What are the implications of this experiment?

[Varon]

And why precisely this happens? And if all energy from the field goes to that one little electron, isn't it a kind of collapse of the field?

No. Not from the field but within the detector. See message #30 in https://www.physicsforums.com/showthread.php?t=490492&page=2

"Each electron feels just the piece of the quantum wave reaching it. The electron responds by random ionization, with a rate proportional to the intensity. It takes the energy from its surrounding.

The detector as a whole receives the energy everywhere, also with a rate proportional to the intensity. This energy is redistributed (fast, but with a speed slower than that of light) through the whole detector, roughly according to hydrodynamic laws.

Thus there is no violation of conservation of energy."

Refute it and extra points to Bohmian Mechanics whose mortal enemy is Neumaier QFT Interpretation (it's really QFT direct interpretation if one will take seriously that particles are just momentum and energy of the field... meaning there are really no particles).

 

[Demystifier]

"Each electron feels just the piece of the quantum wave reaching it. The electron responds by random ionization, with a rate proportional to the intensity. It takes the energy from its surrounding.

I still don't get it. If EACH electron responds, then why do we observe a localized event? If only one responds, then why only one?

 

[IllyaKuryakin]

... I don't find the appearance of Bhomian-like trajectory plots in support the notion that quantization should involve tiny billiard-ball-like obects following definite trajectories that convincing.

I don't think that quantum physicists, as a whole, have sufficiently internalized the notion that their theories can be sufficiently correct without formulations that are not inconsistant with spacetime, not as a flat Lorenzian sheet, but requiring correctness on the inclusion of curvature.

It is not that specualative formulations cannot be 'good enough' in many cases, but can still be inconsistant with the nature of spacetime as we know it. Where are the attempts at formulating coordinate indepedent quantum mechanics?...

...Rather, the focus should be on the consistency of the stuff hypothesized to exist on some given spacelike hypersurface to be consistent with the stuff on another non-intersecting hypersurface.

The first item on your list seems to me like two items. First, I understand and respect your skepticism that Bohmain Mechanics is THE solution to the mystery of the double slit. I believe we can definitely say that deBB theory has not been falsified by Steinberg's elegant experiment. I won't address all the many physical models that were falsified by Steinbergs experiment, since you didn't bring it up, but they are many in number. My understanding is Steinberg's experiment falsifies any model that does not require the photon to have a definite position at every point during it's trajectory. If you read the paper on the details of his experiment, I believe you will come to the same conclusion. Of course, that is not the same as saying that a definate position of every photon is observable at every point in it's trajectory. According to deBB theory, the exact position of every photon is always (at least partially) a hidden variable due to HUP.

I also agree that there could be other solutions, perhaps equivalent but better in some respect, and if so I'd hope we could discriminante between them through further experimentation. I would prefer that any model suggested be accompanied with a solid theoretical foundation and an experimental test, along the lines of Einstein's suggested experimental tests of GR.

As to the second point, I agree completely. There is no reason I know of why the "best" model could not exist in Hilbert space, or some other space independent of our regular spacetime. Of course, Bohm preferred polar coordinates for some of his math in his 1952 paper, available here: http://prola.aps.org/abstract/PR/v85/i2/p166_1

But to really get into the internals of this model, you need to go back to de Broglie and understand it's basis. Unfortunately, de Broglie's papers are all in French and my French is rusty. Fortunately, my daughter speaks fluent French and helps me from time to time. There are some translations available, but I'd be careful of translations not made by qualified individuals.

My only concern with a model that exists outside of our spacetime is that it must be tested experimentally in our regular spacetime, which is of course the only space we can experiment in. Though as long as a transform is provided, I don't see that as a problem.

Well, all that's just my own humble opinion, of course.

 

[SpectraCat]

I still don't get it. If EACH electron responds, then why do we observe a localized event? If only one responds, then why only one?

Neumaier's argument is that the probability of an individual electron in the detector is proportional to the amplitude of the wavefunction of the impinging electron. So while all of the electrons in the detector interact with the delocalized wavefunction of the impinging particle, only a single, probabilistically determined one gives a localized response. Thus the wavefunction of the impinging particle never collapses, rather the collapse happens in the detector, where (I guess) it is more easily explained via decoherence.

I should state that I haven't read Arnold's book yet .. I am paraphrasing this from his forum posts.

 

[IllyaKuryakin]

I guess everyone sees what they want to .. you and yoda apparently see evidence to support the formulation of Bohmian mechanics. I do not see that, and do not understand why you see it. In Bohmian mechanics, the pilot waves are not observable, only the particles are observable, right? Bohmian mechanics predicts that the pilot wave defines the probabilistically weighted set of possible trajectories allowed for the particle, but that any single particle only follows one trajectory, right? So that notion can only be definitively demonstrated by observing individual trajectories for individual particles, which has not been realized.

With regard to the CI, it predicts that the wavefunction defines a probability amplitude for finding the particle anywhere in space. The wavefunction propagates through both slits at once, which gives rise to the interference effect. So, the *average* trajectory for the particles through the slits can be obtained simply by solving for $|\Psi^2|$ at every point in space.

This latest experiment uses weak measurements to reveal the *average* trajectories of a large ensemble of particles. From what I can tell, that result is completely consistent with both dBB and CI. I am not as familiar with MWI, but I imagine they are fine too.

Thus, while the result is a spectacular experimental tour de force, I do not see how it sheds light on any foundational issues in QM.

Please read the original paper on the experiment. If individual photons did not have a specific trajectory, their path could not have been sampled with the experimental setup.

As to the alternative to the CI, which places the observer is some mystical special position, I'll cite J. S. Bell, 1987:

"Bohm showed explicitly how parameters could indeed be introduced, into nonrelativistic wave mechanics, with the help of which the indeterministic description could be transformed into a deterministic one. More importantly, in my opinion, the subjectivity of the orthodox version, the necessary reference to the ‘observer,’ could be eliminated. ..."

If I had to bet on John Bell being right or wrong, I'd bet on John Bell, and give very good odds.

It's not a proof. I understand that. But it's the best I can offer at this point in my understanding.

 

[SpectraCat]

Please read the original paper on the experiment. If individual photons did not have a specific trajectory, their path could not have been sampled with the experimental setup.

As to the alternative to the CI, which places the observer is some mystical special position, I'll cite J. S. Bell, 1987:

"Bohm showed explicitly how parameters could indeed be introduced, into nonrelativistic wave mechanics, with the help of which the indeterministic description could be transformed into a deterministic one. More importantly, in my opinion, the subjectivity of the orthodox version, the necessary reference to the ‘observer,’ could be eliminated. ..."

If I had to bet on John Bell being right or wrong, I'd bet on John Bell, and give very good odds.

It's not a proof. I understand that. But it's the best I can offer at this point in my understanding.

I most certainly have read the paper, have you? Most of my points and arguments on this thread are expressed BY THE AUTHORS IN THE ORIGINAL WORK. For example, consider this quote from p. 1173.

"For the experimentally reconstructed trajectories for our double slit (Fig. 3), it is worth stressing that photons are not constrained to follow these precise trajectories; the exact trajectory of an individual quantum particle is not a well-defined concept. Rather, these trajectories represent the average behavior of the ensemble of photons when the weakly measured momentum in each plane is recorded contingent upon the final position at which a photon is observed."

Please explain where in that paper the authors present results or interpretations that support your claim:

If individual photons did not have a specific trajectory, their path could not have been sampled with the experimental setup.

 

[IllyaKuryakin]

I most certainly have read the paper, have you? Most of my points and arguments on this thread are expressed BY THE AUTHORS IN THE ORIGINAL WORK. For example, consider this quote from p. 1173.


Please explain where in that paper the authors present results or interpretations that support your claim:

Yes, sorry. I thought these points were self evident. Shows what i know. Of course you cannot know the exact trajectory of any individual photon. That would violate the HUP.

But if there was no definite trajectory, what did the experiment measure?

I don't mean to stir up trouble, but there has to be a position to measure a tiny bit of information about it. If the photon was spread out across the apparatus in a probability wave, the results would have just been so much statistical noise.

Of course, this violates Bohr's belief (never proven) about complementarity, and you are right, the authors did not choose to jump into that briar patch. I don't balme them. I'm sorry I did now.

No offence was intended, I hope none was taken.

 

[SpectraCat]

Yes, sorry. I thought these points were self evident. Shows what i know. Of course you cannot know the exact trajectory of any individual photon. That would violate the HUP.

Right.

But if there was no definite trajectory, what did the experiment measure?

It measures precisely what the authors say it measured ... the *average trajectories* of the photons. As I tried to indicate above, that concept is independent of any particular interpretation ... the authors themselves state this on p. 1173:

Single-particle trajectories measured in this fashion reproduce those predicted by the Bohm–de Broglie interpretation of quantum mechanics (8), although the reconstruction is in no way dependent on a choice of interpretation.

I don't mean to stir up trouble, but there has to be a position to measure a tiny bit of information about it. If the photon was spread out across the apparatus in a probability wave, the results would have just been so much statistical noise.

As far as I can tell, that is your *opinion*, not demonstrated scientific fact. If I am not correct about that, please provide support for that claim from the theory of weak measurements, and I will be happy to reconsider. From my understanding of weak measurements, they represent constraints on experimental observables that are less stringent than traditional von Neumann-style measurements that collapse the wavefunction. These constraints allow you to say things like, "the momentum of particle a at position b was confined to be in <range q>". An ensemble of position measurements on the same system will then reveal a probability distribution that is different from that of the unperturbed system, but not so different that all information about the complementary property is lost.

In the current experiment, the authors used the polarization to get information about the particle momentum. Evidently the coupling was so weak that the interference pattern is essentially unchanged from the unperturbed pattern at a given measuring plane. On the other hand, the authors only make statements about the *average* momentum of the particles measured in this way. If you look at figure 2, it shows that measurements for both polarization states created by the weak measurement show interference patterns that extend over the entire spread of x-values.

In figure 3, the reconstructed *average* trajectories are not seen to cross the line of symmetry between the slits. This does NOT mean that particles that pass through the left hand slit only contribute to the left hand part of the interference pattern. Rather it means that if you average the momenta of all the particles passing through the left hand slit, there is a slight preference for them to have a momentum in the left-hand direction. I have not taken the time to work through the math, but I expect this is *precisely* what would be expected if you work through the math for the wavefunction-based approach, taking into account the effect of the birefringent calcite crystal that is responsible for the weak measurement.

Of course, this violates Bohr's belief (never proven) about complementarity, and you are right, the authors did not choose to jump into that briar patch. I don't balme them. I'm sorry I did now.

Again, this seems to be only your personal opinion. The authors' comments seem to indicate not an unwillingness to "choose sides" in the interpretation debate, but rather a belief that their experiment does not favor one side or the other ... I guess that is why they explicitly pointed out that the trajectory reconstructions were interpretation independent.

No offence was intended, I hope none was taken.

I am never offended by scientific debate .. I just want to make these points clear, and perhaps learn something if my own understanding of the experiment is somehow flawed.

 

[IllyaKuryakin]

...I have not taken the time to work through the math, but I expect this is *precisely* what would be expected if you work through the math for the wavefunction-based approach, taking into account the effect of the birefringent calcite crystal that is responsible for the weak measurement.

This then is the gist of the debate, as I understand it. My understanding was that to make weak measurements of position, there had to be a definite position. Your expectation is that the small part of the photon position probability distribution that travels through the crystal, prior to the colapse of the entire waveform, can account for the weak measurement of position, proving nothing. Correct me if I have misunderstood you.

I can follow the math of the weak measurement of position, but I'm not sure I have the information, or the skill, to do the math to determine if the waveform based approach would produce different results or not. To be honest, I'm not even sure how to approach the calculation of change in polarization of a small section of the probability distribution of a waveform that has not been already collapsed passing through the calcite crystal?

Perhaps you have these skills, or perhaps someone else in this forum does. Otherwise, it's your expectation vs. my understanding, and I don't think we can move further with this, since the authors never specifically provided this calculation to show their results were different then what a waveform calculation would produce. I suppose, sometimes we just have to do the math. It does sound like a great thesis for a followup paper.

And yes, I often state my opinions in posts. Usually, I will add the footer, this is my own opinion, to make that clear. But generally, unless I am specifically quoting the author of a paper, then I am offering my opinion as to the "implications of this experiment", which was the subject of the thread. Anyone can read the paper and see what research teams beliefs are regarding the implications of their experiment, but I get the feeling they see themselves as experimentalists and are not going to stick out their necks too far with regards to implications of their experiment.

From what I've seen, this is as far as they were willing to go, "Our measured trajectories are consistent, as Wiseman had predicted, with the realistic but unconventional interpretation of quantum mechanics of such influential thinkers as David Bohm and Louis de Broglie," said Steinberg. Considering the venomous attacks often levied against scientists who make even the smallest overreach, especially in the field of physics, I can understand their hesitancy.

 

[unusualname]

The experiment is not so trivial as people are arguing, if confirmed it is certainly a refutation of the strict 1927 Copenhagen Interpretation, which would have nothing to do with trajectories, averaged or otherwise. But it is not a refutation of the more modern "improvements" to the Copenhagen Interpretation. However, it is an an impressive vindication of the Bohmian analysis to construct some kind of trajectories (though not a confirmation of their determistic nature, since it is only an averaging)

Even Griffiths, the originator of Consistent Histories tried to argue that the Bohmian Paths were inconsistent with his own interpretation Bohmian mechanics and consistent histories, this analysis was argued to be flawed by promoters of the Bohmian approach, eg Consistent Histories and the Bohm Approach = Hiley, Maroney

Well, I don't think we can completely laugh at supposedly "naive" attempts to construct trajectories anymore.

However I fully agree that the experiment does not discriminate between the modern interpretations (at least I don't know of any attempt by MWIers to construct ensemble trajectories ;-) )

 

[IllyaKuryakin]

Yes, my head is spinning from trying to flip back from orthodox QM and Bohmian Mechanics and understand the implications of this experiment. I'm not sure anything I'm saying makes any sense anymore. My original thought was that to reconstruct average trajectories of an ensemble of photons, individual photons must have definate trajectries, since the weak measurements are made on the individual photons one at a time.

Just knowing that a single photon has a definite trajectory, even if that individual trajectory can never be exactly measured, seems very significant to me. However, I can't prove that for an ensemble of photons, measured one at a time with a weak measurement to have a clear average trajectory, then individual photons must have definite trajectories, even if they can't be measured. So, I guess I'm kinda stuck at this point, for the moment.

 

[unusualname]

Yes, my head is spinning from trying to flip back from orthodox QM and Bohmian Mechanics and understand the implications of this experiment. I'm not sure anything I'm saying makes any sense anymore. My original thought was that to reconstruct average trajectories of an ensemble of photons, individual photons must have definate trajectries, since the weak measurements are made on the individual photons one at a time.

Just knowing that a single photon has a definite trajectory, even if that individual trajectory can never be exactly measured, seems very significant to me. However, I can't prove that for an ensemble of photons, measured one at a time with a weak measurement to have a clear average trajectory, then individual photons must have definite trajectories, even if they can't be measured. So, I guess I'm kinda stuck at this point, for the moment.

To make it clear, the experiment doesn't even discount naive interpretations of the Feynman path integral approach where some of the photons might have visited Jupiter and back before hitting the detector.

But it does show an "averaged" trajectory is measurable.

 

[Varon]

Yes, my head is spinning from trying to flip back from orthodox QM and Bohmian Mechanics and understand the implications of this experiment. I'm not sure anything I'm saying makes any sense anymore. My original thought was that to reconstruct average trajectories of an ensemble of photons, individual photons must have definate trajectries, since the weak measurements are made on the individual photons one at a time.

Just knowing that a single photon has a definite trajectory, even if that individual trajectory can never be exactly measured, seems very significant to me. However, I can't prove that for an ensemble of photons, measured one at a time with a weak measurement to have a clear average trajectory, then individual photons must have definite trajectories, even if they can't be measured. So, I guess I'm kinda stuck at this point, for the moment.

This also bothers me as it seems to contradict Bohr postulate yet Demystifer and SpectraCat disagree.

Bohr Postulate is: "In the absence of measurement to determine its position, a particle has no position"

Now in the latest experiment. Ensemble of photons have trajectories.. meaning they at least have positions. And you said individual photons must have definite trajectories, even if they can't be measured. This is logical yet full degree physics and chemistry holders Demystifier and SpectraCat rejected this. How could it be? Unless the ensemble of photons measured don't actually made up inteference patterns but just take the left and right slits... but then interference pattern indeed show up. Anyway. How many such ensemble of photons are measured? If they are just hundreds or thousands, perhaps they show up in the screen not as interference but as blobs and this is simply not noticed? Demystifer suggests papers but they are entirely Bohmian in essence, so hope someone can clarify this whole thing as it violates the Bohr Postulate yet these two don't agree.

 

[SpectraCat]

This also bothers me as it seems to contradict Bohr postulate yet Demystifer and SpectraCat disagree.

Bohr Postulate is: "In the absence of measurement to determine its position, a particle has no position"

Where are you getting that? The only Bohr postulates that pop up in a google search are those having to do with his atomic model. I don't even think that is correctly stated the way that Bohr might have expressed it. I guess he would have said something like:

"it does not make sense to talk about quantum particles having well-defined positions in the absence of measurement"

or maybe just

"particle properties become well-defined when they are measured, but not before"

The differences between those statements and your rephrasing of it are significant. I don't think Bohr would have found anything inconsistent about those statements and the current results for weak measurements on the double slit. I know I don't, but that's just my opinion.

Now in the latest experiment. Ensemble of photons have trajectories.. meaning they at least have positions.

No, I don't think so .. by saying that they "have positions", I assume you mean that individual photons have well-defined positions at all times. That has not been demonstrated. That the average position of a large ensemble of particles is well-defined is hardly surprising.

And you said individual photons must have definite trajectories, even if they can't be measured.

That was a personal opinion expressed by one or more posters on this thread, yes. It is not shared by the authors of the paper, as they explicitly state more than once. Also I don't think IllyaKuryakin said he thought individual photons have definite trajectories .. in fact, in an earlier post he said that he thought that was impossible according to the HUP.

This is logical yet full degree physics and chemistry holders Demystifier and SpectraCat rejected this. How could it be?

I didn't reject the *possibility* that might be true .. I only reject the statement that the experimental results somehow provide evidence for that supposition.

Unless the ensemble of photons measured don't actually made up inteference patterns but just take the left and right slits... but then interference pattern indeed show up. Anyway. How many such ensemble of photons are measured? If they are just hundreds or thousands, perhaps they show up in the screen not as interference but as blobs and this is simply not noticed?

I have absolutely no idea what you are trying to express with the above statement ... the experiment shows interference, even in the presence of weak momentum measurements. The weak momentum measurements allow the AVERAGE trajectories of the particles passing through the slits to be reconstructed .. see my previous replies in this thread for some further details. The authors state that they measured 31000 separate photons at each position of the CCD detector screen.

 

[Varon]

Where are you getting that? The only Bohr postulates that pop up in a google search are those having to do with his atomic model. I don't even think that is correctly stated the way that Bohr might have expressed it. I guess he would have said something like:

"it does not make sense to talk about quantum particles having well-defined positions in the absence of measurement"

or maybe just

"particle properties become well-defined when they are measured, but not before"

The differences between those statements and your rephrasing of it are significant. I don't think Bohr would have found anything inconsistent about those statements and the current results for weak measurements on the double slit. I know I don't, but that's just my opinion.

I read about it in the book "Quantum: Einstein, Bohr, and the Great Debate about the Nature of Reality"
https://www.amazon.com/dp/0393339882/?tag=pfamazon01-20

Apparently. Bohr made the radical hypothesis to challenge Einstein EPR attack.. The book mentioned that before that Bohr thought it was merely disturbances that was why position and momentum can't be accurately measured together. But after EPR. Bohr proposed the particles position didn't even exist in principle before measurement. This is to avoid superluminal information exchange. Because if there is no position, there is nothing to be non-local about. This is how Bohr won the EPR debate by proposing the radical. That in the absence of measurement to determine its position, a particle has no position.

No, I don't think so .. by saying that they "have positions", I assume you mean that individual photons have well-defined positions at all times. That has not been demonstrated. That the average position of a large ensemble of particles is well-defined is hardly surprising.

No. It's not about having well-defined positions. Bohr postulate as expressed in the book mentioned above said it's not about there being or not being well-defined positions. The fact is that there is not even position before measurement. This radical hypothesis by Bohr was only made after EPR.

That was a personal opinion expressed by one or more posters on this thread, yes. It is not shared by the authors of the paper, as they explicitly state more than once. Also I don't think IllyaKuryakin said he thought individual photons have definite trajectories .. in fact, in an earlier post he said that he thought that was impossible according to the HUP.

Maybe the authors of the experiments assume Bohr only meant not having well-defined positions. But as I have said. EPR arguments changed his idea to challenge Einstein.

I didn't reject the *possibility* that might be true .. I only reject the statement that the experimental results somehow provide evidence for that supposition.



I have absolutely no idea what you are trying to express with the above statement ... the experiment shows interference, even in the presence of weak momentum measurements. The weak momentum measurements allow the AVERAGE trajectories of the particles passing through the slits to be reconstructed .. see my previous replies in this thread for some further details. The authors state that they measured 31000 separate photons at each position of the CCD detector screen.

So this experiment disproved Bohr post EPR argument that "in the absence of measurement to determine its position, a particle has no position" supposing the book was accurate Bohr indeed hold that belief??

 

[Varon]

I read about it in the book "Quantum: Einstein, Bohr, and the Great Debate about the Nature of Reality"
https://www.amazon.com/dp/0393339882/?tag=pfamazon01-20

Apparently. Bohr made the radical hypothesis to challenge Einstein EPR attack.. The book mentioned that before that Bohr thought it was merely disturbances that was why position and momentum can't be accurately measured together. But after EPR. Bohr proposed the particles position didn't even exist in principle before measurement. This is to avoid superluminal information exchange. Because if there is no position, there is nothing to be non-local about. This is how Bohr won the EPR debate by proposing the radical. That in the absence of measurement to determine its position, a particle has no position.



No. It's not about having well-defined positions. Bohr postulate as expressed in the book mentioned above said it's not about there being or not being well-defined positions. The fact is that there is not even position before measurement. This radical hypothesis by Bohr was only made after EPR.




Maybe the authors of the experiments assume Bohr only meant not having well-defined positions. But as I have said. EPR arguments changed his idea to challenge Einstein.




So this experiment disproved Bohr post EPR argument that "in the absence of measurement to determine its position, a particle has no position" supposing the book was accurate Bohr indeed hold that belief??

If you will enter the passage "In the absence of measurement to determine its position, a particle has no position" in the Search Inside this Book portion of amazon preview of the book i mentioned above. The following definitive paragraph will come out:

"Bohr did not object to EPR predicting the results of possible measurements of particle B based on knowedge acquired by measuring particle A. Once the momentum of particle A is measured, it is possible to predict accurately the result of a similar measurement of the momentum of particle B as outlined by EPR. However, Bohr argued that that does not mean that momentum is an independent element of B's reality. Only when an 'actual' momentum measurement is carried out on B can it be said to possesses momentum. A particle's momentum becomes 'real' only when it interacts with a device designed to measure its momentum. A particle does not exist in some unknown but 'real' state prior to an act of measurement. In the absence of such a measurement to determine either the position or the momentum of a particle, Bohr argued that it was meaningless to assert that it actually possessed either."

Can anyone clarify if this book history of the debate is accurate? If it is. Does the new experiment falsify it? Meaning there is position but just not well-defined??

 

[SpectraCat]

If you will enter the passage "In the absence of measurement to determine its position, a particle has no position" in the Search Inside this Book portion of amazon preview of the book i mentioned above. The following definitive paragraph will come out:

"Bohr did not object to EPR predicting the results of possible measurements of particle B based on knowedge acquired by measuring particle A. Once the momentum of particle A is measured, it is possible to predict accurately the result of a similar measurement of the momentum of particle B as outlined by EPR. However, Bohr argued that that does not mean that momentum is an independent element of B's reality. Only when an 'actual' momentum measurement is carried out on B can it be said to possesses momentum. A particle's momentum becomes 'real' only when it interacts with a device designed to measure its momentum. A particle does not exist in some unknown but 'real' state prior to an act of measurement. In the absence of such a measurement to determine either the position or the momentum of a particle, Bohr argued that it was meaningless to assert that it actually possessed either."

That sounds a lot more like my version of the statement than yours. I think Bohr would have said that the assertion that "a particle has no position in the absence of measurement" was just as meaningless as "a particle has a position in the absence of measurement". I think his point was just that QM tells you nothing about what is going on "behind the scenes" when no measurements are carried out. Anyway, who says these statements by Bohr in ancient arguments with Einstein over the EPR experiment somehow define the conversation about these latest experiments?

Can anyone clarify if this book history of the debate is accurate? If it is. Does the new experiment falsify it? Meaning there is position but just not well-defined??

Suppose it does falsify Bohr's idea ... why would that be relevant? As I have explained repeatedly on this thread, the experimental results are INTERPRETATION INDEPENDENT! That means they are consistent with modern (correct) interpretations of QM, which would include both CI and dBB, and perhaps others.

 

[Varon]

That sounds a lot more like my version of the statement than yours. I think Bohr would have said that the assertion that "a particle has no position in the absence of measurement" was just as meaningless as "a particle has a position in the absence of measurement". I think his point was just that QM tells you nothing about what is going on "behind the scenes" when no measurements are carried out. Anyway, who says these statements by Bohr in ancient arguments with Einstein over the EPR experiment somehow define the conversation about these latest experiments?



Suppose it does falsify Bohr's idea ... why would that be relevant? As I have explained repeatedly on this thread, the experimental results are INTERPRETATION INDEPENDENT! That means they are consistent with modern (correct) interpretations of QM, which would include both CI and dBB, and perhaps others.

But know that there are many variants of Copenhagen. The experiment may be consistent with the modern intepretations of QM, but not ancient. Now this ancient intepretation by Bohr is supported by other writers like Nick Herbert. But it really boils down to whether Bohr really said that. Although you are right that it doesn't matter if he said said or not. But for us who follow the variants. It is important. Nick Herbert as a proponent of it described thus in his book Quantum Reality:

"Quantum Reality #1 The Copenhagen Interpretation, Part I (There is no deep reality.) No one has influenced more our notions of what the quantum world is really about than Danish physicist Niels Bohr, and it is Bohr who puts forth one of quantum physics' most outrageous claims: that there is no deep reality. Bohr does not deny the evidence of his senses. The World we see around us is real enough, he affirms, but it floats on a world that is not as real. Everyday phenomena are themselves built not out of phenomena but out of an utterly different kind of being.

Far from being a crank or minority position, "There is no deep reality" represents the prevailing doctrine of establishment physics. Because this quantum reality was developed at Niels Bohr's Copenhagen institute, it is called the "Copenhagen interpretation." Undaunted by occasional challenges by mavericks of realist persuasion, the majority of physicists swear at least nominal allegiance to Bohr's anti-realist creed. What more glaring indication of the depth of the reality crisis than the official rejection of reality itself by the bulk of the physics community?

(... some paragraphs skipped... )

Werner Heisenberg, the Christopher Columbus of quantum theory, first to set foot on the new mathematical World, took an equally tough stand against reality-nostalgic physicists such as Einstein when he wrote: "The hope that new experiments will lead us back to objective events in time and space is about as well founded as the hope of discovering the end of the world in the unexplored regions of the Antarctic."

What do you make of it SpectraCat? Don't you think this is a mainstream view? Or maybe Nick Herbert just made it mystical more than necessarity to attract certain proponents?

 

[Varon]

That sounds a lot more like my version of the statement than yours. I think Bohr would have said that the assertion that "a particle has no position in the absence of measurement" was just as meaningless as "a particle has a position in the absence of measurement". I think his point was just that QM tells you nothing about what is going on "behind the scenes" when no measurements are carried out. Anyway, who says these statements by Bohr in ancient arguments with Einstein over the EPR experiment somehow define the conversation about these latest experiments?

Also note there is a serious problem if this argument "a particle has a position in the absence of measurement" is true. Going back to the EPR debate. Einstein and company proposed it to question the claim that definite values don't exist before measurement. So Einstein proposed what if entangled pair is sent out. If you measure position of A particle. And since they are related, the B particle has the same position as well. Unless they are link together superluminaly in which case measurement of A can produce disturbance of B particle. Since this violated relativity. Einstein put up the challenge to Bohr. Now Bohr argument or defence was that there was no position in the absence of measurement, hence values were not definite before measurement.

Of course if Bohmian mechanics was right, then this invalidates Bohr EPR argument. But the bottom line is that if the latest experiment holds, an old variant of the Copenhagen is already falsified. Well?

Suppose it does falsify Bohr's idea ... why would that be relevant? As I have explained repeatedly on this thread, the experimental results are INTERPRETATION INDEPENDENT! That means they are consistent with modern (correct) interpretations of QM, which would include both CI and dBB, and perhaps others.

 

[StevieTNZ]

I see the paper automatically, because my institution pays for it. I don't know how much.

I can also view New Scientist articles through a variety of article databases Massey University of New Zealand subscribes to. However, the latest edition I can search articles for is 11th May 2011. Do you read the article through the New Scientist website, or through another article channel?

I have the option of viewing it in (once available):
* Australia/New Zealand Reference Centre
* MAS Ultra - School Edition
* MasterFILE Premier
* Academic Search Premier

 

[Demystifier]

Neumaier's argument is that the probability of an individual electron in the detector is proportional to the amplitude of the wavefunction of the impinging electron. So while all of the electrons in the detector interact with the delocalized wavefunction of the impinging particle, only a single, probabilistically determined one gives a localized response. Thus the wavefunction of the impinging particle never collapses, rather the collapse happens in the detector, where (I guess) it is more easily explained via decoherence.

So the collapse either does happen (in the detector), which Neumaier denies, or decoherence makes the illusion of collapse. But decoherence ALONE can explain the illusion of collapse only in MWI, while Neumaier does not accept MWI. So there must be something missing in his interpretation.

 

[Demystifier]

My understanding was that to make weak measurements of position, there had to be a definite position.

But any observable can be weakly measured, not only position. So in analogy with your statement, one could say, e.g., that to make weak measurement of spin, there had to be a definite spin. Yet, in the Bohmian interpretation there is no definite spin. How would you explain that?

If you are still puzzled, I recommend to read
http://xxx.lanl.gov/abs/quant-ph/9601013

 

[StevieTNZ]

I like the graph on page 111 of 'The Quantum Challenge' (2nd edition).

http://books.google.co.nz/books?id=...uantum Challenge&pg=PA110#v=onepage&q&f=false - starts on page 110.

 

[Phrak]

Please allow me to address the second item on your list first. I believe causality to be an essential ingredient of science. All science to date includes the pre-requisite of causality, ...

But you make my point for me. Old school physics denies theory not consistant with internalized notions of casuality, prima facie. They can't get past it. Without giving too much away, this miopia blinds them to mathematical models not 18 inches away from their eyeballs telling them it ain't so.

 

[SpectraCat]

So the collapse either does happen (in the detector), which Neumaier denies, or decoherence makes the illusion of collapse. But decoherence ALONE can explain the illusion of collapse only in MWI, while Neumaier does not accept MWI. So there must be something missing in his interpretation.

I can't really comment, since both you and he are far better versed in foundational issues than I am. I am sure he would be happy to discuss it on https://www.physicsforums.com/showthread.php?t=490492", in fact most of that thread is devoted to explanations of his thermal interpretation.

In my view, his theory makes experimentally testable predictions that could distinguish it from other interpretations. However, I suspect (and Neumaier agrees) that he would probably be able to deflect any negative results based on "loopholes", since foundational issues tend to be slippery.

 

[Varon]

So the collapse either does happen (in the detector), which Neumaier denies, or decoherence makes the illusion of collapse. But decoherence ALONE can explain the illusion of collapse only in MWI, while Neumaier does not accept MWI. So there must be something missing in his interpretation.

SpectraCat & Demystifier. Take note that there was never any collapse in Neumaier QFT Interpretation. So it is wrong to say that collapse happens in the detector. Neumaier who is equal to von Neumann in mathematical ability answered SpectraCat inquiry "What else could happen? What would be the nature of a "delocalized particle stuck to a surface?"

Neumaier replied:

"This question is only strange if you think in terms of particles. But buckyballs actually form a field - with particle being localized features of the field.

The analogous question of what happens if a delocalized drop of water (in the form of a faint mist) reaches a detector. It just stays there delocalized and is virtually unmeasurable at the resolution of typical water drops. There is no conceptual problem.
The quantum case is essentially the same."

Demystifier. There was no collapse, no measurement problem, and foremost there is no particle. It is total opposite of Bohmian Mechanics.. this is the reason why I emphasized Neumaier arguments in this thread which are Bohmian in essence (in a subtle way).

 

[Demystifier]

Demystifier. There was no collapse, no measurement problem, and foremost there is no particle. It is total opposite of Bohmian Mechanics.. this is the reason why I emphasized Neumaier arguments in this thread which are Bohmian in essence (in a subtle way).

If you want to convince me, answer my questions in the post #72.

 

[Varon]

I still don't get it. If EACH electron responds, then why do we observe a localized event? If only one responds, then why only one?

Ok, here's why. I asked Neumaier a month ago:

I asked: "But in one-electron (or photon or buckyball) at a time double slit experiment, how does the wave after the slits select only one electron among the 10^20 in the detector?"

Neumaier answered:

"The wave selects nothing. It arrives at the various places of detector with different intensities, and these intensities stimulate all the electrons. But because of conservation of energy, only one can fire since the first one that fires uses up all the energy available for ionization (resp. jumping to the conduction band), and none is left for the others."

 

[Demystifier]

"The wave selects nothing. It arrives at the various places of detector with different intensities, and these intensities stimulate all the electrons. But because of conservation of energy, only one can fire since the first one that fires uses up all the energy available for ionization (resp. jumping to the conduction band), and none is left for the others."

Fine, but let us discuss what it implies.

Since all electrons are stimulated, each of them must take a little bit of energy. On the other hend, since only one of them fires, it means that this energy distributed among all electrons somehow must go to only one of them. Moreover, it must happen almost instantaneously, i.e., faster than light. That's all logically possible, but still a natural questions is: How exactly all this energy distributed among all electrons suddenly comes to only one of them?

 

[camboy]

"The wave selects nothing. It arrives at the various places of detector with different intensities, and these intensities stimulate all the electrons. But because of conservation of energy, only one can fire since the first one that fires uses up all the energy available for ionization (resp. jumping to the conduction band), and none is left for the others."

Picture a perfectly spherical phosphorescent screen ten light years in diameter, in which a radioactive atom is at the exact centre (there's an engineering challenge for you). When it decays the atom emits a perfectly spherical wave which travels outwards. Long afterwards, the wave hits the 10 gazillion billion twillion atoms making up the spherical detector simultaneously. How do the atoms which are supposedly 'stimulated' in some sense decide amongst themselves which will accept the conserved energy on offer? Nonlocality? I thought Neumaier doesn't believe in that.

 

[Varon]

Fine, but let us discuss what it implies.

Since all electrons are stimulated, each of them must take a little bit of energy. On the other hend, since only one of them fires, it means that this energy distributed among all electrons somehow must go to only one of them. Moreover, it must happen almost instantaneously, i.e., faster than light. That's all logically possible, but still a natural questions is: How exactly all this energy distributed among all electrons suddenly comes to only one of them?

I have asked him many questions. The following is collection of my questions to him and his answers in the form of a FAQ.
Let us go to the beginning (this is related to this thread because the latest experiment here if true can I think falsify Neumaier thermal interpretation as well as other similar attempts).

Varon: Let us focus on the double slit experiment as Feymann said it's the main mystery. If it's solved, the entire quantum mystery solved.

I can't understand what you meant by "passing the screen turns the electron into a delocalized object". You said the electron is a particle before it passes the screen. Since it is already a particle, how can it turned into a delocalized particle at the screen?

Neumaier: The electron is always a quantum field. The quantum field can be regarded to describe a particle if and only if the field has a nonzero expectation only in a region small compared to the whole system considered. Thus we may say that the field is a particle as long as this condition is satisfied. Because of the dispersion of the field caused by the slits, this condition stops to be satisfied almost immediately after the field (with support large enough to cover both slits) passed the double slit. Thus it is no longer justified to talk about a particle.

The situation is similar as with a sphere of glass. If you throw it, you may regard it as a particle. But if it hits an obstacle and fragmentizes, it is no longer localized enogh to deserve the name of a particle.

Varon: Let's go from the beginner in the emission. So the electron is emitted. You believed it travels as particle? But where does it pass, the left or right slit? And what caused the interferences in the screen. Standard explanation says it interferes with itself because it is a wave after it is emitted.. and only become a particle at the detection screen. Pls. elaborate what happened to your electron after emission.. before it reaches the slits.. after it exits the slits and after detection in the screen.

Neumaier: The field passes the doulbe slit in a fashion similar as a water wave would do, except with quantum corrections."

Varon: Interesting. But how come the detector detects one electron and not the fragmentized parts (after passing thru the slits)?

Neumaier: The quantum field does not fragmentize like a broken glass sphere. It just expands into a superposition of two spherical waves. The outer electrons of the detector respond to the incident quantum field by an approximate Poisson process with rate proportional to the incident density. This accounts correctly for the simple statistics obtained for an ordinary electron beam. See post #4 of this thread, and the longer discussion of the case of photons in
https://www.physicsforums.com/showthr...39#post3187039
and in the thread
https://www.physicsforums.com/showthread.php?t=480072

Varon: What "outer electrons"?

Neumaier: The detector wouldn't be able to respond if it hadn't loosely bound electrons that could be freed when responding to the impinging quantum field formed by your single electron. The response of the detector to the field is a multibody problem, and solving it in the semiclassical approximation gives the desired effect."

Varon: Are you saying your interpretation only work for an ensemble of electrons?

Neumaier: No. I am considering your situation: precisely one elctron moving theough the double slit. But once this electron reaches the detector is meets a host of electrons in the detector. The latter are responsible for the measurable response (since ultimately a current is measured, not the single electron)."

Varon: I want only one electron at a time. What do you mean "The detector wouldn't be able to respond if it hadn't loosely bound electrons that could be freed when responding to the impinging quantum field formed by your single electron." Please rephase it in clearer words. As I understand it. The emitter emits one electron. After it pass thru the slits, it became smeared. Now how does the smeared field converge back into a single electron detected at the screen?

Neumaier: It doesn't. It remains smeared. But one of the electrons in the detector fires and (after magnification) gives rise to a measurable current.. This will happen at exactly one place. Thus it _seems_ that the electron has arrived there, while in fact it has arrived everywhere within its extent.

If a water wave reaches a dam with a hole in it, the water will come out solely through this hole although the wave reached the dam everywhere. A detector is (in a vague way) similar to such a dam with a large number of holes, of which only one per electron can respond because of conservation of energy

Varon: But your theory doesn't explain one electron at a day double slit experiment or in instance where only one buckyball is sent out in a year. It still interferes with itself. Because after 20 years. The 20 buckyball would still form interference patterns added up one year at a time.
Hence your model may not tally with reality.

Neumaier: Each electron capable of responding has a response rate proportional to the intensity of the incident field. This is enough to correctly account for the interference pattern. No memory is necessary to achieve that.

If you send one buckyball a year in a coherent fashion (I doubt that one can prepare this, but suppose one could) then at positions of destructive interference the response rate would be zero while at positions of constructive interference, the resonse rate would be zero except once a year where it would be maximal. Thus it is most likely that the yearly recorded event comes from an electron sitting at a point of constructive interference. After 20 years, one would see the pattern emerging.

Varon: Something that puzzles me greatly. First of all. How many electrons do typical detectors have? Let's say there are a thousand.

Neumaier: Its more like 10^20.

Varon: How can the uniform quantum wave after the slits trigger just one of the electrons in the detectors and not others. How can the principle of energy conservation cause it? Pls. elaborate. Thanks.

Neumaier: Each electron feels just the piece of the quantum wave reaching it. The electron responds by random ionization, with a rate proportional to the intensity. It takes the energy from its surrounding.

The detector as a whole receives the energy everywhere, also with a rate proportional to the intensity. This energy is redistributed (fast, but with a speed slower than that of light) through the whole detector, roughly according to hydrodynamic laws.

Thus there is no violation of conservation of energy.

Varon: But in one-electron (or photon or buckyball) at a time double slit experiment, how does the wave after the slits select only one electron among the 10^20 in the detector?

Neumaier: The wave selects nothing. It arrives at the various places of detector with different intensities, and these intensities stimulate all the electrons. But because of conservation of energy, only one can fire since the first one that fires uses up all the energy available for ionization (resp. jumping to the conduction band), and none is left for the others.

Varon: In other words. There are really no particles?

Neumaier: Particles are semiclassical approximations for field phenomena concentrated along narrow beams. It is not very different from water - which is in particle form if a tab is dripping but not if the water flows in a river.

The particle concept loses its meaning when applied outside its domain of applicability. Trying to keep the concept then leads to all sorts of weird things.

Varon: So in the photoelectric experiment, what makes each electron eject from the material?

Neumaier: Its the same principle as in the double slit experiment. This is explained in the entry ''The photoelectric effect'' in Chapter A4 of my theoretical physics FAQ at http://arnold-neumaier.at/ph...photodetection ,
and discussed in the thread
https://www.physicsforums.com/showthread.php?t=480072

Varon: Come on PF members. If Neumaier was right. Others would have figured this out already for more than a century.

Neumaier: How could this have been figured out before 1911, at a time where not even the Schroedinger equation was discovered? The reason why it hasn't been discovered is that those working on the foundations rarely also work on quantum fields, and those who work on the latter usually have more pressing things to do than to indulge in foundational issues. So the interface between foundations and quantum fields has been very little explored.

Varon: I'll start with Camboy criticism (A. Neumaier, pls. comment on it):

"I'm sorry - this sounds like nonsense to me. He says only 1 electron in the detector responds because of conservation of energy. What happens when the screen is the inner surface of a hollow sphere a light-year across, and the emitter is a point source dead in the middle emitting a spherical moving quantum field? How is the energy transported across space via the quantum field? Across the whole wave front? In which case, what kind of process involving conservation of energy takes place around the whole surface of the sphere instantaneously when the wave hits the screen? How does this work? if you wish to provide an 'interpretation' one must do more than simply state something happens."

Well?

Neumaier: A quantum field transports the energy in the same way as a classical field, namely by evolution according to the field equations. The energy of a radially expanding field is distributed uniformly.
So an extremely tiny amount of energy arrives at any place of the hollow sphere, integrating over the sphere to the energy of one electron. Thus energy is conserved. The probability of response anywhere is extremely tiny, too, so that uncertainties in the sphere by far dominate the effect, and nothing can be concluded

--------

Look. Demystifier. I didn't say I follow his QFT based interpretation. I'm just open minded. Anyway. This latest experiment mentioned in this thread that shows trajectories to either left or right... did they really show them passing either left or right? In Neumaier approach.. the wave uniformly passes the slits. So does the latest experiment falsify Neumaier approach where he treats the QFT field as having ontological reality and not just calculational tools?

 

[Demystifier]

Look. Demystifier. I didn't say I follow his QFT based interpretation. I'm just open minded.

Fair enough.

Anyway. This latest experiment mentioned in this thread that shows trajectories to either left or right... did they really show them passing either left or right?

No.

In Neumaier approach.. the wave uniformly passes the slits. So does the latest experiment falsify Neumaier approach where he treats the QFT field as having ontological reality and not just calculational tools?

No. (Which does not mean that I find Neumaier approach consistent.)

 

[Varon]

Demystifier,

Fritjof Capra, Nick Herbert and dozens of other physicists who write Pop-sci books emphasize that before measurements, there is only wave of possibiilty and the particles only popping into existence after measurement or wave function collapse. The latest experiment refutes at least them right? Or not too? If not. I just can't imagine how something existing as waves of possibilities can be compatible with trajectories of ensemble actually being measured before they collapse??

 

[Demystifier]

Demystifier,

Fritjof Capra, Nick Herbert and dozens of other physicists who write Pop-sci books emphasize that before measurements, there is only wave of possibiilty and the particles only popping into existence after measurement or wave function collapse. The latest experiment refutes at least them right? Or not too?

Unfortunately, not.

If not. I just can't imagine how something existing as waves of possibilities can be compatible with trajectories of ensemble actually being measured before they collapse??

Have you studied the papers to which I gave links?
Or at least, have you seen the analogy I gave in my blog:
https://www.physicsforums.com/blog.php?bt=4681#comment4681

 

[Samo84]

I don't know if i did miss something or the article of BBC wasn't well written.
As i know the weak measurement do not destroy the interference pattern, this is well known years before now, and it doesn't contract the principles of quantum mechanics... i explain :
Weak measurement = using low intensity light to detect electrons going from slit one or two, low intensity means very few photons and by consequences we will miss a lot of electrons that are going on the two slits, if we say that we did send 100 electrons , weak measurement can only measure like 10 to 20 of them the rest goes unperturbed and so the interference is not destroyed by this kind of measurements.
I guess i should go ahead and read the full article, now days they publish whatever to make noise :(