De Broglie all the way down

  • #1

jshrager

Gold Member
24
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This is going to seem like it should be an educational question, and perhaps it should, but please bear with me, because I think that it has theoretical content.

A nice quote that I recently heard someplace went something like: "We used to argue about whether electrons [etc] were particles or waves or both or what. Well, the argument is over and the waves won."

de Broglie taught us that macroscopic objects have wave nature, and we embrace this. But, odd to say, we still don't seem to embrace this at the microscopic scale, even though there is where it would seem to be most obvious setting, and is the source of the concept to begin with. Specifically, whereas we are taught to think of particles as complexes of waves, when we depict things like subatomic particles -- or for that matter atomic nuclei, or for that matter whole atoms -- we draw them as though there are actually particles, whereas no one thinks that just because a neutron decays into a proton + electron + neutrino, that these things are "inside" the neutron, nor that they, in any sense, are the composite parts of the neutron, except in the abstract mathematical (specifically fourier) sense that a set of sine waves are the composite parts of a violin's sound.

One can see that this may merely be an educational complaint to please stop drawing pictures of atoms that have nuclei with electrons "around" them (in any sense of "around", whether the planetary or statistical sense), and to stop drawing pictures of nuclei with a bunch of balls in them. But my (possibly) technical question is this: Is there any sense OTHER than the Fourier sense, in which, let's say, electrons actually retain their identity (in any sense, again other than the Fourier sense) after absorption? It seems not, in which case all that can be said about an atom of whatever sort, is that it differs in such-and-so ways from another atom of a different sort (and the same for nuclei and nuclear particles, and, for that matter, molecules, and perhaps even macro-molecules, and where does it end?). And all the descriptions of there being, say, more or fewer bonding electrons, and so on and so forth are essentially identical to saying that the Fourier decomposition of a given complex waveform contains such-and-so series of component since waves.
 

Answers and Replies

  • #2
This is going to seem like it should be an educational question, and perhaps it should, but please bear with me, because I think that it has theoretical content.

A nice quote that I recently heard someplace went something like: "We used to argue about whether electrons [etc] were particles or waves or both or what. Well, the argument is over and the waves won."

de Broglie taught us that macroscopic objects have wave nature, and we embrace this. But, odd to say, we still don't seem to embrace this at the microscopic scale, even though there is where it would seem to be most obvious setting, and is the source of the concept to begin with. Specifically, whereas we are taught to think of particles as complexes of waves, when we depict things like subatomic particles -- or for that matter atomic nuclei, or for that matter whole atoms -- we draw them as though there are actually particles, whereas no one thinks that just because a neutron decays into a proton + electron + neutrino, that these things are "inside" the neutron, nor that they, in any sense, are the composite parts of the neutron, except in the abstract mathematical (specifically fourier) sense that a set of sine waves are the composite parts of a violin's sound.

One can see that this may merely be an educational complaint to please stop drawing pictures of atoms that have nuclei with electrons "around" them (in any sense of "around", whether the planetary or statistical sense), and to stop drawing pictures of nuclei with a bunch of balls in them. But my (possibly) technical question is this: Is there any sense OTHER than the Fourier sense, in which, let's say, electrons actually retain their identity (in any sense, again other than the Fourier sense) after absorption? It seems not, in which case all that can be said about an atom of whatever sort, is that it differs in such-and-so ways from another atom of a different sort (and the same for nuclei and nuclear particles, and, for that matter, molecules, and perhaps even macro-molecules, and where does it end?). And all the descriptions of there being, say, more or fewer bonding electrons, and so on and so forth are essentially identical to saying that the Fourier decomposition of a given complex waveform contains such-and-so series of component since waves.
All you say about how misleading those depictions are is true, but it is similarly misleading to maintain that "waves won". It is as wrong to think in terms of little billiard balls as in terms of waves. The argument about duality is indeed over but neither won.
 
  • #3
Specifically, whereas we are taught to think of particles as complexes of waves, when we depict things like subatomic particles -- or for that matter atomic nuclei, or for that matter whole atoms -- we draw them as though there are actually particles,

You are reading the wrong books. Modern textbooks are way beyond that eg:
https://www.amazon.com/dp/019969933X/?tag=pfamazon01-20

Its only at the beginner level or popularisations that is done - its wrong - anyone that knows the details understands its wrong - but we all have to start somewhere.

De Broglie was consigned to the dustbin of history in 1926 when Dirac came up with his transformation theory (likely even earlier - but certainly by then):
http://www.lajpe.org/may08/09_Carlos_Madrid.pdf

The key thing is the quantum state - which is neither particle or wave - although it can be expanded in eigenfunctions of position and called a wave-function - its not in any sense a wave.

Thanks
Bill
 
  • #4
Okay, look, skip the "waves won"; I'm sorry I brought that into it. My point was, however, not about books (well, it's about books too), but (esp.) about things like this:

http://en.wikipedia.org/wiki/Atomic_nucleus

from which everyone who isn't a physicist gets their physics, and which just shouldn't be depicting a bunch of particles in any sense. (BTW, this wp page on the atom is a bit better, but also devolves into there being particle components in various places.) We need a new way to depict these things, if we depict them at all.

Anyway, okay, so it turns out that this is an education issue, and I should prob. just take it there.

Thanks!
 
  • #5
One can see that this may merely be an educational complaint to please stop drawing pictures of atoms that have nuclei with electrons "around" them (in any sense of "around", whether the planetary or statistical sense), and to stop drawing pictures of nuclei with a bunch of balls in them. But my (possibly) technical question is this: Is there any sense OTHER than the Fourier sense, in which, let's say, electrons actually retain their identity (in any sense, again other than the Fourier sense) after absorption?
Yes certainly, electrons retain their identity as occupied orbitals. And orbitals are distinguishable by the angles between different bonds in molecules.
 

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