The parent comment implies these things would follow the old "seems like magic" trope. They would not seem like magic if you explained these concepts to (educated) people of the time.

I did not read that comment in that way. But I think you'd need to explain for a pretty long time to get engineers to believe your story of nuclear fission power plants. In 1912 we didn't even know about neutrons and protons.

We knew about radioactivity then, and Radium-powered superdevices were just entering science fiction.

I mean with just a few semesters of physics education you can bring people who don't know anything about physics at all to a Bachelor's degree. So in principle you can explain basically anything to an intelligent person of any time period if you put sufficient effort into it.

But to me that feels different than saying that inventions where sufficiently small steps away from a general engineer's education that you could "simply" explain them and not be met with wonder.

Knowing radioactivity is just the first step toward discovering the internal structure of the atom. You need a measuring instrument that is much smaller than a whole atom to make any progress.

The atom nucleus was discovered by counting how many alpha particles bounced off the nucleus of a piece of gold foil and how many simply passed through it. The bounce rate was incredibly low and therefore the nucleus must have been orders of magnitude smaller than the gap between the next nucleus.

Those experiments were conducted between 1908 and 1913.

Personally I think you could tell a GE engineer in 1912 that their company would be building a radiation-powered electrical plant and they'd be keen to find out how, not baffled at the very concept. No way of knowing for sure, of course. Just that, this was an era when radioactivity and (what became) nuclear research was very much something the educated were reading about in their monthly magazines.

Sure, I grant that these may not be forthcoming and obvious developments to everyone, and that you may need to "fill in the blanks" for many when it comes to atomic energy (a jet engine is not a complex machine, however; it is a precision machine). But my comment is more about how much we underestimate the state of the world that came before us and our historical forebears, and the ability of otherwise open-minded, educated people to adapt to new ideas and work with black box abstractions. These ideas would be for example far from a caveman looking at a nuclear submarine (or Bob Lazar looking at a UFO heh).

There are a lot of nuances here, but overall I think you make a good point.

On the one hand the idea for nuclear fission was still fairly far off in 1912, since even in the 30's many physicists were still skeptical that radioactive energy could be released more rapidly than it normally is in natural substances. On the other hand a couple of major factors leading to it were already known in 1912: the fact that radioactive decay released large amounts of energy and Einstein's discovery of mass-energy equivalence.

As for jet engines the situation is clearer since a pulsejet was already patented in 1906.

I think in 1912 these technologies would seem like semi-plausible science fiction, but not magic.

That wasn't when it was discovered, that was just the first practical implementation. The theory side was developed earlier. The Manhattan project was an engineering problem.

Saying it was just an engineering problem is really understating the level of theory and experiment had to happen at the same time. It was a huge scientific and engineering endeavor that happened simultaneously. Some good books that go into the crazy intricacies are American Prometheus and The Making of the Atomic Bomb if you are interested.

I'm reasonably sure that fission was discovered by Otto Hahn and Lise Meitner sometime in the late 1930s, few years after Fermi accidentally split the atom without realizing it.

Yea the theory was not really much before this (https://en.wikipedia.org/wiki/Nuclear_fission#History).

There really couldn't be much theory on this before 1900's anyway because of our understanding of the atom/nucleus.

The World Set Free by H.G. Wells is from about 1912is, I mean scifi could be considered far fetched but he isn't exactly an obscure author, radium was already a thing.