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


bangstrom
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11 hours ago, bangstrom said:

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

That’s grossly inaccurate. The double slit is generally considered to be evidence of the wave nature of light.

https://en.wikipedia.org/wiki/Double-slit_experiment

 

11 hours ago, bangstrom said:

 

 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.

The detection or ability to detect is what causes the loss of interference. The detectors are not merely present; e.g. sitting in a corner of the room is insufficient.

 

 

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1 hour ago, swansont said:

That’s grossly inaccurate. The double slit is generally considered to be evidence of the wave nature of light.

https://en.wikipedia.org/wiki/Double-slit_experiment

 

The detection or ability to detect is what causes the loss of interference. The detectors are not merely present; e.g. sitting in a corner of the room is insufficient.

 

 

 

It should be noted that the screen upon which the pattern, interference or otherwise , impinges is also a detector.

The results with and without that screen should be considered.

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3 minutes ago, studiot said:

 

It should be noted that the screen upon which the pattern, interference or otherwise , impinges is also a detector.

The results with and without that screen should be considered.

What about the slits? Are they detectors too?

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4 minutes ago, geordief said:

What about the slits? Are they detectors too?

Good question.

Detectors of what ?

There are some subtle differences in the meanings and usage of the word detectors , interactors, and observers.

There is no difference from the point of view of QM itself.

Edited by studiot
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12 minutes ago, studiot said:

Detectors of what ?

There are some subtle differences in the meanings and usage of the word detectors , interactors, and observers.

There is no difference from the point of view of QM itself.

As in "does the wave interact with them"  (their edges) ?Does  it cause decoherence (am just learning to use that word)?

 

ps I don't think I  have any hangups about  human or sentient observers -they are all just interactors to me at my present stage of understanding.

Edited by geordief
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29 minutes ago, geordief said:

As in "does the wave interact with them"  (their edges) ?Does  it cause decoherence (am just learning to use that word)?

 

ps I don't think I  have any hangups about  human or sentient observers -they are all just interactors to me at my present stage of understanding.

Yes I get that you are trying to understand and not trying to force through a particular point of view. +1

 

So starting with a plane wave (do you know that all the slit experiments start with a plane wave, not any other sort ?)

There are no slits and not screens or other 'detectors'

So the plane wave just travels or progresses in the space.

An 'observer' will see (detect) nothing at all ( as he has no means to detect the wave)

Now introduce a screen detector.

The observer will see a light on the screen, but no interference pattern.

He will see this because the screen interacts with the plane wave (blocking it in this case) and illuminates.
The screen therefore allows an observer to detect the wave.

Now introduce a suitable slit or slits and the observer's view on the screen will change.
Depending upon the size and configuration of the slits an interference pattern may observed on the screen.

This is because the interaction of the slit array is not blocking but modifying the wave, changing it from planar to circular or spherical.

 

Is the terminology becoming clear ?

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42 minutes ago, studiot said:

This is because the interaction of the slit array is not blocking but modifying the wave, changing it from planar to circular or spherical.

This is completely  new to me . It seems to be very important. It  counts as  an interaction ,doesn't it?

43 minutes ago, studiot said:

(do you know that all the slit experiments start with a plane wave, not any other sort ?

Again I was blissfully unaware of plane waves ;even polarized light I have not too well assimilated as a phenomenon 

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14 hours ago, swansont said:

That’s grossly inaccurate. The double slit is generally considered to be evidence of the wave nature of light.

https://en.wikipedia.org/wiki/Double-slit_experiment

The double slit is evidence of light waves but it also works with particles. Small particles also have a wave nature so the two properties are not mutually exclusive. The presence of which-path information is characteristic of the particle nature of light and the presence of which-path information destroys the interference, so in experiments where which-path information appears to be critical to the outcome, light is considered to be to be acting as a particle. A wave should not be expected to demonstrate which-path information.

13 hours ago, studiot said:

 

It should be noted that the screen upon which the pattern, interference or otherwise , impinges is also a detector.

The results with and without that screen should be considered.

Yes, the screen is a detector. The Wheeler Delayed-Choice experiment uses two electronic versions of a screen looking for interference. One receives light from both slits and indicates the presence or lack of interference. The other is a Mach-Zehnder interferometer that looks for both interference and which-path information. The second is located meters behind the first so interference is noted first and the which-path information is determined later.

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I like Rovelli's approach,  that it's all about the interaction and not about any properties intrinsic to the object of observation.  It's the observer (device)-photon relation that is wavelike or particle-like,  not light in and of itself.  You can even have device interactions with buckyballs (C60) that are wavy and say nothing about intrinsic ballsy-ness in the absence of which-path info (the experimenter is another matter).   

 

Bangstrom,  if you recall Marshall at SCF,  he was a big Rovelli fan, owing to the relational perspective.  

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6 hours ago, TheVat said:

Bangstrom,  if you recall Marshall at SCF,  he was a big Rovelli fan, owing to the relational perspective.  

I remember Marshall but I will have to look into what Rovelli has to say.

20 hours ago, studiot said:

Good question.

Detectors of what ?

My answer is at the bottom.

In my view of the double slit experiment, the slits are detectors of nothing when light is involved. This may be a different matter with electrons. Light as a wave should pass through both slits so there is no which-path information because the light wave took both paths. The which-path information must be indicating something different.

In experiments modeled after the Wheeler Delayed-Choice experiment there is a beta barium borate crystal (BBO) directly behind the double slits. The purpose of the BBO crystal is to generate pairs of entangled photons...No, forget the photons. The crystal generates entangled pairs of wavelets of light energy.

In Wheeler’s Delayed-Choice, light enters the BBO crystal as an extremely powerful laser beam of UV light and it passes directly through the crystal. On extremely rare occasions, a quantum of UV energy is absorbed by a BBO molecule and an electron in one of the atoms is boosted to a much higher energy level. Instead of dropping back down to its original energy level in one big jump, the electron drops down in two steps releasing two entangled photons wavelets.

If the two wavelets are of equal energy, they are called “parametric” and the whole process is called “spontaneous parametric down conversion” SPDC. I think SPDC is largely a distraction from what else is happening. The original UV light from the laser and any light except for the feeble red light having half the energy and twice the wavelength of the UV light is used for the rest of the experiment. Everything else is removed by color filters. BBO crystals are used because they are the only birefringent crystals that can survive the heat of the UV laser.

The BBO crystal is a nonlinear, birefringent crystal with optical properties nearly identical to calcite. When a light wavelet enters a birefringent crystal it can take one of two paths. It can go straight through the crystal on the “p” path or it can take a slight jog to the side on the “s” path. Also, when light travels through a nonlinear crystal as an electromagnetic wave, the wave is slowed upon entry more on the electro plane than on the magnetic plane. This gives the wave an apparent spiral called circular polarization. Light can be both circularly and linearly polarized at the same time and this is the condition of light when it emerges from a birefringent crystal.

I suspect the which-path information that is determined later is more likely to indicate which path the light wave took as it passed through the BBO crystal (the p or s path) than which path it took through the double slit.

19 hours ago, studiot said:

This is because the interaction of the slit array is not blocking but modifying the wave, changing it from planar to circular or spherical.

Other than myself, I don't know of anyone who has looked into the effect of circular polarization on the simple double slit experiment but I have read some hear-say accounts that orthogonol beams of circularly polarized light will not interfere. If they do interfere that would give you which-path information and interference at the same time which is claimed to be impossible. I have tried it and it works for me.

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36 minutes ago, bangstrom said:

My answer is at the bottom.

In my view of the double slit experiment, the slits are detectors of nothing when light is involved. This may be a different matter with electrons. Light as a wave should pass through both slits so there is no which-path information because the light wave took both paths. The which-path information must be indicating something different.

In experiments modeled after the Wheeler Delayed-Choice experiment there is a beta barium borate crystal (BBO) directly behind the double slits. The purpose of the BBO crystal is to generate pairs of entangled photons...No, forget the photons. The crystal generates entangled pairs of wavelets of light energy.

In Wheeler’s Delayed-Choice, light enters the BBO crystal as an extremely powerful laser beam of UV light and it passes directly through the crystal. On extremely rare occasions, a quantum of UV energy is absorbed by a BBO molecule and an electron in one of the atoms is boosted to a much higher energy level. Instead of dropping back down to its original energy level in one big jump, the electron drops down in two steps releasing two entangled photons wavelets.

If the two wavelets are of equal energy, they are called “parametric” and the whole process is called “spontaneous parametric down conversion” SPDC. I think SPDC is largely a distraction from what else is happening. The original UV light from the laser and any light except for the feeble red light having half the energy and twice the wavelength of the UV light is used for the rest of the experiment. Everything else is removed by color filters. BBO crystals are used because they are the only birefringent crystals that can survive the heat of the UV laser.

The BBO crystal is a nonlinear, birefringent crystal with optical properties nearly identical to calcite. When a light wavelet enters a birefringent crystal it can take one of two paths. It can go straight through the crystal on the “p” path or it can take a slight jog to the side on the “s” path. Also, when light travels through a nonlinear crystal as an electromagnetic wave, the wave is slowed upon entry more on the electro plane than on the magnetic plane. This gives the wave an apparent spiral called circular polarization. Light can be both circularly and linearly polarized at the same time and this is the condition of light when it emerges from a birefringent crystal.

I suspect the which-path information that is determined later is more likely to indicate which path the light wave took as it passed through the BBO crystal (the p or s path) than which path it took through the double slit.

Thank you for your replies, but remember my intention here is not to interfere in your discussion with swansont.
It is to help geordief beter understand waves and the slits experiment.

So I will just ask you the simple question how do you view light as a wave when you are working at the one photon at a time scale as I believe you are trying to do ?

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I see light as a wave and never as a particle. Light is quantized for certain but that does not mean it is a particle. Light is emitted and absorbed by electrons in  discrete amounts representing the many differences in energy levels from one electron orbital to the next and that is why light waves appear as quanta. The photoelectric effect converts light energy into a stream of electrons but counting electrons thinking that each electron represents a photon is not a valid assumption.

BTW it is not "my" discussion or even my OP. I am just another butinski.

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57 minutes ago, bangstrom said:

BTW it is not "my" discussion or even my OP

Oh ?

About a dozen exchanges in thread between yourself and swansont sure fooled me into thinking you two were have a discussion.

I did not say it was your thread.

59 minutes ago, bangstrom said:

I see light as a wave and never as a particle. Light is quantized for certain but that does not mean it is a particle. Light is emitted and absorbed by electrons in  discrete amounts representing the many differences in energy levels from one electron orbital to the next and that is why light waves appear as quanta. The photoelectric effect converts light energy into a stream of electrons but counting electrons thinking that each electron represents a photon is not a valid assumption.

Thank you for clarifying your position.

 

 

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11 hours ago, bangstrom said:

The double slit is evidence of light waves but it also works with particles. Small particles also have a wave nature so the two properties are not mutually exclusive. The presence of which-path information is characteristic of the particle nature of light and the presence of which-path information destroys the interference, so in experiments where which-path information appears to be critical to the outcome, light is considered to be to be acting as a particle. A wave should not be expected to demonstrate which-path information.

Except, as you point out, a single slit still gives diffraction, which is a wave property.

The experiment under consideration is a which-path experiment. The salient detail is that quantum particles have wave properties and show interference. It is not required that they exhibit particle properties when which-path information is present.

 

2 hours ago, bangstrom said:

BTW it is not "my" discussion or even my OP.

!

Moderator Note

As such, and since we've strayed from the OP, I have split this into a new thread

 
2 hours ago, bangstrom said:

I see light as a wave and never as a particle. Light is quantized for certain but that does not mean it is a particle.

That's actually one reason why it's described as a particle. Also the localization, which I think I mentioned earlier.

Quote

Light is emitted and absorbed by electrons in  discrete amounts representing the many differences in energy levels from one electron orbital to the next and that is why light waves appear as quanta. The photoelectric effect converts light energy into a stream of electrons but counting electrons thinking that each electron represents a photon is not a valid assumption.

You might have a 1 eV transition in an atom, but a 2 eV photon will not cause two atoms to be excited, even though the light could interact with both particles, and is what you would expect if you had a wave. It will not absorb 1 eV of a 1.5 eV photon and let the rest pass by, another thing you would expect of a wave.

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7 hours ago, swansont said:

Except, as you point out, a single slit still gives diffraction, which is a wave property.

The experiment under consideration is a which-path experiment. The salient detail is that quantum particles have wave properties and show interference. It is not required that they exhibit particle properties when which-path information is present.

 

!

Moderator Note

As such, and since we've strayed from the OP, I have split this into a new thread

 

That's actually one reason why it's described as a particle. Also the localization, which I think I mentioned earlier.

You might have a 1 eV transition in an atom, but a 2 eV photon will not cause two atoms to be excited, even though the light could interact with both particles, and is what you would expect if you had a wave. It will not absorb 1 eV of a 1.5 eV photon and let the rest pass by, another thing you would expect of a wave.

 

7 hours ago, swansont said:

Except, as you point out, a single slit still gives diffraction, which is a wave property.

The experiment under consideration is a which-path experiment. The salient detail is that quantum particles have wave properties and show interference. It is not required that they exhibit particle properties when which-path information is present.

 

!

Moderator Note

As such, and since we've strayed from the OP, I have split this into a new thread

 

That's actually one reason why it's described as a particle. Also the localization, which I think I mentioned earlier.

You might have a 1 eV transition in an atom, but a 2 eV photon will not cause two atoms to be excited, even though the light could interact with both particles, and is what you would expect if you had a wave. It will not absorb 1 eV of a 1.5 eV photon and let the rest pass by, another thing you would expect of a wave.

 

7 hours ago, swansont said:

Except, as you point out, a single slit still gives diffraction, which is a wave property.

The experiment under consideration is a which-path experiment. The salient detail is that quantum particles have wave properties and show interference. It is not required that they exhibit particle properties when which-path information is present.

 

!

Moderator Note

As such, and since we've strayed from the OP, I have split this into a new thread

 

You might have a 1 eV transition in an atom, but a 2 eV photon will not cause two atoms to be excited, even though the light could interact with both particles, and is what you would expect if you had a wave. It will not absorb 1 eV of a 1.5 eV photon and let the rest pass by, another thing you would expect of a wave.

Why would more than one atom need to be involved?

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Some misunderstand quantum particle behaviour, thinking that they are waves in some circumstances, and particles in other circumstances.
They are not !
What they are, in 'reality', we're not really sure.
But we have two models, one which treats them as waves, and the other which treats them as particles.
If we set up an experiment to test our wave model, we detect wave behaviour from the quantum particles; if, on the other hand, we set up an experiment to test the particle model we find quantum particles to exhibit particle behaviour.
All we are confirming is one or the other particular model, and its area of applicability.
We are NOT confirming any underlying 'reality'.

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3 hours ago, bangstrom said:

Why would more than one atom need to be involved?

Because we investigate all possibilities. You don’t just look at circumstances that support your thesis; that’s cherry-picking. I gave examples that show your claim to be wrong.

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6 hours ago, swansont said:

Because we investigate all possibilities. You don’t just look at circumstances that support your thesis; that’s cherry-picking. I gave examples that show your claim to be wrong.

I am all in favor of looking at a problem from multiple points of view but I don’t follow the physics behind your example. If an electron within an atom, can make a 2eV transition and emit a 2eV photon, why can’t a receptive atom receive a 2eV photon. That is also my understanding of how it also works with waves. I don’t understand why more than one atom must be involved in the case of waves.

 

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3 hours ago, bangstrom said:

I am all in favor of looking at a problem from multiple points of view but I don’t follow the physics behind your example. If an electron within an atom, can make a 2eV transition and emit a 2eV photon, why can’t a receptive atom receive a 2eV photon. That is also my understanding of how it also works with waves. I don’t understand why more than one atom must be involved in the case of waves.

That wasn’t the example I presented. It was a 1 eV transition. A wave doesn’t deliver its energy in a localized fashion.

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47 minutes ago, swansont said:

That wasn’t the example I presented. It was a 1 eV transition. A wave doesn’t deliver its energy in a localized fashion.

 

47 minutes ago, swansont said:

That wasn’t the example I presented. It was a 1 eV transition. A wave doesn’t deliver its energy in a localized fashion.

My understanding is that light does deliver its energy in a localized fashion. This is why many suspect it must be a particle. Is there any evidence to support your statement that light is not localized. That is, delivering energy from one charged particle to more than one other charged particle.

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1 hour ago, bangstrom said:

My understanding is that light does deliver its energy in a localized fashion. This is why many suspect it must be a particle.

And yet you previously stated that it does not exhibit any particle-like behavior. ("I see light as a wave and never as a particle.")

If it exhibits particle-like behavior, you can't then deny it does so. You can't have it both ways.

 

1 hour ago, bangstrom said:

Is there any evidence to support your statement that light is not localized. That is, delivering energy from one charged particle to more than one other charged particle.

No, I don't. My position is the opposite of this, and that's the point: such wave behavior is not observed when the light interacts. This is the second time in as many posts you have misread/misconstrued what I wrote.

You stated that your view is that light never behaves as a particle. I am rebutting this claim. Thus, I am giving examples of where particle-like properties are observed, and contrasting them with what wave behavior would be expected but is not observed.

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1 hour ago, bangstrom said:

My understanding is that light does deliver its energy in a localized fashion. This is why many suspect it must be a particle. Is there any evidence to support your statement that light is not localized. That is, delivering energy from one charged particle to more than one other charged particle.

 

A perfect example of why you are not listening to others.

Which is particularly counterproductive here as swansont has graced you with far more detailed answers than his usual terse responses.

On 10/21/2021 at 11:28 AM, swansont said:

You might have a 1 eV transition in an atom, but a 2 eV photon will not cause two atoms to be excited, even though the light could interact with both particles, and is what you would expect if you had a wave. It will not absorb 1 eV of a 1.5 eV photon and let the rest pass by, another thing you would expect of a wave.

 

I really suggest you stop looking for esoteric special cases and start learning the basics.

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7 hours ago, swansont said:

And yet you previously stated that it does not exhibit any particle-like behavior. ("I see light as a wave and never as a particle.")

If it exhibits particle-like behavior, you can't then deny it does so. You can't have it both ways.

No, I don't. My position is the opposite of this, and that's the point: such wave behavior is not observed when the light interacts. This is the second time in as many posts you have misread/misconstrued what I wrote.

You stated that your view is that light never behaves as a particle. I am rebutting this claim. Thus, I am giving examples of where particle-like properties are observed, and contrasting them with what wave behavior would be expected but is not observed.

The point at which the light is observed upon its arrival is consistent with the probability of light behaving as a wave all the way from signal to sink. I don’t consider the condition of light at the instant of its annihilation as indicative of its properties prior to that event.

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2 minutes ago, bangstrom said:

The point at which the light is observed upon its arrival is consistent with the probability of light behaving as a wave all the way from signal to sink. I don’t consider the condition of light at the instant of its annihilation as indicative of its properties prior to that event.

How is that consistent with "never"?

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2 minutes ago, swansont said:

How is that consistent with "never"?

Light is emitted and absorbed from a single point. Its emission from a point doesn't indicate that it must be a particle and it absorption at a point doesn't mean it must be a particle. A vibrating guitar string is a point at both ends but a wave between. Light's absorption at a single point does not necessarily indicate that it was ever a particle.

8 hours ago, studiot said:

 

A perfect example of why you are not listening to others.

Which is particularly counterproductive here as swansont has graced you with far more detailed answers than his usual terse responses.

 

I really suggest you stop looking for esoteric special cases and start learning the basics.

The statement that a 2 eV “photon” should interact with two particles having a 1 eV transition if it is a wave is a personal opinion that “swansont” has not supported with either evidence or an explanation so why should I take it as creditable? The basic is that light never acts that way.

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