Entanglement swapping and Bohmian mechanics

[Morbert]

You may consider Huggett’s words below to echo my position precisely. I’m not sure if English is your first language or not, but tense is important here.

Where does Huggett say "Ma's equation (2) is post-measurement"?

[edit] - If you are instead now saying Ma's equation (2) is not post-measurement, and that it is instead (1) rewritten in bell bases of 1&4 and 2&3, great. We can progress the conversation.

 

[Sambuco]

A little bit of humor, that has nothing to do with physics or this thread:

Bill Clinton and the meaning of “Is”

I'm really tempted to say something about monogamy of entanglement, but I'll bite my tongue...

Lucas.

 

[DrChinese]

Where does Huggett say "Ma's equation (2) is post-measurement"?

“But whatever the [measurement] outcome, particles 2 and 4 will end up in a Bell state, and hence be entangled. The [Bell State] measurement of 1 and 3 alone induces the entanglement of 2 and 4; no interaction, either unitary or involving their measurement, occurs between 2 and 4."

For anything else, I think you need to check with Bill. (That’s a joke.)

To be as clear as possible: the physical connection between Ma’s (1) and (2) requires a BSM to occur. Any of these authors would laugh if you told them otherwise. The algebraic derivation you present is completely senseless without the BSM. Hopefully, I’ve left nothing ambiguous about this point. Which as I’ve also said several times, doesn’t matter to this thread.

I know your position, you know mine, but I’m asking questions about Bohmian mechanics. I’m hoping you or @Demystifier or another reader can help me to understand how the BSM causes the entanglement between 2 and 4 (Huggett’s labels), regardless of when the BSM occurs. I’m still working through that, it’s a lot to take in. Especially for someone like myself who has “poor intuition”.

Hey, I’m still interested in your opinion regardless of how wrong you are about the other point. Maybe you support the wrong political party too. (That’s also a joke.)

 

[DrChinese]

I'm really tempted to say something about monogamy of entanglement, but I'll bite my tongue...

Lucas.

Good one!!!

 

[Morbert]

“But whatever the outcome, particles 2 and 4 will end up in a Bell state, and hence be entangled. The measurement of 1 and 3 alone induces the entanglement of 2 and 4; no interaction, either unitary or involving their measurement, occurs between 2 and 4."

This has nothing to do with the fact that (2) is the same state as (1). It is the initial state, expressed in a different basis. Nothing Huggett says contradicts this.

Until you understand this, you have no hope of understanding interpretations premised on it like BM.

 

[DrChinese]

This has nothing to do with the fact that (2) is the same state as (1). It is the initial state, expressed in a different basis. Nothing Huggett says contradicts this.

…you have no hope of understanding interpretations premised on it like BM.

I don’t think BM is premised on it at all. I’ve never seen a Bohmian author outside of this thread write that. You know, like a paper you could quote. (Like those I did.)

So a simple question for you, should be easy: is BM an interpretation? Or a theory? Your opinion.

 

[gentzen]

So a simple question for you, should be easy: is BM an interpretation? Or a theory? Your opinion.

BM is an interpretation.
Consistent histories is an interpretation.
John Cramer's transactional interpretation is NOT an interpretation. It is not a theory either. It is a story or a narrative, intended as a complement to Copenhagen.
Many worlds is a class of interpretations.
Copenhagen are two complementary interpretations.
Orthodox QM is an interpretation.
The minimal statistical interpretation is an interpretation.
GRW is not an interpretation, but a theory.

 

[Demystifier]

Second, of course I don’t believe that the apparatus is entangled with photon B. They are “obviously” in a product state. No experiment is gonna show otherwise.

Assume Photon A is observed to be |- >. We already know photon B will be observed to be |+>. Exactly what spin State is the measurement apparatus now in, post measurement? Writing down an entangled state does not make it entangled.

Ah, I see now the source of confusion. When you say they are in a product state, you are talking about one photon B and one apparatus. Since the apparatus has shown a definite known state, its state effectively collapsed, which effectively destroyed the entanglement. In that sense, even BM accepts that there is an effective collapse and hence an effective destruction of entanglement.

However, that is not what we are talking about. We are not talking about one B and one apparatus. We are talking about a statistical ensemble. The entanglement is observed by measuring correlations, and for that purpose we need to repeat the measurement many times, so we are really dealing with an ensemble. In the ensemble the apparatus sometimes shows one outcome, and sometimes the other. Hence the state of the ensemble does not describe only one of the outcomes, but both outcomes simultaneously. In other words, the system, viewed as a statistical ensemble, is in the superposition. It is this superposition at the ensemble level which is responsible for the entanglement. In other words, the ensemble is not in a product state, even though any individual B+apparatus system is.

To understand all this properly, Bohm is not very important. Much more important is Ballentine, who emphasizes that the quantum state is a description of a statistical ensemble, not of a single system. Without understanding that, the DCES experiment cannot be understood properly. More generally, the ensemble perspective is crucial whenever we do post-selection (as we do in the DCES experiment), because the post-selection changes the ensemble. Without post-selection, we don't see any entanglement in the DCES experiment, do you agree? Hence, at an instrumental level, we may say that the post-selection creates entanglement. (Mathematically, post-selection is represented by a projection, and the projector is not a unitary operator.) That's how even the apparatus becomes entangled.

Or to make the long story short, at the operational instrumental level, entanglement is a property of an ensemble, not of an individual system. At the ensemble level the apparatus does not show only one definite outcome, so the system is not in the product state. Instead the system is in the superposition, namely, in an entangled state.

 

[Demystifier]

Copenhagen are two complementary interpretations.

Which two?

 

[gentzen]

Which two?

The epistemic one, think of
R. Peierls, "In defence of “measurement”", Physics World, 19-20, January (1991).
The contextual one, think of
A. Peres, "Unperformed experiments have no results", Am. J. Phys. 46, 745-747 (1978).

 

[Morbert]

I don’t think BM is premised on it at all. I’ve never seen a Bohmian author outside of this thread write that. You know, like a paper you could quote. (Like those I did.)

In BM, the quantum state yields the pilot wavefunction. If you misrepresent the state after measurement as (2) when it is in fact the state before measurement, you get the wrong state, and hence the wrong pilot wavefunction, and hence the wrong time evolution.

No understanding of quantum states -> no understanding of BM.

 

[Demystifier]

The epistemic one, think of
R. Peierls, "In defence of “measurement”", Physics World, 19-20, January (1991).
The contextual one, think of
A. Peres, "Unperformed experiments have no results", Am. J. Phys. 46, 745-747 (1978).

I think Peres understood QM much deeper than did Peierls. In fact, some version of the Peierls point of view is ruled out by the PBR theorem.

 

[gentzen]

I think Peres understood QM much deeper that did Peierls.

Then why did his close collaborator Christopher Fuchs join the epistemic camp?

In fact, some version of the Peierls point of view is ruled out by the PBR theorem.

Before I learned about density matrices, it was a complete mystery to me how epistemic interpretations can be consistent. So when I read in https://en.wikipedia.org/wiki/Pusey–Barrett–Rudolph_theorem that

This theorem concerns the interpretational status of pure quantum states.

I get the impression that the PBR theorem mostly nails down the true core behind such gut feelings.

Peierls himself seems to occur "explicitly" in the context of the PBR theorem:

The PBR theorem employs the concept of an "antidistinguishable" set of quantum states. [...] This concept was introduced by Carlton M. Caves, Christopher A. Fuchs and Rüdiger Schack under the name "post-Peierls incompatibility", as it generalizes a condition proposed by Rudolf Peierls. An antidistinguishable, or post-Peierls incompatible, set is also sometimes termed a set that allows "conclusive exclusion".

Maybe he made a mistake which could be corrected explicitly. This is at least better than "not even wrong", if you ask me.

 

[Demystifier]

Then why did his close collaborator Christopher Fuchs join the epistemic camp?

Just because Peres was deep doesn't mean his view was completely satisfying. I guess Fuchs thought that Peierls was on the right track and found a way to better develop this perspective.

By the way, one of my first papers on quantum foundations, before I became a "Bohmian", was a critique of a paper by Peres. https://arxiv.org/abs/quant-ph/0109120

 

[Sambuco]

At the ensemble level the apparatus does not show only one definite outcome, so the system is not in the product state. Instead the system is in the superposition, namely, in an entangled state.

I might be misinterpreting something you said, but if we assume the system after the measurement of photon A can be described by a product state for each run, shouldn't the statistical ensemble be described as a mixture of product states?

It seems to me that an entangled state would be appropriate for describing the system after the apparatus interacts with photon A (pre-measurement), but before "cutting" the other branches (effective collapse). However, in that case, I don't see why we couldn't associate that entangled state with each run.

Lucas.

 

[Demystifier]

I might be misinterpreting something you said, but if we assume the system after the measurement of photon A can be described by a product state for each run, shouldn't the statistical ensemble be described as a mixture of product states?

It seems to me that an entangled state would be appropriate for describing the system after the apparatus interacts with photon A (pre-measurement), but before "cutting" the other branches (effective collapse). However, in that case, I don't see why we couldn't associate that entangled state with each run.

Lucas.

That's a good question. Yes, by applying the collapse postulate at the level of ensemble, we can describe it as a mixture, which is not a product. The mixture is a superposition too, but not a coherent superposition. Thus, it does not describe an entangled state, which is consistent with the intuition of @DrChinese. However, my problem with such a description is an explicit violation of unitarity. Namely, unitary evolution of a closed system does not allow a transition from a pure state to a mixed one.

Note also that I am not against a collapse rule (described by a non-unitary projection operator) in an open subsystem. Indeed, as I said previously, that's exactly how one describes the creation of entanglement by post-selection in the DCES experiment. However, the post-selection is done by an observer, who is a part of the system. The post-selection describes how one part of the system (the observer) sees the other part. But at the level of the full closed system, no such non-unitary description should be allowed. At the level of the full system we should have entanglement (coherent superposition), even if it looks like a mixture (incoherent superposition) to an observer who describes the world external to himself.

 

[DrChinese]

If you misrepresent the state after measurement as (2) when it is in fact the state before measurement, you get the wrong state, and hence the wrong pilot wavefunction, and hence the wrong time evolution.

No understanding of quantum states -> no understanding of BM.

No quotes supporting your position -> Just more circular quoting of your own viewpoint. The only paper I have ever seen agreeing with you is that of Mjelva 2024 (who is equally incorrect). Where is all the published support for your assertion? Should be hundreds of easily available references, as you say it's not even a Bohmian thing. On the other hand

DrC: There is no physical connection in the initial setup between the two pairs 1 & 2 and 3 & 4 - no hidden Bell state - any more than there is between any other pair (5 & 6, 7 & 8, etc) in the entire universe. No preferred connection, until and unless there is a subsequent BSM. IFF.
Huggett, Megidish, Ma:
-"We emphasize that in this [initial] state neither 1 nor 2 is entangled with 3 or 4."
-"It is also evidence that the first and last photons [1 & 4] did not somehow share any entanglement before the projection of the middle photons. [2 & 3]"
-"Only after Victor’s measurement [BSM], we can assert the quantum states shared by Alice and Bob."

But I am starting to see why this is important from the Bohmian perspective. @Demystifier has pointed out previously that these pairs exist in a Hilbert space. If that space initially preferred these pairs, then subsequent entanglement operations would make more sense and be easier to explain. Of course, those pairs start out with no preferred connection at all. It's a big universe, and those pairs do not physically overlap or otherwise have any special connection (vis a vis the rest of the universe) until the later BSM.

Why would they? Even accepting Bohmian universal evolution, there is no future lookahead. All nonlocal influences still occur in the present - even with deterministic evolution.

 

[DrChinese]

Indeed, as I said previously, that's exactly how one describes the creation of entanglement by post-selection in the DCES experiment.

Post-selection does not create any entanglement, it merely identifies the final entangled state. I don't even understand why post-selection is relevant in any aspect of this discussion. It is a technical detail as to why and which states are chosen for reporting.

 

[Morbert]

No quotes supporting your position.

i) Ma says (2) is a rewriting of (1). Huggett says (1.4) is a rewriting of (1.3). The literature agrees with me, not you.
ii) It's basic algebra that has been demonstrated to you many times.

Do you accept that quantum states can be expressed using different bases?

 

[Demystifier]

Post-selection does not create any entanglement, it merely identifies the final entangled state. I don't even understand why post-selection is relevant in any aspect of this discussion. It is a technical detail as to why and which states are chosen for reporting.

As I said before, post-selection defines the ensemble, which also defines the state because the state is a description of the ensemble. In this way, the post-selection participates in the creation of the state. But the entanglement is defined as a property of the state, so this also participates in the creation of entanglement.

Of course, the above refers to a subjective notion of state defined by an experimentalist who have chosen to ignore some measurement outcomes. It does not create entanglement in some objective sense independent on the observer. In this objective sense, you are right that it should be irrelevant. But then, if you are looking for an objective description of the whole experiment that does not depend on the observer, then you must use a definition of entanglement that does not depend on the observer. And the only way to do that consistently is to take into account the wave function of the whole closed system, rather than just focusing on one part of the system (the photons) that the observer can directly observe and manipulate. And when you take the whole system into the account, then unitarity implies entanglement with the apparatus. I am aware that this concept does not make sense to you, but that's because you are taking a perspective of an experimentalist, which is not consistent if you also want to take an objective point of view that does not depend on the experimentalist.

So you have to choose, either you are taking a subjective point of view depending on the experimentalist, or you don't. If you do, then post-selection matters. If you don't, then entanglement with the apparatus is a meaningful concept. You have to choose one perspective, and then stick to it consistently. You should not mix two perspectives, because this creates inconsistencies resulting in a wrong impression that DCES is a mystery. It isn't mystery at all, if you are being consistent.

 

[martinbn]

No quotes supporting your position -> Just more circular quoting of your own viewpoint. The only paper I have ever seen agreeing with you is that of Mjelva 2024 (who is equally incorrect). Where is all the published support for your assertion? Should be hundreds of easily available references, as you say it's not even a Bohmian thing.

Suppose you have a qubit prepared in the state $|0\rangle$. If you want to make a measurement in the $\{|+\rangle, |-\rangle\}$ basis, what do you need to do. You write the state in that basis, namely it can be rewritten as $\frac1{\sqrt2}\left(|+\rangle + |-\rangle\right)$. Do you think that this state is the same as the original or not? Do you think that it represents the state of the qubit before or after the measurment?

 

[martinbn]

Post-selection does not create any entanglement, it merely identifies the final entangled state. I don't even understand why post-selection is relevant in any aspect of this discussion. It is a technical detail as to why and which states are chosen for reporting.

Suppose that in the swap set up, nothing is done to photons 2 and 3. But the usual measurments are done on 1 and 4. This goes for all the runs. Then in the data of the results of the measurements on 1 and 4 you can find a subset of runs which show non-classical correlations. According to you that would mean that post-selection can create entanglement just as the swap can. Right?

 

[Demystifier]

Let me also comment the argument by @DrChinese that the computer memory cannot be entangled with anything because it doesn't change, while entanglement in BM implies a change of the particle position. Let me demonstrate by an explicit counterexample that it is not true. We model computer memory by an electron in a double-well potential, with the two potentials widely separated so that each of the two wells can be approximated by a single harmonic oscillator potential. Let us label the two wells as 0 and 1, corresponding to the logical bits 0 and 1. So, when the electron is in the ground state of well 0 the memory is in the logical state 0, and likewise, when the electron is in the ground state of well 1 the memory is in the logical state 1. Since the wells are widely separated, the probability of tunneling from one well to another is negligible. The wave function of the ground state for each well is a standard harmonic oscillator ground state wave function. This wave function is real, it doesn't have an $x$-dependent phase, so the Bohmian velocity associated with this wave function is zero. In other words, the Bohmian position does not change. Since we have two such ground state wave functions, we denote them as $g_0(x)$ and $g_1(x)$. When the memory is in the state 0, the particle B has the wave function $\psi_+(x_B)$, so the full wave function is the product $g_0(x)\psi_+(x_B)$. Likewise, when the memory is in the state 1, the particle B has the wave function $\psi_-(x_B)$, so the full wave function is the product $g_1(x)\psi_-(x_B)$. We assume that the wave functions $\psi_+(x_B)$ and $\psi_-(x_B)$ do not overlap, namely, that $\psi_+(x_B)\psi_-(x_B)=0$ for each $x_B$. But we want to describe the statistical ensemble, so we are describing the system with the superposition
$$g_0(x)\psi_+(x_B) + g_1(x)\psi_-(x_B)$$
The superposition is, by definition, an entangled state. And yet, the Bohmian velocity of the particle with position $x$ is zero. Hence the Bohmian position of this particle does not change, despite the entanglement. But still, the Bohmian position $x$ can vary at the level of ensemble. Some members of the ensemble have a constant position in the region of non-negligible $g_0(x)$, and some in the region of non-negligible $g_1(x)$.

 

[DrChinese]

Suppose you have a qubit prepared in the state $|0\rangle$. If you want to make a measurement in the $\{|+\rangle, |-\rangle\}$ basis, what do you need to do. You write the state in that basis, namely it can be rewritten as $\frac1{\sqrt2}\left(|+\rangle + |-\rangle\right)$. Do you think that this state is the same as the original or not? Do you think that it represents the state of the qubit before or after the measurment?

If you have a |V> photon stream (say from a laser) that you can only measure on the $\{|+\rangle, |-\rangle\}$ basis, yes, that is meaningful. I would not call them the same state though. Naturally, I can distinguish them experimentally using a suitably oriented PBS.

Similarly, I can distinguish the difference between Ma's (1) and (2) experimentally. As they do. Megidish as well. Disagree?

 

[DrChinese]

Suppose that in the swap set up, nothing is done to photons 2 and 3. But the usual measurments are done on 1 and 4. This goes for all the runs. Then in the data of the results of the measurements on 1 and 4 you can find a subset of runs which show non-classical correlations. According to you that would mean that post-selection can create entanglement just as the swap can. Right?

In the actual experiments, it is not done as you describe/imagine at all. There is a specific BSM signature for selecting the subsets. The same signature is required for reporting on either Entangled State or Product State statistics. That way the comparison is apples to apples. When there is physical overlap of Photons 2 and 3, there is a swap. Always. And when the bells ring for |HH> or |VV> on opposite ports of the Beam Splitter (BS), that is the signature for the Phi- Bell state: |Φ−〉23 = (|𝐻𝐻〉23 − |𝑉𝑉〉23)/√2. On the other hand: when there is no physical overlap of Photons 2 and 3, there is no swap. But the bells still ring for HH> or |VV> on opposite ports of the Beam Splitter (BS).

So... no. Of course the selection process does not create entanglement. It is the physical overlap, and nothing else, that varies. No more than a post-selection filter causes cancer (or the appearance thereof) in medical studies.

 

[DrChinese]

1. As I said before, post-selection defines the ensemble, which also defines the state because the state is a description of the ensemble. In this way, the post-selection participates in the creation of the state. But the entanglement is defined as a property of the state, so this also participates in the creation of entanglement.

2. Of course, the above refers to a subjective notion of state defined by an experimentalist who have chosen to ignore some measurement outcomes. It does not create entanglement in some objective sense independent on the observer. In this objective sense, you are right that it should be irrelevant. But then, if you are looking for an objective description of the whole experiment that does not depend on the observer, then you must use a definition of entanglement that does not depend on the observer. ...

3. ... because this creates inconsistencies resulting in a wrong impression that DCES is a mystery. It isn't mystery at all, if you are being consistent.

1. All of this is wordplay. Post-selection identifies an observed state - it does not in any manner participate in its creation.

A scientist defines a fixed criteria for events that meet some threshold. He studies or experimentally varies a single variable, and reports the A/B results. In this case, there is exactly one variable: Is there physical overlap of Photons 2 and 3, yes or no. That, and only that, is what is reported by Ma. Overlap: Entangled State statistics. No overlap: Separable (Product) State statistics. If you disagree with the scientists' criteria, then reject the paper.


2. Here you essentially deny everything you just said. Then you introduce a criteria that is essentially anti-science at its root: Only accept evidence that meets an "observer independent/objective" criteria that you manufacture - but has no experimental support whatsoever. I think everyone who reads these papers is well aware that the experiment is performed in a laboratory by human scientists. If your explanation for Bohmian Mechanics' outcomes is that the lab+scientist is entangled with Photons 2 and 3 (or maybe Photons 1 and 4), then as I have already said: I will accept that. But please, don't try to sell me that your perspective is "more objective". There is already a generally accepted definition of entanglement, and it doesn't include lab+scientist.


3. Whether I call DCES "mysterious" or not isn't really a scientific issue. Gravity is mysterious. Inflation is mysterious. Initial conditions of the universe are mysterious. Am I consistent in this labeling? The label doesn't change the science.

 

[DrChinese]

Do you accept that quantum states can be expressed using different bases?

Sure. If a photon is entangled on the H/V basis, it is also entangled on the +/- basis. If you are looking individually (just one side, not pairwise correlations) on the +/- basis only, you cannot distinguish those photons from entangled (but not polarization entangled) photons created on the |V> basis. (Note: PDC can create pairs of either type.) You will see a 50-50 mix, right?

But you can sense a difference if other bases are selected, or you look at correlations with the entangled partner. The point being: Expressing on a particular basis may or may not uniquely identify its state. That's because experiments might differentiate between one basis as compared to another, right? This happens in the Ma paper. There, we got Entangled (Bell) State or Product (separable) State stats depending on whether or not there is indistinguishable physical overlap of Photons 2 and 3. That's our independent variable.

But: If you tell me an entangled pair labeled 1 & 2 is in a Product State with a pair labeled 3 & 4, and is also in a "hidden" Bell state with Photons 3 & 4 [Ma's (2)]; and also simultaneously in Product states with Photon pairs 5 & 6, 7 & 8, etc - none of which have ever interacted: I'm going to say there is no physical meaning to that. Photons 1 & 2 have no deeper relationship than a Product State with Photons 3 & 4 (or Photons 5 & 6) as compared with any other entangled pair in the entire universe unless and until they overlap.

No ticket, no laundry: indistinguishable physical overlap. And this is true regardless of whether we have Delayed Choice or not. What I am saying is pretty simple, I'm really not sure where there is any controversy here.

 

[DrChinese]

1. Ah, I see now the source of confusion. When you say they are in a product state, you are talking about one photon B and one apparatus. Since the apparatus has shown a definite known state, its state effectively collapsed, which effectively destroyed the entanglement. In that sense, even BM accepts that there is an effective collapse and hence an effective destruction of entanglement.

2. However, that is not what we are talking about. We are not talking about one B and one apparatus. We are talking about a statistical ensemble. The entanglement is observed by measuring correlations, and for that purpose we need to repeat the measurement many times, so we are really dealing with an ensemble. In the ensemble the apparatus sometimes shows one outcome, and sometimes the other. Hence the state of the ensemble does not describe only one of the outcomes, but both outcomes simultaneously. In other words, the system, viewed as a statistical ensemble, is in the superposition. It is this superposition at the ensemble level which is responsible for the entanglement. In other words, the ensemble is not in a product state, even though any individual B+apparatus system is.

To understand all this properly, Bohm is not very important. Much more important is Ballentine, who emphasizes that the quantum state is a description of a statistical ensemble, not of a single system. Without understanding that, the DCES experiment cannot be understood properly. More generally, the ensemble perspective is crucial whenever we do post-selection (as we do in the DCES experiment), because the post-selection changes the ensemble. Without post-selection, we don't see any entanglement in the DCES experiment, do you agree? Hence, at an instrumental level, we may say that the post-selection creates entanglement. (Mathematically, post-selection is represented by a projection, and the projector is not a unitary operator.) That's how even the apparatus becomes entangled.

Or to make the long story short, at the operational instrumental level, entanglement is a property of an ensemble, not of an individual system. At the ensemble level the apparatus does not show only one definite outcome, so the system is not in the product state. Instead the system is in the superposition, namely, in an entangled state.

1. Sounds about right. Note that there is a simple reason that I consider the measurement apparatus itself to be "outside" of our consideration here. And, as might be expected from me, it's because of experimental considerations.

I have an entangled pair being measured by Alice (apparatus+lab+human) and Bob (apparatus+lab+human) on the same basis. The results are always correlated and certain, correct? If (apparatus+lab+human) as a factor is our hypothesis, then either:
a) Alice and Bob affect the results the same way in all cases. If only one of them were a factor occasionally, we could not have perfect correlation. So Alice and Bob are subject to yet another nonlocal link affecting them both the same way. But nothing else in the entire universe can affect Alice differently than Bob.
b) Hypothesis is rejected pending evidence of its existence. I hesitate to even mention this corny line from a movie*, but "the simplest explanation tends to be the right one" ...


2. I see you are making distinctions about the ensemble. The part I agree with is that the post-selection criteria defines a subset or sub-ensemble. I don't really follow the rest of what you are saying. If you call a collection of experimental runs an ensemble or sub-ensemble or subset, what changes? In principle: one subset produces perfect 100% correlation when there is a swap, while the other produces 0%. Yes, the tool we use to accumulate this result can be called statistical and experiments do not produce 100% anything. But I don't think the character of the conclusion changes, nor do I see how that factors into the Bohmian view. I responded to another post where you mention this as well. Can you elaborate?

Thanks.


*Yes, Contact. I liked it as entertainment, I'm easily amused. And no, I really don't strictly subscribe to Occam's Razor. It's more of a utility for a starting point in a discussion.

 

[Demystifier]

There is already a generally accepted definition of entanglement, and it doesn't include lab+scientist.

So what is the definition of entanglement that you have in mind?

 

[Demystifier]

If your explanation for Bohmian Mechanics' outcomes is that the lab+scientist is entangled with Photons 2 and 3 (or maybe Photons 1 and 4), then as I have already said: I will accept that. But please, don't try to sell me that your perspective is "more objective". There is already a generally accepted definition of entanglement, and it doesn't include lab+scientist.

OK, I'm glad that you accept that it is so according to (my version of) Bohmian Mechanics (BM). But what I try to emphasize is that such a view is not an exclusive feature of BM. Instead, that's a feature of any interpretation that accepts the following assumptions:
1. Universality: Everything, including the lab and the scientists, is ultimately described by QM.
2. Objectivity: The quantum state of the system is not merely a description of knowledge of an observer, but represents some objective feature of the physical system not depending on the observer's knowledge.
3. Unitarity: The time evolution of the quantum state (of a closed system) is unitary, i.e., at the fundamental level, there is no collapse of the state.

Of course, it is not trivial to satisfy all these requirements in a single interpretation. BM satisfies them all, and so does the many-world interpretation, but many interpretations don't. Also note that the Bohmian point of view is "more objective" in the sense that it satisfies the objectivity assumption 2., not in the sense that it is "more right" than some other interpretation.

At the end, I have a question for you: Which of the assumptions 1, 2 and 3 do you find implausible or unacceptable? (it seems to me that you accept 1. and 2., but deny 3. But I'm not sure, so I would like if you could be explicit about it.)