Interpretation of a state in quantum entanglement

[Ken G]

I have never heard a challenge by quantum entanglement to the concept that a state is a "property" of a particle, which I don't understand. I cannot see any way someone can interpret a state as a property of a system, rather than as a means of treating information about the system, given how quantum entanglement works. A lot of hay is made about the idea that when one particle in an entangled pair gets measured, the state of the other changes "instantaneously", but I rarely see it questioned that "instantaneous" has no meaning at all when applied to particles that are well separated, and possibly even in quite different reference frames. In particular, if two electrons are entangled to have opposite spins, and one of the spins is measured, how can the other's spin be regarded as a property of that electron when we cannot say when the other electron acquired that new property? Certainly a property must have a unique meaning in the proper time of the particle in question, but here, it simply does not, because there is no unique association of that property with that proper time. How does that not destroy the concept that the spin of an individual electron is a property inherent to that electron?

 

[Nugatory]

I have never heard a challenge by quantum entanglement to the concept that a state is a "property" of a particle, which I don't understand. I cannot see any way someone can interpret a state as a property of a system, rather than as a means of treating information about the system, given how quantum entanglement works.

No matter where you're going with the distinction between "a property of a system" and "a means of treating information about the system", any suggestion that individual particles have a state in a multi-particle system is a straw man. The mathematical formalism doesn't allow a description in terms of the state of a single particle (at best, you might find that the state is factorizable), and we spend a fair amount of time here trying to talk beginners out of their classical intuition that an entangled pair can be thought of as two particles each with their own state before measurement.

 

[Ken G]

I don't think that answer is quite going to cut it, because there certainly are situations where entangled particles do very much end up "having their own state," in every sense of the term "state," and those are the situations to which I refer. For example, let's take the classic example of two electrons in the Bell state where they both have the same spin, but that spin is completely indeterminate. We'll take the example with the + sign, so we can write u as spin up and d as spin down, so the two-particle state is uu+dd (I won't bother to normalize, states don't need normalizations if we simply normalize the expectation value formulas instead). That representation of that state works fine for any angle of determination of the spin direction, so we can separate the two particles and send one of the electrons through a Stern-Gerlach experiment along any angle of our own choosing, resulting in either a u or d result on the electron used. Let's say it is u, without loss of generality. At this point we can now make the following quite normal claims:
1) the electron we tested is now in state u
2) the other electron is now also in state u
There is no ambiguity here in treating the two particles as if they had their own states, indeed, if there were, quantum mechanics as we know it would be impossible, because we are always taking particles out of entangled histories and preparing them in individual states. So your objection doesn't apply.

Now for the problem. If we are to regard the state u as being a "property" of the second electron, as it normally is claimed to be, certainly we must be able to answer this question: at what point in that second electron's proper time history did it acquire the property u?

I cannot see that this question has any answer that allows u to be interpreted as an actual property that is inherent to the second electron, which is the source of my question. It seems to me this simple example destroys the possibility that states, or properties associated with states, are inherent to individual particles, without going to great extremes to allow ourselves to continue to hold to that language. Indeed, so far backwards do we need to bend, that it really starts to look like a simple prejudice. But perhaps someone can explain to me how the property concept can be retained in the example I gave without seeming like it is being force fed here.

 

[zonde]

Now for the problem. If we are to regard the state u as being a "property" of the second electron, as it normally is claimed to be, certainly we must be able to answer this question: at what point in that second electron's proper time history did it acquire the property u?

I cannot see that this question has any answer that allows u to be interpreted as an actual property that is inherent to the second electron, which is the source of my question. It seems to me this simple example destroys the possibility that states, or properties associated with states, are inherent to individual particles, without going to great extremes to allow ourselves to continue to hold to that language. Indeed, so far backwards do we need to bend, that it really starts to look like a simple prejudice. But perhaps someone can explain to me how the property concept can be retained in the example I gave without seeming like it is being force fed here.

As I understand you are trying to argue that non-local collapse can not possibly lead to consistent single particle model.
But what kind of reasoning leads you to that conclusion? You just stated your conclusion without any reasoning: "I cannot see that this question has any answer ...".
And I see no problem there. Let's say we pick lab reference frame and say that other particle from entangled pair acquired it's property at the same time (in lab's reference frame) when the first particle left PBS in either output. Does there appear any inconsistency that would force us to give up that model as one of the possible explanations?

 

[Ken G]

So you are saying that the answer to my question is not unique, correct? After all, you can answer it differently from someone else, in a different coordinate system. So your answer to "when did the particle acquire that property" is "it depends on the coordinates chosen?" But how could that be a property of the particle, you are talking about a property of a chosen coordinate, which is exactly what I was saying-- the property is a property of your analysis. That's exactly what a coordinate choice is, is it not? So it's not a problem of inconsistency, the problem is non-uniqueness. How can a property of a particle be acquired at a non-unique time? But a property of a chosen analysis scheme can certainly depend on that analysis scheme!

 

[zonde]

So you are saying that the answer to my question is not unique, correct?

No. What I am saying that there is parameter in the model that has unknown value. But that parameter has to be set the same for any observer.

 

[Ken G]

Yet the way you answered my question was that the property was obtained simultaneously with the other observation. So that's clearly a matter of coordinate choice-- you agree that simultaneity is a coordinate issue, and that two different observers will associate a different moment in the proper time of the second particle as being "simultaneous" with the observation on the first, correct? Or is there something more implied when you said "left PBS" (which I wasn't quite sure what you meant)?

 

[zonde]

Yet the way you answered my question was that the property was obtained simultaneously with the other observation.

Simultaneously in lab frame. Of course it might not be simultaneous in reference frame that moves relative to lab's frame. For observer in that other reference frame the property would be obtained earlier or later (or still simultaneously if his motion is in perpendicular plane to the line connecting two events).

 

[Ken G]

But this is not going to work. You are saying that the "lab" is a global frame, that applies to both particles. But you are aware that in general there are not such things as global frames, yes? They are kind of an invention of special relativity. So if your whole basis for saying the second electron has an intrinsic state is based on the concept of a global lab frame, that's going to be a pretty big problem, is it not?

Worse, even if we stick to special relativity, and even if we think there is something more than pure convention to the concept of a global lab frame, it still doesn't work. Because we can separate the particles, put them in two very different "lab frames," and do observations on both of the particles! Now which one is the "lab frame" that counts as the one where the "properties of the particles" get simultaneously established in that case?

So at present we still have no acceptable answer to "when in the proper time of the two particles did each one acquire the property of u" that is described in the example, unless we allow the answer to depend on our analysis approach. That is my point-- the properties are being shown to be properties of the analysis, because to hold that the properties are intrinsic to the particles themselves requires that we be able to do what we cannot: say when they were acquired in the proper time of the particles, in a unique and unambiguous way (and it would be nice if they were also demonstrably so).

 

[zonde]

But this is not going to work. You are saying that the "lab" is a global frame, that applies to both particles. But you are aware that in general there are not such things as global frames, yes? They are kind of an invention of special relativity. So if your whole basis for saying the second electron has an intrinsic state is based on the concept of a global lab frame, that's going to be a pretty big problem, is it not?

There are no global inertial frames when we bring gravity into consideration. There can be global non-inertial frame. There might be some issues about establishing elegant convention but that can not be an argument for impossibility of global non-inertial frames.

Worse, even if we stick to special relativity, and even if we think there is something more than pure convention to the concept of a global lab frame, it still doesn't work. Because we can separate the particles, put them in two very different "lab frames," and do observations on both of the particles! Now which one is the "lab frame" that counts as the one where the "properties of the particles" get simultaneously established in that case?

As I understood you are arguing for inconsistency of the idea with any choice of reference frame. So basically your statement is that whatever reference frame I choose the idea is inconsistent. So I choose one (whatever) reference frame and see no inconsistencies.
Now it seems you are arguing that I have not specified my choice unequivocally enough. Ok, then let's take Sun's rest frame.

because to hold that the properties are intrinsic to the particles themselves requires that we be able to do what we cannot: say when they were acquired in the proper time of the particles, in a unique and unambiguous way (and it would be nice if they were also demonstrably so).

To claim tentatively that properties are intrinsic to the particles themselves would require some specific experimental predictions based on that claim and then to verify them.
Then to not discard that possibility as possible explanation it's enough to check that it is self consistent and consistent with present experimental observations.
But I do not know from where comes the requirement on which you are trying to insist.

 

[Ken G]

There are no global inertial frames when we bring gravity into consideration. There can be global non-inertial frame.

Hang on-- can be? Remember, your whole position is that the "property" u is intrinsic to the particle, so you need a time when that property is acquired, in every situation. How can it only be a property if there is a global frame, that is not purely stitched together by pure convention and fickle preference of the scientist doing it? So "can be" is not going to cut it.

There might be some issues about establishing elegant convention but that can not be an argument for impossibility of global non-inertial frames.

Elegant convention? Your position is about the truth of the particle. I'm the one talking about elegant convention-- for me the property is in the analysis, so I can look for elegant conventions.

As I understood you are arguing for inconsistency of the idea with any choice of reference frame.

Where did I use the word "inconsistency"? I said that if the property is intrinsic to the particle, then we need much more than "consistency," we need the unique time (in the particle's proper time) when the property was acquired. If you will freely admit there is no such unique time of acquisition, but rather that the time of acquisition is chosen by our analysis technique (perhaps in some search for elegance, or just plain convenience), then I'm perfectly happy-- because those are all properties of an analysis, not properties of a particle.

So basically your statement is that whatever reference frame I choose the idea is inconsistent.

Quite the opposite-- I'm saying that one can choose almost any time one wants to say when the particle acquired that state! So the state is in the choice, if when it was acquired is in the choice. It is therefore not an intrinsic property of the particle.

Ok, then let's take Sun's rest frame.

Exactly my point, as you will see if you review my comments. We have established what I claimed above: the time in the particle's proper time when the property was acquired is completely a matter of the analysis technique applied. If you agree with that, this is enough for me, the significance of that fact can then be considered.

To claim tentatively that properties are intrinsic to the particles themselves would require some specific experimental predictions based on that claim and then to verify them.
Then to not discard that possibility as possible explanation it's enough to check that it is self consistent and consistent with present experimental observations.
But I do not know from where comes the requirement on which you are trying to insist.

The argument follows from what you said above: "What I am saying that there is parameter in the model that has unknown value. But that parameter has to be set the same for any observer." So to be intrinsic to a particle, all observers must agree on the property. But now you are saying they don't need to agree on when in the particle's proper time stream that property was acquired! Does that really sound like something intrinsic to the particle?

 

[zonde]

Hang on-- can be? Remember, your whole position is that the "property" u is intrinsic to the particle, so you need a time when that property is acquired, in every situation. How can it only be a property if there is a global frame, that is not purely stitched together by pure convention and fickle preference of the scientist doing it? So "can be" is not going to cut it.

Ok, let me try to say it differently. The non-local collapse requires that there is some preferred spacetime foliation so that collapse for entangled pair happens within the same spacelike hypersurface.
Is it better now?

 

[martinbn]

Wait, I don't get it. Why aren't there global frames?

 

[Ken G]

Ok, let me try to say it differently. The non-local collapse requires that there is some preferred spacetime foliation so that collapse for entangled pair happens within the same spacelike hypersurface.
Is it better now?

Hardly. On what basis do you claim there is a "preferred spacetime foliation" as you describe? Can you point to a shred of observational evidence that this is actually true? Because if you cannot, I call it a classic example of what I said above-- force-feeding a prior prejudice onto a set of experiments that show no trace of what you are talking about. Instead, all we find is a glaring absence of a preferred spacetime foliation! To wit, we have a wide array of possible foliations, all of which work just fine, and all give different answers to the proper time wherein the second electron "acquired" the property u. Can you deny the truth of that statement?

 

[Ken G]

Wait, I don't get it. Why aren't there global frames?

There are arbitrary ways to cluge together various local coordinate charts, but no need for any kind of "preferred" global frame, be it inertial or any other. But even this is not the essential point, because we can remain in the gravity-free environment of special relativity, and we can even imagine that the Einstein simultaneity convention has some kind of special importance, yet we still have the problem that simultaneity is a coordinate-dependent notion, and therefore is an aspect of our analysis rather than an intrinsic aspect of the particles themselves. In particular, you and I could do measurements on both particles, and in each of our own frame we can regard the measurement as not yet having happened to the other particle, so we can view our own result as fixing the "property" u for the other electron at the time of our own measurement, and prior to the other person's-- but that means we will not agree on the proper times for each of the electrons where the property u was acquired, since we are basing that reckoning on when we do our own measurement, viewing that as we do as prior to the other person's measurement. Thus we each regard the other electron as the one which acquired the u property at the time that we did our own measurement, and that's a different time in the proper time stream of the electrons.

So my question is this: if you regard what I just said as perfectly true, then how could we hold that each electron acquired a property u that was intrinsic to the electrons at some point along the way, if we cannot even agree on when that happened in the electron's own proper time, or whether or not it preceded the measurement on the electron?

 

[martinbn]

There are arbitrary ways to cluge together various local coordinate charts, but no need for any kind of "preferred" global frame, be it inertial or any other. But even this is not the essential point, because we can remain in the gravity-free environment of special relativity, and we can even imagine that the Einstein simultaneity convention has some kind of special importance, yet we still have the problem that simultaneity is a frame-dependent notion.

I assumed that in this discussion there was no gravity involved, that's why I asked. Otherwise you need a quantum gravity theory. So one can perfectly well consider global frames.

In particular, we can do measurements on both particles, and in each one's own frame they can regard the measurement as not yet having happened to the other particle, so we can view our result as fixing the "property" u for the other electron at the time of our own measurement-- but that will represent different moments in the proper time of the other electron, based on when they do their measurement and regard our electron as the one which acquired the u property at the time that they did their measurement!

Why should the "acquiring the property" be absolute and frame independent? Simultaneity is not, nor are many other things.

So my question is this: if you regard what I just said as perfectly true, then how can you hold that each electron acquired an intrinsic property u at some point along the way, if you cannot even decide when that happened or whether or not it preceded the measurement on the electron?

If I don't hold that, then what am I suppose to hold. That the electron never, even after the measurement, acquired the property u?

 

[Ken G]

I assumed that in this discussion there was no gravity involved, that's why I asked. Otherwise you need a quantum gravity theory. So one can perfectly well consider global frames.

So you are saying that to hold that a particle has the intrinsic property of "u" requires a theory of quantum gravity? Because note I don't need any global frames, so can associate properties with particles coming out of entanglement in a perfectly normal way, even near black holes with no problem at all, and no need for any quantum gravity theory. But this is definitely not the key issue here, so we can always restrict to SR.

Why should the "acquiring the property" be absolute and frame independent? Simultaneity is not, nor are many other things.

If you are willing to say that the particle has the intrinsic property u, and that property is an attribute of the particle and not the reference frame of a scientist or the analysis technique used, yet you cannot say when the particle acquired that property without said reference frame or analysis technique, then I'm completely satisfied. If we can agree on that, it is plenty for me. I will be happy to be the one in the enviable position of not having to claim that a particle has an intrinsic property that the particle does not acquire at any uniquely discernible time in its proper time history!

If I don't hold that, then what am I suppose to hold. That the electron never, even after the measurement, acquired the property u?

The natural alternative, it seems to me, is that the property is a result of my analysis, so is not an intrinsic property of the particle alone. Then it makes perfect sense that the proper time it acquires that property during the particle history should depend on my analysis, and someone else could say it acquired that property at a different proper time in the particle history, as it is not intrinsic to the particle at all, it is more like a way of thinking, by a scientist, in order to make correct predictions, by a scientist. Note this is quite different from the invariants of relativity, which have no ambiguity in regard to the proper times of the particles they refer to.

In other words, what I'm saying is twofold:
1) many people wonder about what properties are, and if they are intrinsic or deal only with computational techniques, but I don't understand why that conversation does not seem to be often informed by what looks to me to be a crucial element: the issue of when in the proper time of a particle does it acquire its so-called intrinsic properties when coming out of entanglement.
2) many people also worry about how entangled particles can be subject to mysterious "instantaneous influences," yet they never seem to worry that there's no such thing as "instantaneous" that isn't simply an arbitrary coordinate convention. So why would I be bothered that the connection is instantaneous, but not be bothered that two different scientists have two different ideas about what instantaneous means?

 

[DrChinese]

1. If we are to regard the state u as being a "property" of the second electron, as it normally is claimed to be, certainly we must be able to answer this question: at what point in that second electron's proper time history did it acquire the property u?

2. I cannot see that this question has any answer that allows u to be interpreted as an actual property that is inherent to the second electron, which is the source of my question.

3. The natural alternative, it seems to me, is that the property is a result of my analysis, so is not an intrinsic property of the particle alone. Then it makes perfect sense that the proper time it acquires that property during the particle history should depend on my analysis, and someone else could say it acquired that property at a different proper time in the particle history, as it is not intrinsic to the particle at all, it is more like a way of thinking, by a scientist, in order to make correct predictions, by a scientist.

1. There is no requirement that "when" be answered specifically, . It occurred prior to or coincident with measurement, as part of the overall context. That context can span both space and time, as experiment demonstrates.

2. The entire concept of the HUP is that the electron does not have well defined quantum properties at all times. In fact, EPR concluded quantum theory must be incomplete precisely because it implied properties were not intrinsic (but rather were subject to how the observer chose to measure).

3. This, to me, is simply a restatement that we live in world governed by context, i.e. subjective to the observer. An entangled quantum context includes a source and related observers. We know from experiment that the context can span space (non-local features) and time (defying identification of even so much as causal direction).

It always comes back to one's interpretation. So are you asking this question only of people who think u's properties are intrinsic (objective)? Because I don't think they are.

 

[Ken G]

1. There is no requirement that "when" be answered specifically, . It occurred prior to or coincident with measurement, as part of the overall context.

I agree there is no requirement that when be answered, but there is also no requirement that we regard "u" as a property intrinsic to the particle! So this isn't really about what is required, it is about whether or not we can say that a particle has, intrinsically and by itself, the u property, if we also admit it would be impossible to say when it actually did acquire that property in its own proper time.

2. The entire concept of the HUP is that the electron does not have well defined quantum properties at all times.

We're not discussing a situation where there is any ambiguity in the particle state-- it is quite clearly in state u in the example I gave. All that is at issue is when it acquired that property, in its own proper time sequence, and by extension, to what extent can the particle be said to have that property by itself, and to what extent must we admit our own role in that particle being regarded as having that property. If we are to hold that u is a property intrinsic to the particle, yet we also admit that nature does not appear to even adjudicate the issue of when it acquired that property in its own proper time sequence, to me that quite clearly calls into question the coherence of the claim that the property is intrinsic to the particle. Shouldn't we be able to imagine that a property, to be intrinsic, must have a real existence that actually initiates at some proper time for the particle it is supposed to be intrinsic to? What kind of intrinsic property does not have that simple feature? But instead, what we actually find is that the particle proper time that we associate with the acquisition of that property depends on our analysis approach. Does that situation not describe a property of our analysis approach?

In fact, EPR concluded quantum theory must be incomplete precisely because it implied properties were not intrinsic (but rather were subject to how the observer chose to measure).

I'm not concerned with the measurement choice, I'm simply concerned with when the property u is acquired by the particle. Again, there is no ambiguity about the property or the measurement choice-- it is "u", that's not in dispute in this example.

3. This, to me, is simply a restatement that we live in world governed by context, i.e. subjective to the observer.

I agree completely, and couldn't have said it better myself. But that also means that "u" is not an intrinsic property of the particle, it exists in a context, and when it is acquired, as reckoned by some scientist, also exists in that context. Hence, the same can be said about a quantum state. Nevertheless, most people seem willing to adopt language that treats a quantum state like an intrinsic property of a system, all by itself, and independent of any means being used to analyze said system by various scientists in various reference frames and with various ideas about when that property was acquired in the particle's own invariant proper time.

It always comes back to one's interpretation. So are you asking this question only of people who think u's properties are intrinsic (objective)? Because I don't think they are.

Yes, for anyone who does not already regard "u" as an intrinsic property of the particle, my line of reasoning will only support their current stance.

 

[Blue Scallop]

1. There is no requirement that "when" be answered specifically, . It occurred prior to or coincident with measurement, as part of the overall context. That context can span both space and time, as experiment demonstrates.

2. The entire concept of the HUP is that the electron does not have well defined quantum properties at all times. In fact, EPR concluded quantum theory must be incomplete precisely because it implied properties were not intrinsic (but rather were subject to how the observer chose to measure).

3. This, to me, is simply a restatement that we live in world governed by context, i.e. subjective to the observer. An entangled quantum context includes a source and related observers. We know from experiment that the context can span space (non-local features) and time (defying identification of even so much as causal direction).

It always comes back to one's interpretation. So are you asking this question only of people who think u's properties are intrinsic (objective)? Because I don't think they are.

If true. This is very elegant thought. We tend to think matter is separate from spacetime. But the truth may be matter and spacetime are one or joined or two sides of the coin. But in original Copenhagen. Did they think properties only only intrinsic to the particle? Isn't it contextuality means the properties are intrinsic to both the particles and spacetime? Since Copenhagen is contextuality.. why did they think the properties u are intrinsic to the particle only?

 

[zonde]

Hardly. On what basis do you claim there is a "preferred spacetime foliation" as you describe?

Hmm, I am trying to be careful and not insist on such a "preferred spacetime foliation". I rather criticize alternative explanations.
So if to you it seems that I have insisted on non-local collapse as something more than just an interpretation then please point out where I did that.

Can you point to a shred of observational evidence that this is actually true?

No

Because if you cannot, I call it a classic example of what I said above-- force-feeding a prior prejudice onto a set of experiments that show no trace of what you are talking about.

[sarcasm on]I will try to remember that you have specific vocabulary.[sarcasm off]

Instead, all we find is a glaring absence of a preferred spacetime foliation! To wit, we have a wide array of possible foliations, all of which work just fine, and all give different answers to the proper time wherein the second electron "acquired" the property u. Can you deny the truth of that statement?

No, I don't deny that.

Look, there are many highly respected and knowledgeable people on this forum who do not like non-local collapse. But their objections are usually softer. They say - there are no-collapse interpretations so it's purely interpretation issue. But it seems that your position is much stronger - you seem to say that non-local collapse leads to inconsistency.

 

[kith]

Certainly a property must have a unique meaning in the proper time of the particle in question [...]

The proper time of a classical particle is the time which is displayed by a clock which travels along the worldline of the particle. Having a worldline means having a well-defined position at every instant of time, something which isn't true for quantum particles. So I'm wondering how do you even define the proper time of a quantum particle?

 

[Ken G]

If true. This is very elegant thought. We tend to think matter is separate from spacetime. But the truth may be matter and spacetime are one or joined or two sides of the coin. But in original Copenhagen. Did they think properties only only intrinsic to the particle? Isn't it contextuality means the properties are intrinsic to both the particles and spacetime? Since Copenhagen is contextuality.. why did they think the properties u are intrinsic to the particle only?

Actually my argument applies equally well if you think the properties are intrinsic to only the particles, or intrinsic to the particles and the spacetime they occupy. It's really no help to involve the spacetime-- for there is still no unique or discernible time in the particle's proper time stream where the property is acquired, so including spacetime doesn't help.

 

[Ken G]

Look, there are many highly respected and knowledgeable people on this forum who do not like non-local collapse. But their objections are usually softer. They say - there are no-collapse interpretations so it's purely interpretation issue. But it seems that your position is much stronger - you seem to say that non-local collapse leads to inconsistency.

I have not said that, indeed I have no problem with non-local collapse at all because the "non-locality" I see is a scientist using a thought in his/her head and applying that thought to a system that is nonlocal to them. That's what we actually see when we look at "non-local collapse," so my only point is the difficulties people seem to sweep under the rug when they wish to interpret properties as intrinsic to the particles, yet they cannot say when the property was acquired, and as you admit, can regard the properties as being acquired at essentially arbitrary points in the particle proper time stream. So the inconsistency is not in the collapse, it is in the use of the "intrinsic property" concept.

In fact, it seems to me the only plausible way to hold that a property is intrinsic to the particle is to say that the time the property is acquired is always during the measurement, and that holds for both particles-- they both need to be measured to acquire the u property. At least then the acquisition is not ambiguous. However, that is not normally the language used when people talk about "non-local collapse," so it is people's own language about it that is inconsistent, not the phenomena itself.

 

[Ken G]

The proper time of a classical particle is the time which is displayed by a clock which travels along the worldline of the particle.

Precisely.

Having a worldline means having a well-defined position at every instant of time, something which isn't true for quantum particles. So I'm wondering how do you even define the proper time of a quantum particle?

Your point brings up some subtleties, but it's not a serious problem for my argument, because I have gobs of proper time to play with here. I can entangle two electron spins, take one electron to alpha Centauri, and wait a thousand years to do the measurement on its pair particle. Do you really think I cannot define a concept of proper time for that electron that will create issues with the question of when that particle acquired the u property? Remember, a classic argument for the existence of time dilation is that unstable particles require longer to decay in the lab frame than they do in their own proper time, so the proper time of a quantum particle is not some kind of new invention by me!

 

[zonde]

yet they cannot say when the property was acquired, and as you admit, can regard the properties as being acquired at essentially arbitrary points in the particle proper time stream.

You are mixing two different things together.
1. Property is acquired at arbitrary point in time.
2. Property is acquired at unknown point in time.
First conclusion would support your position while second conclusion gives no support to your position.
Non-local collapse leads to second conclusion. So no, I do not admit that properties are acquired at arbitrary points in time.

 

[Ken G]

Actually, you left out the most important one:
3. Property is acquired at an unknowable point in time.
You must admit, it is that third case that we have here, must you not? And doesn't that seem like a problem to the "intrinsic property" idea? After all, we booted the aether as soon as we found it was unknowable what some "aether frame" must be, so here we have the same issue-- when nature herself does not adjudicate the question "when was the property acquired,", then we must seriously face that problem and admit that perhaps there is something bogus in the entire concept of "acquiring an intrinsic property." Put differently, your position rests on the ability to distinguish between "unknowable" and "arbitrary", and I cannot see how you can support any such distinction.

But even if you insist on that distinction, we can still agree that we have it down to two possibilities for anyone who wishes to think that u is an intrinsic property of the particle:
1) It is an intrinsic property that is acquired at an unknowable point in the proper time history of the particle. (In which case we have the problem similar to an unknowable aether frame.)
2) It is an intrinsic property that is acquired when the measurement is done on the particle itself. (In which case people need to significantly change the language they use about when entangled states undergo their changes!)

Alternatively, we have the perspective that suffers none of these problems:
3) It is not an intrinsic property, a property is a concept a scientist uses to achieve understanding and make predictions, and so there is no problem about when the scientist attributes the property as it is a free choice by the scientist that is not intrinsic to the particle anyway.

 

[zonde]

1) It is an intrinsic property that is acquired at an unknowable point in the proper time history of the particle. (In which case we have the problem similar to an unknowable aether frame.)

People are different. Some will say unknowable parameter in a model is problem some will say that alternative poses even bigger problem for them. As log as experimental predictions come out the same there are no pragmatic grounds for confrontation between those people.

2) It is an intrinsic property that is acquired when the measurement is done on the particle itself. (In which case people need to significantly change the language they use about when entangled states undergo their changes!)

Can you construct a causal model based on this idea that is at least in some sense better that alternative?

Alternatively, we have the perspective that suffers none of these problems:
3) It is not an intrinsic property, a property is a concept a scientist uses to achieve understanding and make predictions, and so there is no problem about when the scientist attributes the property as it is a free choice by the scientist that is not intrinsic to the particle anyway.

Any element in our models is a concept that a scientist uses to achieve understanding and make predictions.
You are simply dodging the question of correspondence between elements in our models and reality.

 

[member 11137]

Actually, you left out the most important one:
3. Property is acquired at an unknowable point in time.
You must admit, it is that third case that we have here, must you not? And doesn't that seem like a problem to the "intrinsic property" idea? After all, we booted the aether as soon as we found it was unknowable what some "aether frame" must be, so here we have the same issue-- when nature herself does not adjudicate the question "when was the property acquired,", then we must seriously face that problem and admit that perhaps there is something bogus in the entire concept of "acquiring an intrinsic property." Put differently, your position rests on the ability to distinguish between "unknowable" and "arbitrary", and I cannot see how you can support any such distinction.

But even if you insist on that distinction, we can still agree that we have it down to two possibilities for anyone who wishes to think that u is an intrinsic property of the particle:
1) It is an intrinsic property that is acquired at an unknowable point in the proper time history of the particle. (In which case we have the problem similar to an unknowable aether frame.)
2) It is an intrinsic property that is acquired when the measurement is done on the particle itself. (In which case people need to significantly change the language they use about when entangled states undergo their changes!)

Alternatively, we have the perspective that suffers none of these problems:
3) It is not an intrinsic property, a property is a concept a scientist uses to achieve understanding and make predictions, and so there is no problem about when the scientist attributes the property as it is a free choice by the scientist that is not intrinsic to the particle anyway.

Entangled particles are animating the research and your discussion here is one supplementary proof for that. The fact that two entities may be “instantaneously” correlated over a distance, any distance, is highly contradicting one of the pillars of relativity. This explains the intensity of the debates. Discussing about this item forces us to reconsider basic concepts (chronology, instantaneity, etc.) which we believed were totally understood and mastered.

Let me bring my modest contribution. Let examine the situation. It is of course impossible for a given object to be in two different places at the same time (the time here being an instant in a chronology for an observer working outside that object. In extenso: I observe for example a plane or a wave staying on the ground, not in the plane or on the back of the wave). This impossibility is mainly based on the fact that the human brain realizes a short cut, often unconsciously, between observed object and point. Within a very classical vision, this is resulting into an abusive confusion between observed object and locality. Any given object is necessarily localized at a given and relatively restricted small place.

This interpretation of the reality doesn’t hold true for waves. Let fall a stone in the water of a quiet lake and observe the front of the wave. The same object (the front of the wave) is occupying a whole circle at the same time in my chronology. Now imagine the same or a similar scenario at a quite greater scale. For example, consider a tsunami starting somewhere in the ocean with a front wave arriving in Sumatra and in Los Angeles. Imagine that each observer (the one in Sumatra and the one in Los Aneles) only have a radio to communicate. Imagine they speak together about anything. Imagine that they suddenly see a wave front arriving at the same instant in their respective local chronology but have no knowledges about wave propagations. They probably will conclude that two waves are arriving at the same time on their respective coasts. Only a third observer owning a satellite and a deeper understanding of the physics acting there will be able to tell them: “In fact, it’s the same and unique object!”

Analyzing this fictive scenario is telling us that an object may have a spatial size and may not always be reduced to a local position. It also tells us that it is not always easy to understand that two spatially separate phenomenon may eventually be two manifestations of a unique one object. This effectively pushes us back to the beginning of that dissertation: “How can we concretely be certain that we are observing an entangled objet?”

Coming also back to the main topic of your conversation: “Is an observed property intrinsic to the (eventually entangled) object? Or is the property just the result of a local analysis which has been developed by the observer… Or is that property only a property of the place where the manifestation of the object has been observed?” This is really not an easy task, although a really interesting and deep question.

Let consider as a simple example: the mass of a proton or the charge of an electron which may be easier to measure. Why is this charge a universal value (1, 6. 10-19 Coulomb)? I mean: “What can explain that, you or me, where ever we are measuring it, will always find the same value?”

A analysis of that fact exhibits a first information: what is interpreted as a charge depends neither on our localization, nor on the one of the observed electron, nor on our relative motion to it. The value is frame and motion-independent. This is the reason why we believe that it is intrinsic to the electron.

But exactly here, I come back to my second paragraph above. In extenso, in believing that the charge is intrinsic, we intuitively have though that that electron was a local particle and we have automatically put a flag on its back: its charge.

This is probably not a totally correct way to think about the reality because of the duality particle-wave, because of the non-locality of any electron (around an atom for example).

So, my questioning: “From your perspective (the property is highly depending on the observer and on his/her technology): what do we measure when we try to measure the charge of an electron?”Thanks in advance for criticism concerning that short dissertation.

 

[Ken G]

So, my questioning: “From your perspective (the property is highly depending on the observer and on his/her technology): what do we measure when we try to measure the charge of an electron?”

It's an interesting question if the invariants of a particle, like charge, rest mass, and spin, have a different status than properties that can be changed by observation, like spin direction. I tend to imagine the invariants are a bit different, but then, we do have strange situations like with the neutrino, which oscillates flavors. Can we entangle two electron neutrinos, and let them both oscillate, and will those flavor oscillations also be entangled? If so, then by the above argument, even the identity of the particle is either not an intrinsic property of the particle itself, or else is a property of the particle that is only acquired when the flavor is determined by measurement. Charge may be more difficult to get this effect, however. Still, I agree with you that we don't seem to have fully probed the degree to which reality can behave differently from our classical experience, in regard to things like localization of objects and intrinsic aspects of object properties.

 

[Ken G]

People are different. Some will say unknowable parameter in a model is problem some will say that alternative poses even bigger problem for them. As log as experimental predictions come out the same there are no pragmatic grounds for confrontation between those people.

True, but the same can be said about the aether. When we looked for it, we decided it was not to be found. So we dropped it, though people are still free to keep it if they like-- as Poincare and Lorentz tried to do. But science tends to like to drop its affectations when they are found irrelevant, and I argue that saying that a property is acquired at some unknowable moment when its entangled partner is measured is a similar kind of irrelevant affectation. To drop it, we should either say that properties are aspects of a thought process and therefore are acquired when our minds find it necessary to use them, such as when they are about to be measured to check our expectation, or that properties are indeed aspects of particles but are acquired only when measured, as that is the only time something happens to the particle in question. Those are the two possibilities that include no irrelevant affectations, but neither are ever the language we find connected with entanglement!

Can you construct a causal model based on this idea that is at least in some sense better that alternative?

Sure, the causal model is that properties are not intrinsic to particles, they are intrinsic to the mathematics of quantum mechanics. Or, if that seems not realist enough, you can say that properties are intrinsic to particles, but the constraints on them are not, and properties are always only acquired during actual local interactions, i.e., measurements. In the first case, the causation is local because it is a relationship among the information in the head of the scientist, and in the latter, the causation is nonlocal because it applies to the constraints on the properties, but in neither case are the properties altered nonlocally.

Any element in our models is a concept that a scientist uses to achieve understanding and make predictions.
You are simply dodging the question of correspondence between elements in our models and reality.

I could say the same thing about the aether. Was banishing it a case of dodging the question of the medium of light? When we don't need something, we drop it, even if we used to think we really needed it-- that's not a dodge.

 

[zonde]

True, but the same can be said about the aether. When we looked for it, we decided it was not to be found. So we dropped it, though people are still free to keep it if they like-- as Poincare and Lorentz tried to do. But science tends to like to drop its affectations when they are found irrelevant, and I argue that saying that a property is acquired at an unknowable moment is a similar kind of irrelevant affectation. To drop it, we should either say that properties are aspects of a thought process and therefore has no importance as to when we say they are acquired, except when they are about to be measured, or that properties are indeed acquired only when measured. Those are the two possibilities that include no irrelevant affectations, but neither are ever the language we find connected with entanglement!

Let me just say that, I don't see correspondence between model and physical reality as irrelevant affectation.

Sure, the causal model is that properties are not intrinsic to particles, they are intrinsic to the mathematics of quantum mechanics. Or, if that seems not realist enough, you can say that properties are intrinsic to particles, but the constraints on them are not, and properties are always only acquired during actual local interactions, i.e., measurements. In the first case, the causation is local because it is a relationship among the information in the head of the scientist, and in the latter, the causation is nonlocal because it applies to the constraints on the properties, but in neither case are the properties altered nonlocally.

So the first version is solipsistic, right? But I don't get the second version. Constraints and causality is nonlocal but properties are determined locally? Sorry, you lost me.

I could say the same thing about the aether. Was banishing it a case of "dogging the question" of the medium of light? When we don't need something, we drop it, that's not a dodge.

Correspondence between model and reality is certainly something we need. I don't see the analogy with "medium of light". There is no requirement that model has to answer any conceivable question about reality. But some concepts in the model have to have correspondence to physical reality.

 

[Ken G]

Let me just say that, I don't see correspondence between model and physical reality as irrelevant affectation.

The problem is, you want there to be a preferred foliation of spacetime, as you said, such that when a property is acquired by one particle, we can say the property is also acquired by the entangled particle. But you have also admitted there is no evidence of any such preferred foliation, nor could we ever do any experiment to determine when the property was acquired, because we can do the measurement at any time and get the property u in the example I gave. So what you want to be the correspondence of which you speak, and what you can actually get, are simply not the same. This has happened many times in the history of science, and the upshot is always the same-- eventually, begrudgingly, we just stop wanting what we can't get. It happened to circular orbits, it happened to the aether, it happened to local realism, and I'm saying this is where we are with the concept of a property of a particle. All we can actually get is that either the property was always in the mind of the scientist, and all that was real was the constraint on the property, or that the property of each particle was acquired when the measurement was done on that particle, and the constraint on that outcome does not have a time associated with it. I don't object to either language, because I don't see how we could distinguish them and neither asserts more than we actually get from the experiments. But neither language is what we see in actually parlance about entanglement, and that's my issue.

So the first version is solipsistic, right? But I don't get the second version. Constraints and causality is nonlocal but properties are determined locally? Sorry, you lost me.

I wouldn't call the first version solipsistic, it is more like "it from bit" in Wheeler's language. But I can see that you are closer to preferring the second perspective, so let me explain it more. If we simply say that u is an intrinsic property of the particle, then it is natural to look for the particle's proper time when that property was acquired. We have two options:
1) it was acquired at some unknowable moment that somehow relates to when the measurement was done on the other particle, but of course we cannot even say with clarity which observation happened first, so this is never going to make much sense, or
2) it was acquired by the particle when the measurement was done on that particle, which at least allows properties to change via local interactions, but of course from Bell's theorem we all know that the result is going to have to satisfy some nonlocal constraint that will compromise to a significant degree the idea that the property is intrinsic to the particle. Still, we can save intrinsic properties if we allow them to be subject to nonlocal constraints that are intrinsic to the system to which the particle belongs, but not intrinsic to the particle itself. For me, if we cannot make the constraints intrinsic to the particle, then I see little advantage in making the properties intrinsic to the particle either, especially when I see that I only use the property concept to build expectations (in my mind) about the outcomes of observations, so it seems natural to allow that properties are mental constructs that require no "time of acquisition" in the particle proper time. But I can see that the strategy of a realist will be to maintain as far as possible to the notion of intrinsic properties of individual particles-- but if they do it at the expense of requiring a preferred foliation of spacetime, that's where the prejudice has been carried too far, and begins to sound like epicycles to me.

Correspondence between model and reality is certainly something we need. I don't see the analogy with "medium of light". There is no requirement that model has to answer any conceivable question about reality. But some concepts in the model have to have correspondence to physical reality.

Correspondence can mean nothing more than that our models create correct expectations about outcomes. What more is there, in science? We can ask for more, and hope to get more, but when we don't get more (as in the case I'm discussing), I say that the history of science has been quite clear about what will eventually happen-- we will just stop asking for what we don't get. It's happened so many times before, I wonder why we tend to think the modern era is special, and that we are not subject to our own philosophical prejudices like the ancient Greeks were, or the determinists of DesCartes' day were. But I admit that if you are a Bohmian, you are going to retain realism at all costs, and you will always need a preferred foliation whether or not there is any observational evidence of it, just as a determinist will always see a determined outcome even in what looks like the random decay of an unstable particle. That doesn't make you wrong, it makes you committed to a particular mindset and future observations might eventually corroborate you. It just doesn't usually seem to work out that way, but since I have no crystal ball I'm not saying your perspective is wrong, I'm merely trying to shed light on the difference between an aspect of a model that we actually need to get correct expectations, versus an aspect we have added for essentially purely personal reasons. What I find odd is how the normal language about entanglement so often does exactly that, almost without even noticing.

 

[zonde]

The problem is, you want there to be a preferred foliation of spacetime, as you said, such that when a property is acquired by one particle, we can say the property is also acquired by the entangled particle. But you have also admitted there is no evidence of any such preferred foliation, nor could we ever do any experiment to determine when the property was acquired, because we can do the measurement at any time and get the property u in the example I gave. So what you want to be the correspondence of which you speak, and what you can actually get, are simply not the same.

It goes a bit deeper than preferred foliation of spacetime. It's about difference between "objective" and "subjective". And I take it as a basic assumption that there is a difference given realism. Our history of acquiring knowledge seems to give support for the idea that there is such a difference. So even when there is symmetry between objective and subjective I hold on to the idea that "objective" and "subjective" are different. And here we come to correspondence between reality and model. Objective elements of model do have correspondence to reality while subjective don't (at least not direct correspondence).

For me, if we cannot make the constraints intrinsic to the particle, then I see little advantage in making the properties intrinsic to the particle either, especially when I see that I only use the property concept to build expectations (in my mind) about the outcomes of observations, so it seems natural to allow that properties are mental constructs that require no "time of acquisition" in the particle proper time.

All the reasoning in our models have to produce something that we can check against observation. So what do you need in addition to expectations about observations to say that the concept is something more than mental construct?

Correspondence can mean nothing more than that our models create correct expectations about outcomes. What more is there, in science? We can ask for more, and hope to get more, but when we don't get more (as in the case I'm discussing), I say that the history of science has been quite clear about what will eventually happen-- we will just stop asking for what we don't get.

We don't stop asking for objective world view.

But I admit that if you are a Bohmian, you are going to retain realism at all costs, and you will always need a preferred foliation whether or not there is any observational evidence of it, just as a determinist will always see a determined outcome even in what looks like the random decay of an unstable particle. That doesn't make you wrong, it makes you committed to a particular mindset and future observations might eventually corroborate you.

Realism is basic assumption of scientific approach. I will retain realism as long as I will consider scientific approach meaningful. And you should too.
Btw Bohmian mechanics is a no-collapse interpretation. Didn't you know that? So if I am arguing for non-local collapse I can't be Bohmian.

 

[Ken G]

Objective elements of model do have correspondence to reality while subjective don't (at least not direct correspondence).

So motion is objective, rather than subjective? Wasn't the whole point of relativity that motion is in the eye of the beholder, whereas Newton always thought it was an objective attribute of an object? So that's what I mean about the historical inevitability that when we don't get what we want, it takes us a long time to realize that we are wanting the wrong thing.

All the reasoning in our models have to produce something that we can check against observation.

Yes, on this we agree, this is science.

So what do you need in addition to expectations about observations to say that the concept is something more than mental construct?

The realist will always wish to say that a property is more than a mental construct, even though they will never get any evidence that it is more than a mental construct. So I can accept that realists will wish to imagine that properties of particles are intrinsic to particles. But that brings up a question that we don't even encounter if we relax our demands of realism: when was the property acquired, in the proper time stream of the particle? So already the realist has a new problem that is not even necessary to have, but if they find value in their realism, then they will tolerate having this new problem. But even so, the realist must answer the question. Your answer is that there is a preferred foliation which we have no access to and can never gain access to, but is there all the same. I'm saying we must recognize this claim is being made, and is generally made when people use language like "at the same time one particle is measured, the other particle acquires the property," yet normally people using that language are not called on to admit they are assuming an unknowable and inaccessible preferred reference frame-- something that we always admonish people not to do in relativity, but apparently have no objection to in quantum mechanics!

That's why I say if we are to be consistent, and are to reject preferred reference frames when we cannot gain any experimental access to what those preferred frames are (think "aether frame"), then the only way to allow properties to be intrinsic to particles is to say they are acquired at the only non-arbitrary time in the problem, which is when the measurement occurs on each particle. And at least that also means something is actually happening to the particle, which I would have thought realists would like! But this is not standard language, for some reason, presumably because we know the observational outcome must satisfy non-local constraints, and we don't like to separate the constraints on a property from the property itself-- even though the fact that we have to do that is more or less the point of Bell's theorem.

We don't stop asking for objective world view.

Yet we always do stop asking for something after a long enough time that we aren't getting it-- that's what happened to circular orbits, to absolute motion, to deterministic outcomes, and to local realism. But we must dig a bit deeper into the term "objective", because it can have two very different meanings that are often confused. The way you mean it is in the sense of separating the object from the scientist studying it, so you regard an intrinsic property as an objective one. But the other meaning is that "objective" means "all reasonable people can agree to it," whereas subjective means that we can have widely different opinions, but that carries no connotation that the property is intrinsic to the particle, only that reasonable people agree on the property. That latter meaning is the only one essential to science, and is preserved when saying that properties are a form of information used to make predictions. But I know that realists, like Einstein famously was, will not be easily led down that road, so that's why I offer the alternative view that still avoids the need for a preferred reference frame.

Realism is basic assumption of scientific approach.

It's nowhere in the scientific method, and that's a crucial point. The historical track record of adding requirements to the scientific method, beyond the method itself, is rather dubious!

I will retain realism as long as I will consider scientific approach meaningful.

That is a choice you are free to make. But people are also free to imagine there is an aether frame, such that the basis of relativity is incorrect. There could be a preferred foliation to motion also, such that motion is actually absolute, but there just isn't any evidence this is true or reason to hold that it is true in the absence of evidence. If your priority was really to stick to the scientific method, then you would not add aspects to it that are not in the method!

Btw Bohmian mechanics is a no-collapse interpretation. Didn't you know that? So if I am arguing for non-local collapse I can't be Bohmian.

I'm not sure what you mean there, Bohmians are not free to violate Bell's theorem. All they do is choose realism over locality-- they hold that the property of a system is determined as it unfolds in its own proper time. The "pilot wave" is their nonlocal device for enforcing the necessary correlations, so in a preferred foliation of spacetime the pilot wave would appear to move instantaneously, and in some frames it would appear to move backward in time. So the collapse in the measurement on one particle is not the issue, it is how the correlation is enforced that is the issue here. Since I start the whole question after the property is acquired, whether or not there is any collapse is of no consequence to me, that's a whole other issue. No-collapse does not mean the property was always there, it only means the property was deterministically established by nonlocal pilot waves, and in some preferred foliation of spacetime, the two properties were acquired simultaneously. The Bohmian does not say properties cannot be acquired, rather, they say they are acquired deterministically and at non-arbitrary times, and that's why I view the appeal to a preferred reference frame as Bohmian realism.