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Delayed Choice Quantum Eraser Experiment

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I recently came across this experiment while researching about Quantum Phenomenon. There are a large number of articles and videos claiming that the results imply something like retrocausality or a backward in time influence. At the same time there are also a lot of articles and papers claiming that there is nothing mysterious about this experiment and it's simple correlation.

I was just curious whether the implications of this experiment are actually a debatable topic which could allow either of the above interpretations to be true or has it been conclusively proven that one theory is correct while the other is wrong ?

Thank You

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These are just different interpretations (descriptions) of the same theory. You can think of this experiment in terms of retrocausaility or instantaneous (non-local) collapse of the wave function or many other ways. But the underlying theory, and the mathematics, is the same in all cases. So there is no way of distinguishing between interpretations, because the theory makes the same prediction, whatever interpretation you choose.

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Some interpretations/explanations sound weird because they are couched in classical physics language, which doesn't translate into quantum physics. Particularly with entanglement, where the explanation is put in terms of an interaction, which is not something that is part of the QM.

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These experiments certainly do not prove any retrocausality or backward in time influence or similar esoterics.  This is a simple proven result, given that there exists a causal interpretation of quantum theory which does not have any retrocausality, namely de Broglie-Bohm (dBB) theory.  And those experiments can be described in dBB theory as well. 

That there may be other interpretations which use retrocausality is irrelevant - you know that from everyday life, there are also sometimes situation where some retrocausality seems quite plausible (at least as a nice joke).  Nobody takes such explanations seriously in everyday life.  But in quantum theory they are, for whatever reasons, somehow taken seriously by some physicists.  In reality, they deserve the same laughing as similar every day life explanations. 

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4 hours ago, Schmelzer said:

These experiments certainly do not prove any retrocausality or backward in time influence or similar esoterics.  This is a simple proven result, given that there exists a causal interpretation of quantum theory which does not have any retrocausality, namely de Broglie-Bohm (dBB) theory.  And those experiments can be described in dBB theory as well. 

That there may be other interpretations which use retrocausality is irrelevant - you know that from everyday life, there are also sometimes situation where some retrocausality seems quite plausible (at least as a nice joke).  Nobody takes such explanations seriously in everyday life.  But in quantum theory they are, for whatever reasons, somehow taken seriously by some physicists.  In reality, they deserve the same laughing as similar every day life explanations. 

Just because you don't like a particular interpretation does not mean it should not be taken seriously. No doubt there are some people who think deBroglie-Bohm they is equally laughable.

 

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Moderator Note

Just an FYI, the OP of this thread has been identified as a spam bot. Feel free to continue discussion, but don’t expect them to contribute.

 

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On 11/19/2019 at 3:10 PM, Strange said:

Just because you don't like a particular interpretation does not mean it should not be taken seriously. No doubt there are some people who think deBroglie-Bohm they is equally laughable.

 

If you want to take retrocausality seriously, your choice.  

Extraordinary claims need extraordinary evidence.  Causal influences into the past is certainly extraordinary.  And there is zero evidence for this, given that already good old dBB theory explains all this nicely without any retrocausality.  

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3 hours ago, Schmelzer said:

And there is zero evidence for this, given that already good old dBB theory explains all this nicely without any retrocausality.  

There is, of course, exactly the same amount of evidence for all interpretations of quantum theory. Because they are all interpretations of the same theory. There can’t, by definition, be evidence that favours one over another, either. 

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I'm arguing not about about a particular theory, but about causality.  Once all leading theories have interpretations compatible with classical causality, there is no evidence in favor of its rejection.  Accepting retrocausality would require the rejection of classical causality.  There should be quite serious justifications for this, but there are none. 

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12 minutes ago, Schmelzer said:

I'm arguing not about about a particular theory, but about causality.  Once all leading theories have interpretations compatible with classical causality, there is no evidence in favor of its rejection.  Accepting retrocausality would require the rejection of classical causality.  There should be quite serious justifications for this, but there are none. 

That is irrelevant. There is only one theory under discussion: quantum mechanics. There are multiple interpretations (descriptions that appeal to human intuition). You prefer one, other people prefer another. There is no other reason to choose between them. 

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I disagree. The different interpretations are not at all on equal foot.

Choices between interpretations are essential for an important part of fundamental science, namely the development of more fundamental theories. Interpretations are simply starting points for research programs. The principles which are preserved in a given interpretation are also those to be preserved in those more fundamental theories.  If you start with an interpretation which rejects causality, your research program gives up causality.  Your choice.  

If you think that research programs for more fundamental theories are not relevant, then the next important point is which interpretation is easier to understand, and gives the best intuitions for those who learn it.  Here, different interpretations are also in no way on equal foot.  Those in better agreement with common sense are clearly easier to understand and, given that one can use the intuitions related with the principles which have not been given up, gives better intuitions too.  If you want to prevent pupils from using their intuitions related with classical causality, and think this will help them, your choice.  

The choice of a research program is a personal guess of the researchers, which have to pay for a wrong choice with a personal complete failure of their whole scientific research.  But this harms only the researcher himself. So, given this penalty, here it is reasonable to leave complete freedom.  

This is not the case if we consider the pedagogical differences.  Here the wrong choice by the teacher confuses the students, thus, harms other people.  

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Just now, Schmelzer said:

I disagree. The different interpretations are not at all on equal foot.

Then you would need to show an experiment that can distinguish between them. 

 

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Just now, Strange said:

Then you would need to show an experiment that can distinguish between them. 

No. I have given arguments which you obviously decide to ignore.  

The questions of choice between research programs is, IYO, not part of science?  And the question how to teach students too?  

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1 minute ago, Schmelzer said:

No. I have given arguments which you obviously decide to ignore.  

The questions of choice between research programs is, IYO, not part of science?  And the question how to teach students too?  

They are only "part of science" in the sense that libraries and lecture theatres are. They are not part of scientific theory. 

If you want to argue that a particular interpretation is right or wrong, then you need to show that it predicts different results that can be distinguished experimentally. But if that were possible, they would not be interpretations, they would be new theories. 

6 minutes ago, Schmelzer said:

Choices between interpretations are essential for an important part of fundamental science, namely the development of more fundamental theories. Interpretations are simply starting points for research programs. The principles which are preserved in a given interpretation are also those to be preserved in those more fundamental theories.  If you start with an interpretation which rejects causality, your research program gives up causality.  Your choice.  

One can't rule out a line of investigation because you don't like it. 

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On 11/19/2019 at 9:06 PM, hypervalent_iodine said:
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Moderator Note

Just an FYI, the OP of this thread has been identified as a spam bot. Feel free to continue discussion, but don’t expect them to contribute.

 

Sorry for going off topic, but I'm confused, what type of spam is this? what's the purpose?. This is very high brow spam, I normally get sent click bait and funeral plans, crap like that.

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15 minutes ago, Curious layman said:

Sorry for going off topic, but I'm confused, what type of spam is this? what's the purpose?. This is very high brow spam, I normally get sent click bait and funeral plans, crap like that.

They posted spam links another, now hidden, post.

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18 hours ago, Strange said:

They are only "part of science" in the sense that libraries and lecture theatres are. They are not part of scientific theory. 

If you want to argue that a particular interpretation is right or wrong, then you need to show that it predicts different results that can be distinguished experimentally. But if that were possible, they would not be interpretations, they would be new theories. 

One can't rule out a line of investigation because you don't like it. 

So I do not argue that particular interpretations are right vs. wrong, but about reasonable vs. unreasonable.  

This holds for interpretations understood as research programs (where the mainstream-supported interpretations have not given anything more fundamental beyond QM and GR despite the open problem of finding a consistent theory of QG, thus, have completely failed.) as well as their pedagogical value (where you can see the failure to understand essential parts of QM as well as GR in forum discussions like here).  

I do not propose to rule out lines of investigation.  I argue in favor of adding some competition in form of other lines of investigation, namely the line of investigation to find interpretations as close to classical common sense as possible and then to try to find a theory of QG starting with those interpretations as the research program.  

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42 minutes ago, Schmelzer said:

So I do not argue that particular interpretations are right vs. wrong, but about reasonable vs. unreasonable.  

But that is a purely subjective judgment.

Whether such subjective opinions should influence funding decisions, research directions, etc is not something I have any opinion about (or knowledge of).

Although it seems very foolish (to put it mildly) to limit research to things that match "common sense".

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44 minutes ago, Schmelzer said:

So I do not argue that particular interpretations are right vs. wrong, but about reasonable vs. unreasonable.  

This holds for interpretations understood as research programs (where the mainstream-supported interpretations have not given anything more fundamental beyond QM and GR despite the open problem of finding a consistent theory of QG, thus, have completely failed.) as well as their pedagogical value (where you can see the failure to understand essential parts of QM as well as GR in forum discussions like here).  

I do not propose to rule out lines of investigation.  I argue in favor of adding some competition in form of other lines of investigation, namely the line of investigation to find interpretations as close to classical common sense as possible and then to try to find a theory of QG starting with those interpretations as the research program.  

But isn't the stuff surrounding QG and such physics beyond commonsense by default?

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On 11/26/2019 at 6:43 PM, Strange said:

Although it seems very foolish (to put it mildly) to limit research to things that match "common sense".

I certainly do not propose that foolish idea.  I simply oppose the even more foolish idea to limit research to things that are in contradiction to common sense. 

This is essentially what has been done.  See 

Freire, O. (2005) Science and exile: David Bohm, the hot times of the Cold War, and his struggle for a new interpretation of quantum mechanics. Historical Studies on the Physical and Biological Sciences  36(1), 1-34, arXiv:physics/0508184

for how the most common sense compatible interpretation of quantum theory has been handled. Here the situation has improved somewhat, dBB is now an interpretation one is allowed to consider, if one does not care that much about the mainstream and does not depend on getting grants or so.  The situation with the Lorentz ether is much worse, here you risk being banned from forums for publishing references to peer-reviewed journals like Foundations of Physics

Quote

But that is a purely subjective judgment.

Whether such subjective opinions should influence funding decisions, research directions, etc is not something I have any opinion about (or knowledge of).

I disagree. If something is reasonable or unreasonable depends on the arguments proposed.  If the arguments are valid or not depends, in part, on quite objective things like agreement with the rules of logic. Moreover, one can certainly argue about this, by presenting counterarguments. The phrase "purely subjective" refers to something where this is not possible, for example if one likes a particular meal or so. Of course, every reasonable argumentation is a statement made by some subject, and in this trivial sense subjective.  But this would not make something "purely subjective" because it would require the exclusion of non-subjective things like arguments playing a role. 

Funding decisions will always depend on subjective judgments of the science bureaucrats, there is no way to avoid this. And the choice of a research direction will also be a subjective choice, either of the scientist himself (which would be what is required by freedom of science) or by the scientific bureaucracy (by the prescription what has to be done in a grant) or by the latest mainstream fad (what has to be expected in a "publish or perish" environment).  All one could hope for would be that the subjective element remains small, and that reasonable arguments would play a large role. 

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