B Bohr's duality paradox 100 years later?

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Nugatory

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Question of whether Britain is up or down from Australia can be answered by simply posing the correct question and that is, from what vantage point? Can a physicist answer the question of whether an electron is a wave or particle from a given vantage pointe? I submit vague answers simply means The physicist providing such answers has not solved the problem.
The vague answer is because the question not posed correctly, just as in the Australia/Britain up/down case.

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

So 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 (because it has four legs). If you want a clear answer about sheep you should ask what a sheep is instead of investigating the “paradox” of a sheep’s table-like and pillow-like behavior, and if you want a clear answer about electrons you should ask what the theory says about electrons instead of demanding that they be explained in terms of waves and particles. The difference is that we’re all familiar with sheep while many fewer people have put in the (seriously non-trivial) intellectual effort required to understand the behavior of electrons without recourse to familiar notions of waves and particles.

Two posts above to which you should pay particular attention:
1) @PeroK #23 where he points out that wave-particle duality doesn’t appear in modern textbooks (and the same is true of the QM texts I studied 40 years ago, so this is not exactly a new development). This should suggest to you that your understanding of what QM really says about electrons is not based on completely reliable sources.
2) @Demystifier #4 where he points out that we feel no need to ask whether phonons are waves or particles. There’s a serious question there for you: why do YOU believe that discussing electrons as waves or particles is necessary, but not phonons? There’s a historical reason why we do: electrons were known and discussed before the wave-particle duality notion was abandoned whereas phonons were not; but that tends to suggest that the wave-particle question is indeed badly posed.
 

Demystifier

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There’s a serious question there for you: why do YOU believe that discussing electrons as waves or particles is necessary, but not phonons?
Well, I think that both should be discussed on an equal footing. See the paper linked in my signature below.
 
Well, I think that both should be discussed on an equal footing. See the paper linked in my signature below.
And if the question of waves or particles with respect to electrons has been settled for decades ( which seems to be the consensus I've gathered here ), why would it need to be discussed for phonons?
 

Demystifier

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And if the question of waves or particles with respect to electrons has been settled for decades ( which seems to be the consensus I've gathered here ), why would it need to be discussed for phonons?
Because, given the existence of Bohmian interpretation of quantum mechanics, the question has not been settled.
 
Let me clarify: With respect to phonons only?
 
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

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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

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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.
 
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?
 
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?
 

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DrChinese

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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. :smile:

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

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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.
 
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 text books on QM is by Griffiths. Wave-particle duality is mentioned once, as a historical footnote....
In the other QM text books 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 text book 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.
 
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

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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

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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.
 

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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.
 
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?
 
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 acknowledgement that there may be unknowable aspects to our underlying reality that are outside the boundaries of the scientific method?
 

PeroK

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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 modelled 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

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Is that an acknowledgement 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

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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 acknowledgement 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

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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).
 

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