Undergrad Find your ideal quantum interpretation

[microsansfil]

I don't think that's saying there's no external world or that things aren't there when not observed, it's just the standard "measurement creates measurement outcomes" you have in Copenhagen views like Haag's

Qbism is about the interpretation of QM and, therefore, examines the epistemic foundation of quantum mechanics, placing the subject at the heart of the construction of our knowledge.

https://www.quantamagazine.org/quantum-bayesianism-explained-by-its-founder-20150604/

Schrödinger thought that the Greeks had a kind of hold over us — they saw that the only way to make progress in thinking about the world was to talk about it without the “knowing subject” in it. QBism goes against that strain by saying that quantum mechanics is not about how the world is without us;

QBism treats the wave function as a description of a single observer’s subjective knowledge.

/Patrick

 

[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?

Yes.

They simply think that configuration space is what is real as such, or more that reality is some kind of "object" that is directly described by the wavefunction. They would say that space as we normally see it is just something effective that arises through decoherence.

 

[Mentz114]

No, it doesn't.

I agree there a no contradiction but a restatement both of which are impossible.

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".

I think the proponents should produce the equations. It is not possible to prove existence (by maths) except for mathematical objects, so that can't be done.

(PS: I end up in the same preferences as you did. But things don't look good for stochastic QT)

 

[martinbn]

They simply think that configuration space is what is real as such, or more that reality is some kind of "object" that is directly described by the wavefunction. They would say that space as we normally see it is just something effective that arises through decoherence.

So we are back to the beginning. To me it seems meaningless to say that configuration space is real.

 

[DarMM]

So we are back to the beginning. To me it seems meaningless to say that configuration space is real.

Again it's just a shorthand, sometimes expanding this stuff is tedious and physicists will just say "the Riemann curvature is strong near a black hole" rather than "that element of physical reality whose consequences upon the trajectories of objects close to the black hole seems to be near isomorphic to the effect of large Riemann curvature upon nearby geodesics in a Lorentzian manifold".

Similarly here Many Worlds people would just mean a physically real system that is directly described by configuration space.

In simplest terms in a state like:
$$\frac{1}{\sqrt{2}}\left(|\uparrow\downarrow\rangle + |\downarrow\uparrow\rangle\right)$$
MWI people would say that there are elements of physical reality directly corresponding to and modeled by both terms in the sum.

 

[DarMM]

So we are back to the beginning. To me it seems meaningless to say that configuration space is real.

If you want an even simpler analogy from Kolmogorov probability, when we write down for a dice:
$$p(1) = p(2) = \cdots = p(6) = \frac{1}{6}$$
Some would say (analogue to $\psi$-epistemist) that these numbers just reflect one's knowledge, where as Many Worlders would say they reflect something out there in the world like the values $h \in \mathbb{Q}$ used in discussing height reflect something out there in the world.

 

[martinbn]

Similarly here Many Worlds people would just mean a physically real system that is directly described by configuration space.

That is the problem for me. The original statement was that the wavefunctions is all there is, the only ontological object. Now you say that is just a short hand for - there is a physically real system that is described by... So which one is it? Is the wavefunction the only real thing or is there a physically real system described by it?

 

[DarMM]

That is the problem for me. The original statement was that the wavefunctions is all there is, the only ontological object. Now you say that is just a short hand for - there is a physically real system that is described by... So which one is it? Is the wavefunction the only real thing or is there a physically real system described by it?

Will it's not intended as an "or" choice. I'm saying the "Wavefunction is physically real" is a shorthand for the more explicit expression, it's not an alternative to it, i.e. "The wavefunction is physically real" is a shorthand for "There is a physical object that acts exactly like the wavefunction describes". This is no different from saying "$\textbf{B}(x)$ is real/ontological" in electromagnetism, it's just a shorthand for "The magnetic field exists and behaves as described by the vector field $\textbf{B}(x)$"

Post #66 states things about as succinctly as I can. Take that post, what isn't clear?

 

[bhobba]

Where are its observation records?

As usual you hit the crux of the matter. I do not believe an observation needs to leave a record. If you have some apparatus that measures say position and there is no record kept I think its position has still been measured. In the case of the dust particle it has a position to a high degree of accuracy, so I think it still has been measured. What I believe an observation does is put the system in a state that if you were to look at it, record it, etc then you would get a sensible answer. Even in classical physics if nobody observes the moon (in the usual sense of observation) then there is no record so you can say the moon is not there if you do not look at it. What makes it silly in a classical sense is we know the moon has the same properties if you look at it or not - that's one of the assumptions of classical physics. So I would say observation by the environment on a system means we know it properties to a high degree of accuracy regardless of if it is actually recorded or not. I suppose a better way of expressing it is interaction with the environment makes it behave classically to very good accuracy.

Thanks
Bill

 

[bhobba]

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

One can view the wave-function like probabilities - simply as an aid to calculation of results observations that are very real. There is an issue Dr Neumaier has correctly bought up with my view of what an observation is. You may wish to think about that one yourself rather than be swayed by what I think.

Thanks
Bill

 

[bhobba]

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

As I have said before - Dirac and possibly Feynman would be proud of you. But some theorists find such questions interesting. Of value? That's a matter of opinion. Still I enjoy the counter argument which is basically - who cares.

Thanks
Bill

 

[A. Neumaier]

So I would say observation by the environment on a system means we know its properties to a high degree of accuracy regardless of if it is actually recorded or not

This is usually called a preparation, not a measurement. If you prepare a spin up state, you know that the system has spin up, whether measured/recorded or not. But if you measure the spin in another direction (neither parallel nor orthogonal to it), you know nothing.

How would the environment achieve the feat of making the properties of a quantum system known to a high degree of accuracy if it is prepared in an unknown state? Decoherence only changes the pure state into a mixture, but does not reduce the uncertainty about the result obtainable by measurement.

 

[akvadrako]

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?

I'd say if they are completely orthogonal it wouldn't matter much. Otherwise, you should be most convinced where they agree and most unsure where they disagree. [more]

 

[Demystifier]

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?

In your case, I would recommend to use statistical ensemble for practical purposes and Nelson for the conceptual/philosophic ones. That would be quite close to my own practice, as I use statistical ensemble for practical purposes and Bohm for the conceptual/philosophic ones. Essentially, Nelson is just Bohm with an additional stochastic force on particles.

 

[Demystifier]

I am stuck on the first question.

Why?

 

[martinbn]

Will it's not intended as an "or" choice. I'm saying the "Wavefunction is physically real" is a shorthand for the more explicit expression, it's not an alternative to it, i.e. "The wavefunction is physically real" is a shorthand for "There is a physical object that acts exactly like the wavefunction describes". This is no different from saying "$\textbf{B}(x)$ is real/ontological" in electromagnetism, it's just a shorthand for "The magnetic field exists and behaves as described by the vector field $\textbf{B}(x)$"

Post #66 states things about as succinctly as I can. Take that post, what isn't clear?

This is perfectly clear. But I don't see how saying " the wave function is the only real thing" is a short hand for "there is a physical object described by the wavefunction". It isn't shorter and the meaning is very different. Also it is not specific to MWI.

 

[martinbn]

Why?

Both answers are equally important, I cannot say which one I consider the main.

 

[bhobba]

How would the environment achieve the feat of making the properties of a quantum system known to a high degree of accuracy if it is prepared in an unknown state? Decoherence only changes the pure state into a mixture, but does not reduce the uncertainty about the result obtainable by measurement.

The detail can be found in Schlosshauer and has to do with the radial nature of most interactions. I have posted it before many times. If you are interested I can dig up a previous thread.

Thanks
Bill

 

[DarMM]

This is perfectly clear. But I don't see how saying " the wave function is the only real thing" is a short hand for "there is a physical object described by the wavefunction". It isn't shorter and the meaning is very different. Also it is not specific to MWI.

It'd be standard enough usage in papers on MWI and many papers on interpretations in general. I'm not going to claim one can derive standard phraseology from first principles logically, it's just the type of phrase that's ended up being used.

Also it is short in full for "There is a physical object described by the wavefunction with each component of the wavefunction corresponding to an aspect of that object, furthermore there are no more objects in existence aside from this"

It's certainly shorter than that.

How would you phrase it?

 

[A. Neumaier]

How would the environment achieve the feat of making the properties of a quantum system known to a high degree of accuracy if it is prepared in an unknown state? Decoherence only changes the pure state into a mixture, but does not reduce the uncertainty about the result obtainable by measurement.

The detail can be found in Schlosshauer and has to do with the radial nature of most interactions. I have posted it before many times. If you are interested I can dig up a previous thread.

Please dig it up. As I recall, Schlosshauer does not claim to have a solution for the problem of unique outcomes - which is the only way uncertainty in a superposition is reduced.

 

[DarMM]

Qbism is about the interpretation of QM and, therefore, examines the epistemic foundation of quantum mechanics, placing the subject at the heart of the construction of our knowledge.
/Patrick

Sorry only saw this now. I don't disagree at all, QBism has the subject directly because it takes a De Finetti/Subjective Bayesian view of probability. That's a separate issue to what I was discussing with @Demystifier however.

 

[Demystifier]

Both answers are equally important, I cannot say which one I consider the main.

I understand. But if you force yourself to chose one of the answers, can you then answer the other questions? And if you can, what are the two interpretations (one Copenhagenish and one ontological) that you finally arrive at?

 

[stevendaryl]

So we are back to the beginning. To me it seems meaningless to say that configuration space is real.

Okay, to get an idea about your notion of "real", in General Relativity, is the spacetime manifold "real"? What's an example of something that it is meaningful to say is "real"?

 

[*now*]

Of a and b, I think if a is more concerned about epistemic book keeping and less about extra ontology, then a.

However, regarding the question of the moon vanishing, I don’t think a relational view would agree with a vanishing moon. Anything we have info about like the moon would involve physical regularities, e.g. energy conservation that we have info about too. Despite these problems I think Bhobba’s post is interesting from this view. It could be like asking to extricate an entity from all associated consistent, coherent physical information, and that doesn’t sound like that view.

If “observation” or having information is like frames of reference in relativity possibly these just seem part and parcel.

Probabilities involved with possible physical observational frames of reference would involve physical effects (physically registered effects).

 

[AlexCaledin]

Let us agree, together with Feynman, that we are merely participating in Nature's self-observing!

 

[microsansfil]

That's a separate issue to what I was discussing with @Demystifier however.

Following your remark, I was just trying to point out that QBism personalizes the famous dictum of Asher Peres : Unperformed experiments have no results and thus experience do not "exist" prior to being experienced.

https://arxiv.org/pdf/1311.5253.pdf

The outcome of an experiment is the experience it elicits in an agent. If an agent experiences no outcome, then for that agent there is no outcome. Experiments are not floating in the void, independent of human agency. They are actions taken by an agent to elicit an outcome. And an outcome does not become an outcome until it is experienced by the agent. That experience is the outcome.

Many seem to have forgotten (Or have not yet fully realized this) that any scientific investigation, among other things, begins with our awareness. The "qbism" reminds us in a clear way, for those who manage to become aware of it and recalls the scaffolding that is used in our objectification processes.

https://arxiv.org/pdf/1311.5253.pdf

What is "real" for an agent rests entirely on what that agent experiences, and different agents have different experiences. An agent-dependent reality is constrained by the fact that different agents can communicate their experience to each other, limited only by the extent that personal experience can be expressed in ordinary language. Bob’s verbal representation of his own experience can enter Alice’s, and vice-versa. In this way a common body of reality can be constructed, limited only by the inability of language to represent the full flavor — the “qualia” — of personal experience.

/Patrick

 

[bhobba]

Please dig it up. As I recall, Schlosshauer does not claim to have a solution for the problem of unique outcomes - which is the only way uncertainty in a superposition is reduced.

I will dig it up. You are of course correct - he does not claim that, nor do I, but we will be in a better position to discuss what exactly is being said when it is spelled out. I will get it from the textbook. On reflection that would be a better source than past threads.

Thanks
Bill

 

[vanhees71]

In your case, I would recommend to use statistical ensemble for practical purposes and Nelson for the conceptual/philosophic ones. That would be quite close to my own practice, as I use statistical ensemble for practical purposes and Bohm for the conceptual/philosophic ones. Essentially, Nelson is just Bohm with an additional stochastic force on particles.

Hm, isn't Nelson himself now convinced that the stochastic interpretation is flawed? I'm not sure, where I read something along these lines of arguments...

 

[Demystifier]

Hm, isn't Nelson himself now convinced that the stochastic interpretation is flawed? I'm not sure, where I read something along these lines of arguments...

The Nelson stochastic interpretation has some internal problems (which interpretation doesn't?), but people are working on it. See e.g. https://lanl.arxiv.org/abs/1510.06391

 

[vanhees71]

The Nelson stochastic interpretation has some internal problems (which interpretation doesn't?)

Which internal problems does the minimal statistical interpretation have, despite the fact that some philosophers cannot accept that nature doesn't behave as the wishful thinking from their macroscopic experience based prejudices suggest?

The more I think about it the more I get convinced that the minimal statistical interpretation is all there is to QM. The question, whether or not QM is the last word on the most fundamental theory we can ever discover, is of course an open one.