Is Wave-Particle Duality Still Relevant in Modern Physics?

[Dadface]

https://www.nature.com/search?journal=nphys&q=wave particle duality&page=1

When people come to this forum enquiring about the concept of wave particle duality the usual advice seems to be based on the idea that the concept is outdated and has historical interest only.
The problem is that many of the people who make those enquiries probably look at other sources of information and many of those sources seem to suggest that wave particle duality is not outdated at all and is still being actively researched. A quick google search will show that to be the case. just one example of this can be shown by clicking on the link above.
It seems that people get contradictory information and that can only lead to confusion.
Thank you

 

[PeroK]

 

[Dadface]

I'm not sure I like the implications of your post PeroK. I'm not sure what you mean but it's easy to interpret your post as being dismissive and somewhat rude.
Let me rephrase my post which is based on the possible reactions of people, not me, who come here for advice. Those people are often told here that wave particle duality is an outdated concept. That's fine and the people should be grateful for that advice. But those self same people often look elsewhere and find that duality is still being discussed. That can be confusing so what's wrong with me pointing that out?

 

[PeroK]

That can be confusing so what's wrong with me pointing that out?

You've pointed it out before. And before that. And before that.

Time to move on.

 

[Nugatory]

It seems that people get contradictory information...

The problem of contradictory information on the internet is unfortunately beyond our power to fix.

and that can only lead to confusion.

Someone following the links in your google search will become unconfused when they see that the linked articles are not using the phrase "wave-particle duality" in the popular sense. If we do a broader search that includes popular sources, then the sad fact is that many of these popular sources are confusing. I don't have any better ideas than to explain that the popular sources are unreliable and to provide pointers to better explanations.

 

[Demystifier]

It is my impression that the term "wave-particle duality" is used only by experimentalists as a means to make their technical experimental work more interesting to a wider community (that is, to sell it in high impact journals such as Nature Physics), and not by theoreticians who really want to better understand the principles of quantum mechanics.

 

[Dadface]

You've pointed it out before. And before that. And before that.

Time to move on.

Yes I have pointed it out before but my enquiry about duality being discussed elsewhere had been overlooked. In the previous thread I provided a link to Nature Journals which referred to duality. But the thread was then closed for moderation. I never did get any replies as to why such a prestigious journal should be amongst those numerous sources that referred to duality. The thread was eventually re opened but my link had been removed.I had been stopped in my enquiries then and now it seems you are trying to stop me by telling me to "move on".

 

[Demystifier]

@Dadface does my post #6 make sense to you?

 

[Dadface]

The problem of contradictory information on the internet is unfortunately beyond our power to fix.

Someone following the links in your google search will become unconfused when they see that the linked articles are not using the phrase "wave-particle duality" in the popular sense. If we do a broader search that includes popular sources, then the sad fact is that many of these popular sources are confusing. I don't have any better ideas than to explain that the popular sources are unreliable and to provide pointers to better explanations.

Thank you. A big problem with the Nature and other non pop science articles is getting access to them. Since they refer to duality in "the non popular sense" it might be helpful to get a definition of what duality actually is.

 

[Dadface]

@Dadface does my post #6 make sense to you?

Yes post six does make sense and thank you. My main interest is experimental physics and most references I've seen to duality refer to experimental work.

 

[UsableThought]

Thank you. A big problem with the Nature and other non pop science articles is getting access to them. Since they refer to duality in "the non popular sense" it might be helpful to get a definition of what duality actually is.

Someone following the links in your google search will become unconfused when they see that the linked articles are not using the phrase "wave-particle duality" in the popular sense.

@Dadface, looking at the search result you post in #1, as far as I can see, the only hit you got that actually related to "wave particle duality" was the first hit, for a 2014 paper; the other hits are for individual words and not the full phrase. So why not look at that first hit to see what that paper is about?

Go to this page - https://arxiv.org/abs/1501.03713 - and you can download the full PDF via this link: https://arxiv.org/pdf/1501.03713.pdf

If you (and others in this thread) read the paper, you may be able to discuss whether and how it supports your claim that wave-particle duality, as such, is "still being actively researched."

 

[Demystifier]

Yes post six does make sense and thank you. My main interest is experimental physics and most references I've seen to duality refer to experimental work.

Well, I am a theorist and I can say that wave-particle duality does not make much sense from a theoretical point of view. I hope that some experimentalist can help you more about the experimental perspective.

 

[ftr]

Well, I am a theorist and I can say that wave-particle duality does not make much sense from a theoretical point of view. I hope that some experimentalist can help you more about the experimental perspective.

So what is your view then of these fundamental entities? Neither wave nor particle, or what. Just the mathematics, correct. What is particle, hydrogen atom maybe?

 

[Demystifier]

So what is your view then of these fundamental entities? Neither wave nor particle, or what. Just the mathematics, correct. What is particle, hydrogen atom maybe?

See my https://arxiv.org/abs/quant-ph/0609163 Sec. 2.

 

[DrClaude]

It is my impression that the term "wave-particle duality" is used only by experimentalists

This is also my take on it. I think it is sloppy language.

I had a theoretician colleague who would also cringe every time he heard someone talk about "quantum jumps."

 

[ftr]

See my https://arxiv.org/abs/quant-ph/0609163 Sec. 2.

quote from your paper
"If any known interpretation of QM respects a kind of wave-particle duality, then it is the Bohmian interpretation."
I see a hint of contradiction with the myth statement.
1. What is your view of QFT then considering electron as zero dimensional.
2. Does BM consider electron as a lump or a Dirac delta.

 

[Demystifier]

1. What is your view of QFT then considering electron as zero dimensional.
2. Does BM consider electron as a lump or a Dirac delta.

1. I don't understand the question.
2. What do you mean by lump?

 

[Paul Colby]

It is my impression that the term "wave-particle duality" is used only by experimentalists

I was trained as an experimentalist and I approve this message. There is much quantum hype.

 

[vanhees71]

It's really annoying that particularly in Nature, which is a journal with a very high reputation, still admits the use of such sloppy language, but you can't help it. If I'd have been the referee, I had tried to fight against it. I've not yet reviewed articles for Nature, but for other journals it works.

Again, there's no need for wave-particle duality anymore since 1926, and one shouldn't use the phrase anymore. I think we have discussed that of course one can describe everything said in the first link in the search results in #1

http://www.nature.com/nphys/journal/v10/n4/full/nphys2931.htm

in terms of modern QED without any reference to a classical-particle picture. There's no other quantum which is less adequate described as a classical particle than the photon. It doesn't even admit to define a position observable etc. etc. We have discussed this indeed endlessly in this forum.

 

[Nugatory]

Since they refer to duality in "the non popular sense" it might be helpful to get a definition of what duality actually is.

There is no rigorous definition. When someone who knows what they're talking about uses the term "wave-particle duality", they're generally making an informal reference to some position measurement - a particle is something with a reasonably well-known position. However, the phrase is pretty much meaningless when taken out of context.

 

[Paul Colby]

Well, I have a feeling it's actually worse than just poor language. The Quantum Eraser experiments I recall looking at come off as culling the data after the fact when the fine print is read. This coupled with editorial comments on the verge of being misleading kind of clinch it for me. Just an opinion.

 

[Demystifier]

It's really annoying that particularly in Nature, which is a journal with a very high reputation, still admits the use of such sloppy language, but you can't help it.

Nature will do almost anything which will increase their impact factor, and you can't help it.

 

[Demystifier]

Well, I have a feeling it's actually worse than just poor language. The Quantum Eraser experiments I recall looking at come off as culling the data after the fact when the fine print is read. This coupled with editorial comments on the verge of being misleading kind of clinch it for me. Just an opinion.

Speaking of quantum erasers, you might be interested in my
https://arxiv.org/abs/1703.08341
Sec. 5.1.

 

[vanhees71]

Well, I have a feeling it's actually worse than just poor language. The Quantum Eraser experiments I recall looking at come off as culling the data after the fact when the fine print is read. This coupled with editorial comments on the verge of being misleading kind of clinch it for me. Just an opinion.

Quantum eraser experiments have nothing to do with wave-particle duality. The one by Walborn makes this as clear as one can get. It uses polarization-entangled photon pairs and takes carefully a coincidence-measurement protocol, so that you can after the photons have been irreversibly detected on the screen, choose partial ensembles out of the full ensemble. Without choosing the partial ensemble, it's in principle possible to gain "which-way information", i.e., with which quarter-wave plate in the corresponding slit the photon has interacted. Choosing the one or the other partial ensemble, however leads to the impossibility to gain which-way information in addition, and an interference pattern appears. The one subensemble's pattern is shifted against the other such that both together lead to the full ensemble's non-interference pattern. This is all well understood from standard Quantum Optics. No old-fashioned notion of wave-particle duality is necessary.

 

[Paul Colby]

I've always equated "shut up and calculate" with the positivist interpretation. The quantum eraser experiment all use data taken "in the past".

 

[Paul Colby]

Quantum eraser experiments have nothing to do with wave-particle duality.

Certainly, but the sociological issues are similar.

 

[Ddddx]

An unfortunate situation today in physics is that if someone says he is talking about the "Copenhagen interpretation", then it is 100% certain that what he says has absolutely nothing to do with the actual Copenhagen view of Niels Bohr.

If you want to find out what that is, you have to read Bohr's original papers. If you ask the people here who say wave-particle duality is outdated what they mean by wave-particle duality, each one will give you a different answer. I suggest you read the original works where this idea was introduced before you make up your mind whether it is outdated.

I felt that it was more so that if one created a photon, then one had made a knot in existence, a knot which was of a very difficult kind to say, and only when that photon was absorbed, annihilated, that knot was untied. And that [view] I felt, was nothing, but [that] it had to be done in that kind of way was really something which was formidable. But now we know that these are solved by the non-commutation rules, and therefore, the non-commutation rules are certainly something great. But in order to understand what they mean — You cannot get over that problem of the particle and the wave. And, therefore, it is also so nice that this lies in the complementary description.

 

[Simon Phoenix]

I hesitate to get embroiled in a thread about wave-particle duality but it is a source of confusion, and with good reason. That reason is to do with our desire to 'understand' the world in terms of intuitive pictures that make sense to us. Classical physics is a world of waves and particles - or perhaps, more generally, extended objects (fields, fluids, etc) and not-so extended objects (particles, golf balls, vortices, etc). These notions have some correspondence with what we can actually see and touch in our everyday experience and classical physics gives us great tools and pictures to understand the behaviour of these things, by and large. So it's only natural that we would want to try to explain quantum theory in these kinds of terms. It's natural that we want to build 'pictures' in terms of things we are already familiar with. So when Bohr writes :

"But in order to understand what they mean — You cannot get over that problem of the particle and the wave" [my emphasis added]

I strongly suspect this is what's behind that word 'understand' in there. So $\mathbf {IF}$ we want to cast our world-view in these familiar classical terms and pictures then we're going to have to grapple with 'duality' at some level when we enter the quantum world. Duality is more of an expression of the inadequacy of our classical pictures than any fundamental property in my view. It's only necessary if we absolutely insist on trying to straightjacket our thinking in terms of classical pictures and ideas.

And as Bohr more or less points out, ultimately, in one guise or another, it all comes down to the fact that QM requires us to represent physically observable quantities as linear operators which may not commute with one another.

In a restricted sense it is my view that wave-particle duality is still interesting and useful - after all, it's one way in which the difference between classical and quantum thinking can be starkly highlighted, just as Bell's inequality highlights another. So it's a useful notion as one way to illustrate the split between quantum and classical world views, but it's not really overly useful to either calculate stuff or to explain things.

 

[UsableThought]

It's only necessary if we absolutely insist on trying to straightjacket our thinking in terms of classical pictures and ideas.

Great post. I've pulled out the isolated snippet above just to comment that this sort of insistence on our part is very likely to be unconscious; it is after all a natural human desire to want "intuitive pictures that make sense to us." That's why commentary that brings this contrast to the surface & makes it explicit can be so helpful.

 

[ftr]

1. I don't understand the question.
2. What do you mean by lump?

1. I mean QFT clearly says that the objects are "particles" although there is a controversy about whether its position status. I was asking about your understanding regarding that.

2.quote from your paper

"Typically, the wave attains such a localized-particle shape through..."
so which one is it "localized-particle shape" or the though ...

 

[Dadface]

@Dadface, looking at the search result you post in #1, as far as I can see, the only hit you got that actually related to "wave particle duality" was the first hit, for a 2014 paper; the other hits are for individual words and not the full phrase. So why not look at that first hit to see what that paper is about?

Go to this page - https://arxiv.org/abs/1501.03713 - and you can download the full PDF via this link: https://arxiv.org/pdf/1501.03713.pdf

If you (and others in this thread) read the paper, you may be able to discuss whether and how it supports your claim that wave-particle duality, as such, is "still being actively researched."

Thank you very much. I have printed the paper off and have started to plough my way through it. After page two I find it rather heavy going and I think this illustrates a problem other people may have with the concept of duality. Most people who enquire about the subject are likely to not be theoreticians but interested amateurs or students and by doing simple searches they will come across numerous references to wave particle duality, not only in the popular science works but in academic works as well. The net is absolutely awash with the stuff. Some people might want to know what the duality referred to in the academic papers is and that is where they can get stuck.

 

[ftr]

wave-particle duality is still interesting and useful

That is the whole point, I think people want to know actually what is it exactly and not whether it is useful or not. I think there are many such things in physics giving a strong hint that something is a miss.

 

[Dadface]

There is no rigorous definition. When someone who knows what they're talking about uses the term "wave-particle duality", they're generally making an informal reference to some position measurement - a particle is something with a reasonably well-known position. However, the phrase is pretty much meaningless when taken out of context.

My take on what is meant by duality is based on what is observed not on the theories used in an attempt to explain those observations.

 

[Paul Colby]

1. I mean QFT clearly says that the objects are "particles" although there is a controversy about whether its position status. I was asking about your understanding regarding that.

(the following has nothing to do with the wave nature of light)

I don't know about this one. What do you mean by particle? For example, take a steel plate with two holes. Mount a machine gun on a flimsy trunnion designed to distribute bullets (our particles) in a gaussian distribution over the holes. Each bullet that passes through a hole is collected and counted. Now bullets that pass through hole 1 didn't pass through hole 2 and visa versa. This fact implies a anti-correlation between the bullet count between those through hole 1 and through hole 2. This correlation is independent of how many machine guns and how randomly the fire in time. Now do the same replacing the machine gun with a single mode optical fiber connected to an led. The holes are separated by a distance that interference (wavy nature) of the light plays no role at the collection point. One will find zero correlation between photons collected, nada, zip, zero. This actually has nothing to do with photons as particles in some sense and everything to do with an led being a classical light source.

One point I'd like to add. What I think QFT actually says is quanta are energy transitions between energy eigenstate of the field in question.

 

[ftr]

photons collect

But that doesn't say anything about whether the photon is a particle or a some lump or an extended object throughout the universe but an effect of it seen at that place.