What are the implications of this experiment?

[SpectraCat]

I don't know if i did miss something or the article of BBC wasn't well written.

...

I guess i should go ahead and read the full article, now days they publish whatever to make noise :(

Yes, do read the article .. some people here (and elsewhere) seem to be attaching more foundational significance to this result than the authors do. It is an impressive experimental result to be sure, but I do not see how it resolves anything regarding interpretations of QM.

 

[DevilsAvocado]

Neumaier who is equal to von Neumann in mathematical ability

Could you please stop this PR nonsense? John von Neumann was one of the founding fathers of QM and generally regarded as one of the greatest mathematicians in modern history. Known for:

von Neumann Equation
Abelian von Neumann algebra
Artificial viscosity
Axiom of regularity
Backward induction
Duality Theorem
Durbin–Watson statistic
Game theory
Ergodic theory
EDVAC
Lattice theory
Lifting theory
Inner model
Merge sort
Middle-square method
Pseudorandomness
PRNG
Radiation implosion
Operator theory
von Neumann algebra
von Neumann architecture
Von Neumann bicommutant theorem
Von Neumann cellular automaton
Von Neumann Ordinals
Von Neumann universal constructor
Von Neumann entropy
Von Neumann regular ring
Von Neumann–Bernays–Gödel set theory
Von Neumann universe
Von Neumann conjecture
Von Neumann's inequality
Stone–von Neumann theorem
Von Neumann stability analysis
Minimax theorem
Monte Carlo method
Quantum statistical mechanics
Von Neumann extractor
Von Neumann ergodic theorem
Direct integral
Ultrastrong topology​

Who is Arnold Neumaier? Well, he’s not a kid:
http://www.dieuniversitaet-online.at/typo3temp/pics/0455063a7d.jpg

And Neumaier do have http://arxiv.org/find/quant-ph/1/au:+Neumaier_A/0/1/0/all/0/1", of which 2 (with co-writers) are peer reviewed, but only 1 peer reviewed paper by him solely...

Arnold Neumaier is not a contemporary John von Neumann, period.

If you do some deeper research on this guy and what he stands for and what his real agenda is, I’m sure you will fall of your chair (unless you’re the same 'kind').



emphasis mine

... 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."
...
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
...
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.
...
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.

This must be one of the most 'advanced gibberish' I’ve seen on PF in years. Arnold Neumaier has not only a new 'interpretation' of QM – he’s delivering completely new 'solutions' that no one has seen before – and it doesn’t make sense.

I’m only an ignorant layman, but I’m sure I can prove in simple English that everything Neumaier is saying above is false.

Let’s start from the beginning whit the ordinary two-slit diffraction pattern:

[URL]http://upload.wikimedia.org/wikipedia/commons/2/2c/Two_sources_interference.gif[/URL]

If we look at this from above in the the Double-slit experiment, it looks like this:

[URL]http://upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Double_slit_diffraction.svg/400px-Double_slit_diffraction.svg.png[/URL]
When the waves are added together, their sum is determined by the relative phases as well as the amplitudes to cause an effect which is known as wave interference.

There is nothing strange about this and it works in any medium, like water for example:

https://www.youtube.com/watch?v=-8a61G8Hvi0

Now, let’s jump directly to a Single Electron Double-slit experiment:


https://www.youtube.com/watch?v=FCoiyhC30bc

So what’s causing the electrons to from this interference pattern? Well, (until Neumaier) everybody agrees it’s because of the higher probability amplitude in the constructive interference, caused by interference of the split wave (function).

We all understand that we could send out one electron every second, or every one hundred thousand year – and still get exactly the same results as above.

So how does Neumaier explain this? Well he uses "a multibody problem", "conservation of energy", "the intensity of the incident field", "no memory", "hydrodynamics", and "a speed slower than that of light" ...

Everybody understands that this is nuts. It won’t work, period.

But, in case you’re not convinced, let’s stress Neumaier’s "innovative science" just a little bit. Let’s assume that detector in the single electron double-slit experiment above is 10 light-years wide, and the source at matching distance.

Now, the wavefunction propagates from double-slit towards the detector at the speed of light. After several years it finally hits all particles in the detector simultaneously, and according to Neumaier – "conservation of energy" and "the intensity of the incident field" will decide which single spot on the detector will "do the detection" ...

Problem:
To 'signal' to all the other particles on the detector; that there has already been a "hole-in-one", and the game is over for this run – you will need superluminal speed or some non-local/non-real function, and Neumaier strongly reject this, as he is a devoted believer in the very sound and divine classical physics of the very old masters Newton, Maxwell, etc.

I would say Arnold Neumaier has a infinite "multibody problem" to solve here ...

End of story

 

[unusualname]

I agree DA but you should post this (or at least cc it) in his discussion thread https://www.physicsforums.com/showthread.php?t=490492.

His interpretation has not much hope to explain GHZ or any other multi-entangled states, or many of the other experiments by Zeilenger and co.

But it is notable that the Bohmian approach actually predicts what the (ensemble) paths discovered in this experiment ought to look like.

 

[DrChinese]

Could you please stop this PR nonsense? John von Neumann was one of the founding fathers of QM and generally regarded as one of the greatest mathematicians in modern history. ...

Avocado! I've been missing your posts...

 

[IllyaKuryakin]

I agree DA but you should post this (or at least cc it) in his discussion thread https://www.physicsforums.com/showthread.php?t=490492.

His interpretation has not much hope to explain GHZ or any other multi-entangled states, or many of the other experiments by Zeilenger and co.

But it is notable that the Bohmian approach actually predicts what the (ensemble) paths discovered in this experiment ought to look like.

I agree with that. Anytime a theory predicts something found 50 years later in experiment, and it's as close a match as this is to Bohmian Mechanics, I sit up and take notice. The only problem(s) with it that I am aware of is it's not orthodoxy and it requires a pilot wave. I'm not in favor of adding anything unnecessary, but it might be necessary to add the pilot wave to obtain a deterministic model. Essentially, the advantage of a deterministic model is it can be developed, tested by experiment, refined and built upon. Of course, the same can be done to some extent with a statistical model, but if a deterministic model can be developed, it seems like a better way to go for some applications. Remember, we are not talking about something crackpot here. It has rock solid theory, math and experimental verification. Just my opinion.

 

[Varon]

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 :(

Are you sure of that? That weak measurements only measure 10 to 20 out of the 100 electrons? Whatever, the 10 to 20 electrons still form interferences. The pattern is not like when you shoot bullets in the slits where the detector has 2 blobs in front of the slits. Now in the Copenhagen variant where electrons are just wave of possibilities and don't exist as particles before measurement. I still have a hard time seeing how the latest experiment is compatible with them. Demystifier is very advanced physicist who may not be able to get it down to the level for laymen to understand. So please try to explain it yourself. Maybe I can understand.

But I'll try it one last time with Demystifier and other very advanced experts. Demys, I've read your blog about the paper weights. But hope you can directly address this Copenhagen variant where particles don't exist before measurement and only waves of possibilities with measurement materializing the particles out of thin air just like in magic. Then try to explain how this latest experiment is compatible with it. My understanding is that since the particles don't exist before measurement. They shouldn't form any trajectories. Of course the latest belief is the particles exist before measurement.. only the positions are not well-defined.

Also let's resolve something. Let's be clear what positions and "well-defined" mean. It's three possibilities:

1. Particles exist but no position even in principle.
2. Particles don't exist and hence no position.
2. Particles exist and position exist but only not well-defined.

Are you talking of 1 or 2 above when you said it's compatible with the latest experiment? What I'm asking is if 1 is compatible with the latest experiment. Also which of the above Bohr really believed in? And which mainstream physicists believe nowadays (like the writers of the latest experiment paper)?

 

[dlgoff]

Avocado! I've been missing your posts...

Me too.

 

[Varon]

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.

As answered in my FAQ message. It is possible nothing would be triggered. Remember that even in double slit. The buckyball is lost after it hits the detector. Neumaier explains:

"Therefore you can't find any single buckyball at the detector. They are smeared all over the detector. I don't know if he means the atoms of say a 430-atom buckyball became become fragmentalized all over the detector or the buckyball just divides into many parts that is still interconnected. Hope others can clarify.
While in flight and when arriving, the atoms of a delocalized buckyball are just as delocalized as the buckyball itself. Afterwards it is a complex many-body problem involving thev field and the detector, which nobody has looked at so far. Thus I can't say what QM predicts about what happens afterwards.

Maybe, or may be not, there is a tendency to reconsitute a particle, catalyzed by the detector."

To DevilAvodaco. The answer is the same. It is possible no electron in the light year distance detector would be triggered, in other words, nothing would be seen by the detector, the quantum field are distributed in all the detector just like the buckyball lost among the detector.

Just go to his forum. Many physicists initially thought it was silly. But when they go to his site. They were met by shock and awe and weakened into submission that his interpretation can't be refuted.

 

[Fyzix]

Varon you have to stop this ********, and no i won't answer what's wrong with many minds, I'm 100% certain you are a troll.
Stop wasting everybody's time.

 

[StevieTNZ]

Varon you have to stop this ********, and no i won't answer what's wrong with many minds, I'm 100% certain you are a troll.
Stop wasting everybody's time.

I'm pretty sure he's all those 'new people' that have appeared and asked questions in the last week.

 

[Varon]

Varon you have to stop this ********, and no i won't answer what's wrong with many minds, I'm 100% certain you are a troll.
Stop wasting everybody's time.

You know something is wrong with Many Worlds. It can't produce the born rule. In Bohmian mechanics, position is preferred which is somewhat ad hoc. Copenhagen is incomplete. Its possible all the existing quantum interpretations are far from the truth. Therefore its not bad to explore others especially those that only take QFT seriously without additional ad hoc additions.

Steven, I am not those persons.

 

[Fyzix]

Varon, maybe you aren't those people, but even if you aren't the whole way you interact on this forum is counter productive.

First you ask 500 questions, then you cherry pick some random stuff out of it, then you bash other people for not believing that, then you let it go, pick up some other thing and repeat the process.
Then other times you just say straight out "shocking" things in a hope that someone will waste their time trying to refute the statement, such as: "Neumaier is on von Neumans level of math" etc.
or "Neumaier is going to win a Nobel Prize".

Just stop it, you enter threads, derail them and ruin them for everybody else...


Just accept that you will not figure out what is the answer to the measurement problem, there, let it go.
Why not?

 

[Varon]

Varon, maybe you aren't those people, but even if you aren't the whole way you interact on this forum is counter productive.

First you ask 500 questions, then you cherry pick some random stuff out of it, then you bash other people for not believing that, then you let it go, pick up some other thing and repeat the process.
Then other times you just say straight out "shocking" things in a hope that someone will waste their time trying to refute the statement, such as: "Neumaier is on von Neumans level of math" etc.
or "Neumaier is going to win a Nobel Prize".

Just stop it, you enter threads, derail them and ruin them for everybody else...


Just accept that you will not figure out what is the answer to the measurement problem, there, let it go.
Why not?

Quantum interpretation is not figurative or subjective. It is objective. This thread attracks me because I thought it can filter out some interpretations like some magazines say. I have to mention Neumiuer because no one can refute him in his forum. Id like it refuted so I can focus on the others remaining. Of course I don't mean to disturb some of you.

Whatever, interpretation is objective. Our belief system won't let reality conform to us or our fallacy. Unlike choosing Republicans or Dominicans, the right interpretation would be independent of our devotions or preference. It is hard data. It is where I go.

In the end. The right intrepretations can set us free. It can solve the middle east problems and everything. Do you know mob behavior and action is due to some kind of entanglement in the masses? And we in a race against time. It has go be solved before the end of 2012 or else all hell may break lose. Hence sometimes I am in panic state, but I'll remember what you dislike so I can adjust. No problem dude. Now to get on topic. Let's ponder on the weak measurement. It is said to be part of original QM so perhaps its not actually revolutionary as the articles said? To those who bought the $15 paper, is it worth it?

 

[Fyzix]

It has to be solved before 2012 because mob mentality is entangled through quantum entanglement in the masses and it'll kill us all?

Is this a joke I didn't get or are you in need of a psychiatrist?

 

[Varon]

It has to be solved before 2012 because mob mentality is entangled through quantum entanglement in the masses and it'll kill us all?

Is this a joke I didn't get or are you in need of a psychiatrist?

It's classified.

Anyway. You keep sharing how you hated Many Worlds and Neumaier QFT interpretation. It's time now you share what interpretation you prefer since you said you have direct contacts with many researchers. Id just shut up and listen from now on. I have seen the heart and soul of many interpretations already and just need to sit back and reflect on all this.

 

[Fyzix]

Dude, you are obviously borderline psychotic.
Take your medication and just let sane people worry about these issues.
Mentally unstable people shouldn't really do deep philosophy...

Nothing will happen in 2012 by the way, it's all a hoax...
I think you should log off the internet and try to get some therapy and get back into the real world.

Good luck on your road to recovery.

 

[Varon]

Dude, you are obviously borderline psychotic.
Take your medication and just let sane people worry about these issues.
Mentally unstable people shouldn't really do deep philosophy...

Nothing will happen in 2012 by the way, it's all a hoax...
I think you should log off the internet and try to get some therapy and get back into the real world.

Good luck on your road to recovery.

Whatever to make you feel happy.

Anyway. To those who know. So what is the implications of the latest trajectory experiment "Observing the Average Trajectories of Single Photons in a Two-Slit Interferometer?" Nothing? Perhaps those sensational magazine articles about it are just to awe the laymen?

 

[unusualname]

I agree with that. Anytime a theory predicts something found 50 years later in experiment, and it's as close a match as this is to Bohmian Mechanics, I sit up and take notice. The only problem(s) with it that I am aware of is it's not orthodoxy and it requires a pilot wave. I'm not in favor of adding anything unnecessary, but it might be necessary to add the pilot wave to obtain a deterministic model. Essentially, the advantage of a deterministic model is it can be developed, tested by experiment, refined and built upon. Of course, the same can be done to some extent with a statistical model, but if a deterministic model can be developed, it seems like a better way to go for some applications. Remember, we are not talking about something crackpot here. It has rock solid theory, math and experimental verification. Just my opinion.

The point is, could the results be predicted by a more simpler argument, or from alternative interpretations? And does anybody care? :-)

You see, in MWI you even have trouble with justifying the basic born rule, nevermind establishing an ensemble path, and no one really cares about that.

 

[IllyaKuryakin]

The point is, could the results be predicted by a more simpler argument, or from alternative interpretations? And does anybody care? :-)

You see, in MWI you even have trouble with justifying the basic born rule, nevermind establishing an ensemble path, and no one really cares about that.

Right. The question is, is there a simpler model that explains these results, or even better, can predict these results beforehand? I don't know of any simpler deterministic models that have solid theory and math behind them.

Of course, there might be a near infinite number of possibilities, but it's up to the creator of other models to develop the math and theory to answer all questions about their model. If the model is more complex, it should be presented with a method for experimental verification or discrimination to prove it is superior in some way.

I suspect there can be additional experimentation using weak measurement theory or other methods that will aid in developing and building upon the Bohmian Mechanics model. At this point, I believe we have two good methods with solid theory and math to describe quantum wierdness, statistical and deterministic. I really believe theory should focus on experimental methods to futher refine these models and explore their limits to see if they break down at some point. This has been done for decades in orthodox QM, but I believe the deterministic model has not received adaquate experimental attention until now.

 

[unusualname]

Right. The question is, is there a simpler model that explains these results, or even better, can predict these results beforehand? I don't know of any simpler deterministic models that have solid theory and math behind them.

Of course, there might be a near infinite number of possibilities, but it's up to the creator of other models to develop the math and theory to answer all questions about their model. If the model is more complex, it should be presented with a method for experimental verification or discrimination to prove it is superior in some way.

I suspect there can be additional experimentation using weak measurement theory or other methods that will aid in developing and building upon the Bohmian Mechanics model. At this point, I believe we have two good methods with solid theory and math to describe quantum wierdness, statistical and deterministic. I really believe theory should focus on experimental methods to futher refine these models and explore their limits to see if they break down at some point. This has been done for decades in orthodox QM, but I believe the deterministic model has not received adaquate experimental attention until now.

I would rather just ask whether there is ANY explanation of the (ensemble) paths found in this experiment other than the Bohmian analysis?

 

[yoda jedi]

I really believe theory should focus on experimental methods to futher refine these models and explore their limits to see if they break down at some point. This has been done for decades in orthodox QM, but I believe the deterministic model has not received adaquate experimental attention until now.

even for super deterministic models.

Testing super-deterministic hidden variables theories.
http://arxiv.org/PS_cache/arxiv/pdf/1105/1105.4326v1.pdf


.

 

[IllyaKuryakin]

I would rather just ask whether there is ANY explanation of the (ensemble) paths found in this experiment other than the Bohmian analysis?

Good question. I haven't seen anyone else derive this result with any deterministic model other than Bohmian Mechanics. Someone claimed they could derive the same results with orthodox QM, but I haven't seen the math. I'm not sure if that's possible either really, since orthodox QM doesn't contain the equation for the particle positions interpreted as the pilot wave in Bohmian Mechanics. Perhaps someone else here knows the answer?

 

[Varon]

I've re-read this thread for the past 3 hours as well as all the articles except the original paper where I don't have access to.

I'm still a bit confused about something so hope someone can clarity.

Trajectories of ensemble is detected. Yet we are not sure if a single particle has trajectory or not? Or does this confirm there is at least trajectory? If none. How could a single particle doesn't have trajectory yet ensemble of it have??

For years I was exposed to laymen books which say between measurement, the particle turns into a wave.. this means there is no trajectory as waves are everywhere. So does this experiment refutes at least this incorrect laymen book explanations? I think the reason many of you like SpectraCat don't think this experiment has any relevance is because he assumes that particles are always particles (right?) in between measurement, compared to laymen books which say the particle turns into wave without any trajectories in between measurements.

Whatever, this experiment at least gives the idea now that the only valid Copenhagen are those with so called Bohmian trajectories? Or is it still compatible with laymen books which says particle turns into wave between measurement. But I still can't understand how a pure wave has trajectories. Pls. explain. Thanks.

 

[Varon]

I've re-read this thread for the past 3 hours as well as all the articles except the original paper where I don't have access to.

I'm still a bit confused about something so hope someone can clarity.

Trajectories of ensemble is detected. Yet we are not sure if a single particle has trajectory or not? Or does this confirm there is at least trajectory? If none. How could a single particle doesn't have trajectory yet ensemble of it have??

For years I was exposed to laymen books which say between measurement, the particle turns into a wave.. this means there is no trajectory as waves are everywhere. So does this experiment refutes at least this incorrect laymen book explanations? I think the reason many of you like SpectraCat don't think this experiment has any relevance is because he assumes that particles are always particles (right?) in between measurement, compared to laymen books which say the particle turns into wave without any trajectories in between measurements.

Whatever, this experiment at least gives the idea now that the only valid Copenhagen are those with so called Bohmian trajectories? Or is it still compatible with laymen books which says particle turns into wave between measurement. But I still can't understand how a pure wave has trajectories. Pls. explain. Thanks.

http://scienceblogs.com/principles/2011/06/watching_photons_interfere_obs.php

The above is the clearest explanation ever of the original paper. Even if you only do weak measurement of momentum of a particle without collapsing it, the mere fact you can measure its momentum at a particle position means a single particle at least has trajectory. But if you still insist it doesn't prove a single particle has trajectory, pls. explain how so as this is what really confused me all day. In laymen books. They emphased a particle which morphs into a wave has no trajectory in between measurement. Can an expert here confirm it is plain wrong? I just want to know if I'm understanding the whole arguments right.

 

[Varon]

What concerns me is this. The purpose of the wave function in the double slit in Copenhagen is to cause interference. It is only after interference that the particle re-appears. So when the particle have trajectory, then it doesn't make sense that upon collapse, it materializes. Also what pushes it to either the left or the right? Implication of it is that if the particle has existing trajectory (even not well-defined), then it's some variant of Bohmian Mechanics. Unless those who want to retain Copenhagen have to shift positions and state Copenhagen have Bohmian trajectory. But this doesn't make sense. What pushes the particle to the left or right? Hope someone can clarify all this as this is the bottom of the confusion in some of us (or at least me if most of you understood already).

 

[IllyaKuryakin]

even for super deterministic models.

Testing super-deterministic hidden variables theories.
http://arxiv.org/PS_cache/arxiv/pdf/1105/1105.4326v1.pdf


.

Yes, a good example of an experiment design to prove the existence of a deterministic model. I'm not sure if the technology esists currently, but if the experiment is important enough, it seems someone somewhere always finds a way to perform it.

Maybe it also indicates another interpretation of Steinberg's results. Namely, in a one at a time photon source that produces 31,000 photons in 15 seconds, many of those must have been in nearly the same state, and if the results deviate from a regular probability distribution, something other than a statistical probability distribution would seem to be occurring. Not sure about that one, but something interesting to think about.

 

[StevieTNZ]

Good question. I haven't seen anyone else derive this result with any deterministic model other than Bohmian Mechanics. Someone claimed they could derive the same results with orthodox QM, but I haven't seen the math. I'm not sure if that's possible either really, since orthodox QM doesn't contain the equation for the particle positions interpreted as the pilot wave in Bohmian Mechanics. Perhaps someone else here knows the answer?

Here's sentences I read last night in the book "Einstein, Bohr and the Quantum Dilemma" by Andrew Whitaker (publisher: Cambridge University Press):

I have used the term 'hidden-variable theories' rather than 'hidden-variable interpretations', because, although hidden variables may start as an attempt merely to interpret the formalism, their properties must be developed as a genuine addition to it. Thus the word 'theory' seems more appropriate.

 

[IllyaKuryakin]

Will someone please correct me if I'm wrong, but I don't believe orthodox QM could have predicted Steinbergs results? I believe that orthodox QM would have predicted a random probability distribution of photons according to schrodinger's wave equation, yielding NO ensemble trajectories. Have I got that wrong somehow?

 

[IllyaKuryakin]

Here's sentences I read last night in the book "Einstein, Bohr and the Quantum Dilemma" by Andrew Whitaker (publisher: Cambridge University Press):

I have used the term 'hidden-variable theories' rather than 'hidden-variable interpretations', because, although hidden variables may start as an attempt merely to interpret the formalism, their properties must be developed as a genuine addition to it. Thus the word 'theory' seems more appropriate.

Agreed, what follows from Stanford Encyclopedia of Philosophy is more than an interpretation:

"For Bohmian mechanics the state of a system of N particles is described by its wave function ψ = ψ(q1,...,q N) = ψ(q), a complex (or spinor) valued function on the space of possible configurations q of the system, together with its actual configuration Q defined by the actual positions Q1,...,QN of its particles. The theory is then defined by two evolution equations: Schrödinger's equation

iℏ(∂ψ/∂t) = Hψ

for ψ(t), where H is the nonrelativistic (Schrödinger) Hamiltonian, containing the masses of the particles and a potential energy term, and a first-order evolution equation,

The Guiding Equation:
dQk/dt = (ℏ/mk) I am [ψ*∂kψ/ ψ*ψ] (Q1,...,QN)"

So I'd agree that any interpretation must evolve into a theory, or fall apart.

 

[Varon]

I got this disturbing comment that even on purely classical waves, one can get the same result. If true. This means the implications of the experiment is nothing significant. Ken G wrote in the philosophy thread (hope experts here can comment especially when Demystifier returns on monday):

(Ken G wrote:)

"What I'm saying is, I'm not convinced that "weak measurement" is any different from "compiling average trajectories from treating the wave energy flux like a divergenceless scalar field and drawing 2D lines of force for that field." I maintain you could get that exact same picture by measuring the energy flux of a classical wave passing between two slits, and drawing trajectories such that the line density is proportional to the energy flux density. This would be completely consistent with a macroscopic treatment of an energy flux as a photon number flux. Those trajectories don't really mean anything beyond a statistical treatment of where photons go in large aggregations, that they could get the same picture with "weak measurement" of "one photon at a time" doesn't strike me as being at all profound.

Let me put it another way. The key statement that we don't know the trajectory of an individual photon is that we cannot know which slit it went through, and still have that photon participate in an interference pattern. Does this experiment tell us which slit any of those photons went through? No. So what? There are still no trajectories in the physical reality of what happened to those photons, and it's not at all clear that an "average trajectory" is anything different from the usual macro aggregate measurement in the classical limit. To me, all this experiment is is a kind of consistency check that "weak measurement" can recover statistical aggregates, but I see no threat to the CI interpretation that the reality is still only what you measure and not what happens between the measurements. So they can create weak measurements that don't completely collapse the wave function, then recover the aggregate behavior in the same way that complete measurements that do collapse the wavefunction could easily do also. What does that tell us? That weak measurements don't mess up aggregate results? Why should we be surprised-- the weak measurements don't tell us the trajectories of any of those particles."

----

Is it true you can produce the same result using classical waves that don't even have particles?

 

[SpectraCat]

I believe that it is possible to reproduce the results using classical E&M waves, but I haven't finished the math yet. However, I can say that there is nothing in the experiment (aside from the single photon source) that suggests any problem with a classical E&M description. That is, if the quantum dot were replaced by a CW laser, I don't see why the results would be any different. I think the only interpretive issues arise from knowing that single photons travel through the apparatus one by one.

 

[Varon]

I believe that it is possible to reproduce the results using classical E&M waves, but I haven't finished the math yet. However, I can say that there is nothing in the experiment (aside from the single photon source) that suggests any problem with a classical E&M description. That is, if the quantum dot were replaced by a CW laser, I don't see why the results would be any different. I think the only interpretive issues arise from knowing that single photons travel through the apparatus one by one.

I asked Ken:

Varon: They can do weak measurement on a particle before full collapse. This means the particle has trajectory in contrast to pure Copenhagen concept where a particle only pops up upon collapse of the wave function (which stand for wave of possibility of where the particle would be detected).

Ken G: "It doesn't mean that. The second article gives a much more nuanced description than the first. Nothing in that experiment is the trajectory of an individual photon, instead, what they have seems to me is equivalent to what you'd get if you put the detecting screen at various different places and create a field of detection densities, attribute the detection densities to trajectory densities such as could be done with any divergence-free field, and draw the "field lines" and call them average trajectories. I'll wager doing that would generate precisely the same figure. Much ado about nothing.

What they seem to be missing is that the classical picture of waves going through two slits could generate the same figure. What makes the quantum realm so weird is the quantization-- not the averaged behavior. I really don't see what "weak measurement" is adding to the question, it still is not true that you can say which slit any of those electrons went through."

------------------------------------------

SpectraCat. Do "detection densities", trajectory densities", "divergence-free field" got anything to do with the results of the latest experiment? Are these even standard terms? How do you understand them?

 

[unusualname]

I believe that it is possible to reproduce the results using classical E&M waves, but I haven't finished the math yet. However, I can say that there is nothing in the experiment (aside from the single photon source) that suggests any problem with a classical E&M description. That is, if the quantum dot were replaced by a CW laser, I don't see why the results would be any different. I think the only interpretive issues arise from knowing that single photons travel through the apparatus one by one.

This would be a publishable result if you can manage it. The trajectories predicted by Bohmian mechanics seem to be non-intuitive/non-classical.

A bohmian mechanics calculation for a few systems are here (pictures of the trajectories are on the last three pages)
Bohmian Trajectories for photons

 

[IllyaKuryakin]

This would be a publishable result if you can manage it. The trajectories predicted by Bohmian mechanics seem to be non-intuitive/non-classical.

A bohmian mechanics calculation for a few systems are here (pictures of the trajectories are on the last three pages)
Bohmian Trajectories for photons

So, as I read the answers, there are many who claim they can reproduce these results using only orthodox statistical QM, but none have done it. Until I see the math, I remain skeptical since the orthodox QM lacks the guiding equation that provides the basis for the calculated average trajectories in Bohmian Mechanics. If I've missed something here, please correct me, but please be prepared to do the math as I can't see how to get to a calculated average trajectory from a random Schrodinger waveform probability distribution.

I'm even more skeptical that the average trajectories can be calculated in advance using classical e-m waves. I can't even see how classical e-m waves could relate to the average trajectories of an ensemble of photons. I agree, if someone can do this, they should publish the results.

 

[SpectraCat]

@Ilya ... what you seem to be missing is that the trajectories themselves were NOT measured in the experiment. Rather, they were reconstructed mathematically based on the average momenta resulting from the comparison of the slightly different interference patterns measured in the two polarization channels.

What I am saying is that I don't see any reason why the classical wave analysis of the experiment wouldn't give rise to precisely the same interference patterns. Once you have those, the reconstructed average trajectories would be the same.