Re: Double Slit variant

Blake Winter

<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>After looking around for a while I also found this:\nhttp://www.arxiv.org/abs/quant-ph/0109148 which seems to talk about\nthe same sort of effect. However, I think the variation I mentioned\nis simpler than the one in the paper.\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>After looking around for a while I also found this:
http://www.arxiv.org/abs/http://www....ant-ph/0109148 which seems to talk about
the same sort of effect. However, I think the variation I mentioned
is simpler than the one in the paper.

Caroline Thompson

<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>"Blake Winter" <blake.winter@houghton.edu> wrote in message\nnews:87423d2a.0411121006.3602e941@posting.google.com...\n\n&gt ; Let\'s say we have a source of back-to-back equal energy,\n> opposite momentum photons ... These photons are clearly\n> entangled. Now let\'s put a double slit diffraction\n> experiment on two sides of the source, so that we can do\n> double slit diffraction with each photon from the same event.\n> We see the usual patterns build up, and nothing particularly\n> odd happens.\n>\n> [double slit experiment] *source* [double slit experiment]\n>\n> However, let\'s say that on the experiment on the left we\n> decide to determine which slit the particle passes through.\n> It strikes me that because of the correlation between\n> the photons, if we know which direction the photon going\n> left went, we know that the photon going right had to go\n> the opposite direction, and therefore we know which\n> slit it passed through. Now, we know that on the experiment\n> on the left the interference pattern disappears, but would\n> not the interference pattern disappear on the right even\n> though we have changed nothing there? In other words,\n> we change the probability distribution on the experiment\n> in the left by placing a detector in each slit. From\n> conservation laws, we can then figure out which slit\n> the photon on the right went through. Then the probability\n> distribution on the right should no longer correspond to\n> the usual double slit pattern.\n>\n> This seems reasonable to me (as in, I don\'t see why my\n> conclusion is wrong).\n\nDidn\'t Popper suggest a rather similar experiment?\n\n> However, it does seem to violate locality in a noticeable\n> way, because by measuring the probability distribution\n> on the right, we can tell whether a measurement of which\n> slit is made on the left without comparing our data from\n> the right with the data from the left. This would open the\n> possibility of sending real information faster than light,\n> which seems like a bad thing. So my conclusion would be\n> offhand that this couldn\'t happen, but I can\'t actually\n> figure out quantum mechanically why this wouldn\'t work.\n> Are there any ideas?\n\nI don\'t know what QM has to say on the matter, but it wouldn\'t work for the\ngood reason that light is really just a wave. The existence of photons is\nan illusion created by the detectors. Moreover, there is no conclusive\nevidence that quantum entanglement *ever* happens, since all existing\nexperiments have had "loopholes".\n\nThe struggle to find conclusive evidence, in the form of loophole-free Bell\ntests, has been going on now for over 30 years. For a realist view on this\nsee Emilio Santos\' latest article:\nSantos, E, "Bell´s theorem and Increasing empirical support to local\nrealism?", http://arXiv.org/abs/quant-ph/0410193\n\nI don\'t agree with all that he says but his conclusion is logical:\n" The validity of local realism may be either refuted by a single\nloophole-free experiment or increasingly confirmed by the passage of time\nwithout such an experiment."\n\nFor the latest ideas for loophole-free tests see:\nR. García-Patrón Sánchez, J. Fiurácek , N. J. Cerf , J. Wenger , R.\nTualle-Brouri , and Ph. Grangier, "Proposal for a Loophole-Free Bell Test\nUsing Homodyne Detection", Phys. Rev. Lett. 93, 130409 (2004)\nhttp://arxiv.org/abs/quant-ph/0403191\n\nfor which more detail is available in:\nR. Garcia-Patron, J. Fiurasek, N.J. Cerf, "Loophole-free test of quantum\nnon-locality using high-efficiency homodyne detectors",\nhttp://arxiv.org/abs/quant-ph/0407181\n\nCaroline\nCaroline H Thompson\n\nch.thompson1@virgin.net\nhttp://freespace.virgin.net/ch.thompson1/\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>"Blake Winter" <blake.winter@houghton.edu> wrote in message
news:87423d2a.0411121006.3602e941@posting.google.com...

> Let's say we have a source of back-to-back equal energy,
> opposite momentum photons ... These photons are clearly
> entangled. Now let's put a double slit diffraction
> experiment on two sides of the source, so that we can do
> double slit diffraction with each photon from the same event.
> We see the usual patterns build up, and nothing particularly
> odd happens.
>
> [double slit experiment] *source* [double slit experiment]
>
> However, let's say that on the experiment on the left we
> decide to determine which slit the particle passes through.
> It strikes me that because of the correlation between
> the photons, if we know which direction the photon going
> left went, we know that the photon going right had to go
> the opposite direction, and therefore we know which
> slit it passed through. Now, we know that on the experiment
> on the left the interference pattern disappears, but would
> not the interference pattern disappear on the right even
> though we have changed nothing there? In other words,
> we change the probability distribution on the experiment
> in the left by placing a detector in each slit. From
> conservation laws, we can then figure out which slit
> the photon on the right went through. Then the probability
> distribution on the right should no longer correspond to
> the usual double slit pattern.
>
> This seems reasonable to me (as in, I don't see why my
> conclusion is wrong).

Didn't Popper suggest a rather similar experiment?

> However, it does seem to violate locality in a noticeable
> way, because by measuring the probability distribution
> on the right, we can tell whether a measurement of which
> slit is made on the left without comparing our data from
> the right with the data from the left. This would open the
> possibility of sending real information faster than light,
> which seems like a bad thing. So my conclusion would be
> offhand that this couldn't happen, but I can't actually
> figure out quantum mechanically why this wouldn't work.
> Are there any ideas?

I don't know what QM has to say on the matter, but it wouldn't work for the
good reason that light is really just a wave. The existence of photons is
an illusion created by the detectors. Moreover, there is no conclusive
evidence that quantum entanglement *ever* happens, since all existing
experiments have had "loopholes".

The struggle to find conclusive evidence, in the form of loophole-free Bell
tests, has been going on now for over 30 years. For a realist view on this
see Emilio Santos' latest article:
Santos, E, "Bell´s theorem and Increasing empirical support to local
realism?", http://arXiv.org/abs/http://www.arxi...ant-ph/0410193

I don't agree with all that he says but his conclusion is logical:
" The validity of local realism may be either refuted by a single
loophole-free experiment or increasingly confirmed by the passage of time
without such an experiment."

For the latest ideas for loophole-free tests see:
R. García-Patrón Sánchez, J. Fiurácek , N. J. Cerf , J. Wenger , R.
Tualle-Brouri , and Ph. Grangier, "Proposal for a Loophole-Free Bell Test
Using Homodyne Detection", Phys. Rev. Lett. 93, 130409 (2004)
http://arxiv.org/abs/http://www.arxi...ant-ph/0403191

for which more detail is available in:
R. Garcia-Patron, J. Fiurasek, N.J. Cerf, "Loophole-free test of quantum
non-locality using high-efficiency homodyne detectors",
http://arxiv.org/abs/http://www.arxi...ant-ph/0407181

Caroline
Caroline H Thompson

ch.thompson1@virgin.net
http://freespace.virgin.net/ch.thompson1/

scerir

<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>\nBlake Winter\n> I think the variation I mentioned\n> is simpler than the one in the paper.\n\n\nTwoSlit1 <----S----------------> TwoSlit2\n\nS is a perfect, clean, ideal source\nof entangled photons, one going to\nTwoSlit1, the other to TwoSlit2.\nThe path between S and the TwoSlit1\ninterferometer is shorter than the path\nbetween S and the TwoSlit2 interferometer.\nNow the photon going left, to TwoSlit1,\nis recorded (by a screen or whatever)\nbefore the photon going right enters the\nTwoSlit2. Do you really think that the spot\nrecorded by the screen at TwoSlit1\nis changed by whatever you might choose\nto do at TwoSlit2? If nothing changes,\nhow can the observer at TwoSlit-1 get\nsome information?\ns.\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>Blake Winter
> I think the variation I mentioned
> is simpler than the one in the paper.

TwoSlit1 <----S----------------> TwoSlit2

S is a perfect, clean, ideal source
of entangled photons, one going to
TwoSlit1, the other to TwoSlit2.
The path between S and the TwoSlit1
interferometer is shorter than the path
between S and the TwoSlit2 interferometer.
Now the photon going left, to TwoSlit1,
is recorded (by a screen or whatever)
before the photon going right enters the
TwoSlit2. Do you really think that the spot
recorded by the screen at TwoSlit1
is changed by whatever you might choose
to do at TwoSlit2? If nothing changes,
how can the observer at TwoSlit-1 get
some information?
s.

Blake Winter

<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>\n\n> TwoSlit2. Do you really think that the spot\n> recorded by the screen at TwoSlit1\n> is changed by whatever you might choose\n> to do at TwoSlit2? If nothing changes,\n> how can the observer at TwoSlit-1 get\n> some information?\n> s.\n\nI don\'t, especially being a rather firm believer in the no-signaling\ntheorem. I merely got confused as to how the math works out, ie why\nexactly this effect doesn\'t occur. Although I think that I understand\nthings a little bit better now by thinking about them in the path\nintegral approach.\nActually having read the FTL by down converting posts more carefully\nand hearing stuff like this referred to as being like the "barn door"\nparadox (or as my physics professor had us work it out, the\n"Enterprise in spacedock" paradox), I\'m especially itching to\ncalculate it fully. But alas, I have not yet suceeded.\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>TwoSlit2. Do you really think that the spot
> recorded by the screen at TwoSlit1
> is changed by whatever you might choose
> to do at TwoSlit2? If nothing changes,
> how can the observer at TwoSlit-1 get
> some information?
> s.

I don't, especially being a rather firm believer in the no-signaling
theorem. I merely got confused as to how the math works out, ie why
exactly this effect doesn't occur. Although I think that I understand
things a little bit better now by thinking about them in the path
integral approach.
Actually having read the FTL by down converting posts more carefully
and hearing stuff like this referred to as being like the "barn door"
paradox (or as my physics professor had us work it out, the
"Enterprise in spacedock" paradox), I'm especially itching to
calculate it fully. But alas, I have not yet suceeded.

scerir

<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>Blake Winter:\n> Actually having read the FTL by down converting\n> posts more carefully and hearing stuff like this\n> referred to as being like the "barn door" paradox\n> (or as my physics professor had us work it out, the\n> "Enterprise in spacedock" paradox), I\'m especially\n> itching to calculate it fully. But alas, I have not\n> yet suceeded.\n\nThere is a good paper by Zeilinger\nhttp://www.physik.fu-berlin.de/~simons/Publikationen/RevModPhys99.pdf\ndiscussing an experiment performed in Austria.\nNote also that Zeilinger points out the book\nby Klyshko showing the possible physical\ninterpretation of the correlations between\nmomenta of the entangled particles (\'ghost\'\neffects).\nRegards,\ns.\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>Blake Winter:
> Actually having read the FTL by down converting
> posts more carefully and hearing stuff like this
> referred to as being like the "barn door" paradox
> (or as my physics professor had us work it out, the
> "Enterprise in spacedock" paradox), I'm especially
> itching to calculate it fully. But alas, I have not
> yet suceeded.

There is a good paper by Zeilinger
http://www.physik.fu-berlin.de/~simo...vModPhys99.pdf
discussing an experiment performed in Austria.
Note also that Zeilinger points out the book
by Klyshko showing the possible physical
interpretation of the correlations between
momenta of the entangled particles ('ghost'
effects).
Regards,
s.

Thomas Trotter

<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>blake.winter@houghton.edu (Blake Winter) wrote in message news:<87423d2a.0411121006.3602e941@posting.google.com>...\n[snip]\n> In other words, we change the probability\n> distribution on the experiment in the left by placing a detector in\n> each slit. From conservation laws, we can then figure out which slit\n> the photon on the right went through. Then the probability\n> distribution on the right should no longer correspond to the usual\n> double slit pattern.\n>\n> This seems reasonable to me (as in, I don\'t see why my conclusion is\n> wrong). However, it does seem to violate locality in a noticeable\n> way, because by measuring the probability distribution on the right,\n> we can tell whether a measurement of which slit is made on the left\n> without comparing our data from the right with the data from the left.\n> This would open the possibility of sending real information faster\n> than light, which seems like a bad thing. So my conclusion would be\n> offhand that this couldn\'t happen, but I can\'t actually figure out\n> quantum mechanically why this wouldn\'t work. Are there any ideas?\n\nSend the light to the left through 1 slit. Send the light to\nthe right through 2 slits. You\'ll get no interference on the left\nand interference on the right. Then do it the other way around.\nSame result, reversed. A single slit produces a single wave and,\nthus, no interference. A double slit produces two waves which\ninterfere with each other. No useful information is passed between\nthe left and right sides, because no signal or disturbance of any\nsort is passed between the left and right sides. That\'s really all\nthere is to it.\n\nNow, there are all sorts of ways to complicate things so that it\n*seems* like one side is affecting the other, but it\'s just a\nresult of the way the data is processed.\n\nQuantum entanglement really has nothing whatever to do with\ncausal influences between the entangled entities themselves.\nTheir relationship is purely correlational -- the analysis\nof common properties (from a common source) via a common\nobservational context.\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>blake.winter@houghton.edu (Blake Winter) wrote in message news:<87423d2a.0411121006.3602e941@p...google.com>...
[snip]
> In other words, we change the probability
> distribution on the experiment in the left by placing a detector in
> each slit. From conservation laws, we can then figure out which slit
> the photon on the right went through. Then the probability
> distribution on the right should no longer correspond to the usual
> double slit pattern.
>
> This seems reasonable to me (as in, I don't see why my conclusion is
> wrong). However, it does seem to violate locality in a noticeable
> way, because by measuring the probability distribution on the right,
> we can tell whether a measurement of which slit is made on the left
> without comparing our data from the right with the data from the left.
> This would open the possibility of sending real information faster
> than light, which seems like a bad thing. So my conclusion would be
> offhand that this couldn't happen, but I can't actually figure out
> quantum mechanically why this wouldn't work. Are there any ideas?

Send the light to the left through 1 slit. Send the light to
the right through 2 slits. You'll get no interference on the left
and interference on the right. Then do it the other way around.
Same result, reversed. A single slit produces a single wave and,
thus, no interference. A double slit produces two waves which
interfere with each other. No useful information is passed between
the left and right sides, because no signal or disturbance of any
sort is passed between the left and right sides. That's really all
there is to it.

Now, there are all sorts of ways to complicate things so that it
*seems* like one side is affecting the other, but it's just a
result of the way the data is processed.

Quantum entanglement really has nothing whatever to do with
causal influences between the entangled entities themselves.
Their relationship is purely correlational -- the analysis
of common properties (from a common source) via a common
observational context.

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