Exploring Photon Trajectories in Double Slit Experiments

[Ken G]

Whoops, not fine anymore .. strictly speaking there is no classical physics context in which it makes sense to talk about particles like photons, electrons and neutrons *at all*, let alone the fact that massive bodies have wavelengths associated with them.

Once again, you have gone off into left field, telling me perfectly obvious things that have nothing to do with what I said. I'm not saying you are stupid, you obviously aren't. There is just something blocking you from actually hearing what I'm saying, so you keep telling me things that any first-year student knows. It's irrelevant, what I'm saying is that Bragg did not need to know that light was quanta to get Bragg scattering, and he wouldn't have needed to know that electrons or neutrons were quanta to extend his classical insights to electron and neutron diffraction. He might not have obtained quantum mechanics, but he would have gotten insights into it-- classically. Or maybe he would have gotten quantum mechanics, using those insights, just as Schroedinger himself did.

I just don't know how else to get this across to you. Only after it was discovered that electrons and neutrons were particles, had the Braggs not known that (or just choosed not to use it, like they didn't use the knowledge with photons), could someone have taken adantage of the classical-wave analog to say "hey, we must have wave/particle duality here." Indeed, wave/particle duality itself, the cornerstone of what is "strictly quantum", is a perfect example of the value of classical analogs. So although you have gone on and on about wave/particle duality of electrons and how there can't be any useful classical analog there, the ultimate irony is: that is a classical analog, in that very language. Yes, it is, we are invoking a classical analog to understand quantum behavior, as is so extremely common in all of physics (consider the examples I gave above in that addendum to my last post, you might have missed it).

Classical laws of physics treat space, time and matter as infinitely divisible, and as such there is no way in classical physics for massive bodies to have wave-like properties.

Of course there is, you just put it into a classical wave theory. You might not even know you are dealing with massive bodies, and do the classical physics anyway-- that was the point of that student experiment I mentioned. Physics has lots of different theories, and we will have a lot more. We might get a working string theory, we might unify gravity and quantum physics, we might understand what intelligence is, who knows. They'll all look a lot different from the previous theories, but the clever physicist will always look for the analogs from the previous theories, like classical analogs-- that's the correspondence principle. Read the whole thread again, realizing that this is what I have been saying, and recognizing that I know quantum mechanics, and I know classical mechanics, and I see the value of classical analogs-- and you can too.

Once you are talking about space (or phase space) as having a fundamental limit of divisibility, or about matter as consisting of discrete subatomic particles with associated wavelengths, then the concepts you are invoking are strictly quantum mechanical.

There's that language again, that's just baloney. In Newton's day, did they say "acceleration is a strictly Newtonian concept" simply because they had F=ma and no one else had a theory to make sense of dynamics? Would we say today that acceleration is strictly Newtonian? Physical theories are just that-- theories. They never own the phenomena they describe-- never. There is no such thing as any phenomenon that is "strictly classical", or "strictly quantum", there are just concepts, and the concepts have analogs very often, and it's useful to know those analogs, because they help you understand the concepts, and they help you form the new theories. As they did for Bragg, as they did for Schroedinger, as they certainly did for Bohr.

Whoops! What makes Bragg's law a *classical* law? Absolutely nothing

Whoops? Are you kidding? Are you aware that Maxwell's equations are classical laws? Bragg's law is a consequence of Maxwell's equations applied to a regular lattice interacting with a classical E&M field. If your argument rests on the idea that Bragg's law was not obtained via classical reasoning, I think that sums up the quality of your argument.

.. it is a *physical* law describing wave phenomena that was simply first discovered in a classical context. It describes classical phenomena when applied to classical systems, and quantum phenomena when applied to quantum systems.

Ah, so now we see that your argument rests solely on a tautology: you simply define electrons as quantum systems, so any law that electrons obey is automatically a quantum law, so there can be no correspondence to electron diffraction because electrons are doing it. Well, I can't argue against a tautology, but I can sure question its information content.

It may have great relevance in terms of Ken's correspondence principle of analogies, but that is not what I have been talking about ... ever.

Which is exactly what I have been telling you all along. Nothing that you are talking about has anything to do with the point I raised, and clearly described, and told you that your comments were irrelevant to it, yet still somehow you thought you were proving me wrong.

On the other hand, Heisenberg's Uncertainty Principle is a *quantum law* of physics, in that it applies exclusively to the phenomena of quantum systems.

Obviously, and again because of a semantic tautology: the HUP is a classical analog of how classical waves behave, applied, to our surprise, to particles-- but since it applies to particles, you get to label it a "quantum law"! And in so labeling, you miss my entire point: the HUP is a perfect example of the value of a classical analogy, the Fourier analysis of classical waves. As I said about a zillion posts ago.

The de Broglie wavelength is also a purely quantum concept.

Yes, again tautologically true, because you think what matters is the quantum label, not noticing that what actually matters about the de Broglie wavelength is the classical analog. That's why it is called a "wavelength" in the first place, it's invoking a classical analog that is of great value in understanding it. And like I said above, it does relate to a classical treatment in the limit of a huge ensemble of particles all with that deBroglie wavelength-- just as it did for Bragg's derivation of Bragg's law.

Both the HUP and the de Broglie wavelength may be ANALOGOUS to concepts found in classical physics, but the specific concepts don't themselves apply to classical physics.

Well this is progress-- you now see that those "strictly QM" concepts benefit from classical analogs! That's what I've been saying, by the way-- just read the thread. Obviously they don't apply to classical physics in your mind, because you simply haven't yet taken the classical limit of lots and lots of particles, in which case they do apply to classical wave mechanics, which is why Bragg's law is useful for diffraction of beams of electrons and neutrons. That was the whole point of that "student experiment" I explained that I thought would make this all immediately clear.

Finally, since these are purely quantum concepts, the phenomena they predict (such as diffraction of massive bodies) must be "averaged out" in such a away that they are undetectable in the classical limit .. that is what is required by Bohr's principle of quantum-classical correspondence.

Diffraction is undetectable in the classical limit? Then we must revoke the Bragg's Nobel prize, that's a pity. (Oh yes, once again you will think I mean the classical limit of large particle energies, though we all know that would eliminate the diffraction and I have said so many times I know that and I am talking about the limit that Bragg was actually involved in-- the limit of large particle fluxes, such that indeed there was no need to know there were even particles there to get Bragg's results. Read that again if needed.)

Note that there is no such requirement that diffraction of massless photons be "averaged out" in the same fashion, because photons are just a way of counting up the population of the harmonic modes of the underlying field, which ends up having the same basic description in both (quantum) QED and (classical) E&M.

No, the reason you think it works for photons but not electrons is simply that a high quantum number for a photon field is the same as a high occupation number, so we have just one classical limit instead of two separate ones. I made perfectly clear which classical limit I'm talking about, whether photons or electrons-- the limit of large enough fluxes that you can measure them as classical energy fluxes, and use a classical wave theory to interpret that as Poynting flux. I don't know how many times I need to say that this is the classical limit I have been referring to in regard to the correspondence principle for both electrons and photons, just look back at that "student experiment" post again, if you can find it in all the misconstruals I've had to suffer.

So the quantum character of photons has nothing to do with the wavelength of the field, but only it's intensity, which means that the wave-like character persists even in the classical limit.

I'm not sure why you would make such a false statement, that "the quantum character of photons has nothing to do with the wavelength of the field." I'm going to presume you had a momentary lapse and let that go, no doubt you will immediately see your error.

If you had said what you wrote in the quoted paragraph above in the first place, then I never would have disagreed with you.

I tried very hard to tell you that your objections were not relevant to what I was saying. I thought I was being pretty clear-- the problem is that you still don't recognize a classical limit of high phase-space density, even after I explained exactly how purely classical experiments can be done on such systems, and how one can generally avoid invoking particle concepts, as is done in hydrodynamics, wave mechanics, and continuum mechanics of all kinds. I said all that, many times. Which finally brings us back to the OP-- the correspondence principle I was talking about, right from the very start, was about interpreting Bohmian trajectories in terms of large ensemble averages of weak measurements, and I claimed, and still do, that was tantamount to taking exactly the kind of "averaging out" classical-wave limit that we are just now talking about. That was the motivation right from the start.

But you didn't say that, you made incorrect claims about physics, which I corrected.

No. There is not one single incorrect claim I made that isn't basically a technicality, like issues with quantum chaos. In every case, your "corrections" were telling me basic physics I've known for decades. Every time, you told me nothing I didn't already know, and it was always just plain irrelevant to the correspondence principle applied to ensemble averages of weak measurements.

You refused to accept my corrections for a while, but if you now accept that I was right all along, and that you were wrong to claim (among other things, but this is the biggie) that it is possible to formulate a classical theory that can predict electron diffraction (which you did in post #113, and several times thereafter), then fantastic!

We certainly see that Bragg's approach is purely classical and can be applied to electron diffraction. So that's a pretty good start. Whether we wish to count that as a "theory" is less clear, you may want more from it than just its ability to probe the structure of a lattice. There are many types of diffraction theories, and they all work to various degrees in different situations-- such is the nature of physics, we make idealizations to get somewhere. So we would not ask a classical theory of electron diffraction to do more than help us understand what is going on when we have large ensembles of diffracting electrons, and that's what Bragg's approach, and scalar diffraction theory in general, can do for us. It's just that we have quantum mechanics, so we only use classical concepts as analogs to help us understand the quantum mechanics, that is often the main point of classical analogs. Bragg's law is a perfect example of a classical analog helping us understand how electrons and neutrons diffract in a crystal.

If you want to use your fuzzy philosophical definition of the correspondence principle that is based in analogies, then fine .. feel free.

Excellent, then we are actually in a position to get the whole point here: classical analogs are a useful way to understand phenomena that closedminded people tend to brand as "strictly quantum." And that was the whole point, in particular about using Poynting fluxes to understand streamline diagrams like the one in the OP.

Just be clear about it and don't confuse others by pretending that it is equivalent to the physical correspondence principle laid out by Bohr to help relate and distinguish quantum and classical theories.

Bohr's correspondence principle is itself a fuzzy philosophical rule, and it is the reason that physics is successful, in a nutshell. I'm sure Bohr understood that, but the point seems to have been rather lost to the years.

You may have "known" the facts I have used to explain my arguments, but your posts make it quite obvious that you have never understood many of them in the proper context.

Correction, your interpretation of them made you believe that. It's just not true. For fear of making you think you completely wasted your time telling me things I already knew, the course of the discussion has helped me hone some of the stickier issues, and certainly has helped me see the areas that are most easily misconstrued. Really the only thing I said that I have not backed up is the extent to which quantum theories can be used to generate classical ones-- that remains a bit vague, though I think it's mostly that there just isn't much payoff for doing it when all one really wants is the classical analog concepts (and there is a nice payoff for those, like the Lorentz wings of a resonance line, like the Thomson cross section, like the concept of a "classical radius of the electron", the list just goes on and on). My real point is to look for classical analogs, which in the case of Bohmian trajectories may well just be Poynting flux streamlines.

 

[zenith8]

Slightly off topic.. can anyone point me to a thread on Physics Forums where any contributor with more than - say - 10 posts changes their mind about anything, ever? Just curious.

 

[Ken G]

That'll be hard to find-- communication is always the hardest thing. What's really amazing is how long a thread got spawned from how completely misunderstood was a very simple concept: that averaging lots of weak measurements together over an ensemble creates a classical limit for understanding "average trajectories", yielding something very akin to a classical concept like Poynting flux streamlines. The pity is that had we spent the energy actually analyzing the connection between Bohmian trajectories and classical Poynting fluxes, we might have actually arrived at a conclusion relevant to the OP. Because Poynting fluxes in a two-slit experiment must generate, by symmetry, streamlines that connect the left slit to the left side of the wall, and right to right, yet people still tried to argue that somehow the "average trajectories" can be used to conclude that photons passing through the left slit have to hit the left wall, even when there's an interference pattern. My entire motivation for discussing the correspondence principle was to expose how empty that logic was.

 

[SpectraCat]

Once again, you have gone off into left field, telling me perfectly obvious things that have nothing to do with what I said. I'm not saying you are stupid, you obviously aren't. There is just something blocking you from actually hearing what I'm saying, so you keep telling me things that any first-year student knows. It's irrelevant, what I'm saying is that Bragg did not need to know that light was quanta to get Bragg scattering, and he wouldn't have needed to know that electrons or neutrons were quanta to extend his classical insights to electron and neutron diffraction. He might not have obtained quantum mechanics, but he would have gotten insights into it-- classically. Or maybe he would have gotten quantum mechanics, using those insights, just as Schroedinger himself did.

I just don't know how else to get this across to you. Only after it was discovered that electrons and neutrons were particles, had the Braggs not known that (or just choosed not to use it, like they didn't use the knowledge with photons), could someone have taken adantage of the classical-wave analog to say "hey, we must have wave/particle duality here." Indeed, wave/particle duality itself, the cornerstone of what is "strictly quantum", is a perfect example of the value of classical analogs. So although you have gone on and on about wave/particle duality of electrons and how there can't be any useful classical analog there, the ultimate irony is: that is a classical analog, in that very language. Yes, it is, we are invoking a classical analog to understand quantum behavior, as is so extremely common in all of physics (consider the examples I gave above in that addendum to my last post, you might have missed it).
Of course there is, you just put it into a classical wave theory. You might not even know you are dealing with massive bodies, and do the classical physics anyway-- that was the point of that student experiment I mentioned. Physics has lots of different theories, and we will have a lot more. We might get a working string theory, we might unify gravity and quantum physics, we might understand what intelligence is, who knows. They'll all look a lot different from the previous theories, but the clever physicist will always look for the analogs from the previous theories, like classical analogs-- that's the correspondence principle. Read the whole thread again, realizing that this is what I have been saying, and recognizing that I know quantum mechanics, and I know classical mechanics, and I see the value of classical analogs-- and you can too.

There's that language again, that's just baloney. In Newton's day, did they say "acceleration is a strictly Newtonian concept" simply because they had F=ma and no one else had a theory to make sense of dynamics? Would we say today that acceleration is strictly Newtonian? Physical theories are just that-- theories. They never own the phenomena they describe-- never. There is no such thing as any phenomenon that is "strictly classical", or "strictly quantum", there are just concepts, and the concepts have analogs very often, and it's useful to know those analogs, because they help you understand the concepts, and they help you form the new theories. As they did for Bragg, as they did for Schroedinger, as they certainly did for Bohr.


Whoops? Are you kidding? Are you aware that Maxwell's equations are classical laws? Bragg's law is a consequence of Maxwell's equations applied to a regular lattice interacting with a classical E&M field. If your argument rests on the idea that Bragg's law was not obtained via classical reasoning, I think that sums up the quality of your argument.

Ah, so now we see that your argument rests solely on a tautology: you simply define electrons as quantum systems, so any law that electrons obey is automatically a quantum law, so there can be no correspondence to electron diffraction because electrons are doing it. Well, I can't argue against a tautology, but I can sure question its information content.

Which is exactly what I have been telling you all along. Nothing that you are talking about has anything to do with the point I raised, and clearly described, and told you that your comments were irrelevant to it, yet still somehow you thought you were proving me wrong.
Obviously, and again because of a semantic tautology: the HUP is a classical analog of how classical waves behave, applied, to our surprise, to particles-- but since it applies to particles, you get to label it a "quantum law"! And in so labeling, you miss my entire point: the HUP is a perfect example of the value of a classical analogy, the Fourier analysis of classical waves. As I said about a zillion posts ago.

Yes, again tautologically true, because you think what matters is the quantum label, not noticing that what actually matters about the de Broglie wavelength is the classical analog. That's why it is called a "wavelength" in the first place, it's invoking a classical analog that is of great value in understanding it. And like I said above, it does relate to a classical treatment in the limit of a huge ensemble of particles all with that deBroglie wavelength-- just as it did for Bragg's derivation of Bragg's law.


Well this is progress-- you now see that those "strictly QM" concepts benefit from classical analogs! That's what I've been saying, by the way-- just read the thread. Obviously they don't apply to classical physics in your mind, because you simply haven't yet taken the classical limit of lots and lots of particles, in which case they do apply to classical wave mechanics, which is why Bragg's law is useful for diffraction of beams of electrons and neutrons. That was the whole point of that "student experiment" I explained that I thought would make this all immediately clear.

Diffraction is undetectable in the classical limit? Then we must revoke the Bragg's Nobel prize, that's a pity. (Oh yes, once again you will think I mean the classical limit of large particle energies, though we all know that would eliminate the diffraction and I have said so many times I know that and I am talking about the limit that Bragg was actually involved in-- the limit of large particle fluxes, such that indeed there was no need to know there were even particles there to get Bragg's results. Read that again if needed.)

No, the reason you think it works for photons but not electrons is simply that a high quantum number for a photon field is the same as a high occupation number, so we have just one classical limit instead of two separate ones. I made perfectly clear which classical limit I'm talking about, whether photons or electrons-- the limit of large enough fluxes that you can measure them as classical energy fluxes, and use a classical wave theory to interpret that as Poynting flux. I don't know how many times I need to say that this is the classical limit I have been referring to in regard to the correspondence principle for both electrons and photons, just look back at that "student experiment" post again, if you can find it in all the misconstruals I've had to suffer.
I'm not sure why you would make such a false statement, that "the quantum character of photons has nothing to do with the wavelength of the field." I'm going to presume you had a momentary lapse and let that go, no doubt you will immediately see your error.
I tried very hard to tell you that your objections were not relevant to what I was saying. I thought I was being pretty clear-- the problem is that you still don't recognize a classical limit of high phase-space density, even after I explained exactly how purely classical experiments can be done on such systems, and how one can generally avoid invoking particle concepts, as is done in hydrodynamics, wave mechanics, and continuum mechanics of all kinds. I said all that, many times. Which finally brings us back to the OP-- the correspondence principle I was talking about, right from the very start, was about interpreting Bohmian trajectories in terms of large ensemble averages of weak measurements, and I claimed, and still do, that was tantamount to taking exactly the kind of "averaging out" classical-wave limit that we are just now talking about. That was the motivation right from the start.



No. There is not one single incorrect claim I made that isn't basically a technicality, like issues with quantum chaos. In every case, your "corrections" were telling me basic physics I've known for decades. Every time, you told me nothing I didn't already know, and it was always just plain irrelevant to the correspondence principle applied to ensemble averages of weak measurements.

We certainly see that Bragg's approach is purely classical and can be applied to electron diffraction. So that's a pretty good start. Whether we wish to count that as a "theory" is less clear, you may want more from it than just its ability to probe the structure of a lattice. There are many types of diffraction theories, and they all work to various degrees in different situations-- such is the nature of physics, we make idealizations to get somewhere. So we would not ask a classical theory of electron diffraction to do more than help us understand what is going on when we have large ensembles of diffracting electrons, and that's what Bragg's approach, and scalar diffraction theory in general, can do for us. It's just that we have quantum mechanics, so we only use classical concepts as analogs to help us understand the quantum mechanics, that is often the main point of classical analogs. Bragg's law is a perfect example of a classical analog helping us understand how electrons and neutrons diffract in a crystal.Excellent, then we are actually in a position to get the whole point here: classical analogs are a useful way to understand phenomena that closedminded people tend to brand as "strictly quantum." And that was the whole point, in particular about using Poynting fluxes to understand streamline diagrams like the one in the OP.

Bohr's correspondence principle is itself a fuzzy philosophical rule, and it is the reason that physics is successful, in a nutshell. I'm sure Bohr understood that, but the point seems to have been rather lost to the years.
Correction, your interpretation of them made you believe that. It's just not true. For fear of making you think you completely wasted your time telling me things I already knew, the course of the discussion has helped me hone some of the stickier issues, and certainly has helped me see the areas that are most easily misconstrued. Really the only thing I said that I have not backed up is the extent to which quantum theories can be used to generate classical ones-- that remains a bit vague, though I think it's mostly that there just isn't much payoff for doing it when all one really wants is the classical analog concepts (and there is a nice payoff for those, like the Lorentz wings of a resonance line, like the Thomson cross section, like the concept of a "classical radius of the electron", the list just goes on and on). My real point is to look for classical analogs, which in the case of Bohmian trajectories may well just be Poynting flux streamlines.

So basically, what happened is that you came on a physics website, and started posting unsubstantiated claims based on your personal definitions and interpretations of well-established physical concepts, like the distinction between quantum and classical, the distinction between occupation numbers and quantum numbers, and Bohr's principle of quantum classical correspondence. When challenged by actual physicists who require precise definitions, you could not clearly translate your theories into mathematical equations (i.e. translate them into the language of physics), or substantiate them with references. So you softened your claims by emphasizing the vagueness of your ideas, and the fact that you don't use the standard physical definitions for common concepts.

There is no real problem with any of that, EXCEPT for that fact that you presumed to advise and educate others that your personal ideas about how the connections between these concepts have a deeper physical significance than the mathematical similarities that are already well-known and commonly used in pedagogical settings. It is not helpful for you to continually claim that just because two concepts share a mathematical similarity, that there is a meaningful physical relationship between them. This is what has blinded you to the reason why your statement that there can be a classical theory of electron diffraction not only misleading, but is wrong when analyzed in the proper physical context. This is also why you failed to produce an equation that assumed a continuous distribution of mass and charge, yet could predict diffraction of that mass-charge distribution off a double slit scaled to produce electron diffraction.

 

[Ken G]

So basically, what happened is that you came on a physics website, and started posting unsubstantiated claims based on your personal definitions and interpretations of well-established physical concepts, like the distinction between quantum and classical, the distinction between occupation numbers and quantum numbers, and Bohr's principle of quantum classical correspondence.

No, that is what you imagined happened. What actually happened is what I just said to zenith8-- I pointed out that the people who were claiming that averaging lots of weak measurements could demonstrate that photons going through the left slit had to hit the left wall were making a preposterous argument, which can be understood by simply understanding the information that gets lost when one takes a classical limit over a large ensemble. Then a few people who seemed unable to grasp that very clear truth went off on it. My main mistake was in imagining that people understood the classical analogs of wave diffraction and Poynting fluxes, and why the correspondence principle assures that those notions are going to be relevant when you do an ensemble average over individual quantum measurements. This is also why Bragg's law, discovered for X-rays, would have also been tried as an application to electron and neutron diffraction, even if the Braggs had not known that electrons and neutrons were particles, and even if there had been no quantum mechanics. It's simply the way physics is done-- we find concepts and look for places to apply them, and classical limits admit to classical analysis-- just like the "average trajectories" in the two-slit experiment. Analysis doesn't mean you can answer all the questions, it means you have made useful discoveries and gained useful insights, using classical approaches like Maxwell's equations and Huygen's principle. I wonder if you even understand this now.

ETA:
What's more, the way I characterized the correspondence principle was perfectly mainstream, and actually insightful if you can just get over yourself. The correspondence principle is the reason the way we do physics works-- it is why we don't have to completely throw out a classical theory every time a more fundamental description comes along, or why we won't have to throw out quantum mechanics when string theory comes along, and so forth. It is the reason our approach to physics works. You could also say it that whatever is the reason that physics works is the reason for the correspondence principle, and in support I cite basic logic and a rudimentary understanding of the history of science.

 

[unusualname]

Actually, nothing in this thread has anything to do with my understanding of QM, which is actually just fine thank you. This thread is all about classical analogs of QM, which has to do with other approaches to understanding similar concepts (like diffraction). I'm not even sure you quite understand how physics works in the first place, so let's start at the beginning.

In physics, we do observations, see phenomena that seem strange-- whether it be acceleration, diffraction, or entanglement. We then design theories to help us understand and predict. At what point do those theories take ownership of the observed phenomena, such that we could correctly say that phenomena is "strictly classical" or "strictly quantum mechanical" or "strictly field theoretic?" Never. At no time do those claims make any sense at all, because the phenomena are just phenomena, owned by themselves, not by any theory. Yes, theories can explain them to some degree, but all theories have their domains of applicability, like classical physics, like quantum mechanics. Eventually, a new theory comes along that is more fundamental, and everything that used to be "strictly classical" or "strictly quantum mechanical" is now not so strictly those things, because they never actually were in the first place.

This is the point of the correspondence principle, to understand the connections between these different theories and the observations they help understand, and why a phrase like "diffraction of particles that have mass is strictly quantum mechanical" is really just a mistake about how physics works. That you see it in many places is just because people get a bit lazy about it, but when you look at the endeavor of physics from a safe height, it's obvious what I'm saying here is true. Forest for the trees, I'm afraid.

Yes but as I've explained the correspondence principle was just a wishy-washy prelude to the much more specific Decoherence argument, which your hero Bohr never managed to quite formulate.

The correspondence principle is just an out-dated, though sometimes useful, aid to thinking.

Decoherence has a precise (and pure quantum mechanical) formulation.

The only thing decoherence doesn't solve is the "measurement problem", it otherwise explains the macroscopic world "strictly quantum mechanically" as you say.

 

[zenith8]

Slightly off topic.. can anyone point me to a thread on Physics Forums where any contributor with more than - say - 10 posts changes their mind about anything, ever? Just curious.

Blah.. Blah.. Blah.. Blah.. Blah.. Blah blah blah blah blah.. Blah.

Not the answer I was looking for, Kenny..

 

[Ken G]

Yes but as I've explained the correspondence principle was just a wishy-washy prelude to the much more specific Decoherence argument, which your hero Bohr never managed to quite formulate.

The correspondence principle goes way past Bohr and classical/quantum. It is the reason we can do physics, even though we don't get the fundamental theory out of the blocks, we have to muddle along with better and better theories that nevertheless work quite well in their domains of application. That's all Bohr was saying, I think his point there was pretty obvious and will be just as true for quantum/string as it was for classical/quantum.

The correspondence principle is just an out-dated, though sometimes useful, aid to thinking.

Useful aids to thinking are rare and valuable-- and never out-dated.

The only thing decoherence doesn't solve is the "measurement problem", it otherwise explains the macroscopic world "strictly quantum mechanically" as you say.

Yes, more fundamental theories can always describe the less fundamental ones, plus more.{EDIT} But the physicist tailors the theory used to the depth of the question at hand, not to the most fundamental theory available. That's why Newton's gravity still gets used far more often than Einstein's{EDIT}. So that's why the issue here is, we should not fool ourselves into thinking we are making a quantum-mechanical argument when we do so much averaging of the quantum data that we end up with nothing but the classical limit.

 

[Ken G]

Not the answer I was looking for, Kenny..

Then I guess you'll just miss the point of the thread. No problem for me there.

 

[DevilsAvocado]

General warning to laymen:

[PLAIN]http://www.governamerica.com/images/animated_siren.gif [/URL][SIZE="7"][B][/URL] Ken G [/B][PLAIN][PLAIN]http://www.governamerica.com/images/animated_siren.gif[/URL]
[PLAIN]http://en.wikipedia.org/wiki/Not_even_wrong"[/URL][/CENTER]

It’s a long time since I saw this much crap on PF. Either Ken G is very very old ([I]born around 1900?[/I]) and maybe missed the last 40+ years in physics, or he is very very religious ([I]creationist?[/I]). Either way, he is trying to turn the clock back to the glorious and divine days of Sir Isaac Newton and Classical physics.

He’s jumping back and forth among different levels of completely preposterous and home-cooked 'arguments' & 'claims'. He mixing apples and oranges so widely and without shame, that it all becomes hilarious in the end. In fact he reminds me of [URL]http://www.youtube.com/watch?v=ZN5PoW7_kdA"[/URL]...

Therefore, let’s sort things out:
[QUOTE][SIZE="1"] [url]http://en.wikipedia.org/wiki/Analogy[/url]
[B]Analogy[/B]
Analogy (from Greek "ἀναλογία" – analogia, "proportion") is a cognitive process of transferring information or meaning from a particular subject (the analogue or source) to another particular subject (the target), and a linguistic expression corresponding to such a process. In a narrower sense, analogy is an inference or an argument from one particular to another particular, [B]as opposed to deduction[/B], induction, and abduction, where at least one of the premises or the conclusion is general.

[SIZE="1"] [url]http://en.wikipedia.org/wiki/Physical_law[/url]
[B]Physical law[/B]
A physical law or scientific law is a scientific generalization [B]based on empirical observations of physical behaviour[/B] (i.e. the law of nature). Laws of nature are observable. Scientific laws are empirical, describing observable patterns. Empirical laws are typically conclusions based on repeated scientific experiment and observation, over many years, and which have become accepted universally within the scientific community. The production of a summary description of our environment in the form of such laws is a fundamental aim of science. These terms are not used the same way by all authors. Some philosophers e.g. Norman Swartz use "physical law" to mean what others mean by "natural law"/"law of nature".

[SIZE="1"] [url]http://en.wikipedia.org/wiki/Natural_law[/url]
[B]Natural law[/B]
Natural law or the law of nature (Latin: lex naturalis) has been described as a law whose content is set by nature and is thus universal. As classically used, natural law refers to the use of reason to analyze human nature and deduce binding rules of moral behavior. The phrase natural law is opposed to the positive law (meaning "man-made law", not "good law"; cf. posit) of a given political community, society, or nation-state, and thus can function as a standard by which to criticize that law.

[SIZE="1"] [url]http://en.wikipedia.org/wiki/Philosophy_of_science[/url]
[B]Philosophy of science[/B]
The philosophy of science is concerned with the assumptions, foundations, methods and implications of science. It is also concerned with the use and merit of science and sometimes overlaps metaphysics and epistemology by exploring whether scientific results are actually a study of truth. In addition to these central problems of science as a whole, many philosophers of science also consider problems that apply to particular sciences (e.g. philosophy of biology or philosophy of physics). Some philosophers of science also use contemporary results in science to reach conclusions about philosophy.

Philosophy of science has historically been met with mixed response from the scientific community. Though scientists often contribute to the field, many prominent scientists have felt that the practical effect on their work is limited: [B]“Philosophy of science is about as useful to scientists as ornithology is to birds,” according to physicist Richard Feynman[/B].[/QUOTE]


These are the 'cornerstones' of Ken G’s home-cooked messy 'thesis':
[LIST]
[*][I]"many quantum effects do have classical analogs that we take advantage of all the time, especially when testing quantum mechanics"[/I]


[*][I]"any quantum theory gives birth to a classical theory in the limit of large occupation numbers"[/I]


[*][I]"the correspondence principle is a law of nature"[/I]
[/LIST]

Right away we can see that the fist "analogy claim" could be okay, if used the right way. The intimation that quantum experimentalist generally are depending on "classical analogs" to successfully perform their tasks, is completely hooey. Ask Dr. Anton Zeilinger about http://www.nature.com/nature/journal/v390/n6660/full/390575a0.html" for god’s sake!

The other two points, is a mix of home-cooked speculations and completely crackpot madness.

The first obvious question: What is the name of [I]any[/I] quantum theory that has given birth to a classical theory?? The [I]classical[/I] theory of Entangled Elephants?? The [I]classical[/I] theory of wave–particle duality in the Elephant-Anaconda?? The [I]classical[/I] theory of spin-½ Elephants?? The [I]classical[/I] theory of the Double-Elephant-slit experiment?? The [I]classical[/I] theory of Elephant teleportation??

This is completely hilarious.

Surely, one could probably entangle elephants if it was possible to completely get them 'screened off', but then they would not be 'classical elephants', but very cold 'quantum elephants' in their 'ground state'.

It’s very hard to get a grip on what Ken G is talking about, and Ken G himself probably has similar problems, because sometimes classical mechanics is [B][I]not[/I][/B] Newton's laws, and sometimes [B][I]it is[/I][/B]... Utterly confusing and completely illogical.

If we try to find any logic in this excessive gobbledygook of Ken G, we must come to the conclusion that if all quantum theories give birth to a classical theory, then must also every quantum effects have a classical analog. But this is not what the genius Ken G bring to table of home-cooked classical spaghetti...

He hasn’t even followed his own line of thinking.

He says the correspondence principle is a "law of nature"? Where and when stated Niels Bohr this? Any reference? No, of course not, because this something Ken G just made up. Niels Bohr would never say anything like this, and he would certainly not used the word "law of nature". What "law of nature" is Ken G referring to? A physical law? Or a natural law? Or some new 'invention' of Ken G’s "philosophical law"?

We don’t get any clear information from Ken G on this, only insinuations, because he knows it takes a lot more than mumbling a few words to establish a physical law. This is complete and totally ridiculous nonsense, and a sever violation of PF rules.

As if this wasn’t enough, Ken G manage to exchange the meaning of the correspondence principle, when he gets cornered with undisputable facts – from something that’s suppose to be the (final) view of Niels Bohr, to some fluffy philosophical speculation on "the reduction of a new scientific theory".
[QUOTE][SIZE="1"] [url]http://en.wikipedia.org/wiki/Correspondence_principle#Other_scientific_theories[/url]

[B]Correspondence principle – Other scientific theories[/B]
The term "correspondence principle" is used in a more general sense to mean the reduction of a new scientific theory to an earlier scientific theory in appropriate circumstances. This requires that the new theory explain all the phenomena under circumstances for which the preceding theory was known to be valid, the "correspondence limit".

For example, Einstein's special relativity satisfies the correspondence principle, because it reduces to classical mechanics in the limit of velocities small compared to the speed of light. General relativity reduces to Newtonian gravity in the limit of weak gravitational fields.[/QUOTE]

Wikipedia explanation is fine, but there is only problem – Ken G is [I]swapping[/I] the whole thing in his home-cooked mess... Thus we end up in a situation where [I]classical mechanics has to explain all the phenomena in quantum mechanics[/I], for these quantum phenomena to be valid!? This is TOTALLY nuts!

And this "correspondence limit" was certainly not something Bohr was advocating:
[QUOTE][SIZE="1"] [url]http://en.wikipedia.org/wiki/Correspondence_principle#Quantum_mechanics[/url]

[B]Correspondence principle – Quantum mechanics[/B]
Because quantum mechanics only reproduces classical mechanics in a statistical interpretation, and because the statistical interpretation only gives the probabilities of different classical outcomes, [B]Bohr has argued that classical physics does not emerge from quantum physics[/B] in the same way that classical mechanics emerges as an approximation of special relativity at small velocities. [B]He argued that classical physics exists independently of quantum theory and cannot be derived from it[/B]. His position is that it is inappropriate to understand the experiences of observers using purely quantum mechanical notions such as wavefunctions because the different states of experience of an observer are defined classically, and do not have a quantum mechanical analog.[/QUOTE]

Ken G has certainly created a great mess here. The most voluminous I’ve seen in years. He’s jumping back and forth, guessing and talking and changing 'arguments' on the run, without any clue whatsoever on where he’s going – except that classical mechanics has the answer to everything ([I]he believes[/I]).

It gets tragicomic when Ken G without any doubts concludes his baloney thoughts; [I]"the way I characterized the correspondence principle was perfectly mainstream"[/I] ...

Which way might that be?? :bugeye:

To make things even more 'amusing', from start, Ken G picked and intermediate version of Bohr’s Correspondence principle that has been completely obsolete for almost a hundred years - [B]The Weak form of the Correspondence principle[/B], with the 'classical limit' of quantum mechanics, which Niels Bohr abandon long time ago. The only "logical" explanation for this very weird behavior, is that Ken G is fond of 'old things' – really old. He’s probably the only 'cultivator' of the weak form of the correspondence principle still alive on this planet...

As said, Ken G is bungee jumping between the extremes. Sometimes he’s on an 'educational quest', helping laymen to 'understand thru analogies'. Next time, he’s mixing up the [PLAIN]http://en.wikipedia.org/wiki/Wave_equation"[/URL] could easily be replaced with a classical 'substitute'...?? :confused:

What could one say? :eek:

This is a graphical representation of the classical wave equation:
[PLAIN][URL]http://upload.wikimedia.org/wikipedia/commons/1/1f/Wave_equation_1D_fixed_endpoints.gif[/URL]

And the Schrödinger equation for a harmonic oscillator:
[URL]http://upload.wikimedia.org/wikipedia/commons/9/90/QuantumHarmonicOscillatorAnimation.gif[/URL]
A harmonic oscillator in classical mechanics (A-B) and quantum mechanics (C-H). In (A-B), a ball, attached to a spring, oscillates back and forth. (C-H) are six solutions to the Schrödinger Equation for this situation. The horizontal axis is position, the vertical axis is the real part (blue) or imaginary part (red) of the wavefunction. (C,D,E,F), but not (G,H), are stationary states (energy eigenstates), which come from solutions to the Time-Independent Schrödinger Equation.

I would recommend Ken G to play around with this 'simple' http://www.falstad.com/qm1d/"[/URL], and wait for the classical [B][I]mathematical[/I][/B] solution for that. How hard could it be...? :-p

[PLAIN]http://www.falstad.com/qm1d/"[/URL]
[I](Maximize the window for better resolution)[/I]
[ATTACH=full]197131[/ATTACH]

[PLAIN]http://www.falstad.com/qmatom/"[/URL]
[I](Click & drag to rotate in 3D)[/I]
[ATTACH=full]197132[/ATTACH]

What a thriller! Good luck! :biggrin:

[I]... Maybe it’s appropriate to inform Ken G that Niels Bohr once tried, and failed with a classical wave description of the electromagnetic field, in the [PLAIN]http://en.wikipedia.org/wiki/BKS_theory"[/URL] ...[/I]

[INDENT][I]"For Bohr the lesson to be learned from the disproof of the BKS theory was not that photons do exist, but rather [B]that the applicability of classical space-time pictures in understanding phenomena within the quantum domain is limited[/B]. This theme would become particularly important a few years later in developing the notion of complementarity."[/I][/INDENT]

Ken G says – [I]"we might understand what intelligence is"[/I]. That’s a very interesting and challenging thought... but we’ll probably not solve that particular question in this thread...

There has been a lot of inconsistent mumbling and words from Ken G, but almost no facts and references. How about some words from the man himself, Niels Bohr?

[I](I recommend everyone who is interested in the Bohr–Einstein debates to read the full text, it’s very interesting.)

(emphasis mine)[/I]
[QUOTE][SIZE="1"] [PLAIN]http://www.mpa-garching.mpg.de/~lxl/personal/images/science/BE.htm[/URL]

[B]DISCUSSION WITH EINSTEIN ON EPISTEMOLOGICAL PROBLEMS IN ATOMIC PHYSICS

NIELS BOHR[/B]

Originally published in Albert Einstein: Philosopher-Scientist, P. A. Schilpp, ed., pp. 200-41 The Library of Living Philosophers, Evanston (1949).

...
From the very beginning the main point under debate has been the attitude to take to the departure from customary principles of natural philosophy characteristic of the novel development of physics which was initiated in the first year of this century by Planck's discovery of the universal quantum of action. This discovery, which revealed a feature of atomicity in the laws of nature going far beyond the old doctrine of the limited divisibility of matter, [B]has indeed taught us that the classical theories of physics are idealizations which can be unambiguously applied only in the *limit* where all actions involved are large compared with the quantum[/B].

...
These ideas, which were soon confirmed by the experiments of Franck and Hertz (I9I4) on the excitation of spectra by impact of electrons on atoms, involved a further renunciation of the causal mode of description, since evidently the interpretation of the spectral laws implies that an atom in an excited state in general will have the possibility of transitions with photon emission to one or another of its lower energy states. In fact, the very idea of stationary states is incompatible with any directive for the choice between such transitions and leaves room only for the notion of the relative probabilities of the individual transition processes. [B]The only guide in estimating such probabilities was the so-called correspondence principle[/B] which originated in the search for the closest possible connection between the statistical account of atomic processes and the consequences to be expected from classical theory, [B]which should be valid in the *limit* where the actions involved in all stages of the analysis of the phenomena are large compared with the universal quantum[/B].

...
The new progress in atomic physics was commented upon from various sides at the International Physical Congress held in September I927, at Como in commemoration of Volta. In a lecture on that occasion [8], I advocated a point of view conveniently termed "complementarity," suited to embrace the characteristic features of individuality of quantum phenomena, and at the same time to clarify the peculiar aspects of the observational problem in this field of experience. For this purpose, it is decisive to recognize that, [B]however far the phenomena transcend the scope of classical physical explanation, the account of all evidence must be expressed in classical terms[/B]. The argument is simply that by the word "experiment" we refer to a situation where we can tell others what we have done and what we have learned and that, therefore, the account of the experimental arrangement and of the results of the observations must be expressed in unambiguous language with suitable application of the terminology of classical physics

...
In the quantum-mechanical description our freedom of constructing and handling the experimental arrangement finds its proper expression in the possibility of choosing the classically defined parameters entering in any proper application of the formalism. Indeed, in all such respects quantum mechanics exhibits a correspondence with the state of affairs familiar from classical physics, [B]which is as close as possible when considering the individuality inherent in the quantum phenomena[/B]. Just in helping to bring out this point so clearly, Einstein's concern had therefore again been a most welcome incitement to explore the essential aspects of the situation.

...
As a more appropriate way of expression [B]I advocated the application of the word phenomenon exclusively to refer to the observations obtained under specified circumstances, including an account of the whole experimental arrangement[/B]. In such terminology, the observational problem is free of any special intricacy since, in actual experiments, all observations are expressed by unambiguous statements referring, for instance, to the registration of the point at which an electron arrives at a photographic plate. Moreover, speaking in such a way is just suited to emphasize that the appropriate physical interpretation of the symbolic quantum-mechanical formalism amounts only to predictions, of determinate or statistical character, pertaining to individual phenomena appearing under conditions defined by classical physical concepts.[/QUOTE]

I’m sorry Ken G, these are Niels Bohr’s own words from 1949, and unless there’s something wrong with my browser – he’s only mentioning the word (classical) [B]*limit*[/B] twice (2) and it originates from around 1914. From 1927 and later on, Niels Bohr has moved towards the experimental arrangement ([I]Strong form of the correspondence principle[/I]), and as you see – there’s of course no talk about a [I]"law of nature"[/I]. Bohr was too intelligent to make a simple blunder like that when dealing with epistemology.

It’s time for you to say: [I]– Okay guys, I was wrong. I’m sorry I don’t know what happened...[/I]

Anything else will only make it worse for you.

Finally, I have to mention your logical core meltdown when it comes to entanglement, which in a way is symptomatic for all your baloney claims lately. Your Catch-22 goes like this; every quantum theory gives birth to a classical theory in the limit of large occupation numbers. If a quantum theory doesn’t give birth to a corresponding classical theory, then that quantum theory is wrong, and therefore every quantum theory must give birth to a classical theory, the classical domain is default.

I’ve seen a lot on PF, but this must be the crankiest "idea" put forth in QM forums this far.​

 

[DevilsAvocado]

Ken G, I urge you to leave the past, and welcome you to the future, err, the present!

http://en.wikipedia.org/wiki/Quantum_mechanics#Quantum_mechanics_and_classical_physics

Quantum mechanics and classical physics
Predictions of quantum mechanics have been verified experimentally to a extremely high degree of accuracy. According to the correspondence principle between classical and quantum mechanics, all objects obey the laws of quantum mechanics, and classical mechanics is just an approximation for large systems (or a statistical quantum mechanics of a large collection of particles). The laws of classical mechanics thus follow from the laws of quantum mechanics as a statistical average at the limit of large systems or large quantum numbers.

Quantum coherence is an essential difference between classical and quantum theories, and is illustrated by the Einstein-Podolsky-Rosen paradox. Quantum interference involves adding together probability amplitudes, whereas when classical waves interfere there is an adding together of intensities. For microscopic bodies, the extension of the system is much smaller than the coherence length, which gives rise to long-range entanglement and other nonlocal phenomena characteristic of quantum systems. Quantum coherence is not typically evident at macroscopic scales, although an exception to this rule can occur at extremely low temperatures, when quantum behavior can manifest itself on more macroscopic scales (see Bose-Einstein condensate and Quantum machine).


http://en.wikipedia.org/wiki/Quantum_machine

The first Quantum Machine
The first quantum machine was created on August 4, 2009 by Aaron D. O'Connell while pursuing his Ph.D. under the direction of Andrew N. Cleland and John M. Martinis at the University of California, Santa Barbara. O'Connell and his colleagues coupled together a mechanical resonator, similar to a tiny springboard, and a qubit, a device that can be in a superposition of two quantum states at the same time. They were able to make the resonator vibrate a small amount and a large amount simultaneously — an effect which would be impossible in classical physics. The mechanical resonator was just large enough to see with the naked eye — about as long as the width of a human hair. The groundbreaking work was subsequently published in the journal Nature in March 2010. The journal Science declared the creation of the first quantum machine to be the "Breakthrough of the Year" of 2010.

Photograph of the quantum machine developed by O'Connell. The mechanical resonator is located to the lower left of the coupling capacitor (small white square). The qubit is connected to upper right of the coupling capacitor.

Scanning electron micrograph of the film bulk acoustic resonator. The mechanically active part of the resonator is supported to the left by two metal leads which act as electrical connections.

The paper on nature.com http://www.nature.com/nature/journal/v464/n7289/full/nature08967.html".

TED – http://en.wikipedia.org/wiki/Aaron_D._O%27Connell"[/URL]: Making sense of a visible quantum object
[url]http://www.youtube.com/watch?v=dvYYYlgVAao&hd=1[/url]
https://www.youtube.com/watch?v=dvYYYlgVAao

There’s a lot of very interesting projects going on at [PLAIN]http://www.physics.ucsb.edu/~martinisgroup/"[/URL]:

Generation of Three-Qubit Entanglement Using Josephson Phase
[url]http://www.physics.ucsb.edu/~martinisgroup/theses/Neeley2010b.pdf[/url]

[ATTACH=full]143933[/ATTACH]


Finally an interview with Anton Zeilinger about QM now and in the future:

[MEDIA=youtube]kIzMZtQ9NwQ[/MEDIA]
https://www.youtube.com/watch?v=kIzMZtQ9NwQ


[B]TIME TO WAKE UP KEN G, IT’S 2011 – NOT 1911![/B]

 

[Ken G]

A very interesting flight of fancy. Obviously missed my point completely, you think I don't understand quantum mechanics, or don't believe in it, or some other baloney that only shows you really missed everything I said (my main point dates back to my pointing out the flaws in a claim that "average trajectories" are a quantum mechanical concept, but as you missed all that completely, I'm certainly not going to reprise it now). But I should correct one factual error-- I never claimed, nor thought, that the correspondence principle was a "law of nature." In fact, I don't believe there is any such thing as a law of nature. But there are quite a few "laws" that physicists have found great use from, and what we choose to call a law is a pretty irrelevant exercise in scientific sociology. But feel free to decide what you personally do and do not consider to be a law of nature, just don't expect anyone else to care.

What actually matters is what we use, and how it helps us, and we certainly use the correspondence principle, writ large, constantly in physics. I described what I meant by that principle-- that more fundamental theories that apply in wider domains of application must still be consistent with less fundamental theories in the domain of demonstrable success of the latter. And it is certainly of tremendous value in physics, being in fact the reason that physics works at all. It is certainly the reason that Newton's gravity is used after Einstein, that classical wave mechanics is used after quantum mechanics, that both continuum and fluid mechanics are used after the discovery of the atom, and that Bragg's law applies to ensemble averages of electron and neutron diffraction in crystals. And, more to the point, it is why a simple classical-wave treatment of photon diffraction can yield Poynting fluxes that look an awful lot like the "average trajectories" of the OP experiment, which also look a lot like deBB trajectories, which therefore tell us nothing conclusive about what individual members of the ensemble are doing. Which was the point all along, and I notice that in none of your pointless diatribes did you even mention or recognize this fact. Methinks though doth protest too much, there actually is a science matter on the table here.

 

[unusualname]

But I should correct one factual error-- I never claimed, nor thought, that the correspondence principle was a "law of nature." In fact, I don't believe there is any such thing as a law of nature. But there are quite a few "laws" that physicists have found great use from, and what we choose to call a law is a pretty irrelevant exercise in scientific sociology. But feel free to decide what you personally do and do not consider to be a law of nature, just don't expect anyone else to care.

The correspondence principle is not a law of nature, it simply a rule for us dumb humans to check that our (quantum mechanical) model of reality is consistent.

I'm afraid that's a pretty good definition of a "law of nature." Why you see a distinction there is certainly outside anything that could be called science.

Ken G, struggling with the logic really

 

[DevilsAvocado]

But I should correct one factual error-- I never claimed, nor thought, that the correspondence principle was a "law of nature." In fact, I don't believe there is any such thing as a law of nature.

I’m afraid you’re making a fool of yourself again. You apparently missed the "First law of internet":

Never deny a statement of yours that’s only a few posts away and that can never be erased.​

The correspondence principle is not a law of nature, it's simply a rule for us dumb humans to check that our (quantum mechanical) model of reality is consistent.

I'm afraid that's a pretty good definition of a "law of nature."

(Edit: Ops, thanks unusualname for 'beating' me! )

And it doesn’t get any better...

But there are quite a few "laws" that physicists have found great use from, and what we choose to call a law is a pretty irrelevant exercise in scientific sociology.

Wow! Is this what you call an "irrelevant exercise in scientific sociology"??

• Archimedes’ principle
• Kepler’s three laws of planetary motion
• Newton’s three laws of motion
• Euler's laws of rigid body motion
• Newton’s law of universal gravitation
• Newton’s law of heat conduction
• Boyle’s law
• Law of conservation of energy
• Joule’s first and second law
• The four laws of thermodynamics
• Coulomb's law
• Maxwell's equations
• Special Relativity
• General Relativity
• Planck's law of black body radiation
• Heisenberg Uncertainty Principle
• Matter wavelength
• Schrödinger equation
  ... etc ...

What actually matters is what we use, and how it helps us, and we certainly use the correspondence principle, writ large, constantly in physics. I described what I meant by that principle-- that more fundamental theories that apply in wider domains of application must still be consistent with less fundamental theories in the domain of demonstrable success of the latter.

Thanks a lot Ken, finally something that looks like logical mainstream. The sole reason for this 'diatribe' is of course that you’re mixing apples and oranges wildly, and you’re bungee jumping between inconsistent standpoints of yours. On this very same page, in post #181 you said:

I don't know how many times I need to say that this is the classical limit I have been referring to in regard to the correspondence principle for both electrons and photons, just look back at that "student experiment" post again, if you can find it in all the misconstruals I've had to suffer.

I hope you understand the contradiction in advocating two different and completely incompatible versions of the correspondence principle? One is old and obsolete (classical limit), and the other (backward compatibility) is rejected by Niels Bohr, since he argued that classical physics does not emerge from quantum physics in the same way that classical mechanics emerges as an approximation of special relativity at small velocities.

Get it? None of your versions works...

(On the other hand this is quite interesting... since this looks like some "psychological superposition" of "counterfactual thinking"... )

I think anyone reading this thread understands what’s "going on" here. I don’t have anything further to add.

Finally, a quote from Shakespeare’s Hamlet:

There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.​

Take care!

 

[Ken G]

Ken G, struggling with the logic really

Sorry, but you once again failed to make your point. I did not claim it was a law of nature, I claimed that you were making an arbitrary distinction between what is and is not a "law of nature." As I just said, I personally don't think "law of nature" applies to anything that physics does, but it may apply to lots of things physics does, including the correspondence principle, using someone else's meaning of the phrase. My actual point was that your attempt to deny the value of the correspondence principle on the grounds that it was "not a law of nature" was ridiculous. Which it was. I might as well say Newton's laws are not laws of nature either, which they aren't-- but it would be an equally meaningless argument. We don't do physics by labeling things.

 

[Ken G]

I’m afraid you’re making a fool of yourself again. You apparently missed the "First law of internet":

Never deny a statement of yours that’s only a few posts away and that can never be erased.​

See above. You failed to understand my point once again,which was that the whole "law of nature" hooey, not even brought up by me, was a complete red herring, because the term is completely nonspecific and can be applied to the correspondence principle or not applied to it, depending on how one defines it. I also pointed out that the important attributes of the correspondence principle could easily be construed as that, unless someone wanted to offer a more specific definition. Which they did not, of course. Pray tell, do you know what a law of nature is? Be sure to include references, of course, I'm sure the textbooks will be quite informative on the topic. Oh and, it would be nice if that completely arbitrary list that you seem to think are laws of nature would actually conform to the definition you dig up, but the correspondence principle does not. And it doesn't even matter if you can shoehorn a definition into that space, because my argument did not rest on what we call things, it rested on what is necessary for the endeavor of physics to actually work.

Getting back to the real science, and the OP, let me ask you one simple question. Do you think an "average trajectory" diagram, which makes weak measurements and combines them into a streamline picture, could ever be used as evidence that photons passing through the left slit hit the left side of the screen? Yes or no, this is the actual science question on the table here.

I hope you understand the contradiction in advocating two different and completely incompatible versions of the correspondence principle? One is old and obsolete (classical limit), and the other (backward compatibility) is rejected by Niels Bohr, since he argued that classical physics does not emerge from quantum physics in the same way that classical mechanics emerges as an approximation of special relativity at small velocities.

That the principle has many sides does not make them incompatible. Is your face incompatible with your posterior? Is it different?

 

[unusualname]

Sorry, but you once again failed to make your point. I did not claim it was a law of nature, I claimed that you were making an arbitrary distinction between what is and is not a "law of nature." As I just said, I personally don't think "law of nature" applies to anything that physics does, but it may apply to lots of things physics does, including the correspondence principle, using someone else's meaning of the phrase. My actual point was that your attempt to deny the value of the correspondence principle on the grounds that it was "not a law of nature" was ridiculous. Which it was. I might as well say Newton's laws are not laws of nature either, which they aren't-- but it would be an equally meaningless argument. We don't do physics by labeling things.

A law of nature is something we humans conceive to be the way nature works .The correspondence principle is a now not very important philosophical principle, since we have a much more sophisticated understanding of how the macroscopic emerges from the microscopic.

Your argument on this thread amounts to this - the flux lines for single photons can be (qualitatively) classically constructed (thanks to my references) so there is no quantum mystery here, so let's just move on. However you then claim that if a two-photon entangled trajectory was "measured" you would still find a classical flux analog (nope, you won't)

You also ignore the recent measurement of a QM wavefunction article, dismissing it as some silly people who can't understand the correspondence principle or similar (you need to be specific why you dismiss this experiment otherwise I have to portray you dismissing it for this reason)

And you have also claimed that delayed choice experiments can be explained by maxwell's equations

 

[Ken G]

A law of nature is something we humans conceive to be the way nature works .The correspondence principle is a now not very important philosophical principle, since we have a much more sophisticated understanding of how the macroscopic emerges from the microscopic.

So your argument is that when we have a more sophisticated understanding of something, the more basic principles disappear? We have a more sophisticated understanding of gravity, but Newton's gravity has not disappeared from scientific journals. We have a more sophisticated understanding of the statistical mechanics of van der Waals forces, but the ideal gas law has not disappeared. We have a more sophisticated understanding of quantum mechanics, but classical mechanics has not disappeared. This is all the beating heart of the correspondence principle, writ large-- science is an endeavor that routinely matches the complexity of the description to the domain of interest of the outcome. None of that has disappeared, no.

Your argument on this thread amounts to this - the flux lines for single photons can be (qualitatively) classically constructed (thanks to my references) so there is no quantum mystery here, so let's just move on.

Completely wrong. That is not at all what I said, thought, or advocated in any way. As I've told you over and over, that is some make believe version of what I said, that you invented so you could attack it. I frankly have no idea where you got that from. Oh, and I pointed this out prior to your reference, so the point was not "thanks to" your reference, it was merely supported by your reference. A fact which seems to have escaped you here, but thank you.

What I actually said is that since the average flux trajectories are ensemble concepts, not individual particle concepts, expressly because they are averaged over an ensemble, it means they are the same concepts that are addressible in a more classical ensemble treatment of the phenomenon (where once again, by "classical" I mean classical wave treatment, not classical mechanics treatment), similar to how the Braggs analyzed X-ray diffraction in crytals, and how it also applied to diffraction of ensembles of electrons and neutrons. Therefore, the average trajectory diagram does not tell us squat about what any individual particles are doing, because we could generate a similar figure with the techniques I described, without even knowing that we were ever dealing with individual particles (just as the Braggs could do everything they did without knowing they were dealing with individual photons). So this is what I actually said, and since I see little resemblance to your caricature, not a single one of your many objections has even the least relevance to what I actually said.

However you then claim that if a two-photon entangled trajectory was "measured" you would still find a classical flux analog (nope, you won't)

Another make-believe idea in your head, never said, or even thought, by me. I understand two-particle entanglement, and I understand classical limits, and I understand the difference. It is you who do not, and that is why you cannot understand, yet must instead insert your klunky caricatures in place of what was actually said.

You also ignore the recent measurement of a QM wavefunction article, dismissing it as some silly people who can't understand the correspondence principle or similar (you need to be specific why you dismiss this experiment otherwise I have to portray you dismissing it for this reason)

More make believe on your part. What thread have you been reading? Didn't someone just quote a rule of the internet that it is silly to make claims about what was said when it's right there in black and white? What I actually said about that experiment is:
1) it is not the subject of this thread
2) I have not analyzed it, but I can say right off the bat that part of their claim is unsubstantiated. They claimed they could measure the real and imaginary parts of the wave function independently, but I pointed out that no wave function can be measured, or even attributed meaning, to within an arbitrary global complex phase. So yes, I know with complete certainty that they did not actually measure the real and imaginary parts of the wave function independently, but if one chooses to view that as a nitpick, I can only say that I did not dismiss the article nor reach any other conclusions about it at all. Why you have to imagine I did is a question only you can know the answer to. Why do you think that is?

And you have also claimed that delayed choice experiments can be explained by maxwell's equations

No, actually I did not ever say that either. I do wonder what can be learned about them from a judicious understanding of the classical analogs Maxwell's equations might provide, and I suspect that there are indeed useful analogs there, but I certainly never said the experiments could be "explained" by them. Indeed, all I"ve ever claimed is that classical limits of such experiments can be understood classically, but you've never really appreciated that nuance, or indeed almost any nuance of my argument.

 

[unusualname]

I don't understand you because there is no classical limit related to entanglement, the wavefunction or delayed choice experiments.

So what on Earth are you talking about?

The whole point of QM is that it is a spectacularly non-classical theory of nature, why would anyone want to emphasize classical limits?

I suspected you got carried away with a partly reasonable anti-bohmian stance which seems to have developed over several threads into an "everything has a classical analog if you look at it from a certain point of view" argument.

 

[Ken G]

I don't understand you because there is no classical limit related to entanglement, the wavefunction or delayed choice experiments.

So what on Earth are you talking about?

Whether or not there are classical analogs of entanglement that could be informative is not yet clear. But there certainly are classical analogs to the wavefunction, indeed that's the whole reason it is called a wavefunction in the first place (and classical analogs is exactly how Schroedinger arrived at his celebrated equation in the first place). There certainly is a long history of using insights from classical analogs in quantum mechanics.

The whole point of QM is that it is a spectacularly non-classical theory of nature, why would anyone want to emphasize classical limits?

Just ask Schroedinger, it worked for him.

I suspected you got carried away with a partly reasonable anti-bohmian stance which seems to have developed over several threads into an "everything has a classical analog if you look at it from a certain point of view" argument.

Let's agree that the usefulness of classical analogs is something that is better demonstrated than postulated. I really was only using classical analogs to show that average trajectories are not strictly quantum mechanical objects because they don't apply to quanta, they apply to ensembles of quanta and so are amenable to being understood with classical-wave analogs.