Anti-realist Interpretations of QM

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  • #51
Paul Colby
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I'm talking in the more general sense of any property whatsoever. To my understanding the "anti-realist" position says that the quantum system has no properties whatsoever, in the general sense. My interpretation is that the alternative to this is to say that the system does have some [unquantified] properties. My understanding is that to say the system has unquantified properties would be to say that it has hidden variables and is realistic.
What anti-realist believe or say is beyond me. You're best listening to people more versed in what they actually say. They sound unhinged but that's only my opinion based on the snippets in this thread.

So, the axioms of QM actually provide a means of being clear about "properties." I read property as an observable. An observable is an operator which has a spectrum, a set of allowed values that may be observed. This spectrum is unchanging and I would call it a property.

Now, upon measurement only one of the spectrum set is obtained as a result. This result is the property-value.
 
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  • #52
DrChinese
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1. Apologies, I'm not clear on what you mean by the sentence I emboldened above, as in how do you mean it is by definition?

2. I'm not sure if I've used the relevant terms accurately enough...
1. At some point, everyone reverts to their own language to describe things. And similarly, it is impossible to say if your words are close in meaning to mine. If you believe the following, that a particle in a superposition of states lacks a well-defined value independent of a measurement basis chosen by an observer, then I would say you have adopted an "anti-realist" position. I would call it "non-realistic" rather than "anti-realist" but I can't see any difference.

"An entangled electron, for example, lacks well defined values for its entangled properties. You could say those properties are in a superposition of states."


2. This is why there is an Interpretations sub forum. No one is...
 
  • #53
DrChinese
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What anti-realist believe or say is beyond me.
Bell's Theorem says: No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics.

Quantum Mechanics requires us to abandon at least one of "locality" and "realism" (hidden variables which may be unknowable). The anti-realist position would be that realism is abandoned, presumably so you can retain locality.

There are a number of interpretations that reject realism. In the time symmetric group, there is a mechanism of "handshake" (however that works) between the quantum object being observed and the observer. Therefore there is observer dependence and you have a subjective reality - retaining locality.
 
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Lynch101
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So, the axioms of QM actually provide a means of being clear about "properties." I read property as an observable. An observable is an operator which has a spectrum, a set of allowed values that may be observed. This spectrum is unchanging and I would call it a property.

Now, upon measurement only one of the spectrum set is obtained as a result. This result is the property-value.
Definining "properties" as "observables" seems to come back, somewhat, to the point about what we can say about the system prior to measurement.

My difficulty in defining properties as observables, but that might just be due to the fact that I don't have a good working knowledge of the various terms, so I can't articulate my point using the more precise terms. "Beable" might be the more suitable term - I just haven't used it enough yet. From @Demystifier's paper in his signature:
Beable: That word was coined by John Bell. It means the same as ontology: stuff which is there irrespective of observation. The concept of a beable is central to Bohmians, but not to instrumentalists.
Another difficulty I have with defining "properties" as "observables" is that "beables" are distinguished from observables but we might still talk about the properties of beables or perhaps say nothing more than the statemement, "beables have properties". Is there also a question of whether or not the observable can be said to be an inherent property of the system?

If we talk about the properties of a system prior to measurement, it also distinguishes a property from an observed property.


It's in this broad sense of the term property that I tend to talk, to try to clarify my interpretation of "anti-realism". To try and use the term "beable": the "anti-realist" position seems to say that there are no beables prior to measurement.

In terms that seem more intuitive to me, I would say that the anti-realist position says that the system has no properties whatsoever prior to measurement. It is this which leads me to question how anything without properties can interact with a measurement device in the first place?
 
  • #55
Lynch101
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1. At some point, everyone reverts to their own language to describe things.
Thank you DrChinese, this is reassuring (if not comforting :oldbiggrin:).

And similarly, it is impossible to say if your words are close in meaning to mine. If you believe the following, that a particle in a superposition of states lacks a well-defined value independent of a measurement basis chosen by an observer, then I would say you have adopted an "anti-realist" position. I would call it "non-realistic" rather than "anti-realist" but I can't see any difference.
I would be inclined to distinguish between "non-realist" and "anti-realist", where non-realism and instrumentalism are effectively one and the same. My understanding is that it says that a particle in a superposition of states lacks a well-defined value independent of a measurement basis chosen by an observer. It does not make any ontological inferences from the mathematical formalism.

"Anti-realism" on the other hand goes further, it does make ontological inferences from the mathematical formalism. It seems to say that a particle in a superposition of states lacks a well-defined value independent of a measurement basis chosen by an observer, because a particle in a superposition does not have any properties prior to measurement.

"An entangled electron, for example, lacks well defined values for its entangled properties. You could say those properties are in a superposition of states."
This might be where my limited understanding of the mathematics is hindering me. My understanding is that, according to the "anti-realist" position, the mathematical formalism which describes the superposition only gives the probabilities for the measurement outcome of the entangled particles, meaning that it doesn't describe the ontic state of the particles prior to measurement.

If the entangled state defined by the mathematics is an ontic state that would make it a realistic interpretation, wouldn't it? Whereas, if the superposition described by the mathematical formalism is just a tool for predicting the outcome of experiments, then it doesn't describe the system prior to measurement. The instrumentalist/"non-realist" position stops there, but the "anti-realist" position would go further, as above.

That would be my understanding of it.


2. This is why there is an Interpretations sub forum. No one is...
:oldbiggrin::bow:
 
  • #56
Paul Colby
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Quantum Mechanics requires us to abandon at least one of "locality" and "realism" (hidden variables which may be unknowable). The anti-realist position would be that realism is abandoned, presumably so you can retain locality.
So, would it be accurate to say;

realism = systems have property values prior to measurement?

Since the realism view is born out of a classical macroscopic intuition we evolved with, I say that it's unsupported by the measurements and should be abandoned. There is no reason to expect it to hold for purely quantum objects.
 
  • #57
Paul Colby
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In terms that seem more intuitive to me, I would say that the anti-realist position says that the system has no properties whatsoever prior to measurement. It is this which leads me to question how anything without properties can interact with a measurement device in the first place?
I can only repeat what I've said. I believe you are conflating having a value with having a possible set of observable values. Things interact because they do and we have the formalism and data to prove it.
 
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In terms that seem more intuitive to me, I would say that the anti-realist position says that the system has no properties whatsoever prior to measurement. It is this which leads me to question how anything without properties can interact with a measurement device in the first place?
Anti-realism re/ QM pertains to the anti-realism of properties considered by QM (i.e. those represented by regions of Hilbert space), as opposed to all properties entirely.
 
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  • #59
Demystifier
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Am I correct in saying that, according to the instrumentalist and anti-realist positions, the wave function doesn't describe the properties of the system prior to measurement?
Yes.

In this sense then, the properties of the system prior to measurement - if such properties exist - would be considered hidden variables according to 1) above?
Yes.

I had thought that hidden variables necessarily implied an underlying deterministic Universe, but would stochastic interpretations that treat the wave function realistically also involve hidden variables?
Yes, in the sense 1) and 2).
 
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It is this which leads me to question how anything without properties can interact with a measurement device in the first place?
Exactly!
 
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  • #61
Lord Jestocost
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.......that there is no mind-independent reality?
You have to distinguish between the "empirical reality" and the "ultimate reality". As Bernard d'Espagnat points out:

What quantum mechanics tells us, I believe, is surprising to say the least. It tells us that the basic components of objects – the particles, electrons, quarks etc. – cannot be thought of as "self-existent". The reality that they, and hence all objects, are components of is merely "empirical reality".

This reality is something that, while not a purely mind-made construct as radical idealism would have it, can be but the picture our mind forces us to form of ... Of what ? The only answer I am able to provide is that underlying this empirical reality is a mysterious, non-conceptualisable "ultimate reality", not embedded in space and (presumably) not in time either.


From: https://www.theguardian.com/science/blog/2009/mar/17/templeton-quantum-entanglement
 
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Lynch101
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I can only repeat what I've said. I believe you are conflating having a value with having a possible set of observable values. Things interact because they do and we have the formalism and data to prove it.
Apologies, I don't quite follow this point because I'm not sure that I am conflating those two.

If we go back to the contention that "it is meaningless to talk about the quantum system prior to measurement", this begs the question as to why it is meaningless. This usually stems from the instrumentalist notion that the mathematical formalism only gives probabilistic predictions for the outcomes of measurements. If the mathematics only describes the outcome of experiments i.e. only gives the probability that a particular measurement will be observed, then it doesn't appear to describe the properties of the system prior to measurement.

The istrumentalist position doesn't go any further than to say the mathematics only allows us to make probabilistic predictions. It is essentially the shut up and calculate position and isn't an interpretation of the mathematical formalism.

The anti-realist interpretation does go further and makes ontological deductions from the instrumentalist position. It says that properties don't have well defined values prior to measurement because there are no properties prior to measurement.

So, would it be accurate to say;

realism = systems have property values prior to measurement?
I would be more inclined to say that realism, at its most fundamental, is simply the position that systems have properties prior to measurement, not necessarily property values.


Since the realism view is born out of a classical macroscopic intuition we evolved with, I say that it's unsupported by the measurements and should be abandoned. There is no reason to expect it to hold for purely quantum objects.
If we take realism to be as outlined above, then anti-realism has, what I would think, is an insurmountable issue, namely, how something without any properties can interact with a measurement device in the first place.
 
  • #63
Lynch101
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Anti-realism re/ QM pertains to the anti-realism of properties considered by QM (i.e. those represented by regions of Hilbert space), as opposed to all properties entirely.
Thanks Morbert, this offers a different insight that I haven't come across before. I need a bit of help parsing what it means though.

I keep coming back to the shared position of instrumentalism and anti-realism, which says that the mathematical formalism is only a predictive tool which gives us the probability that a certain measurement outcome will be observed.

If the mathematical formalism only describes the probability that a certain measurement outcome will be observed, then it wouldn't seem to describe the properties of the system prior to measurement. The statement about the meaninglessness of talking about the quantum system prior to measurement seems to stem from this idea.

The instrumentalist position remains agnostic on the question of the properties of the system prior to measurement, while the anti-realist position appears to say that the mathematical formalism doesn't describe an ontic state and only gives us probabilistic measurement outcomes because there is no ontic state prior to measurement i.e. there are no properties whatsoever.


If we take the interpretation you propose above that the anti-realist position of QM refers to anti-realism of properties considered by QM, does that mean that there are other properties which QM does not consider? Would these then qualify as hidden variables?
 
  • #64
Lynch101
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You have to distinguish between the "empirical reality" and the "ultimate reality". As Bernard d'Espagnat points out:

What quantum mechanics tells us, I believe, is surprising to say the least. It tells us that the basic components of objects – the particles, electrons, quarks etc. – cannot be thought of as "self-existent". The reality that they, and hence all objects, are components of is merely "empirical reality".

This reality is something that, while not a purely mind-made construct as radical idealism would have it, can be but the picture our mind forces us to form of ... Of what ? The only answer I am able to provide is that underlying this empirical reality is a mysterious, non-conceptualisable "ultimate reality", not embedded in space and (presumably) not in time either.


From: https://www.theguardian.com/science/blog/2009/mar/17/templeton-quantum-entanglement
Thanks Lord Jestocost, I would be inclined to ideas like that. I have only recently been introduced to d'Espagnat but I find myself nodding along in agreement with much of what I have read so far. I must read some more of his work.

This position would be a denial of the anti-realist position, wouldn't it?
 
  • #65
Lord Jestocost
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This position would be a denial of the anti-realist position, wouldn't it?
I don't think so. David J. Chalmers writes in "Ontological Anti-Realism":

"The basic question of ontology is “What exists?”. The basic question of metaontology is: are there objective answers to the basic question of ontology? Here ontological realists say yes, and ontological anti-realists say no."
 
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  • #66
DrChinese
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So, would it be accurate to say;

realism = systems have property values prior to measurement?

Since the realism view is born out of a classical macroscopic intuition we evolved with, I say that it's unsupported by the measurements and should be abandoned. There is no reason to expect it to hold for purely quantum objects.
My thoughts exactly. :smile:

Einstein (1935, 1948) thought systems DID have property values prior to measurement. He defined the essential debate early on.

"According to [QM], the particle possesses neither a sharply defined momentum nor a sharply defined position. In which sense shall I imagine that this representation describes a real, individual state of affairs? Two possible points of view seem to me possible and obvious and we will weigh one against the other:

(a) The (free) particle really has a definite position and a definite momentum, even if they cannot both be ascertained by measurement in the same individual case. According to this point of view, the ψ-function represents an incomplete description of the real state of affairs. ...

(b) In reality the particle has neither a definite momentum nor a definite position; the description by ψ-function is in principle a complete description. The sharply-defined position of the particle, obtained by measuring the position, cannot be interpreted as the position of the particle prior to the measurement. ..."


Einstein believed (a). Bohr and most all other believed (b). Bell and Aspect had not yet come along to settle matters. So formulated as above, (a)=realist; (b)=anti-realist.

If you extend the "anti-realist" concept to a quantum interpretation, then you would reject Bohmian Mechanics and certain other interpretations. Those assert (a) explicitly. Of course, you can accept (b) - which is essentially a rejection of "local realism" - without picking a particular interpretation. But even then, you would essentially be adopting your perspective anyway, which translates to this:

anti-realism = systems don't have [well-defined] property values prior to measurement
 
  • #67
Paul Colby
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If we take realism to be as outlined above, then anti-realism has, what I would think, is an insurmountable issue, namely, how something without any properties can interact with a measurement device in the first place.
You keep repeating this and people here keep reinforcing this. It's a non-sensical statement, IMO.

Neglecting the point I was trying to make, let's take the DrChines's response to my Lotto number choice for example. His point was that classically he could take whatever picking device I chose and replace it with a prior device that would preselect the very same choice. This of course is nonsensical even from a classical perspective. Errors and noise would rapidly accumulate the further back in time one pushes the next choosing device. At some point, the residual quantum noise due to macroscopic objects really being composed of quantum ones would prevail. So even in the macroscopic case extrapolating a system to its infinite past is nonsense.

Now that said, Bell's theorem is a statement about the statistics of measurement. One uses measurements and statistics of those measurements showing that predefined values for a system can't exist. Okay, that not the same as the system doesn't exist or the system can't interact or the system isn't real.
 
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DrChinese
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Now that said, Bell's theorem is a statement about the statistics of measurement. One uses measurements and statistics of those measurements showing that predefined values for a system can't exist. Okay, that not the same as the system doesn't exist or the system can't interact or the system isn't real.
Agreeing with your essential comment: The quantum object is real and exists. Properties (of that object) don't seem to appear until a final measurement. The measurement requiring an interaction with a measuring device.

Obviously, my perspective gives weight to the concept of a "final measurement" - with all the problems associated with that. So again, that's where one's interpretation comes to the rescue (or not). :smile:
 
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The instrumentalist position remains agnostic on the question of the properties of the system prior to measurement, while the anti-realist position appears to say that the mathematical formalism doesn't describe an ontic state and only gives us probabilistic measurement outcomes because there is no ontic state prior to measurement i.e. there are no properties whatsoever.

If we take the interpretation you propose above that the anti-realist position of QM refers to anti-realism of properties considered by QM, does that mean that there are other properties which QM does not consider? Would these then qualify as hidden variables?
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.
 
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  • #70
Lynch101
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I don't think so. David J. Chalmers writes in "Ontological Anti-Realism":

"The basic question of ontology is “What exists?”. The basic question of metaontology is: are there objective answers to the basic question of ontology? Here ontological realists say yes, and ontological anti-realists say no."
I'm mindful of the possibility of deviating too far from a discussion of QM interpretations on this point but the above would seem to turn on the meaning of "objective answers".

There are probably more than two ways to interpret the idea of "objective answers", but two examples I can think of that relate to QM would be taking it to mean:
a) measurables or observables
b) objective reality, independent from the mind of each person.

If the ontological anti-realist says that we cannot measure/observe ultimate reality, then this would be more a statement of realism with the implication being that there is a fundamental limit on how deep we can probe the world around us. But if that is the anti-realist position with respect to QM, to my mind, it would be tantamount to saying that there are hidden-variables and, again, would essentially be a realist position. It might be contrasted with an alternative realist position that says it will be possible to measure fundamental reality in the future, when we further refine our instruments.

In short, both ontological realism and anti-realism would, in this sense of "objective answers", point to an incomplete theory and the existence of hidden-variables (or "beables").


The interpretations of anti-realism in QM, which I have encountered, don't seem to point to hidden-variables rather they deny the presence of them.


Apologies for continually returning to this point, but I find it the easiest to digest and use as the basis for explanation and inquiry; if we go back to the question of the quantum system prior to measurement and talk about the mathematical formalism:

If we say that the mathematical formalism only gives us probabilistic predictions for the outcomes of experiments then it would seem to imply that the mathematics doesn't describe the quantum system prior to measurement. Am I correct in saying that this is what lead to the EPR paper and the charge of incompleteness?

If the mathematical formalism doesn't describe the quantum system prior to measurement we might then ask the question, is there a quantum system prior to measurement? If there is a quantum system prior to measurement then I think it is reasonable to state that it must have some/any properties, even if we cannot ascribe definite values to these properties. It might be down to my misinterpretation, but this to me sounds like a statement that there are hidden-variables.

The alternative to this, as far as I have reasoned thus far, would be the position that either there is no quantum system prior to measurement or that it has absolutely no properties whatsoever.
 
  • #71
Lynch101
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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.
 
  • #72
Lynch101
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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.
 
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PeterDonis
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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.
 
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  • #74
Lynch101
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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).
 
  • #75
PeterDonis
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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.
 

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