11 ms·

Atoms aren't anything like that though. There are no little billiard balls, probability densities don't "bump", electrons don't actually orbit, and so on. Atoms

Atoms aren't anything like that though. There are no little billiard balls, probability densities don't "bump", electrons don't actually orbit, and so on. Atoms just are what they are, and what they are does not admit a good "macrophysical analogy".

TedDoesntTalk 4y ago
> There are no little billiard balls … electrons don't actually orbit Wait, what? What do they do then? My physical science education ended in high school.
- consilient 4y ago
  The next useful falsehood on the ladder is that electrons in an atom exist as probability densities around the nucleus. Fire a photon here, and knock an electron off with this probability; fire it there, and get that probability instead. But before they interact with something, electrons aren't anywhere in particular. https://en.wikipedia.org/wiki/Atomic_orbital https://en.wikipedia.org/wiki/Atomic_orbital The real answer is that constituent parts of bound states like atoms don't really exist as separate things. An atom is a particular very complicated field configuration, and if you want anything deeper than that you're going to have to learn QFT.
  - tux3 4y ago
    If constituent parts of bound states like atoms don't really exist as separate things, how come electrons in metals can move around readily? Is it that they're not really bound, or is it just that they 'attach' and 'detach' easily? When I think of chemistry, it seems like even if there's some sense in which the bound atom is one big writhing mass of fields, the whole atom doesn't interract in a uniform way with the outside, right? The electrons interract with the outside a lot, the nucleus is harder to get to? Is it wrong to say the layer of my onion exist as separate entities, when they seem to interract largely independently from the core of the onion, like they do in metals and chemistry? (I guess the answer is still "you're going to have to learn QFT" :) But the next falsehood down seems fun to ask about too!)
    - consilient 4y ago
      > If constituent parts of bound states like atoms don't really exist as separate things, how come electrons in metals can move around readily? Is it that they're not really bound, or is it just that they 'attach' and 'detach' easily? Some of both. Valence electrons in a conductor are delocalized over the entire surface. > When I think of chemistry, it seems like even if there's some sense in which the bound atom is one big writhing mass of fields, the whole atom doesn't interract in a uniform way with the outside, right? The electrons interract with the outside a lot, the nucleus is harder to get to? Right, at least for stable atoms at low energy scales.
  - chias 4y ago
    Thank you, this is the first time I've read a description of what an electron probability density means that has made real sense to me.
- HyperSane 4y ago
  Field theory: David Tong: Quantum Fields https://youtu.be/zNVQfWC_evg?t=1168 https://youtu.be/zNVQfWC_evg?t=1168
  - TedDoesntTalk 4y ago
    Thank you
dools 4y ago
Well for some definition of the word “bump”. What I mean is that the mechanism by which sound travels is the same as the mechanism by which I can punch a punching bag and see it swing. Even if the two materials never “come into contact” because it’s actually the result of charges repelling each other or whatever, the way it works in both cases is the same.
- consilient 4y ago
  Sure, but at that level of generality you're also talking about the mechanism by which light propagates.
  - dools 4y ago
    Really? How does light travel in a vacuum then?
    - consilient 4y ago
      In the absence of charges, Maxwell's equations reduce to `\nabla^2 F = d^2/dt^2 F`, (where F is the electromagnetic field tensor) which has solutions given by superpositions of traveling waves. What I suspect you want, however, is some sort of substance or essential nature that makes the thing go. If that's the case, then the answer is that there are no such things. Not for light, not for ordinary classical mechanics, not for anything. Physical systems are what they do.
      - anankaie 4y ago
        You could say that the thing that makes light go is the distribution and motion of charges in the electric field. As they move, they generate waves in the amplitude of the EM field, and these waves are what we perceive as light.
      - dools 4y ago
        Right that’s the point of my original post. I see lots of people trying to understand how QM “works” when it’s just a thing that’s works the way it does. I have never seen anyone trying to understand how light moves in a vacuum, which (at least to me) seems just as mysterious if you were to try and understand it in some sort of intuitive macro physical sense.

TedDoesntTalk 4y ago

> There are no little billiard balls … electrons don't actually orbit Wait, what? What do they do then? My physical science education ended in high school.

consilient 4y ago
The next useful falsehood on the ladder is that electrons in an atom exist as probability densities around the nucleus. Fire a photon here, and knock an electron off with this probability; fire it there, and get that probability instead. But before they interact with something, electrons aren't anywhere in particular. https://en.wikipedia.org/wiki/Atomic_orbital https://en.wikipedia.org/wiki/Atomic_orbital The real answer is that constituent parts of bound states like atoms don't really exist as separate things. An atom is a particular very complicated field configuration, and if you want anything deeper than that you're going to have to learn QFT.
- tux3 4y ago
  If constituent parts of bound states like atoms don't really exist as separate things, how come electrons in metals can move around readily? Is it that they're not really bound, or is it just that they 'attach' and 'detach' easily? When I think of chemistry, it seems like even if there's some sense in which the bound atom is one big writhing mass of fields, the whole atom doesn't interract in a uniform way with the outside, right? The electrons interract with the outside a lot, the nucleus is harder to get to? Is it wrong to say the layer of my onion exist as separate entities, when they seem to interract largely independently from the core of the onion, like they do in metals and chemistry? (I guess the answer is still "you're going to have to learn QFT" :) But the next falsehood down seems fun to ask about too!)
  - consilient 4y ago
    > If constituent parts of bound states like atoms don't really exist as separate things, how come electrons in metals can move around readily? Is it that they're not really bound, or is it just that they 'attach' and 'detach' easily? Some of both. Valence electrons in a conductor are delocalized over the entire surface. > When I think of chemistry, it seems like even if there's some sense in which the bound atom is one big writhing mass of fields, the whole atom doesn't interract in a uniform way with the outside, right? The electrons interract with the outside a lot, the nucleus is harder to get to? Right, at least for stable atoms at low energy scales.
- chias 4y ago
  Thank you, this is the first time I've read a description of what an electron probability density means that has made real sense to me.
HyperSane 4y ago
Field theory: David Tong: Quantum Fields https://youtu.be/zNVQfWC_evg?t=1168 https://youtu.be/zNVQfWC_evg?t=1168
- TedDoesntTalk 4y ago
  Thank you

dools 4y ago

Well for some definition of the word “bump”. What I mean is that the mechanism by which sound travels is the same as the mechanism by which I can punch a punching bag and see it swing. Even if the two materials never “come into contact” because it’s actually the result of charges repelling each other or whatever, the way it works in both cases is the same.

consilient 4y ago
Sure, but at that level of generality you're also talking about the mechanism by which light propagates.
- dools 4y ago
  Really? How does light travel in a vacuum then?
  - consilient 4y ago
    In the absence of charges, Maxwell's equations reduce to `\nabla^2 F = d^2/dt^2 F`, (where F is the electromagnetic field tensor) which has solutions given by superpositions of traveling waves. What I suspect you want, however, is some sort of substance or essential nature that makes the thing go. If that's the case, then the answer is that there are no such things. Not for light, not for ordinary classical mechanics, not for anything. Physical systems are what they do.
    - anankaie 4y ago
      You could say that the thing that makes light go is the distribution and motion of charges in the electric field. As they move, they generate waves in the amplitude of the EM field, and these waves are what we perceive as light.
    - dools 4y ago
      Right that’s the point of my original post. I see lots of people trying to understand how QM “works” when it’s just a thing that’s works the way it does. I have never seen anyone trying to understand how light moves in a vacuum, which (at least to me) seems just as mysterious if you were to try and understand it in some sort of intuitive macro physical sense.