Anti-realist Interpretations of QM

[Lynch101]

You keep repeating this and people here keep reinforcing this. It's a non-sensical statement, IMO.

Apologies for the repetition. I was trying to delineate what I saw as a key difference but it is one that you allude to below.

Now that said, Bell's theorem is a statement about the statistics of measurement.

It might help if I outline, by way of a crude example, the point I am trying to make on this particular point. It might offer insight into where I am going wrong.

If we imagine the crudest of crude quantum experiments where we have a black box with two screens at either end, divided into two panels, the top (or up) panel and the bottom (or down) panel. There is a button that we can press and a little while after pressing the button a flash of light appears on each screen on the end. The flashes of light always appear in opposite panels - if the flash appears on the up panel on the left screen then the flash on the right screen will always appear in the down panel, and vice versa.

If the mathematical formalism only tells us the probability of each flash, where it appears, and their always being in opposite panels then it doesn't appear to tell us what is happening inside the box. We can reasonably ask the question, what is happening inside the box.

One uses measurements and statistics of those measurements showing that predefined values for a system can't exist.

OK, so we cannot assign predefined values to what is happening inside the box but surely there must be something happening inside the box and it must have some properties, in some sense of the word - even if they aren't predefined values.

If we say yes, there is something happening inside the box but the mathematical formalism only gives us information about the measurement outcomes, then this would seem to suggest that there are hidden-variables in the box that the mathematics doesn't describe.

Okay, that not the same as the system doesn't exist or the system can't interact or the system isn't real.

My understanding is that the anti-realist position must say that there is nothing whatsoever happening inside the box because the alternative would be that there are realistic hidden-variables.

I think the idea that these hidden variables must have predefined values is a sticking point. If we drop the idea of the properties inside the box having predefined values then we are left with unqauntified properties, or what I am inclined to think are hidden-variables.

 

[Lynch101]

The quantum object is real and exists.

Would objects which exist and are real not have properties by necessity? Would real and existing not be properties in and of themselves?

Properties (of that object) don't seem to appear until a final measurement. The measurement requiring an interaction with a measuring device.

This is the part that I can't seem to get my head around. With what does the measurement device interact to give rise to the final measurement, if not the properties of the system?

I have a bit of an understanding of the idea that the system doesn't have predefined values prior to measurement and how properties might appear upon measurement. The analogy I think of is that of a single molecule of water in a dark box. We dip a piece of paper into the box and it comes out a little "wet". Here, the property of wetness only manifests upon measurement, with the interaction between the measuring device and the molecule of water, but we cannot say that the molecule was "wet" prior to measurement.

To my mind, the system must have properties to first, be considered to exist and be real, and second to interact with the measurement device.

 

[PeterDonis]

Would objects which exist and are real not have properties by necessity?

Why would they have to?

Would real and existing not be properties in and of themselves?

No. Bertrand Russell got this one right a century ago. "Existence" is a quantifier, not a property. He didn't explicitly talk about "real", but it seems to me like it would work the same way.

With what does the measurement device interact to give rise to the final measurement, if not the properties of the system?

Um, with the system?

Even in classical physics, we don't say the properties of one system interact with the properties of another system. We just say the systems interact.

 

[Lynch101]

We should distinguish between a system having no ontic state, and the ontology of the system.

When we we say there is no ontic state, what we mean is we do not model the physics of the system terms of an ontic state or ontic state space. But we can still discuss the ontology/metaphysics of the system apart from our physical models. E.g. We can say the system exists. We can say the system interacts with our measurement apparatus in a predictable way. We can discuss the system as perhaps possessing some lawmaker property that's responsible for its dynamics etc.

Argh! That's what happens when I start trying to use certain terms. Apologies for retreating to more familiar ground on this one, I keep relating it back to the statement about how its meaningless to talk about the system prior to measurement.

I wrote a post in reply to Paul Colby with a crude analogy which outlines my thinking. I hope you don't mind me referencing that to save writing it out again.

My reasoning, which is often flawed (especially when it comes to physics), is that if the mathematical formalism of QM only makes probabilistic predictions about the flashes of light that will appear at either end of a black box, then it doesn't tell us what is happening inside the box.

There are at least two conclusions that we can draw:
a) something is happening inside the box which causes the flashes
b) there is absolutely nothing happening inside the box

If we accept a) and the proposition that the mathematical formalism doesn't describe what happens inside the box it would seem to point to realistic hidden variables, even if they don't have defined values.

My understanding is that the anti-realist position says b).

 

[PeterDonis]

There are at least two conclusions that we can draw

No, there are three. Here's the third:

c) Since we are not observing or measuring anything inside the box, we cannot make any meaningful statements about whether or not anything is happening inside the box.

My understanding is that the anti-realist position says b)

I think an anti-realist would be more likely to say c). Saying that "nothing is happening" inside the box is a realist statement: it says there is a real "reality" inside the box, and nothing is happening in that real "reality". In other words, it's a positive claim about "the way things are".

Anti-realism is about not making positive claims about the way things are, unless you absolutely have to.

 

[Paul Colby]

We can reasonably ask the question, what is happening inside the box.

Well, not all questions have a meaning. For example asking classically motivated questions about quantum systems can and often have no meaning. Are electrons red? Which trajectory did the photon take? Things like that. Valid scientific questions one might ask have to be consistent and well framed relative to the current theoretical understanding.

OK, so we cannot assign predefined values

Where this actually mean assign a specific eigenvalue (or hidden variable for that matter) of the observation device prior to measurement. There are edge cases but this really isn't a point anyone would make.

If we say yes, there is something happening inside the box but the mathematical formalism only gives us information about the measurement outcomes, then this would seem to suggest that there are hidden-variables in the box that the mathematics doesn't describe.

Yeah, no.

This is where I lose the bubble. There is a system. If it's been prepared, like in an experiment, it has a known quantum mechanical state or density matrix. This is a far cry from not having anything. In all likelihood it's as much as one can know. If you perform the Schrodinger cat experiment and never open the box you will still have a dead cat in the box after some mean time. To think otherwise is counter-factual.

My understanding is that the anti-realist position must say that there is nothing whatsoever happening inside the box because the alternative would be that there are realistic hidden-variables.

Yes, if they say this they are wrong. The system is evolving in time by well understood rules. Evolving in time as in something is happening.

 

[DrChinese]

This is where I lose the bubble. There is a system. If it's been prepared, like in an experiment, it has a known quantum mechanical state or density matrix. This is a far cry from not having anything. In all likelihood it's as much as one can know.

If it is as much as we can know, then it is complete in the Einstein sense (he thought QM to be incomplete). There is no more "complete" specification of the system. This is generally accepted in pretty much all interpretations.

OK, it has a density matrix. You can call this whatever you want. But whatever you want to describe it as, it must consider Bell. The Bell requirement was that it have a specific value prior to final measurement (and a measurement choice here should not affect an outcome there). So the question to you (or anyone) is: does it? When is the value assigned?

a) If it is preassigned: you are forced to conclude that the measurement itself forced a result that must be carried to a distant entangled partner and changes it as well. That so the statistical results match the predictions of QM. So you have an FTL influence to deal with.

b) If it is not preassigned, you are fine. Of course a new problem appears, which is how the result of the distant system will meet the statistical requirements. So you now need a mechanism for that. The non-realistic interpretations attempt to supply that.

 

[Paul Colby]

does it? When is the value assigned?

Question: what is it?

An observable is assigned an operator acting on a space of state vectors. An observable + the measurement device produces one eigenvalue. So the value produced by the observable + the measuring device is assigned when the measurement is made. The measurement can be non-local as in correlations between distant devices.

b) If it is not preassigned, you are fine. Of course a new problem appears, which is how the result of the distant system will meet the statistical requirements. So you now need a mechanism for that. The non-realistic interpretations attempt to supply that.

Why isn't the standard quantum mechanics just this mechanism?

 

[Morbert]

There are at least two conclusions that we can draw:
a) something is happening inside the box which causes the flashes
b) there is absolutely nothing happening inside the box

My understanding is that the anti-realist position says b).

Anti-realism is a claim about how our quantum model relates to the system, rather than a claim about the system alone. Our quantum model consists of:

a quantum state and state space
dynamics
a sample space
event algebras

These ingredients let us assign probabilities to different possible measurement outcomes. Anti-realism is the position that the properties in our sample space do not correspond to actually existing properties of the system we are modelling, and are instead part of the procedure for computing probabilities for outcomes of measurements on the systems.

Note that this is different from your position b). A physicist can adopt an anti-realist position regarding her model of the system in the black box, while still rejecting the claim that "there is absolutely nothing happening inside the box".

If we accept a) and the proposition that the mathematical formalism doesn't describe what happens inside the box it would seem to point to realistic hidden variables, even if they don't have defined values.

Variables are a feature of models a physicist constructs, and if a physicist does not model the inner happenings of the box, then there would be no need to use hidden variables in the model.

 

[Lynch101]

Why would they have to?

That's a good question! It might just be an unquestioned assumption on my behalf. I have been giving it some thought so it would be great to try to tease it out, although I am wary of the potential for it to turn into an exercise in navel gazing . Prior to that though, would my initial summation be accurate then, that the anti-realist position says that the quantum system has no properties whatsoever prior to measurement?

Thinking about the question, I was thinking in terms of a materialist paradigm, as opposed to say the paradigm of Cartesian Dualism. Again, I might have a hidden assumption in here but I was thinking that the materialist paradigm says that all things which exist are physical i.e. they are made of material substances which have physical properties.

As the "resident realist" , I would be interested to hear if @Demystifier has any thought on the idea that things can exist without any properties. He might be able to articulate it better than myself maybe.

Um, with the system?

How can a system without properties interact with something else? What part of the system is interacting with what part of the measuring device? When preparing the system, how can something with properties pepare a system that has absolutely no properties?

I know this might seem like a re-statement of the "measurement problem" but how can the system being measured contribute to the measurement outcome, if its properties don't play a part?

If the mathematical formalism only gives us the probability of a measurement outcome then it can't really be said to describe what goes on inside "the box", can it?

We might deduce from the mathematics that the properties cannot have predefined values, but that wouldn't be the same as saying there are no properties whatsoever, would it?

Even in classical physics, we don't say the properties of one system interact with the properties of another system. We just say the systems interact.

If we think about a baseball bat striking a baseball I feel like they interact the way they do because of their respective properties, in contrast to how neutrinos don't interact in the same way because of their properties. But again, that might be down to an assumption or a heuristic on my part.

 

[Lynch101]

I've just re-arranged the order of the points you make. I hope this doesn't misrepresent your post.

I think an anti-realist would be more likely to say c). Saying that "nothing is happening" inside the box is a realist statement: it says there is a real "reality" inside the box, and nothing is happening in that real "reality". In other words, it's a positive claim about "the way things are".

Anti-realism is about not making positive claims about the way things are, unless you absolutely have to.

This would be how I interpret the instrumentalist position and would distinguish it as being "non-realist". Instrumentalism doesn't make ontological claims while anti-realism does. I would take anti-realism to be the denial of realism.

No, there are three. Here's the third:

c) Since we are not observing or measuring anything inside the box, we cannot make any meaningful statements about whether or not anything is happening inside the box.

Again to my mind, that would be the instrumentalist position. It says that we cannot choose between the two options but I would still think there can only be two options a) something happening b) nothing happening.

I'll try and clarify my thinking in terms of Schroedinger's cat. We might say that we cannot say whether the cat is alive or dead until we open the box, and we might even say that the cat is in a superposition until we measure it, but I would say that there is still something inside the box or something happening inside the box.

 

[Demystifier]

As the "resident realist" , I would be interested to hear if @Demystifier has any thought on the idea that things can exist without any properties. He might be able to articulate it better than myself maybe.

I think they can't, but I don't have a particularly enlightening way to articulate it.

 

[PeterDonis]

Instrumentalism doesn't make ontological claims while anti-realism does.

You could be right, but I would want to see some actual references to anti-realist papers.

How can a system without properties interact with something else?

I don't know, but I also don't know that it isn't possible. Questions like this have a very poor track record of getting at real issues in quantum interpretations. Pretty much any a priori assumption you make about how things "must" be is likely to be wrong.

I would still think there can only be two options a) something happening b) nothing happening.

Same comment as above.

 

[Morbert]

You could be right, but I would want to see some actual references to anti-realist papers.

Lynch101 is using a nonstandard definition of anti-realism, one that does not square with its use in literature. E.g. Asher Peres is a contemporary anti-realist and in his book "Quantum Theory: Methods and Concepts" he says

"The role of physics is to study relationships between these [objective experimental] records. Some people prefer to use the word intersubjectivity, which means all observers agree on the outcome of any particular experiment. Whether or not there exists an objective reality beyond the intersubjective reality may be an interesting philosophical problem, but this is not the business of quantum theory. Quantum theory in a strict sense is nothing more than the set of rules whereby physicists compute probabilities of the outcomes of macroscopic tests."

Anti-realism is the claim that , whether or not there is an objective reality beyond the intersubjective reality, the variables that manifest in quantum mechanics are not to be interpreted as elements of that objective reality.

What Lynch is describing is more akin to property nihilism than anti-realism.

 

[Lynch101]

Well, not all questions have a meaning. For example asking classically motivated questions about quantum systems can and often have no meaning. Are electrons red? Which trajectory did the photon take? Things like that. Valid scientific questions one might ask have to be consistent and well framed relative to the current theoretical understanding.

That's very true. There may also be questions which have meaning but which we cannot answer due to limitations on our ability to probe the world around us. I'm inclined to think that the question of what happens prior to measurement is of the second variety.

Where this actually mean assign a specific eigenvalue (or hidden variable for that matter) of the observation device prior to measurement. There are edge cases but this really isn't a point anyone would make.

I might be misunderstanding this point, but I'm interpreting "observation device" to mean measurement device. So, instead of saying that we can't assign a value to the measurement device prior to measurement, I'm talking about the quantum system prior to measurement. The idea I'm trying to get at might be termed an unquantified property. Would that be what the term "beable" refers to?

This is where I lose the bubble. There is a system. If it's been prepared, like in an experiment, it has a known quantum mechanical state or density matrix. This is a far cry from not having anything. In all likelihood it's as much as one can know. If you perform the Schrodinger cat experiment and never open the box you will still have a dead cat in the box after some mean time. To think otherwise is counter-factual.

My misunderstanding might lie in what the mathematical formalism describes.

So there is a system and, not to be pedantic, but there is a system prior to measurement. As you say, it has been prepared. My first question would be how a system without properties can be prepared; what is it that is being prepared? To my mind, a system would have to be prepared with at least some properties, any properties, even if we cannot ascribe definitive values to the properties of the system.

You mention the density matrix. Does it describe the system prior to measurement or does it - please forgive my loose description here - simply form part of the probabilistic predictions for the outcome of the experiment? My understanding is that the anti-realist position says that it only forms part of the prediction.

 

[Lynch101]

tl;dr: I might be missing something somewhere, but it reads to me that what you and others are describing as "anti-realism" is what I understand as instrumentalism or Shut up and Calculate (SUAC).

Anti-realism is a claim about how our quantum model relates to the system, rather than a claim about the system alone. Our quantum model consists of:

a quantum state and state space
dynamics
a sample space
event algebras

These ingredients let us assign probabilities to different possible measurement outcomes. Anti-realism is the position that the properties in our sample space do not correspond to actually existing properties of the system we are modelling, and are instead part of the procedure for computing probabilities for outcomes of measurements on the systems.

This is what I understand to be the instrumentalist position or the SUAC position. It says that the mathematics is just a predictive tool. If it is necessary to make a distinction, I would interpret this more as "non-realism" than anti-realism.

The SUAC position stops short of making ontological inferences from the mathematics while the anti-realist position, as I understand it, does make ontological inferences from the mathematics. It goes further than simply saying the position that the properties in our sample space do not correspond to actually existing properties of the system we are modelling, it says that they do not correspond to actually existing properties because there are no existing properties. It denies the reality of such properties, which is what makes it an anti-realist interpretation, as opposed to the non-realist, SUAC position which remains silent on such questions of the state of the system prior to measurement.

Note that this is different from your position b). A physicist can adopt an anti-realist position regarding her model of the system in the black box, while still rejecting the claim that "there is absolutely nothing happening inside the box".

I might not be picking up on some nuance, but it reads to me like saying a physicist can adopt an instrumentalist (SUAC) position while rejecting claim b). That I would completely agree with it. But that would just bring us back to the question about the description of the system prior to measurement.

Variables are a feature of models a physicist constructs, and if a physicist does not model the inner happenings of the box, then there would be no need to use hidden variables in the model.

This would then relate back to the issue Einstein had about QM not being a complete description of "the world", wouldn't it? The question about what happens prior to measurement, or what the description is, of the quantum system prior to measurement, is a question about the inner workings of the box. If the model doesn't account for the inner workings of the box then it wouldn't be considered a complete description of the system, would it?

Again, this is just my interpretation of the descriptions and arguments that I've read, and I might be missing something along the way.

 

[Lynch101]

If it is as much as we can know, then it is complete in the Einstein sense (he thought QM to be incomplete). There is no more "complete" specification of the system. This is generally accepted in pretty much all interpretations.

I think this is where I am falling between the cracks, so to speak.

I think we can ask a further question here: why is it as much as we can know? I think there are at least two answers to that question:
1) because there is a limit to our ability to probe nature.
2) because there is nothing more to know i.e. there is nothing inside the box.

Answer 1) would imply that our model is not a complete description of nature but it also says that there is no more complete specification of the system. Am I correct in saying that those parts of the system which cannot be modeled would be referred to as "beables"? I have been referring to them as properties of the system prior to measurement, but beables might be the more accurate term. I have been thinking of beables as hidden-variables, but I might be conflating two terms there.

Answer 2) is what I have come to understand as the "anti-realist" position.

OK, it has a density matrix. You can call this whatever you want. But whatever you want to describe it as, it must consider Bell. The Bell requirement was that it have a specific value prior to final measurement (and a measurement choice here should not affect an outcome there). So the question to you (or anyone) is: does it? When is the value assigned?

a) If it is preassigned: you are forced to conclude that the measurement itself forced a result that must be carried to a distant entangled partner and changes it as well. That so the statistical results match the predictions of QM. So you have an FTL influence to deal with.

b) If it is not preassigned, you are fine. Of course a new problem appears, which is how the result of the distant system will meet the statistical requirements. So you now need a mechanism for that. The non-realistic interpretations attempt to supply that.

Is it possible to talk about unquantified properties of the system. I'm thinking of properties at a fundamental level without preassigned values. I'm not exactly sure how that would work, but to my mind it seems like a conclusion that can be drawn.

 

[Lynch101]

I think they can't, but I don't have a particularly enlightening way to articulate it.

It's infuriating isn't it?! It's a bit like that quote about time " If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know."

 

[Lynch101]

You could be right, but I would want to see some actual references to anti-realist papers.

I don't know, but I also don't know that it isn't possible. Questions like this have a very poor track record of getting at real issues in quantum interpretations. Pretty much any a priori assumption you make about how things "must" be is likely to be wrong.

Same comment as above.

I guess that's part of what makes it so fascinating.

 

[Paul Colby]

I'm inclined to think that the question of what happens prior to measurement is of the second variety.

Please define what you mean by happen.

My definition is the system state vector evolves in time according to QM.

So, instead of saying that we can't assign a value to the measurement device prior to measurement, I'm talking about the quantum system prior to measurement.

And hence the eternal problem I see with many such discussions. No macroscopic measurements device, no data. These arguments are like the sound of one hand clapping.

System preparation, where to begin? For Schrodinger's cat experiment you've selected some cats to kill and put them in boxes and filled the poison vials. For a particle experiment you've turned on and tuned the accelerator and selected a target etc.

My first question would be how a system without properties can be prepared;

Again, define what you mean by system property. I have no problem finding cats.

In QM properties involves operators and state vectors plus an implied ideal measurement device which is always macroscopic AFAICT.

 

[Lynch101]

Lynch101 is using a nonstandard definition of anti-realism, one that does not square with its use in literature. E.g. Asher Peres is a contemporary anti-realist and in his book "Quantum Theory: Methods and Concepts" he says

"The role of physics is to study relationships between these [objective experimental] records. Some people prefer to use the word intersubjectivity, which means all observers agree on the outcome of any particular experiment. Whether or not there exists an objective reality beyond the intersubjective reality may be an interesting philosophical problem, but this is not the business of quantum theory. Quantum theory in a strict sense is nothing more than the set of rules whereby physicists compute probabilities of the outcomes of macroscopic tests."

Anti-realism is the claim that , whether or not there is an objective reality beyond the intersubjective reality, the variables that manifest in quantum mechanics are not to be interpreted as elements of that objective reality.

What Lynch is describing is more akin to property nihilism than anti-realism.

I would interpret Peres's description (abvoe) as being a statement of instrumentalism or akin to SUAC. It doesn't seek to address the question of whether or not there exists an objective reality beyond the intersubjective reality, which is the question of the description of the quantum state prior to measurement.

As I see it, there are only two possible answers to that question:
1) Yes there is an objective reality
2) No there is no objective reality.

1) would be the realist position and would seem to imply that QM is not a complete description of nature, which I think was [at least part of] what Einstein was arguing. Would I be correct in saying that 1) would imply that there are "beables"?

2) is what I would interpret as the anti-realist position, as opposed to the instrumentalist position.

 

[Lynch101]

Please define what you mean by happen.

I'm using it in the broadest possible sense. Radioactive decay of a particle, triggering a geiger counter, which breaks a vile of poison to kill a cat, would be an example of something happening. A pilot wave directing a particle through an apparatus to interact with a measurement device would be another example. It's a place holder in lieu of a more complete description of the process unfolding in the box.

My definition is the system state vector evolves in time according to QM.

Would you say that the system state vector describes the process occurring prior to measurement, or does it ONLY give us information about the measurement outcome? If it only gives us information about the outcome then it doesn't describe the system prior to measurement. But you seem to be in agreement that the system does indeed exist prior to measurement. If it does exist prior to that, then there is something there to be described. At least that would be my thinking.

To try and give a different analogy. If we imagine looking at the outside wall of a building, with 5 windows and we set up a baseball pitching machine at the opposite side of the building to fire baseballs at the windows. If we have a mathematical formalism that ONLY tells us the probability of which window will get broken by a baseball then it doesn't tell us anything about the system prior the window breaking i.e. how the baseball got form the machine to the window.

I am inclined to think there is something to be described inside the building. It might never be possible to look inside the building and baseballs may not behave the way we think they do inside the building, but I think there is something to be described.

And hence the eternal problem I see with many such discussions. No macroscopic measurements device, no data. These arguments are like the sound of one hand clapping.

In the analogy above the windows would represent the macroscopic measurement device but there appears to be some information missing about what the baseball does from when it leaves the device to when it breaks the window. We don't have data for that, but that doesn't mean that there is nothing to be described inside the building.

System preparation, where to begin? For Schrodinger's cat experiment you've selected some cats to kill and put them in boxes and filled the poison vials. For a particle experiment you've turned on and tuned the accelerator and selected a target etc.

But how do you prepare a system to have absolutely no properties whatsoever? How does the particle get from the preparation device to the target, does it follow a specific trajectory through the apparatus? Can we describe the path that the particle takes through the apparatus before hitting the target? Is it reasonable to think that it must travel through the apparatus to get to the target?

Again, define what you mean by system property. I have no problem finding cats.

In the EPR paper, EPR tried to demonstrate that particles must have the very specific properties of location and momentum prior to measurement. I'm talking in a much more general sense, not about specific properties, but any properties whatsoever.

In QM properties involves operators and state vectors plus an implied ideal measurement device which is always macroscopic AFAICT.

The question I guess I'm trying to get at, in terms of the analogy of the baseball and the windows, is the question of what happens inside the building, prior to the window being smashed.

If our formalism only tells us the probability for any given window getting smashed, then it doesn't describe what happens inside the building. The question then becomes: is there something to be described inside the building?

 

[DrChinese]

I think we can ask a further question here: why is it as much as we can know? I think there are at least two answers to that question:
1) because there is a limit to our ability to probe nature.
2) because there is nothing more to know i.e. there is nothing inside the box.

Answer 1) would imply that our model is not a complete description of nature but it also says that there is no more complete specification of the system. Am I correct in saying that those parts of the system which cannot be modeled would be referred to as "beables"? I have been referring to them as properties of the system prior to measurement, but beables might be the more accurate term. I have been thinking of beables as hidden-variables, but I might be conflating two terms there.

Answer 2) is what I have come to understand as the "anti-realist" position.

Is it possible to talk about unquantified properties of the system. I'm thinking of properties at a fundamental level without preassigned values. I'm not exactly sure how that would work, but to my mind it seems like a conclusion that can be drawn.

Answer 2) is mostly the standard view of physicists. That QM is complete as is. Although Bohmians might argue that a more complete specification of the system is possible. No quibble as interpretations each address this.

The unquantified properties of an ENTANGLED system can be discussed. They follow conservation rules. A+B=zero/constant/initial value.

 

[Morbert]

tl;dr: I might be missing something somewhere, but it reads to me that what you and others are describing as "anti-realism" is what I understand as instrumentalism or Shut up and Calculate (SUAC).

This is what I understand to be the instrumentalist position or the SUAC position. It says that the mathematics is just a predictive tool. If it is necessary to make a distinction, I would interpret this more as "non-realism" than anti-realism.

What I have described is anti-realism as it is used in literature: The claim that the properties in QM do not refer to real properties of the system.

It goes further than simply saying the position that the properties in our sample space do not correspond to actually existing properties of the system we are modelling, it says that they do not correspond to actually existing properties because there are no existing properties.

The bit in bold is not a prerequisite for anti-realism. It is only physical properties present in our models that an anti-realist rejects as real. Before we can discuss Einstein's concerns, we have to square away nomenclature as it is used in literature.

If we were to distinguish anti-realism from instrumentalism, we could say an anti-realist is agnostic towards the nature of the reality of quantum systems, and rejects physical properties in our models as real, while an instrumentalist is agnostic towards both the nature of reality of quantum systems and also the ontic status of the physical properties present in our models.

As I see it, there are only two possible answers to that question:
1) Yes there is an objective reality
2) No there is no objective reality.

1) would be the realist position and would seem to imply that QM is not a complete description of nature, which I think was [at least part of] what Einstein was arguing. Would I be correct in saying that 1) would imply that there are "beables"?

Beables are a feature of a particular category of physical models. If it is the case that there is an objective reality, but it cannot be modeled with beables or hidden variables, then beables would not be a good description of this objective reality. It may be the case, for example, that reality cannot be thoroughly accounted for with physical theories.

 

[Paul Colby]

Would you say that the system state vector describes the process occurring prior to measurement, or does it ONLY give us information about the measurement outcome?

Yes and yes.

How does the particle get from the preparation device to the target,

By the time development of the system state vector.

Can we describe the path that the particle takes through the apparatus before hitting the target?

Well, yes just not at all in the manner you describe. One can show experimentally for fields in $\alpha$-states that the photons in fact have no trajectory (in fact the entire question isn't meaningful). Closest one can get is the wave nature of the field. Again, asking a classically motivated question about quantum systems isn't at all meaningful. Similar arguments hold for electrons and nuclei. If this is the picture you hold in mind, it's counter-factual.

The question I guess I'm trying to get at, in terms of the analogy of the baseball and the windows, is the question of what happens inside the building, prior to the window being smashed.

So your classical biases are showing through. You clearly want to paint a nice neat real number on each property ignoring the fact it's been shown by experiment that this isn't possible. It's simply not the way the world is observed to work, ever. Classical macroscopic physics is an approximation superseded by QM, a better one. It's now the case that one must provide a theory of measurement justifying classical mechanics in terms of quantum measurements, not the reverse. Your philosophical machinations really aught to be inverted.

 

[Lord Jestocost]

Would you say that the system state vector describes the process occurring prior to measurement, or does it ONLY give us information about the measurement outcome? If it only gives us information about the outcome then it doesn't describe the system prior to measurement. But you seem to be in agreement that the system does indeed exist prior to measurement. If it does exist prior to that, then there is something there to be described. At least that would be my thinking.

Even if a quantum entity “exists” prior to a measurement, what would it mean that there is something to be described. At first, one has to state, how the quantum entity exists, i.e., what is the character of its “existence” (realism).^** That’s a requirement for a “pictorial representation” in relation to the quantum formalism.

As remarked by Jan Faye in “Copenhagen Interpretation of Quantum Mechanics” (https://plato.stanford.edu/entries/qm-copenhagen/):

“In these four statements Bohr mentions the absence of “pictorial representation” twice in relation to the quantum formalism. The term “pictorial representation” stands for a representation that helps us to visualize what it represents in contrast to “symbolic representation”. A pictorial representation is a formalism that has an isomorphic relation to the objects it represents such that the visualized structure of the representation corresponds to a similar structure in nature. Conversely, a symbolic representation does not stand for anything visualizable. It is an abstract tool whose function it is to calculate a result whenever this representation is applied to an experimental situation.”

^** Regarding claims concerning the character of the “existence” of a quantum entity, the problems were clearly expressed by J. Robert Oppenheimer in “Atom and Void: Essays on Science and Community”:

If we ask, for instance, whether the position of the electron remains the same, we must say "no"; if we ask whether the electron's position changes with time, we must say "no"; if we ask whether the electron is at rest, we must say "no"; if we ask whether it is in motion, we must say "no."

 

[Demystifier]

It's infuriating isn't it?! It's a bit like that quote about time " If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know."

Well, concepts the meaning of which is intuitive but cannot be defined precisely are called primitive. Similarly, claims the truth of which seems obvious but can be neither proved nor disproved are called axioms. Any system of thought must contain some primitive concepts and some axioms. Once one realizes that, it's no longer infuriating.

 

[Morbert]

As an aside, it's worth emphasising that, according to modern anti-realist accounts, what comes into existence upon measurement is the record of that measurement expressed by properties of the apparatus. The measured property of the quantum system remains fictitious even after measurement.

I suspect statements like "spin of a particle becomes real after measurement" are common because, in experimental contexts like the EPR experiment, we don't violate complementarity if we construct event algebras that only reference spins after the corresponding measurements have occurred. But these are not the only valid algebras consistent with complementarity that we can construct. We can construct algebras that reference spin before measurement has occurred that will still produce the same correct predictions.

 

[Lord Jestocost]

As an aside, it's worth emphasising that, according to modern anti-realist accounts, what comes into existence upon measurement is the record of that measurement expressed by properties of the apparatus. The measured property of the quantum system remains fictitious even after measurement.

Is this a modern anti-realist account?
Sir Arthur Stanley Eddington in “THE NATURE OF THE PHYSICAL WORLD” (Cambridge, At the University Press (1929)):

"But now we realize that science has nothing to say as to the intrinsic nature of the atom. The physical atom is, like everything else in physics, a schedule of pointer readings. The schedule is, we agree, attached to some unknown background."

 

[Morbert]

Is this a modern anti-realist account?
Sir Arthur Stanley Eddington in “THE NATURE OF THE PHYSICAL WORLD” (Cambridge, At the University Press (1929)):

"But now we realize that science has nothing to say as to the intrinsic nature of the atom. The physical atom is, like everything else in physics, a schedule of pointer readings. The schedule is, we agree, attached to some unknown background."

Yes. It would be in line with A. Peres R. Omnes etc

 

[DrChinese]

We can construct algebras that reference spin before measurement has occurred that will still produce the same correct predictions.

Unless I don't understand your comment, Bell precludes that.

There are no data sets or statistical averages for quantum spins independent of the measurement setting(s). Keeping in mind that there are a multitude of statistical requirements due to the multitude of possible settings (thinking of typical Bell tests here).

 

[Lynch101]

Answer 2) is mostly the standard view of physicists. That QM is complete as is.

That is the understanding I had gotten, although I wasn't exactly sure what the breakdown of proponents was.

I just think there is a serious issue with the idea that there is nothing at all "inside the box", because if there were something "inside the box" then to my mind there is something to be described. If there is nothing at all inside the box, then it raises the question of how nothing can interact with a measurement device to produce something i.e. a measurement outcome.

Although Bohmians might argue that a more complete specification of the system is possible. No quibble as interpretations each address this.

The Bohmian picture seems to be the most intuitive to me but I think there is a middle ground between the idea that a more complete specification of the system is possible and the idea that there is nothing in need of description. There might be something "inside the box" to be described, but it might not be possible to probe it in such a way that we can meaningfully describe it. We could still make certain limited deductions however.

The unquantified properties of an ENTANGLED system can be discussed. They follow conservation rules. A+B=zero/constant/initial value.

Is this more a statement about rules that they follow as opposed a description of the properties?

 

[Lynch101]

If we were to distinguish anti-realism from instrumentalism, we could say an anti-realist is agnostic towards the nature of the reality of quantum systems, and rejects physical properties in our models as real, while an instrumentalist is agnostic towards both the nature of reality of quantum systems and also the ontic status of the physical properties present in our models.

Ah thank you Morbert, I think I see the distinction you're making, now. Is the following accurate?

The anti-realist in QM says that the (for want of a better term) mathematical elements of QM don't have a 1-to-1 correspondence with the quantum system itself, or with reality we might say. It says that the model only enables us to make the probabilistic predictions we see in QM. It says that there might be something "inside the box" or there might not, either way the mathematical formalism doesn't describe what is "inside the box"?

On the other hand, instrumentalism says the model might have a direct correspondence to reality or it might not, who cares, just SUAC?

Beables are a feature of a particular category of physical models. If it is the case that there is an objective reality, but it cannot be modeled with beables or hidden variables, then beables would not be a good description of this objective reality. It may be the case, for example, that reality cannot be thoroughly accounted for with physical theories.

Ah, I see. Thanks for the clarification on that too.

 

[Lynch101]

I've re-ordered your post to reply to a specific point first. Hopefully this doesn't distort it in any way.

So your classical biases are showing through. You clearly want to paint a nice neat real number on each property ignoring the fact it's been shown by experiment that this isn't possible. It's simply not the way the world is observed to work, ever. Classical macroscopic physics is an approximation superseded by QM, a better one. It's now the case that one must provide a theory of measurement justifying classical mechanics in terms of quantum measurements, not the reverse. Your philosophical machinations really aught to be inverted.

Classical bias would be to say that the baseball follows a simple trajectory through the building with a definite location and momentum at every point en route to the window. Experiment shows that this isn't the case when we have say two slits, inside the building, through which the baseball can travel and both are open. If we open one slit at a time then it would appear as though we could infer our classical notions of trajectory. Of course, this wouldn't account for what happens when both slits are open, so we can't simply infer our classical notions of trajectory.

To account for what happens when both slits are open we might try to infer a different classical bias. We might say that the baseball spreads out like a wave and goes through both slits, interferes with itself and then strikes the one of the windows. We might say that the mathematical formalism is a description of what is happening inside the building and the process it describes is that of a baseball riding on top of a pilot wave and that it is the pilot wave that interferes with itself, carrying the baseball to one of the windows to smash it. All of these offer an explanation as to how the baseball gets from the machine to the window to smash it.

If, however, we reject all of these and say that our mathematical formalism only tells us the probability of which window will get broken, and nothing more, we are then left with the question of what is actually happening inside the building? How does the baseball get from the machine to the window to break it?

There are essentially two broad answers to this question:
1) There is something happening inside the building. For a complete model of nature we would need to describe the process occurring inside the building.
2) There is absolutely nothing happening inside the building and therefore nothing to describe.

Yes and yes.
By the time development of the system state vector.

Hopefully I'm phrasing this correctly but, do you attribute ontic status to these?

In my own terminology I would ask if you believe that these parts of the model correspond directly to reality?

Well, yes just not at all in the manner you describe. One can show experimentally for fields in $\alpha$-states that the photons in fact have no trajectory (in fact the entire question isn't meaningful). Closest one can get is the wave nature of the field. Again, asking a classically motivated question about quantum systems isn't at all meaningful. Similar arguments hold for electrons and nuclei. If this is the picture you hold in mind, it's counter-factual.

My apologies, I think my wording is a little to imprecise at times, or perhaps carries with it certain connotations that I don't intend. I try not to have any specific picture in mind.

Apologies again for coming back to this basic point, but it helps me to frame the issue in my mind; the question of the description of the system prior to measurement. If we say it is meaningless to talk about it or that the formalism only gives us predictions, then I interpret that to mean that it doesn't describe what happens "inside the building".

I may be misinterpreting what you are saying but in one sense you appear to be saying that the formalism does describe the system prior to measurement i.e. saying that it describes how the "particle" makes its way through the experimental set-up, prior to measurement.

 

[PeterDonis]

Experiment shows that this isn't the case when we have say two slits, inside the building, through which the baseball can travel and both are open.

Experiment shows no such thing. Nobody has done a double slit experiment showing interference with baseballs. Buckyballs, yes, but not baseballs. Buckyballs are many, many, many orders of magnitude smaller.