"Wave-particle duality" and double-slit experiment

PeterDonis said:

Not at the same time, no.

Sorry, your answer refers to the fact that both momentum and position cannot be known at the same time with arbitrary precision, right?
Or are you referring to the fact that both momentum and position cannot be known at the same time in any way?

Just to be sure.

HighPhy said:

your answer refers to the fact that both momentum and position cannot be known at the same time with arbitrary precision, right?

Yes.

HighPhy said:

Sorry to open a new thread.
There are plenty of threads on PF dealing with the issue of "wave-particle duality".
Although not unanimously, many agree that the concept of "wave-particle duality" is outdated. Electrons, photons and all of the underlying entities are neither waves nor particles, but quantum fields, and we can do certain wave-like experiments that let quantum fields behave like particles, and other particle-like experiments that let them behave like waves.

I have doubts not only about the term "duality," but also about "wave-particle duality" in the double-slit experiment. I'll try to put my doubt within a context.

From the very beginning, I was taught in school that:

Bohr conceived the atom with electron making circular orbits around the nucleus with its levels (by following Planck's quantization of energy). Later Schroedinger, thanks to Young's double-slit experiment demonstrating "wave-particle duality", abandoned the concept of an orbit to introduce that of an orbital and to see how the electron does not perform a well-defined orbit, but rather is chaotic.
The electron can be in an area described by the wave function, and the square modulus of the wave function (always greater than or equal to zero) returns the probability that the electron is at a given point, which, however, cannot be known because of Heisenberg's Undeterminacy Principle.
So the real model of an atom is not the one with a ball of mass formed by protons and neutrons and precise orbits of electrons surrounding it, but the one that predicts an electron cloud in which there is a greater probability of finding an electron.

Having finished with the context, of which I am not sure, I express my confusion.

It is said that the double-slit experiment demonstrates "wave-particle duality".
In this Insight article it is said that:



So my question is:
Is the fact that the double-slit experiment demonstrates wave-particle duality a misconception?
Or does the double-slit experiment (1801) really prove "wave-particle duality" but must be overcome due to the fact that the latter is an outdated concept?
Or are there particular explanations that allow this experiment to be placed in the perspective of "modern quantum theory" despite the fact that it could demonstrate "wave-particle duality"?

Historically we know two very different types of double-slit (two-slit) experiments: 1) with light and 2) with mass particles, mainly electrons.

LIGHT

First two-slit experiments with light were made by T. Young 220 years ago (in 1801 – 1803). These experiments together with many other experiments made in optics over past 220 years can be explained by the concept of light as an electromagnetic wave (based on classical Maxwell equations). However, it became clear 120 years ago that some experiments cannot be explained within the framework of the wave theory of light (such as laws of thermal radiation, photoelectric effect and some others). In 1900-1905 M. Planck and A. Einstein introduced new concept of light as a flux of some no-mass-transferring but energy and momentum carrying particles called photons a bit later. The photoelectric effect was easily explained within the framework of the photon concept. But then the unexpected happened. For 120 years, right up to the present day (2024), no one was able to combine the two concepts (light as electromagnetic wave and light as flow of photons) into one and create a satisfactory quantum field theory. An obvious and easy to understand (but very far from the only one) challenge in the existing theory (quantum electrodynamics) – no one is able to describe consistently 3D- structure and typical sizes of quantized electromagnetic waves/ photons radiated by atoms/ free electrons. For this reason, we are forced to use the concept of wave-particle duality of light until today. This means the consensus in scientific society that it is correct if we explain some experiments within frames of wave approach but explain some other experiments within concept of light as photons flow.

ELECTRONS

J.J. Thomson discovered the electron as a particle in 1897. Thirty years later, in 1927, his son G.P. Thomson discovered that the electron may exhibit wave properties when flying through crystals. In many cases diffraction of electrons in crystals may be relatively easily explained either within context of waves or within frameworks of particles or in both ways – see this video as an example.

www.wininfin.com



In 1965 R. Feynman illustrated mystic properties of wave-particle duality in case of realization of the double-slit experiment with electrons. If quantum mechanics applied to mass particles and based on the Schrodinger equation (or Feynman path integrals which is almost the same) is correct then the electron either will pass through two slits at the same time or pass through one slit but feel presence of another slit at huge distance in an inexplicable way. In 1965 R. Feynman introduced his idea as just a thought experiment, but several attempts to make such experiments have been done in recent 30 years thanks to development of nanotechnologies. Despite numerous questions and unclear points in the experimental methodologies (G. Pozzi et al, R. Bach et all, B. Barwick et al, etc.), each time very similar stable striped wave interference pictures were observed. We can say that electrons exhibit wave properties in double-slit experiments as photons do.

So, I would answer to questions raised in the post as follows: 1) double-slit experiment does not demonstrate that the wave-particle duality is a misconception 2) double-slit experiment proves validity of the “wave part” in the concept of wave-particle duality 3) ability to explain double-slit experiment will be treated as an evidence of correctness of "modern quantum theory" developed in the future.

AntonN said:

1) double-slit experiment does not demonstrate that the wave-particle duality is a misconception

The problem isn't that it's a "misconception". The problem is that it's not a useful concept; it doesn't allow you to generate any actual predictions.

AntonN said:

2) double-slit experiment proves validity of the “wave part” in the concept of wave-particle duality

That assumes that the concept of wave-particle duality is a useful concept that can generate predictions. But it isn't (see above). The double slit experiment does show that something that used to be thought of as just a wave (light) can have particle-like properties, and that something that used to be thought of as a particle (electron) can have wave-like properties. But to actually generate predictions you have to go beyond that and look at the math, and there is no "wave-particle duality" in the math. There's just the math.

AntonN said:

3) ability to explain double-slit experiment will be treated as an evidence of correctness of "modern quantum theory" developed in the future.

Um, we already have a quantum theory that can explain the double-slit experiment. We don't have to wait for some future theory.

PeterDonis said:

Um, we already have a quantum theory that can explain the double-slit experiment. We don't have to wait for some future theory.

Do you want me to respond to this comment?

AntonN said:

Do you want me to respond to this comment?

Only if you disagree with the proposition that we already have a quantum theory that explains the double-slit experiment.

Nugatory said:

Only if you disagree with the proposition that we already have a quantum theory that explains the double-slit experiment.

Sixty years ago quantum theory placed an unofficial order for the double-slit experiment with electrons because theoretically predicted its results. But unfortunately, quantum theory has not been able fully explain expected results until the present day. Thus, following our above agreements, I am responding to your comment.

Within the given thread (wave-particle duality for the double-slit experiment), one obvious challenge (among many, many others) of quantum theory can be highlighted by a very simple question- what are the trajectories of electrons inside the slits and in the near zone?

Quantum theory answers us – “sorry, I am just the math” [this is a quote from PeterDonis’s above comment and we should completely agree with Peter that the theory is just the math – AntonN] and then continues - “I give just excellent statistical (probabilistic) predictions but do not work with real (not virtual) trajectories at all. In my equations an electron is just a material point with mass, charge, energy, very often with coordinates and momentums and even with virtual paths, but all the time without real trajectories”. And these words are the undeniable truth. Quantum mechanics does not work with real trajectories.

But that is what quantum mechanics does. But our nature - it works just in the opposite way, it works with trajectories and, moreover, cannot exist without them. Denial of trajectories in quantum mechanics means its correct understanding. Denial of trajectories of real mass particles as carriers of mass (e.g. electrons) in the real atomic world around us means a huge misconception.

I am not alone in such understanding of the problem. The father of the concept of the double-slit experiment Richard Feynman invented path integrals which predict not only these particular experimental results, but also a large number of effects in worlds of atomic and elementary particles. At the same time, this great founder of quantum theory drew real trajectories of electrons in his famous “Lections” https://www.feynmanlectures.caltech.edu/III_01.html#Ch1-S4 (see fig.1-6 in there and related wording) and discussed possible changes in their momentums.

However, despite the interesting discussion, Feynman could not explain what exactly happens to the incident electrons inside the slit and how they interact with internal electrons/ atomic nuclei of the slit’s material (called him as the wall with slits and rollers for simplicity). Realizing that there was no good explanation within the “mas-particle” approach, Richard Feynman wrote “We cannot make the mystery go away by “explaining” how it works. We will just tell you how it works”.

Of course, the words spoken above are quite suitable for scientists, students and their professors, but they are absolutely not suitable for ordinary people. Due to development of informational public networks the shortcomings of quantum theory have become known to the general public and the public is demanding clarity. However, this unusual situation is beyond the scope of our thread.

Thus, there is no full-fledged quantum theory that would fully explain the double-slit experiment. There is no quantum theory that would explain many, many other effects/ experiments/ observations and answer many, many unanswered questions accumulated in existing theory. We need new quantum theory or improvement of the existing one. Again, I am not alone in such understanding. Both Einstein and de Broglie were confident in the need for a new theory and worked on its development until the end of their days.

Why many scientists/professors/PhD candidates do not have time, do not wish and sometimes aggressively react even to mentioning the need for updated quantum theory (here I mean the “oldie-goodie” quantum theory based on the Schrodinger equation and path integrals) – this is very interesting topic that has simple and clear explanations, but it is out of scope of the present thread.