Delayed choice experiment (split from Question: Does the Double Slit Experiment prove Free Will?)

[bangstrom]

I have been searching for the answer to the question of whether either observation or consciousness can influence the outcome of the double slit experiment for several years now and I feel I have made a lot of progress in understanding the problem but I have possibly reached the limits of my expertise to come to any definite conclusion except to say that this is an extremely thorny issue with no easy answers.

 

It is my understanding that it is nearly the mainstream conclusion that observation and consciousness can influence the outcome of the double slit experiment. I have little interest in the philosophical or psychological aspects of this issue as long as the physics is remains in doubt. My gut instinct is that there is a simple laboratory experiment involving either QM or classical optics that can give us a definitive answer but so far any answer has remained elusive.

 

https://video.search.yahoo.com/yhs/search?fr=yhs-trp-001&ei=UTF-8&hsimp=yhs-001&hspart=trp&p=fre+will%2C+consciousness%2C+and+the+double+slit+experiment&type=Y167_F163_202037_052821#id=59&vid=e8429fb72c2e23f62b116d966d534327&action=view

 

https://video.search.yahoo.com/yhs/search?fr=yhs-trp-001&ei=UTF-8&hsimp=yhs-001&hspart=trp&p=fre+will%2C+consciousness%2C+and+the+double+slit+experiment&type=Y167_F163_202037_052821#id=2&vid=04b26854bc21b244bfbacf0d96dec6d1&action=view

[swansont]

1 hour ago, bangstrom said:

It is my understanding that it is nearly the mainstream conclusion that observation and consciousness can influence the outcome of the double slit experiment.

Observation, to be sure, but I don't see where consciousness enters into it.

[Brian King of Trolls]

Isn't the quantum realm a strange place to look for answers about free will? The mind is a better place. Quanta is so small, it is so distant from significant human experience. It's like looking in the trash for the moon.

Edited October 7, 2021 by Brian King of Trolls

[MigL]

Quantum Mechanics is clearly defined and mathematically consistant.
It somewhat difficult to understand, but, once you do, it is not strange or ambiguous at all.

Free will ( and consciousness ), on the other hand, is not clearly defined, nor consistant.

So which of the two is strange ?

[bangstrom]

2 hours ago, MigL said:

Quantum Mechanics is clearly defined and mathematically consistant.
It somewhat difficult to understand, but, once you do, it is not strange or ambiguous at all.

Free will ( and consciousness ), on the other hand, is not clearly defined, nor consistant.

So which of the two is strange ?

Both are strange. There is speculation that we would have no free will and everything would be deterministic if it were not for the Heisenberg uncertainty of Q M giving either Nature or our consciousness a chance to role the dice and change the future. I will leave that question to the philosophers. The HUP is predictably inconsistant.

[Markus Hanke]

5 hours ago, bangstrom said:

There is speculation that we would have no free will and everything would be deterministic if it were not for the Heisenberg uncertainty of Q M

It’s far more complex than that, because determinism does not imply predictability; and determinism+predictability don’t imply computability. 

That notwithstanding, it has been known for some time that consciously intentional actions (eg moving your arm) are preceded by motor neuron activity in the brain by ~10ms. That means the brain physically initiates motor action before you ever become aware of any decision-making to act. Where does that leave free will?

I personally think free will is a silly concept, as you need to make a ‘causal gap’ argument to postulate it. It also requires independent agency, which is also an extremely dubious concept, to say the least.

[bangstrom]

This is an account of the double slit Delayed Choice Quantum quantum Eraser experiment that I have been trying to understand.

https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser

Here is a concise explanation of the Yoon Ho-Kim et al experiment described in the wiki article.

https://video.search.yahoo.com/yhs/search;_ylt=Awr9NVWc2F9h4F0AFzg0nIlQ;_ylu=c2VjA3NlYXJjaAR2dGlkAw--;_ylc=X1MDMTM1MTE5NTcwMARfcgMyBGFjdG4DY2xrBGNzcmNwdmlkAzZsVDY3REV3TGpJS185VkZXNkh5Z2dENU5qY3VOZ0FBQUFDLi5PZ2EEZnIDeWhzLXRycC0wMDEEZnIyA3NhLWdwBGdwcmlkA3hOVDVab3JTUzE2QWkwWm1rQXQyOUEEbl9yc2x0AzYwBG5fc3VnZwMwBG9yaWdpbgN2aWRlby5zZWFyY2gueWFob28uY29tBHBvcwMwBHBxc3RyAwRwcXN0cmwDBHFzdHJsAzQ0BHF1ZXJ5AyUyMGRvbiUyMGRlbGF5ZWQlMjBjaG9pY2UlMjBxdWFudHVtJTIwZXJhc2VyBHRfc3RtcAMxNjMzNjcxNDI3?p=+don+delayed+choice+quantum+eraser&ei=UTF-8&fr2=p%3As%2Cv%3Av%2Cm%3Asa&fr=yhs-trp-001&hsimp=yhs-001&hspart=trp&type=Y167_F163_202037_052821#id=18&vid=44c8973728d6255afd71e2d1effc7cd3&action=view

This is a crude demonstration of the double slit experiment that I have found key to understanding the more elaborate experiment above.

https://video.search.yahoo.com/yhs/search?fr=yhs-trp-001&ei=UTF-8&hsimp=yhs-001&hspart=trp&p=you+tube+diy+quantum+erasers&type=Y167_F163_202037_052821#id=1&vid=0e2094e2c615986a3d91004bbf995aba&action=click

In later posts I hope to explain how this last double slit experiment works and how it exposes errors in the convention thinking about the double slit experiment that make it so impossible to understand.

[Eise]

On 10/7/2021 at 10:47 AM, bangstrom said:

I have been searching for the answer to the question of whether either observation or consciousness can influence the outcome of the double slit experiment for several years now and I feel I have made a lot of progress in understanding the problem but I have possibly reached the limits of my expertise to come to any definite conclusion except to say that this is an extremely thorny issue with no easy answers.

It has an easy answer: consciousness has no influence for a given setting of the experiment. Consciousness might decide what kind of experiment you are doing (e.g. a 'which way' experiment, or a 'phase' experiment), but once chosen the experimental setup, consciousness has no influence whatsoever. The only 'real problem' I see is the problem of QM at large: the measurement problem. (± collapse of the wave function).

23 hours ago, Brian King of Trolls said:

Isn't the quantum realm a strange place to look for answers about free will? The mind is a better place. Quanta is so small, it is so distant from significant human experience.

Right. Physics present basically 2 options: classical determinism or quantum probability. Both do not work together with the idea of libertarian free will. Whatever free will 'really is', that your actions are random does not belong to any reasonable concept of free will. So QM is no help here.

20 hours ago, MigL said:

Free will ( and consciousness ), on the other hand, is not clearly defined, nor consistant.

But one can define free will pretty clearly. One of the reasons however that these discussions are so difficult is that people often refuse to stick to a single definition. Above I mentioned one kind, libertarian free will, but there are other definitions. 

Just to clarify

1. Incompatibilism: determinism and free will are incompatible
   a. Hard determinism: determinism is true. therefore we have no free will
   b. Libertarian free will: determinism cannot be completely true, because we have a direct experience of free will
2. Compatibilism: there is no contradiction between determinism and free will
   a. Conceptual compatibilism: mind, motivations, beliefs, actions, etc are a complete different way to look at our human world than looking with a physical (chemical, biological, neurological) eye to humans. Both are valid in their domains, and you shouldn't mix them up.
   b. 'Hard compatibilism' (I never found a real name for this): Determinism is a necessary condition for free will. This means for 'real free will' that the world must be 'sufficient determinism'; with other words too much randomness will make our character and with that our actions to chaos.

1b is inconsistent (we would need non-physical causes: what would those be? The soul?) 2a might hide an inconsistency. But 1a and 2b seem consistent to me. But both must be explained in much more detail before one can start a fruitful discussion.

12 hours ago, Markus Hanke said:

It’s far more complex than that, because determinism does not imply predictability; and determinism+predictability don’t imply computability. 

But predictability has nothing to do with free will. Free will means just that I am able to act according my motivations and beliefs (to the latter belong justified true beliefs, i.e. knowledge). 

13 hours ago, Markus Hanke said:

That means the brain physically initiates motor action before you ever become aware of any decision-making to act. Where does that leave free will?

You mean "Where does that leave libertarian free will?" Yep, nowhere. But there is no contradiction with the compatibilist concept of free will.

And btw, I think libertarian free will would be worse than wrong from a none-dualistic viewpoint.

 

[swansont]

19 hours ago, bangstrom said:

Both are strange. There is speculation that we would have no free will and everything would be deterministic if it were not for the Heisenberg uncertainty of Q M giving either Nature or our consciousness a chance to role the dice and change the future.

Radiative or radioactive decay are probabilistic, and yet not tied to the HUP; there is nothing about them that involves commutation properties of conjugate variables.

 

19 hours ago, bangstrom said:

The HUP is predictably inconsistant.

How so?

[dimreepr]

As a human, I'm free to be a human...

[MigL]

Thanks for the elaboration Eise.
But it does sort of prove the point about free will.

Quantum Mechanics has multiple interpretations also, but, of a single, well defined, mathematical model.

Free will only has multiple interpretations.

[studiot]

4 hours ago, Eise said:

It has an easy answer: consciousness has no influence for a given setting of the experiment. Consciousness might decide what kind of experiment you are doing (e.g. a 'which way' experiment, or a 'phase' experiment), but once chosen the experimental setup, consciousness has no influence whatsoever. The only 'real problem' I see is the problem of QM at large: the measurement problem. (± collapse of the wave function).

Right. Physics present basically 2 options: classical determinism or quantum probability. Both do not work together with the idea of libertarian free will. Whatever free will 'really is', that your actions are random does not belong to any reasonable concept of free will. So QM is no help here.

But one can define free will pretty clearly. One of the reasons however that these discussions are so difficult is that people often refuse to stick to a single definition. Above I mentioned one kind, libertarian free will, but there are other definitions. 

Just to clarify

1. Incompatibilism: determinism and free will are incompatible
   a. Hard determinism: determinism is true. therefore we have no free will
   b. Libertarian free will: determinism cannot be completely true, because we have a direct experience of free will
2. Compatibilism: there is no contradiction between determinism and free will
   a. Conceptual compatibilism: mind, motivations, beliefs, actions, etc are a complete different way to look at our human world than looking with a physical (chemical, biological, neurological) eye to humans. Both are valid in their domains, and you shouldn't mix them up.
   b. 'Hard compatibilism' (I never found a real name for this): Determinism is a necessary condition for free will. This means for 'real free will' that the world must be 'sufficient determinism'; with other words too much randomness will make our character and with that our actions to chaos.

1b is inconsistent (we would need non-physical causes: what would those be? The soul?) 2a might hide an inconsistency. But 1a and 2b seem consistent to me. But both must be explained in much more detail before one can start a fruitful discussion.

But predictability has nothing to do with free will. Free will means just that I am able to act according my motivations and beliefs (to the latter belong justified true beliefs, i.e. knowledge). 

You mean "Where does that leave libertarian free will?" Yep, nowhere. But there is no contradiction with the compatibilist concept of free will.

And btw, I think libertarian free will would be worse than wrong from a none-dualistic viewpoint.

 

 

Once again a masterful summary. +1

I can only add my comment that trying to deduce facts about 'free will' from the separable actions of single (elementary) particles and transferring these observations from systems of the order of 10⁰ particles to systems of the order of 10²⁵ particles is about as sensible as arguing over Schrodinger's Cat's Tale  (Which tail(pun intended) is based on the same macro v micro difficulty)/

[Markus Hanke]

9 hours ago, Eise said:

Free will means just that I am able to act according my motivations and beliefs (to the latter belong justified true beliefs, i.e. knowledge). 

So does it require agency? Does it presuppose an independent agent who ‘has’ free will, or is it more akin to a self-regulating complex system with multiple feedback loops?

9 hours ago, Eise said:

But there is no contradiction with the compatibilist concept of free will.

Could you explain further? If (in my specific example) the action is initiated before the motivation and decision making process becomes conscious, then how was the decision ‘free’?

10 hours ago, Eise said:

The only 'real problem' I see is the problem of QM at large: the measurement problem.

Are you familiar with Carlo Rovelli’s ‘relational QM’? It resolves the issue rather elegantly.

[bangstrom]

18 hours ago, swansont said:

 How so?

It may be sloppy semantics but I equate inconsistency with uncertainty so the Uncertainty Principle self identifies as inconsistent.

 

18 hours ago, Eise said:

 The only 'real problem' I see is the problem of QM at large: the measurement problem. (± collapse of the wave function).

 

 

Here is a quote from Wiki”

"Which-way" experiments and the principle of complementarity

“A well-known thought experiment predicts that if particle detectors are positioned at the slits, showing through which slit a photon goes, the interference pattern will disappear.[6] This which-way experiment illustrates the complementarity principle that photons can behave as either particles or waves, but cannot be observed as both at the same time.”

Contrary to many experts such as Don Lincoln at Fermi Labs, whom I cited in my previous post, the interference pattern never disappears and becomes a particle pattern. An interference pattern bears no resemblance to a particle pattern so it should be impossible to confuse the two but many do.

I find it unambiguous to say that there is no evidence of complementarity in the double slit experiment so we should be able to interpret the experiment as a straight forward classical experiment with light waves.

[swansont]

1 hour ago, bangstrom said:

It may be sloppy semantics but I equate inconsistency with uncertainty so the Uncertainty Principle self identifies as inconsistent.

That's hardly a rigorous or objective explanation.

[bangstrom]

On 10/9/2021 at 4:58 AM, swansont said:

That's hardly a rigorous or objective explanation.

OK

On 10/8/2021 at 8:17 AM, Eise said:

 The only 'real problem' I see is the problem of QM at large: the measurement problem. (± collapse of the wave function).

And I see no collapse of the wave function.

A paper by Fresnel and Arago (see Fresnel-Arago Laws) published two centuries ago explained why orthogonal polarized lights do not produce an interference pattern. The two beams collide in such a way that the interference is so rapid and random that the light is no longer coherent and the interference is no longer discernible. This has nothing to do with which-path information.

I have found that light “marked” with circularly polarized light does produce an interference pattern so it is possible to have which-path information and an interference pattern both. This is consistent with the observations of Fresnel and Arago.

There is no indication of a collapse of the wave function at any point in the double slit experiment,so even at low light levels where the light signal becomes intermittent and is observed as quanta of energy, there is no evidence to support the idea that light has become a particle. A quantum of energy can have the form of a wave packet and is not necessarily a particle.

The classical view of the double slit experiment holds that light passes through both slits and both beams fan out and produce an interference pattern on the back side.

The photon theory of light offers a more speculative view where a photon particle splits in two and passes through both slits and then both particles become waves that interfere with each other on the other side. Neither of these scenarios is consistent with the later determination of which-way information where the photon is observed to pass through only one of the two slits. So what can be passing through one slit but not the other?

Light waves are transverse electromagnetic waves as discovered by Fresnel. One wave lies on the dielectric plane and the other is on the magnetic plane. When light passes through a birefringent crystal it is refracted upon entry into two divergent paths. One path is diverted more strongly than the other because the light wave on that path is slowed more on the electric plane than on the magnetic plane. This gives the transverse wave an apparent spiral. The two light paths that emerge from a birefringent crystal are oppositely polarized both linearly and circularly.

In the “Wheeler Delayed Choice Double Slit Experiment” there are two color filters and three birefringent crystals directly behind the double slit. The first birefringent is the BBO crystal and the other two are found in the Glen-Thompson prism. These are usually calcite crystals.

I suspect that the later determination of which-path information in the Wheeler DCE is not telling us which slit the photon went through but which path the light went through on the dielectric plane. And since the light in the experiment is second hand light generated within the BBO crystal, (not the UV light from the laser) it may not even be telling us which slit the original light from the laser went through.

Sorry about the font size. I don't know how to change it or why it didn't go to default size.

[swansont]

49 minutes ago, bangstrom said:

Sorry about the font size. I don't know how to change it or why it didn't go to default size.

Fixed (cut, paste as plain text)

[Markus Hanke]

12 hours ago, bangstrom said:

There is no indication of a collapse of the wave function at any point in the double slit experiment,so even at low light levels where the light signal becomes intermittent and is observed as quanta of energy, there is no evidence to support the idea that light has become a particle.

You don’t need to use light, you can use any type of quantum object (electrons, protons,...), or even something as large as a C-60 molecule. The result is always the same - you get individual local hits on the screen (particle), and many such dots will over time produce an interference pattern. This is true also if the emitter only produces one such object at a time.

[bangstrom]

On 10/15/2021 at 5:44 PM, Markus Hanke said:

You don’t need to use light, you can use any type of quantum object (electrons, protons,...), or even something as large as a C-60 molecule. The result is always the same - you get individual local hits on the screen (particle), and many such dots will over time produce an interference pattern. This is true also if the emitter only produces one such object at a time.

One question is, How do the objects that follow 'know' where to land in order to produce an interference pattern characteristic of a wave? With light, it is said that the wave becomes a particle when observed and it will no longer produce an interference pattern. This same scenario continues to say that the photon 'knows' it is being watched when a 'sentient'? observer discovers which path it took when going through the double slit and alters the outcome of the experiment accordingly. This is the interpretation of the Wheeler Delayed-Choice Double Slit experiment and it brings us back to the question in the OP.

"Does the ability of an observer to affect an outcome simply by choosing to observe it mean that the choice had to have been made outside of all universal conditions?"

One problem with scenario above is that, if the photon passed through just one slit, a single photon can't produce an interference pattern. If it split and passed through both slits or if it passed through both slits as a wave, there could be no which-path observation since it went through both. Also, if the wave has become a photon particle, it should produce a pattern characteristic of a particle like this || . Instead, it produces a diffraction pattern which is a long horizontal line with a few horizontal lines to the side. This is also characteristic of light as a wave. There is no evidence in any tests of the double slit experiment where light is behaving as a particle. That only happens in the cartoon illustrations of the experiment.

If the above part is clear, i think I can explain how the experiment works with no human involvement.

[swansont]

1 hour ago, bangstrom said:

One question is, How do the objects that follow 'know' where to land in order to produce an interference pattern characteristic of a wave? With light, it is said that the wave becomes a particle when observed and it will no longer produce an interference pattern. This same scenario continues to say that the photon 'knows' it is being watched when a 'sentient'? observer discovers which path it took when going through the double slit and alters the outcome of the experiment accordingly. This is the interpretation of the Wheeler Delayed-Choice Double Slit experiment and it brings us back to the question in the OP.

"Does the ability of an observer to affect an outcome simply by choosing to observe it mean that the choice had to have been made outside of all universal conditions?"

One problem with scenario above is that, if the photon passed through just one slit, a single photon can't produce an interference pattern. If it split and passed through both slits or if it passed through both slits as a wave, there could be no which-path observation since it went through both. Also, if the wave has become a photon particle, it should produce a pattern characteristic of a particle like this || . Instead, it produces a diffraction pattern which is a long horizontal line with a few horizontal lines to the side. This is also characteristic of light as a wave. There is no evidence in any tests of the double slit experiment where light is behaving as a particle. That only happens in the cartoon illustrations of the experiment.

If the above part is clear, i think I can explain how the experiment works with no human involvement.

The characterization that "the wave becomes a particle" lacks the nuance of the physics; it's a shorthand that tries to keep us grounded in classical physics (and there are multiple examples of this lazy description), but QM is not classical physics. Waves don't become particles nor do particles become waves. Quantum objects have characteristics of both, and we observe those characteristics depending on what kind of observation we do.

Particle characteristics include being detected (interacting) in a localized region (and also possibly in time) so if you are detecting photons in a double slit experiment you have evidence of light behaving as a particle. A visible-light photon is of order half a micron in wavelength and an atom is much, much smaller than this (e.g. Si lattice constant is about half a nanometer) meaning the absorption of that photon by a single atom is a localization inconsistent with its wave nature.

 

The point of a which-path experiment is not to confirm the wave/particle nature of light; that's already done. So the observation that we see a diffraction pattern isn't a revelation here. The salient detail is whether or not you observe an interference pattern, indicating you have which-path information.

[Markus Hanke]

14 hours ago, bangstrom said:

How do the objects that follow 'know' where to land in order to produce an interference pattern characteristic of a wave?

So long as the relationship between emitter and observer remains the same, the particles are subject to the same probability distribution.

14 hours ago, bangstrom said:

If the above part is clear, i think I can explain how the experiment works with no human involvement.

You don’t need human involvement. You can just set this up and let it run without a human observer being present; the result is the same.

[bangstrom]

On 10/18/2021 at 6:46 AM, swansont said:

Your salient detail is wrong and in reverse. If you have which-way information or some means to access that information you don’t get an interference pattern. If you don’t have which-way information or if the necessary information was recorded and later destroyed before you observed the test results, then you do have interference.

This is a quote from Anton Zeilinger.

“Thus, even though a sub-quantum amount of light is received at a detector, the probability of a detection event occurring at the detector increases with the amplitude of the received light signal. Thus, even sub-quantum amounts of light can cause detectors to trigger and generate “click” events.

It is sufficient to destroy the interference pattern, if the path information is accessible in principle from the experiment or even if it is dispersed in the environment and beyond any technical possibility to be recovered, but in principle still ‘‘out there.’’ The absence of any such information is the essential criterion for quantum interference to appear.” A. Zeilinger

Zeilinger is saying that even if the light level is so low that you have only one light event at a time passing through the double slit, a “click” of the which-path detectors is sufficient to prevent the formation of the interference pattern for as long as the “which-path” information is “out there”. 

However, if the which-path information is destroyed beyond recovery before you observe the results of the experiment, then an interference pattern appears.

The results suggest that a person has free will to determine the outcome of the double slit experiment. If he chooses to learn the which-path information before observing the results of the results he will see no interference. If he has no means of learning the which-path information, then there will be interference. The results suggest that the interference pattern is not possible if someone has access to which-path information but interference is only possible if the which-path information is unknown and unknowable. 

The obvious explanation is that the which-path detectors are interfering causing the loss of interference but that possibility has been ruled out. The detectors were moved from the front of the double slit to the back with no change in the results. They were even moved all the way back so the which-path information was not determined until after the interference should have taken place but the interference pattern does not appear whenever the experiment is observed while the which-path information is “out there.” 

This is the difficulty behind the question in the OP.

 

11 hours ago, Markus Hanke said:

So long as the relationship between emitter and observer remains the same, the particles are subject to the same probability distribution.

You don’t need human involvement. You can just set this up and let it run without a human observer being present; the result is the same.

I agree with both statements.

The Wheeler Delayed-Choice Double-Slit experiment is a good example to consider because it contains all the elements that are interpreted as having observer involvement- not necessarily human but possibly just sentient. I think this is the sort of explanation the OP is asking for so let it run.

On 10/18/2021 at 6:46 AM, swansont said:

 The point of a which-path experiment is not to confirm the wave/particle nature of light; that's already done. So the observation that we see a diffraction pattern isn't a revelation here. The salient detail is whether or not you observe an interference pattern, indicating you have which-path information.

 

On 10/18/2021 at 6:46 AM, swansont said:

 The point of a which-path experiment is not to confirm the wave/particle nature of light; that's already done. So the observation that we see a diffraction pattern isn't a revelation here. The salient detail is whether or not you observe an interference pattern, indicating you have which-path information.

 

7 hours ago, bangstrom said:

 

I agree with both statements.

The Wheeler Delayed-Choice Double-Slit experiment is a good example to consider because it contains all the elements that are interpreted as having observer involvement- not necessarily human but possibly just sentient. I think this is the sort of explanation the OP is asking for so let it run.

 

 

Sorry about the confused quotes, I am new to this forum and haven't figured out the editing yet. That short quote from "swansont" should have been at the beginning.

[swansont]

7 hours ago, bangstrom said:

This is a quote from Anton Zeilinger.

“Thus, even though a sub-quantum amount of light is received at a detector, the probability of a detection event occurring at the detector increases with the amplitude of the received light signal. Thus, even sub-quantum amounts of light can cause detectors to trigger and generate “click” events.

It is sufficient to destroy the interference pattern, if the path information is accessible in principle from the experiment or even if it is dispersed in the environment and beyond any technical possibility to be recovered, but in principle still ‘‘out there.’’ The absence of any such information is the essential criterion for quantum interference to appear.” A. Zeilinger

Zeilinger is saying that even if the light level is so low that you have only one light event at a time passing through the double slit, a “click” of the which-path detectors is sufficient to prevent the formation of the interference pattern for as long as the “which-path” information is “out there”. 

However, if the which-path information is destroyed beyond recovery before you observe the results of the experiment, then an interference pattern appears.

 

 

And none of that has to do with the wave-particle nature, which is the source of my comment. The experiment is, as you confirm here, about which-path.

7 hours ago, bangstrom said:

 

The results suggest that a person has free will to determine the outcome of the double slit experiment.

Which is an issue for philosophy and not physics.

7 hours ago, bangstrom said:

If he chooses to learn the which-path information before observing the results of the results he will see no interference. If he has no means of learning the which-path information, then there will be interference. The results suggest that the interference pattern is not possible if someone has access to which-path information but interference is only possible if the which-path information is unknown and unknowable. 

 

Yes. If you can't know which path, you get interference. 

7 hours ago, bangstrom said:

 

The obvious explanation is that the which-path detectors are interfering causing the loss of interference but that possibility has been ruled out.

 

I wouldn't say that detectors interfering is an obvious solution, because that makes no sense.

 

7 hours ago, bangstrom said:

Sorry about the confused quotes, I am new to this forum and haven't figured out the editing yet. That short quote from "swansont" should have been at the beginning.

Fixed

[bangstrom]

10 hours ago, swansont said:

And none of that has to do with the wave-particle nature, which is the source of my comment. The experiment is, as you confirm here, about which-path.

Yes, the experiment is about which-path information and there is no evidence from the experiment to indicate that light is a particle. Light appears as a wave through out the experiment. The results that are said to be lacking interference are diffraction patterns which are just a less elaborate demonstration of wave interference.

The conventional interpretations of the double slit experiments is to consider light as a particle and that approach leads to a dead end.

 

10 hours ago, swansont said:

Which is an issue for philosophy and not physics.

The conventional interpretation of the Wheeler Delayed-Choice experiment is that an observer can decide the outcome of the experiment by determining the which-path information even if the determination is made after the experiment is completed. The retroactive nature of which-way information is a problem for physics.

 

10 hours ago, swansont said:

Yes. If you can't know which path, you get interference.

Yes, that is the way it works.

 

10 hours ago, swansont said:

I wouldn't say that detectors interfering is an obvious solution, because that makes no sense.

There is an interference pattern when there are no detectors of which-way information but the interference pattern is lost when the detectors are present. This makes it suspicious that the detectors are causing the loss of interference.

In one test of the double slit experiment, the detectors were placed behind the double slit and recorded the which-path information. This destroyed the interference pattern. The test was then repeated with the detectors active but unplugged from the recorders and the interference returned. The interference pattern is destroyed whenever the which-path information is “out there” but the interference pattern is present even when the detectors are present and active but there is no record of which-path information. This places the suspicion on the presence or absence of which-path information as a cause for the loss of interference.

 

 

 

[Markus Hanke]

18 hours ago, bangstrom said:

not necessarily human but possibly just sentient

No sentience is required either. An observer in the QM sense is simply an external physical system interacting with the setup.