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On a slightly different topic: do you think it would theoretically be possible to build stable 3D structures composed on positrons and electrons (and not have t

On a slightly different topic: do you think it would theoretically be possible to build stable 3D structures composed on positrons and electrons (and not have them annihilate each other)? I don't really understand the physics of why electrons don't collapse into the positive nucleus, since positives and negatives should attract, but I'm wondering if the same interaction keeping protons and electrons apart in an atom could come into play with smaller particles like electrons and positrons alone.

IntrepidWorm 5y ago
> On a slightly different topic: I don't really understand the physics of why electrons don't collapse into the positive nucleus, since positives and negatives should attract. Good question- this was a clear and troubling problem in the classical atomic models before quantum mechanics. Thinking of electrons as little balls whizzing around, being attracted and repelled by various field forces does seem to lend itself to this question. The current understanding is that since electrons are quantum particles, they can only gain or lose energy through quantized packets, and can only occupy certain energy states. In fact, it's much more accurate to describe electrons by their probability fields, and not as those little balls. Quantum mechanics then describes probability shells called Sommerfeld orbits, where the chance of finding an electron at any given point peaks. Unless energy is added or removed from the system by those aformentioned quantized packets, electrons tend to remain at their respective energy levels and shells.
- wcoenen 5y ago
  > The current understanding is that since electrons are quantum particles, they can only gain or lose energy through quantized packets Just to clarify. An electron moving freely through a vacuum can move at any speed; it is not restricted to certain energy levels. (Speed and therefore kinetic energy is relative to the reference frame anyway.) The quantization of energy comes into play when the electron is spatially confined in some system. This is related to the wave behavior of the particle, and because energy is related to wavelength. Much like how a standing wave on a string can only have wavelengths such that an integer multiple of them fit on the string.
  - IntrepidWorm 5y ago
    Good clarification- my wording was clunky.
- danwills 5y ago
  Great answer! I'm still left wondering exactly what it is about the behaviour of an electron in the lowest orbit that is stopping it from getting closer to the nucleus. Maybe even thinking of it as 'stopping' at all is my problem. Guess the standing-wave analogy below is actually pretty good for understanding that aspect and also accepting that it's a probability field, which does have nonzero values 'inside' the lowest orbital, so it can be 'found' (measured to be) closer in, just much less often. I'd guess having an intuition about why only the first orbital is spherical is probably part of understanding this all properly too, will keep-on reading!
povik 5y ago
> I don't really understand the physics of why electrons don't collapse into the positive nucleus, since positives and negatives should attract My (student of physics) answer to that would be that they are pretty much collapsed as much as they can. It’s just that under quantum mechanics that least energetic state is not the one in which the electron is perfectly co-localized with the positive charge. (As that perfect co-localization is not even physically attainable.)
- perl4ever 5y ago
  >As that perfect co-localization is not even physically attainable It seems to me this is simply a statement that an electron is a fermion not a boson, right? But if a layperson wants an intuitive sense of the situation, then that doesn't really illuminate. It's a fermion, but why should it be?
  - danwills 5y ago
    Fascinating! I would love to gain more of an intuitive grasp on how subatomic particles all work and fit together, i'm not a physicist though. Could you suggest any good introductory reading?
    - perl4ever 5y ago
      layperson = me. I like to read Wikipedia and popularized stuff. The problem is I come away unsatisfied, because even the best writing directed at people who aren't good at math, is more about giving the feeling of understanding than actual understanding. My point about bosons and fermions, is I read the summary on Wikipedia, but they are just labels to me. I don't have the intuition or math except that it says the one kind of thing can "overlap" in ways the other can't. Richard Feynman's "QED: The Strange Theory of Light and Matter" has been much praised though. What did I get out of it? I guess that quantum mechanics has something to do with multiplying complex numbers. I'm not sure exactly what I'm missing, but I get the impression that if I could understand Hamiltonians, Lagrangians, or variational calculus, then I would have some insight into modern physics. Some of it sounds tantalizingly straightforward, but at the same time beyond my mental capacity - imagine a space, a field, etc. - but it's infinite-dimensional or something. Or it's a space of functions. Still, on Wikipedia you can keep clicking on things - what's a "fiber bundle", etc.
alecst 5y ago
Maybe you'll find this interesting. https://en.wikipedia.org/wiki/Earnshaw%27s_theorem https://en.wikipedia.org/wiki/Earnshaw%27s_theorem > Earnshaw's theorem states that a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges. This was first proven by British mathematician Samuel Earnshaw in 1842. It is usually referenced to magnetic fields, but was first applied to electrostatic fields.

IntrepidWorm 5y ago

> On a slightly different topic: I don't really understand the physics of why electrons don't collapse into the positive nucleus, since positives and negatives should attract. Good question- this was a clear and troubling problem in the classical atomic models before quantum mechanics. Thinking of electrons as little balls whizzing around, being attracted and repelled by various field forces does seem to lend itself to this question. The current understanding is that since electrons are quantum particles, they can only gain or lose energy through quantized packets, and can only occupy certain energy states. In fact, it's much more accurate to describe electrons by their probability fields, and not as those little balls. Quantum mechanics then describes probability shells called Sommerfeld orbits, where the chance of finding an electron at any given point peaks. Unless energy is added or removed from the system by those aformentioned quantized packets, electrons tend to remain at their respective energy levels and shells.

wcoenen 5y ago
> The current understanding is that since electrons are quantum particles, they can only gain or lose energy through quantized packets Just to clarify. An electron moving freely through a vacuum can move at any speed; it is not restricted to certain energy levels. (Speed and therefore kinetic energy is relative to the reference frame anyway.) The quantization of energy comes into play when the electron is spatially confined in some system. This is related to the wave behavior of the particle, and because energy is related to wavelength. Much like how a standing wave on a string can only have wavelengths such that an integer multiple of them fit on the string.
- IntrepidWorm 5y ago
  Good clarification- my wording was clunky.
danwills 5y ago
Great answer! I'm still left wondering exactly what it is about the behaviour of an electron in the lowest orbit that is stopping it from getting closer to the nucleus. Maybe even thinking of it as 'stopping' at all is my problem. Guess the standing-wave analogy below is actually pretty good for understanding that aspect and also accepting that it's a probability field, which does have nonzero values 'inside' the lowest orbital, so it can be 'found' (measured to be) closer in, just much less often. I'd guess having an intuition about why only the first orbital is spherical is probably part of understanding this all properly too, will keep-on reading!

povik 5y ago

> I don't really understand the physics of why electrons don't collapse into the positive nucleus, since positives and negatives should attract My (student of physics) answer to that would be that they are pretty much collapsed as much as they can. It’s just that under quantum mechanics that least energetic state is not the one in which the electron is perfectly co-localized with the positive charge. (As that perfect co-localization is not even physically attainable.)

perl4ever 5y ago
>As that perfect co-localization is not even physically attainable It seems to me this is simply a statement that an electron is a fermion not a boson, right? But if a layperson wants an intuitive sense of the situation, then that doesn't really illuminate. It's a fermion, but why should it be?
- danwills 5y ago
  Fascinating! I would love to gain more of an intuitive grasp on how subatomic particles all work and fit together, i'm not a physicist though. Could you suggest any good introductory reading?
  - perl4ever 5y ago
    layperson = me. I like to read Wikipedia and popularized stuff. The problem is I come away unsatisfied, because even the best writing directed at people who aren't good at math, is more about giving the feeling of understanding than actual understanding. My point about bosons and fermions, is I read the summary on Wikipedia, but they are just labels to me. I don't have the intuition or math except that it says the one kind of thing can "overlap" in ways the other can't. Richard Feynman's "QED: The Strange Theory of Light and Matter" has been much praised though. What did I get out of it? I guess that quantum mechanics has something to do with multiplying complex numbers. I'm not sure exactly what I'm missing, but I get the impression that if I could understand Hamiltonians, Lagrangians, or variational calculus, then I would have some insight into modern physics. Some of it sounds tantalizingly straightforward, but at the same time beyond my mental capacity - imagine a space, a field, etc. - but it's infinite-dimensional or something. Or it's a space of functions. Still, on Wikipedia you can keep clicking on things - what's a "fiber bundle", etc.

alecst 5y ago

Maybe you'll find this interesting. https://en.wikipedia.org/wiki/Earnshaw%27s_theorem https://en.wikipedia.org/wiki/Earnshaw%27s_theorem > Earnshaw's theorem states that a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges. This was first proven by British mathematician Samuel Earnshaw in 1842. It is usually referenced to magnetic fields, but was first applied to electrostatic fields.