Afshar and interpretations [Archive]

Joel Gilmore

Aug4-04, 01:19 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Hi all,\n\nI\'ve been thinking about Afshar\'s recent experiment (see\nhttp://www.kathryncramer.com/wblog/archives/000688.html and others)\nwhich purports to destroy the Copenhagen interpretation (and if you\nread New Scientist, shake quantum mechanics to the core, etc, etc) It\nis a modification of the double slit experiment - see Oz\'s recent post\n(25/7/04 - "Afshars experiment) for a brief summary. The result is we\ncan detect both the particle like behaviour (detectors determine which\nslit the particle went through) and the wave like behaviour (we place\nbarriers (wires) at where interference nodes would be and see no change\nin the results). Supposedly, this then contradicts the Complementarity\nprinciple (and the Copenhagen interpretation?), which says no\nexperiment can see both the wave and particle like nature of matter. I\nwas hoping to get people\'s thoughts on how significant this is\n(assuming that it\'s right - it hasn\'t been published yet!)\n\nWhen I did undergrad QM (I\'m now PhDing), AFAIK we never actually\ntalked about Complementarity principle. We DID use the Copenhagen\ncollapse hypothesis, but on the whole we just started with the basic\npostulates (wave function giving probability, Schroedinger equation\ngiving evolution) and derived everything from there. As I understand\n(and I\'d appreciate any corrections here!) there isn\'t really a\nwave/particle conflict - everything is a particle, but it has\nassociated with it a wave function that determines the probabiltiy of\nfinding a particle at a given position/state. They don\'t "sometimes\nact as waves, sometimes act as particles" - they simply are particles\nwhich have probability distributions. So, in the double slit\nexperiment, whether you have photons or elecrons, the wave function of\nthe particle gets diffracted by the slit (evolved by the approriate\nHamiltonian) until finally the screen makes an "observation" and forces\nthe particle to be somewhere. I don\'t really see "conflict" between\nthe two pictures.\n\nSo, how important is it if the complementarity princple doesn\'t hold?\nIt was an interesting theory perhaps, but it seems to an extent to be a\nhold over from "earlier" theories of QM, before everything was\nformalised. Would you agree with this? It\'s not needed to formulate\nquantum mechanics - does it really change anything if it\'s not true?\n\nFurthermore, do these results really say anything about the Collapse\nhypothesis, which really seems to be what\'s identified with the\nCopenhagen interpretation these days?\n\nAll discussions and thoughts would be welcome :)\n\nCheers,\nJoel\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>Hi all,

I've been thinking about Afshar's recent experiment (see
http://www.kathryncramer.com/wblog/archives/000688.html and others)
which purports to destroy the Copenhagen interpretation (and if you
read New Scientist, shake quantum mechanics to the core, etc, etc) It
is a modification of the double slit experiment - see Oz's recent post
(25/7/04 - "Afshars experiment) for a brief summary. The result is we
can detect both the particle like behaviour (detectors determine which
slit the particle went through) and the wave like behaviour (we place
barriers (wires) at where interference nodes would be and see no change
in the results). Supposedly, this then contradicts the Complementarity
principle (and the Copenhagen interpretation?), which says no
experiment can see both the wave and particle like nature of matter. I
was hoping to get people's thoughts on how significant this is
(assuming that it's right - it hasn't been published yet!)

When I did undergrad QM (I'm now PhDing), AFAIK we never actually
talked about Complementarity principle. We DID use the Copenhagen
collapse hypothesis, but on the whole we just started with the basic
postulates (wave function giving probability, Schroedinger equation
giving evolution) and derived everything from there. As I understand
(and I'd appreciate any corrections here!) there isn't really a
wave/particle conflict - everything is a particle, but it has
associated with it a wave function that determines the probabiltiy of
finding a particle at a given position/state. They don't "sometimes
act as waves, sometimes act as particles" - they simply are particles
which have probability distributions. So, in the double slit
experiment, whether you have photons or elecrons, the wave function of
the particle gets diffracted by the slit (evolved by the approriate
Hamiltonian) until finally the screen makes an "observation" and forces
the particle to be somewhere. I don't really see "conflict" between
the two pictures.

So, how important is it if the complementarity princple doesn't hold?
It was an interesting theory perhaps, but it seems to an extent to be a
hold over from "earlier" theories of QM, before everything was
formalised. Would you agree with this? It's not needed to formulate
quantum mechanics - does it really change anything if it's not true?

Furthermore, do these results really say anything about the Collapse
hypothesis, which really seems to be what's identified with the
Copenhagen interpretation these days?

All discussions and thoughts would be welcome :)

Cheers,
Joel

Aaron Bergman

Aug5-04, 03:23 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>In article <2004080316131816807%gilmore@phyuqeduau>,\nJoel Gilmore <gilmore@phy*****.uq.edu.au> wrote:\n\n> Hi all,\n>\n> I\'ve been thinking about Afshar\'s recent experiment (see\n> http://www.kathryncramer.com/wblog/archives/000688.html and others)\n> which purports to destroy the Copenhagen interpretation (and if you\n> read New Scientist, shake quantum mechanics to the core, etc, etc) It\n> is a modification of the double slit experiment - see Oz\'s recent post\n> (25/7/04 - "Afshars experiment) for a brief summary. The result is we\n> can detect both the particle like behaviour (detectors determine which\n> slit the particle went through) and the wave like behaviour (we place\n> barriers (wires) at where interference nodes would be and see no change\n> in the results). Supposedly, this then contradicts the Complementarity\n> principle (and the Copenhagen interpretation?), which says no\n> experiment can see both the wave and particle like nature of matter.\n\nI\'d hope the Copenhagen interpretation doesn\'t say this or it would\ncontradict even the single photon two slit experiment.\n\n> I\n> was hoping to get people\'s thoughts on how significant this is\n> (assuming that it\'s right - it hasn\'t been published yet!)\n\nI believe the experiment, but it certainly contradicts nothing in the\ninterpretation of quantum mechanics.\n\n[...]\n\n> So, how important is it if the complementarity princple doesn\'t hold?\n> It was an interesting theory perhaps, but it seems to an extent to be a\n> hold over from "earlier" theories of QM, before everything was\n> formalised. Would you agree with this? It\'s not needed to formulate\n> quantum mechanics - does it really change anything if it\'s not true?\n>\n> Furthermore, do these results really say anything about the Collapse\n> hypothesis, which really seems to be what\'s identified with the\n> Copenhagen interpretation these days?\n\nComplementarity holds. I think the answer is that you just have to be\ncareful how you define things.\n\nAfshar claims that because he has imaged the slits using a lens, he\nknows which slit each photon passes through. However, let\'s say we added\nthe usual particle detector at one of the slits. If we do this, the\ninterference pattern disappears and Afshar\'s wires detect some current.\nBut, if we already knew which slit the photon was passing through, why\nwould the addition of the detector change anything?\n\nIn other words, I think you have to be careful what you\'re talking about\nwhen you want to use complementarity. I believe the whole concept has\nbeen formalized, but I\'m not sure.\n\nAaron\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>In article <2004080316131816807%gilmore@phyuqeduau>,
Joel Gilmore <gilmore@phy*****.uq.edu.au> wrote:

> Hi all,
>
> I've been thinking about Afshar's recent experiment (see
> http://www.kathryncramer.com/wblog/archives/000688.html and others)
> which purports to destroy the Copenhagen interpretation (and if you
> read New Scientist, shake quantum mechanics to the core, etc, etc) It
> is a modification of the double slit experiment - see Oz's recent post
> (25/7/04 - "Afshars experiment) for a brief summary. The result is we
> can detect both the particle like behaviour (detectors determine which
> slit the particle went through) and the wave like behaviour (we place
> barriers (wires) at where interference nodes would be and see no change
> in the results). Supposedly, this then contradicts the Complementarity
> principle (and the Copenhagen interpretation?), which says no
> experiment can see both the wave and particle like nature of matter.

I'd hope the Copenhagen interpretation doesn't say this or it would
contradict even the single photon two slit experiment.

> I
> was hoping to get people's thoughts on how significant this is
> (assuming that it's right - it hasn't been published yet!)

I believe the experiment, but it certainly contradicts nothing in the
interpretation of quantum mechanics.

[...]

> So, how important is it if the complementarity princple doesn't hold?
> It was an interesting theory perhaps, but it seems to an extent to be a
> hold over from "earlier" theories of QM, before everything was
> formalised. Would you agree with this? It's not needed to formulate
> quantum mechanics - does it really change anything if it's not true?
>
> Furthermore, do these results really say anything about the Collapse
> hypothesis, which really seems to be what's identified with the
> Copenhagen interpretation these days?

Complementarity holds. I think the answer is that you just have to be
careful how you define things.

Afshar claims that because he has imaged the slits using a lens, he
knows which slit each photon passes through. However, let's say we added
the usual particle detector at one of the slits. If we do this, the
interference pattern disappears and Afshar's wires detect some current.
But, if we already knew which slit the photon was passing through, why
would the addition of the detector change anything?

In other words, I think you have to be careful what you're talking about
when you want to use complementarity. I believe the whole concept has
been formalized, but I'm not sure.

Aaron

richard miller

Aug5-04, 03:24 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>I apologise in advance that this does not seriously answer your question,\nsince my posting is a quick note on New Scientist - the Comic!\n\n> read New Scientist, shake quantum mechanics to the core, etc, etc)\n\nI think your \'etc. etc.\' is well warranted. Every week they write this\nnonsense. Some publication analogues...\n\nNature (The Times)\nThe Journal of Mathematical Physics (The Universe)\nNew Scientist (The Sport - bare chests, chatlines, escort agencies, that\nsort of thing)\n\nI put it semi jokingly, NS does spread some news, but so does \'The Sport\'\n\n\'Afshar recent experiment\' - wait for the publication of the recent\nexperiment.\n\nI won\'t trivialise your time any further\n\nEnjoy your PhD\n\nRichard Miller\n\n\n"Joel Gilmore" <gilmore@phy*****.uq.edu.au> wrote in message\nnews:2004080316131816807%gilmore@phyuqedu au...\n> Hi all,\n>\n> I\'ve been thinking about Afshar\'s recent experiment (see\n> http://www.kathryncramer.com/wblog/archives/000688.html and others)\n> which purports to destroy the Copenhagen interpretation (and if you\n> read New Scientist, shake quantum mechanics to the core, etc, etc) It\n> is a modification of the double slit experiment - see Oz\'s recent post\n> (25/7/04 - "Afshars experiment) for a brief summary. The result is we\n> can detect both the particle like behaviour (detectors determine which\n> slit the particle went through) and the wave like behaviour (we place\n> barriers (wires) at where interference nodes would be and see no change\n> in the results). Supposedly, this then contradicts the Complementarity\n> principle (and the Copenhagen interpretation?), which says no\n> experiment can see both the wave and particle like nature of matter. I\n> was hoping to get people\'s thoughts on how significant this is\n> (assuming that it\'s right - it hasn\'t been published yet!)\n>\n> When I did undergrad QM (I\'m now PhDing), AFAIK we never actually\n> talked about Complementarity principle. We DID use the Copenhagen\n> collapse hypothesis, but on the whole we just started with the basic\n> postulates (wave function giving probability, Schroedinger equation\n> giving evolution) and derived everything from there. As I understand\n> (and I\'d appreciate any corrections here!) there isn\'t really a\n> wave/particle conflict - everything is a particle, but it has\n> associated with it a wave function that determines the probabiltiy of\n> finding a particle at a given position/state. They don\'t "sometimes\n> act as waves, sometimes act as particles" - they simply are particles\n> which have probability distributions. So, in the double slit\n> experiment, whether you have photons or elecrons, the wave function of\n> the particle gets diffracted by the slit (evolved by the approriate\n> Hamiltonian) until finally the screen makes an "observation" and forces\n> the particle to be somewhere. I don\'t really see "conflict" between\n> the two pictures.\n>\n> So, how important is it if the complementarity princple doesn\'t hold?\n> It was an interesting theory perhaps, but it seems to an extent to be a\n> hold over from "earlier" theories of QM, before everything was\n> formalised. Would you agree with this? It\'s not needed to formulate\n> quantum mechanics - does it really change anything if it\'s not true?\n>\n> Furthermore, do these results really say anything about the Collapse\n> hypothesis, which really seems to be what\'s identified with the\n> Copenhagen interpretation these days?\n>\n> All discussions and thoughts would be welcome :)\n>\n> Cheers,\n> Joel\n>\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>I apologise in advance that this does not seriously answer your question,
since my posting is a quick note on New Scientist - the Comic!

> read New Scientist, shake quantum mechanics to the core, etc, etc)

I think your 'etc. etc.' is well warranted. Every week they write this
nonsense. Some publication analogues...

Nature (The Times)
The Journal of Mathematical Physics (The Universe)
New Scientist (The Sport - bare chests, chatlines, escort agencies, that
sort of thing)

I put it semi jokingly, NS does spread some news, but so does 'The Sport'

'Afshar recent experiment' - wait for the publication of the recent
experiment.

I won't trivialise your time any further

Enjoy your PhD

Richard Miller

"Joel Gilmore" <gilmore@phy*****.uq.edu.au> wrote in message
news:2004080316131816807%gilmore@phyuqeduau...
> Hi all,
>
> I've been thinking about Afshar's recent experiment (see
> http://www.kathryncramer.com/wblog/archives/000688.html and others)
> which purports to destroy the Copenhagen interpretation (and if you
> read New Scientist, shake quantum mechanics to the core, etc, etc) It
> is a modification of the double slit experiment - see Oz's recent post
> (25/7/04 - "Afshars experiment) for a brief summary. The result is we
> can detect both the particle like behaviour (detectors determine which
> slit the particle went through) and the wave like behaviour (we place
> barriers (wires) at where interference nodes would be and see no change
> in the results). Supposedly, this then contradicts the Complementarity
> principle (and the Copenhagen interpretation?), which says no
> experiment can see both the wave and particle like nature of matter. I
> was hoping to get people's thoughts on how significant this is
> (assuming that it's right - it hasn't been published yet!)
>
> When I did undergrad QM (I'm now PhDing), AFAIK we never actually
> talked about Complementarity principle. We DID use the Copenhagen
> collapse hypothesis, but on the whole we just started with the basic
> postulates (wave function giving probability, Schroedinger equation
> giving evolution) and derived everything from there. As I understand
> (and I'd appreciate any corrections here!) there isn't really a
> wave/particle conflict - everything is a particle, but it has
> associated with it a wave function that determines the probabiltiy of
> finding a particle at a given position/state. They don't "sometimes
> act as waves, sometimes act as particles" - they simply are particles
> which have probability distributions. So, in the double slit
> experiment, whether you have photons or elecrons, the wave function of
> the particle gets diffracted by the slit (evolved by the approriate
> Hamiltonian) until finally the screen makes an "observation" and forces
> the particle to be somewhere. I don't really see "conflict" between
> the two pictures.
>
> So, how important is it if the complementarity princple doesn't hold?
> It was an interesting theory perhaps, but it seems to an extent to be a
> hold over from "earlier" theories of QM, before everything was
> formalised. Would you agree with this? It's not needed to formulate
> quantum mechanics - does it really change anything if it's not true?
>
> Furthermore, do these results really say anything about the Collapse
> hypothesis, which really seems to be what's identified with the
> Copenhagen interpretation these days?
>
> All discussions and thoughts would be welcome :)
>
> Cheers,
> Joel
>

pseudospin

Aug6-04, 03:04 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"richard miller" <richard@microscitech.freeserve.co.uk> wrote in message news:<cer4f9\\$pkt\\$1@news5.svr.pol.co.uk>...\n> I apologise in advance that this does not seriously answer your question,\n> since my posting is a quick note on New Scientist - the Comic!\n>\n> > read New Scientist, shake quantum mechanics to the core, etc, etc)\n>\n> I think your \'etc. etc.\' is well warranted. Every week they write this\n> nonsense. Some publication analogues...\n>\n\nHave you read the letters page in New Scientist this week? They\npublished three response letters all of which said the same thing:\nthat the wires on the lens constitute a diffraction grating thereby\nsaving the copenhagen interpretation.\n\nThen there is a brief, and correct, dismissal of this from Afshar.\n\nWhy did they publish three identical replies? Why didn\'t they publish\nmy letter pointing out, in clear terms, exactly why this experiment is\nflawed?(I\'m not bitter, honest) I\'m sure plenty of other people sent\nin correct refutations of Afhsar\'s experiment, why not publish one of\nthose?\n\nDetection of the photon at either detector does not tell you which\npinhole the photon came from, whether the wires are there or not.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>"richard miller" <richard@microscitech.freeserve.co.uk> wrote in message news:<cer4f9$pkt$1@news5.svr.pol.co.uk>...
> I apologise in advance that this does not seriously answer your question,
> since my posting is a quick note on New Scientist - the Comic!
>
> > read New Scientist, shake quantum mechanics to the core, etc, etc)
>
> I think your 'etc. etc.' is well warranted. Every week they write this
> nonsense. Some publication analogues...
>

Have you read the letters page in New Scientist this week? They
published three response letters all of which said the same thing:
that the wires on the lens constitute a diffraction grating thereby
saving the copenhagen interpretation.

Then there is a brief, and correct, dismissal of this from Afshar.

Why did they publish three identical replies? Why didn't they publish
my letter pointing out, in clear terms, exactly why this experiment is
flawed?(I'm not bitter, honest) I'm sure plenty of other people sent
in correct refutations of Afhsar's experiment, why not publish one of
those?

Detection of the photon at either detector does not tell you which
pinhole the photon came from, whether the wires are there or not.

Franz Heymann

Aug6-04, 03:05 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"Joel Gilmore" <gilmore@phy*****.uq.edu.au> wrote in message\nnews:2004080316131816807%gilmore@phyuqedu au...\n> Hi all,\n>\n> I\'ve been thinking about Afshar\'s recent experiment\n\n[snip]\n\nAfahar should consider repeating his experiment using surface waves on\na large pool of mercury. I am happy to lay ten to one that he will\nobtain results compatible with those he obtained in his experiment.\nIn other words, his experiment might tell us a lot about the behaviour\nof a wave subjected to a complicated set of obstacles, and that is\nabout all there is to it. The connection with quantum mechanics\nescapes me.\n\nFranz\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Joel Gilmore" <gilmore@phy*****.uq.edu.au> wrote in message
news:2004080316131816807%gilmore@phyuqeduau...
> Hi all,
>
> I've been thinking about Afshar's recent experiment

[snip]

Afahar should consider repeating his experiment using surface waves on
a large pool of mercury. I am happy to lay ten to one that he will
obtain results compatible with those he obtained in his experiment.
In other words, his experiment might tell us a lot about the behaviour
of a wave subjected to a complicated set of obstacles, and that is
about all there is to it. The connection with quantum mechanics
escapes me.

Franz

Jesse Mazer

Aug7-04, 05:03 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Aaron Bergman wrote:\n\n>Complementarity holds. I think the answer is that you just have to be\n>careful how you define things.\n>\n>Afshar claims that because he has imaged the slits using a lens, he\n>knows which slit each photon passes through. However, let\'s say we added\n>the usual particle detector at one of the slits. If we do this, the\n>interference pattern disappears and Afshar\'s wires detect some current.\n>But, if we already knew which slit the photon was passing through, why\n>would the addition of the detector change anything?\n>\nEven without doing any calculations, there seems to be an important\nconceptual difference between these cases. Suppose we modify Afshar\'s\nexperiment so that the wires are no longer placed exactly at the minima\nof the interference valleys, and we send photons through the slit one at\na time, in each case noting where the photon was registered, either at a\nwire or at one of the detectors. If we have placed a detector at the\nslits, then regardless of whether a given photon hits a wire or one of\nthe detectors, we know which slit that photon went through. But if our\nonly way of gaining which-path information is through the focusing lens\nbehind the wires, then we will only know which slit the photon went\nthrough if it avoids the wires and hits one of the detectors. If we look\nonly at the subset of cases where the photon hit a wire, in these cases\nwe had no information about which slit the photon went through, so\nnaturally we should expect to see an interference pattern when we look\nat the frequency the photon hit each of the wires in this subset of cases.\n\nAfshar seems to be arguing that "complementarity" would lead you to\npredict that the frequency the photon hits each wire should show no\ninterference pattern, that it should be the same as the frequency you\'d\npredict if you placed a detector next to each slit. But this doesn\'t\nmake sense to me, since again, if you send photons through one by one\nand look only at the subset of cases where the photon hit a wire, you\nwill have no information about which slit the photon went through in\nthese cases, and wouldn\'t complementarity say that it\'s which-path\ninformation that destroys interference in the double-slit experiment?\n\nMaybe one could think of the Afshar experiment as a limiting case, where\nyou start off with many wires in a row and keep removing the ones\nclosest to the interference peaks until all that\'s left are the wires\nexactly at the minima of the interference valleys. As you remove wires,\nthe fraction of cases where a photon hit a wire instead of a detector\ngoes down, and if you look only at this subset of cases, you\'ll always\nsee that the frequency that the photon hit one wire vs. another shows an\ninterference pattern, so the photon *never* hits the wires placed\nexactly at the minima. If you think of it this way, it seems pretty\nintuitive that when you remove the last of the wires that wasn\'t at one\nof the minima, the photons will continue to never hit any of the wires\nplaced exactly at the minima.\n\n--\nJesse Mazer\nhttp://www.jessemazer.com\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>Aaron Bergman wrote:

>Complementarity holds. I think the answer is that you just have to be
>careful how you define things.
>
>Afshar claims that because he has imaged the slits using a lens, he
>knows which slit each photon passes through. However, let's say we added
>the usual particle detector at one of the slits. If we do this, the
>interference pattern disappears and Afshar's wires detect some current.
>But, if we already knew which slit the photon was passing through, why
>would the addition of the detector change anything?
>
Even without doing any calculations, there seems to be an important
conceptual difference between these cases. Suppose we modify Afshar's
experiment so that the wires are no longer placed exactly at the minima
of the interference valleys, and we send photons through the slit one at
a time, in each case noting where the photon was registered, either at a
wire or at one of the detectors. If we have placed a detector at the
slits, then regardless of whether a given photon hits a wire or one of
the detectors, we know which slit that photon went through. But if our
only way of gaining which-path information is through the focusing lens
behind the wires, then we will only know which slit the photon went
through if it avoids the wires and hits one of the detectors. If we look
only at the subset of cases where the photon hit a wire, in these cases
we had no information about which slit the photon went through, so
naturally we should expect to see an interference pattern when we look
at the frequency the photon hit each of the wires in this subset of cases.

Afshar seems to be arguing that "complementarity" would lead you to
predict that the frequency the photon hits each wire should show no
interference pattern, that it should be the same as the frequency you'd
predict if you placed a detector next to each slit. But this doesn't
make sense to me, since again, if you send photons through one by one
and look only at the subset of cases where the photon hit a wire, you
will have no information about which slit the photon went through in
these cases, and wouldn't complementarity say that it's which-path
information that destroys interference in the double-slit experiment?

Maybe one could think of the Afshar experiment as a limiting case, where
you start off with many wires in a row and keep removing the ones
closest to the interference peaks until all that's left are the wires
exactly at the minima of the interference valleys. As you remove wires,
the fraction of cases where a photon hit a wire instead of a detector
goes down, and if you look only at this subset of cases, you'll always
see that the frequency that the photon hit one wire vs. another shows an
interference pattern, so the photon *never* hits the wires placed
exactly at the minima. If you think of it this way, it seems pretty
intuitive that when you remove the last of the wires that wasn't at one
of the minima, the photons will continue to never hit any of the wires
placed exactly at the minima.

--
Jesse Mazer
http://www.jessemazer.com

Oz

Aug7-04, 05:04 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>pseudospin <mrh@thsun1.ph.bham.ac.uk> writes\n>\n>Detection of the photon at either detector does not tell you which\n>pinhole the photon came from, whether the wires are there or not.\n\nIndeed, as soon as you pointed this out (somewhat indirectly but the\nthought direction was clear), its clearly so.\n\nWhich is a pity really, if not unexpected.\n\n--\nOz\nThis post is worth absolutely nothing and is probably fallacious.\n\nBTOPENWORLD address about to cease. DEMON address no longer in use.\n>>Use oz@farmeroz.port995.com<<\nozacoohdb@despammed.com still functions.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>pseudospin <mrh@thsun1.ph.bham.ac.uk> writes
>
>Detection of the photon at either detector does not tell you which
>pinhole the photon came from, whether the wires are there or not.

Indeed, as soon as you pointed this out (somewhat indirectly but the
thought direction was clear), its clearly so.

Which is a pity really, if not unexpected.

--
Oz
This post is worth absolutely nothing and is probably fallacious.

BTOPENWORLD address about to cease. DEMON address no longer in use.
>>Use oz@farmeroz.port995.com<<
ozacoohdb@despammed.com still functions.

Jesse Mazer

Aug7-04, 05:05 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Aaron Bergman wrote:\n\n>Complementarity holds. I think the answer is that you just have to be\n>careful how you define things.\n>\n>Afshar claims that because he has imaged the slits using a lens, he\n>knows which slit each photon passes through. However, let\'s say we added\n>the usual particle detector at one of the slits. If we do this, the\n>interference pattern disappears and Afshar\'s wires detect some current.\n>But, if we already knew which slit the photon was passing through, why\n>would the addition of the detector change anything?\n>\nEven without doing any calculations, there seems to be an important\nconceptual difference between these cases. Suppose we modify Afshar\'s\nexperiment so that the wires are no longer placed exactly at the minima\nof the interference valleys, and we send photons through the slit one at\na time, in each case noting where the photon was registered, either at a\nwire or at one of the detectors. If we have placed a detector at the\nslits, then regardless of whether a given photon hits a wire or one of\nthe detectors, we know which slit that photon went through. But if our\nonly way of gaining which-path information is through the focusing lens\nbehind the wires, then we will only know which slit the photon went\nthrough if it avoids the wires and hits one of the detectors. If we look\nonly at the subset of cases where the photon hit a wire, in these cases\nwe had no information about which slit the photon went through, so\nnaturally we should expect to see an interference pattern when we look\nat the frequency the photon hit each of the wires in this subset of cases.\n\nAfshar seems to be arguing that "complementarity" would lead you to\npredict that the frequency the photon hits each wire should show no\ninterference pattern, that it should be the same as the frequency you\'d\npredict if you placed a detector next to each slit. But this doesn\'t\nmake sense to me, since again, if you send photons through one by one\nand look only at the subset of cases where the photon hit a wire, you\nwill have no information about which slit the photon went through in\nthese cases, and wouldn\'t complementarity say that it\'s which-path\ninformation that destroys interference in the double-slit experiment?\n\nMaybe one could think of the Afshar experiment as a limiting case, where\nyou start off with many wires in a row and keep removing the ones\nclosest to the interference peaks until all that\'s left are the wires\nexactly at the minima of the interference valleys. As you remove wires,\nthe fraction of cases where a photon hit a wire instead of a detector\ngoes down, and if you look only at this subset of cases, you\'ll always\nsee that the frequency that the photon hit one wire vs. another shows an\ninterference pattern, so the photon *never* hits the wires placed\nexactly at the minima. If you think of it this way, it seems pretty\nintuitive that when you remove the last of the wires that wasn\'t at one\nof the minima, the photons will continue to never hit any of the wires\nplaced exactly at the minima.\n\n--\nJesse Mazer\nhttp://www.jessemazer.com\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>Aaron Bergman wrote:

>Complementarity holds. I think the answer is that you just have to be
>careful how you define things.
>
>Afshar claims that because he has imaged the slits using a lens, he
>knows which slit each photon passes through. However, let's say we added
>the usual particle detector at one of the slits. If we do this, the
>interference pattern disappears and Afshar's wires detect some current.
>But, if we already knew which slit the photon was passing through, why
>would the addition of the detector change anything?
>
Even without doing any calculations, there seems to be an important
conceptual difference between these cases. Suppose we modify Afshar's
experiment so that the wires are no longer placed exactly at the minima
of the interference valleys, and we send photons through the slit one at
a time, in each case noting where the photon was registered, either at a
wire or at one of the detectors. If we have placed a detector at the
slits, then regardless of whether a given photon hits a wire or one of
the detectors, we know which slit that photon went through. But if our
only way of gaining which-path information is through the focusing lens
behind the wires, then we will only know which slit the photon went
through if it avoids the wires and hits one of the detectors. If we look
only at the subset of cases where the photon hit a wire, in these cases
we had no information about which slit the photon went through, so
naturally we should expect to see an interference pattern when we look
at the frequency the photon hit each of the wires in this subset of cases.

Afshar seems to be arguing that "complementarity" would lead you to
predict that the frequency the photon hits each wire should show no
interference pattern, that it should be the same as the frequency you'd
predict if you placed a detector next to each slit. But this doesn't
make sense to me, since again, if you send photons through one by one
and look only at the subset of cases where the photon hit a wire, you
will have no information about which slit the photon went through in
these cases, and wouldn't complementarity say that it's which-path
information that destroys interference in the double-slit experiment?

Maybe one could think of the Afshar experiment as a limiting case, where
you start off with many wires in a row and keep removing the ones
closest to the interference peaks until all that's left are the wires
exactly at the minima of the interference valleys. As you remove wires,
the fraction of cases where a photon hit a wire instead of a detector
goes down, and if you look only at this subset of cases, you'll always
see that the frequency that the photon hit one wire vs. another shows an
interference pattern, so the photon *never* hits the wires placed
exactly at the minima. If you think of it this way, it seems pretty
intuitive that when you remove the last of the wires that wasn't at one
of the minima, the photons will continue to never hit any of the wires
placed exactly at the minima.

--
Jesse Mazer
http://www.jessemazer.com

Jesse Mazer

Aug7-04, 05:06 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>pseudospin wrote:\n\n>Why did they publish three identical replies? Why didn\'t they publish\n>my letter pointing out, in clear terms, exactly why this experiment is\n>flawed?(I\'m not bitter, honest) I\'m sure plenty of other people sent\n>in correct refutations of Afhsar\'s experiment, why not publish one of\n>those?\n>\n>Detection of the photon at either detector does not tell you which\n>pinhole the photon came from, whether the wires are there or not.\n>\nYou\'re saying that even without the wires, the "focusing lens" depicted\nin the diagram at\nhttp://wiz.cath.vt.edu/exper/kcramer/blogpix/Ashargraphic.jpg is not\nactually enough to insure that photons going through the left slit\nalways end up at the right detector, and photons going through the right\nslit end up at the left detector? Can you post the explanation here?\n\n--\nJesse Mazer\nhttp://www.jessemazer.com\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>pseudospin wrote:

>Why did they publish three identical replies? Why didn't they publish
>my letter pointing out, in clear terms, exactly why this experiment is
>flawed?(I'm not bitter, honest) I'm sure plenty of other people sent
>in correct refutations of Afhsar's experiment, why not publish one of
>those?
>
>Detection of the photon at either detector does not tell you which
>pinhole the photon came from, whether the wires are there or not.
>
You're saying that even without the wires, the "focusing lens" depicted
in the diagram at
http://wiz.cath.vt.edu/exper/kcramer/blogpix/Ashargraphic.jpg is not
actually enough to insure that photons going through the left slit
always end up at the right detector, and photons going through the right
slit end up at the left detector? Can you post the explanation here?

--
Jesse Mazer
http://www.jessemazer.com

Mad Arab

Aug12-04, 08:29 AM

I think the flaw in this setup is that the lens introduces an additional "measuring event" and the output to the detectors is not telling you what slit the photon went through, but instead what side of the lens the photon hit. I'm still wresting with the formalism for it at this time.

dankomed

Apr28-05, 05:04 PM

Hello I just want to paste a link to my recent paper at Phil Sci
http://philsci-archive.pitt.edu/archive/00002281/

called
"Complementarity is not violated – Shahriar Afshar and John Cramer suggest wrong interpretation of Afshar's experimental setup"

I will be glad to receive any comments and suggestions for improvement of the paper. Today I have seen that in different web forums a lot of people have reached identical conclusions as I did, and i have curiously read that New Scientist published only those objections which were flawed, so that Afshar succesfully replied them. Also my impresion is that Afshar is focusing reader's attention on the problem "is there inerference", while the REAL PROBLEM is "is there which way info". This seems to me like fraud, or "conscious manipulation of reader's attention".

Best,

Danko Georgiev

dankomed

May10-05, 06:33 AM

Here you can find revised paper dealing with complementarity and Afshar's experiment

http://www.geocities.com/dankomed/afshar.pdf

Danko

dankomed

May10-05, 06:34 AM

Here you can find revised paper dealing with complementarity and Afshar's experiment

http://www.geocities.com/dankomed/afshar.pdf

Danko