Undergrad Find your ideal quantum interpretation

[DarMM]

It's utter nonsense. Already the conservation laws prevent the moon from vanishing when nobody looks at it. This is really superfluous philosophical gibberish!

I don't think that's what they say as I mentioned above, just that certain interactions results don't pre-exist in the sense of being determined from the prior state. It isn't even a particularly unique element of the interpretation, other Copenhagen views would say similar things.

 

[Demystifier]

Already the conservation laws prevent the moon from vanishing when nobody looks at it.

Unless the conservation laws refer only to the observed phenomena.

 

[Demystifier]

just that certain interactions results don't pre-exist in the sense of being determined from the prior state.

Then I don't understand what QBist's say about the following. Consider an EPR pair. Suppose that Alice measures one member of the pair at time $t_{\rm meas}$ (in the laboratory frame) and Bob measures the other member of the pair at the same time $t_{\rm meas}$. Latter Charlie at time $t_{\rm comp}>t_{\rm meas}$ compares the results of Alice and Bob and finds out that their results are correlated. At the time $t_{\rm meas}$ Alice and Bob know their measurement results, but they don't know that their results are correlated. Are the results correlated already at time $t_{\rm meas}$? I think the QBists insist that they are not correlated already at $t_{\rm meas}$, which is how they save locality.

 

[DarMM]

Then I don't understand what QBist's say about the following. Consider an EPR pair. Suppose that Alice measures one member of the pair at time $t_{\rm meas}$ (in the laboratory frame) and Bob measures the other member of the pair at the same time $t_{\rm meas}$. Latter Charlie at time $t_{\rm comp}>t_{\rm meas}$ compares the results of Alice and Bob and finds out that their results are correlated. At the time $t_{\rm meas}$ Alice and Bob know their measurement results, but they don't know that their results are correlated. Are the results correlated already at time $t_{\rm meas}$? I think the QBists insist that they are not correlated already at $t_{\rm meas}$, which is how they save locality.

Well Alice and Bob would assign a state that models the particles as being correlated or not and then afterward look at the statistics when they compare them, at which point they'd discover whether that is the correct state to be using for particles produced in this manner or not via De Finetti's theorem. QBism uses De Finetti's view of probability theory, i.e. Subjective Bayesianism. I won't go into this too much as their view in this regard isn't really much beyond the Subjective Bayesian view of correlations in completely classical cases and it'll be hard to describe Subjective Bayesianism and QBism in one go.

How they save locality is in a way unrelated to this, but is basically the same as other views that see the core¹ of QM as little more than an extension of probability theory. That is the outcomes pairs don't exist on the same sample space, so there is no requirement for consistency with a counterfactual. If you measure angles $a,c$ in a Bell experiment there is no need to be consistent with counterfactual outcomes associated with separate angles $b,d$ and hence the expectation value $E(a,c)$ is less constrained than in the Classical case. There simply is no value for $b,d$ as they don't arise in that experimental context. This would be shared among QBism, Healey, many Neo-Copenhagen views, Consistent Histories, @RUTA 's acausal view and perhaps the Ensemble view, maybe @bhobba or @vanhees71 can say more.

¹ By the core of QM I mean the basic machinery of Hilbert Spaces and Operators, one can view this as purely an extension of probability without all of QM being so.

 

[AlexCaledin]

Consistent Histories is usually presented as a Copenhagen style interpretation, explicitly so in the books of Griffiths and Omnès. Also in both it and QBism the Moon is there when nobody looks.

Griffiths ends his book with "...quantum theory indicates that the nature of this independent reality is in some respects quite different from what was earlier thought to be the case."

 

[bhobba]

It's utter nonsense. Already the conservation laws prevent the moon from vanishing when nobody looks at it. This is really superfluous philosophical gibberish!

Indeed. It's caused by not being careful about what you mean by observation. The moon is observed all the time by the environment so is never not observed.

Thanks
Bill

 

[bhobba]

Griffiths ends his book with "...quantum theory indicates that the nature of this independent reality is in some respects quite different from what was earlier thought to be the case."

Well probably - but things are not quite as simple as a quote like that would indicate:
https://www.sciencenews.org/blog/context/gell-mann-hartle-spin-quantum-narrative-about-reality

Note the above just uses the formalism of QM - no interpretation. You can take questions like that a long way without an actual interpretation. Maybe, just maybe, when all the issues of the above are sorted out we will not really need an interpretation other than something minimal like the Ensemble. Fingers crossed.

Thanks
Bill

 

[A. Neumaier]

The moon is observed all the time by the environment so is never not observed.

This is a quite nonstandard view. What then do you call an observation?

 

[bhobba]

This is a quite nonstandard view. What then do you call an observation?

An example would be a dust particle. A few stray photons from the CBMR is enough to give the dust particle an exact position. And since it's bombarded all the time by such the wave-packet will not spread. I consider the photons an observer.

Thanks
Bill

 

[A. Neumaier]

I consider the photons an observer.

Where are its observation records?

 

[DarMM]

Well probably - but things are not quite as simple as a quote like that would indicate:
https://www.sciencenews.org/blog/context/gell-mann-hartle-spin-quantum-narrative-about-reality

Note the above just uses the formalism of QM - no interpretation. You can take questions like that a long way without an actual interpretation. Maybe, just maybe, when all the issues of the above are sorted out we will not really need an interpretation other than something minimal like the Ensemble. Fingers crossed.

Thanks
Bill

I always found this an interesting view, in some ways you can't say much else if you go Copenhagen/Ensemble or any of the other non-representational views. QM doesn't talk about the microscopic world as it is, only its statistics, but you can prove in some regimes those statistics become/are compatible with Kolmogorov probability and thus in that regime you're fine to think about objects with comprehensible properties.

It's like "The world is fundamentally ineffable, but you can track when it becomes effable". Perhaps there is nothing more than this (combined with ones favorite view on probabilities) as you say.

 

[Lord Jestocost]

Just choose one of the offered answers to a couple of questions on the graph.

As an experimental physicist, I would say - using Adan Cabello's words: A map of madness

 

[martinbn]

I am stuck on the first question.

The ontology is simple: all that exists is the wavefunction.

To me this makes absolutely no sense. The verb exist cannot be applied to the wavefunction.

 

[DarMM]

To me this makes absolutely no sense. The verb exist cannot be applied to the wavefunction.

I think it's just shorthand for the wavefunction represents an actual "field" or "fluid" rather than representing the observer's knowledge. Like how $\textbf{B}(x)$ is meant to represent the Magnetic field in Maxwellian electromagnetism.

 

[martinbn]

I think it's just shorthand for the wavefunction represents an actual "field" or "fluid" rather than representing the observer's knowledge. Like how $\textbf{B}(x)$ is meant to represent the Magnetic field in Maxwellian electromagnetism.

But if you have more than one particle, this doesn't work.

 

[julcab12]

I am stuck on the first question.
To me this makes absolutely no sense. The verb exist cannot be applied to the wavefunction.

I'm(They) referring to the wavefunction treated as a classical field (i.e. a field that actually exists, despite being complex valued and of indefinite dimension) which obeys causal, local, relativistic laws and so never collapses. In the purest form, the universal wavefunction encodes a surfeit of splitting timelines, one for each possible history. No filler just a straight on "take something at face value" but that is a natural direction given of what we have. Whether it is true, intuitive or not. It's an honest approach. But for me, I'm a bit squeamish. It would be funny if interpreting it like Einstien ring or any extended images.

 

[DarMM]

But if you have more than one particle, this doesn't work.

How so? Are you referring to the wave function being a function on configuration space?

 

[George Jones]

I am stuck on the first question.

I, too, am stuck on the first question, but possibly for a different reason.

My answer to the first question is "a) and b)."

 

[Mentz114]

If you follow along the path of clean QM formalism. I would say you would likely end up with Many World on face value. Simply because it is simple. The ontology is simple: all that exists is the wavefunction. The dynamics are simple: the wavefunction obeys unitary evolution according to the Schrodinger equation. Measurement problem is simple: decoherence selects a basis, and the relative state gives you definiteness; both of these are natural quantum processes and don't have to be added in. The derivation of the Born rule for probability is -- well maybe not simple -- but it is elegant: proceeding in analogy to classical Savage decision theory. It is an entirely local theory. It generalizes straightforwardly to quantum field theories... Ok I get it. But my personal bias led me to Relational bec of my GR mentality-- Mirages and Gravitational Effect produces illusions.

Probability (nor amplitude) is not stuff. How can the universe be made of something that is not energy/matter or anything detectable ?

 

[julcab12]

Probability (nor amplitude) is not stuff. How can the universe be made of something that is not energy/matter or anything detectable ?

Please read post 46.

 

[PeterDonis]

Probability (nor amplitude) is not stuff.

But not all QM interpretations interpret the wave function as a probability amplitude. The MWI, for example, interprets it as describing an actual reality in which every branch exists; there are no probabilities. (Which is why one of the main issues with the MWI is how to make sense of the fact that, when we are actually using the wave function to do practical calculations, we do interpret it as giving probability amplitudes, and that practical method works.)

 

[PeterDonis]

My answer to the first question is "a) and b)."

So is mine. And if I just go ahead and follow both answer trees, I end up with the statistical ensemble interpretation and the Nelson stochastic interpretation. So now I have the problem of interpreting what this means: does it mean I have some probability of using one or the other of these interpretations, or does it mean I'm in a superposition of using both?

 

[Mentz114]

Please read post 46.

Treat the wave function as a classical field ? I don't think that is what the MWI proponents are saying.
Apologies if I seemed to be critical of you personally. MWI brings on the red mist !

Believing that QM is a fundamental theory and that probability is stuff is wildly optimistic.

 

[StevieTNZ]

An example would be a dust particle. A few stray photons from the CBMR is enough to give the dust particle an exact position. And since it's bombarded all the time by such the wave-packet will not spread. I consider the photons an observer.

Thanks
Bill

all that happens is entanglement. No 'wave function' collapse occurs. Otherwise the measurement problem doesn't exist, as I've stated many times before if you go with your reasoning.

 

[Mentz114]

But not all QM interpretations interpret the wave function as a probability amplitude. The MWI, for example, interprets it as describing an actual reality in which every branch exists; there are no probabilities. (Which is why one of the main issues with the MWI is how to make sense of the fact that, when we are actually using the wave function to do practical calculations, we do interpret it as giving probability amplitudes, and that practical method works.)

The bit I've bolded seems to contradict the MWI axiom : "the wave function is all that there is."
The existence of branches is plucked from nothing and amounts to new physics.

 

[julcab12]

Treat the wave function as a classical field ? I don't think that is what the MWI proponents are saying.
Apologies if I seemed to be critical of you personally. MWI brings on the red mist !

Believing that QM is a fundamental theory and that probability is stuff is wildly optimistic.

I don't know about believing. But they interpret exactly like that(Originally-- Some versions). Well. I'm not saying I adhere to it. To be honest, I'm still in a superposition of a) and b) of the first question.

 

[PeterDonis]

The bit I've bolded seems to contradict the MWI axiom : "the wave function is all that there is."

No, it doesn't.

The existence of branches is plucked from nothing

No, it isn't; the branches are right there in the wave function. Nothing needs to be added.

If you disagree, then please show me explicitly, with math, where branches get "plucked from nothing".

 

[martinbn]

I, too, am stuck on the first question, but possibly for a different reason.

My answer to the first question is "a) and b)."

So is mine.

 

[martinbn]

How so? Are you referring to the wave function being a function on configuration space?

Yes.

 

[MathematicalPhysicist]

Just sum over all possible interpretations of QM, if what you get is nonsense then as you know - "no one understands QM".