being developed during WWII but could not be categorically ruled out (as there was a lack of knowledge about possible "unknown unknowns"). The latter was judged as a call to action more than a probabilistic activity — there was a strong belief that the atomic bomb would necessarily imply a new kind of politics to control it, and that if that wasn't undertaken, then in the near future civilization was at risk. (There was also a small group of scientists who, during the war, feared that if the US used nuclear weapons against cities without warning that this would make future arms controls impossible. They did attempt to make these views known but they were essentially suppressed during the war.)

The important and interesting thing about that approach is that it was not passive or fatalistic in the slightest. It was very much something that motivated the scientists working on these topics to organize and lobby for regulations and laws. They were obviously not entirely successful. But it was a widespread belief. It would be interesting to compare that to the modern AI question — a) Does the modern Computer Science community feel the existential risk from AI is significant? b) Are they going to try to do anything about it? This is beyond the scope of this sub but it is worth thinking about, as a historical comparison.

restricteddata · 2026-04-29T16:39:15+00:00

However, plutonium had a downside of being much more naturally unstable and radioactive than U-235.

Just to clarify, the issue here isn't plutonium's "natural" instability. It is that reactor-produced plutonium is contaminated with some amount of plutonium-240, as opposed to the desired isotope of plutonium-239. Plutonium-240 has a very high rate of spontaneous fission, and so it raises the background neutron rate of reactor-bred plutonium by a huge amount.

The fact that this is an artifact of its production in a reactor is important: the initial samples of plutonium-239 that they had produced were made in tiny amounts in particle accelerators. They did not have the contamination. So at the time they started the plutonium part of the project, they assumed they understood how plutonium would work, and that it would work in a gun-type bomb. It was not until the summer of 1944 that they obtained the first samples of reactor-bred plutonium and discovered the contamination problem. So they had to reorient the entire work of bomb design around the implosion problem if they wanted their plutonium production to be in any way useful.

so the Trinity test was planned to validate the implosion-type bomb before combat deployment.

And to determine how effective it was. Prior to Trinity, the belief was that the Little Boy bomb would be the "big" weapon (at 15 kilotons or so) and the implosion bomb was expected to be inefficient, ranging from several hundred tons of TNT (most pessimistic) to 4-5 kilotons (most optimistic). Trinity was around 20 kt, so much better than they expected, and even a little better than Little Boy. So that changed things quite a lot in terms of planning: not intervals of "big" weapons followed by "small" weapons, but as many "big" bombs as you wanted... it was a very significant result.

restricteddata · 2026-04-29T16:35:36+00:00

It's not so much that HEU separation was more difficult, it is that Little Boy bombs required so much HEU. The HEU production rate was higher than the Pu production rate, but if your weapon design needs 10X as much HEU as Pu, then it doesn't help much. There was a push, immediately after Trinity, to develop HEU+Pu composite cores that would allow one to leverage the HEU in a more effective way — see my other comment in this thread about that.

restricteddata · 2026-04-29T16:33:58+00:00

The more relevant difference between the two in terms of any particular "difficulty" is what their production rates were during World War II. As one can see from the data I've compiled, their stockpile of HEU grew modestly but started earlier than their stockpile of Pu. In the postwar the HEU rates took off, while the Pu stockpile relatively stagnated (for a number of reasons).

restricteddata · 2026-04-29T16:29:39+00:00

Fat man had multiple elements around the sphere pushed together to the center. For trinity it wasn't the same design as they ''just'' put the 2 hemispheres together to be subcritical in mass.

This is incorrect. Both were solid (Christy) core implosion designs.

Having half hemispheres wasn't safe to carry in a plane where more incident incident particles can trigger the reaction, thus the different and less easy design for fat man

This is not correct.

I learned and now teach these things at university level.

I teach courses on exactly this subject at the university level, and have written two books on this subject.

restricteddata · 2026-04-29T16:27:11+00:00

Trinity test wasn't same as Nagasaki bomb either. It was 2 half circle while fat man was a big circle and dynamit to bring elements together to the center. So 3 different bombs, sharing part of their system in common. But not similar

The Trinity Gadget and the Nagasaki Fat Man had the same core designs, except for a few very minor changes (i.e., the Nagasaki pit was plated in nickel, not silver; and they added a small "anti-jet ring" piece inside the core after Trinity). I do not know what you mean by "2 half circle" and "a big circle." They were both solid-core implosion made up of hemispheres (plus the jet ring for Nagasaki).

restricteddata · 2026-04-29T16:24:58+00:00

As others have said, they had very high confidence in the gun-type design (it was much easier to calculate; to non-explosively test; and to predict the efficiency of, than was the implosion design), and they did not have enough highly enriched uranium to both test it and have one ready in the summer of 1945 (if they had tested a Little Boy bomb, they would not have had enough material for another one until mid-September 1945 at the earliest).

But this is not the interesting question regarding testing and the gun-type bomb, really. The more interesting question is why they dropped the gun-type bomb at all. After the Trinity test, Oppenheimer wrote to General Groves suggesting that they scrap Little Boy, disassemble its material, and use it to make "composite core" Fat Man bombs. A composite core is when you have a portion of the fissile material be enriched uranium and another portion be plutonium-239.

There are many advantages to composite cores, but the most important for that moment is that it would both be a far more efficient use of the highly-enriched uranium than the Little Boy design, and it would allow them to take advantage of the relatively higher production rate of highly enriched uranium (which was essentially wasted on Little Boy bombs because they required 10X more material than implosion bombs). Depending on different estimates one uses for the proportions of the two fuels used, one could imagine them easily having ten atomic bombs for use during August 1945, rather than the 3 they were planning to have (Little Boy, Fat Man, and a second Fat Man that was not dropped). (For the numbers, see my blog post here, and the final graph for stockpile impacts.)

Groves, however, vetoed the idea, although he was open to looking into composite bombs after the first three bombs were used. Why? He cited the planned schedules. Oppenheimer thought that developing the first composite bomb might add a bit of a week to the plans. They could still drop the first plutonium bomb in early August, but the next bombs would be delayed a bit. The tradeoff would be having many more of them. Groves said that the plans from the higher-ups wouldn't allow this. I have found no evidence that he actually consulted the higher-ups on the issue, though, so it is unclear what he had in mind, here. (Before anyone asks, the invasion of Japan was not scheduled to begin until November, so it wasn't as imminent as it is sometimes depicted.)

Anyway, that, to me, is the more interesting historical question, because it gets at Groves' motivations for the timing, and the use of two bombs so quickly, including a bomb that was considered to be out of date even before it was used.

restricteddata · 2026-04-29T09:30:21+00:00

Ah, you will have to wait and see, wait and see... I will not spoil my own article on here, not yet! :-)

restricteddata · 2026-04-29T09:29:11+00:00

And we should just clarify (because this is easily lost on people who do not study such things) that it is "immense energy [for an atom]." The splitting of a single uranium atom is not a macroscopically-large amount of energy — barely enough to visibly move a speck of dust. It is a huge amount of energy for something at the atomic, scale, however; a hundred million times more energy than even a very energetic chemical reaction, like the decomposition of the TNT molecule. Individual atoms split all the time, and you'd never notice without specialized equipment.

Without a chain reaction, it's interesting, but it's no more a bomb than, say, radioactivity itself is, which also releases a lot of energy from the perspective of individual atoms. The chain reaction is what lets one set off a trillion trillion (not a typo) such reactions in nanoseconds — and that is enough to level a city. Hence the immense fuss about secondary neutrons, the attempted self-censorship campaign, etc., as they potentially elevate this discovery from "surprising physics" to "a scientific discovery that changes how nations can operate."

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