I Is GRW theory an interpretation of quantum mechanics or a rival theory?

[vanhees71]

The vacuum is Poincare invariant, which means that it's not (!) defining a preferred reference frame.

 

[WernerQH]

Sure. The reference frame is no longer relevant.

 

[MathematicalPhysicist]

The meaning of most words is not learned through their definitions. When I say "Jack is walking", no one will ask me to define "Jack", to define "is" or to define "walking". Even in pure math, if I say "The set exists", no mathematician will ask me to define "The", to define "set" or to define "exists". The meaning of most words is learned gradually, through examples. (Artificial neural networks in machine learning also learn through examples, but humans usually need much smaller number of examples to learn it efficiently.)

The word ontic is one such word. The meaning of "ontic" is somewhat similar to "real", but "ontic" has a narrower meaning. There is no precise definition, but it can be learned through examples. Here are some examples:

1. In classical mechanics, the particle position as a function of time $x(t)$ is ontic. Its Fourier transform $\tilde{x}(\omega)$ is not ontic.

2. In classical mechanics, anything that can directly be derived from $x(t)$ is ontic. The meaning of "directly" also has to be learned through examples. For instance, the velocity $\dot{x}(t)$ and acceleration $\ddot{x}(t)$ are directly derived from $x(t)$. The momentum $p(t)=m\dot{x}(t)$ and the force $F(x)$ are not directly derived from $x(t)$.

3. In classical mechanics, quantities that cannot be directly derived from $x(t)$ are not ontic. For example, mass $m$, momentum $p$, force $F$ and Lagrangian $L(x,\dot{x})$ are not ontic.

4. A classical wave $\phi(x,t)$ is ontic. Its spatial Fourier transform $\tilde{\phi}(k,t)$ is not ontic.

From those examples, one can use intelligent extrapolation to determine whether many other concepts in classical physics are ontic or not. (But in some cases it may not be obvious, so we may have have different interpretations of classical physics. That's particularly true in the theory of relativity.)

When one grasped the meaning of "ontic" in classical physics, one can start to think and talk about "ontic" in quantum physics.

Does this word solves any known problems or only creates more problems?

 

[Demystifier]

Does this word solves any known problems or only creates more problems?

Yes.

More seriously, this word helps to explain what's the point of quantum interpretations such as Bohmian mechanics, many worlds or GRW. But interestingly, it often turns that those who don't get the point of such interpretations also don't get the meaning of that word. So I think it's safe to say that the o-word is helpful to some and creates even more problems to others.

 

[MathematicalPhysicist]

Yes.

More seriously, this word helps to explain what's the point of quantum interpretations such as Bohmian mechanics, many worlds or GRW. But interestingly, it often turns that those who don't get the point of such interpretations also don't get the meaning of that word. So I think it's safe to say that the o-word is helpful to some and creates even more problems to others.

I am Copenhagen if I understand it correctly.

 

[Fra]

What I find most interesting with the dicussion is the relation between the ontic and the epistemological views. It is more interesting to see how they are related than how the oppose each other.

It's even a central point for me from and agent interpretation. The whole point there is that BOTH perspectives are required. The agent does inference, but this requires a context, which is can be thought ontic. It the pure epistemic interpretaiton, the information has no physical encoding, it's just imagine to be relative to some non-interacting observer. I think we are cure this, buy trying insisting that the epistemic view is attached to an "ontic" observer. Ie. a physical agent, part of the universe. Not just an abstraction. But the "ontics" in that view as kind of subjective. This is weird both from the classical ontic view and the CI view.

So I sort of see myself in the middle here.

/Fredrik

 

[Jarvis323]

What I find most interesting with the dicussion is the relation between the ontic and the epistemological views. It is more interesting to see how they are related than how the oppose each other.

It's even a central point for me from and agent interpretation. The whole point there is that BOTH perspectives are required. The agent does inference, but this requires a context, which is can be thought ontic. It the pure epistemic interpretaiton, the information has no physical encoding, it's just imagine to be relative to some non-interacting observer. I think we are cure this, buy trying insisting that the epistemic view is attached to an "ontic" observer. Ie. a physical agent, part of the universe. Not just an abstraction. But the "ontics" in that view as kind of subjective. This is weird both from the classical ontic view and the CI view.

So I sort of see myself in the middle here.

/Fredrik

Is there a good source for learning what the agent interpretation you're referrring to is? Are you talking about Bayesianism?

 

[Fra]

Is there a good source for learning what the agent interpretation you're referrring to is? Are you talking about Bayesianism?

I guess it's the case with many interpretations and research directions, that there are variants of things. I do not feel that my stance is properly represented by one single source. But yes, it's strongly related to qbism, but my take on this is not just an "pure interpretation", but a reconstruction, which if you take it seriously has deep implications not just for the basic interpretations of stuff like wavefunction, the reconstruction should have implications for dynamics and the hierarchy of interactions and unification. This is NOT something that is part of the "basic Qbism" camps. But the question for som sort of reconstruction is part of the qbism think as well, but I recall many that declare themselves as qbists that i disagree with, this is why I avoid the label.

Other inspirational ideas that I align to are for example, to throw in some random quotations that paints the picture.

"Here we wish to entertain a far more radical hypothesis: perhaps the laws of physics are nothing but rules of inference."
-- Ariel Caticha, https://arxiv.org/pdf/0808.1260.pdf

But while Caticha seems to think of this in an objective bayesian sense, and hence presumes the existence of observer equivalence, and use it as a constraint. I think have the same hypthesis but from the subjective perspective. But doing it that way, one needs to replace the "constraint" but something else. And this sometihng else in my view is evolution in the agen population. This supposedly solve the "problem" with the subjective bayesianism. (Except the details are open, how to actually do it, what kind of math etc)

I am also influenced a bit by algorithmic information theory, that does not merely consider measures of information, but the RATE of information processing. Ie. putting information in a dynamical context, of coding/decoding and compression under time pressure etc. But many of these programs, have an objective stance to them that will not work for the agent view. I am looking for the view where the agent itself constitutes the hardware on where the algorithms run. This puts CONSTRAINTS on the subjective inferences, and supposedly prevents the chaos that opponents otherwise would expect from a subjective inference program. These constraints serve the purpose of making the variation SMALL in the evolutionary picture and there may be other advantages as well.

Another inspiring paper
"In this work, I propose a rigorous approach of this kind on the basis of algorithmic information
theory. It is based on a single postulate: that universal induction determines the chances of what any observer sees next. That is, instead of a world or physical laws, it is the local state of the observer alone that determines those probabilities. Surprisingly, despite its solipsistic foundation, I show that the resulting theory recovers many features of our established physical worldview: it predicts that it appears to observers as if there was an external world that evolves according to simple, computable, probabilistic laws. In contrast to the standard view, objective reality is not assumed on this approach but rather provably emerges as an asymptotic statistical phenomenon."
-- Markus P Müller, https://arxiv.org/abs/1712.01826

That's in short what it is. If someone is aware of any spot on sources for similar views no one would be more happy to learn about it than me. There are many nice papers, but there is still many missing steps before a consistent model is in place. Another problem is that the most basic reconstructions likely are so abstract that the gap to make contact to current physics is huge. Just look at how hard string theory has to make contact to reality.

/Fredrik

 

[Fra]

To stay on topic, about ontics and realism.

This is also an angle to what "realism" can mean in qbism.

"These views have lately been termed “participatory realism” to emphasize that rather than relinquishing the idea of reality (as they are often accused of), they are saying that reality is more than any third-person perspective can capture. Thus, far from instances
of instrumentalism or antirealism, these views of quantum theory should be regarded as attempts to make a deep statement about the nature of reality. "
-- C. Fuchs, https://arxiv.org/abs/1601.04360

/Fredrik

 

[AlexCaledin]

reality is more than any third-person perspective can capture

- that's precisely why the 3rd persons ought to stay at the Copenhagen!

 

[vanhees71]

The meaning of most words is not learned through their definitions. When I say "Jack is walking", no one will ask me to define "Jack", to define "is" or to define "walking". Even in pure math, if I say "The set exists", no mathematician will ask me to define "The", to define "set" or to define "exists". The meaning of most words is learned gradually, through examples. (Artificial neural networks in machine learning also learn through examples, but humans usually need much smaller number of examples to learn it efficiently.)

The word ontic is one such word. The meaning of "ontic" is somewhat similar to "real", but "ontic" has a narrower meaning. There is no precise definition, but it can be learned through examples. Here are some examples:

1. In classical mechanics, the particle position as a function of time $x(t)$ is ontic. Its Fourier transform $\tilde{x}(\omega)$ is not ontic.

This already shows how nonsensical the word "ontic" is. A Fourier transformation is a one-to-one mapping within a appropriately defined space of functions. This $\tilde{x}(\omega)$ and $x(t)$ provide precisely the same information on the considered aspect of nature, in this case the trajectory of a classical point particle.

2. In classical mechanics, anything that can directly be derived from $x(t)$ is ontic. The meaning of "directly" also has to be learned through examples. For instance, the velocity $\dot{x}(t)$ and acceleration $\ddot{x}(t)$ are directly derived from $x(t)$. The momentum $p(t)=m\dot{x}(t)$ and the force $F(x)$ are not directly derived from $x(t)$.

The Fourier transform is as directly derived from $x(t)$ as are the various derivatives. Why is momentum not ontic. You just need to consider another property of matter with a clear operational meaning, i.e., mass. So it's totally arbitrary what you call ontic and non-ontic. That's the impression I always have when discussing philosophical issues: The entire system of notions depends on the subjective world view of each of the individual philosopher. It's nothing well defined as in the natural sciences, where you have clear operational definitions of the fundamental notions within a theory (provided you deals with a more or less "closed theory" like classical mechanics, classical field theory, or quantum theory).

3. In classical mechanics, quantities that cannot be directly derived from $x(t)$ are not ontic. For example, mass $m$, momentum $p$, force $F$ and Lagrangian $L(x,\dot{x})$ are not ontic.

If $m$ is non-ontic

4. A classical wave $\phi(x,t)$ is ontic. Its spatial Fourier transform $\tilde{\phi}(k,t)$ is not ontic.

From those examples, one can use intelligent extrapolation to determine whether many other concepts in classical physics are ontic or not. (But in some cases it may not be obvious, so we may have have different interpretations of classical physics. That's particularly true in the theory of relativity.)

When one grasped the meaning of "ontic" in classical physics, one can start to think and talk about "ontic" in quantum physics.

As you explain it, I've no clue what "ontic" means in classical physics nor in QT.

 

[Fra]

- that's precisely why the 3rd persons ought to stay at the Copenhagen!

There are different flavours of these things as well, but IMO the Copenhagen interpretation is not fully participatory, at least not in the deep sense I mean.

It is participatory in that the observer, perturbs the system, reads the backreaction and then revises it's state of information. The hilbert space is not revised or changed. But it should be clear that this is not the full participation.

A fully participating agent would IMO have to not only in the differential sense, update it's information state, relative to the prior information that defins the "information space", it also have to - when required - evolve (recode and grow) the information space itself.

All the flavours here is why attempting to use the existing labels is imperfect.

CI corresponds to a massive dominant agent, whose evolution in information/"hilbert" space, is small in comparastion to the changes that corresponds to the state revision. This is IMO comparable to the assumption of a background spacetime in relativity. This approximation holds for a "testa particle" interacting with the galaxy. The test particles influence on geometry is neglectable.

By the same token, if we neglect the influence of hte measuremnt feedback of the prior STRUCTURE of the agent, we arreive at something that is pretty much CI or ensemble views. But this fails to describe the complex part.

So I think of QM as we know it, as the "tangent space view" of some yet unknown theory. (Space referring to hypotehsis space, not spacetime)

/Fredrik

 

[AlexCaledin]

I think of QM as we know it, as the "tangent space view" of some yet unknown theory.

Of course! It's the tangent view of the consistent histories approach. The observer is looking what history is actual, using the Copenhagen QM to predict what he's to see next. Still, he may be participating in the choice, but it seems unscientific to investigate how exactly that participation works.

 

[Fra]

but it seems unscientific to investigate how exactly that participation works.

Here we disagree, but it would be a separate discussion I think.

/Fredrik

 

[RUTA]

Another problem is that the most basic reconstructions likely are so abstract that the gap to make contact to current physics is huge. Just look at how hard string theory has to make contact to reality.

/Fredrik

I’m not sure you’re referring to axiomatic reconstructions of QM from information-theoretic principles, but if so, this paper is aiming to make their ideas more tangible https://arxiv.org/abs/2107.06942 . In these approaches, the aim is to advance QM from an operational theory to a principle theory, like special relativity. This does not say anything about the ontology (constructive account), but that’s also true for special relativity and very few physicists care to work on that problem anymore.

 

[physika]

. I think have the same hypthesis but from the subjective perspective. But doing it that way, one needs to replace the "constraint" but something else. And this sometihng else in my view is evolution in the agen population. This supposedly solve the "problem" with the subjective bayesianism.

Personal approach, personal theory ?
Are allowed in this forum ?

 

[PeterDonis]

Personal approach, personal theory ?
Are allowed in this forum ?

First, if you think someone else's post violates the forum rules, please use the Report button. Don't make a public post like this.

Second, in this particular forum, since the subject matter (QM interpretations) in itself is essentially personal opinion, the ground rules are somewhat looser. The post you quoted from gives references and explains how the poster's own opinions relate to the references. That appears to me to be within bounds for this forum.

 

[physika]

First, if you think someone else's post violates the forum rules, please use the Report button. Don't make a public post like this.

Second, in this particular forum, since the subject matter (QM interpretations) in itself is essentially personal opinion, the ground rules are somewhat looser. The post you quoted from gives references and explains how the poster's own opinions relate to the references. That appears to me to be within bounds for this forum.

understood, loose
thought.

...

 

[Lynch101]

More seriously, this word helps to explain what's the point of quantum interpretations such as Bohmian mechanics, many worlds or GRW. But interestingly, it often turns that those who don't get the point of such interpretations also don't get the meaning of that word. So I think it's safe to say that the o-word is helpful to some and creates even more problems to others.

Does the justification for quantum interpretations require the term 'ontic' at all?

Quantum interpretations are justified in that they are simply an expression of how the mathematics [potentially] corresponds to the physical universe, or 'the physical reality' in the parlance of EPR, and how those things in the physical universe are represented in the mathematics aka 'elements of the physical reality'.

These questions can be posed without recourse to the 'o-word'. Although it would simply be a case of 'a rose by any other name...'

 

[physika]

More seriously, this word helps to explain what's the point of quantum interpretations such as Bohmian mechanics, many worlds or GRW. But interestingly, it often turns that those who don't get the point of such interpretations also don't get the meaning of that word. So I think it's safe to say that the o-word is helpful to some and creates even more problems to others.

Does the justification for quantum interpretations require the term 'ontic' at all?

Quantum interpretations are justified in that they are simply an expression of how the mathematics [potentially] corresponds to the physical universe, or 'the physical reality' in the parlance of EPR, and how those things in the physical universe are represented in the mathematics aka 'elements of the physical reality'.

These questions can be posed without recourse to the 'o-word'. Although it would simply be a case of 'a rose by any other name...'

GRW Theory (Ghirardi-Rimini-Weber) is not an interpretation.
(...apart definitively ontic).

https://plato.stanford.edu/entries/qm-collapse/

"They are also related to the fact that, in its standard formulation and interpretation, quantum mechanics is a theory which is excellent (in fact it has an unprecedented success in the history of science) in telling us everything about what we observe, but it meets with serious difficulties in telling us what there is. We are making here specific reference to the central problem of the theory, usually referred to as the measurement problem"

"fact is that the resulting theory is capable, on the basis of a single dynamics which is assumed to govern all natural processes, to account at the same time for all well-established facts about microscopic systems as described by the standard theory...as well completely satisfactory way for the classical behavior of macroscopic systems."

"Last but not least, Collapse Theories qualify themselves as rival theories of quantum mechanics and one can easily identify some of their physical implications which, in principle, would allow crucial tests discriminating between the two. "

.