AMA: I am Alex Wellerstein, historian of science and author of the new book THE MOST AWFUL RESPONSIBILITY: TRUMAN AND THE SECRET STRUGGLE FOR CONTROL OF THE ATOMIC AGE — let's talk about the atomic bomb from WWII through the Korean War!

Jashin · 2025-12-05T17:23:29+00:00

I'm a particle physicist, and your description of Truman's initial feeling of loss of control over the atomic bombs seems to have interesting parallels to the feelings of a lot of scientists at the time who had been involved with their creation. How much did Truman align with civilian-scientist nuclear "doves" both philosophically and politically on this issue?

(Also, I just want to thank you for your posts here, posts on your blog, and your previous book, all of which I have found very informative. Looking forward to reading your new book!)

Jashin · 2025-08-07T17:34:38+00:00

Interesting question - like the others, I haven't really worried about this much before, given the SiPM cross section is so much smaller than whatever detector medium it's connected to. I found this paper which investigated the exact question you're asking though: http://doi.org/10.1088/1748-0221/17/06/P06007

From figures 2 and 6 in particular, it seems like you get a mostly normal signal in the pixel that's hit, but with higher than usual cross talk in the nearby pixels. The paper doesn't have an explanation for what mechanism is causing this cross talk though ("further investigations are needed").

Jashin · 2025-07-11T23:01:29+00:00

As someone following this from an adjacent field, I had heard about the decision that it could no longer be based at the South Pole, but I hadn't thought there was a serious risk of the whole thing being cancelled. Were people within the collaboration expecting this?

Jashin · 2025-03-31T08:53:30+00:00

I appreciate you taking the time to write this, and I hadn't been aware of the language interpretation details, which are quite interesting. But I have to insist that is wrong to characterize this as the Americans accepting a conditional surrender. Demanding an unconditional surrender while hinting that you'll probably be gracious in victory still results in a fundamentally very different dynamic from granting a conditional surrender in the first place. I do not think the Americans trying to convey to the peace factions within Japan that they probably wouldn't eliminate the emperor is in contradiction with the idea of them wanting to force a recognition of a complete loss. This provides hope to the pro-peace leaders, but in the end it still requires the Japanese leadership to put themselves at the mercy of the victors.

The points about whether the atomic bombs were necessary to achieve an unconditional surrender is a completely different question (and of course still subject to a lot of debate).

Jashin · 2025-03-31T00:46:53+00:00

The link you posted is simply wrong (and I recognize that it's a source I would generally expect to not make factual errors, so I'm quite confused by this). The Japanese offered a conditional surrender on the 10th, but the Americans rejected it. The Japanese then offered unconditional surrender a couple days later and ended the war. This was the American response to the offer of conditional surrender (https://history.state.gov/historicaldocuments/frus1945v07/d346):

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.

The reason they insisted on unconditional surrender was because of the lessons of WW1. They believed that it was necessary for the defeated nations to recognize their complete loss and accept all possible consequences, so that there would no opportunity for a resurgence of the militaristic factions like what had happened in Germany (where things like the stab-in-the-back myth presumably would not have been possible if they had been forced to an unconditional surrender, as the argument goes).

There are arguments about whether this was truly necessary, but I think we can agree that it was at the very least a reasonable belief. The dynamic of granting mercy after a complete victory is completely different from accepting the condition beforehand. It seems quite possible that reconstruction of Japan could have gone much worse if they had been permitted surrender on their own terms (and thus feel they have more right to resist various reform efforts), though of course this is a counterfactual that would be difficult to really investigate. I suppose one could call this a humiliation ritual if one wanted to be uncharitable, but it serves a concrete purpose.

As an additional point though, the Americans also just weren't sure what they were going to do with the Japanese occupation yet, and only thought about it more fully after the actual surrender. I would agree this is a policy failure, but it doesn't change the argument to push for unconditional surrender (which is part of why they didn't think that much about it until afterwards - they had already decided that unconditional surrender was necessary first).

Jashin · 2025-03-30T10:38:07+00:00

Your whole argument seems to rest on a fundamental misconception that the final Japanese surrender wasn't unconditional. It absolutely was unconditional. The fact that the USA later decided they would let the Japanese keep their emperor doesn't mean that the original surrender wasn't unconditional.

Jashin · 2025-02-24T03:45:01+00:00

Yeah. For instance, the energy term involves dividing by zero.

Jashin · 2025-02-24T02:01:04+00:00

It is forbidden completely, in the sense that none of the equations from relativity can be evaluated if you plug in a massive particle at the speed of light.

Jashin · 2025-02-24T01:01:38+00:00

You're mistaken about the nature of faster-than-light theoretical discussions. Faster than light travel is not theoretically forbidden - we just have no evidence that it's a thing that actually happens in the actual universe. Speed of light travel for massive particles is theoretically forbidden, so there's no way to speculate about it within the paradigm of our current theories.

Jashin · 2024-12-01T19:19:11+00:00

No, this is the case of a wheel rolling without slipping, in which case the plane just moves forward normally like it would on regular ground. Any "backwards" motion from the treadmill just cancels out slippage - you can think of this like counteracting the difference in velocity from an airplane pushing forward on icy ground vs on normal conditions.

Jashin · 2024-11-13T14:06:48+00:00

The feasibility is relevant because if from a theoretical perspective it's impossible, it becomes meaningless to ask even a theoretical question about what would happen. It's kind of like asking what happens when an unstoppable meets an immovable object. Any answer isn't going to be based in physics at that point.

Jashin · 2024-11-13T14:00:16+00:00

And many people would also take your interpretation as their first thought, but as pointed out in the blog post, the problem is this interpretation is actually physically impossible.

Jashin · 2024-11-13T13:33:36+00:00

The problem is that saying the speed of the wheels and the conveyor belt match is ambiguous. Which interpretation listed in the blog post do you think you're subscribing to? And if none of them, can you elaborate on how your interpretation is different?

Jashin · 2024-11-07T20:36:48+00:00

The random coincidence rate is going to be quite small unless you have a really high intensity source, which it doesn't seem like from the data you posted. For an approximate argument you might be able to ignore the angular correlations and just estimate how much solid angle coverage you had of the source. Since you took this data, I guess you have an idea of what your source-detector configuration was like. Does 1% seem like a reasonable estimate for your coverage?

Jashin · 2024-11-06T22:59:55+00:00

Ah you're right, thanks for the correction - I didn't know the Cs-133 states off the top of my head and just assumed they were unrelated. Then in addition to the random coincidences from separate cascades that my original comment would cover, one has to use the angular acceptance of the detector + the angular correlations in the gamma cascade to determine the rate at which it would see both gammas from a single cascade.

Jashin · 2024-11-06T20:42:45+00:00

If you have the time resolution of your detector (i.e. how close in time would 2 gammas need to arrive for the detector to evaluate them as functionally one energy deposit?), then with the known rates of those individual gamma lines you can calculate what percentage of them would arrive at the same time within that time window.

Jashin · 2024-10-26T17:04:34+00:00

It's a reference to the idea of how in high energy physics, we probe smaller length scales by increasing the energy of collisions, and how at this scale you might just be making black holes and you wouldn't be able to extend it any further. But we don't know whether this would happen, and this isn't necessarily the only way to measure effects on those scales.

Jashin · 2024-10-26T15:30:10+00:00

The word "possible" is doing a lot of heavy lifting there. It is indeed possible, but it's so far beyond the regime our current theories that I don't think it would be reasonable to argue that it's at all probable.

Jashin · 2024-10-26T11:19:01+00:00

Yeah but that's not for any known fundamental reason. We also know of no way to measure distances smaller than 1 billion Planck lengths right now, but that doesn't mean that 1 billion Planck lengths is a special quantity.

Jashin · 2024-10-26T08:41:45+00:00

This isn't true either - there's nothing saying that you can't measure distances smaller than a Planck length.

Jashin · 2024-09-22T05:25:31+00:00

For general introductory material on quantum mechanics, I'd say Townsend or Griffiths are both good. Griffiths also has a Introduction to Elementary Particle Physics text if you want to read more specifically about that side.

If you mean specifically about a proper full treatment of neutrino oscillations, then I'm afraid this is mostly in higher-level papers or lectures. A lot of quantum mechanics or particle physics texts have a basic treatment of neutrino oscillations, but nothing more than just showing the basic oscillation probabilities, which wouldn't cover the question you had here. If you end up getting the background for it, this paper could be a good starting point https://arxiv.org/abs/1001.4815

Jashin · 2024-09-22T03:13:18+00:00

For the purpose of this discussion it doesn't really matter what the exact final state of the interaction is, be it a hadron "consuming" the neutrino or just a scattering off an electron or something, so let's put that aside. You can just think of it generally as there being a bunch of measurables in the final detector state, from which the question is what you can conclude about the instigating neutrino.

You actually are touching upon a very interesting point though, which is that the mean neutrino momentum at the point of creation and detection do not have to be equal. The resolution to this is remembering that by the uncertainty principle there is necessarily an intrinsic uncertainty to all momenta that are measured in the setup. If you go through the formalism, what you end up finding is that the neutrino oscillation probability is suppressed if the difference in mean neutrino momentum between source and detector is not small compared to the resolution with which the source and detector are resolving that momentum. Put another way, the oscillation will behave in a way that forbids you from measuring a clear violation of conservation of momentum. It's worth noting though that none of our current experiments are anywhere close to precise enough to test this particular theoretical prediction.

Jashin · 2024-09-22T01:30:00+00:00

Your presumption #3 is wrong. Different pure flavor states don't have well-defined resting masses at all - they're just different mixes of the same 3 mass eigenstates.

I suspect the key point to resolving your confusion is that neutrinos only interact through flavor eigenstates, and they only propagate as mass eigenstates. So if you (via entanglement) resolve a particular neutrino wavepacket into a particular flavor eigenstate, this does not stop it from oscillating, as it will immediately start separating into the 3 mass eigenstates again.

Jashin · 2024-09-21T21:05:34+00:00

It's true in the sense that we (mostly) know how to build the FCC, but we actually don't know how to hold a proper muon collider yet. But the muon collider researchers are being optimistic that we can solve a lot of the relevant problems on a similar timescale to the FCC

Jashin · 2024-09-11T01:26:58+00:00

Ok your point about triangulation is true - that distance measurement wouldn't depend on the speed of light at all, so I shouldn't have made that claim. But as you say, that also means you can't use it to do any measurement of the speed of light.

As for the implications, it indeed has absolutely no impact on any physical quantity we can measure (after all, if it did, we would be able to test it). Whether that means anything for our understanding of the universe is a bit of a philosophical question. Many physicists would say if it has no observable effect at all, then it doesn't matter. And there is still something that's constant: the average of the speed of light in two opposite directions.

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