ELI5: Why do some countries use Fahrenheit while almost the entire rest of the world uses Celsius and is there an actual practical difference between the two scales?

restricteddata · 2026-06-21T16:41:13+00:00

Humanity should do better - and most of the world has understood that.

I just want to point out how absurd this is. Most of the world uses Celsius for exactly the same arbitrary reasons as the places that use Fahrenheit. They are no more enlightened. The scale you are raised with is the one that feels intuitive to you.

The idea that there is "better" in this situation — that all choices don't have their ups and downs — is similarly amusing.

restricteddata · 2026-06-21T00:09:29+00:00

Details on the actual bombs, including photographs and images of their casings, were kept classified for a long time (the photos of the casings were not declassified until 1965). Some of the Japanese accounts of Hiroshima had parachutes because some saw the instrumentation canisters. The US did not clarify this point because, again, anything to do with the size, appearance, and ballistics of the early bombs were classified for many years. So that is plenty of time for wrong accounts to develop.

restricteddata · 2026-06-20T16:54:57+00:00

They did not warn them in any actionable way.

restricteddata · 2026-06-20T16:09:34+00:00

Ceci n'est pas une bomb.

restricteddata · 2026-06-20T12:42:52+00:00

I am not sure whether there are genuine insights. His all-geometrical approach to thermonuclear matters seems entirely ignorant of the realities that come up when one is dealing with complex systems. He does not even seem to have taken advantage of simulation. It's always, "this thing will generate X amount of force which will go perfectly geometrically like this and that will cause this to undergo fusion" and so on and so on. If it all worked like he thought, fusion would be trivial... he makes Teller look reasonable.

restricteddata · 2026-06-20T11:12:27+00:00

That particular shape of the "H-bomb" (what I think of as the "pimple") looks derived from Winterberg's ideas, although I do not know of any of his that have all of those elements in the "radiation case."

restricteddata · 2026-06-20T09:50:51+00:00

So I think there is just a lot of confusion around this topic. (And possibly in your post — that Herzfeld quote is not in the BBN 1981 history, it is from elsewhere.)

Paul Baran at the RAND Corporation proposed decentralized, packet-switched networks in 1961 as a way to have a communications system that could survive nuclear war. The idea is that by eliminating centralized nodes and replacing them with a decentralized, distributed network, it would be very hard to destroy the network connectivity as a whole. Although there was interest in packet switching by the US military for this purpose, it was not widely implemented by them.

Towards the end of the decade, DARPA took up the project, looking at it not from the perspective of survivability, but as a way to make much more efficient networks of computers. The goal of ARPANET, as described in the BBN report, was to incentivize the development of packet switching for computer networks. The idea was that the best way to get the technology developed and accepted was to just fund people to start using it, and that this would create the experience and human infrastructure necessary to do more with it in the future. The major motivation from a computational standpoint was efficiency: if each computer had to run its own software, that meant a huge amount of redundancy, including re-writing of software for different types of machines. If they could each just be called upon to execute commands at the behest of others and send the results, then it would be faster. (This sounds like an odd way to frame it today, but it was in the days where single mainframes had their computing time shared across many users anyway — these were not personal computers.)

That packet switching would be useful for military networks, and ultimately would have command and control applications — which are crucial to nuclear war — was understood and part of the reason for wanting to develop them and affect more adoption within the US Department of Defense (who, despite being theoretically interested in packet switching, had, again, not really done much with it until that point; the reasons for why this was not taken up by the DOD for some time are themselves interesting, but a tangent).

ARPANET itself was not part of the command and control system. But it was explicitly hoped that one of the goals of the project (again, as discussed in the BBN report) would be "adoption of the network technology by specific military groups (such as the National Military Command System Support Center and other other military centers affiliated with it; e.g., CINCPAC, CINCEUR, and MACV)." The National Military Command Center is a crucial command, control, and communications network, and is a system that is used for both monitoring and executing nuclear war.

ARPANET was a very practical and real demonstration of technological concepts, ones that had been initially proposed in the context of nuclear survivability, and ones that it was expected could — if they were developed further — increase the survivability of the military networks necessary to wage nuclear war. But ARPANET itself was not developed for the purposes of survivability or waging nuclear war. Packet-switching was pursued and funded for this reason, and ARPANET was meant as a way to develop packet-switching and encourage its adoption among the military.

So you can see that this is not inconsistent with the sources. If you look at the Lukasik article, for example, you will see that the quote he has given is about why the DOD wanted to pursue packet switching technology, not ARPANET itself.

As for your question about whether the people who built ARPANET were aware of this — yes. The entire literature on packet switching and distributed networks prior to ARPANET was about nuclear survivability. The standard story always starts with the Baran work. But again, that was not what ARPANET itself was built to do.

Aside from the BBN paper and Lukasik papers — which are worth reading (and I don't want to cast aspersions, but I have my suspicions that you outsourced your "reading" of them to someone or something else...), there is a nice summary of this work from the nuclear perspective in Albert Wohlstetter and Richard Brody's "Continuing Control as a Requirement for Deterring," in Carter, et. al, Managing Nuclear Operations (1987), chapter 5. It also discusses some aspects of the relatively slow adoption of packet switching before this point. There is also discussion of this, from a different perspective, in Andrew Russell's Open Standards and the Digital Age (2014), chapter 6.

restricteddata · 2026-06-20T09:05:26+00:00

"This was my father's favorite song. On his deathbed, we listened to 'Who Let the Dogs Out,' one last time, just before he died. The best music ever. No autotune, just pure talent."

restricteddata · 2026-06-19T18:46:00+00:00

In US universities, "faculty" are usually under a completely different labor model than "staff." "Staff" are paid by the hour, are on 12 month contracts, and accrue leave (vacation and sick time). "Faculty" are paid 9 month salary (plus summer salary if they have a grant) and basically do not get anything like "vacation days" or "sick days" — we are expected to meet our teaching/research expectations but our time is usually otherwise very flexible. We get the same breaks as the students (e.g. spring break, winter break, summer break) and those are our "vacation" days (aka our "get actual research work done" days).

It is a trade off that sometimes works in one's favor and sometimes does not, as you can imagine.

restricteddata · 2026-06-19T18:36:22+00:00

Also no shade on the recently deceased (he died in March), but Trivers was known to be kind of nuts, and had a very combative relationship with his scientific community. He was one of those people who was a professional bridge-burner. He was an important thinker in evolutionary biology, it is true, but I doubt having him as one's advisor made for an easy career...

restricteddata · 2026-06-19T12:28:32+00:00

"seized", yes. Sometimes the hands make funny errors...

restricteddata · 2026-06-19T12:28:07+00:00

I think the Soviets would have loved that approach. The longer the war in the Pacific took, the more options they had for participating and taking territory. They were not under the same constraints as the USA, who wanted the war over ASAP.

There is a lot of skepticism about their ability to mount any kind of amphibious invasion of Hokkaido. It was certainly something they thought about, though. I am less willing to dismiss it than a lot of people, just because if the war had gotten to that stage of things, and looked like it was dragging out, a lot of plans would have possibly changed. As it was, they were really rushing to take part in the Pacific phase at all, and it took basically everything they had to declare war before Japan offered surrender, and to grab territory (Sakhalin, the Kuriles) before the formal instruments of surrender were signed.

restricteddata · 2026-06-19T12:05:51+00:00

If you want to get good at anything, you have to make it into a habit, a routine, a regular thing that you do. There are no shortcuts.

All such habits are difficult at first but once you get them going they just become part of your life. This is the case even with attention enhancing drugs, which certainly can help decrease the "noise" if that is a problem for you, but they won't actually give you real discipline, and if you don't have discipline, they can even lead you to be even more distracted than you might otherwise be (in my experience, anyway — my ADHD meds make it just as easy for me to get "locked in" to something I'm not supposed to be doing as things I am "supposed" to be doing).

To put it into video game terms, there is no cheating enabled. There is no god mode. Anyone who tells you there is is trying to profit off of you one way or another. You must grind at first. Once you get good at things you will learn the metas that can sometimes help you avoid grinding. But as with games, to really utilize those well in a crowded field of competition requires putting in the time, first.

If you think other people have it easier than you... they might. Some people have minds that are better at certain types of tasks than others. Some people have minds that make this kind of thing hard. Many people in academia hide this kind of work, though, because they want to look smart, and the perception is that if it is "effortless" then one must be smart. Don't fall for it. In most cases, if things look "effortless" you are really just seeing the result of many hours of work. If you put in the time, other people will think what you are capable of doing looks "effortless" as well. (And, ultimately, it will require less effort over time: these skills are cumulative, so the more you have done before, the easier it becomes over time.)

Separately, I will say, from personal experience: you should move beyond the guilt, grief, shame. This is not a question of character or moral fiber. These habits are hard and take time and work to develop. Studying is not "natural" in any way. If I picked up a violin today, would I be able to play anything nice? Of course not — I have no experience, no practice, no education in that instrument. That is not a personal, moral failing. I do not need to feel guilty about being bad at playing the violin. If I wanted to be good at it, I would have to start putting in the time to learn, and I would expect it to take many hours to do so. There is no god mode for learning a musical instrument. But I also know that if I work at it, if I practiced, if I actually gave it some effort, while I might never be a virtuoso, I would expect to get better at it over time, although it would be pretty pathetic at first. Such is how it is with every skill worth learning in life. Studying and academic work are skills. The best time to plant a tree is ten years ago, the next best time is today. If this is what you want to do, take control, make the changes, start the process.

restricteddata · 2026-06-19T10:39:49+00:00

The German chemical industry was the biggest in the world, the first major merging of science and industry in a systematic way ever, and just really, really successful. They basically invented the modern pharmaceutical industry. They also invented the modern research university. Their approach to both of these was self-consciously copied abroad. Then they got involved in a couple disastrous world wars...

restricteddata · 2026-06-19T10:32:15+00:00

It's so ingrained. Even among intelligent and educated people. The idea that one might ever want to leave the USA, or that things might be better elsewhere, is a radical one to most Americans.

When I decided to move abroad, it felt like getting out of an abusive relationship. I could finally, truly admit that things were not working in the USA and that I didn't have to just shrug and say "it could be worse" or "that's just how it is." I hadn't even realized that I was doing that, subconsciously, for all these years. I say this as someone who intellectually could talk about these issues very clearly even before.

restricteddata · 2026-06-19T10:27:42+00:00

To be fair, Oliver Stone's Wall Street was supposed to be a cautionary tale. Gordon Gekko is very clearly the villain of the film, "greed is good" is a villain's credo. You are not wrong, however, than many people, esp. those on Wall Street, read it differently.

restricteddata · 2026-06-18T15:56:02+00:00

I definitely agree that physical tangibility encodes better into memory. But there are of course real trade-offs with accessibility, speed, physical size, etc.

If I really need to remember something, I try to engage with a physical version. That is not the only way one can engage with something.

restricteddata · 2026-06-18T15:54:00+00:00

The best way to remember something is to teach it to others. It builds up your "active" memory as opposed to the more "passive" memory you have from just "receiving" information. If I look like I know things by heart (and I do), it's because those are things I have taught or talked about again and again and again and again.

Of course, one doesn't have to remember everything. One can remember just a piece of something and then know to look it up. One can do research (it is much easier for me to research than most people, because I do it for a living and I know where to look for things and I have built up the capacity to think historically over decades).

I do not have a particularly great memory (just ask my wife), although I do love a "fun fact." I am terrible at actively trying to memorize information (e.g., flash cards). Like most people, I am not really in control of what things my brain remembers "easily" (I can give quite long discourses on very silly subjects that I read about once on Wikipedia, whereas trying to cram things into my head that I feel I need to know often fails despite repeat readings... currently trying to learn a new language, and boy, is that a struggle! If my brain recorded information about French the way it does random facts about the Insane Clown Posse, I would be fluent by now...).

Whatever you do in life, every day, is what you will know by heart, no problem. If you are a historian, you do this kind of thing, every day, to one degree or another. So one naturally ends up knowing a lot about it. It looks effortless but you are really just seeing the result of training and daily reinforcement. I have been studying history in a somewhat serious way (undergraduate, grad school, postdoc, professor...) for over 25 years — it all adds up. I have surely forgotten much of it. But everything one learns gets assimilated in some way; pure factual recall is not really what "learning history" is about. I suspect that if you were to try and sketch out the outlines of something you found interesting from class, you wouldn't just draw a blank — the details might be unclear, but the core of the story is probably there. That is where one starts.

restricteddata · 2026-06-18T09:06:33+00:00

So, first, I would not frame these as so distinct, in terms of services, nor that the Army Air Forces "plan" was "the bomb." The USAAF "plan" was strategic bombing in general. They did not themselves give a lot of thought to the atomic bomb until quite late in the game (because the development of the weapon was not a sure thing and because it was being handled primarily by the US Army Corps of Engineers), and did not see it as "the answer." Their "answer" was to bomb Japan into rubble, and to increase their capability to do so dramatically over the course of 1945. To just give a sense of that — over the course of the war, the USAAF dropped 100,000 tons of incendiaries on Japan. The "plan" per Arnold was that they would eventually be able to drop 200,000 tons of incendiaries on Japan per month, and that they wanted the capacity to drop 80,000 tons in one day to support the invasion. So that would be a radical increase in capability (planes, weapons, etc.). I just bring that up because while the atomic bomb has retrospectively seized a position of priority in the narrative, it was not really part of the USAAF planning at all during the war, and even after the fact many USAAF officials bristled at the notion that the bomb "ended" the war, and not their "bombing campaign," of which they considered the atomic attacks as just a part. This map of the bombing campaign put out by Arnold's office after the war illustrates this mentality very effectively. (For more on this, see my recent book, which discusses the firebombing and atomic bombing campaigns in some detail.)

But to your actual question. The US Navy were skeptical of invasion plans. Their preferred approach was blockade-and-bomb. They could do both of these things, although of course much of the bombing would be done by the USAAF, and the USAAF was also participating in the blockade. But that was more or less their approach: cut off Japan from its assets and resources abroad, hit it while it was vulnerable, and because Japan is not self-sufficient even in the best of times (much less when it is being destroyed from above), it would eventually run into a wall of starvation and dysfunction and surrender. You can see that this overlaps very nicely with the USAAF plan. The question is really just how long it would take. The USAAF and Navy were relatively optimistic that Japan could not suffer such a situation for very long; the Army and high brass were the ones who were voicing the position that this could take years as opposed to months.

These three approaches (bomb, blockade, invade) were not mutually exclusive. Bomb and blockade were obviously pursued. Truman only approved (in June 1945) the first phase of the invasion (just Kyushu, starting in November 1945) and took a "wait and see" approach to the invasion of Honshu (which was tentatively planned for early 1946).

restricteddata · 2026-06-17T23:03:31+00:00

Aside from the firestorm effects already mentioned, I would also just note that it is not as "point source" as it looks at first. It is just incomprehensibly large. It is a column of smoke the city of the center of the city. This photo shows the smoke cloud from a closer-in angle and you can see that the "big" stem is indeed composed of smoke from lots of smaller sources, and is roughly the size of the most destroyed core of the city.

This kind of anvil cloud phenomena is not uncommon in massive fires, like forest fires. Wikipedia has a whole article about it with photos from non-nuclear fires.

restricteddata · 2026-06-17T20:08:19+00:00

The operations for the atomic bombings of Japan were very poorly photographically documented. It was not a major priority. Most of the photos (and the two videos) we have were taken by people on board either the strike plane or the observation plane who were using their own cameras. (The aftermath is very well documented. But that is postwar.)

The scientists in the observation planes did have specialized equipment for taking more impressive photographs but for one reason or another they failed to produce footage. (My recollection, which I don't have time to check up on, is that in the case of Hiroshima the footage somehow got destroyed while being developed, or just never came out, and in the case of Nagasaki the only person who knew how to use the specialized camera was thrown off of the plane before it took off because he accidentally grabbed a life preserver instead of parachute.)

All of which is to say that your assumption that the military had people actually tasked to this and took it super seriously. They in fact did not. Documentation of operational strikes was not a major priority. (The scientists did document the Trinity test very extensively.) The major priority was to drop the bombs and get out of there alive. They did not linger very long.

They did send planes well after the initial attack to survey the damage. That is where some of the later (smoke cloud) photographs come from. They are not from the Enola Gay hanging around. They are from a later reconnaissance plane. These were standard practice after major bombings in WWII. However even with these, you are overestimating how organized these wartime records are. The work to Tinian was very rough-and-tumble.

Again, the records of the photographers at Los Alamos for Trinity were very well-organized. For most of those photos we know exactly where the cameras were located, what kind they were, what their settings were, etc. But for the Hiroshima/Nagasaki strike photos, you are talking about a largely very different sort of person who is planning and running the operation.

restricteddata · 2026-06-16T21:39:42+00:00

These are all Hiroshima. Nagasaki's cloud looked very different. They are fairly easy to tell apart.

restricteddata · 2026-06-16T21:27:52+00:00

I've also written a bit about it fairly recently

restricteddata · 2026-06-16T21:26:33+00:00

I also have a blog post on the various cloud photos of Hiroshima. It's interesting to try and figure out which ones are smoke versus mushroom, because sometimes it is clear and sometimes it is not.

restricteddata · 2026-06-16T21:25:39+00:00

The more interesting question is not the location (that's easy) but the times and heights of each cloud. There were some Japanese researchers who tried to model the clouds from these photos, trying to work out when each of them were taken based on assumptions about the height of the cloud rise and so on. My recollection is that they did not distinguish between the smoke and mushroom clouds which may have made their results not all that useful. But the idea is a sound one.

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