I Is Wave-Particle Duality Still Relevant in Modern Physics?

[weirdoguy]

Do you know quantum field theory? If not, it's hard to answer this question.

 

[UsableThought]

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.

Sorry, I don't understand. Why do you say a photon does not have a position observable?

@Ralph Dratman, some previous forum threads touching on this:

April 1, 2010 Photon-observer meaningless?

July 4, 2010 Is position not an observable of a photon?

Jan. 6, 2012 How Does QFT Describe or Predict the Position of a Particle?

Oct. 24, 2014 Quantum objects and Electromagnetic waves

Feb. 6, 2016 Interference pattern, one particle at a time

April 8, 2016 What is quantum equation of single photon?

April 19, 2016 Lower speed of light inside a transparent medium

July 17, 2016 What is a Photon

 

[Joseph M. Zias]

Well just a note from a practitioner. This week I am re-reading QED by Feynman, that little paper back book. Feynman is emphatic that all EM radiation is in particles, i.e. Photons. OK, who am I to disagree. However, while my education was in education/physics I am also a PE in Electrical Engineering. I assure you that when thinking of antennas I am thinking of waves. It's easy, the math isn't bad, and what I build works. In many cases we are given a theory that is Wrong but it gives us some comfort thinking we know why something works, Feynman argued that we don't know Why and may never but we can calculate. This is so often seen in textbooks trying to give the reader a theory on why an electric circuit works. You could skip all that and just give the laws, Kirchoff's etc. But we just can't leave it alone as-it-were, the author just has to give the reader some theory he can grasp (author and reader). So we have all those Bad theories on why an electric current flows in a circuit. A few physicists actual knew the answer but it was just a page or so in their texts and I don't think a lot of engineers read them.
I am currently teaching a first year college physics course from a Modern text. Yep, particle/wave duality is there. Some really good texts still avoid the issue as much as possible.

 

[bhobba]

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.

The fact is physicists often resort to heuristics and wave-particle duality, plus tons of other stuff falls into that category.

And yes based on the writings of Neils Bohr and others what Copenhagen is, is reasonably well known:
https://en.wikipedia.org/wiki/Copenhagen_interpretation#Overview

And yes it includes the idea of wave particle duality.

But how long ago was that around? A long long time ago. Along with complementary that I never understood anyway. Since then a lot of water has passed under the bridge and its well and truly outdated. Interestingly Einstein had his own interpretation - the Ensemble interpretation that has survived a lot better. Interesting isn't it.

These days, while Copenhagen is still about its modern variant is Consistent Histories which makes an interesting read:
http://quantum.phys.cmu.edu/CQT/index.html

I much prefer it to Copenhagen, but for me the Ensemble cuts right to the heart of the matter and is my preferred interpretation. Maybe Einstein was correct after all even though its generally assumed Bohr won their debates.

Weinberg thinks both of them wrong and Copenhagen deeply flawed:
http://www.fisica.ufmg.br/dsoares/cosmos/10/weinberg-einsteinsmistakes.pdf

I wouldn't go that far - but there is no doubt the modern view of QM has changed a lot from the early pioneers, and yes wave-particle duality is gone except as a sometimes useful heuristic helpful in beginner texts for developing intuition.

Thanks
Bill

 

[vanhees71]

Was Planck really too optimistic in thinking that "old-fashioned wrong ideas" die out with the people who have been using them, because the new generation of physicists will be trained using the "modern right ideas"?

There seems to be a lot more inertia an teaching physics students than Planck had envisaged. Particularly most new textbooks on QT start with (a) a very bad picture of photons, (b) wave-particle duality, and even some with (c) the Bohr-Sommerfeld model of the hydrogen atom, hammering into the students' minds the very wrong idea of trajectories of electrons around the nucleus and all kinds of other "old-fashioned wrong ideas".

The same holds for electromagnetism, where most textbooks follow the classic textbooks of the late 19th/early 20th century (the overwhelming influence of Hertz's and Lorentz's then brillant texts might be a reason) and introduce a version, where the matter is treated non-relativistically and then discussing apparent "paradoxes" of the old times before Einstein ein Minkowski.

It's so sad!

 

[bhobba]

It's so sad!

Indeed it is.

But the rot seems to start at HS. What's done in grade 11 and 12 should be done in 9 and 10 then they can start on a proper calculus based general physics course in 11 and 12. That can be revamped to teach people QM properly from the start. Then at university you can start with something like Griffiths then Ballentine in the senior years. You will not believe in wave-particle duality once you have studied that book and you will know where Schrodinger's equation etc really comes from.

And the quality of HS physics teachers needs a revamp. I well remember it was in black and white in our textbook - magnetic fields do not affect light. I remember taking that one up with my physics teacher since I knew of the classic experiment by Faraday - yes that long ago by the great scientist - that showed otherwise. He ran some light through crossed polarizes so obviously no light came out. Then he inserted a magnetic field and wondrously light now came out. What was my physics teacher answer - polarized light is not normal light. At that point I gave up.

Thanks
Bill

 

[Jaydwill10]

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

@Dadface I can understand your frustration with this subject. It is sort of a discontinuous description of the "wave - particle duality" phenomenon. I agree with @Nugatory, there's nothing we can do about the incorrect or misleading information inn the internet. But if you just want a better explanation of this part of nature, Quantum Field Theory has a great explanation of the phenomenon that's rooted in experiment.

Check out these videos:

For a quick overview:


For a deeper look at the mathematics:
Zee QFT Lectures:
Zee QFT Lectures: http://www.youtube.com/playlist?list=PLFGkcCB1-x2cVDcUJHu0XFbfYFUzELcxR

Let me know if this helps, or if I'm preaching to the choir.

 

[fanieh]

Indeed it is.

But the rot seems to start at HS. What's done in grade 11 and 12 should be done in 9 and 10 then they can start on a proper calculus based general physics course in 11 and 12. That can be revamped to teach people QM properly from the start. Then at university you can start with something like Griffiths then Ballentine in the senior years. You will not believe in wave-particle duality once you have studied that book and you will know where Schrodinger's equation etc really comes from.

And the quality of HS physics teachers needs a revamp. I well remember it was in black and white in our textbook - magnetic fields do not affect light. I remember taking that one up with my physics teacher since I knew of the classic experiment by Faraday - yes that long ago by the great scientist - that showed otherwise. He ran some light through crossed polarizes so obviously no light came out. Then he inserted a magnetic field and wondrously light now came out. What was my physics teacher answer - polarized light is not normal light. At that point I gave up.

Thanks
Bill

Bill. You often recommended this book Fields of Color https://www.amazon.com/dp/B017YCDXNM/?tag=pfamazon01-20 that I indeed bought one.

Do you think Feynman is to be blamed too for believing in particles? What do you make of the following excerpt in the book:

"A minority view. I should warn you that most physicists today do not accept this view. They either follow Feynman in believing that photons are particles, or they believe in wave-particle duality, paradoxical as these views may be. And many, like Stephen Hawking, just don't worry about the problem. To me, the persistence of and insistence on a belief in particles or in wave-particle duality, despite the phenomenal success of QFT (see Chapter 7), is in itself a bit of a paradox."

The view the author described was field collapse, but let's just focus on Feynman, did he really believe in particles?

 

[dextercioby]

I believe in mathematics. A lot of what's not spelled out mathematically in theories of physics is merely unuseful philosophy.

 

[bhobba]

Do you think Feynman is to be blamed too for believing in particles? What do you make of the following excerpt in the book:

Rodney wrote what I think is a good book at the lay level but he did get a few things wrong. Feynman didn't advocate particles and Schwinger fields. They both advocated exactly the same thing - Quantum Field Theory but had different approaches.

Feynman was the inuitionist without peer. He liked private languages he invented and doing things his own way. He invented Feynman diagrams and the language of virtual particles etc. It turned out to greatly simplify QFT calculations. Schwinger on the other hand was a perfectionist - his lectures were a thing of beauty and he relished doing long complicated calculations. Then we have this guy called Dyson who was a good friend of Feynman but never really got a grip on him as a person - I don't think many did - Feynman was a bit of a maverick character in his world view and the way he acted. At first Dyson called Feynman half genius and half buffoon, but after a while changed that to all genius and all buffoon. You could not find two characters different than Feynman and Schwinger. Well Dyson thought this state of affairs rather odd - two different characters and two different approaches - yet they both seem to work. Why? Well he figured it out - they were really the same theory in different language. Since Feynman's methods were simpler to apply and more intuitive he triumphed and Schwinger's long laborious approach became a backwater. But I must again emphasize - they are the same theory as shown by Dyson.

Just as an amusing anecdote when Dyson gave a lecture on his derivation Feynman was in the audience cracking jokes and leaving those near him in stitches - he never took it that seriously because he knew his methods worked. At the end he said - your in doc. This was obviously a reference to the fact Dyson never got a PhD. He published many brilliant works and getting a PhD is only one way to get a doctorate - you can get a doctorate by simply applying and presenting your published works. If they are good enough - and without a doubt Dyson's was - you then get what's called a Sc D - Doctor Of Science - actually considered above a PhD. I don't think Dyson even did that. This would have appealed greatly to a non conformist like Feynman. He secretly wished he had done the same - he would have relished the idea of saying to someone - even I know that and I don't even have a PhD. In fact one of my professors did it that way. He left unii and went to work immediately for IBM on operations research. He never got a PhD but using his published papers got a Sc D. I never heard him say it, but a number of my friends told me he would often say - these guys with PhD's - they shouldn't be calling themselves doctors. Mostly he berated me saying I could do better because I didn't do as well in his OR class as he thought I should have - I still got an Honor but evidently my exam paper wasn't up to the standard he thought I could achieve. Actually he was right - I was concentrating more on my computing subjects - Data Structures and Systems Analysis at the time knowing I wasn't going into a career in OR.

Feynman, and to some extent even Dyson were/are indeed characters.

Thanks
Bill

 

[Simon Phoenix]

I thought it might be useful for some to see one situation where 'wave-particle' duality arises. I think it's useful to remind ourselves why the idea ever arose in the first place. I'm going to imagine a world in which we can perform perfect experiments and I'm going to be a little bit cavalier with language in an attempt to get the basic ideas across. For this I hope I can be forgiven.

We're going to imagine that we have something we're going to call a 'single-photon source' that spits out these (hypothetical) photons at the rate of 1 every second. We've done experiments on this source and, sure enough, if we put a detector at the output we see that we get a 'click' every second. Furthermore, we don't seem to ever be able to generate 'half a click'. So we feel justified in thinking that we have some source that is producing little blobs of energy that can't be divided.

Now it's perfectly possible to construct a theory in which the supposed photons are just classical fields and the discrete clicks occur because of quantum 'stuff' in the atoms of the photodetector. Whilst this works OK for a source feeding directly into the detector, it's not really all that good when we put beamsplitters in there. Classical fields behave in a certain way at beamsplitters - for a 50:50 splitter, half of the field goes one way and half the other way. So let's see why we might think we actually have 'particles' we call photons.

Let's look at experiment 1 here. We fire our single photons into the BS (we assume 50:50). We find that one of the detectors, at random, clicks every second, but never both. That's very hard to explain if we had a classical EM field going in there - we'd get 'half' of the field going to detector A and half going to detector B. If 'half' of a field is sufficient to fire a detection event, why do we never see both detectors fire? Furthermore, we find that all of the energy ends up at one detector - so if something was going on both paths the energy only arrives at one place or t'other. Echoes of non-locality here.

But there is a neat explanation for experiment 1. Suppose we really did have these indivisible blobs we call particles - then if the particle goes one way or the other, at random, at the beamsplitter we'd get exactly the observed behaviour. So at this point we feel fairly confident, armed with such a neat and simple explanation, that we have particles.

But now we do experiment 2. We bring the outputs from the first BS and feed them into a second BS. Based on our interpretation of experiment 1 we'd expect that we're going to get exactly the same behaviour at detectors C and D - one or other will fire at random, but never both.

But suppose we put a phase modulator in the output arms from the first BS. Now what do we find? We find that we can find settings such that detector C fires every second, or detector D fires every second - in other words we have a switch. This depends on the $relative$ setting of the modulators. How can this be? Haven't we already established that we have something going one way, and nothing the other? So one modulator acts on something, but what is the other modulator acting on? So clearly $something$ must be going on both paths. This is just the interference we'd expect from classical waves so problem solved! It's a classical wave after all.

But hang on - now we can't explain the properties of experiment 1. So we're left with a dilemma. Particles explain experiment 1 very nicely, but fail at explaining experiment 2. Waves explain experiment 2 very nicely, but can't explain experiment 1. Therein lies our problem. Do we have 'waves' or 'particles'?

There's nothing paradoxical about nature, of course, the problem, or apparent paradox, here is generated by our attempt to explain things in terms of particles and waves. It just doesn't work. So what do we conclude? That nature is somehow schizophrenic - or that there's something wrong with the way we're trying to explain things? Obviously it has to be the latter

So we see in this really simple couple of experiments why there's an issue at all - the correct conclusion to draw isn't that wave-particle duality exists, it's that there's something wrong with our interpretation of what's going on. I'm sorry if I'm just teaching my grandmother to suck eggs here* - but I hope some find it useful.

*this is a bizarre UK phrase which means "stating the bleedin' obvious"

 

[fanieh]

If particles are just momentum and energy of the fields. How come we don't see several pieces of the electrons in the detectors in the double slit experiments just only one hit?

According to Neumaier. The electrons are indeed scattered in the detectors but only one detector got visible because the detectors have limited energy and only one detector can be energized. Could he be right. Neumaier math skills exceed that of Einstein many times over so we can't just discount him easily.

 

[vanhees71]

I thought it might be useful for some to see one situation where 'wave-particle' duality arises. I think it's useful to remind ourselves why the idea ever arose in the first place. I'm going to imagine a world in which we can perform perfect experiments and I'm going to be a little bit cavalier with language in an attempt to get the basic ideas across. For this I hope I can be forgiven.

We're going to imagine that we have something we're going to call a 'single-photon source' that spits out these (hypothetical) photons at the rate of 1 every second. We've done experiments on this source and, sure enough, if we put a detector at the output we see that we get a 'click' every second. Furthermore, we don't seem to ever be able to generate 'half a click'. So we feel justified in thinking that we have some source that is producing little blobs of energy that can't be divided.

Now it's perfectly possible to construct a theory in which the supposed photons are just classical fields and the discrete clicks occur because of quantum 'stuff' in the atoms of the photodetector. Whilst this works OK for a source feeding directly into the detector, it's not really all that good when we put beamsplitters in there. Classical fields behave in a certain way at beamsplitters - for a 50:50 splitter, half of the field goes one way and half the other way. So let's see why we might think we actually have 'particles' we call photons.

View attachment 205440
Let's look at experiment 1 here. We fire our single photons into the BS (we assume 50:50). We find that one of the detectors, at random, clicks every second, but never both. That's very hard to explain if we had a classical EM field going in there - we'd get 'half' of the field going to detector A and half going to detector B. If 'half' of a field is sufficient to fire a detection event, why do we never see both detectors fire? Furthermore, we find that all of the energy ends up at one detector - so if something was going on both paths the energy only arrives at one place or t'other. Echoes of non-locality here.

But there is a neat explanation for experiment 1. Suppose we really did have these indivisible blobs we call particles - then if the particle goes one way or the other, at random, at the beamsplitter we'd get exactly the observed behaviour. So at this point we feel fairly confident, armed with such a neat and simple explanation, that we have particles.

But now we do experiment 2. We bring the outputs from the first BS and feed them into a second BS. Based on our interpretation of experiment 1 we'd expect that we're going to get exactly the same behaviour at detectors C and D - one or other will fire at random, but never both.

But suppose we put a phase modulator in the output arms from the first BS. Now what do we find? We find that we can find settings such that detector C fires every second, or detector D fires every second - in other words we have a switch. This depends on the $relative$ setting of the modulators. How can this be? Haven't we already established that we have something going one way, and nothing the other? So one modulator acts on something, but what is the other modulator acting on? So clearly $something$ must be going on both paths. This is just the interference we'd expect from classical waves so problem solved! It's a classical wave after all.

But hang on - now we can't explain the properties of experiment 1. So we're left with a dilemma. Particles explain experiment 1 very nicely, but fail at explaining experiment 2. Waves explain experiment 2 very nicely, but can't explain experiment 1. Therein lies our problem. Do we have 'waves' or 'particles'?

There's nothing paradoxical about nature, of course, the problem, or apparent paradox, here is generated by our attempt to explain things in terms of particles and waves. It just doesn't work. So what do we conclude? That nature is somehow schizophrenic - or that there's something wrong with the way we're trying to explain things? Obviously it has to be the latter

So we see in this really simple couple of experiments why there's an issue at all - the correct conclusion to draw isn't that wave-particle duality exists, it's that there's something wrong with our interpretation of what's going on. I'm sorry if I'm just teaching my grandmother to suck eggs here* - but I hope some find it useful.

*this is a bizarre UK phrase which means "stating the bleedin' obvious"

This only shows once more that there is no wave-particle duality but only QFT, and photons cannot be adequately described otherwise. They are neither particles nor waves in any classical way but single-photon Fock states of the quantized em. field.

 

[Dadface]

Thank you very much Jaydwill10. I had sat through the David Tong video before. Overall I think he's a good speaker and considering the time he had I think he gives a good introductory talk on what QFT is about. I haven't yet looked at the Zee lectures but i will do.

 

[fanieh]

Why haven't we heard the words "vector-particle" duality.. why always "wave-particle" duality?

 

[Nugatory]

Why haven't we heard the words "vector-particle" duality.. why always "wave-particle" duality?

Because the vector space formalism of modern (post 1925) quantum mechanics is what replaced the older notion of wave-particle duality. There's no duality needed in the modern formalism, just a uniform treatment of quantum particles whose position is more or less well defined.

 

[Simon Phoenix]

This only shows once more that there is no wave-particle duality but only QFT, and photons cannot be adequately described otherwise. They are neither particles nor waves in any classical way but single-photon Fock states of the quantized em. field.

Absolutely - I was aiming at people who might be viewing this thread who were a little bit puzzled over what the issue was and why it still crops up. So I was hoping a simple example would help illustrate why thinking in terms of 'waves' or 'particles' is a problem - again for those reading who might still be questioning these things. I don't know whether I helped or hindered, or even whether my target audience even exists on these forums

 

[UsableThought]

I don't know whether I helped or hindered, or even whether my target audience even exists on these forums

I used to run into a gap like this when I was a writing coach for professionals in various fields (law, business, psychology, etc.). If someone wanted to write a book, say, but had never done it, I could teach them how a book worked in terms of writing for a particular audience, structuring the content, etc. A huge number of professionals need to write as part of their work; but very few could be my clients. I used to envision them as a spectrum: On one side were the small number who already wrote well; clearly they knew the importance of craft, since they practiced it; and clearly they had no need of my services. On the other side, and far more numerous, were those who wrote poorly & neither knew nor cared; they too had no need of my services. This left only a skinny slice in the middle to whom my services might appeal: these persons not only cared very much, but they knew they needed help: perhaps they were out of practice, or had a block of some sort (not uncommon), or simply needed to learn a genre that was new to them, e.g. full-length books. They were strong in the basic skills; all they lacked was a small but essential set of advanced skills. For them, I was perfect. But they were very few in number. I get the impression a similar divide exists in many other areas involving teaching or presentation. Humbleness is the road to learning, but not everyone wants to take that road.

 

[Dadface]

Much of this discussion relates to peoples interpretation and definition of what wave particle duality is. In response to a question I posed earlier in this thread Nugatory replied; "There is no rigorous definition" and that, I think, illustrates the problem.

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.

It seems that a lot of people here are theoreticians and professionals and it seems that their take on duality relates to the theory used in an attempt to explain the observations. My take on duality relates not to the theory but to the observations themselves: to the experiments and the results obtained when carrying out their experiments. And when I do google searches it seems I'm not on my own.

I came across loads of things with a quick search this morning and I'll mention just one of them, a publication in Letters to Nature entitled "Wave Particle Duality" of C60 molecules. The paper is co authored by Zeilinger, a Mr Big in the world of quantum optics. From what I've gathered so far C60 molecules display many characteristics of classical particles but can also display interference.

 

[Dadface]

I thought it might be useful for some to see one situation where 'wave-particle' duality arises. I think it's useful to remind ourselves why the idea ever arose in the first place. I'm going to imagine a world in which we can perform perfect experiments and I'm going to be a little bit cavalier with language in an attempt to get the basic ideas across. For this I hope I can be forgiven.

We're going to imagine that we have something we're going to call a 'single-photon source' that spits out these (hypothetical) photons at the rate of 1 every second. We've done experiments on this source and, sure enough, if we put a detector at the output we see that we get a 'click' every second. Furthermore, we don't seem to ever be able to generate 'half a click'. So we feel justified in thinking that we have some source that is producing little blobs of energy that can't be divided.

Now it's perfectly possible to construct a theory in which the supposed photons are just classical fields and the discrete clicks occur because of quantum 'stuff' in the atoms of the photodetector. Whilst this works OK for a source feeding directly into the detector, it's not really all that good when we put beamsplitters in there. Classical fields behave in a certain way at beamsplitters - for a 50:50 splitter, half of the field goes one way and half the other way. So let's see why we might think we actually have 'particles' we call photons.

View attachment 205440
Let's look at experiment 1 here. We fire our single photons into the BS (we assume 50:50). We find that one of the detectors, at random, clicks every second, but never both. That's very hard to explain if we had a classical EM field going in there - we'd get 'half' of the field going to detector A and half going to detector B. If 'half' of a field is sufficient to fire a detection event, why do we never see both detectors fire? Furthermore, we find that all of the energy ends up at one detector - so if something was going on both paths the energy only arrives at one place or t'other. Echoes of non-locality here.

But there is a neat explanation for experiment 1. Suppose we really did have these indivisible blobs we call particles - then if the particle goes one way or the other, at random, at the beamsplitter we'd get exactly the observed behaviour. So at this point we feel fairly confident, armed with such a neat and simple explanation, that we have particles.

But now we do experiment 2. We bring the outputs from the first BS and feed them into a second BS. Based on our interpretation of experiment 1 we'd expect that we're going to get exactly the same behaviour at detectors C and D - one or other will fire at random, but never both.

But suppose we put a phase modulator in the output arms from the first BS. Now what do we find? We find that we can find settings such that detector C fires every second, or detector D fires every second - in other words we have a switch. This depends on the $relative$ setting of the modulators. How can this be? Haven't we already established that we have something going one way, and nothing the other? So one modulator acts on something, but what is the other modulator acting on? So clearly $something$ must be going on both paths. This is just the interference we'd expect from classical waves so problem solved! It's a classical wave after all.

But hang on - now we can't explain the properties of experiment 1. So we're left with a dilemma. Particles explain experiment 1 very nicely, but fail at explaining experiment 2. Waves explain experiment 2 very nicely, but can't explain experiment 1. Therein lies our problem. Do we have 'waves' or 'particles'?

There's nothing paradoxical about nature, of course, the problem, or apparent paradox, here is generated by our attempt to explain things in terms of particles and waves. It just doesn't work. So what do we conclude? That nature is somehow schizophrenic - or that there's something wrong with the way we're trying to explain things? Obviously it has to be the latter

So we see in this really simple couple of experiments why there's an issue at all - the correct conclusion to draw isn't that wave-particle duality exists, it's that there's something wrong with our interpretation of what's going on. I'm sorry if I'm just teaching my grandmother to suck eggs here* - but I hope some find it useful.

*this is a bizarre UK phrase which means "stating the bleedin' obvious"

Hello Simon. The experimental set up is similar to what I've seen elsewhere and I think it illustrates nicely the point you were making. However, on a technical point can I enquire as to whether the experiment has actually been carried out?

 

[Simon Phoenix]

My take on duality relates not to the theory but to the observations themselves: to the experiments and the results obtained when carrying out their experiments

Hi Dadface, I'm afraid I really don't know what you mean by this.

You run an experiment, you get results. If you try to interpret the experiment then you might think in terms of 'waves' in order to explain those results, or you might think in terms of 'particles' (or indeed, something else perhaps). The 'wave' or 'particle' bit comes in whenever we try to interpret things - be that theory, or experimental results. So what are you trying to say here? That somehow experiments 'show' wave-particle duality in a way that is not dependent on the interpretation of that experiment?

 

[UsableThought]

It seems that a lot of people here are theoreticians and professionals and it seems that their take on duality relates to the theory used in an attempt to explain the observations. My take on duality relates not to the theory but to the observations themselves: to the experiments and the results obtained when carrying out their experiments.

If you really want to make a claim of this sort, you have to support it; which means pointing to specific instances where this has occurred. You need to quote from posts & build the argument that "theoreticians and professionals" are ignoring observations from what they say.

Before you even attempt it, stop & think what your claim implies. You are saying that "theoreticians and professionals" have gone off into a blind alley where their explanations of observations are false because they no longer refer to wave-particle duality in the same way as before. (You have not used the actual word "false" but I'd contend you are implying falsity). You are further saying that although you have admitted to struggling with the material (e.g. the paper I linked to & suggested you read), you are somehow wiser than these theoreticians and professionals. I am trying to imagine a world in which this could be true: someone who is not a professional himself, and who has only a limited understanding of the subject at hand, somehow is right while the professionals are wrong. How is this going to happen? The poverty of trying to rely on web searches to support your argument has already been explained to you; but it has not dented your self-confidence that somehow your stance as an amateur who relies on search results he doesn't understand is superior to persons who have actually put in long hard years of study within a shared scientific community.

Here is the quote where you admit that you can't grasp the paper you downloaded; I have bolded what seems especially pertinent:

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.

Just to say it, the net is awash with many things, including badly written articles and papers, articles and papers we don't understand, and beyond that conspiracy theories and lies. Our increasing inability to handle this flood of information wisely is a massive & growing problem in today's culture, as I mentioned in an earlier comment (which I would encourage you to reread).

The hard thing for you to do would be to first see & then admit that you are caught in a trap; specifically, trapped by a stubborn insistence that although you lack full understanding of the subject, you don't require this understanding to be skeptical. I am not criticizing you personally and I apologize if it seems that way; what I am criticizing here is only the stance you are taking. You are willing to doubt the scientific community and the methods they use with very little evidence; but apparently unwilling to doubt the methods you are relying on yourself. Whereas to me, the capacity for self-doubt is an important part of how we learn. There have been many times I've finally realized I've been wrong on a subject & others have been right; it's been hard every time to actually admit it; but it's been important for me to do so. If I couldn't admit those times I've been wrong, I'd never learn. I'm thinking about mathematics right now, but I think it applies to all fields.

P.S. Your smaller claim that interested amateurs may find the change in presentation confusing is quite different; this seems fully supportable, even just using your own experience as an example. That claim has been responded to; however it seems you are not satisfied by the answers. I mention this only because back when I taught essay-writing, including argumentative essays, I often had students run into trouble with overly broad claims that they felt deeply, but couldn't support. One of my suggestions was to rephrase their claim so as to present it entirely in terms of their personal experience; e.g. rather than claim "Such-and-such must be wrong because I am puzzled," they could simply say, "It seems to me as if such-and-such is wrong because of how it puzzles me." This could lead to a line of questioning that would ultimately be more fruitful for them.

 

[vanhees71]

Much of this discussion relates to peoples interpretation and definition of what wave particle duality is. In response to a question I posed earlier in this thread Nugatory replied; "There is no rigorous definition" and that, I think, illustrates the problem.

There is not only no rigorous definition, there's no wave-particle duality. This is an idea from the socalled "old quantum theory", which was a way to describe phenomena that are not accuartly described by classical physics in an ad hoc way. In 1925/26 modern quantum theory has been discovered, which lead to a consistent description of all phenomena, and particularly inconsistent ad hoc ideas of the old QT, among them wave-particle duality, are no longer necessary. According to modern QT, there is no wave-particle theory but just QT with its probabilistic implications about the behavior of matter.

It seems that a lot of people here are theoreticians and professionals and it seems that their take on duality relates to the theory used in an attempt to explain the observations. My take on duality relates not to the theory but to the observations themselves: to the experiments and the results obtained when carrying out their experiments. And when I do google searches it seems I'm not on my own.

There are no observations of wave-particle duality. As I said, wave-particle duality is an obsolete theory from over 90 years ago. All what we observe is interpretible within modern QT, and there is no wave-particle duality anymore.

I came across loads of things with a quick search this morning and I'll mention just one of them, a publication in Letters to Nature entitled "Wave Particle Duality" of C60 molecules. The paper is co authored by Zeilinger, a Mr Big in the world of quantum optics. From what I've gathered so far C60 molecules display many characteristics of classical particles but can also display interference.

Yes, but it's all modern QT, no wave-particle duality. What's showing interference effects are the probability amplitudes of modern QT. The interference effects are gone, if the C60 molecules are interacting with their environment, e.g., if they are not kept at very low temperatures and thus emit photons ("thermal radiation"). That's enough to lead to decoherence and a more classical-particle like behavior of the corresponding probabilities.

 

[Dadface]

Hi Dadface, I'm afraid I really don't know what you mean by this.

You run an experiment, you get results. If you try to interpret the experiment then you might think in terms of 'waves' in order to explain those results, or you might think in terms of 'particles' (or indeed, something else perhaps). The 'wave' or 'particle' bit comes in whenever we try to interpret things - be that theory, or experimental results. So what are you trying to say here? That somehow experiments 'show' wave-particle duality in a way that is not dependent on the interpretation of that experiment?

Thank you .My take on duality has nothing to do with interpretation of the results its about the results themselves and the experiments carried out to obtain those results.

"You run an experiment, you get results". I agree with that. Also you run a different experiment and depending on what that experiment is you can get different results. That in a nutshell is what I consider duality to be about, the results not the theory. Most people here seem to be theoreticians and their take is that duality is about the interpretation of the results That's different to my take but it's good.

Let me put it differently; In the early days the results were interpreted in a particular way which I suppose was widely accepted at the time. Today it's widely accepted that the original interpretation was incorrect and the results are now interpreted in a different way. That's good, and has been the way that a lot of science has progressed with one theory being replaced by a better theory. But it can go on and it's possible that today's theories will be replaced by even better theories and so on. The one thing that seems to be constant, however, seems to be the observations. they might be replaced by observations which are more precise but the basic observations are likely to remain.
Look at it from a practical point of view and consider those people who work for, example, with radio communications. I bet a lot, if not most of them, work successfully with the model that radio waves can be modeled as waves.

One impression I get about theoreticians is that a lot of them are not particularly well genned up on the practical experiments that Inform their theories and I think that could hinder progress to some degree. Anyway, that's just my opinion.

 

[vanhees71]

But to say "the results" show "wave-particle duality" is an interpretation. For me, no observation shows anything like "wave-particle duality". Which observations should this be in your opinion?

 

[Dadface]

If you really want to make a claim of this sort, you have to support it; which means pointing to specific instances where this has occurred. You need to quote from posts & build the argument that "theoreticians and professionals" are ignoring observations from what they say.

Before you even attempt it, stop & think what your claim implies. You are saying that "theoreticians and professionals" have gone off into a blind alley where their explanations of observations are false because they no longer refer to wave-particle duality in the same way as before. (You have not used the actual word "false" but I'd contend you are implying falsity). You are further saying that although you have admitted to struggling with the material (e.g. the paper I linked to & suggested you read), you are somehow wiser than these theoreticians and professionals. I am trying to imagine a world in which this could be true: someone who is not a professional himself, and who has only a limited understanding of the subject at hand, somehow is right while the professionals are wrong. How is this going to happen? The poverty of trying to rely on web searches to support your argument has already been explained to you; but it has not dented your self-confidence that somehow your stance as an amateur who relies on search results he doesn't understand is superior to persons who have actually put in long hard years of study within a shared scientific community.

Here is the quote where you admit that you can't grasp the paper you downloaded; I have bolded what seems especially pertinent:

Just to say it, the net is awash with many things, including badly written articles and papers, articles and papers we don't understand, and beyond that conspiracy theories and lies. Our increasing inability to handle this flood of information wisely is a massive & growing problem in today's culture, as I mentioned in an earlier comment (which I would encourage you to reread).
The hard thing for you to do would be to first see & then admit that you are caught in a trap; specifically, trapped by a stubborn insistence that although you lack full understanding of the subject, you don't require this understanding to be skeptical. I am not criticizing you personally and I apologize if it seems that way; what I am criticizing here is only the stance you are taking. You are willing to doubt the scientific community and the methods they use with very little evidence; but apparently unwilling to doubt the methods you are relying on yourself. Whereas to me, the capacity for self-doubt is an important part of how we learn. There have been many times I've finally realized I've been wrong on a subject & others have been right; it's been hard every time to actually admit it; but it's been important for me to do so. If I couldn't admit those times I've been wrong, I'd never learn. I'm thinking about mathematics right now, but I think it applies to all fields.

P.S. Your smaller claim that interested amateurs may find the change in presentation confusing is quite different; this seems fully supportable, even just using your own experience as an example. That claim has been responded to; however it seems you are not satisfied by the answers. I mention this only because back when I taught essay-writing, including argumentative essays, I often had students run into trouble with overly broad claims that they felt deeply, but couldn't support. One of my suggestions was to rephrase their claim so as to present it entirely in terms of their personal experience; e.g. rather than claim "Such-and-such must be wrong because I am puzzled," they could simply say, "It seems to me as if such-and-such is wrong because of how it puzzles me." This could lead to a line of questioning that would ultimately be more fruitful for them.

Thanks for your reply but I can't find where it is I stated or suggested that theoreticians and professionals have gone off into a blind alley etc. It seems that I may not have expressed myself clearly enough. But can I please say it out loud:

I'm not questioning the theory at all. Not one little bit.

I might go into the theory at some time but at this present time I'm not too bothered about it. What I've been trying to point out is that although theories may change observations remain and it's those observations that informed any original theories any present theories and which will partly or wholly inform any future theories. The original interpretations of the observations may be dead but the observations themselves are alive and kicking.

If I have one comment to make about theoreticians it is that some of them they might find it useful to look more thoroughly at the the results of the experiments they refer to and in particular the experimental arrangements used to get those results. I know that probably a lot of them do that anyway.

 

[vanhees71]

Well, if you want to understand QT you have to learn it. I you don't bother about it, then don't. But, why then are you insisting on nonsensical old-fashioned ideas which are long abandoned for a better theory, called "New QT", where "new" is a bit strange since it's now over 90 years old!

 

[Dadface]

As I pointed out at the beginning wave particle duality is a title that is widely used even by people like Zeilinger. That's not my fault and as Nugatory pointed out it's "beyond our powers to fix.

But to say "the results" show "wave-particle duality" is an interpretation. For me, no observation shows anything like "wave-particle duality". Which observations should this be in your opinion?

 

[Dadface]

Well, if you want to understand QT you have to learn it. I you don't bother about it, then don't. But, why then are you insisting on nonsensical old-fashioned ideas which are long abandoned for a better theory, called "New QT", where "new" is a bit strange since it's now over 90 years old!

Please read my posts. I'm not insisting on nonsensical old fashioned ideas at all. Let me repeat.

I am not questioning the more up to date theory at all.

I am claiming that the observations remain. They may not show duality but they remain. And it also looks like you're criticising me for using the word "new".

 

[UsableThought]

But to say "the results" show "wave-particle duality" is an interpretation. For me, no observation shows anything like "wave-particle duality". Which observations should this be in your opinion?

As I pointed out at the beginning wave particle duality is a title that is widely used even by people like Zeilinger. That's not my fault and as Nugatory pointed out it's "beyond our powers to fix.

That answer is completely evasive.

There is no pinning down or explaining things to Dadface, who knows what he knows but refuses to put it in terms that anyone else can understand. I'm abandoning ship & suggest that perhaps the thread should be given up as a lost cause.