Sorry but it's wave particle duality again...

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  • #51
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Sure they do. It's just not a 'mechanism' that satisfies your notion of what a 'mechanism' ought to be.

While it true that the wavefunction sort of give the "mathematical" mechanism, but I did emphasize the word clear, otherwise PF would not have been the fun place that it is.:smile:
 
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In an attempt to get people to read Bohr, I offer the following remarks. I hinted in my previous post that there is a deceptive situation in physics today where people are always talking about the "Copenhagen interpretation" even though what they say has absolutely nothing to do with it. It is quite similar to a hypothetical situation where people believe that Minkowski discovered special relativity because he found t2 - x2, and they ignore Einstein's conceptual insights. It is true that the formalism of quantum theory was discovered by Heisenberg, Dirac etc. but it was really Niels Bohr who understood it conceptually. Even Heisenberg's original paper on the uncertainty relations has a note at the end where he says that his explanation of the uncertainty relation is wrong, and Bohr has explained to him the correct way to look at it.
Indeed, without Bohr the Copenhagen interpretation would be even more confusing than it is with him, but if you want to understand quantum theory, it's not good advice to read Bohr or Heisenberg. The most clear writer of the founding fathers in my opinion is Dirac; then Pauli and Born. Bohr and Heisenberg are too much into philosophy rather than sticking to the "hard facts" of physics.
 
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concretely

This implies a classical world which we insist that QM does not follow. Hence, we believe in the almighty QM realm which the solution to the equations imply and we have no direct access to.
 
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I have been trying to point out that my emphasis is on observations. For example if you look up fundamental data from NIST you will see that the electron mass is measured to an incredibly high degree of accuracy.

I myself know nothing at all about quantum theory; and very, very little about classical mechanics; etc. But I do know something about the nature of argument. So a couple of comments on that basis:

Observation vs. theory. It seems to me a mistake to speak of the observation of particles (e.g. the electron, as has been mentioned) as somehow being so separate from quantum theory that the ability to make certain kinds of observations & measurements places the theory in jeopardy. Speech of this sort seems to imply that we are able to observe electrons with our naked senses, thus moving our observations into the realm of hard reality vs. soft theory. From what I read, this isn't the case at all: we can only detect these particles via instrumentation - e.g. cloud chambers, newer devices such as used in KATRIN, etc. Even without knowing a thing about something like the KATRIN experiment, I am willing to bet there is a long history of mathematical modeling to support detection with these devices. A cloud chamber is not quite the same thing as a pair of binoculars; to know what you are looking at requires more than just naked eyesight. So it is not the case that observation in physics is utterly separate from theory.

Observation leading to theory. To take this an obvious step further, isn't it the case that in the development of quantum theory (as throughout the history of physics and other hard sciences), experimental observation & theory have been interwoven from very early on, rather than being seen as separate and opposed? I apologize for the primitiveness of my sources, but even a glance at Wikipedia's article on the positron would suggest this: Dirac predicted an "anti-electron" and cloud-chamber observations in the late 1920s and early 1930s led to the detection of what was then called the positron.

The above points lead me to wonder what the arguments in this thread are really about. For example this statement -
This implies a classical world which we insist that QM does not follow. Hence, we believe in the almighty QM realm which the solution to the equations imply and we have no direct access to.
- is puzzling. What does "direct access" mean here? What does it mean to say that quantum theory doesn't provide a "mechanism" that "makes sense"? For that matter, getting back to the OP's original complaint, what is really at issue when he notes that the Internet yields hits from various sources which speak of "wave particle duality", and then contends that explanations that this is a dated phrase are not satisfactory?

In my opinion a couple of things are going on:

1) First, in my opinion @Simon Phoenix is dead on target when he notes that yearning for things to "make sense" and have a "mechanism" reflect our desire for "intuitive pictures" of how reality operates. I think this yearning is made especially powerful if (a) we are daunted by high levels of abstraction, and (b) we ourselves don't entirely understand the theories we are questioning.

2) There is a growing tendency in the era of Google to assume that we can know things through Googling without having to do the work of understanding. So if we get a smattering of Google hits that dredge up confusing or contradictory information, we then assume that this dredged-up information is enough for us to be skeptical about what the experts tell us about a particular theory or model - in this case quantum theory - without our having done the hard, lengthy work of studying that model enough to understand it. If we find ourselves struggling with basic papers in the field, then that might be considered a clue: we are not ready to question that field ourselves!

I am familiar with my point #2 from a different context, which I will offer up as an example of what I mean. About 8 or 9 years ago, I was very interested in a kind of behavioral psychology known as relational frame theory, or RFT, which purports to explain verbal behavior in humans. RFT is not only extremely technical, but it happens to be built on top of a previous model known as operant behavior, which is part of B.F. Skinner's radical behaviorism. I wanted to learn RFT, so I went through an enormous amount of journal articles and books - not only on the development of RFT, but on alternate theories which had been proposed for verbal behavior, but which failed to be born out by experiment as RFT was born out.

Because this was a highly abstruse theory, with many departures from "folk psychology" or "common sense," I had many questions as I read along. From an expert's point of view, these questions were naive; but I still had to ask them in order to gain traction on the subject. I listed them, and then used this list to help guide my reading. Once I felt I had got the "right answer" to each question per the theory, I then queried experts in the field (I knew a lot of the researchers already from early discussions) to make sure my understanding was correct. What I did NOT do was suppose that in my naiveté, I had somehow stumbled across questions that the experts themselves, in developing RFT, had failed to consider.

So to me, the question is, what is the goal of asking a naïve question about a particular theory, whether in psychology or physics? Is it to show that we, in our naiveté, are showing that the experts have it all wrong? Or are we asking as an aid to doing the hard work of studying & learning something new and difficult, so that we may finally understand the theory as it is actually proposed? In this case, I think it is useful for a student to ask something like, "Help me understand why wave particle duality is no longer a problem in QT" or some such; but not so useful for a student to assert that "The availability of 'wave particle duality' as a search term on the Internet, with lots of hits that I haven't really sorted out, means that somehow QT must be inadequate."

The above may sound offensive and if so I apologize; I don't mean to be that way. But it does seem to be that in this thread, we have a division between those who understand a particular theory and its historical development, and are patiently trying to explain these things; and those who for one reason or another are bent on pursuing their own highly personal objections to the theory. One objection is that the Internet coughs up results that to a naïve reader seem important grounds for skepticism; the other is to abstraction itself as being unsatisfactory for explaining a reality that is in any case quite distant from any mental picture we might draw of it - see my note above on "observation vs. theory."

Regarding the first of these objections - the role of the Internet in coughing up seemingly important search results - I would like to quote from a book I have been reading, The Death of Expertise, 2017 from Oxford U. Press; the author is Tom Nichols, who happens himself to be an expert on foreign policy & international security. The book is about the general decay of trust in U.S. society in experts and expertise; Nichols has a chapter specifically on the role of the Internet in this loss of trust, and this excerpt is from that chapter:

Plugging words into a browser window isn't research; it's asking questions of programmable machines that themselves cannot actually understand human beings. Actual research is hard, and for people raised in an environment of constant electronic stimulation, it's also boring. Research requires the ability to find authentic information, summarize it, analyze it, write it up, and present it to other people. It is not just the province of scientists and scholars, but a basic set of skills a high school education should teach every graduate . . .

In some ways, the convenience of the Internet is a tremendous boon, but mostly for people already trained in research and who have some idea of what they're looking for. It's much easier to subscribe to the electronic version of, say, Foreign Affairs or International Security than it is to decamp to the library or impatiently check an office mailbox. This is no help, unfortunately, for a student or an untrained layperson who has never been taught how to judge the provenance of information or the reputability of a writer.​

@Dadface, let me finish by saying this: Why not turn your question about "wave particle duality" into a research project? You would have to do a lot of research - lots of long slow difficult reading - but this way, you would get a real grasp on the subject. You could make a note of your questions, then set out to find answers to those questions in the literature. This is how I approached relational frame theory. If I had merely stuck to asking my naïve questions flat-out, with no attempt at study and research, I might have gotten answers from experts on a forum like this; but I couldn't have really understood those answers and so my skepticism would remain. And worst of all I would never really come to understand or learn anything new; I would be stuck within my own self-imposed limits.
 
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  • #56
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What I did NOT do was suppose that in my naiveté, I had somehow stumbled across questions that the experts themselves, in developing RFT, had failed to consider.

Quite - and it's true even for most 'experts' too - or at least it ought to be :wideeyed:

In a charitable light I might be considered to have developed some expertise in QM and quantum optics, but I'm hardly in the same class as a Zeilinger or a Zurek, let alone a Feynman or a Dirac!! That's not to say these 'superstars' are always right, but it would, I think, be astonishing if they turned out to be wrong for entirely trivial reasons. I'd be willing to bet that these kinds of folk, when they do get it 'wrong', get things wrong for really interesting reasons most of the time. We could say that Einstein (and Podolsky and Rosen) got it 'wrong' in their original EPR paper - but, heck, they were wrong for one of the most interesting reasons possible :cool:

The internet is a tool - and like all tools must be used judiciously. It's easy, perhaps, for someone who hasn't put in the kind of careful study required, to get bamboozled by techno-speak. I mean if I wrote something like "the diffeomorphic character of the inverse Waffle transformation means that the compact sub-group of the affine connection is positive definite on the semi-finite mapping of Killjoy vectors to the parallelized sphere of adjoint Blochhead transformations", then to a casual (non-technical) observer it might seem that I know what I'm talking about when, in truth, it's just outrageous nonsense - techno word salad. The internet is full of such egregious drivel. It's also full of some wonderful and brilliant stuff - the trick is in knowing the difference.

I've been on a couple of other forums and blogs over the years where I have been frankly astonished by the sheer number of crackpots who proudly proclaim, in really quite authoritative terms, that physics went wrong with Einstein (SR and GR) and even more wrong with QM. These maroons then usually go on to expound their own completely bonkers 'theory of everything' which mostly consists of techno word salad.

The problem is that an internet search will throw up a fair number of hits ranging from the brilliant and expert, through the mostly correct but slightly misleading or not too incorrect, right through to the bat guano insane. A casual observer would then get the impression that 'physics' is in some kind of turmoil with nobody really having a clue what's going on.

Although the moderation on these forums borders on the over-enthusiastic at times - I think we should be grateful that we have a forum that is mercifully free from the hordes of marauding loons out there; a forum where some truly expert and knowledgeable people share their time freely to enlighten us all.
 
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  • #57
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I myself know nothing at all about quantum theory; and very, very little about classical mechanics; etc. But I do know something about the nature of argument. So a couple of comments on that basis:

Observation vs. theory. It seems to me a mistake to speak of the observation of particles (e.g. the electron, as has been mentioned) as somehow being so separate from quantum theory that the ability to make certain kinds of observations & measurements places the theory in jeopardy. Speech of this sort seems to imply that we are able to observe electrons with our naked senses, thus moving our observations into the realm of hard reality vs. soft theory. From what I read, this isn't the case at all: we can only detect these particles via instrumentation - e.g. cloud chambers, newer devices such as used in KATRIN, etc. Even without knowing a thing about something like the KATRIN experiment, I am willing to bet there is a long history of mathematical modeling to support detection with these devices. A cloud chamber is not quite the same thing as a pair of binoculars; to know what you are looking at requires more than just naked eyesight. So it is not the case that observation in physics is utterly separate from theory.

Observation leading to theory. To take this an obvious step further, isn't it the case that in the development of quantum theory (as throughout the history of physics and other hard sciences), experimental observation & theory have been interwoven from very early on, rather than being seen as separate and opposed? I apologize for the primitiveness of my sources, but even a glance at Wikipedia's article on the positron would suggest this: Dirac predicted an "anti-electron" and cloud-chamber observations in the late 1920s and early 1930s led to the detection of what was then called the positron.

The above points lead me to wonder what the arguments in this thread are really about. For example this statement -

- is puzzling. What does "direct access" mean here? What does it mean to say that quantum theory doesn't provide a "mechanism" that "makes sense"? For that matter, getting back to the OP's original complaint, what is really at issue when he notes that the Internet yields hits from various sources which speak of "wave particle duality", and then contends that explanations that this is a dated phrase are not satisfactory?

In my opinion a couple of things are going on:

1) First, in my opinion @Simon Phoenix is dead on target when he notes that yearning for things to "make sense" and have a "mechanism" reflect our desire for "intuitive pictures" of how reality operates. I think this yearning is made especially powerful if (a) we are daunted by high levels of abstraction, and (b) we ourselves don't entirely understand the theories we are questioning.

2) There is a growing tendency in the era of Google to assume that we can know things through Googling without having to do the work of understanding. So if we get a smattering of Google hits that dredge up confusing or contradictory information, we then assume that this dredged-up information is enough for us to be skeptical about what the experts tell us about a particular theory or model - in this case quantum theory - without our having done the hard, lengthy work of studying that model enough to understand it. If we find ourselves struggling with basic papers in the field, then that might be considered a clue: we are not ready to question that field ourselves!

I am familiar with my point #2 from a different context, which I will offer up as an example of what I mean. About 8 or 9 years ago, I was very interested in a kind of behavioral psychology known as relational frame theory, or RFT, which purports to explain verbal behavior in humans. RFT is not only extremely technical, but it happens to be built on top of a previous model known as operant behavior, which is part of B.F. Skinner's radical behaviorism. I wanted to learn RFT, so I went through an enormous amount of journal articles and books - not only on the development of RFT, but on alternate theories which had been proposed for verbal behavior, but which failed to be born out by experiment as RFT was born out.

Because this was a highly abstruse theory, with many departures from "folk psychology" or "common sense," I had many questions as I read along. From an expert's point of view, these questions were naive; but I still had to ask them in order to gain traction on the subject. I listed them, and then used this list to help guide my reading. Once I felt I had got the "right answer" to each question per the theory, I then queried experts in the field (I knew a lot of the researchers already from early discussions) to make sure my understanding was correct. What I did NOT do was suppose that in my naiveté, I had somehow stumbled across questions that the experts themselves, in developing RFT, had failed to consider.

So to me, the question is, what is the goal of asking a naïve question about a particular theory, whether in psychology or physics? Is it to show that we, in our naiveté, are showing that the experts have it all wrong? Or are we asking as an aid to doing the hard work of studying & learning something new and difficult, so that we may finally understand the theory as it is actually proposed? In this case, I think it is useful for a student to ask something like, "Help me understand why wave particle duality is no longer a problem in QT" or some such; but not so useful for a student to assert that "The availability of 'wave particle duality' as a search term on the Internet, with lots of hits that I haven't really sorted out, means that somehow QT must be inadequate."

The above may sound offensive and if so I apologize; I don't mean to be that way. But it does seem to be that in this thread, we have a division between those who understand a particular theory and its historical development, and are patiently trying to explain these things; and those who for one reason or another are bent on pursuing their own highly personal objections to the theory. One objection is that the Internet coughs up results that to a naïve reader seem important grounds for skepticism; the other is to abstraction itself as being unsatisfactory for explaining a reality that is in any case quite distant from any mental picture we might draw of it - see my note above on "observation vs. theory."

Regarding the first of these objections - the role of the Internet in coughing up seemingly important search results - I would like to quote from a book I have been reading, The Death of Expertise, 2017 from Oxford U. Press; the author is Tom Nichols, who happens himself to be an expert on foreign policy & international security. The book is about the general decay of trust in U.S. society in experts and expertise; Nichols has a chapter specifically on the role of the Internet in this loss of trust, and this excerpt is from that chapter:

Plugging words into a browser window isn't research; it's asking questions of programmable machines that themselves cannot actually understand human beings. Actual research is hard, and for people raised in an environment of constant electronic stimulation, it's also boring. Research requires the ability to find authentic information, summarize it, analyze it, write it up, and present it to other people. It is not just the province of scientists and scholars, but a basic set of skills a high school education should teach every graduate . . .

In some ways, the convenience of the Internet is a tremendous boon, but mostly for people already trained in research and who have some idea of what they're looking for. It's much easier to subscribe to the electronic version of, say, Foreign Affairs or International Security than it is to decamp to the library or impatiently check an office mailbox. This is no help, unfortunately, for a student or an untrained layperson who has never been taught how to judge the provenance of information or the reputability of a writer.​

@Dadface, let me finish by saying this: Why not turn your question about "wave particle duality" into a research project? You would have to do a lot of research - lots of long slow difficult reading - but this way, you would get a real grasp on the subject. You could make a note of your questions, then set out to find answers to those questions in the literature. This is how I approached relational frame theory. If I had merely stuck to asking my naïve questions flat-out, with no attempt at study and research, I might have gotten answers from experts on a forum like this; but I couldn't have really understood those answers and so my skepticism would remain. And worst of all I would never really come to understand or learn anything new; I would be stuck within my own self-imposed limits.

Thank you for your response usable thought. It is rather lengthy and I will need to go through it a few times. I have been stressing that observation is key to this topic and indeed to every other area of physics. It is observation that informs and gives credence to theory, not the other way round. In the early days of QM De Broglie postulated that atomic size particles can have a demonstrable wave nature. At approximately the same time and in a different part of the world Davison and Germer, who were not aware of De Broglies work, carried out an experiment with an electron tube which can be interpreted as electrons displaying wavelike properties. Since then the theory has moved on but the basic observations remain.
In a nutshell theory is about interpreting observations and as far as wave particle duality is concerned I think the interpretations that have been made are flawed. To me there seems to be something very simple basic and obvious that has been overlooked. I don't believe in the concept of duality as it has been framed and that's why I have been making enquiries here as to why the concept can appear to be alive and kicking.
I
 
  • #58
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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.
See my https://arxiv.org/abs/quant-ph/0609163
Sec. 8 (especially 8.3) and Sec. 9 (especially 9.7).

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 ....
In that sense, Bohmian particle position is a Dirac delta, but not of Eq. (1).
 
  • #59
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roger that.:biggrin:

So, if one concedes that "particle" doesn't refer to "classical particle" then to what does it refer? The answer in QM is to irreps of the Poincare group. This leads one to the full QFT formalism and wave-particle vanishes as a poorly defined concept in a puff of formalism. The example I gave in #34 isn't a random example. I actually did the experiment to test for correlation. I expected to find correlation based on a completely specious essentially classical intuition of the photon which is completely wrong (and frankly stupid). In my case trying to apply an incomplete picture leads to a false conclusion. Subsequent reading of the fine print (and there is a great deal of fine print) in Mandel and Wolf makes the issue very clear. Many of the things (especially statistical things) people view as properties allegedly possessed by photons are actually properties of photon sources. Moral of the story is learn the formalism and it's implications to actual experiments.
 
  • #60
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.
Sorry, I don't understand. Why do you say a photon does not have a position observable?
 
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Do you know quantum field theory? If not, it's hard to answer this question.
 
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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
 
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  • #63
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 text books 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.
 
  • #64
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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
 
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  • #65
vanhees71
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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! :frown:
 
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  • #66
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It's so sad! :frown:

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
 
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  • #67
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.
 
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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?
 
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dextercioby
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I believe in mathematics. A lot of what's not spelled out mathematically in theories of physics is merely unuseful philosophy.
 
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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 whats 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
 
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Simon Phoenix
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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.

Wave_Particle.gif

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 :smile:

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"
 
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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.
 
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vanhees71
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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 :smile:

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.
 
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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.
 
  • #75
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Why haven't we heard the words "vector-particle" duality.. why always "wave-particle" duality?
 

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