4 ms·

Can someone explain what an electron is? I remember from my high school physics that electrons are "point-like" particles, which are "elementary" (not built out

by p1esk 4y ago

Can someone explain what an electron is? I remember from my high school physics that electrons are "point-like" particles, which are "elementary" (not built out of any smaller particles). And electron clouds are like all possible or probable trajectories of how electrons move around an atom's nucleus. Or something like that, it was many years ago. Then what is a "cloud of negative charge"?

notfish 4y ago
My model for understanding phenomena where quantum effects matter is this: if you think of the universe like a big sheet of something stretchy, an electron/proton/particle is just a knot tied in the sheet. Outside of some small region local to the knot the sheet looks flat.
- jacquesm 4y ago
  It looks flat but the tension isn't flat. That's why that analogy is so beautiful because it suggests the existence of another force that works at any distance and weakens the further away you get from the point of the knot (gravity).
scotty79 4y ago
There is an "electron field" everywhere. Electron is a persistent, energetic disturbance of this field that can travel and interact through electroweak force. It's most convenient mathematical description is as if it was a "cloud" of probability of all of it's charge and mass being concentrated at a single point in space. If we forcefully interact with electron we can reshape this "cloud" to be as small as we need to at the cost of imparting on it random monentum through uncertainty principle. I think what they measure is that when you interact with electron then its electric field seems to be very spherical to the point that we can rule out a lot of ideas about electron having any internal substructure that might cause the field to be a little bumpy.
- p1esk 4y ago
  This cloud of probability you're talking about - is it different from the cloud of probabilities of electron's position relative to the atomic nucleus?
  - wiml 4y ago
    The cloud of probable location is the magnitude of the electron's wavefunction, as I understand it. So they're the same thing, but there's extra information in there too beyond simply position (wavefunctions are complex-valued, not real-valued). Source: Dimly remembered undergrad physics.
  - scotty79 4y ago
    It's the same thing for electron that freely propagates as for the one bound, for example inside atom or a molecule. It's just that the shape is different. I think it's worth mentioning it's not exactly a probability understood as a theoretical chance of something being somewhere. This wave function is what actually is the physical reality. But we can't measure this reality without interacting with it and when we do interact multiple times and interpret those interactions as if they were caused by pointlike particle being in particular spot then we see that results of those interactions have distribution matching this "probability" "cloud" (square of a wave function).
    - p1esk 4y ago
      I'm curious what would it look like if we could expand the size of an atom by a billion times, preserving all its quantum properties.
      - scotty79 4y ago
        If you want to see how electron (wave function) can look when it's stuck to a nucleus check out orbital shapes: https://www.google.com/search?q=orbital+shapes https://www.google.com/search?q=orbital+shapes As more and more electrons get stuck to nucleus it gets crowded around it so further electrons form more and more bizarre shapes of larger and larger sizes as only two electrons can stably fit in a single specific shape of a specific size (Pauli exclusion principle). They do it by taking opposite spins.
simcop2387 4y ago
Disclaimer: I have a theoretical degree in armchair physics, not a real one. So that's where the fun of Quantum Mechanics and uncertainty comes in. Electrons are not just point-like particles, they're sort of both particles and waves. If you nail down exactly where the electron "particle" is, then you end up with it's momentum being less defined, meaning that you're not going to be able to say anything at all about where it came from, where it's going, or how fast. Similarly if you can nail down it's momentum perfectly it won't have a definition of where it is anymore. This isn't the Observer effect, where you making the measurements changes the system, but in fact that the other related property actually ceases to have a valid definition anymore (I'm not well versed enough to say it stops existing with any confidence but that's my understanding). This leads to a situation where you end up measuring a probability density of the property of the electron, so you get a density of it being "around this point +/- some amount" and with a "momentum +/- this amount, and sort of in this direction". This means that you now have a probability density of the electron where you'll see it's effects of the negative charge and kinetic energy and those are the things that describe that "cloud of negative charge". The main effect of this that affects things is that you end up with this cloud of all the electrons around an atom and you don't ever observe the individual electrons, just the shells/clouds around the atom and how they change as energy is inserted into the system. My layman's understanding is that essentially as you make a measurement/system/whatever where it's designed to see the position more than the momentum you'll see more point-like particle behavior, but never only just that (you can't ever nail it down to an infinite precision, if you did it'd have a momentum that could send it off at the speed of light as if it had no mass) and in the other case if you could measure infinite precision on the momentum you'd end up measuring the electron as if it was "everywhere" in the universe all at once, which is just as nonsensical of a result as the first one.
- marcosdumay 4y ago
  > I'm not well versed enough to say it stops existing That's a small detail, but no, it's not that the particle "stops existing". It's that we can't describe the momentum and position of something with indefinite detail with mathematics that is still coherent. The data type we have for describing things can not go there (on the QM language, of course). And the surprising thing is that QM predicts our experiments with as much detail as we can experiment with. So, we have this language that can't describe something with known position and speed, and as far as anybody is concerned, it's perfectly correct.

by p1esk 4y ago

notfish 4y ago

My model for understanding phenomena where quantum effects matter is this: if you think of the universe like a big sheet of something stretchy, an electron/proton/particle is just a knot tied in the sheet. Outside of some small region local to the knot the sheet looks flat.

jacquesm 4y ago
It looks flat but the tension isn't flat. That's why that analogy is so beautiful because it suggests the existence of another force that works at any distance and weakens the further away you get from the point of the knot (gravity).

scotty79 4y ago

There is an "electron field" everywhere. Electron is a persistent, energetic disturbance of this field that can travel and interact through electroweak force. It's most convenient mathematical description is as if it was a "cloud" of probability of all of it's charge and mass being concentrated at a single point in space. If we forcefully interact with electron we can reshape this "cloud" to be as small as we need to at the cost of imparting on it random monentum through uncertainty principle. I think what they measure is that when you interact with electron then its electric field seems to be very spherical to the point that we can rule out a lot of ideas about electron having any internal substructure that might cause the field to be a little bumpy.

p1esk 4y ago
This cloud of probability you're talking about - is it different from the cloud of probabilities of electron's position relative to the atomic nucleus?
- wiml 4y ago
  The cloud of probable location is the magnitude of the electron's wavefunction, as I understand it. So they're the same thing, but there's extra information in there too beyond simply position (wavefunctions are complex-valued, not real-valued). Source: Dimly remembered undergrad physics.
- scotty79 4y ago
  It's the same thing for electron that freely propagates as for the one bound, for example inside atom or a molecule. It's just that the shape is different. I think it's worth mentioning it's not exactly a probability understood as a theoretical chance of something being somewhere. This wave function is what actually is the physical reality. But we can't measure this reality without interacting with it and when we do interact multiple times and interpret those interactions as if they were caused by pointlike particle being in particular spot then we see that results of those interactions have distribution matching this "probability" "cloud" (square of a wave function).
  - p1esk 4y ago
    I'm curious what would it look like if we could expand the size of an atom by a billion times, preserving all its quantum properties.
    - scotty79 4y ago
      If you want to see how electron (wave function) can look when it's stuck to a nucleus check out orbital shapes: https://www.google.com/search?q=orbital+shapes https://www.google.com/search?q=orbital+shapes As more and more electrons get stuck to nucleus it gets crowded around it so further electrons form more and more bizarre shapes of larger and larger sizes as only two electrons can stably fit in a single specific shape of a specific size (Pauli exclusion principle). They do it by taking opposite spins.

simcop2387 4y ago

Disclaimer: I have a theoretical degree in armchair physics, not a real one. So that's where the fun of Quantum Mechanics and uncertainty comes in. Electrons are not just point-like particles, they're sort of both particles and waves. If you nail down exactly where the electron "particle" is, then you end up with it's momentum being less defined, meaning that you're not going to be able to say anything at all about where it came from, where it's going, or how fast. Similarly if you can nail down it's momentum perfectly it won't have a definition of where it is anymore. This isn't the Observer effect, where you making the measurements changes the system, but in fact that the other related property actually ceases to have a valid definition anymore (I'm not well versed enough to say it stops existing with any confidence but that's my understanding). This leads to a situation where you end up measuring a probability density of the property of the electron, so you get a density of it being "around this point +/- some amount" and with a "momentum +/- this amount, and sort of in this direction". This means that you now have a probability density of the electron where you'll see it's effects of the negative charge and kinetic energy and those are the things that describe that "cloud of negative charge". The main effect of this that affects things is that you end up with this cloud of all the electrons around an atom and you don't ever observe the individual electrons, just the shells/clouds around the atom and how they change as energy is inserted into the system. My layman's understanding is that essentially as you make a measurement/system/whatever where it's designed to see the position more than the momentum you'll see more point-like particle behavior, but never only just that (you can't ever nail it down to an infinite precision, if you did it'd have a momentum that could send it off at the speed of light as if it had no mass) and in the other case if you could measure infinite precision on the momentum you'd end up measuring the electron as if it was "everywhere" in the universe all at once, which is just as nonsensical of a result as the first one.

marcosdumay 4y ago
> I'm not well versed enough to say it stops existing That's a small detail, but no, it's not that the particle "stops existing". It's that we can't describe the momentum and position of something with indefinite detail with mathematics that is still coherent. The data type we have for describing things can not go there (on the QM language, of course). And the surprising thing is that QM predicts our experiments with as much detail as we can experiment with. So, we have this language that can't describe something with known position and speed, and as far as anybody is concerned, it's perfectly correct.