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

[studiot]

1 hour ago, bangstrom said:

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.

I really am amazed how completely you have just proved my words in your desire to argue, instead of listen.

You have completely twisted swanson't words round in your reply to me.

How can "will not interact" (swansont) ever mean "should interact" (bangstrom)  ?

 

Just to continue my suggestion that you should leran the basics properly here is a really good book by Arthur Beiser (fourth edition or later)

Concepts of Modern Physics  -  McGraw-Hill.

The book lays out all the areas of modern physics in a way that can be easily understood with excellent summaries and diagrams and contains the answers to many of the questions you seem to want to debate.

[bangstrom]

1 hour ago, studiot said:

I really am amazed how completely you have just proved my words in your desire to argue, instead of listen.

You have completely twisted swanson't words round in your reply to me.

How can "will not interact" (swansont) ever mean "should interact" (bangstrom)  ?

Just to continue my suggestion that you should leran the basics properly here is a really good book by Arthur Beiser (fourth edition or later)

 

I have listened to your complaint and have no intention to argue the semantics.

[studiot]

20 minutes ago, bangstrom said:

I have listened to your complaint and have no intention to argue the semantics.

It is not a question of semantics.

You plain and simple misquoted the man.

You really owe him an apology.

[Markus Hanke]

3 hours ago, bangstrom said:

doesn't mean it must be a particle

I think you are missing the point entirely throughout this discussion - quantum object “are” neither waves nor particles, nor are they both or neither. You are attempting to shoehorn something that isn’t classical into a classical category. 

The point is that quantum objects sometimes exhibit particle-like behaviour, and sometimes wave-like behaviour, depending on the relationship between the object and the observer; this is called contextuality. It is meaningless to say that a quantum object “is” something or “has” certain properties, unless within the context of interaction with another system. These aspects are relational in nature, not ontic. 

A limited analogy (!) in the classical world would be electromagnetic fields - sometimes you see magnetic fields, sometimes electrical ones, and sometimes a mix - depending on the relationship between observer and source. But the underlying entity is the electromagnetic field, which “is” neither of these. Wave-particle duality is similar, except that now you are in the quantum world, so you have to also consider counterfactual definiteness.

[geordief]

15 minutes ago, Markus Hanke said:

The point is that quantum objects sometimes exhibit particle-like behaviour, and sometimes wave-like behaviour, depending on the relationship between the object and the observer; this is called contextuality

I like that description.Would that be the consensus view,or are there other widely held  interpretations?

[swansont]

4 hours ago, bangstrom said:

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.

Nobody is making the argument that it was. You’re attacking a straw man.

The argument is that localized interaction is particle-like behavior, and inconsistent with wave-like behavior. Please take the time to notice that this does not mention the behavior at other places or times.

Also that this is inconsistent with “never acts like a particle”

4 hours ago, bangstrom said:

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.

No, light doesn’t act that way, but waves do. If you have objects floating on water and a wave goes by, the wave interacts with all the objects. It doesn’t pick one.

This is not merely my opinion, this is what physicists deduced over a century ago.

[bangstrom]

6 hours ago, swansont said:

No, light doesn’t act that way, but waves do. If you have objects floating on water and a wave goes by, the wave interacts with all the objects. It doesn’t pick one.

Light waves and water waves are much different things. Light is a transverse electromagnetic wave unlike water.

The only thing I really have to say about the particle theory of light is that it fails to explain some of the experiments involving the quantum nature of light. Specifically, the Wheeler Delayed-Choice Quantum Eraser.

Since the particle approach fails, I am exploring the idea that the wave approach should work better and I am finding that it does.

[studiot]

8 hours ago, geordief said:

I like that description.Would that be the consensus view,or are there other widely held  interpretations?

Yes Markus has nailed it.

I was wondering whether to recommend the Beiser book to you anyway but here is the contents page.

Note carefully that his choice of chapters and their order.

1.

2.  Particle properties of waves.

3. Wave properties of particles.

4.

 

It really is a well thought out book.

In particular it describes the observations and experiments that led to the 'quantum theory of light' really well.

3 hours ago, bangstrom said:

Since the particle approach fails, I am exploring the idea that the wave approach should work better and I am finding that it does.

So let me ask you some simply physics question.

In the single slit or double slit experiment, is diffraction or interference possible in the region before the slit barrier i.e. can diffraction or interference be observed ?

Are both interference and diffraction possible in

a) The single slit ?

b) The double slit ?

[bangstrom]

I may not be following your first question correctly but interference is possible before the slit barrier and it can be observed if a screen is placed in that position to make the observation. Interference can be observed if the light source is coherent but not if the light is incoherent. For example coherent light from a laser does not appear uniform. Instead it appears as many tiny dots when viewed up close. Interference is also possible if the light has passed close to the edge of an object on the way to the screen.

(a) Diffraction is obvious with a single slit and interference is possible but not so obvious as in the case of unobstructed coherent light.

(b) Diffraction and interference are both obvious with a double slit. The two forms of interference converge on the same broad line perpendicular to the double slits.

[studiot]

1 hour ago, bangstrom said:

I may not be following your first question correctly but interference is possible before the slit barrier and it can be observed if a screen is placed in that position to make the observation. Interference can be observed if the light source is coherent but not if the light is incoherent. For example coherent light from a laser does not appear uniform. Instead it appears as many tiny dots when viewed up close. Interference is also possible if the light has passed close to the edge of an object on the way to the screen.

(a) Diffraction is obvious with a single slit and interference is possible but not so obvious as in the case of unobstructed coherent light.

(b) Diffraction and interference are both obvious with a double slit. The two forms of interference converge on the same broad line perpendicular to the double slits.

Thank you for your answers to the questions.

Yes I think from your answers you have correctly understood the questions.

However you questions demonstrate that you need to understand the basics better.

This is not a personal criticism but an attempt to help you.

Diffraction and interference are different phenomena.

Interference ony occurs when two separate waves overlap (occupy the same space).
Changes of direction (spreading) of the waves is not involved.

Diffraction is the result of a single wave interacting with a wave blocking object.
It is the name given to the spreading of (single) waves when they pass through apertures or around objects.

Until recently it has not been possible to show interference from two different light sources, but has been possible with other waves. That is way classical interference experiments split the light from a single source.

The slit(s) experiment require a single plane wave in the space between the source and the slit(s) barrier.

So interference is not possible or observable in that space.
Insertion of an observation screen will show an even illumination.
Insertion of a blocking object may show diffraction effects around its edges or in its shadow zone.

With a single slit, the result of the passage of the wave depends upon the geometry of both the wave and the slit.
Some results are also dependent upon the distances of the source and observing screen from the slits.
For instance this distinguishes Fraunhofer and Fresnel diffraction.

 

All of these phenomena are well tested experimentally, some have been known for hundreds of years.

As regards the difference between the wave and photon models of light consider the quantity I, the intensity of illumination at any point on the screen.

We have for photons

[math]I = nh\nu [/math]

And for waves

[math]I = {\varepsilon _0}c{E^2}[/math]

The key point here is that for either model the I must be equal as they refer to the same observable quantity.

Edited October 23, 2021 by studiot

[swansont]

6 hours ago, bangstrom said:

Light waves and water waves are much different things. Light is a transverse electromagnetic wave unlike water.

The only thing I really have to say about the particle theory of light is that it fails to explain some of the experiments involving the quantum nature of light. Specifically, the Wheeler Delayed-Choice Quantum Eraser.

Since the particle approach fails, I am exploring the idea that the wave approach should work better and I am finding that it does.

You continue to attack a straw man. Nobody is arguing for the particle theory of light, or the wave theory of light. It’s not one or the other. That was settled more than a century ago. 

If you continue to claim that light never exhibits particle properties you will continue to be wrong, and also contradict your own descriptions of light exhibiting particle behavior. 

[geordief]

4 hours ago, studiot said:

Yes Markus has nailed it.

I was wondering whether to recommend the Beiser book to you anyway but here is the contents page.

Note carefully that his choice of chapters and their order.

1.

2.  Particle properties of waves.

3. Wave properties of particles.

4.

 

It really is a well thought out book.

In particular it describes the observations and experiments that led to the 'quantum theory of light' really well.

 

 

Thanks for the suggestion.I will look into it.Books  are another approach for sure.A pity I now find them so hard to use.Even so they can be very pleasurable.

Edited October 23, 2021 by geordief

[bangstrom]

17 hours ago, swansont said:

 The argument is that localized interaction is particle-like behavior, and inconsistent with wave-like behavior. Please take the time to notice that this does not mention the behavior at other places or times.

The particle-wave debate was largely settled in favor of a wave around 1800 with Arago’s discovery of Poinclair’s dot. The particle theory later returned to serious consideration with the success of Einstein’s explanation of the photo-electric effect.

I don’t care to debate the matter at this time so I am content to remain wrong. Anyhow, it won’t be decided here.

 

5 hours ago, studiot said:

The slit(s) experiment require a single plane wave in the space between the source and the slit(s) barrier.

So interference is not possible or observable in that space.
Insertion of an observation screen will show an even illumination.

I have one point of disagreement about your discussion of light. You can’t get an evenly distributed light from an undisturbed coherent light source. Try it yourself with a laser pointer. Red works best because of its longer wavelength. The light appears as many minute dots on a screen.

[studiot]

32 minutes ago, bangstrom said:

The particle-wave debate was largely settled in favor of a wave around 1800 with Arago’s discovery of Poinclair’s dot. The particle theory later returned to serious consideration with the success of Einstein’s explanation of the photo-electric effect.

I don’t care to debate the matter at this time so I am content to remain wrong. Anyhow, it won’t be decided here.

 

I have one point of disagreement about your discussion of light. You can’t get an evenly distributed light from an undisturbed coherent light source. Try it yourself with a laser pointer. Red works best because of its longer wavelength. The light appears as many minute dots on a screen.

 

33 minutes ago, bangstrom said:

I have one point of disagreement about your discussion of light. You can’t get an evenly distributed light from an undisturbed coherent light source. Try it yourself with a laser pointer. Red works best because of its longer wavelength. The light appears as many minute dots on a screen.

So what ?

How does that disagree with what I said  and where exactly did I say you could ?

[swansont]

44 minutes ago, bangstrom said:

The particle-wave debate was largely settled in favor of a wave around 1800 with Arago’s discovery of Poinclair’s dot. The particle theory later returned to serious consideration with the success of Einstein’s explanation of the photo-electric effect.

You persist in focusing on the wrong argument 

 

44 minutes ago, bangstrom said:

I don’t care to debate the matter at this time so I am content to remain wrong. Anyhow, it won’t be decided here.

Yes, causality is a separate issue.

[bangstrom]

9 hours ago, studiot said:

The slit(s) experiment require a single plane wave in the space between the source and the slit(s) barrier.

So interference is not possible or observable in that space.
Insertion of an observation screen will show an even illumination.
Insertion of a blocking object may show diffraction effects around its edges or in its shadow zone

 I=ε0

I have underlined the statement I have in mind. When you say "single plane wave" I assume that means both even illumination and in the same direction  and I assume by "in that space" you mean the space between the light source and the double slits.

It is my observation that interference is possible and observable on a screen inserted in that space with coherent light. Specifically, with laser light because the light on the screen is not even. The light appears as many minute dots rather than uniform. The dots are too closely spaced to disrupt the interference pattern that forms after passing through the double slits but the the original, undisturbed light source is not interference free.

[swansont]

1 hour ago, bangstrom said:

It is my observation that interference is possible and observable on a screen inserted in that space with coherent light. Specifically, with laser light because the light on the screen is not even. The light appears as many minute dots rather than uniform. The dots are too closely spaced to disrupt the interference pattern that forms after passing through the double slits but the the original, undisturbed light source is not interference free.

Laser light is not a plane wave; usually it has a gaussian profile, and some (e.g. laser diodes) diverge because of diffraction. The dots are likely laser speckle

[Markus Hanke]

5 hours ago, bangstrom said:

Anyhow, it won’t be decided here.

You are still missing the crucial point: there is nothing to be decided. Quantum objects sometimes exhibit particle-like behaviour, and sometimes wave-like behaviour, while not “being” either of those things. It’s not an “A or B” kind of situation, but a duality. 

[studiot]

1 hour ago, bangstrom said:

I have underlined the statement I have in mind. When you say "single plane wave" I assume that means both even illumination and in the same direction  and I assume by "in that space" you mean the space between the light source and the double slits.

It is my observation that interference is possible and observable on a screen inserted in that space with coherent light. Specifically, with laser light because the light on the screen is not even. The light appears as many minute dots rather than uniform. The dots are too closely spaced to disrupt the interference pattern that forms after passing through the double slits but the the original, undisturbed light source is not interference free.

I have already confirmed that you understand I am referring to the wave approaching the slits from the source, by specifying in that space.

As with diffraction and interference, there are differences between polarisation and planarity (plane waves), and coherence.
Some waves cannot be polarised, but can still come in planar form, for example longitudinal waves.

I'm suprised you respond to my specifying a plane wave by offering a laser, since as swansont has already noted, they are not plane sources.
I agree that small optical lasers yield granular images on screen, though if you had an integrating screen over time you would achieve even illumination.
True plane waves would indeed illuminate a detector screen evenly.
In fact I do not know of any light sources that directly emit plane waves.
Most light sources approximate to point sources (there are no true point sources).
Such sources usually generate circular or spherical waves.
A good guide to the type of wave is the shape of the wavefront - linear, circular, spherical etc.
These have to be generated by special conditioning of the light from the source.
So, if you do not know the reason for working with them, it would be suprising that you do not ask.

The Arago experiment you referred to (the bright centre dot) is shown by Wiki to employ a point source.
Do you think there would also be a dot if the waves were planar ?

 

 

https://en.wikipedia.org/wiki/Arago_spot

 

However Arago is also known for lots of careful experiments in collaboration with Fresnel using plane waves.

 

All of this shows, as we have been telling you, that light has some wave character, some corpusucular character and some quantum character and possibly some additional characters as well.

 

[bangstrom]

3 hours ago, studiot said:

I'm suprised you respond to my specifying a plane wave by offering a laser, since as swansont has already noted, they are not plane source

This is the source of my confusion. I am not familiar with the term “plane” wave. From your later description, what you call a “plane” wave sounds like what I am familiar with as a longitudinal wave, a scalar wave, a compression wave, or generally something like a sound wave. 

  I was trying to divine what you meant by “plane” wave in this statement,” The slit(s) experiment require a single plane wave in the space between the source and the slit(s) barrier. “

The slits usually use light as a source so the word “plane” wave must be something that applies to light such as uniform. If a plane wave is what I am familiar as a longitudinal wave, the statement makes no sense.

Did you use the wrong word here?

3 hours ago, studiot said:

The Arago experiment you referred to (the bright centre dot) is shown by Wiki to employ a point source.
Do you think there would also be a dot if the waves were planar ?

If by planar you mean planar light (longitudinal) light, I don't think there is such an animal.

If by planar you mean you mean linear polarized light, there should be a dot. 

If by planar you mean sound waves, the dot should be there as what is called a standing wave.

[MigL]

1 hour ago, bangstrom said:

I am not familiar with the term “plane” wave.

How about 'google'; are you familiar with that ?

"n physics, a plane wave is a special case of wave or field: a physical quantity whose value, at any moment, is constant over any plane that is perpendicular to a fixed direction in space."

Plane wave - Wikipedia

[bangstrom]

2 hours ago, MigL said:

How about 'google'; are you familiar with that ?

"n physics, a plane wave is a special case of wave or field: a physical quantity whose value, at any moment, is constant over any plane that is perpendicular to a fixed direction in space."

Plane wave - Wikipedia

Thanks for the information. I forgot about my old friend-What's his name?- Google?

[studiot]

On 10/24/2021 at 3:30 AM, bangstrom said:

This is the source of my confusion. I am not familiar with the term “plane” wave. From your later description, what you call a “plane” wave sounds like what I am familiar with as a longitudinal wave, a scalar wave, a compression wave, or generally something like a sound wave. 

  I was trying to divine what you meant by “plane” wave in this statement,” The slit(s) experiment require a single plane wave in the space between the source and the slit(s) barrier. “

The slits usually use light as a source so the word “plane” wave must be something that applies to light such as uniform. If a plane wave is what I am familiar as a longitudinal wave, the statement makes no sense.

Did you use the wrong word here?

If by planar you mean planar light (longitudinal) light, I don't think there is such an animal.

If by planar you mean you mean linear polarized light, there should be a dot. 

If by planar you mean sound waves, the dot should be there as what is called a standing wave.

70 something posts into this thread an it sounds like you are actually asking a question, instead of laying down incorrect law.

Progress.

So you have been told that light is a transverse wave (swansont again).

The point of using planar waves in the models is that they don't spread out.

They are particularly simple to work with because the three dimensions can be separated mathematically.

All segments of the wavefront have the same direction of propagation, and all the oscillatory action take place in planes that the line of direction is normal to.
Each plane is a plane of constant phase.

 

A

[studiot]

I also meant to say that phase is one of the important basic characteristics of all waves, shape is another and strength is a third.

Simple plane waves have the characteristic of not loosing strength they propagate because they don't spread out.

[bangstrom]

10 hours ago, studiot said:

70 something posts into this thread an it sounds like you are actually asking a question, instead of laying down incorrect law.

Progress.

If you prefer, here is something more Socratic.

You posted a picture of two pages from a book. On page 358 “Polarized Light” it states:

"(1) Two beams of light plane-polarized in mutually perpendicular planes do not produce interference fringes under any condition."

Why do they not produce interference?

One possibility proposed by Fresnel and Arago is that the two beams interfere so rapidly and in such a random manner that the light is no longer coherent.

Another possibility proposed by Scully and Druhl is that polarization places a which-path tag on the individual photons providing certainty of their positions and the mere possibility of obtaining such information destroys interference.

Neither of these explanations is complete as stated. I am just suggesting possibilities but what would be your explanation?

 

Also, the answer to the question is relevant to the Yoon Ho-Kim et al double slit experiment among others for which the Scully and Druhl explanation applies.

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

Quote from wiki-

“ Significance"

"This result is similar to that of the double-slit experiment, since interference is observed when it is not known from which slit the photon originates, while no interference is observed when the path is known.”