What are the implications of this experiment?

[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.

with additional information from the article in question in this thread:

However, it is possible to “weakly” measure a system, gaining some information about
one property without appreciably disturbing the future evolution (7); although the information obtained from any individual measurement is limited, averaging over many trials determines an accurate mean value for the observable of interest, even for subensembles defined by some subsequent selection (perhaps even on a complementary)."

Some information = still a bit of interference, as the book link in the first quote says.

 

[Demystifier]

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?

Average quantities in orthodox QM satisfy deterministic equations. So yes, it's possible to explain it with orthodox QM.

 

[Demystifier]

Trajectories of ensemble is detected.

No, it is not. The experiment does not measure any trajectories. Instead, it measures the vector velocity field v(x). In other words, it measures the average velocity for each possible position. From this velocity field, the trajectories are then CALCULATED as integral curves of the vector field.

 

[Demystifier]

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?

You are wrong. See my two posts above.

 

[Fyzix]

So this experiment has basically yielded no new information that will affect the debate in either direction?

 

[Demystifier]

As far as I can tell, the resemblance is coincidental, but I am far from an expert on BM. Perhaps Demystifier could comment further on this?

No, it is not coincidence. It is a theorem in standard QM that weakly measured trajectories will always coincide with Bohmian trajectories. See
https://www.physicsforums.com/showthread.php?t=252491

 

[Demystifier]

So this experiment has basically yielded no new information that will affect the debate in either direction?

As we see, it affects debates a lot. But only for those who do not understand what they are talking about. Unfortunately, most of those who debate on it belong to that group.

 

[Demystifier]

So go on then, reproduce the average trajectories they found, by instead using standard QM or EM calculations.

I'm feeling that nobody has bothered because nobody thinks it's been worthwhile.

You are talking nonsense. The average trajectories have indeed been calculated with standard QM. See
https://www.physicsforums.com/showthread.php?t=252491

 

[Fyzix]

As we see, it affects debates a lot. But only for those who do not understand what they are talking about. Unfortunately, most of those who debate on it belong to that group.

So what was the real purpose on this experiment?
If nothing new is learned from it?


How exactly does MWI predict these trajectories?

 

[DevilsAvocado]

Demystifier, I haven’t had the time to read all previous post, and maybe you’ve already provided this link, but in case not, the explanation on your blog is excellent:

Bohmian trajectories are no longer "hidden variables"
https://www.physicsforums.com/blog.php?b=3077

 

[Demystifier]

So what was the real purpose on this experiment?

To publish a paper in a respectable journal, and to get attention of people who think that QM is cool, but do not really understand it.

How exactly does MWI predict these trajectories?

In exactly the same way as Copenhagen or ensemble interpretation.

 

[Fyzix]

To publish a paper in a respectable journal, and to get attention of people who think that QM is cool, but do not really understand it.


In exactly the same way as Copenhagen or ensemble interpretation.

I really really hate science journalism, hyping everything up when this was infact not important AT ALL.
Like Deutsch said about this experiment: a cool trick, but a waste of time, the math already told us this.

 

[Demystifier]

Demystifier, I haven’t had the time to read all previous post, and maybe you’ve already provided this link, but in case not, the explanation on your blog is excellent:

Bohmian trajectories are no longer "hidden variables"
https://www.physicsforums.com/blog.php?b=3077

Thanks DevilsAvocado! I hope the others will read it too.

 

[Varon]

Demystifer. Is it true that classical picture of waves going through two slits could generate the same figure? See message #135, #137 here from Ken that argued how classical waves could generate the same figure. Do you agree with it 100% or 80% (if so, which 20% don't you agree?). Thanks.

 

[Demystifier]

I really really hate science journalism, hyping everything up when this was infact not important AT ALL.
Like Deutsch said about this experiment: a cool trick, but a waste of time, the math already told us this.

I both agree and disagree with Deutch. I agree that it is a waste of time for those who already understand it. But I think that this paper is playing a very important role by motivating people to pay more attention to Bohmian mechanics. This is a first step towards a PROPER understanding of its TRUE value.

This is like saying to children: "If you eat vegetables, you will be strong as Supermen". Of course it's not true, but it will make them eat vegetables which is good for other reasons.

 

[DevilsAvocado]

Thanks DevilsAvocado! I hope the others will read it too.

You’re welcome!

Please excuse an ignorant layman, but I have to ask you about Bohmian trajectories. This is the result from Kocsis measurement:

[PLAIN]http://scienceblogs.com/principles/upload/2011/06/watching_photons_interfere_obs/photon_trajectories.png

And this is a calculation of Bohmian trajectories:

[PLAIN]http://m1.ikiwq.com/img/xl/1CZnrM0l5IuTyWElY7ND6c.jpg

As we all see, there are some similarities, but they are not identical.

Does this mean anything at all for dBB? Or was this 'expected'...?

 

[Demystifier]

Demystifer. Is it true that classical picture of waves going through two slits could generate the same figure?

No, classical waves could never do that. You need quantum waves, which differ from quantum ones by having a probabilistic interpretation.

 

[Demystifier]

You’re welcome!

Please excuse an ignorant layman, but I have to ask you about Bohmian trajectories. This is the result from Kocsis measurement:

[PLAIN]http://scienceblogs.com/principles/upload/2011/06/watching_photons_interfere_obs/photon_trajectories.png

And this is a calculation of Bohmian trajectories:

[PLAIN]http://m1.ikiwq.com/img/xl/1CZnrM0l5IuTyWElY7ND6c.jpg

As we all see, there are some similarities, but they are not identical.

Does this mean anything at all for dBB? Or was this 'expected'...?

These pictures differ because they refer to different wave functions. In particular, one of them is a photon wave function, while the other is an electron one.

If the measured trajectory did not coincide with the Bohmian trajectory, it would imply that STANDARD QM is wrong.

 

[DevilsAvocado]

... This is like saying to children: "If you eat vegetables, you will be strong as Supermen". Of course it's not true, but it will make them eat vegetables which is good for other reasons.

This is obvious for an avocado!

P.S: Please... don’t eat me...

 

[DevilsAvocado]

These pictures differ because they refer to different wave functions. In particular, one of them is a photon wave function, while the other is an electron one.

Is there any graph available online for calculated photon Bohmian trajectories?

(just curious)

 

[Varon]

No, classical waves could never do that. You need quantum waves, which differ from quantum ones by having a probabilistic interpretation.

Gee. I'm confused now of what Ken was talking about. The following is the complete context of what he was describing. Do you know what he was talking about when he talked about "detection densities", "divergence-free field", etc. which he claimed was related to the experiment?

(the rest is Ken comment, what part is wrong?)

Ken G: "It doesn't mean that... 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."


"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."

 

[f95toli]

So what was the real purpose on this experiment?
If nothing new is learned from it?How exactly does MWI predict these trajectories?

As I wrote in my earlier post: one nice thing about this experiment is that it tells us something what is possible using weak measurements. Weak measurements are a "hot" topic at the moment because they are potentially very useful in certain applications, such as reading out quantum computers, quantum metrology etc.
Hence, the fact that experiment does not tell us anything "fundamental" does not mean that it was not worth doing.

 

[Demystifier]

(the rest is Ken comment, what part is wrong?)

I don't want to comment statements of someone who is not here to clarify what he meant.

 

[Demystifier]

Weak measurements are a "hot" topic at the moment because they are potentially very useful in certain applications, such as reading out quantum computers, quantum metrology etc.

Can you give some references or links on these applications?

 

[Varon]

I don't want to comment statements of someone who is not here to clarify what he meant.

Hope he'll get here. He is an extreme Copenhagenist. I was discussing with him QM in the Philosophy thread as he is already bored with this forum. I also mentioned how calcite with angles and photons and momentum is different from classical waves. The following is his reply yesterday (maybe it clarifies what he means such that if he didn't get here.. you know how to comment on it as it is very relevant to this thread).

Ken G wrote:

"I'm saying the details of how they generate that figure doesn't matter, what matters is its information content, which I can get in much easier ways. Let me ask if you agree that the "average trajectories" that they plot are indeed exactly the same as we would get via my method #2 above-- running one photon at a time through exactly their configuration, and just putting the wall at different distances, and collect the aggregate detections. Then build up a concept of the aggregate photon flux by taking those measurements, normalizing the total detection numbers to be a constant total for every wall distance used (zero divergence), and then drawing the "field line density" for that divergenceless detection field? That's exactly how we would generate a concept of "aggregate photon flux" in this very two-slit experiment, in a completely classical limit of many iterations of slightly different experimental setups (the distance to the wall being the sole variable).

If we can agree that I can get the exact same figure my way, with no subtle "weak measurements", then the question to ask is: what additional information are they extracting with their clever measurements if they end up with the exact same figure I get?

Note that it makes no difference how clever their measurements are-- if they can tell which slit the photon went through, they won't get that photon to participate in an interference pattern anywhere. That is all the CI needs to hold."

 

[Demystifier]

Ken G wrote:

Let me ask if you agree that the "average trajectories" that they plot are indeed exactly the same as we would get via my method #2 above-- running one photon at a time through exactly their configuration, and just putting the wall at different distances, and collect the aggregate detections. Then build up a concept of the aggregate photon flux by taking those measurements, normalizing the total detection numbers to be a constant total for every wall distance used (zero divergence), and then drawing the "field line density" for that divergenceless detection field? That's exactly how we would generate a concept of "aggregate photon flux" in this very two-slit experiment, in a completely classical limit of many iterations of slightly different experimental setups (the distance to the wall being the sole variable).

If we can agree that I can get the exact same figure my way, with no subtle "weak measurements",

OK, I'll comment, but only briefly. In that way, one cannot obtain the same figure.

 

[Fyzix]

I both agree and disagree with Deutch. I agree that it is a waste of time for those who already understand it. But I think that this paper is playing a very important role by motivating people to pay more attention to Bohmian mechanics. This is a first step towards a PROPER understanding of its TRUE value.

This is like saying to children: "If you eat vegetables, you will be strong as Supermen". Of course it's not true, but it will make them eat vegetables which is good for other reasons.

Why would this motivate anyone to pay anymore attention to BM when this result was predicted by every interpetation?
I don't see how this experiment changes anything in regards to dBB being more likely to be a correct interpretation now...

 

[IllyaKuryakin]

Average quantities in orthodox QM satisfy deterministic equations. So yes, it's possible to explain it with orthodox QM.

I haven't seen this done and I'm skeptical it can be done.

 

[IllyaKuryakin]

You are wrong. See my two posts above.

You've offered no proof of your statements. I do not believe you are correct.

 

[Demystifier]

Why would this motivate anyone to pay anymore attention to BM when this result was predicted by every interpetation?

First, because he/she does not understand that, as can be seen on this thread.

Second, because the role of interpretation is not only to predict, but also to give an intuitive explanation. Even if all interpretations have equal prediction powers, some interpretations are more appealing than others for intuitive explanations.

 

[Demystifier]

You've offered no proof of your statements. I do not believe you are correct.

It's not a matter of belief. It's a matter of reading papers such as those in
https://www.physicsforums.com/showthread.php?t=252491
You can find proofs there, if you want to read ...

 

[Lost in Space]

As well as the distance of the surface behind the slits, what about the distance between the slits? Is there a maximum and minimum distance where these results can be seen and is it determined by the wavelength of the particle?

 

[Demystifier]

Is there a maximum and minimum distance where these results can be seen and is it determined by the wavelength of the particle?

No (at least in principle).

 

[Lost in Space]

So would I be correct then, Demystifier, in saying that there would still be a recognisable diffraction pattern even if the slits were very far apart or that the wall was very close and that it's probability alone that determines it?

 

[Demystifier]

Well, if the wall was too close, then there would be no diffraction pattern. The answers to other questions are - yes. But all this has not much to do with the subject of this thread.

 

[Lost in Space]

Well, if the wall was too close, then there would be no diffraction pattern. The answers to other questions are - yes. But all this has not much to do with the subject of this thread.

Sorry if I was off thread. Thanks for answering my questions. I find the whole subject of probability fascinating - if baffling!

 

[Ken G]

I'm sorry that I have not reviewed this whole long thread, so perhaps this was covered, but it seems like a central objection to the idea that this experimental result has anything important to say about the two-slit experiment or about Bohmian trajectories.

So let me ask this. Can anyone argue (and now that I am around to clarify, I would expect an actual argument, not just making the claim) that I would not get the exact same trajectory figure the following way: I set up their exact apparatus, but I put my detecting wall at various different distances, repeating over and over until I map out not just a 1D detection-rate function, but a full 2D detection-rate field. The field is of course normalized to represent a divergence-free photon flux. Then I simply draw the divergence-free lines of flux of that 2D field. Why am I not getting their exact same figure, using no "weak measurement" at all? Why is their figure nothing but the 2D divergence-free lines of flux of a completely classical wave?

 

[Demystifier]

So let me ask this. Can anyone argue (and now that I am around to clarify, I would expect an actual argument, not just making the claim) that I would not get the exact same trajectory figure the following way: I set up their exact apparatus, but I put my detecting wall at various different distances, repeating over and over until I map out not just a 1D detection-rate function, but a full 2D detection-rate field. The field is of course normalized to represent a divergence-free photon flux. Then I simply draw the divergence-free lines of flux of that 2D field. Why am I not getting their exact same figure, using no "weak measurement" at all? Why is their figure nothing but the 2D divergence-free lines of flux of a completely classical wave?

I've already asked a question on it in the other thread, but if you want you can answer it here as well.

 

[SpectraCat]

I'm sorry that I have not reviewed this whole long thread, so perhaps this was covered, but it seems like a central objection to the idea that this experimental result has anything important to say about the two-slit experiment or about Bohmian trajectories.

So let me ask this. Can anyone argue (and now that I am around to clarify, I would expect an actual argument, not just making the claim) that I would not get the exact same trajectory figure the following way: I set up their exact apparatus, but I put my detecting wall at various different distances, repeating over and over until I map out not just a 1D detection-rate function, but a full 2D detection-rate field. The field is of course normalized to represent a divergence-free photon flux. Then I simply draw the divergence-free lines of flux of that 2D field. Why am I not getting their exact same figure, using no "weak measurement" at all? Why is their figure nothing but the 2D divergence-free lines of flux of a completely classical wave?

Hmmm ... I wonder what you mean here. You say the "exact apparatus", but then you say there is no weak measurement in your treatment. The weak measurement comes from the inclusion of the thin calcite crystal in their apparatus ... the birefringence of that crystal is what provides the weak measurement in the experiment. They also physically separate the left and right circularly polarized components of the signal at the detection screen, so that two separate patterns are observed. Vide infra, you seem to not be considering those aspects in your treatment, so either your hypothetical apparatus is not exactly the same, or you are just glossing over those details somehow. Can you please clarify whether you are incorporating the two detection patterns in your analysis, or just considering the sum of the two patterns that would be measured in the absence of the separation of the two polarization components?

Also, I guess you are aware that the authors of the paper did use 41 separate "detection wall distances" (to use your term) in order to reconstruct their average trajectories in the paper? So it seems like they are already using the same "2D detection rate field" (to use your term) that you are proposing to measure.

 

[Ken G]

Hmmm ... I wonder what you mean here. You say the "exact apparatus", but then you say there is no weak measurement in your treatment. The weak measurement comes from the inclusion of the thin calcite crystal in their apparatus ... the birefringence of that crystal is what provides the weak measurement in the experiment.

True, but I maintain it makes little difference. One could try it either way, either with the calcite, or without it, you'll get virtually the same figure either way. This is my central thesis: the weak measurement is not really doing much of anything at all, other than causing us to confuse an "average trajectory" as somehow different from the standard classical notion of the lines of photon flux. So far, I have not seen any demonstration that these are two different things, so that is what needs to be established before any claim can be made that "weak measurement" is doing anything interesting or profound, beyond beyind a clever but unnecessarily complicated way to achieve a mundane result.

They also physically separate the left and right circularly polarized components of the signal at the detection screen, so that two separate patterns are observed. Vide infra, you seem to not be considering those aspects in your treatment, so either your hypothetical apparatus is not exactly the same, or you are just glossing over those details somehow.

They provide one figure at the end, right? So do I. So yes, it's exactly the same apparatus, just no attention to polarization-- the orientation of the "trajectories" is fixed by the divergence-free requirement.

Can you please clarify whether you are incorporating the two detection patterns in your analysis, or just considering the sum of the two patterns that would be measured in the absence of the separation of the two polarization components?

They give the trajectories of all the photons. So do I. There's no need to distinguish the polarizations, they do not alter the photon trajectories-- all that is just part of the "weak measurement" that I claim is not doing anything of importance if I can get the same figure with strong detections.

Also, I guess you are aware that the authors of the paper did use 41 separate "detection wall distances" (to use your term) in order to reconstruct their average trajectories in the paper? So it seems like they are already using the same "2D detection rate field" (to use your term) that you are proposing to measure.

All right, that's interesting. But the question remains-- what "trajectories" do they get if they ignore polarizations and do it the way I suggest? If we simply don't care what the polarizations are, we have a photon flux going through this apparatus, and that photon flux can be resolved into "lines of flux". Why is that not the "average" trajectories of the photons?

ETA:
What I'm saying is really pretty simple. We can insert our hand into their apparatus anywhere we like and just count the photons hitting it. This is going to have to agree with their "trajectories" picture, or else their trajectories obviously don't mean anything. But if they have to agree, then they also have to be the lines of flux for those photons, which is determined by the divergence-free requirement. It just seems like a very roundabout way to calculate lines in a figure that have a much simpler meaning, and so far I have not seen any arguments that is not what they are getting, nor would it make sense if they got something different.

 

[DevilsAvocado]

These pictures differ because they refer to different wave functions. In particular, one of them is a photon wave function, while the other is an electron one.

Okey, but now I’ve found one dBB graph for photons, and it looks even 'worse'...

[PLAIN]http://scienceblogs.com/principles/upload/2011/06/watching_photons_interfere_obs/photon_trajectories.png

[URL]http://tewlip.com/pics/photons-bohmian-trajectories-double-slit.jpg[/URL]

http://arxiv.org/abs/quant-ph/0102071"
Authors: P. Ghose (S.N.Bose Natl. Centr.), A. S. Majumdar (S.N.Bose Natl. Centr.), S. Guha (IIT Kanpur), J. Sau (IIT Kanpur)
(Submitted on 14 Feb 2001 (v1), last revised 11 Oct 2001 (this version, v2))

"Figure 2. Bohmian trajectories for a pair of photons passing through two identical slits. Note that there is no crossing of trajectories between the upper and lower half planes."​

Any explanation...?

 

[Ken G]

Those figures do not look to me like they have the same ratio of slit width to slit separation. Also, one would want to make sure there is the same ratio of wavelength to slit width. Whether they are electrons or photons should not make any difference, once you have the same de Broglie wavelengths.

 

[DevilsAvocado]

Those figures do not look to me like they have the same ratio of slit width to slit separation. Also, one would want to make sure there is the same ratio of wavelength to slit width. Whether they are electrons or photons should not make any difference, once you have the same de Broglie wavelengths.

I’m not sure about dBB... but I think mass and massless do make a difference...

Calculated dBB electrons:

[PLAIN]http://m1.ikiwq.com/img/xl/1CZnrM0l5IuTyWElY7ND6c.jpg

What bothers me though... is that Demystifier tries to slip out of this nice little trap that I’ve set up for him... by referring to new 'factors'...

I’m more or less ignorant on dBB, but my "naive intuition" tells me that if dBB is correct we should see 'more' similarities between theoretically calculated trajectories and physically measured...

Either the physical measurement is 'deceptive'... or 'something else' might be...

 

[DevilsAvocado]

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

Hey DrMac&Cheese! I’ve been missing you and the entangled guys over here! Sooooo good to be back!

Kindest Regards
SatansGuacamole

(sorry for the late reply)

Me too.

thanks guys you are much too kind

 

[DevilsAvocado]

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.

Thanks for reminding me. I’ll see what I can do about the "divine classical mess"...

 

[Ken G]

I’m not sure about dBB... but I think mass and massless do make a difference...

I fugured the diffraction would only care about the de Broglie wavelength. There are some subtleties (Wigner did something on this) about a relativistic particle not having a "localizable" wavefunction, but it seems to me we just have momentum eigenstates here-- which would mean the wavelength is all that counts. I haven't heard any claims that this result depends sensitively on the actual form of the particle wavefunction, beyond its central wavelength.

Either the physical measurement is 'deceptive'... or 'something else' might be...

When I see figures that look like they have different ratios of slit width to slit separation, I don't expect anything else in the figure to look the same either. Are you saying the slit widths and separations (and particle wavelengths) are the same in all these, or are they not?

 

[rgmcc]

If the trajectories were formed by connecting 'average' velocity vectors, does that mean that some 'actual' trajectories do in fact cross the center-line? (Since, an 'average' velocity of 'straight along the middle' implies that we have some 'actual' velocities going slightly up and some going slightly down, crossing the middle?)

Or am I thinking about 'average' in the wrong sense?

 

[unusualname]

It's funny how demystifier is criticising people for talking nonsense and misinterpreting the paper, the authors themselves say

"These results are the first observation of trajectories in a two-
slit interferometer that display the qualitative features
predicted in the de Broglie-Bohm interpretation [3,4]."

( see http://www.aip.org.au/Congress2010/Abstracts/Monday%206%20Dec%20-%20Orals/Session_3E/Kocsis_Observing_the_Trajectories.pdf )

Where they refer to calculations from this paper: (see fig 1 on page 9)
http://arxiv.org/abs/quant-ph/0102071 (Bohmian trajectories for photons)

So the experiment shows something predicted by dBB interpretation, right?

Er, well according to DeMystifier (a dBB believer), NO it doesn't. The authors are clearly misleading everyone, and should reword that passage.

But then DeMystifier goes on to post a https://www.physicsforums.com/blog.php?b=3077 making the astonishing claim that dBB trajectories are no longer hidden variables - they now have the same status as the wavefunction!

lol. Yeah, so an experiment which shows nothing that interpretations without trajectories can't explain has some effect in raising the status of the trajectories!

dBB trajectories are deterministic and have absolutely no useful predictive worth in science, stop pretending otherwise.

And I was actually trying to assist the dBB side by asking someone to point out how the trajectory lines could be otherwise calculated using standard QM or EM (ie NOT USING dBB mechanics), demystifier pointed me to a thread which didn't answer this, since I still haven't seen a calculation which gives the plots. You know, a calculation, no measurements, gives mathematical expression for trajectories.

More like Mystifier tbh.

 

[DevilsAvocado]

... I haven't heard any claims that this result depends sensitively on the actual form of the particle wavefunction, beyond its central wavelength.

I could be mistaken, but I interpreted Demystifier’s answer as there is a difference between photons and electrons in Bohmian trajectories, and since spin etc doesn’t 'exist' in dBB – I took it for granted (guessed) it had to be mass... maybe wrong...

These pictures differ because they refer to different wave functions. In particular, one of them is a photon wave function, while the other is an electron one.

When I see figures that look like they have different ratios of slit width to slit separation, I don't expect anything else in the figure to look the same either. Are you saying the slit widths and separations (and particle wavelengths) are the same in all these, or are they not?

You’re right, and I was too hasty in my conclusion in post #193 (sorry Demystifier). I’ll get back to that, but first let me elaborate my point.

Let’s pretend you have a theory saying that phenomena X is due to a triangle wave that we can’t see or measure. Then 60 years later someone comes up with a bright idea how to measure this wave, and the result turns out to be a sawtooth wave, and that’s fine because there could be some minor mistakes in the measurement.

But if the measurement shows a square wave, I say you’ve got some bigger 'troubles'...

Maybe this is completely nuts and naive... but it would be interesting to hear what Demystifier has to say about it.

As I said, I’ve found Bohmian photon trajectories that match the experiment much better:

Calculated Bohmian photon trajectories

[PLAIN]http://scienceblogs.com/principles/upload/2011/06/watching_photons_interfere_obs/photon_trajectories.png
Experimental (average) photon trajectories

Here you could at least imagine a 'connection' between theory and measurement.

The BIG question is: What happens if one would use the exact experimental setup (slit width/separation) for calculated Bohmian photon trajectories? Would we get an almost perfect match?

And why didn’t Steinberg et al do this in the paper??


(... please, don’t tell me "they have to match" ...)

 

[IllyaKuryakin]

It's not a matter of belief. It's a matter of reading papers such as those in
https://www.physicsforums.com/showthread.php?t=252491
You can find proofs there, if you want to read ...

I read the papers. It took me two days to work through them. No where in those papers do the authors claim that the same average trajectories can be determined by orthodox QM. There is a very simple reason for that. Orthodox QM is non-deterministic. There are no average trajectories in orthodox QM. In fact, there are not even specific trajectories to take an average of. You can't take an average of the trajectory of a density probability wave since it doesn't have a specific trajectory and doesn't even exist as a physical object until it's waveform collapses upon detection. That's specifically how orthodox QM describes the photon in it's path from emmision to detection.

In fact, I have searched for any paper that predicts the average trajectories measured by Steinberg and predicted by Bohmian Mechanics using simply orthodox QM and no such paper exists.

I'm really beginning to wonder of you truly understand the difference between a statistical non-deterministic theory and a deterministic theory?