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Comment by Vaslo | Hacker News Reader

It will always amaze me that 100 years ago when microscopes were quite primitive that physical chemists could predict the shapes of the electron shells. The knew the inner ones were spherical, a little further out were dumbbell shaped, etc. Now pictures like this help add more context to these more complex structures, but the hybrid dumbbell shape of the shell is easily recognizable.

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At first my reaction was: "No way, it has to be a lot more recent than a 100 years." But then I realized that 1920s was a 100 years ago.

The "History" section of this page was interesting: https://en.wikipedia.org/wiki/Molecular_orbital_theory It apparently took most of 30s and 40s for those theories to mature, and the ideas of the then new quantum mechanics to be applied to molecules.

"Student describes the ‘90s as 'the late 1900s' and now we all feel old" — https://mashable.com/article/late-1900s-student-professor-bu...

:-\

I love how the meaning of "atom" is evolving with our understanding of the world. The origin is from that which is uncuttable/indivisible while our modern understanding of physical atoms are things made up of sub-atomic particles. Even in CS we have "atomic operations" which can be made up of multiple instructions.

I wonder how we will define "atom" in another 100 years.

Always thought we stopped to soon. At some point things may cease to be divisible. Plank scale is still pretty deep down the well.

Or perhaps they'll be some form of Mobius strip-like string-particle item that you can divide in two but still have a single item afterwards. Like self-healing strings that you divide in one [set of] dimension[s] and which simultaneously close up in some other dimension.

Whether such an item is mathematically possible is left as an exercise for the reader ;o) (just an idea I had).

I like it.

There is a super fun ted(?) talk, that I can’t seem to find, with a guy constructing and cutting Möbius strips, and variations on that theme. Pretty unintuitive what a little twist can do!

...and I seemingly still cannot find it. A google will reveal many such videos, I think, but no time to search them out.

Matt Parker has demonstrated this at least a couple of times on YouTube, I bet he’s who you’re thinking of. It is surprising!

https://youtu.be/-u-O_2Hz82I

I think I was thinking of a Matt Parker video. I hadn’t seen this one though, thanks!

perhaps you are thinking of this video from Numberphile with Tadashi Tokieda https://m.youtube.com/watch?v=wKV0GYvR2X8

I forgot about this one. It’s great, thank you! His video with the counterintuitive bead flows was great as well, if I recall. Lots of good stuff from this guy.

Well, both numberphile and Tadashi Tokieda have lots of good stuff, I should say!

An atomic operation is a sequence of steps that are indivisible in their effects. That's a return to the original definition of "atom." Atoms as constituents of molecules are the exception from the trend and a misnomer.

Mostly, I agree. However, in a multitasking environment anything that is multiple instructions can be significantly split up in time. While not the primary effect of the op, the op itself is still divided which can have other non-negligible secondary effects on a large system.

And on your computer, your cpu is doing a lot of stuff during that atomic operation even cutting it in smaller parts...

There are two major uses of the term "atomic" in CS. The sense is either that of database transactions, in which either everything happens together or nothing happens at all, or that of concurrency, in which... really, it's the same thing, but with a focus on whether an intermediate state can be visible from another thread/process, as opposed to whether an intermediate state can be written to persistent media. An atomic operation is one in which, whatever method you use to observe the affected state, you will only see the state from before the operation begins or the state from after it completes.

It doesn't matter whether the CPU does the operation by magic or by some physical process involving the passage of time; that's not part of the concept. The operation is not divisible; it isn't possible for part of it to occur.

Atomicity in CS is about isolation not about the smallest number of operations.

Atomic operations are made up of multiple instructions, but the atomic in the CS sense means that they need to be done together. This is a different concept from being made up of subatomic parts.

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