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

[physika]

So if this is the definition of "ontic", which I thought is indeed the meaning before reading this thread, after which it got a word without any meaning, then it's simply what a physicist would call an objectively observable phenomenon. Then it doesn't make sense to say the one or the other element of a theory were "ontic" or "not ontic", because then all theory is not ontic, because it's just a quantitative mathematical description of the observable phenomena.

Maybe wish to be.

 

[gentzen]

So if this is the definition of "ontic", which I thought is indeed the meaning before reading this thread, after which it got a word without any meaning, then it's simply what a physicist would call an objectively observable phenomenon. Then it doesn't make sense to say the one or the other element of a theory were "ontic" or "not ontic", because then all theory is not ontic, because it's just a quantitative mathematical description of the observable phenomena.

Demystifier's basic premise of this thread was that the meaning of the word "ontic" can be learned by observing how it is actually used. However, instead of actually doing this, he tried to shortcut that process by presenting some borderline examples. Worse, his refernce (Dürr) used the word "primitive ontology" (instead of "ontic") for the concept exemplified by those borderline cases.

A book by Detlef Dürr is probably not good enough to make you happy. So let me instead play this game with the book "Do we really understand quantum mechanics" by Franck Laloë (because I expect that it is easier for you to respect that author). The words "ontic" and "ontology" don't appear often in that book, and basically only in the places where they could not be avoided:

Many authors introduce the words “ontic” and “epistemic” in this context, even if they are more common in philosophy than in physics. An analogy with classical physics is useful to understand their meaning: in classical physics, the position and momenta of all particles of a physical system provide a direct description of its physical properties; this is an “ontic” description. But if the system is described only in a probabilistic way by a statistical distribution in phase space (as in the Liouville theorem) reflecting a partial knowledge of its state, this description is called “epistemic”.

Tumulka has proposed a relativistic version of the GRW theory [704], which he calls “flash ontology”, where the “local beables”(§11.8) are given by a discrete set of space-time points, at which the collapses are centered; these points have a random distribution that is determined by the initial wave function.

Does this help to reduce your impression that it is a "word without any meaning"?

 

[vanhees71]

I've nothing against Dürr. To the contrary his approach to Bohmian mechanics in his book "Understanding quantum mechanics" makes at least sense for non-relativistic single-particle QT, though I'm not a follower of Bohmian mechanics, as long as there's no convincing consistent version for relativistic QFT (and a formulation, where the basic causality principle of relativity is not fulfilled, is not at all convincing form me!).

The above quote also doesn't make sense to me, because for me the probabilistic behavior of quantum systems are also "direct descriptions of its behavior". It's precisely what's observed: E.g., if I shoot an electron with pretty well defined momentum through a double slit, I don't know very precisely, where it will be registered behind the slits, and that's what's observed. The electron will be registered somewhere on the slits. QT predicts a probability distribution which I can calculate as an interference pattern of a Schrödinger wave function, and then repeating the experiment with equally prepared electrons a lot of time, I indeed get the corresponding distribution of registered electrons at my slit. The randomness for me is an objective phenomenon as is the position of a classical particle in phase space within classical mechanics. For sure, a single electron is an example, where the classical "phase space ontology" fails to describe the phenomena, while the "probabilistic ontology" of quantum theory describes them very well.

 

[Morbert]

It seems to me that here you identify decoherent histories with consistent histories. My understanding is that the former is just one version of the latter.

Consistent histories and decoherent histories are ultimately the same formalism. As research projects, the former has concerned itself with minimal decoherence criteria, while the latter focuses on cases with strong decoherence. https://www.webofstories.com/play/murray.gell-mann/161

Ontologically speaking, Griffith's CH interpretation is closer to EPE-DH than to Omnes's CH. And you can see him equate CH with DH here.

 

[martinbn]

Demystifier's basic premise of this thread was that the meaning of the word "ontic" can be learned by observing how it is actually used. However, instead of actually doing this, he tried to shortcut that process by presenting some borderline examples. Worse, his refernce (Dürr) used the word "primitive ontology" (instead of "ontic") for the concept exemplified by those borderline cases.

A book by Detlef Dürr is probably not good enough to make you happy. So let me instead play this game with the book "Do we really understand quantum mechanics" by Franck Laloë (because I expect that it is easier for you to respect that author). The words "ontic" and "ontology" don't appear often in that book, and basically only in the places where they could not be avoided:Does this help to reduce your impression that it is a "word without any meaning"?

The quote includes momentum along with position as ontic.

 

[Killtech]

Without field there is no particle.

Newton's gravity is a special case, given how it is mathematically setup. You could just skip the force entirely and just describe how each particles accelerates another since gravity there works via an action at range. The old classical model could be understood that particles interact directly with each other at range with no intermediary field. This is why in that old model your statement doesn't apply.

 

[physika]

just describe how each particles

Right !

As your said:
"Just describe"
...no more than that.

 

[Killtech]

Right !

As your said:
"Just describe"
...no more than that.

$$\ddot x_1 = G \frac {m_2} {(x_1-x_2)^2}, \ddot x_2 = G \frac {m_1} {(x_1-x_2)^2}$$

 

[gentzen]

I've nothing against Dürr. To the contrary his approach to Bohmian mechanics ...

The above quote also doesn't make sense to me, because for me the probabilistic behavior of quantum systems are also "direct descriptions of its behavior".

If you have already trouble making sense of Franck Laloë's words, then my expectation would be that you should have even more trouble making sense of Detlef Dürr's words.

I'd say the electromagnetic field is indeed not "ontic", because it is just a description of phenomena occurring, according to our description in terms of Maxwell's theory, when this field interacts with some charged matter. One ontic element, i.e., one observable and even directly perceivable by the human senses phenomenon is what we call "light", though ...

I wrote that elaboration on "... the meaning of the word ontic can be learned by observing how it is actually used ..." to have some basis for answering your comment. But apparently that didn't work as planned. So instead I will answer from my own perspective (which is unrelated to this thread and Demystifier's goals):
Concepts like "ontology" and "ontic" depend on context, both on the theory being analysed (like classical mechanics, classical electrodynamics, special relativity, ...) and on the field of study (like mathematics, philosophy, physics, ...). In our context, classical electrodynamics has a field ontology, and classical mechanics has a particle ontology. Explanations why $E$ being ontic is less problematic than force being ontic are just elaborations of those basic facts about the typical usage of the words "ontology" and "ontic" in that context.

 

[vanhees71]

For me force is for sure much more ontic than the electric field. A force is directly having an observable consequence, i.e, the acceleration of a particle the force is acting on. Anyway, it doesn't have the slightest advantage for the understanding of the meaning of either quantity in physics to say it is ontic or not.

 

[Killtech]

For me force is for sure much more ontic than the electric field. A force is directly having an observable consequence, i.e, the acceleration of a particle the force is acting on. Anyway, it doesn't have the slightest advantage for the understanding of the meaning of either quantity in physics to say it is ontic or not.

Force being directly observable is a hard oversimplification. If we go into detail, it's way more complicated and nothing is really directly observable all on its own.

forces represent the interaction between different entities, in this case the field and a particle. But we can measure neither of them directly. For one we cannot measure what happens non-locally at all, so we are reliant on entities that carry such information over distances. Usually light waves and particles are regarded as such carriers.

But in any realistic depiction of a measurement, information changes hands quite a few times until it reaches us. Originally it may be carried by light in a scattering event, then it interacts with something and is then converted by additional interactions into an electric signal which is then converted into either something mechanical (like a moving needle visible to the human eye) or processed digitally. How is anything of this a direct observation? The only thing direct is local interaction and self interaction of entities but all actual measurement is very indirect.

You cannot leave out the intermediary entities that transport information. They have to be modeled to be able to make correct predictions. Same goes for their interaction with other entities, however that is different as it itself does not hold any information on it's own but merely mediates the changing hands of existing information between one entity to another.

I think the question of ontic is about who really holds the actual information.

 

[gentzen]

The quote includes momentum along with position as ontic.

I know. But my comment also pointed out that Dürr talked about "primitive ontology" when he highlighted the ontic importance of position.

You were the one who complained to Demystifier: "My problem is that you are not discussing like a scientist. ... You are discussing like a member of school debate team." And now behave like that and just try to score easy points. Such a behavior encourages others to be careful with what they write, and to not acknowledge the questions they did not address yet.

Do you then think that your engagement on the quantum foundations forum is a waste of time? Or if not, what's your motivation for that?

The motivation is the same as when I read theards (in other forums) about perpetual motion, logical errors in relativity and so on. It is clear that it is nonsense, but figuring out why or reading someone's response to such nonsense usually leads to a better understanding for me.

Do you find this funny? What do you expect how one should react?

What do you expect how I should feel, since I talked about ontological commitment and ontological overcommitment, and might be indirectly be responsible for Demystifier trying to find out how to explain such concepts?

If you analyse the ontological commitments of a theory relying on a particle ontology, the conclusion that particle position is the main ontological commitment seems justified to me. You can include momentum too in your ontology if you wish, but the particle ontology does not force this upon you.

 

[martinbn]

I know. But my comment also pointed out that Dürr talked about "primitive ontology" when he highlighted the ontic importance of position.

You were the one who complained to Demystifier: "My problem is that you are not discussing like a scientist. ... You are discussing like a member of school debate team." And now behave like that and just try to score easy points. Such a behavior encourages others to be careful with what they write, and to not acknowledge the questions they did not address yet.Do you find this funny? What do you expect how one should react?

What do you expect how I should feel, since I talked about ontological commitment and ontological overcommitment, and might be indirectly be responsible for Demystifier trying to find out how to explain such concepts?

If you analyse the ontological commitments of a theory relying on a particle ontology, the conclusion that particle position is the main ontological commitment seems justified to me. You can include momentum too in your ontology if you wish, but the particle ontology does not force this upon you.

Fair enough, i will stop.

 

[Demystifier]

For me it is less vague. I went to a similar school system. In fact it is obvious that position is a kinematics notion while momentum is a dynamics one.

Where i went to school/uni mechanics is always divided into statics, kinematics, dynamics.

Good, since now we have finally some common ground to start with, now we can start to address interesting questions. In your view, what's the kinematics of QM?

 

[physika]

$$\ddot x_1 = G \frac {m_2} {(x_1-x_2)^2}, \ddot x_2 = G \frac {m_1} {(x_1-x_2)^2}$$

a description.

 

[martinbn]

Good, since now we have finally some common ground to start with, now we can start to address interesting questions. In your view, what's the kinematics of QM?

I can only speculate. I've not seen the division into kinematics and dynamics outside of classical mechanics. For example the typical spin/polarization cases I would call kinematics.

 

[vanhees71]

Kinematics: States are represented by self-adjoint positive semidefinite operators with trace 1, the Statistical Operator $\hat{\rho}$ of the system. Observables are represented by self-adjoint operators. The possible values of observables are given by the spectrum of these operators. Expectation values of an observable represented by the operator $\hat{A}$ is given by
$$\langle A \rangle = \mathrm{Tr}(\hat{\rho} \hat{A}).$$

Dynamics: There exists an operator $\hat{H}$, the Hamilton operator of the system, such that the time derivative of an observable $A$ is represented by the operator
$$\mathring{\hat{A}}=\frac{1}{\mathrm{i} \hbar} [\hat{A},\hat{H}]+\partial_t \hat{A}.$$
The statistical operator obeys
$$\mathring{\hat{\rho}}=0.$$

One should note that this defines the physical/covariant time derivative. The mathematical time dependence of the statistical operator and the observable-representing observables are only defined modulo an arbitrary (time-dependent) unitary transformation. The time-dependence can be pretty freely chosen by choice of a picture (e.g., the Schrödinger picture lumps the entire time dependence to the statistical operator, and the observable-representing operators are time-independent, except for possible explicit time dependences; for the Heisenberg picture it's the other way; the general case is due to Dirac).

 

[Morbert]

If QM assigns a probability for some path $q(t)$ through configuation space between intial and final configurations $q_i$, $q_f$ as $$p\left[q(t)\right] = \mathrm{Re}\left[\psi^*(q_f,t_f) e^{i\mathcal{S}\left[q(t)\right]}\psi(q_i,t_i)\right]$$and we sufficiently coarse-grain these paths so that the probabilities obey standard probability calculus, we can presumably identify a classical limit where some coarse-grained path $\alpha$ has a probability close to $1$ and is characterised by classical kinematic equations.

 

[Fra]

Given the corroborated standard QM, IMO the "kinematics" refers to the states of the ensemble, ie. statistics, in line with what Vanhees writes.

But the interesting part is the, why is this not satisfactory to everyone? (and this dissatisfaction is what drives these discussions)

I will speak for myself, and one reason, is that the "ontics" at statistical levels, does not seem to have a weel understood correspondence with to the "ontics" at agent(=observer) level. And this is a serious issue.

One may object to this, and not that the physicists in the scientific commmunity indeed has created this ontic. This is true, but this is at a time scale that is HUGE compare to the interaction time scales! This is why THIS "understanding" is not the same as understanding the nature of interactions themselves. For the group of observes (human scientists) to infer these states and laws at statistical level, one need to prepare and repeat some experiments many many times. This is not a problem, or wrong per see, it's just that it does not correspond to an inside agent. And the "laws" that are created or discovered from the scientific process, have a different constructing principle than the reason why laws exist in the first place. An extension of this issue also leads to Smolins critique to the "Newtonian paradigm". The reason is that the decompisition of kinematics and dynamics is rather an artefact of the human perspective to atomic physics. The mathematics that fits well, seems to break down when it comes to cosmology and unification and finetuning questions.

For someone seeing from the agent perspective, these things are a major defect and can not be ignored. It's just obvious that this is incomplete.

Edit: Unless it's not clear to all. The use of the word AGENT instead of OBSERVER for me is motivated by that it tries to emphasize that the observer need to be neither human, a physicists or even be a biological system. AGENT for me puts emphasis on that the observer is a physical system, and is made of whatver all thing are made of (matter). So an AGENT does not need to have a brain, but it has to have some kind of ENERGY and if localized - MASS. The physical limits of the AGENT, also constrains the physically possible inferences, via throttling of resources. For example communication between agents of grossly different masses, is either necessarily lossy, or in exceptional cases a tuning is in place that allows a non-lossy compression. These abstractions are probably easier to motivate when one ponders about black holes. For atomic physics all this may seem irrelevant, but I still don't think it is. If information is "lost" wrt and agent, it might as well mean it's encrypted beyond decrypting capabilites of that agent.

/Fredrik

 

[physika]

"The decompisition of kinematics and dynamics is rather an artifact"

Similar ideas from Spekkens.

https://arxiv.org/abs/1209.0023

...

 

[vanhees71]

Given the corroborated standard QM, IMO the "kinematics" refers to the states of the ensemble, ie. statistics, in line with what Vanhees writes.

But the interesting part is the, why is this not satisfactory to everyone? (and this dissatisfaction is what drives these discussions)

I will speak for myself, and one reason, is that the "ontics" at statistical levels, does not seem to have a weel understood correspondence with to the "ontics" at agent(=observer) level. And this is a serious issue.

Why? Can you predict all "outcomes of measurements" with certainty in your everyday life? I think a statistical description of the phenomena is quite natural!

 

[Fra]

Why? Can you predict all "outcomes of measurements" with certainty in your everyday life? I think a statistical description of the phenomena is quite natural!

No I can't of course. And that influences my behaviour. I make what I find to be the optimal inference, and this gets me a informationally biased crafted dice, that rules my random walk. In a way this dice is constructed "statisticall as well", but the raw data making up the PROCESSED "staistical" inferences, depneds on the agent. This even explain why I may appear irrational to other agents.

I don't object to statistics itself, it has it's place even in the agent view, and is a natural part of inference itself, but the difference is at which level it's encoded.

From the information theoretic view, to ME the "ontics" are the set of observational facts, that come from distinguishable events. Then can then be processed and encoded in principle in arbitrary ways (up to the agent). But what is observable, depends on the agent (not just energy scale of information, but more than that), so the raw data for the statistical approach, at the leven of a working physicists operating measurement equipment at an accelerator, is obvioulsy much larger than what is available to a hypothetical agent, beeing a component in the detector.

And if we ever want to understand how the various interactions are related, at different energy scales, in a coherent way I think we need to go beyond the pure statistical view of the lab. This may be less clear depending on once perspective. And I totally understand that from the most pragmatic perspective of typical atomic physics experiments, this may seem esotheric. But as one analyse the inference logic used, the problem IMO is obvious.

/Fredrik

 

[Fra]

The idea of the potential explanatory value here if it is not clear: The fact that different observers has different sets of information AND have different "resources" to process and encode it, creates a tensions between the agents. And this could at least potentially EXPLAIN their interactions. (ie a sort of gauge interaction if you wish; where differen gauges implies a tension = force)

This is the simple idea. In a way this IS the way many interaction ARE explained at least in how I understand the standarde model, the "tension" is resolved via transformations that generates symmetry groups etc. So this idea is not new. But the new idea is to take this more seriously, and take it a step further. Also these ideas are not coherent, it's patchwork at the moment, and I thin the problem is precisely that these things aren't sorted out. The emerging picture is a post-observation, it's not there by construction (which it probably could be).

I think this is also partly what I read Fuchs dream is roughly about, in the other thread.

I see components of this alreay in current theories, but it's half baked!

/Fredrik

 

[physika]

because then all theory are not ontic, because IT´S JUST a quantitative mathematical DESCRIPTION of the observable phenomena.

Lamentably, i think that is the status and fate of mathematical theorization (as models of nature), just describing "facts" in an "approximate" manner..

 

[vanhees71]

Of course, all our descriptions are only approximate (though for some very simple systems we get agreement between observation and theory to 12 or more significant digits, which is amazing enough), but it's the best we have, leading to a lot of useful stuff, like this computer connected to the internet etc.

 

[physika]

Of course, all our descriptions are only approximate (though for some very simple systems we get agreement between observation and theory to 12 or more significant digits, which is amazing enough), but it's the best we have, leading to a lot of useful stuff, like this computer connected to the internet etc.

i understand, but the thing goes beyond,
in words of Kant:

"Phenomena are the appearances, which constitute the our experience; noumena are the (presumed) things themselves, which constitute reality"Repost:

Lamentably, i think that is the status and fate of mathematical theorization (as models of nature), just describing "facts".

 

[WernerQH]

Lamentably, i think that is the status and fate of mathematical theorization (as models of nature), just describing "facts" in an "approximate" manner..

There are no isolated "facts"; they are always tied to theory and its (sometimes implicit) ontology. For Maxwell, electrodynamics expressed some "facts" about the aether. He would surely have called it "ontic", which modern physicists are reluctant to do. :-)

 

[vanhees71]

Well Maxwell's aether was so strange that Maxwell himself later seems not have to be too keen about it anymore. I think one can also say that in the late 19th century it was rather reduced in its meaning to some assumed preferred (inertial) reference frame with some hope that Newton's absolute space may be determined by this preferred frame, i.e., by the electromagnetic phenomena. Famously this hope was gone with Einstein's solution of the puzzle with the missing Galilei invariance of Maxwell's theory, i.e., the discovery of special relativity and the necessity for a new spacetime model (Minkowski space). With this any preferred frame and with it the aether was gone.

 

[physika]

There are no isolated "facts"; they are always tied to theory and its (sometimes implicit) ontology. For Maxwell, electrodynamics expressed some "facts" about the aether.

...who said ISOLATED ??

.

 

[WernerQH]

Well Maxwell's aether was so strange that Maxwell himself later seems not have to be too keen about it anymore.

In the year of his death Maxwell actually enquired about the possibility of using eclipses of the satellites of Jupiter to determine the speed of the sun with respect to the aether. (Of course, with the wisdom of hindsight we could have told him that his own equations predict that in vacuum light travels at the speed $1 / \sqrt{\epsilon_0 \mu_0}$). The aether has been replaced by something more symmetric (wrt Lorentz transformations) and much stranger. It's what we now call "vacuum". It plays an important role in quantum field theories, but it sounds somewhat oxymoronic to call the vacuum "ontic".

My point is that there can be shifts in the ontology of physical theories that leave the mathematical formalism essentially unchanged. But they can have a deep impact on our thinking.