The Observer Effect

[Luc Turpin]

In the double-slit experiment, what collapses the wave-function? The act of measurement? The information obtained from the measurement? Or the observer contemplating the information obtained from the measurement? The first is physical, the second informational and the third attributable to consciousness.

[Genady]

Entanglement with a system in a mixed state.

[Luc Turpin]

Thank you! I will investigate entanglement with a system in a mixed state

[Genady]

Sure. Also look for decoherence.

[swansont]

1 hour ago, Genady said:

Entanglement with a system in a mixed state.

Entanglement does not cause a wave function to collapse. The individual states in an entangled state are undetermined, and superposition does not require entanglement.

[Genady]

6 minutes ago, swansont said:

Entanglement does not cause a wave function to collapse. The individual states in an entangled state are undetermined, and superposition does not require entanglement.

Yes, you're right. Perhaps, interaction with a system in a mixed state would've been a correct answer?

[StringJunky]

It travels through the slits as a mathematically-constructed probability wave and when you measure it you will find the photons position. Because a photons energy is discrete we call it a 'particle' after it's measured. We see a dot on the detector. That equates to a quantum of energy. If we collect lots of these dots, we'll see an interference pattern, which tells us that the photons travel in a wave-like manner because of the mutual interference of the split photon.

Edited November 30, 2023 by StringJunky

[Eise]

5 hours ago, Luc Turpin said:

In the double-slit experiment, what collapses the wave-function?

Is a wave function a physical object, that can collapse? 

2 hours ago, StringJunky said:

(...) because of the mutual interference of the split photon.

I like your description, except this 'split photon'. Photons can't be split. And just imagine how the two half photons find together after the split, carefully avoiding the 'dark zones' on the detection screen... 

[Genady]

7 hours ago, StringJunky said:

when you measure it you will find the photons position

I think that the OP refers to a measurement which detects a slit that photon has went through. Such a measurement would make the wave function to collapse and the interference pattern to disappear.

Edited November 30, 2023 by Genady
syntax

[joigus]

11 hours ago, Luc Turpin said:

In the double-slit experiment, what collapses the wave-function? The act of measurement? The information obtained from the measurement? Or the observer contemplating the information obtained from the measurement? The first is physical, the second informational and the third attributable to consciousness.

What you call "the act of measurement", although I prefer a less exalted term: "interaction with the detector". To be more precise: An interaction that is amplified, so that the carrier of the piece of information "the particle was detected here" is a collectivity of quantum particles, each one with its own particular quantum phase, all of them decohering and making the entire universe decohere with respect to the teeny tiny coherent quantum state that you prepared.

You can explain this with entanglement with the rest of the universe. It can be explained away in terms of entanglement. But not a two-particle entanglement. It's a super-dooper super mega entanglement with millions and billions of thermal states.

That entanglement, if you will.

[swansont]

10 hours ago, Genady said:

Yes, you're right. Perhaps, interaction with a system in a mixed state would've been a correct answer?

Yes

[StringJunky]

7 hours ago, Eise said:

Is a wave function a physical object, that can collapse? 

I like your description, except this 'split photon'. Photons can't be split. And just imagine how the two half photons find together after the split, carefully avoiding the 'dark zones' on the detection screen... 

I wasn't totally happy with that that last bit but left it with no alternative at the time. it interferes with itself on passing through the slits.

[nec209]

Is it just an interpretation that it has probability area, it could be some where here but you cannot measure it or sure where it is, only a general areas where it is?  What evidence do they have it shows it is probability area than say it being every where and when you measured it than it breaks down to point?

I guess the idea you learn in school that particles are like small little Christmas balls are not really true and particles are more like cloud spread out.  BUT the interpretation how cloud is spread out or how big of area is the problem.

 

[studiot]

19 hours ago, Luc Turpin said:

Thank you! I will investigate entanglement with a system in a mixed state

Are you still interested in your query ?

[swansont]

1 minute ago, studiot said:

Are you still interested in your query ?

!

Moderator Note

Luc is having difficulty posting replies; we hope that the expiration of the 24 hour limit on new members fixes the problem 

 

[studiot]

1 hour ago, swansont said:

!

Moderator Note

Luc is having difficulty posting replies; we hope that the expiration of the 24 hour limit on new members fixes the problem 

 

Noted, thanks.

 

@Luc Turpin

Since I will be in bed long before your 24 hours is up and you are lurking in the background here the thoughts of a Nobel Physics Laureate on the subject.
He has a remarkable way of making things clear in plain English, picking out the important points.

 

There are several new ideas that to think about.

 

Please let us know if you understand what a differential equation is.
You need to know what they are, not all the maths that goes with them.

 

 

[Luc Turpin]

I was having difficulty posting on the thread.

Here is my response to comments received earlier for my original post:

I am not sure that I obtained an answer to my question! Here is a different take on it! Again, in the double-slit experiment, if a detector just interacts with photon(s) or electron(s) going through either slits and does nothing else (e.g.  does not keep nor share any information afterward), do we get an interference pattern on the back-plate? I am aware that if you physically ‘unplug’ a detector still placed between the slit-screen and back-plate, one does get an interference pattern! But an “unplugged” detector does not interact with photons or electrons! Right? So, what about a “plugged” detector that solely interacts with photons or electrons and then immediately destroys the information after the interaction without sharing any of it with an observer! Does this create an interference pattern? What I am driving at is who or what is collapsing the wave-function? The detector? The observer? Both? All of this might have a bearing on consciousness and the Observer Effect.

Also, I would like to mention that Genady responded to an earlier version of this text in the following manner: “No it does not”.

To this I would respond, has this been tested out in an experiment?

To Studiot

I do not know how to paste your last comment like others do, so I am responding in the best way that I can.

You indicated in your last post, the following: Please let us know if you understand what a differential equation is.

My answer: I have a very vague appreciation of what a differential equation is.

Also, read with great interest the text that you provided.

Two sections piqued my interest:

1.     “……between an independent behavior of the objects and their interaction with the measuring instruments.” Bohr implies that the interaction is with the instruments (detector) and does not mention the observer.

2.     “By observing the world, we participate in making it”. While this by the author implies that the observer is involved,

This is essentially what I am trying to comprehend. I believe, maybe wrongfully, that if we can have an interference pattern coming out of a two-slit experiment when the detector is “on”, but not releasing any information, that this might have a bearing on “The Observer Effect”. It might help us delineate where the line is drawn. See diagram below.

[swansont]

1 minute ago, Luc Turpin said:

I was having difficulty posting on the thread.

Here is my response to comments received earlier for my original post:

I am not sure that I obtained an answer to my question! Here is a different take on it! Again, in the double-slit experiment, if a detector just interacts with photon(s) or electron(s) going through either slits and does nothing else (e.g.  does not keep nor share any information afterward), do we get an interference pattern on the back-plate? I am aware that if you physically ‘unplug’ a detector still placed between the slit-screen and back-plate, one does get an interference pattern! But an “unplugged” detector does not interact with photons or electrons! Right? So, what about a “plugged” detector that solely interacts with photons or electrons and then immediately destroys the information after the interaction without sharing any of it with an observer! Does this create an interference pattern? What I am driving at is who or what is collapsing the wave-function? The detector? The observer? Both? All of this might have a bearing on consciousness and the Observer Effect.

Also, I would like to mention that Genady responded to an earlier version of this text in the following manner: “No it does not”.

To this I would respond, has this been tested out in an experiment?

There can’t be a pattern without the data. If you destroy the data, you have no pattern. But that has nothing to do with the wave function. The wave function collapses as soon as you detect the photon or electron. 

[Luc Turpin]

Swantsont indicated that there can’t be a pattern without the data. If you destroy the data, you have no pattern. But that has nothing to do with the wave function. The wave function collapses as soon as you detect the photon or electron. 

My response, only the data from the detector is destroyed after measurement, not the overall data from the experiment (e.g. photons going through slits and landing on back-plate remains intact)

[joigus]

20 hours ago, joigus said:

[...] To be more precise: An interaction that is amplified, so that the carrier of the piece of information "the particle was detected here" is a collectivity of quantum particles, each one with its own particular quantum phase, all of them decohering and making the entire universe decohere with respect to the teeny tiny coherent quantum state that you prepared.

[...]

In anticipated response to,

7 hours ago, Luc Turpin said:

if a detector just interacts with photon(s) or electron(s) going through either slits and does nothing else (e.g.  does not keep nor share any information afterward), do we get an interference pattern on the back-plate?

Measurement not always involves interaction. Not always involves decoherence. When it does, it is irreversible. I'd say that almost every measurement that your brain is performing by watching what's going on in the room, involves decoherence.

Some people are happy with the description of the wave function being irreversibly entangled with the rest of the universe. You can lead a happy life thinking that and never do anything wrong as concerns physics.

I'm one of the people who isn't. I need to understand what happened to the rest of the amplitude that "collapsed". Some people do.

 

[studiot]

1 hour ago, joigus said:

In anticipated response to,

Measurement not always involves interaction. Not always involves decoherence. When it does, it is irreversible. I'd say that almost every measurement that your brain is performing by watching what's going on in the room, involves decoherence.

Some people are happy with the description of the wave function being irreversibly entangled with the rest of the universe. You can lead a happy life thinking that and never do anything wrong as concerns physics.

I'm one of the people who isn't. I need to understand what happened to the rest of the amplitude that "collapsed". Some people do.

 

Out of interest did you ever watch the film Sliding Doors ?

[joigus]

1 minute ago, studiot said:

Out of interest did you ever watch the film Sliding Doors ?

I did. I also remember an episode on Frasier using the same idea. Very interesting narrative idea back in the day.

[Luc Turpin]

Thank you all! I now have the answer

[studiot]

10 hours ago, Luc Turpin said:

Thank you all! I now have the answer

I'm glad to hear you have your answer.

Does that mean you do not wish to continue our unfinished conversation ?

[Luc Turpin]

Wish to continue our conversation. I am confused, because some see a role for consciousness in quantum mechanics and I see none.