Revolutionary Experiment Confirms Incompleteness of Quantum Mechanics

[Rade]

[Mentor's note: these posts were split off from this thread, because IMO they go far beyond the original thrust of that thread.]

But we read below from recent 2007 experiment that Einstein was correct--we do "know" what happens to electron between slit and screen, e.g., QM really is incomplete as now confirmed by experiment:
http://www.physorg.com/news92937814.html
What am I missing in this discussion ?

Edit: Here is the 2007 publication I talk about--in peer reviewed journal of physics:
http://arxiv.org/ftp/quant-ph/papers/0702/0702188.pdf

 

[cesiumfrog]

Ah, the old Afshar experiment (and with single photons, for what it's worth)! Rade, there are two things to note: it's bad form to overemphasize Einstein (despite his historic contribution it is flatly unscientific to look to him for authority in modern physics; in particular he was generally wrong about quantum mechanics, and it would be exceedingly tenuous to say this experiment is any different), and this Afshar's experiment is open to other interpretations than Afshar's (a basic issue is whether he would find the same results without any double slit).

 

[Rade]

Ah, the old Afshar experiment (and with single photons, for what it's worth)! Rade, there are two things to note: it's bad form to overemphasize Einstein (despite his historic contribution it is flatly unscientific to look to him for authority in modern physics; in particular he was generally wrong about quantum mechanics, and it would be exceedingly tenuous to say this experiment is any different), and this Afshar's experiment is open to other interpretations than Afshar's (a basic issue is whether he would find the same results without any double slit).

Well, I guess the term old is relative, seems like 2007 publication not so old to me. Your second note finds a possible yes answer here if you have interest:http://arxiv.org/ftp/quant-ph/papers/0702/0702210.pdf
As to your first note..I think Einstein not need me to defend his science nor his authority to modern physics.

 

[cesiumfrog]

By old, I mean "the Afshar experiment" is "well-known", and from the physorg description the only difference in the new experiment this year is lower intensity (which I don't find interesting because I couldn't imagine anyone expecting that to change the result, and indeed it apparently did not).

Regards the arxiv, I'd like to point out that it's preferable to link to abstracts rather than pdf directly. The main/abstract pages not only let the user choose which format in which to download the full article, but more importantly tend to cite which peer review journal published the article (aiding the decision whether to bother at all).

 

[RandallB]

But we read below from recent 2007 experiment that Einstein was correct--we do "know" what happens to electron between slit and screen, e.g., QM really is incomplete as now confirmed by experiment:

What am I missing in this discussion ?

Rade

I’ll grant you the Afshar experiment created quit a buss a couple years ago, by claiming a successful “argument against Complementarity” and to refute the completeness of QM by answering the “which way” question in a stunning two slit experiment with real results.
Technical rebuttals obviously has not prevented publication of it. Which is OK – it gives you and me real results to look at and put into proper perspective.
So the question is: 1) have we shown a flaw in QM or 2)is this just a Magic Trick that has fooled many including Mr Afshar.
Lets take a look:

He produced a interference pattern with known number of photons by timing his count of individual photons going though the slits. Putting wires in the dark spots of the pattern and with a lens behind the several wires he focuses all the light back down to with to a single detector with only one of the double slits.
Using the same time interval as before he should observe half the photons with only one slit open; BUT he sees less than that, obviously the wires are blocking some of them!
He does the same with the other slit open – exact same results, except he needed to place a second detector near the other to capture the photon from the other slit.
Now with both slits open both detectors detect a full count of half the photons each! Meaning we know the pattern is there at the wires because the full count means no photons hit any of the wires (kind of like knowing the moon is there without looking). He has collected photons with a known interference pattern and he Knows Which Slit They Came Through!
……..All right! Success time to shine Afsher’s shoes for a trip to Stockholm.

One last question for Afsher before we buy the plane ticket.
For anyone photon he now knows which slit it came from please identify for us between which pair of wires did it go though?

Rade unless someone can define “Which Way” rather than just “Which Slit” with something other than the HUP I’m not chipping in for the plane ride.
You see all he did was exchange one uncertainty with a new one, in a very “Complementarity” way per Niels Bohr.
Just a little magic miss-direction by taking your attention off of “Which Way” and putting it onto “Which Slit” only in this case it seems the magician is the one most fooled by the trick.

 

[Rade]

...Rade unless someone can define “Which Way” rather than just “Which Slit” with something other than the HUP I’m not chipping in for the plane ride.
You see all he did was exchange one uncertainty with a new one, in a very “Complementarity” way per Niels Bohr. Just a little magic miss-direction by taking your attention off of “Which Way” and putting it onto “Which Slit” only in this case it seems the magician is the one most fooled by the trick.

Fair enough. I shall email Dr. Afshar with your comment and report back if I get an answer.

One question of something that concerns me about your post--why is such an obvious falsification of his experiment, that is so clear to you, not so clear to the professional physicists that peer reviewed his publication ? Seems to me (if I am to take your argument seriously) that not only the magician Afshar was the fool, but the entire editorial board of the journal must then be fools--that is, if your argument holds. But you see, I find this hard to agree with when I look at who is on the editorial board--as I post below. Also, do you really believe the editor of the journal at the time of the Afshar paper, Dr. Gerard ’t Hooft, Utrecht University, The Netherlands (1999 Nobel in Physics) did not consider your comment above ? If what you claim is so obviously true, I do not see how this paper would have been sent to a group of peer physicists to review, let alone be published.

Please understand, I am NOT trying to be rude or insulting--I only seek the facts about this experiment, I have no idea for which fools the QM bell tolls. Final question, have you addressed your concerns to Dr. 't Hooft ?

==========================================

Foundations of Physics
An International Journal Devoted to the Conceptual Bases and Fundamental Theories of Modern Physics
Chief Editor: G. 't Hooft
ISSN: 0015-9018 (print version)
ISSN: 1572-9516 (electronic version)
Journal no. 10701
Springer US
Online version available
Online First articles available

Editorial|Description|Editorial Board
Editorial Board
Chief Editor:
Gerard ’t Hooft, Utrecht University, The Netherlands

Associate Editors:
Paul Busch, University of York, UK;
Dennis Dieks, Utrecht University, The Netherlands;
Erik Verlinde, University of Amsterdam, The Netherlands;

Editorial Board:
Jeffrey Bub, University of Maryland, MD, U.S.A;;
Arthur Fine, University of Washington, Seattle, U.S.A;
Bas van Fraassen, Princeton University, NJ, U.S.A.;
Robert Geroch, University of Chicago, IL, U.S.A.;
GianCarlo Ghirardi, University of Trieste, Italy;
Sheldon Goldstein, Rutgers University, NJ, U.S.A.;
Daniel Greenberger, The City College of CUNY, NY, U.S.A.;
Alan Kostelecky, Indiana University, IN, U.S.A
Tim Maudlin, Rutgers University, Bloomington, U.S.A.;
D. Carlo Rovelli, Centre de Physique Theorique de Luminy, Marseilles, France;
Abner Shimony, Boston University, MA, U.S.A.;
Lee Smolin, Perimeter Institute, Canada;
C. Anton Zeilinger, University of Vienna, Austria;
Wojciech H. Zurek, Los Alamos National Laboratory, NM, U.S

 

[cesiumfrog]

Fair enough. I shall email Dr. Afshar with [RandallB's] comment and report back if I get an answer.

That's a little rude, Rade. Why not just email him your own comment ("QM really is incomplete as now confirmed by experiment")?

The journal (or the editorial board) certainly made the right decision publishing the article on Afshar's experiment, simply because its noteworthiness and controversy raise the impact of that journal (and hence increase profits). Whether Afshar's personal interpretation is actually correct is irrelevant to that decision, so it was quite unnecessary for you to recite the editors names to us.

Since you insist only on appealing to higher authorities, rather than directly considering the actual arguments yourself, you need only check http://en.wikipedia.org/wiki/Afshar_experiment" for links to detailed specific responses from reputable other physicists (especially Unruh). So now you need to explain why their claims should carry less weight.

 

[Rade]

...That's a little rude, Rade...

Well, if so, then I offer a public apology to whomever may feel offended. Recall, I was not the first on this thread to imply that someone was a fool--the tone this conversation has taken just did not sit well with me. Obviously, we must wait for peer reviewed dialog and future experiments using Afshar approach to decide status of QM--not the personal opinion of posts on Physics Forum.

 

[RandallB]

Fair enough. I shall email Dr. Afshar with your comment and report back if I get an answer.

...do you really believe ... Dr. Gerard ’t Hooft, Utrecht University, ... would sent to a group of peer physicists to review, let alone be published.
... Final question, have you addressed your concerns to Dr. 't Hooft ?

I did not call Afshar “a Fool”, so please do not represent that I did. I will grant you maybe I should use “In My Opinion” and say that IMO I though he was fooled by his own experiment. Just because we may be tricked by magic, we do not consider ourselves to be fools for it.

As I said in my post, “rebuttals obviously has not prevented publication” of Afsar and that I like that it was published because it gives “you and me real results to look at and put into proper perspective”. I like seeing real results of real experiments rather than relying on the conclusions of others.
Peer review does not require the conclusions that Afsar draws be correct, only that they are worth reading, even if others (like R.E. Kastner) disagree. So I expect folks like Dr. Gerard ’t Hooft, Utrecht University to at time publish ideas they do not agree with.

Yes, I have emailed the Afshar team and others before, but as self taught Local Realist doing individual research with no academic credentials in physics I can hardly expect them to treat me as a “peer” worth reading or replying to.
But, if you know some one willing to review and recommend material based on content rather than background, even for arxiv by all means PM me.

 

[DrChinese]

But we read below from recent 2007 experiment that Einstein was correct--we do "know" what happens to electron between slit and screen, e.g., QM really is incomplete as now confirmed by experiment:
http://www.physorg.com/news92937814.html
What am I missing in this discussion ?

Edit: Here is the 2007 publication I talk about--in peer reviewed journal of physics:
http://arxiv.org/ftp/quant-ph/papers/0702/0702188.pdf

You have to laff at us (and I do include myself here)... we managed to jump WAY past the original post all the way to Afshar in just a couple of posts...

I don't take any issue with the experimental results, but his paper is hardly a refutation of QM and is certainly not proof that QM is incomplete. For QM to be incomplete, a more precise state of a system must possible. Where is it?

You still can't beat the HUP. That is the rigorous version of Bohr's complementarity. I expect that after time, it will be clear that Afshar has created an experiment where Bohr's ideas are only being minimally challenged anyway: He places the wires at places where there are local minima expected. So naturally it doesn't change the outcomes much. I would guess that as the wires are moved into positions in which the probability of a particle being detected increases, you will see that the apparent effect disappears.

But I will say that the editorial board you mentioned blows me away. I had never bothered to look at that before, and those names are all gods to me. :)

 

[Rade]

OK, I trend very lightly here, and it is NOT my intent to be rude to anyone. But, IMO, this is a very important topic, so I will proceed. If the moderators of the Forum decide to remove this post, that is fine with me.

In Post #7, a very specific critical comment concerning "which-way" vs "which-slit" was made about the Afshar et al. (2007) paper on the double-slit experimental design. Here are the links to the 2007 paper and other citations by Dr. Afshar:

::Afshar SS, Flores E, McDonald KF, Knoesel E. (2007). "Paradox in wave-particle duality". Foundations of Physics 37 (2): 295-305. http://arxiv.org/abs/quant-ph/0702188

Other reports:

::Afshar SS (2003). "Sharp complementary wave and particle behaviours in the same welcher weg experiment". IRIMS:quant-ph/030503: 1-33. http://www.irims.org/quant-ph/030503/

::Afshar SS (2005). "Violation of the principle of complementarity, and its implications". Proceedings of SPIE 5866: 229-244. http://arxiv.org/abs/quant-ph/0701027


::Afshar SS (2006). "Violation of Bohr's complementarity: one slit or both?". AIP Conference Proceedings 810: 294-299. http://arxiv.org/abs/quant-ph/0701039


In response to those comments from Post #7, I indicated that I would email Dr. Afshar to see if he had any response. I received permission from Dr. Afshar to post his responses. Here they are.

At this point, I drop out of any further discussion on this issue--I will let the community of professional physicists proceed.

Emails received by Rade (12/1/2007) from Dr. Afshar concerning comments in Post #7:

1. Please feel free to post my words verbatim. I don't think it would resolve anything, as these issues need rigorous analysis and discussion best done through professional conferences and papers, but I see no harm in correcting a misconception even if it is on an internet forum. I just don't have the time to chime in directly myself. Many of these questions (hundreds in fact) have been addressed in my weblog when I had more time to spare couple of years ago http://irims.org/blog/index.php/questions/2004/09/25/questions_welcome#comments Regards--S

2. R--RandallB argues that "which way" is not the same as "which slit". He is incorrect, and to make sure, he can ask Prof. Unruh, whom he seems to accept as the expert. He is also, more than welcome to write a response paper to Found. Phys., where in due course he will get his response, but rest assured, in the context of welcher-weg experiments, as that discussed between Bohr and Einstein, "which way" is exactly "which slit." I can provide various references for this assertion, some of which can be found in my papers, but let him ask Unruh for now. I hope this helps. Regards to both.--S

 

[cesiumfrog]

Hey Rade, would you please post the exact message you sent, so that we can understand the context of that response?

Just as an example, I don't remember RandallB ever mentioning Unruh. I know I mentioned him myself in the very post, where I warned you that it is rude to forward someone else's comments without permission (even just the lost context is enough to misrepresent the person, which is potentially slander; more could be learned by them directing their own emails), but I mentioned him in an argument against blindly accepting someone's opinion (obviously I'd be unimpressed if you had mixed that into your email backwards as Afshar's response suggests).

 

[Rade]

Hey Rade, would you please post the exact message you sent, so that we can understand the context of that response? Just as an example, I don't remember RandallB ever mentioning Unruh. I know I mentioned him myself in the very post, where I warned you that it is rude to forward someone else's comments without permission (even just the lost context is enough to misrepresent the person, which is potentially slander; more could be learned by them directing their own emails), but I mentioned him in an argument against blindly accepting someone's opinion (obviously I'd be unimpressed if you had mixed that into your email backwards as Afshar's response suggests).

The message I sent to Dr. Afshar was to review the post--I sent him the link to the thread and asked him to review it--he read the entire thread--he read your comment about Unruh--he sent to me the response I posted above.

 

[RandallB]

Emails (12/1/2007) from Dr. Afshar ...
2. R--RandallB argues that "which way" is not the same as "which slit". He is incorrect, and to make sure, he can ask Prof. Unruh, whom he seems to accept as the expert. He is also, more than welcome to write a response paper to Found. Phys., where in due course he will get his response, but rest assured, in the context of welcher-weg experiments, as that discussed between Bohr and Einstein, "which way" is exactly "which slit." I can provide various references for this assertion, some of which can be found in my papers, but let him ask Unruh for now. I hope this helps. Regards to both.--S

Don’t know why he thinks Prof. Unruh is my reference (I assume he misread other posts as mine), don’t know Unruh have not read his stuff. I draw my own conclusions based on my own understanding of the meaning of “Bohr's complementarity” which is what the Afsher experiment claims to Violate.
I do agree that the context of ‘welcher-weg’, as discussed between Bohr and Einstein on interference patters is correctly defined as which way through "which slit" as compared to individually observed photons forming an interference pattern. Meaning a certainty of pattern locations, in “complementarity” contrast to the uncertainty of "which slit”.

However IMO Afsher results simple give a new and different observation of certainty vs uncertainty. Knowing "which slit" for each photon down stream of the pattern area, however that also gives a “complementarity” uncertainty of the precise slot between wires “which way” detail for individual photons passing through the interference area. Attempts to observe and regain that detail would remove the possibility of later seeing the "which slit" information in the Afsher experiment.

Thus in my opinion reported observations by Afsher is supporting “Bohr's complementarity” concept. That is:
- as we better ‘know’ position the more uncertain momentum.
- OR converting the idea to a simple experiment where we are certain about the position of individual photons making a pattern on a screen as we are just as uncertain about "which slit" ie. the Bohr and Einstein discussion.
- AND NOW THE AFSHER discussion in a new result that gains certainty about "which slit" at the cost of losing the detail of where individual photons are in the pattern area. Bohr would surly argue that is a “complementarity” uncertainty; as the wires only confirm the pattern exists but fails to provide complete which way information for individual photons.

I think the experiment IS Valuable and am glad it has been published, I just disagree on the conclusions and that is how science should work towards a final conclusion –sorting out the disagreements.
As to having my opinions considered in that debate, I’ll look into how to submit a response to Found. Phys. as Dr Afsher suggests. He has credentialed standing in the scientific community I don’t. Maybe I am being pessimistic but I do think that makes a difference in how submissions are treated.

RB

 

[Hans de Vries]

Some historical context about the complementarity principle and the typical "Bohr was right" and "Einstein was wrong" account of the 1927 Solvay conference might be of interest.

This is a nice piece of historical research:
http://front.math.ucdavis.edu/0212.7090

Neils Bohr vehemently denounced Einsteins idea of the "light quantum" for almost 14 years until just shortly before the Solvay conference. That is, he supported only the "wave behavior" Then, when he finally accepted Einstein's photon it was still in the form of what seems to me a compromise with his partner Heisenberg on the Copenhagen interpretation. This is what became the "complementarity principle"

The most orthodox form of the "complementarity principle" often heard nowadays implies that there are two different types of photons. One is a particle and the other is a wave. One can asks oneself how the "particle type" (which does not interfere) can be correctly refracted by the lens in Afshar's experiment if it has no wave behavior... (refraction IS interference)

In any case, Bohr's partner in the Copenhagen interpretation, Heisenberg, never mentions such an orthodox interpretation. For Heisenberg the "complementarity principle" is just a recognition of the fact that wave behavior and particle behavior are both just approximations. For instance in his book "The physical principles of Quantum Mechanics" he just briefly discusses the "complementarity principle" in 4 pages but never makes such statements as "the photon is either a wave or a particle". Regards, Hans

 

[RandallB]

Yikes

Some historical context about the complementarity principle and the typical "Bohr was right" and "Einstein was wrong" account of the 1927 Solvay conference might be of interest.

This is a nice piece of historical research:
http://front.math.ucdavis.edu/0212.7090

...For Heisenberg the "complementarity principle" is just a recognition of the fact that wave behavior and particle behavior are both just approximations. ...

Yikes
Other than to assume it means approximations in the form of statistical uncertainties will always remain somewhere in real observations (as they do for Ashar) I may never really know what the "complementarity principle" is.

Thanks Hans, good reference.

 

[rkastner]

Post-selecting not the same as defining a trajectory through a particular slit.

The indirectly observed interference pattern (via the grid not diminishing the final intensity) confirms that each photon is in a superposition of slit states at that point. That interference unambiguously means each photon went through both slits. Two Schrodinger waves are in superposition, but (downstream from the grid) the corresponding photon is forced to decide which spot to land in when the beams intercept the final screen. So you can post-select for which spot. That doesn't mean you can infer that the photon in question "really" went through the corresponding slit--it went through both. See my latest paper on arxiv.org.

 

[vanesch]

I would like to point out that a very recent thread was (again) talking about this infamous experiment.

https://www.physicsforums.com/showthread.php?t=210249

 

[vanesch]

The indirectly observed interference pattern (via the grid not diminishing the final intensity) confirms that each photon is in a superposition of slit states at that point. That interference unambiguously means each photon went through both slits. Two Schrodinger waves are in superposition, but (downstream from the grid) the corresponding photon is forced to decide which spot to land in when the beams intercept the final screen. So you can post-select for which spot. That doesn't mean you can infer that the photon in question "really" went through the corresponding slit--it went through both. See my latest paper on arxiv.org.

That's indeed the point. All these errors in interpretation come from a post-experiment re-interpretation of a superposition as a statistical mixture. That's what I've been saying on that experiment for a long time now...

 

[confusedashell]

although, it was peer reviewd and published in Foundations of Physics and bunch of serious phycisist stand behind it.
You don't think Afshar has thought about all the different criticism over the last 7 years he's been doing this experiment ?
It seems a lot of people are just arrogant towards Shariar S. Afshar cause he falsified CI & most likely MWI in a single experiment.
Kinda like how we falsified creation when we found the first fossil record:D

 

[vanesch]

although, it was peer reviewd and published in Foundations of Physics and bunch of serious phycisist stand behind it.
You don't think Afshar has thought about all the different criticism over the last 7 years he's been doing this experiment ?

The EXPERIMENT isn't wrong. Scientifically, it is a nice experiment. But you must admit, when you read a lot of textbooks on quantum theory, and even a lot of research publications (with good research in it), that when it concerns interpretations and a physical picture, that many, many people are far from clear over it. I get nervous when I read the interpretational nonsense that often goes with otherwise very interesting experiments, such as delayed choice quantum erasers and so on. The people writing this, no matter their quality as experimentalists and their "authority", are often very very confused as to the interpretational issues. Maybe it is Afshar's experiment's merit to point out this confusion.

Now, if Afshar or anybody else would have presented me the setup (that is, what they were going to do), I don't think I would have had the slightest difficulty in finding out the expected result, which is what is actually measured. It wouldn't matter what "interpretation" I would have adhered, in fact. I KNOW that single photon experiments are equivalent to classical optics, when one reasons in terms of "intensity at measurement <-> probability of detection".

But the error, I've repeated this very often here, is to ASSIGN PATHS to photons after measurement. This is not "CI", this is not "MWI", this is WRONG. Why is it wrong ? Because we change, AFTER THE FACT, a quantum-mechanical superposition into a mixture.

We KNOW that we cannot do that. The simple 2-slit experiment already does this. We know that the state |slit1> + |slit2> is NOT the same as 50% |slit1> and 50% |slit2>. Otherwise we wouldn't get an interference pattern. Feynman explains it well in his intro course (vol III).

He points out that THIS FACT, that there exist states where you can't say that the photon/electron/whatever went OR through slit 1 OR through slit 2 (but we ignore which way, so we assign 50% to each). In fact, he explains the essence of the superposition principle. He tells (very rightly) that this contains the "whole mystery" of quantum theory. So we can't say that the particle went through slit 1 or through slit 2. It was in ANOTHER state.

So if later, we DETECT the particle somewhere, it is totally absurd to trace it back and "find out through which slit it actually went", because that AMOUNTS TO SAYING that it went through one of the slits, and that means that we DID have a statistical mixture of 50% through slit 1 and 50% through slit 2. And we just said that it WASN'T in one of these states.

Nevertheless, this is Afshar's big "discovery": that, if we track back the particle to one of the slits, meaning, that we assume that the particle DID go through OR slit 1 OR slit 2, that we run into a problem. BUT WE KNEW THAT ALREADY.

That said, Afshar does have the merit to point this out once more, because PLENTY of otherwise good articles DO fall in this trap: "when detector 3 hits, this means that the photon went to the left at beamsplitter 2"... It didn't! The photon was in a superposition, which gave rise to a certain probability for detector 3 to click.
We also understand why: in many circumstances (but of course not in all), we don't make a blatant error when saying so. In many circumstances, the erroneous statistical mixtures DO give the same result as the superpositions: this is the case, each time that we measure in the same basis as the one in which the confusion superposition/mixture is made.

So again, Afshar's experiment is not wrong. But it doesn't show anything special, and it certainly doesn't falsify any interpretation that is coherent with the quantum formalism. It only FALSIFIES INTERPRETATIONS which are not CORRECT wrt. the quantum formalism, namely those that assign statistical mixtures to superpositions that appear between setup and observation. We already KNEW that this doesn't work, even with the double slit experiment. Nevertheless, many people continue to "picture" quantum mechanics that way, even in research papers and textbooks. They CONTINUE to give trajectories to quantum particles. And then, they run into troubles with Afshar's experiment, but even with any quantum experiment where interference is displayed. Sometimes they can talk themselves out of it, sometimes not. But in any case they are conceptually wrong. But these erroneous interpretations are NOT CI, NOR MWI. They are in fact naive hidden variable interpretations where a confusion exists between superpositions and statistical mixtures.

As I say, however, many people (even renowed experimentalists) have this erroneous view. Look at how many people think that the wavefunction of an electron, squared, gives you "the probability that the particle is in position (x,y,z)". They confuse the superposition of position states with a statistical mixture. The wavefunction squared DOESN'T GIVE YOU the probability that the particle IS at position (x,y,z). The wavefunction squared gives you the probability, IF YOU DO A POSITION MEASUREMENT, that you will FIND position (x,y,z). It is the distinction between these notions which is the entire content of the superposition principle, and hence the whole idea of quantum theory. And many people (renowed experimentalists included) never understood this.

 

[confusedashell]

So you would say you are more "authority" on the subject than respected physicists like john g cramer, afshar etc?
EXACTLY WHAT THEY SAY IS THAT MWI / CI proponents has UNINTENTIONALLY "stepped out of line" with the quantum formalism with MWI AND CI.
The afshar experiment shows this, so therefore MWI AND CI doesn't fit the quantum formalism. SIMPLE.

You yourself agreed you are not proponent of MWI because of scientific reasons but wishful philosophical thinking. SO, when nature tells us something through a scientific experiment, you don't listen if it doesn't fit YOUR favourite interpertation.

I doubt afshar and john g cramer would go against MWI and CI to be lame for no reason, sorry, that's too far fetched...
Yes John G Cramer would have something to gain on it, his own interpretation, but his interpretation (not that I like it, i think the "retarded backwards in time" **** is a little too "weird") is the consequence of taking quantum formalism directly without adding anything.

 

[vanesch]

So you would say you are more "authority" on the subject than respected physicists like john g cramer, afshar etc?
EXACTLY WHAT THEY SAY IS THAT MWI / CI proponents has UNINTENTIONALLY "stepped out of line" with the quantum formalism with MWI AND CI.
The afshar experiment shows this, so therefore MWI AND CI doesn't fit the quantum formalism. SIMPLE.

I don't care about their or mine *authority*. I simply say that their conclusions are WRONG, and probably because they don't understand correctly CI and MWI themselves. In other words, they attack a strawman, which is their misunderstanding of CI or MWI.

You yourself agreed you are not proponent of MWI because of scientific reasons but wishful philosophical thinking. SO, when nature tells us something through a scientific experiment, you don't listen if it doesn't fit YOUR favourite interpertation.

Because you CAN'T make any distinction between interpretations on experimental basis, as long as the experimental result follows the predictions of the quantum FORMALISM, which is the case here. ALL (correct) interpretations MAKE THE SAME PREDICTIONS. I would like to see what Afshar EXPECTS MWI for instance to predict for his experiment. I will then point out where he MISUNDERSTANDS MWI. We can then do the same exercise for CI.

I'm pretty sure he's going to say that "detector 2 clicking means that we now know that the photon came through slit 1, nevertheless the absense of blurring means that there was interference at the wires, and hence the photon couldn't come through slit 1 alone".

I'm even guessing at how he will misunderstand MWI, and think that MWI is going to say that the photon going through two slits means that there is now a split in 2 worlds, one in which the photon went through slit 1, and one in which the photon went through slit 2.

BUT BOTH OF THESE STATEMENTS ARE WRONG. They are NOT what CI or MWI say - but maybe what he THINKS they say.

If he says something else, tell me, if he says this, I'll show you why it is wrong.

 

[confusedashell]

Sure your right, serious PhD's are wrong. Ok vanesch.
When you make a experiment that makes as much noise as Afshar experiment and get published in FoP I'll take you serious.

I sincerely believe, both John G Cramer (who has dedicated his whole life to this field in science) and Afshar (who came up with this experiment) are well educated in the different interpretations.
Afshar himself just says it falsified CI and didn't say much about MWI because as he said in his blog "you don't need my experiment to question MWI as I've pointed out to Deutsch before".

By the way I'm not trying to upset you or anything, I just have a low respect level for narcissitic people.
If MWI were true, you'd have the right to be narcissitic, but you just choooose to believe in it without any reason(scientifically).
Dno what other people has done to you to make you sooo wanting people not be in "your branch" for more than aatto second, but I think you'll get lonely eventually:P

 

[vanesch]

Sure your right, serious PhD's are wrong. Ok vanesch.
When you make a experiment that makes as much noise as Afshar experiment and get published in FoP I'll take you serious.

Are you able to follow an argument, or can you only follow "authority" ? I'm a PhD too you know. I even have a professor habilitation. Does that change the quality of my argument ?

Have you read Kastner's paper ? I just read it, it says (totally independently) exactly what I'm claiming here.

 

[confusedashell]

Nope, what have you contributed to science ?:P Just kidding.
No ofcourse I'm following a arguement, it's not like I would follow any PhD saying "Oh god exist" without any EMPERICAL evidence or good arguements for this claim.
By the way, what are you PHD IN?

It's just Many worlds cannot be proven at all, and there are many objections to it, so you chose to believe in it based on philosophical reasons, that's not science.
then you object to a SCIENTIFIC arguement... Get my point?

 

[vanesch]

Nope, what have you contributed to science ?:P Just kidding.

I debunked a few erroneous claims in the scientific literature...

No ofcourse I'm following a arguement, it's not like I would follow any PhD saying "Oh god exist" without any EMPERICAL evidence or good arguements for this claim.
By the way, what are you PHD IN?

In particle physics.

It's just Many worlds cannot be proven at all, and there are many objections to it, so you chose to believe in it based on philosophical reasons, that's not science.
then you object to a SCIENTIFIC arguement... Get my point?

I object to a scientific argument with ANOTHER scientific argument, and then you come in with "authority". Where is YOUR scientific argument ? Where is the scientific error in MY reasoning ?

As to why CI/MWI cannot be proven, I think we went over this already a few times: you CANNOT PROVE OR DISPROVE an interpretation, as an interpretation is a STORY that you tell with a FORMALISM. If you tell different stories over the same formalism, then you are talking about the SAME predictions. So yes, MWI is a philosophical stance, a way of LOOKING at things, in casu the quantum formalism. It is the one that gives me, personally, the best MENTAL PICTURE. I don't claim it to be "true" or "false".

Imagine that I claim that I picture (positive) integer numbers on a line, and someone else claims that integer numbers are "bags with coins in it". These are two different interpretations of the abstract number system. Now what you, or Afshar, or anybody of that style is claiming is that he found A CALCULATION WITH INTEGER NUMBERS showing that the picture of the line is WRONG, but the one with the bags is right...

 

[rkastner]

I think that some of the initial antagonism toward Afshar and his experiment was based on its publication in a popular magazine rather than in a peer-reviewed journal. But I have no personal antagonism toward Afshar, we have met and talked and he has always been very nice to me in our personal meetings (although I think that some of his online responses to my written criticisms have been a bit off target at times). I also want to make clear that I am all for reading about and discussing Afshar's very interesting experiment, contrary to what someone said on this forum earlier.

One thing I regret is the appearance on this forum of at least one thread or forum designated "for proponents only," which explicitly un-invites anyone with a different view or interpretation. I find that rather unfortunate. I also hope that we can refrain from questioning motives and postulating negative personality attributes of posters with whom we might not happen to agree.

Another point: I have been a strong supporter of John Cramer's Transactional Interpretation, but I don't happen to agree with him that Afshar's experiment confirms TI as opposed to other interpretations. I do think that applying TI to Afshar's experiment provides an interesting way to understand what might be going on in a time-symmmetric picture, but when you do that you confirm that it's inappropriate to attribute a true "which-way" trajectory to the photon. This is all contained in my 2005 paper (http://arxiv.org/abs/quant-ph/0502021)

 

[vanesch]

I also want to make clear that I am all for reading about and discussing Afshar's very interesting experiment, contrary to what someone said on this forum earlier.

As I said a few times, although Afshar's experiment is interesting because it points out some commonly helt misunderstandings, I fail to see in Afshar's experiment any deviation from classical optics.

I mean: show your setup to someone who only knows classical optics. He will find out the correct images for the different setups. Of course, now they come in "clicks" at a rate proportional to the classical intensity, which is always the case when detecting light with photon detectors, but that is not specific to this experiment.

If you do (classical) Fourier optics, you do things like this, on a much more sophisticated level: you take an image, you put a converging lens in front of it, and in the focal plane you now have the Fourier transform of the image, which you can filter using patterns. A second lens re-transforms the Fourier transform back into an image, which is now filtered (with low or high spatial frequency components). Afshar's setup is a very simple version of this.

So to me, this is simple classical optics... I always failed to see it differently.

 

[rkastner]

Yes, of course Afshar's experiment is fully consistent with classical optics. At the level of individual photons, at the point where the beams intercept the final screen, each photon has to "decide" where to land, and has a 50% chance of landing at either spot. Up until that point the photon is in an indeterminate state as to which spot it will land in, just as an incoming photon polarized at a 45 degree angle to a linear polarizer will have to "decide" whether to pass or not. I think you're correct to describe the confusion in terms of mistaking a pure state for a statistical ensemble.

 

[colorSpace]

It would seem to me that according to this view, there is never a true which-way-information. Would this mean that using the existence of which-way-information to explain the presence or absence of interference patterns doesn't work in the first place? Wouldn't such a view confirm Afshar's view? Or if not, then how specifically is this experiment different from other situations?

 

[rkastner]

A good question. Whenever you have a source permitted to go through 2 open slits, a photon emanating from the source *will* go through both slits. The closer your "which-way" detector (i.e., something that physically interacts with the source beam) is to those slits, the more meaningful it is to say that you "caught" the photon going through a particular slit. But once you have allowed interference, then obviously the photon went through both. Afshar is mistaken because he wants to claim that he has shown interference and also that the detected particle went through a particular slit (which it didn't--it went through both). If you look at the discussion in the Feynman Lectures, which shows detectors right behind the slits, that setup allows you to say that you "caught" the particle going through that slit--to the extent that further downstream interference is destroyed. But if the Schrodinger wave goes through two slits, then the photon goes through two slits. My recent arxiv.org paper discusses this, as well as my (2005), which discusses the significance of this for "delayed choice" experiments.

 

[lightarrow]

A good question. Whenever you have a source permitted to go through 2 open slits, a photon emanating from the source *will* go through both slits. The closer your "which-way" detector (i.e., something that physically interacts with the source beam) is to those slits, the more meaningful it is to say that you "caught" the photon going through a particular slit. But once you have allowed interference, then obviously the photon went through both. Afshar is mistaken because he wants to claim that he has shown interference and also that the detected particle went through a particular slit (which it didn't--it went through both). If you look at the discussion in the Feynman Lectures, which shows detectors right behind the slits, that setup allows you to say that you "caught" the particle going through that slit--to the extent that further downstream interference is destroyed. But if the Schrodinger wave goes through two slits, then the photon goes through two slits. My recent arxiv.org paper discusses this, as well as my (2005), which discusses the significance of this for "delayed choice" experiments.

Correct me if I'm wrong, the Afshar's experiment with both slits open, when a photon is found in detector A or detector B, is no much different from reducing the multiple-bands interference pattern in two bands only (in A and B), where one detects the photon in one or in another, statistically, so no proving which-way slit at all.

 

[rkastner]

I'm not sure I'd call it "reducing" an interference pattern--there isn't really interference at the final detection plane, but there is still a superposition of two beams. Interference and superposition are two different things--you can have one without the other. More precisely, you can have superposition of two quantum states without interference. For example, let a source emit into two separated collimated beams which don't physically interact. The two beams are in a superposition but there is no interference between them.

 

[gptejms]

There was a discussion on Afsar 3 years back-may like to see the link below
https://www.physicsforums.com/showthread.php?t=62460&highlight=afshar

This is what I wrote(I hope it's of some help):-

...given a field distribution f(x,y) on one plane,you can find the distribution on another parallel to it at a distance d by a convolving f(x,y) with exp(-ia(x^2+y^2) where a =k/2d.The effect of a lens is to multiply the incident phase distribution by exp(ik(x^2+y^2)/f),where f is the focal length.Using the above one can easily show that given some field distribution g(x,y)in the front focal plane of the lens,the distribution on the back focal plane is simply the Fourier tranform of g(x,y).Now in Afshar's experiment,neither the wire grid nor the slits are at a focal distance from the lens.Besides what you obtain on the image plane is not simply the image of the wire grid----you have to distinguish between the case when one slit is open from the case when both are open.So one could follow the following approach:-a single slit gives a wavefunction of the kind \psi(x)=constt. over the slit width,0 elsewhere.Fourier transforming this you get \psi(p)=constt. sin(ap)/p(where a=slit width) in the momentum space.Now the wire grid and lens are some kind of momentum filters.One should work out the whole thing in this manner for the cases of one slit open and both open.I haven't done this but I guess what Afshar gets from simple ray optics should come out---but his conclusions are contestable