Quantum Ball and Cup - Thought Experiment

[PeterDonis]

What do antirealist interpretations say is occurring

Generally, "antirealist" means that asking what "is occurring" is a misguided question, since it presupposes realism.

 

[Lynch101]

I appreciate your patience but I think we might be talking past each other here because I don't think I'm saying anything that you haven't already affirmed above.

What information? Where? Please give a reference. You can't just wave your hands and say the double slit experiment demonstrates some particular thing you have in your head. You need to back up such assertions. So far you haven't.

The information is that some of the positions which were predicted (in the double-slit experiment) lie outside the past light cone of the measurement event.

I'm not suggesting anything new. As far as I can tell, you've already affirmed this to be the case.

Meaning, individual impacts of particles on the detector screen? Yes, it could be [the case that some of the predicted positions lie outside the past light cone].

Parentheses added by me to include context of the question being addressed.

You initially raised an issue pertaining to the use of the word "fact" which I amended to exclude the idea of "observational fact" and instead refer to theoretical information. You have dismissed this as irrelevant, but I think you might meaningless because the information in question - which you have already affirmed - forms the basis of the question. So it is relevant to the question.

The information is there from the predictions and from relativity. The question is how it might be interpreted.

No. you don't even know that, because you don't know the precise deterministic trajectory even after the measurement result is observed. The measurement result doesn't tell you the precise, exact position of the particle, and therefore does not pick out a single deterministic trajectory for the particle. There is a finite measurement error involved. And there will be possible deterministic trajectories within that finite measurement error that do pass through the other detector, because in Bohmian mechanics (since the only accepted version of it is non-relativistic), the deterministic particle trajectories are not limited to the speed of light.

Your analogy is flawed because it is based on, at the very least, an incorrect understanding of Bohmian mechanics (see above). I'll save comments on collapse interpretations for a separate post.

Ah I see, thank you for that clarification. What is the interpretation here of "trajectories that do pass through the other detector"; does this mean that that the system moves through the detector but doesn't register as a measurement event?

 

[Lynch101]

I was defining what the general term "collapse interpretation" means (according to my best understanding) in that quote. But that in itself does not tell you how collapse interpretations would interpret a scenario you made up that doesn't even involve QM (as others have already pointed out). I certainly was not making claims about "collapse interpretations" at this level of detail:

Do different [physical] collapse interpretations offer different explanations of what occurs in the double-slit experiment?

You need to back up this kind of detailed claim with a reference.

In fact, this discussion in general is reaching the point where it is not productive to continue because we are just talking about vague generalities instead of specific interpretations that have actually been proposed in the literature, with specific information about what those interpretations say about scenarios like the one you describe in the above quote. In short, if you want to know what particular interpretations say, you need to go read the literature in which those particular interpretations are proposed and described and used to analyze scenarios. If you have questions about what you read, by all means post them here.

I'll take a look at some of the [physical] collapse theories. You mentioned GRW, are there many others?

Do they all say something different about the physical collapse of the system in the double-slit experiment?

 

[Lynch101]

An antirealist interpretation would say e.g. the probability that your measurement apparatus will record a ball in bag 1 is p1.

And the probability that the ball is in bag 2 would be p2?

 

[Lynch101]

Generally, "antirealist" means that asking what "is occurring" is a misguided question, since it presupposes realism.

It might be worth making a distinction here between assuming the realism of the mathematics and assuming realism simpliciter.

Asking "what is occurring" assumes realism simpliciter but not necessarily the realism of the mathematics. It might be that the mathematics doesn't give us the complete picture.

But I would think assuming realism simpliciter is a necessity, no? Otherwise there would be nothing to interact with the measurement apparatus to give the measurement event. Are there antirealist interpretations that assume realism simpliciter is an incorrect assumption?

 

[Morbert]

And the probability that the ball is in bag 2 would be p2?

No. The probability that the measuring device will register a ball in bag 2 would be p2.

 

[PeterDonis]

The information is that some of the positions which were predicted (in the double-slit experiment) lie outside the past light cone of the measurement event.

Not positions, measurement events. Positions aren't points in spacetime, and it's meaningless to talk about positions as they relate to light cones of points in spacetime.

The fact that, in the kinds of scenarios you are describing, possible measurement events can be spacelike separated is true, but in the absence of relativistic formulations of various QM interpretations, it's outside the scope of this forum to speculate about what various interpretations might make of this in the light of relativity. If you can find a reference that discusses it, that's different, but so far you have given no references at all.

 

[PeterDonis]

What is the interpretation here of "trajectories that do pass through the other detector"

It should be obvious: trajectories in space that pass through the region of space occupied by the other detector.

does this mean that that the system moves through the detector but doesn't register as a measurement event?

Particle trajectories in and of themselves, in Bohmian mechanics, say nothing whatever about measurement events. If you already know that a particle was detected at detector A and not at detector B, then of course you know that, if the particle's Bohmian trajectory passed through detector B, it did not result in a measurement event at detector B. But there is no way to know whether or not that actually happened. Exact particle trajectories in BM are not measurable, because, as I've already said, all real measurements have finite error.

 

[PeterDonis]

Do different [physical] collapse interpretations offer different explanations of what occurs in the double-slit experiment?

I'll take a look at some of the [physical] collapse theories. You mentioned GRW, are there many others?

Do they all say something different about the physical collapse of the system in the double-slit experiment?

I don't have the literature in front of me and I'm not going to take the time to look it up. If you want questions like these answered, you should be looking up the literature.

 

[Lynch101]

No. The probability that the measuring device will register a ball in bag 2 would be p2.

All of the interpretations, in effect, say this, don't they?

CMIIW, but BM says that particles follow deterministic trajectories and always have a definite position, which is why we end up with a single measurement event. The deterministic particle trajectories are not limited to the speed of light and the neither are influences at the level of the pilot wave.

In this case , we have probabilistic interpretations as a result of incomplete information about the system.

Collapse interpretations, meaning interpretations that say collapse is a real physical process, say There are no hidden particles as there are in Bohmian mechanics. Instead, collapse of the wave function is a physical process which involves instantaneous (FTL) localisation.

In this case , we have probabilistic interpretations as a result of the fundamental randomness of nature, which occurs during the physical collapse process.

While these are not very intuitive and defy our classical biases, they offer an explanation as to how we get individual measurements from the probabilistic predictions.

Is there a comparable explanation associated with antirealist interpretations?

 

[Lynch101]

Not positions, measurement events. Positions aren't points in spacetime, and it's meaningless to talk about positions as they relate to light cones of points in spacetime.

Do [the relevant] measurements not give us values for position?

Either way, we don't necessarily need to talk about positions, if it is controversial to do so. We can talk about the possibility of a measurement event (on the system in question). In this context we would say that some of the possible measurement events (on the system in the double-slit experiment) lie outside the past light cone of the actual measurement event (on the system in question). This is just information we can gather from QM predictions and relativity.

It is this information which I am seeking interpretation of. It can't be irrelevant since it is plainly obvious and forms the basis of the question being asked. We might suggest that it doesn't mean anything, but that would be questionable given that both pieces of information alone can be interpreted to have meaning.

The fact that, in the kinds of scenarios you are describing, possible measurement events can be spacelike separated is true, but in the absence of relativistic formulations of various QM interpretations, it's outside the scope of this forum to speculate about what various interpretations might make of this in the light of relativity. If you can find a reference that discusses it, that's different, but so far you have given no references at all.

When we talk about possible measurement events being spacelike separated, are we talking about two separate measurements on entangled photon pairs, for example? If so, that's not the case I am talking about.

I'm talking about the double-slit experiment where there is only a single measurement event and the past light cone of that single event.

Have we, perhaps, been talking past each other?

 

[Lynch101]

It should be obvious: trajectories in space that pass through the region of space occupied by the other detector.


Particle trajectories in and of themselves, in Bohmian mechanics, say nothing whatever about measurement events. If you already know that a particle was detected at detector A and not at detector B, then of course you know that, if the particle's Bohmian trajectory passed through detector B, it did not result in a measurement event at detector B. But there is no way to know whether or not that actually happened. Exact particle trajectories in BM are not measurable, because, as I've already said, all real measurements have finite error.

Sorry, more precisely, it's the "pass through the other detector" that I wasn't clear on. You've qualified it somewhat more here by saying pass through the region of space occupied by the other detector.

I would have thought that, if the trajectory of the particle brought it into contact with the detector then it would necessarily result in a measurement event. I thought that was just a basic feature of BM which made it appealing to some as an answer to "the measurement problem". But this seems to suggest otherwise.

 

[Lynch101]

I don't have the literature in front of me and I'm not going to take the time to look it up. If you want questions like these answered, you should be looking up the literature.

I'll take a look at some of the literature, I just figured it would be worth asking. You mentioned GRW, would that be an example of a physical collapse interpretation?

 

[Lord Jestocost]

I recommend the entry "Collapse theories" by Giancarlo Ghirardi and Angelo Bassi on the "The Stanford Encyclopedia of Philosophy".
https://plato.stanford.edu/entries/qm-collapse/

 

[Morbert]

All of the interpretations, in effect, say this, don't they?

All interpretations accept that the statistical predictions of QM are reproduced in data generated by experiment. You asked if all interpretations involve either physical FTL collapse or BM-like definite positions. Antirealist positions involve neither.

Is there a comparable explanation associated with antirealist interpretations?

Antirealists reject the idea that quantum theories are explained by some thoroughly intelligible ontology of microscopic systems. Instead the intelligibility of microscopic systems is found in those questions which can be resolved by experiment.

 

[Lynch101]

I recommend the entry "Collapse theories" by Giancarlo Ghirardi and Angelo Bassi on the "The Stanford Encyclopedia of Philosophy".
https://plato.stanford.edu/entries/qm-collapse/

Excellent. Thank you LJ. I never thought to look to the SEoP for physics information before.

 

[Lynch101]

Antirealists reject the idea that quantum theories are explained by some thoroughly intelligible ontology of microscopic systems. Instead the intelligibility of microscopic systems is found in those questions which can be resolved by experiment.

There is an important distinction to be made here between rejecting the idea of an ontology of microscopic systems altogether, and rejecting the intelligibility of that ontology.

I've read some positions that take the former position and argue for idealism, although I'm not sure how coherent they are. The latter position, to my mind, seems to imply some form of [forever] hidden information which would mean that a complete** theory of "the physical reality*" is impossible.

Is there an alternative interpretation/conclusion to that?

*"the physical reality" being the physical experimental set-up as opposed to the mathematical description of it.

**complete being where "every element of the physical reality has a counterpart in the theory" (as per EPR). In this case the microscopic ontology would not be represented in the mathematics.

 

[Morbert]

There is an important distinction to be made here between rejecting the idea of an ontology of microscopic systems altogether, and rejecting the intelligibility of that ontology.

I've read some positions that take the former position and argue for idealism, although I'm not sure how coherent they are. The latter position, to my mind, seems to imply some form of [forever] hidden information which would mean that a complete** theory of "the physical reality*" is impossible.

Is there an alternative interpretation/conclusion to that?

*"the physical reality" being the physical experimental set-up as opposed to the mathematical description of it.

**complete being where "every element of the physical reality has a counterpart in the theory" (as per EPR). In this case the microscopic ontology would not be represented in the mathematics.

This is looping back on the completeness discussions so I'll just reiterate that antirealism frames QM as a complete physical theory and refer you to those earlier discussions.

 

[Lynch101]

This is looping back on the completeness discussions so I'll just reiterate that antirealism frames QM as a complete physical theory and refer you to those earlier discussions.

I wouldn't say it's looping back on them but expanding on them. You raised the issue of intelligibility previously. The point above is a clarification of the distinction between denying the ontology of the microscopic system altogether and denying the intelligibility of that ontology.

Perhaps questions about [anti-realist] interpretations will inevitably return to the question of completeness.

 

[PeterDonis]

Do [the relevant] measurements not give us values for position?

Not exact ones, no. Please re-read "all measurements have finite error" again and again until you understand what it means.

Either way, we don't necessarily need to talk about positions, if it is controversial to do so.

If you don't talk about exact positions of the hidden particles in Bohmian mechanics, you can't really talk about Bohmian mechanics at all, since those exact (hidden) particle positions are the key ingredient of BM.

 

[PeterDonis]

I would have thought that, if the trajectory of the particle brought it into contact with the detector then it would necessarily result in a measurement event.

Why? What reference have you read about BM that leads you to believe this?

Once again: you really, really, really need to base your claims about what various interpretations say on actual references about those interpretations. You should not just wave your hands and try to figure out what the interpretations say on your own.

 

[PeterDonis]

In this context we would say that some of the possible measurement events (on the system in the double-slit experiment) lie outside the past light cone of the actual measurement event (on the system in question). This is just information we can gather from QM predictions and relativity.

Yes. But "possible events" are not necessarily actual events, and before you go applying QM plus relativity to "possible events", you should first go look to see whether relativity itself says anything at all about "possible events" that don't become actual. (Hint: it doesn't.)

It is this information which I am seeking interpretation of.

So why don't you go read what the various papers in the literature on the various interpretations say about this?

If your answer is that, well, the various papers in the literature on the various interpretations don't really say anything about it, perhaps you should rethink your belief that this question is a meaningful question.

In fact, I can turn the question around: why do you think this question is a meaningful question?

When we talk about possible measurement events being spacelike separated, are we talking about two separate measurements on entangled photon pairs, for example?

No. I am talking about the cases you have described (a single photon passing through a beam splitter, and a single photon going through a double slit apparatus).

 

[Lynch101]

Not exact ones, no. Please re-read "all measurements have finite error" again and again until you understand what it means.

If you don't talk about exact positions of the hidden particles in Bohmian mechanics, you can't really talk about Bohmian mechanics at all, since those exact (hidden) particle positions are the key ingredient of BM.

I appreciate your exactness in your replies because it helps to further my understanding, so again, thank you for that. In this case, however, I think we might be talking past each other. My misinterpretation of certain features of BM is a primary factor in this. I don't think we need to talk about the exact position of the particle because I'm talking about the probabilistic predictions of measurement events and the interpretation of those positions.

In fact, I can turn the question around: why do you think this question is a meaningful question?

Because I think the probabilistic predictions of QM call for interpretation and, in relativity, the location of an event in relation to the past light cone has meaning.

The interpretation I am trying to get at can, perhaps, be broken into two parts:
1) In what sense is it a genuine possibility for a measurement event to occur at any of the predicted,
non-zero, measurement event positions?
2) In what sense was there a genuine possibility of measuring the system at a measurement event
position which was/is outside the past light cone of the actual measurement event?


In considering the question of the possibility of the system being measured at a position outside the past light cone, of the actual measurement, we might consider a macroscopic example, a spaceship say - solely to attempt to demonstrate the idea.

If we don't know where a spaceship is we might make probabilistic predictions as to where we might find it. Eventually, we measure the location of the spaceship (to within some finite error). If we look back at our predictions we will see that some of the probabilistic predictions lie outside the past light cone. How would we interpret this information?

Incomplete
Someone might suggest that the reason we made such probabilistic predictions in the first place is because our information was incomplete. In truth, some of the positions we predicted weren't genuinely possible, given the actual trajectory of the spaceship and the limiting factor of no-FTL travel.

Simple FTL
Someone else might come along and say, actually, the spaceship might be able to travel faster than the speed of light and so there was a genuine possibility of measuring the position of the spaceship somewhere outside the past light cone.

Collapse
Someone else might say, actually, the "spaceship system" is delocalised in space and when we make a measurement it randomly collapses into a single measurement event. This collapse happens instantaneously (FTL) so there was a genuine possibility of measuring the spaceship somewhere outside the past light cone of the actual measurement event.

BM-like*
Someone else might say, actually, our information is incomplete AND the spaceship can also travel FTL. Not only this, but when the spaceship triggers the measurement device it can result in the spaceship being measured at a spacelike separated position. This process occurs instantaneously (FTL). In this case there was a genuine possibility that the spaceship could have been measured at any of the non-zero predicted positions.

Are there other possible interpretations which don't imply either incompleteness, or some form of FTL causal influence?


*This can be modified to make it a more accurate representation. The instantaneous (FTL) causal influence would carry the explanatory power.

 

[PeterDonis]

The interpretation I am trying to get at

...needs to be "got at" by going and looking at the literature, not by vague discussions in this forum with no basis in the literature. That includes "getting at" what Bohmian mechanics says.

Thread closed.

 

[PeterDonis]

we might consider a macroscopic example

As one other note: if you want to understand QM, you need to look at experiments that need QM for their explanation. Using examples that only need classical physics for their explanation, like the behavior of spaceships, is pointless. Please bear that in mind.