Bohr's duality paradox 100 years later?

[Demystifier]

Let me clarify: With respect to phonons only?

What's your question?

 

[skewzme]

My original question was if the question of waves or particles with respect to electrons has been settled, why would it need to be discussed for phonons? You replied that it has NOT been settled.
I am asking you now to clarify if you mean that specific to phonons only. Others here seem to be saying it HAS been settled with respect to electrons.

 

[Demystifier]

My original question was if the question of waves or particles with respect to electrons has been settled, why would it need to be discussed for phonons? You replied that it has NOT been settled.
I am asking you now to clarify if you mean that specific to phonons only. Others here seem to be saying it HAS been settled with respect to electrons.

I say that it is equally unsettled for electrons and phonons.

 

[DrChinese]

My original question was if the question of waves or particles with respect to electrons has been settled, why would it need to be discussed for phonons? You replied that it has NOT been settled.
I am asking you now to clarify if you mean that specific to phonons only. Others here seem to be saying it HAS been settled with respect to electrons.

Again, different interpretations make different statements about fundamental elements of QM. From Demystifier's Bohmian viewpoint, an electron is a quantum particle with definite position at all times. Most other interpretations won't agree on that.

 

[skewzme]

Thank you for clarifying.
Why then (if I may continue this line of questioning), is this unsettled subject only a footnote in the academic community and it's textbooks? I am not interested in the woo woo propagations of the many who push it to sell books. But as a lay person interested in the subject, it does seem to me a VERY significant point if it is unanswered or still not understood. It goes to the very heart of whether our world is materialistic in nature. Or something else. Is that a fair assertion?

 

[skewzme]

Again, different interpretations make different statements about fundamental elements of QM. From Demystifier's Bohmian viewpoint, an electron is a quantum particle with definite position at all times. Most other interpretations won't agree on that.

DrChinese, I do appreciate your continue followup's to this discussion and the experience you bring to it. If I may ask, are you a Physicist by profession?

 

[Demystifier]

Why then (if I may continue this line of questioning), is this unsettled subject only a footnote in the academic community and it's textbooks?

It may be so in older textbooks, but many new textbooks have whole chapters devoted to unsettled interpretational aspects of quantum mechanics. See https://www.physicsforums.com/threads/qm-textbooks-with-interpretations.912703/

 

[DrChinese]

DrChinese, I do appreciate your continue followup's to this discussion and the experience you bring to it. If I may ask, are you a Physicist by profession?

No, I'm a software guy. And despite my name, I am neither a PhD nor Chinese.

However, I do some original research in various nooks and crannies of QM. Here is a link to one of my papers if you are interested (hopefully fairly readable): http://www.drchinese.com/David/EntangledFrankensteinPhotonsA.pdf

This paper explores an niche area of entanglement that I consider as "standard QM", but that I have never seen written about elsewhere. It is unpublished; and despite its age, I'd like to publish it (as it is still novel and I think it would be useful). Like the paper of Campbell et al, it is a suggestion for an experiment that would test one of the boundaries of QM.

 

[Lord Jestocost]

It goes to the very heart of whether our world is materialistic in nature. Or something else.

Let me again cite Paul Davies (from his introduction to Werner Heisenberg’s “Physics and Philosophy”):

“What, then, is an electron, according to this point of view [Copenhagen approach, LJ]? It is not so much a physical thing as an abstract encodement of a set of potentialities or possible outcomes of measurements. It is a shorthand way of referring to a means of connecting different observations via the quantum mechanical formalism. But the reality is in the observations, not in the electron.”

 

[skewzme]

It may be so in older textbooks, but many new textbooks have whole chapters devoted to unsettled interpretational aspects of quantum mechanics. See https://www.physicsforums.com/threads/qm-textbooks-with-interpretations.912703/

Is that so?
I took a moment to repost some previous replies in this discussion.

PeroK:
Until the 1930's this was a puzzle... Then Quantum Mechanics came along with the quantum model of an electron...
undergraduate textbooks on QM is by Griffiths. Wave-particle duality is mentioned once, as a historical footnote...
In the other QM textbooks it doesn't get a mention... That in many ways exemplifies the difference between physics as a academic subject as taught in universities and physics as popular science...

Peter Donis:
your intuition is not familiar with how quantum objects behave...
The fix for that is to retrain your intuition...

The words “particle” and “wave” were introduced many years before the theory that we now call quantum mechanics was hammered out in the late 1920s . . .

Nugatory:
it was still mistakenly (edit) assumed that those concepts would explain the surprising non-classical phenomena that were being observed at the beginning of the 20th century...

. .there’s no clear answer to the question about whether an electron is a particle or a wave for the same reason that there’s no clear answer to the question of whether a sheep is more like a pillow (because it is soft and fuzzy) or a table ...

With respect to that last entry, would a modern academic textbook on Veterinary medicine explore whether a sheep is a pillow or a table?

So in summary, is it fair to say this remains a mystery that has simply been swept aside?
Interesting.

 

[skewzme]

Let me again cite Paul Davies (from his introduction to Werner Heisenberg’s “Physics and Philosophy”):

“What, then, is an electron, according to this point of view [Copenhagen approach, LJ]? It is not so much a physical thing as an abstract encodement of a set of potentialities or possible outcomes

Okay. Is that to say the fundamental building blocks of our world are not physical things?

 

[PeroK]

Thank you for clarifying.
Why then (if I may continue this line of questioning), is this unsettled subject only a footnote in the academic community and it's textbooks? I am not interested in the woo woo propagations of the many who push it to sell books. But as a lay person interested in the subject, it does seem to me a VERY significant point if it is unanswered or still not understood. It goes to the very heart of whether our world is materialistic in nature. Or something else. Is that a fair assertion?

Let me give you a different, amateur, perspective. Standard QM requires two things.

1) that nature is inherently probabilistic.

2) that measurable quantities do not have well-defined values all the time.

This is a culture shock for anyone learning QM.

There is, however, an alternative to QM, called Bohmian mechanics, which postulates a deterministic non-probabilistic foundation on which QM may be build. @Demystifier is a leading light in This subject.

The modern debate is not about wave-particle duality per se but about this issue.

It does make answering questions on QM a bit awkward, because the convential interpretation may be countered by the Bohmian view.

The irony is that 100 years ago the probabilistic, non-realist view was radical an revolutionary; but now it's the Bohmians with their deterministic realism who are the radicals challenging the QM establishment.

 

[PeroK]

Okay. Is that to say the fundamental building blocks of our world are not physical things?

I would take an agnostic position. There are phenomena and there are (mathematical) models that explain the phenomena. The rest is metaphysics.

The problem with phrases like "building blocks" is that they preempt the debate with notions of a knowable, underlying reality.

 

[Nugatory]

So in summary, is it fair to say this remains a mystery that has simply been swept aside?

No. There are serious foundational questions that are still open (and these are not being swept under the rug - consider, for example, the amount of attention the PBR theorem has received). Bohr’s duality paradox, which is the subject of this thread, is not one of them.

 

[skewzme]

Let me give you a different, amateur, perspective. Standard QM requires two things.

1) that nature is inherently probabilistic.

2) that measurable quantities do not have well-defined values all the time.

This is a culture shock for anyone learning QM.

There is, however, an alternative to QM, called Bohmian mechanics, which postulates a deterministic non-probabilistic foundation on which QM may be build. @Demystifier is a leading light in This subject.

The modern debate is not about wave-particle duality per se but about this issue.

It does make answering questions on QM a bit awkward, because the convential interpretation may be countered by the Bohmian view.

The irony is that 100 years ago the probabilistic, non-realist view was radical an revolutionary; but now it's the Bohmians with their deterministic realism who are the radicals challenging the QM establishment.

I do understand that nature is inherently probabilistic, and that measurable quantities do not have well-defined values all the time.
Having said that, from my amateur point of view ( and I don't mean that facetiously), how does your reply address the fundamental question of whether elementary particles are physical, material objects or waves?

 

[skewzme]

The rest is metaphysics.

The problem with phrases like "building blocks" is that they preempt the debate with notions of a knowable, underlying reality.

Is that an acknowledgment that there may be unknowable aspects to our underlying reality that are outside the boundaries of the scientific method?

 

[PeroK]

I do understand that nature is inherently probabilistic, and that measurable quantities do not have well-defined values all the time.
Having said that, from my amateur point of view ( and I don't mean that facetiously), how does your reply address the fundamental question of whether elementary particles are physical, material objects or waves?

You draw a false distinction. When you say "are" you are glossing over the point that "are" really means " are mathematically modeled by".

This is at the heart of many historical debates in physics and mathematics. The history of non Euclidean geometry is a classic example.

 

[PeroK]

Is that an acknowledgment that there may be unknowable aspects to our underlying reality that are outside the boundaries of the scientific method?

If they are unknowable they are outside science by definition. I am happy to leave such questions to the philosophers and theologians.

 

[Lord Jestocost]

Okay. Is that to say the fundamental building blocks of our world are not physical things?

Not something, which allows physics to return to the reality concept of classical physics or the ontology of materialism.

Is that an acknowledgment that there may be unknowable aspects to our underlying reality that are outside the boundaries of the scientific method?

As remarked by Nick Herbert in “Quantum Reality: Beyond the New Physics”:

"One of the best-kept secrets of science is that physicists have lost their grip on reality."

 

[zonde]

As I understand Bohr with his complementarity principle meant that reality is somehow fundamentally fuzzy and this should be accepted as inevitable property of reality. But then it seems there is nothing much to discuss:
- either you accept this Bohr's philosophical position that reality is fuzzy and then it means you believe that wave-particle duality paradox can not be resolved
- or you do not accept it and in this case you look for some not-so-fuzzy description of reality and there definitely are some option to chose from.
So I would say that wave-particle duality is not really a paradox (it is a paradox only if you believe it is a paradox).

 

[PeroK]

I do understand that nature is inherently probabilistic, and that measurable quantities do not have well-defined values all the time.
Having said that, from my amateur point of view ( and I don't mean that facetiously), how does your reply address the fundamental question of whether elementary particles are physical, material objects or waves?

Let me finish with one example to make you analyse what you mean by physical material object.

Take an electron and a proton. Each has a certain mass. Let's assume that they really are physical material objects and the mass, of course, represents the amount of physical material in each.

Now you put the two together to form a hydrogen atom. The mass of the hydrogen atom must be the sum of its parts.

But, actually, it's not. It is less than the mass of the particles that make it up. It is in fact less by the amount of binding energy in the atom.

Now this doesn't prove that particles aren't particles. But it does show that a simplistic requirement that particles be well-defined material things is misplaced.

It forces you to reconsider the concept of particles, mass and the nature of physical quantities.

How much of your mass is the particles that make you up and how much is binding energy or other nuclear energy? Is nuclear energy material too?

The irony of one of your previous questions is that 20tb century scientists did not sweep anything aside. Instead, they looked in every last nook and cranny to establish as wide and deep an understanding of nature as possible. They discovered more things than were ever imagined in any discussion about wave-particle duality.

 

[zonde]

Take an electron and a proton. Each has a certain mass. Let's assume that they really are physical material objects and the mass, of course, represents the amount of physical material in each.

Now you put the two together to form a hydrogen atom. The mass of the hydrogen atom must be the sum of its parts.

But, actually, it's not. It is less than the mass of the particles that make it up. It is in fact less by the amount of binding energy in the atom.

Now this doesn't prove that particles aren't particles. But it does show that a simplistic requirement that particles be well-defined material things is misplaced.

It forces you to reconsider the concept of particles, mass and the nature of physical quantities.

How much of your mass is the particles that make you up and how much is binding energy or other nuclear energy? Is nuclear energy material too?

I think that you just described one thing that actually is swept under the carpet - that particles do not seem to "contain" the mass.

 

[skewzme]

As I understand Bohr with his complementarity principle meant that reality is somehow fundamentally fuzzy and this should be accepted as inevitable property of reality. But then it seems there is nothing much to discuss:
- either you accept this Bohr's philosophical position that reality is fuzzy and then it means you believe that wave-particle duality paradox can not be resolved
- or you do not accept it and in this case you look for some not-so-fuzzy description of reality and there definitely are some option to chose from.
So I would say that wave-particle duality is not really a paradox (it is a paradox only if you believe it is a paradox).

As I said previously, I do not consider the question a paradox in the truest sense of the word.
With respect to the not-so-fuzzy options to chose from, is there any kind of consensus or majority accepted option at this point in time? Or, is a fuzzy description the more agreed upon option at this stage in our scientific understandings?

 

[Nugatory]

I think that you just described one thing that actually is swept under the carpet - that particles do not seem to "contain" the mass.

How is that being swept under the carpet? If we had a dollar for every time that we pointed out that total energy is a property of a system as a whole and not attached to the individual components Greg would be able to pay us mentors.

There is a big difference between "not fully covered in elementary texts and totally misdescribed by popularizations" and "unsolved problem that's being ignored because it's under the carpet".

 

[Nugatory]

With respect to the not-so-fuzzy options to chose from, is there any kind of consensus or majority accepted option at this point in time?

Quantum mechanics, as covered at the level of for example Ballentine, can reasonably be considered majority-accepted for purposes of a B-level thread. That's not saying that Ballentine is a B-level reference - it's not - nor that it is free of controversy, just that you need that level of understanding to take on the stuff that's not yet settled.

 

[skewzme]

Quantum mechanics, as covered at the level of for example Ballentine, can reasonably be considered majority-accepted for purposes of a B-level thread. That's not saying that Ballentine is a B-level reference - it's not - nor that it is free of controversy, just that you need that level of understanding to take on the stuff that's not yet settled.

Appreciate that reference. I intend to read it.

 

[skewzme]

Why did the electron cross the slit undetected?

So he could "wave" from the other side . . .

 

[A. Neumaier]

I'm surprised that so few physicists ask the following question: Is phonon (the quantum of sound) a wave or a particle?

Because they know that it is a quasiparticle.

 

[Demystifier]

Because they know that it is a quasiparticle.

But photon is also a "quasiparticle", in the sense that photon is not a fundamental object in QED, but a collective excitation of EM field at all spatial points. The similarity between phonon and photon is particularly manifest if one considers QED on a lattice.

Moreover, in principle one could do a two-slit experiment with a single phonon followed by the phonon position detection (such experiment has not yet been done, but it is possible in principle), in which case the question whether the phonon is wave or particle would make perfect sense.

 

[A. Neumaier]

But photon is also a "quasiparticle", in the sense that photon is not a fundamental object in QED

A free (asymptotic) photon, unlike a phonon, is an asymptotic bound state of a QFT (here of QED), in addition to being an elementary excitation of the electromagnetic field.

Thus in solid state physics, a phonon is not a fundamental object while in QED, a photon is fundamental.

Only its particle status is questionable. Unlike free photons, photons in glass are quasiparticles traveling at a speed much lower than the vacuum speed of light (something impossible for a QED photon). Photons in air (with which standard experiments are done) are, strictly speaking, also quasiparticles, but with properties are very close to those of a free photon. When light passes through a prism placed in a vacuum, the nature of the photon changes upon entering and leaving the prism from being a true asymptotic particle to being a quasiparticle to being again a true particle.

This shows that the particleness of an excitation is to 100% a convenient fiction, to be taken seriously only in a figurative sense.