The Observer Effect

[KJW]

1 hour ago, joigus said:

In your answer it seems clear that you invoke the observer in order to distinguish the alternative that comes out of the measurement:

Yes, the observer does have an important role, though it is a passive role.

 

 

1 hour ago, joigus said:

Why do you need an observer?

We don't need observers, we are observers. Without observers, the measuring devices would still do their thing, only there would no longer be any need for the Copenhagen interpretation. The Copenhagen interpretation suggests that it is physics that determine the particular eigenstate that we observe, whereas the many-worlds interpretation implies that it is not physics but the observer that determines the particular eigenstate that we observe, simply through the act of observation.

 

 

1 hour ago, joigus said:

But why do many observers agree upon the same alternative having been realised? Why do these multiple observers all get split into the same "congruence of observers" seeing the same thing?

Because the microscopic quantum state, the macroscopic state of the measurement device, all the observers observing the measurement device, and the world that contains all of these are in an entangled state. Considering Schrödinger's cat, the cat becomes entangled with the radioactive source, and when I open the box, I become entangled with the cat and the radioactive source. By becoming entangled with the cat, I no longer observe the cat state and the radioactive source state as a superposition of states. Any other observers who observe the cat becomes entangled with the same cat state as me, as well as becoming entangled with me, and therefore observes the same cat state and radioactive source state as me.

 

 

Edited December 3, 2023 by KJW

[exchemist]

12 hours ago, Genady said:

QFT is a mathematical framework. QED is a physical model.

Aha, thanks very much. So would it be fair to say QFT is the mathematical underpinning of QED? I suppose it also plays the same role in QCD, doesn't it?  

 

 

[joigus]

9 hours ago, KJW said:

Yes, the observer does have an important role, though it is a passive role.

 

 

We don't need observers, we are observers. Without observers, the measuring devices would still do their thing, only there would no longer be any need for the Copenhagen interpretation. The Copenhagen interpretation suggests that it is physics that determine the particular eigenstate that we observe, whereas the many-worlds interpretation implies that it is not physics but the observer that determines the particular eigenstate that we observe, simply through the act of observation.

 

 

Because the microscopic quantum state, the macroscopic state of the measurement device, all the observers observing the measurement device, and the world that contains all of these are in an entangled state. Considering Schrödinger's cat, the cat becomes entangled with the radioactive source, and when I open the box, I become entangled with the cat and the radioactive source. By becoming entangled with the cat, I no longer observe the cat state and the radioactive source state as a superposition of states. Any other observers who observe the cat becomes entangled with the same cat state as me, as well as becoming entangled with me, and therefore observes the same cat state and radioactive source state as me.

 

 

OK. Thanks very much. Again, one thing I've noticed is people spending considerable time explaining how they interpret this interpretation. You, for example, introduce distinctions like observers playing "a passive role", as opposed --I assume-- to an active role. Now, I don't know what that means, or how is that supposed to be a part of the physics of it. I don't know how to include that in the Schrödinger equation either. Perhaps you mean the quantum system doing something on the apparatus, but the apparatus is doing nothing on the quantum system?

You go on to remind me that it's not that we need observers, but that we are observers. Well, again you seem to insist on the old misguided concept of observing, as if it were some kind of distinct physical influence. Never mind "needed" or "existing" (inevitable). I suspect it has to do with your distinction active/passive. But we know it should not be about observing anything; unless it can be explained in terms of interacting with the system in a certain way (a way that involves decoherence between the salient components of the state). These components involve a perfect correlation between certain macroscopic states and their corresponding "measured" microscopic states.

If you are happy with physics providing you conditional probabilities (in the quantum version, conditional amplitudes), then it's ok. Quantum mechanics is linear and unitary. The combination of both aspects gives you, quite unambigously, a macroscopic universe that is "contaminated" of splitting alternatives.

What, in the mathematics of it, tells me I am the observer that sees one (and not the other)? In other words, what physical variable is the one that tells me I'm in one of the components of the relative state that speaks of conditional probabilities?

You can ask this question over and over to people who abide by this interpretation, or any one of the manifold versions of it, and all you hear is what to me sounds like "let's not talk about that".

That's why I'm not totally satisfied.

Are you?

Edited December 3, 2023 by joigus
minor correction

[Genady]

1 hour ago, exchemist said:

Aha, thanks very much. So would it be fair to say QFT is the mathematical underpinning of QED? I suppose it also plays the same role in QCD, doesn't it?  

 

 

You are right. Yes, it is, and yes, it does. It is the mathematical foundation of the entire Standard Model, including Higgs.

[studiot]

The ancient greeks allegedly threw someone of a boat into the sea for releasing the discovery of irrational numbers like Pi, they were so frightened of them.

Today no one is suprised by them or the fact that you can easily get to them by drawing the diagonal of a square, even though you can't actually write the number down.

The Copenhagen 'interpretation' was meant to avoid a similar crisis, but actually did not do so.

I have shown a simple mechanical example which should dispel the magic and woo associated with decoherence.
Obviously it is not exactly the same but then projectile mechanics and quantum mechanics are not the same and neither is the same as the diagonal of a square so the actual realisation is different in each case.

[Luc Turpin]

On 11/30/2023 at 7:26 AM, joigus said:

all of them decohering and making the entire universe decohere with respect to the teeny tiny coherent quantum state that you prepared.

Please substantiate

 

On 11/30/2023 at 8:55 PM, swansont said:

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. 

I am still having difficutly with what interacts with what! If I have a detector functioning without collecting data, then there is interaction and the interference pattern disapears! And if I place a non-detector obtject instead, do I get an interference pattern? A meaurement has not been made! or am I again wrong on the definition of a term measurement whereby measurement does not mean an actual measurement. Also, is the non-detector object considered a quantum system, and if so, then the pattern disapears? or not?

 

On 12/1/2023 at 4:29 AM, joigus said:

 

Measurement not always involves interaction. Not always involves decoherence.

 

Please substantiate! when does it and when does it not!

On 12/2/2023 at 7:50 AM, joigus said:

The brain is but one particular physical system riddled with decoherence. 

So brain is a quantum system! right? I seems obvious, but I have been wrong so much, that I need a confirmation! I will also push the boundary, be very contentious and claim that where is consciousnes in the brain has not yet been determined. Leaving open that it might be outside.

On 11/30/2023 at 8:48 PM, Luc Turpin said:

 

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

From Studiot's book exerpt: is it still a valid statement

[swansont]

Just now, Luc Turpin said:

I am still having difficutly with what interacts with what! If I have a detector functioning without collecting data, then there is interaction and the interference pattern disapears!

The detector must reveal "which path" information for the pattern to disappear. Having a detector in place doesn't do this, quite obviously, because we can see an interference pattern when it doesn't reveal that information. Seeing a pattern indicates detection.

Just now, Luc Turpin said:

And if I place a non-detector obtject instead, do I get an interference pattern? A meaurement has not been made! or am I again wrong on the definition of a term measurement whereby measurement does not mean an actual measurement. Also, is the non-detector object considered a quantum system, and if so, then the pattern disapears? or not?

If you block one slit you know light went through the other, even if you don't see the light hitting whatever is blocking the slit. There are more elaborate "which path" schemes used in some experiments (e.g. using polarizers and polarized beam splitters) but it's always a matter of whether there is one path or two.

[Luc Turpin]

19 minutes ago, swansont said:

The detector must reveal "which path" information for the pattern to disappear. Having a detector in place doesn't do this, quite obviously, because we can see an interference pattern when it doesn't reveal that information. Seeing a pattern indicates detection.

 

Interact or reveal information on path? a functioning detector not registering is interacting, but not revealing information; unless it is revealing it to the universe??? the pattern still disapears.  Again, I am trying to determine the line when the pattern disapears and when it does not! thank you for your patience with me!

[Genady]

32 minutes ago, Luc Turpin said:

If I have a detector functioning without collecting data, then there is interaction and the interference pattern disapears!

You should also be aware that the situation is not necessarily binary, i.e., pattern or no-pattern. Depending on the interaction, the result can be any of the continuous set of possibilities between a clear interference pattern and no signs of any interference at all.

8 minutes ago, Luc Turpin said:

Interact or reveal information on path? a functioning detector not registering is interacting, but not revealing information; unless it is revealing it to the universe??? the pattern still disapears.  Again, I am trying to determine the line when the pattern disapears and when it does not! thank you for your patience with me!

Let's take an extreme scenario of a detector that can be in three states: 0 - default, L - the particle went through the left slit, R - the particle went through the right slit. Let' assume that the detector is perfect, i.e., starting from the state 0 it always changes to either L or R depending on the interaction with the particle. Immediately after going to the L or to the R state, the detector self-destructs. Then, another such detector interacts with the next particle. And so on.

There will be no interference pattern in this scenario.

[swansont]

34 minutes ago, Luc Turpin said:

Interact or reveal information on path? a functioning detector not registering is interacting, but not revealing information; unless it is revealing it to the universe??? the pattern still disapears.  Again, I am trying to determine the line when the pattern disapears and when it does not! thank you for your patience with me!

Your summary is incorrect. We can see an interference pattern when the light can go through both slits. If there's a pattern, then it has been detected; I hope that's obvious. Whether it's recorded on an electronic detector like a CCD, or it's just photons scattering off the wall into our eyes, the pattern has been detected. That pattern is there whether or not the detector is on.

The pattern goes away when, in principle, you could tell which slit the light went through. The interference pattern depends on each photon being able to go through both slits.

[studiot]

Personally I think slit experiments are about the worst experiments for the study of quantum v non quantum effects.

There are just so many factors to consider.

There is the number of slits, the size of the slits, the spacing of the slits, the distance from the source to the barrier and from the barrier to the detector, there is the positioning of the detector, there is the thickness of the barrier, there is the 'sharpness' of the edges of the slits.

What happens when there is no detector ?

You can find the answer to this out with water waves, but not with light waves.

 

 

[swansont]

OTOH it's a very stark difference when you have a decent setup. There's interference (multiple orders of it with a laser) or not.

[joigus]

1 hour ago, studiot said:

The ancient greeks allegedly threw someone of a boat into the sea for releasing the discovery of irrational numbers like Pi, they were so frightened of them.

Today no one is suprised by them or the fact that you can easily get to them by drawing the diagonal of a square, even though you can't actually write the number down.

The Copenhagen 'interpretation' was meant to avoid a similar crisis, but actually did not do so.

I have shown a simple mechanical example which should dispel the magic and woo associated with decoherence.
Obviously it is not exactly the same but then projectile mechanics and quantum mechanics are not the same and neither is the same as the diagonal of a square so the actual realisation is different in each case.

One of the good things about having these discussions online is that nobody will end up too wet.

18 minutes ago, Luc Turpin said:

On 11/30/2023 at 1:26 PM, joigus said:

all of them decohering and making the entire universe decohere with respect to the teeny tiny coherent quantum state that you prepared.

Please substantiate

How much maths am I allowed to use? Schematically coherence in a state is a precise match between 2 alternatives embodying distinguishable results (mutually orthogonal): ψ1 and ψ2 . These states being coherent means that there is a very steady correlation between their oscillatory states. IOW, they oscillate in phase. These states usually involve preparation and can be mathematically represented by a linear superposition \( \psi=\) ψ1+ψ2. Before the rest of the universe interacts with our \( \psi \)-system, we can represent the situation by a wave function \( \left( \psi_{1}+\psi_{2} \right) \times \Phi \), \( \Phi \) representing the quantum state of the rest of the universe. When this system interacts with the rest of the universe so as to record what the microsystem \( \psi \) is doing, broadly speaking what happens is that the rest of the universe (environment, measuring apparatus, any friends watching it all, etc) records it by means of some macroscopic recording states \( \Phi_{1} \) \( \Phi_{2} \) while getting entangled with the quantum system: \( \psi_{1}\Phi_{1}+\psi_{2}\Phi_{2} \). These states are suposed to be semi-classical at some level of amplification, which means that while all this is happening, they oscillate in a crazy way so that the different components of the microscopic wave function can no longer "read" each other's phase.

2 hours ago, Luc Turpin said:

On 12/1/2023 at 10:29 AM, joigus said:

 

Measurement not always involves interaction. Not always involves decoherence.

 

Please substantiate! when does it and when does it not!

Preparations do not involve decoherence. You just filter the state that you want, and the salient state has certain controlled values of their physical parameters. Typically it involves momentum and/or spin: 

(from Galindo&Pascual, Quantum Mechanics I, a book I do not recommend to learn quantum mechanics, and has probably been outdated.)

I hope that helped, 

[studiot]

Chapter 15 of the second book I recommended by Prof Mills is all about this.

Ch15 treats the data, the observer, the observation, the 'watcher', the role of consciousness, superposition, what is included in the wave function and more.

The maths is not as difficult as Joigus' although he still makes makes use of some specialist quantum notation  -  the bra and ket notation, identified by the < and > symbols.

[KJW]

11 hours ago, joigus said:

You, for example, introduce distinctions like observers playing "a passive role", as opposed --I assume-- to an active role. Now, I don't know what that means, or how is that supposed to be a part of the physics of it.

This thread is titled "The Observer Effect", so in order to meaningfully discuss the observer effect, one needs to distinguish between observers playing a passive role and observers playing an active role. An active role means that the conscious observer somehow affects the measurement of the quantum system so as to collapse the wavefunction. A passive role means that the quantum system affects the measuring device in a way that produces a macroscopic state that through perception affects the mind of the conscious observer. As conscious observers, we have a somewhat solipsistic subjective point of view that needs to be taken into consideration when considering an objective reality.

 

 

11 hours ago, joigus said:

You go on to remind me that it's not that we need observers, but that we are observers. Well, again you seem to insist on the old misguided concept of observing, as if it were some kind of distinct physical influence. Never mind "needed" or "existing" (inevitable). I suspect it has to do with your distinction active/passive.

I'm not applying any "old misguided" concept of observing. I'm certainly not suggesting that it is some kind of physical influence. Indeed, I said precisely the opposite. That is why I consider it important to distinguish between the active and passive role.

 

 

11 hours ago, joigus said:

Perhaps you mean the quantum system doing something on the apparatus, but the apparatus is doing nothing on the quantum system?

I hadn't really considered whether or not the measuring apparatus is doing anything to the quantum system. Wavefunction collapse is ultimately about what the quantum system is doing to the measuring apparatus. In the many-worlds interpretation, there is no wavefunction collapse and that a superposition of quantum states leads to a superposition of measuring apparatus states which leads to a superposition of observer states. It is the superposition of observer states, entangled with the superposition of measuring apparatus states and quantum states that is the essence of the many-worlds interpretation. The role of the observer is then to answer the question: why do we not observe the superposition of observer states, measuring apparatus states, and quantum states?

 

 

11 hours ago, joigus said:

But we know it should not be about observing anything; unless it can be explained in terms of interacting with the system in a certain way (a way that involves decoherence between the salient components of the state). These components involve a perfect correlation between certain macroscopic states and their corresponding "measured" microscopic states.

You've indicated that the many-worlds interpretation is not falsifiable. The reason it is not falsifiable is because the many worlds are not observable (if they were observable, there would be no question about existence). Therefore, it is about observation. At the heart of the matter is where we draw the line between objective reality and subjective observation.

 

 

11 hours ago, joigus said:

I don't know how to include that in the Schrödinger equation either.

...

What, in the mathematics of it, tells me I am the observer that sees one (and not the other)? In other words, what physical variable is the one that tells me I'm in one of the components of the relative state that speaks of conditional probabilities?

There is nothing in the mathematics that says that a measurement selects one eigenstate from the set of possible eigenstates. The mathematics only identifies the set of eigenstates. The selection of a particular eigenstate from the set of eigenstates is artificially imposed on the basis of observation. The mathematics ultimately implies the many-worlds interpretation, or as it was originally called, the "relative state formulation".

 

 

Edited December 3, 2023 by KJW

[studiot]

1 hour ago, KJW said:

here is nothing in the mathematics that says that a measurement selects one eigenstate from the set of possible eigenstates. The mathematics only identifies the set of eigenstates. The selection of a particular eigenstate from the set of eigenstates is artificially imposed on the basis of observation. The mathematics ultimately implies the many-worlds interpretation, or as it was originally called, the "relative state formulation".

I think you need to peer a little more deeply into the mathematics.

[Luc Turpin]

8 hours ago, joigus said:

How much maths am I allowed to use? Schematically coherence in a state is a precise match between 2 alternatives embodying distinguishable results (mutually orthogonal): ψ1 and ψ2 . These states being coherent means that there is a very steady correlation between their oscillatory states. IOW, they oscillate in phase. These states usually involve preparation and can be mathematically represented by a linear superposition ψ=  ψ1+ψ2. Before the rest of the universe interacts with our ψ -system, we can represent the situation by a wave function (ψ1+ψ2)×Φ , Φ representing the quantum state of the rest of the universe. When this system interacts with the rest of the universe so as to record what the microsystem ψ is doing, broadly speaking what happens is that the rest of the universe (environment, measuring apparatus, any friends watching it all, etc) records it by means of some macroscopic recording states Φ1 Φ2 while getting entangled with the quantum system: ψ1Φ1+ψ2Φ2 . These states are suposed to be semi-classical at some level of amplification, which means that while all this is happening, they oscillate in a crazy way so that the different components of the microscopic wave function can no longer "read" each other's phase.

Preparations do not involve decoherence. You just filter the state that you want, and the salient state has certain controlled values of their physical parameters. Typically it involves momentum and/or spin: 

I will take this as a yes! the universe interact's with the system and vice versa

9 hours ago, swansont said:

Your summary is incorrect. We can see an interference pattern when the light can go through both slits. If there's a pattern, then it has been detected; I hope that's obvious. Whether it's recorded on an electronic detector like a CCD, or it's just photons scattering off the wall into our eyes, the pattern has been detected. That pattern is there whether or not the detector is on.

The pattern goes away when, in principle, you could tell which slit the light went through. The interference pattern depends on each photon being able to go through both slits.

Here is what I understand:

• An interference pattern on the back plate when light goes through both slits, even when there is an unplugged detector between slit screen and back plate
• No inteference pattern on the back plate when light goes through only one slit, or a detector positioned between slit screen and back plate that is in the "on" position and whether or not it is registering 

This is what I got from above posts and information gleaned from other sources.

Note: I am a generalist seeking to understand the essential of QM and possible remifications with other science disciplines. Patience with me is imperative. The benefit of helping me out may be to enable you to seek out the essence of QM  and present it in a way understandable to almost anyone. Also, many words you use have a certain meaning that are obvious to you, but not to me.  I will get use to it. I am in the early semantic stage of my quest for knowledge.

[KJW]

1 hour ago, Luc Turpin said:

Here is what I understand:

• An interference pattern on the back plate when light goes through both slits, even when there is an unplugged detector between slit screen and back plate
• No inteference pattern on the back plate when light goes through only one slit, or a detector positioned between slit screen and back plate that is in the "on" position and whether or not it is registering 

The problem with this reply is that it depends on precisely what an "unplugged" or "on" detector does to the light, the term "detector" not being sufficiently specific. It may be useful to consider the following: Suppose one places a horizontally oriented polariser in one slit, and a vertically oriented polariser in the other slit. Then there is no interference pattern even though no which-slit detection has been performed. Each photon has which-slit information by virtue of its polarisation, which is sufficient to prevent the interference pattern even when the polarisation is not measured. The quantum states from both slits are orthogonal, and there is no interference between orthogonal states.

Perhaps you should also explore quantum eraser experiments.

 

 

3 hours ago, studiot said:

I think you need to peer a little more deeply into the mathematics.

I'm quite confident about what I said... or are you telling me you can mathematically predict quantum outcomes?

 

 

Edited December 4, 2023 by KJW

[joigus]

13 hours ago, KJW said:

This thread is titled "The Observer Effect", so in order to meaningfully discuss the observer effect, one needs to distinguish between observers playing a passive role and observers playing an active role.

And a koala is also called "koala bear" even though it has nothing to do with bears. It's a marsupial. That would lead us into the fascinating world of misnomers.

The loss of coherence that connects the quantum domain with the classical domain has to do with interaction, not with the observation of anything. There are planets out there that nobody will ever visit, and electrons, protons, etc, are doing their business giving rise to physics that a potential observer would interpret as classical, because they are in the classical or quasi-classical regime.

Again, it's not about observing, it's about quasi-classical interactions.

13 hours ago, KJW said:

I'm certainly not suggesting that it is some kind of physical influence. Indeed, I said precisely the opposite. That is why I consider it important to distinguish between the active and passive role.

 

Ok. I have no doubt now you've picked this up from somewhere, so I've been looking it up. A minority of people seem to use that distinction "passive" vs "active". Not that it has aroused much interest at all. It seems to come from D. H. Zeh in connection with the Everett interpretation. The rest of the community doesn't seem to be paying much attention to it. I'm certainly not. I don't find such distinction useful. It's only people paying heed to the many-worlds (or relative-state) interpretation of QM that seem to find it necessary. And, then again, not all of them.

13 hours ago, KJW said:

I hadn't really considered whether or not the measuring apparatus is doing anything to the quantum system.

You should. The interaction Hamiltonian depending on the coordinates of the apparatus had better commute with the observable it's measuring. Otherwise it's just smearing things out. If it does, it can't change the statistical weights. If it doesn't... I've reviewed this over and over and over...

And over. And what's inescapable is that it doesn't change the weights (the diagonal elements of the density matrix). But it does change (and how!) the non-diagonal elements of it. And guess how we call the non-diagonal elements of the density matrix. Yes, you guessed it. "Coherences". And that's no misnomer: It contains all the possible interference terms. If the interaction is "classical enough" (the mechanical action of order many times \( \hbar \) ), then the interference terms die out in ridiculously short times.

So yes, in these cases the apparatus does something on the quantum system. And viceversa. But it's very different to telling us anything like probability of cat dead = 1 and probability of cat alive = 0. Superpositions should live forever.

Now, there's a series of paths you can take from there, but I'm afraid they all involve some kind of semantic orgy I'm not willing to get involved in: Pick your alternative (many-worlds, double solution, transactional,...) and adhere to the litany the "natives" use. 

Not for me. I prefer to say, "I don't know".

13 hours ago, KJW said:

You've indicated that the many-worlds interpretation is not falsifiable. The reason it is not falsifiable is because the many worlds are not observable (if they were observable, there would be no question about existence). Therefore, it is about observation. At the heart of the matter is where we draw the line between objective reality and subjective observation.

 

Amen to that. Except the bit about "observation".

13 hours ago, KJW said:

There is nothing in the mathematics that says that a measurement selects one eigenstate from the set of possible eigenstates. The mathematics only identifies the set of eigenstates. The selection of a particular eigenstate from the set of eigenstates is artificially imposed on the basis of observation.

Ditto. Measurement in the formalism of QM selects a basis, not a state from that basis.

13 hours ago, KJW said:

The mathematics ultimately implies the many-worlds interpretation, or as it was originally called, the "relative state formulation".

 

I disagree. There are better alternatives, but they haven't been considered nearly as seriously as they deserve. But that's my view.

Edited December 4, 2023 by joigus
minor addition

[AIkonoklazt]

On 11/29/2023 at 5:02 PM, 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.

When you measure, you could only measure one state. The wave is multiple simultaneous states.

This limitation in measurement is what "collapses" it.

[joigus]

40 minutes ago, joigus said:

Amen to that. Except the bit about "observation".

OK. To be more precise. It shouldn't be about observation. I should be about interaction. 

Let me put it this way: It is as much about observation as it is about interaction. There's no reason to think observation cannot be understood in terms of interaction.

The very reason --whatever it might be-- that we still have to say "when we observe, measure, interact with... the particle, it goes this way" is a sympton that even though everything works for all practical purposes, there is something we would like to understand better. Some of us, anyway.

[Genady]

35 minutes ago, AIkonoklazt said:

When you measure, you could only measure one state. The wave is multiple simultaneous states.

This limitation in measurement is what "collapses" it.

When we measure, we could only measure one value. The question of "collapse" is how it causes the multiple simultaneous states to become a definite state corresponding to the measured value.

[Luc Turpin]

On 12/3/2023 at 5:29 AM, joigus said:

That's why I'm not totally satisfied.

 

You often say in your posts that you are not totally satisfied!!! Can you subtantiate?

[studiot]

13 hours ago, KJW said:

I'm quite confident about what I said... or are you telling me you can mathematically predict quantum outcomes?

Joigus has answered you

4 hours ago, joigus said:

You should. The interaction Hamiltonian depending on the coordinates of the apparatus had better commute with the observable it's measuring. Otherwise it's just smearing things out. If it does, it can't change the statistical weights. If it doesn't... I've reviewed this over and over and over...

 

4 hours ago, joigus said:

The loss of coherence that connects the quantum domain with the classical domain has to do with interaction, not with the observation of anything.

Interaction is the correct word.

 

Luc is one of the few percentage of new arriivals who come here with an open mind and a willingness to listen and learn, rather than the "big I am and know it all" attitude so many arrive with.

As such I am trying to show him the respect he deserves, particularly observing the rules about (mainly) mainstream answers. And also to acknowledge things we genuinely don't know.

4 hours ago, joigus said:

Not for me. I prefer to say, "I don't know".

+1 for a model answer from joigus, even thjough I don't quite agree with all of it.

 

The question of  'what inteferes with what?'   if there is only a single wave function is still open.

In a quantum system there are many wavefunctions so how do we construct the system wave function ?

 

4 hours ago, AIkonoklazt said:

The wave is multiple simultaneous states.

As noted for Luc's sake please preserve the difference between a wave function (appropriate here) and a wave.

Aldo the discussion about what is a wave function might be relevant for Luc as it is such strange beast.

[Luc Turpin]

13 hours ago, KJW said:

The problem with this reply is that it depends on precisely what an "unplugged" or "on" detector does to the light, the term "detector" not being sufficiently specific. It may be useful to consider the following: Suppose one places a horizontally oriented polariser in one slit, and a vertically oriented polariser in the other slit. Then there is no interference pattern even though no which-slit detection has been performed. Each photon has which-slit information by virtue of its polarisation, which is sufficient to prevent the interference pattern even when the polarisation is not measured. The quantum states from both slits are orthogonal, and there is no interference between orthogonal states.

Perhaps you should also explore quantum eraser experiments.

 

I am hesitant at responding as I am struggling with comprehension and semantic. Nonetheless, I will try again. 1- The detector is set-up between slit-screen and back-plate,but does not measure anything (in this case, there is an interference pattern on the back-plate -right?).  2- The detector is set-up between slit-screen and back-plate, makes a measurement, but keeps the measurement information to itself (talking as if it was a sentient being!!!); does not share it!! (in this case, no interference pattern-right?There is collapse of the wave-function! right?) 

Also, I am looking for the simplest answer possible as to whether or not a brain and universe are considered quantum systems. I think they are, but would like to get an acknowledgement on this. And if they are both considered quantum systems, they can QM Interact with one another! right? And can I say that the brain is a sub-quantum system to the universe system. Obviously, this is all conditional upon them being quantum systems.

4 minutes ago, studiot said:

Joigus has answered you

 

Interaction is the correct word.

 

Luc is one of the few percentage of new arriivals who come here with an open mind and a willingness to listen and learn, rather than the "big I am and know it all" attitude so many arrive with.

As such I am trying to show him the respect he deserves, particularly observing the rules about (mainly) mainstream answers. And also to acknowledge things we genuinely don't know.

+1 for a model answer from joigus, even thjough I don't quite agree with all of it.

 

The question of  'what inteferes with what?'   if there is only a single wave function is still open.

In a quantum system there are many wavefunctions so how do we construct the system wave function ?

 

As noted for Luc's sake please preserve the difference between a wave function (appropriate here) and a wave.

Aldo the discussion about what is a wave function might be relevant for Luc as it is such strange beast.

Thank you for this! All the time I thought that I was bugging all of you with my simple questions and lack of basic knowledge.  Also, my ego does not bruise a lot as I have too little of it.

Sorry, last quote "Joigus has answered you" was not the right quote. I was refering to studiot indicating my open mindedness