Entanglement

[immortal]

 

This is nonsense. There was a long thread in speculation forum where it was shown that your 'opinions' are unfounded and based in a misunderstanding of (i) the scientific method and (ii) quantum theory. That thread eventually died because you were unable to answer the critics. You would not hijack this thread with the same nonsense.

 

Which part of it that you do not understand that there is no sense in assuming what we do not measure about a system has an independent reality?Shall we see whether it is unfounded or not?

 

Physicists close two loopholes while violating local realism

http://www.pnas.org/content/early/2010/10/29/1002780107

 

The implications of these experiments which you dodge by making an appeal to authority.

[juanrga]

Which part of it that you do not understand that there is no sense in assuming what we do not measure about a system has an independent reality?Shall we see whether it is unfounded or not?

 

Physicists close two loopholes while violating local realism

http://www.pnas.org/content/early/2010/10/29/1002780107

 

The implications of these experiments which you dodge by making an appeal to authority.

 

I repeat: "You would not hijack this thread with the same nonsense."

 

If you have some 'new argument' about your opinions on reality use the speculations forum specifically devoted to your opinions.

 

This quantum theory thread is about entanglement. This is not the place for reading/discussing your nonsense about photons, quarks, electrons...

Edited December 25, 2012 by juanrga

[immortal]

 

I repeat: "You would not hijack this thread with the same nonsense."

 

If you have some 'new argument' about your opinions on reality use the speculations forum specifically devoted to your opinions.

 

This quantum theory thread is about entanglement. This is not the place for reading/discussing your nonsense about photons, quarks, electrons...

 

Even I am discussing about entanglement, are you still in the illusion that an accepted consensus exists?

[juanrga]

Even I am discussing about entanglement

 

If you go back and read my post #25 you would check that I did not comment/object on the two first phrases of your post, because both were on-topic.

[imatfaal]

!

Moderator Note

immortal - I think it would be best not to raise those questions within this thread. there is ample scope and place for discussion in other existing threads in philosophy or in a new thread. please do not take threads off at such a tangent. please do not continue to derail the thread by replying to this mod note in the thread. your may report or PM the staff if you disagree.

[MigL]

Been away a while, sorry for the late reply J.C. I also apologise for the length of the post, but its a slow day at work.

.

The following is a condensed version ( by me ) of a document by David Harrison of the Physics Dept. @ University of Toronto and is one of the clearest explanations of Bell's Theorem that I've read. It is copyrighted and so I could not post it ( don't recall where I got it from to provide a link ). If you can find it, it is certainly worth the read, and is much more detailed ( and humorous ) than this simplification. It is also the source of the coin slice in an envelope example.

In1935 the EPR paradox was published in which the three authors questioned the completeness of the QM description of reality. The mantle was subsequently taken up by David Bohm who used Einstein as a critic while writing his book on QM, and was greatly influenced by his opinion that QM was incomplete. Bohm would spend many years looking for 'hidden variables' to complete it.

Consider Bell's inequality, or more precisely, d'Espagnat's proof or re-interpretation of the inequalty. We can state the inequality quite simply as

Number(A, not B) + Number(B, not C) greater than or equal to Number(A, not C)

for any collection of objects with differing parameters A, B and C.

This can be easily proven using simple logic. In this proof we make some assumptions...

-Logic is a valid way to reason.

-Parameters exist whether they are measured or not.

 

If we now perform a Stern-Gerlach experiment ( electron spin determination by polarizers, look it up ) to determine spin orientation of electrons we find that, because of the Heisenberg Uncertainty Principle and the speed of light constraint on information transfer, Bell's inequality is violated for QM systems. The same experiment can be performed with polarization of light, ie. spin of photon pairs. Since the 70s numerous experiments have confirmed the violation of the inequality and the predicted quantum correlations are confirmed even with polarizers at 10 or more KM distant. We have also now made a third assumption to 'get around' the HUP, that no information can travel faster than the speed of light.

We can restate the assumptions as

1-Logic is valid.

2-There is a reality separate from observation ie. hidden variables exist.

3-Locality ( local hidden variables or local reality ).

 

Since Bell's inequality is violated we can conclude that one or even all, our assumptions are invalid, so lets examine them in more detail.

We know that Godel proved in the 30s that logic is incomplete ( using logic !! ), and that self-referencing systems cannot be handled, such as the example " This statement is false.". Our deductive logic is either true or false and maybe whats needed is multi-valued logic ( see Zukav's 'The Dancing Wu-Li Masters' ) or inductive logic.

The invalidation of the second assumption, and the one I favour, indicates there are no hidden variables and reality is what we observe ( no matter how strange ). It is only in the correlation of the electron spins that we see something strange. d'Espagnat uses the word influence to describe what may be traveling at superluminal speeds. That correlated wave functions, being non physical can indeed collapse instantaneously across great distances, but any causal interaction ( where information is actually exchanged ) is constrained by locality. This also tells us that the observer is involved, or part of, the observation. But more on this personal opinion later.

David Bohm looked at the hidden variable problem and explored the consequences of non-local hidden variables more deeply than anyone. Eventually he came up with the idea of Quantum Potential as the cause for the non-local effects predicted by theory. The quantum potential, in effect, guides the electron along its path. So that even as the particulate electron goes through one slit or the other ( in the double slit experiment ), the quantum potential, being non-local, can instantaneously change depending on the position of the other slit and so change the guidance of the electron's path ( similar to deBroglie's pilot wave postulated in the 30s ). Even though the electron's motion is deterministic, the quantum potential makes it a chaotic system and seemingly random and unknowable. In Bohm's ideas then, an electron is guided by, and a photon is a wave that manifests particle behaviour on interaction with, the quantum potential, which is identified as the non-local hidden variable that keeps reality separate from observation.

Needless to say there are some serious problems with this model, and though some are still working on refinements ( cellular automation, pseudo random and higher-dimensional thread models ), no experimental evidence or predictions have been put foreward.

 

As a personal opinion, I have no problem being a participatory observer. Any and all observations we make involve some varying degree of interaction and some sort of influence must pass from object to observer. Even the observation of an object as far removed from the quantum world as Jupiter, involves seeing reflected light from its surface which implies a momentum transfer. We never actually observe an object so much as interact with it.

This correlation or 'influence' is also evident in other aspects of QM, not just entanglement. Consider the double slit experiment, which gives the classic interference pattern ( after a statistically significant number of repititions ) even if only one electron is going through at a time. How does the electron 'know' that there is another slit, or if it is open or closed ? This can also be performed with a single electron, through a double slit, onto a photo plate, giving one spot; if the experiment is repeated a statistically significant number of times, at different locations much removed from each other, when all the plates are brought together and supeimposed, the familiar interference pattern again appears. How did all these separate electrons know of each other's intentions ? What 'influence' is dictating the outcome of disparate experiments ?

My belief is that the electron has multiple possible paths ( through any and all slits ) and the paths which are not followed still influence the behaviour of the most probable, actual path. In effect the diffraction pattern is not diffraction of an electron wave ( whatever that may be ), but a diffraction of a probability wave.

Edited December 29, 2012 by MigL

[J.C.MacSwell]

Hi MigL

 

This might be the link?:

 

 

http://www.upscale.utoronto.ca/PVB/Harrison/BellsTheorem/BellsTheorem.html

 

Quoting from it (bolded by me):

 

"Imagine we take a coin and carefully saw it in half so that one piece is a "heads" and the other is a "tails." We put each half in a separate envelope and carry them to different rooms. If we open one of the envelopes and see a heads, we know that the other envelope contains a tails. This correlation "experiment" corresponds to spin measurements when both polarisers have the same orientation. It is when we have the polarisers at different orientations that we see something weird."

 

This is why I stated earlier that the analogy seemed reasonable but in fact it can be shown, by doing the experiment in a certain way, that it does not hold up.

[juanrga]

Been away a while, sorry for the late reply J.C. I also apologise for the length of the post, but its a slow day at work.

.

The following is a condensed version ( by me ) of a document by David Harrison of the Physics Dept. @ University of Toronto and is one of the clearest explanations of Bell's Theorem that I've read. It is copyrighted and so I could not post it ( don't recall where I got it from to provide a link ). If you can find it, it is certainly worth the read, and is much more detailed ( and humorous ) than this simplification. It is also the source of the coin slice in an envelope example.

 

In1935 the EPR paradox was published in which the three authors questioned the completeness of the QM description of reality. The mantle was subsequently taken up by David Bohm who used Einstein as a critic while writing his book on QM, and was greatly influenced by his opinion that QM was incomplete. Bohm would spend many years looking for 'hidden variables' to complete it.

Consider Bell's inequality, or more precisely, d'Espagnat's proof or re-interpretation of the inequalty. We can state the inequality quite simply as

Number(A, not B) + Number(B, not C) greater than or equal to Number(A, not C)

for any collection of objects with differing parameters A, B and C.

This can be easily proven using simple logic. In this proof we make some assumptions...

-Logic is a valid way to reason.

-Parameters exist whether they are measured or not.

 

If we now perform a Stern-Gerlach experiment ( electron spin determination by polarizers, look it up ) to determine spin orientation of electrons we find that, because of the Heisenberg Uncertainty Principle and the speed of light constraint on information transfer, Bell's inequality is violated for QM systems. The same experiment can be performed with polarization of light, ie. spin of photon pairs. Since the 70s numerous experiments have confirmed the violation of the inequality and the predicted quantum correlations are confirmed even with polarizers at 10 or more KM distant. We have also now made a third assumption to 'get around' the HUP, that no information can travel faster than the speed of light.

We can restate the assumptions as

1-Logic is valid.

2-There is a reality separate from observation ie. hidden variables exist.

3-Locality ( local hidden variables or local reality ).

 

Since Bell's inequality is violated we can conclude that one or even all, our assumptions are invalid, so lets examine them in more detail.

We know that Godel proved in the 30s that logic is incomplete ( using logic !! ), and that self-referencing systems cannot be handled, such as the example " This statement is false.". Our deductive logic is either true or false and maybe whats needed is multi-valued logic ( see Zukav's 'The Dancing Wu-Li Masters' ) or inductive logic.

The invalidation of the second assumption, and the one I favour, indicates there are no hidden variables and reality is what we observe ( no matter how strange ). It is only in the correlation of the electron spins that we see something strange. d'Espagnat uses the word influence to describe what may be traveling at superluminal speeds. That correlated wave functions, being non physical can indeed collapse instantaneously across great distances, but any causal interaction ( where information is actually exchanged ) is constrained by locality. This also tells us that the observer is involved, or part of, the observation. But more on this personal opinion later.

David Bohm looked at the hidden variable problem and explored the consequences of non-local hidden variables more deeply than anyone. Eventually he came up with the idea of Quantum Potential as the cause for the non-local effects predicted by theory. The quantum potential, in effect, guides the electron along its path. So that even as the particulate electron goes through one slit or the other ( in the double slit experiment ), the quantum potential, being non-local, can instantaneously change depending on the position of the other slit and so change the guidance of the electron's path ( similar to deBroglie's pilot wave postulated in the 30s ). Even though the electron's motion is deterministic, the quantum potential makes it a chaotic system and seemingly random and unknowable. In Bohm's ideas then, an electron is guided by, and a photon is a wave that manifests particle behaviour on interaction with, the quantum potential, which is identified as the non-local hidden variable that keeps reality separate from observation.

Needless to say there are some serious problems with this model, and though some are still working on refinements ( cellular automation, pseudo random and higher-dimensional thread models ), no experimental evidence or predictions have been put foreward.

 

As a personal opinion, I have no problem being a participatory observer. Any and all observations we make involve some varying degree of interaction and some sort of influence must pass from object to observer. Even the observation of an object as far removed from the quantum world as Jupiter, involves seeing reflected light from its surface which implies a momentum transfer. We never actually observe an object so much as interact with it.

This correlation or 'influence' is also evident in other aspects of QM, not just entanglement. Consider the double slit experiment, which gives the classic interference pattern ( after a statistically significant number of repititions ) even if only one electron is going through at a time. How does the electron 'know' that there is another slit, or if it is open or closed ? This can also be performed with a single electron, through a double slit, onto a photo plate, giving one spot; if the experiment is repeated a statistically significant number of times, at different locations much removed from each other, when all the plates are brought together and supeimposed, the familiar interference pattern again appears. How did all these separate electrons know of each other's intentions ? What 'influence' is dictating the outcome of disparate experiments ?

My belief is that the electron has multiple possible paths ( through any and all slits ) and the paths which are not followed still influence the behaviour of the most probable, actual path. In effect the diffraction pattern is not diffraction of an electron wave ( whatever that may be ), but a diffraction of a probability wave.

 

There is no difficulty to explain the EPR experiments and Bell results using a logical local theory without hidden variables. See the modern textbook cited above. The old mantra that says that we must abandon reality, logic, or locality is incorrect.

 

Regarding Bohm old ideas, not only there is no real "quantum potential" in nature (precisely I am now writing a paper where I criticize this aspect of Bohm), but that the old concept of "quantum potential" is even deprecated in modern Bohmian mechanics

[MigL]

I did see and understand the part that you bolded J.C., however the example does show in an everyday, common sense way how a correlation works. I, and apparently Juanrga also, believe that a correlation is at work even when the polarizers don't have the same orientation. There isn't an everyday, common sense analogy however, and so, the results seem 'weird'.

 

I'll have to look for a copy of the textbook you mentioned Juan. Thanks.

I'd also be interested in eventually reading your paper, as I was once very interested in deBroglie's pilot wave theory and Bohm's work ( a brilliant man by anyone's definition, whose career seems to have gotten derailed just as he was poised to possibly do great things ) .

[J.C.MacSwell]

I did see and understand the part that you bolded J.C., however the example does show in an everyday, common sense way how a correlation works. I, and apparently Juanrga also, believe that a correlation is at work even when the polarizers don't have the same orientation. There isn't an everyday, common sense analogy however, and so, the results seem 'weird'.

 

I'll have to look for a copy of the textbook you mentioned Juan. Thanks.

I'd also be interested in eventually reading your paper, as I was once very interested in deBroglie's pilot wave theory and Bohm's work ( a brilliant man by anyone's definition, whose career seems to have gotten derailed just as he was poised to possibly do great things ) .

I wasn't arguing against any correlation (not sure what "entanglement" might suggest if there was none at all), just thought your analogy was suggesting a fixed or classical correlation with preset but unknown results which has been experimentally proven not to be the case.

 

I think(?) we all agree that there is no hidden variable without non locality, where Juanrga goes further suggesting that neither is necessarily required. I have not read the text ( http://quantum.phys.cmu.edu/CQT/ ) beyond briefly scanning it over but don't yet see how non locality can be avoided (or supported given SR, so I really don't have a consistent picture of what is going on...I didn't think anyone did)

[juanrga]

I think(?) we all agree that there is no hidden variable without non locality, where Juanrga goes further suggesting that neither is necessarily required. I have not read the text ( http://quantum.phys.cmu.edu/CQT/ ) beyond briefly scanning it over but don't yet see how non locality can be avoided (or supported given SR, so I really don't have a consistent picture of what is going on...I didn't think anyone did)

 

Excellent link!!!! Go to the page 318 of the chapter 27 (page 8 of the PDF file):

 

Quantum mechanics, like classical mechanics, is a local theory in the sense that the world can be understood without supposing that there are mysterious influences which propagate over long distances more rapidly than the speed of light. See the discussion in Chs. 23 to 25 of the EPR paradox, Bell’s inequalities, and Hardy’s paradox. The idea that the quantum world is permeated by superluminal influences has come about because of an inadequate understanding of quantum measurements—in particular, the assumption that wave function collapse is a physical process—or through assuming the existence of hidden variables instead of (or in addition to) the quantum Hilbert space, or by employing counterfactual arguments which do not satisfy the single-framework rule. By contrast, a consistent application of quantum principles provides a positive demonstration of the absence of nonlocal influences, as in the example discussed in Sec. 23.4.

Edited December 31, 2012 by juanrga