I had an interesting conversation with CuriousOne the other day about the question Experiment that demonstrates the wave-particle duality of electrons. I thought that wave-particle duality existed, CuriousOne thought it didn't (whether CuriousOne thought this wasn't true for both light and matter, or just matter I'm not really sure). Some of the comments were really interesting, and I wanted to know what some of the physicists here thought.

The comments on the question are just below the main question, and are just below my answer to the question (now moved to chat). Please don't close this with "not enough research" as the reason, I did look into it, but some of CuriousOne's comments left me kind of confused.

In terms of people thinking this is a duplicate: I am asking whether there is experimental evidence for electrons having a wave-particle duality (this duality being like the one light has) and whether the double-slit experiment is an example of experimental evidence for this.


Was de Broglie's hypothesis that electrons (and other matter) have wave-particle duality correct? Does the double-slit experiment prove this, or have anything to do with this? What is some experimental evidence for de Broglie's hypothesis?


  • $\begingroup$ @ACuriousMind, I looked at that question as I was posting this one, and it is not what I'm looking for. $\endgroup$ – karatechop Jul 16 '16 at 12:09
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    $\begingroup$ Well, then you need to be more specific about what you are looking for. The question appears to be pretty much the same, if you are not satisfied with the answers, then start a bounty instead of asking a similar question anew; or ask a more specific question about what exactly you want to know (a non-handwavy definition of "wave-particle duality" would help, because I am under the impression that different people mean different things when they use that phrase, leading to even more confusion). $\endgroup$ – ACuriousMind Jul 16 '16 at 12:11
  • $\begingroup$ Your main problem is that you haven't figured out the difference between a particle and a quantum, yet. In classical mechanics a particle is defined as the approximation of the motion of an extended body (i.e. classical matter) by its center of mass coordinates. What that means is that we simply neglect rotation and all internal degrees of freedom of a real body to make the description "high school level". A plane, for instance, is not a particle for aerospace engineers, but a planet in the Kepler problem is. No such approximation is possible in quantum mechanics. Quanta don't have a COM. $\endgroup$ – CuriousOne Jul 16 '16 at 18:18
  • $\begingroup$ @dmckee: That the OP doesn't know her definitions and that scores of QM textbook authors don't help their struggling students to understand the difference between quanta and particles is not even worth an answer in my books. I don't mind you explaining this in an answer. You got my vote, for sure. $\endgroup$ – CuriousOne Jul 16 '16 at 19:18
  • $\begingroup$ Heather, please don't take any of this personally. I already said in the other thread that it's not your fault and you have nothing to apologize for. QM is being taught the wrong way and has been taught the wrong way for almost a century. We are not going to change this around here, we can only point out that in cases of confusion, it's always a good idea to go back to the basics and ask if what one thinks a word like "particle" means is actually what it means. Once you do that, you will notice that the us of the word in QM is not consistent with its definition in CM. $\endgroup$ – CuriousOne Jul 16 '16 at 20:27

Yes, there is a duality and in the framework of quantum field theory (QFT) it is not even a contradiction at all. It seems pretty natural.

All fields and particles are treated very similarly in the QFT language. Both are fields in space-time, so “waves”. There is a suble difference in the spin statistics, namely that fields corresponding to ordinary matter (fermions) have canonical anticommutation relations whereas “ordinary fields” like photons (bosons) have commutation relations. One consequence is that no two fermions can be in the same state (momentum, position, …).

So far this only describes waves. The commutation relations then limit the excitation of the fields to integer numbers. Those things are called particles.

Therefore QFT describes particles as the smallest quantized excitation of the field.

  • $\begingroup$ thanks for answering so fast...what is the experimental evidence for this? Could you maybe look at some of CuriousOne's comments and explain where CuriousOne slipped, so to speak? I'm just trying to understand it a little more fully now. $\endgroup$ – karatechop Jul 16 '16 at 12:15
  • $\begingroup$ @heather my (pedantic) two cents. I could be wrong, but the use of the word quanta of energy, (an excitation of the field), I see it as a generic term for both fermonic and bosonic fields, so unless you specify what field you are interested in, I believe it's OK to use quanta to cover all particle/wave type questions. Rereading the comments in your post in that light, might make sense. If I am right:) $\endgroup$ – user108787 Jul 16 '16 at 13:15
  • $\begingroup$ QFT says nothing about particles. It only talks about quanta. If you want to recover particles from quantum mechanics, then you need to get into weak measurement theory on high momentum states. $\endgroup$ – CuriousOne Jul 16 '16 at 18:15

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