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

[gentzen]

My problem is that you are not discussing like a scientist. ... You are discussing like a member of school debate team. You simply want, through rhetoric, to present the best possible argument to support your position.

I think this thread proves by empirical evidence that "ontic" is a completely irrelevant property, because it's not defined at all what it means.

OK, another try!

My own approach would be try to avoid "discussing like a member of a school debate team". This means that I should at least acknowledge the questions I did not address yet, even if some questions would be challenging for me to answer (satisfactory).

Say we then move on to the theory of relativity. Now we think about what is ontic again, and we have our commen sense picture that assigns physical meaning. We will have a new meaning of ontic as well. Does it matter if the common sense picture we have now contradicts the one we had with classical physics?

Our common sense picture needs to be right? Or is just an exersize, and/or for comfort, or entertainment?

Now we do the same in QT. Because QT is supposed to describe the microscopic world on a fundamental level, ontic now has more weight? We are talking again just about common sense pictures of the mathematical objects with the same motivation and goal? Or, if we assumed that QT were the complete lowest level description of reality, does this imply that what is ontic in QT is absolutely real? This is what I don't understand the most, what is the end game. If we prove QT is complete, and we prove A is ontic in QT, then we've proven something about the true physical meaning and existence of A?

I do have an opinion on some of those questions, but me trying to answer those questions would (probably) not help.

 

[physika]

I guess now we would need a new thread entitled "Learning the word "feels"", because obviously this word cannot be defined precisely.

Alternatively, to avoid a use of that word, I would say that the spring "just" moves the way it moves and a regularity of this motion can be described by an abstract mathematical quantity we call force.

..."feel", it's just figurative language.

Action-Reaction, Newton.
it doesn't just move, it interacts.
.

 

[physika]

Yes, but it's relative to a theory. Late Durr would say that you can't have a physical theory if you have not fixed what is your theory about. For instance, if you propose a speculative theory of unicorns, then, within the theory, unicorns are treated as ontic.

Sorry,
Treated, but not ontic...

Ontic (from the Greek ὄν, genitive ὄντος: "of that which is") is physical, real, or factual existence.

But that also seems to imply that what fixes the ontic quantities is what you take to be real in the first place (e.g. particles or fields or...)

Maybe both, particles as excitations of the fields.

.

 

[PeterDonis]

What if I define ontic objects as objects that are studied by kinematics?

You would still have to claim that "kinematics" only includes position, which is debatable. And then you would have to claim that, while things that change are "ontic" (kinematics), the things that cause them to change are not (dynamics). Which, again, does not seem to be a "basic intuition" that an ordinary person in the street would have.

 

[physika]

OK, another try! I hope we all know what's the difference between kinematics and dynamics:
http://www.differencebetween.info/difference-between-kinematics-and-dynamics
What if I define ontic objects as objects that are studied by kinematics?

.
maybe fated to fail...

The paradigm of kinematics and dynamics must yield to causal structure.​

https://arxiv.org/abs/1209.0023#

"The distinction between a theory's kinematics and its dynamics, that is, between the space of physical states it posits and its law of evolution, is central to the conceptual framework of many physicists. A change to the kinematics of a theory, however, can be compensated by a change to its dynamics without empirical consequence, which strongly suggests that these features of the theory, considered separately, cannot have physical significance. It must therefore be concluded (with apologies to Minkowski)
that henceforth kinematics by itself, and dynamics by itself, are doomed to fade away into mere shadows,
and only a kind of union of the two will preserve an independent reality."

.

 

[Jarvis323]

I think this thread proves by empirical evidence that "ontic" is a completely irrelevant property, because it's not defined at all what it means. All that's relevant is what's observable, and all you need for a theory is that describes the observable facts (usually within a limited realm of applicability) correctly.

I think the property of being ontic is irrelevant when restricting your universe to one painted by a particular incomplete theory (although not irrelevant as a topic of discussion, since it forces us to try to be more clear about what we think). We know that there is some "onticness" underneath classical physics, because classical physics has predictive power. But it doesn't necessarily mean that any specific mathematical objects in the theory are ontic in the sense that both the theory treats that object as fundamental/irreducible, and that object is fundamental or irreducible in nature. So pointing to this property and that property is misleading, because you can only do that within the universe of the theory. Yet here we are reaching outside of that theory into our own mental models to try and figure out what we think is real in the universe spanned by the theory and our own abstract knowledge. If we go that far, then there is no point in not spanning our entire set of scientific theories. So it is pointless to thinking about ontic in a specific theory unless that theory really completes the picture and we don't need intuition or any outside of the box thinking, only derivation. QT, supplemented with evidence from classical theory might be a foundation for thinking about what is ontic, yet still we have too shaky a formalization of QT to be clear about ontology in QM, and we have no language to connect QT and classical theory. So currently the best we can do is use our understanding of the entire universe of theory, and try to guess which direction of future work to do in an attempt to fill in what is missing. That's my opinion at least.

Even though I realize that ontology in QT in general is probably not knowable in the sense I imagine we want it to be. Rather, it should be that we have some clear formalization of QT that we can rely on in the larger universe of spanning all scientific theory consistently and then we can say what is ontological in an intuitive sense in the consistent global picture. This might be thinking in the spirit of coherentism. Actually I think in the discussion about what is ontic, we are being sort of selective coherentists, and not being clear that we are being coherentists as we try to use our intuition/abstract knowledge and infer meaning from past experience and word usage.

Rather than conceiving the structure of our knowledge on the model of Euclidean geometry, with its basic axioms and derived theorems, these epistemologists favor a holistic picture of justification which does not distinguish between basic or foundational and non-basic or derived beliefs, treating rather all our beliefs as equal members of a “web of belief” (Quine and Ullian 1970, cf. Neurath 1983/1932 and Sosa 1980).

https://plato.stanford.edu/entries/justep-coherence/#CohVerFou

However, I personally have doubts about there existing an accessible coherent language that could give us a theory of everything. It may be that such a language is infinite, or uncomputable.

 

[martinbn]

In the theory before relativity theory, it was $E$ and $B$. In the modern relativistic version it's $F_{\mu\nu}$.

$E$ is force on unit charge. So forces are ontic after all.

 

[Killtech]

Yes. And the mathematical object that most directly represents the particle is $x(t)$. Unless you know an even better mathematical object, in which case I am ready to revise my claim above.

In the theory before relativity theory, it was $E$ and $B$. In the modern relativistic version it's $F_{\mu\nu}$.

I feel that such a choice is strangely specific and yet arbitrary.

Let's query something else first and ask what about $E(x)$ and $E(x')$ or some unit transformation multiplying some additional constants? All of them are equivalently describing the very same thing, yet are different in the explicit expression. Does the "ontic" stuff acknowledge that the objects of interest don't ever appear in a raw naturally unique form but there is always a layer of representation and convention of top such that you can never assign a property to one thing but always have to think of an equivalence class of closely related quantities?

 

[gentzen]

$E$ is force on unit charge. So forces are ontic after all.

$E$ being ontic is less problematic than force being ontic, because $E$ exists in space and time. The force resulting from Newton's law of gravity on the other hand does not have an independent existence in space and time, but can only exist where the particle position already exists. Therefore the particle position is the primary ontology in that case, and force is only one of many possible secondary variables.

This existence in space and time is precisely one of the reasons why ontology with respect to "physical existence" has a slightly different character from ontology with respect to "mathematical existence". The "intuitive notion" of something which exists physically normally implies that it exists at some time and at some point, or at least in some region of space and time. This is one reason why the wavefunction should better not be ontic.

 

[Killtech]

E being ontic is less problematic than force being ontic, because E exists in space and time. The force resulting from Newton's law of gravity on the other hand does not have an independent existence in space and time, but can only exist where the particle position already exists. Therefore the particle position is the primary ontology in that case, and force is only one of many possible secondary variables.

Good point. Newtowns force does not hold any additional information about the system at all. Since it is instantaneous knowing the particle position and its mass we have all information we need so we can derive the force from there. Thus the force field itself merely holds redundant information.

Due to the Maxwell equations however this is different for $E$. The information stored there is irreducible and any theory of classical e-dyn losing it won't be able to make correct predictions.

 

[gentzen]

Does the "ontic" stuff acknowledge that the objects of interest don't ever appear in a raw naturally unique form but there is always a layer of representation and convention of top such that you can never assign a property to one thing but always have to think of an equivalence class of closely related quantities?

This is a tricky one, because those equivalence classes risk to reduce the usefulness of an ontology. On the other hand, sometimes equivalence classes are unavoidable in a strong sense. But one point of studying ontology is actually to identify such situations.

In a certain sense, the equivalence classes similar to many-one reductions are unproblematic, but those similar to Turing reductions are risky.

 

[Jarvis323]

so we can derive the force from there...

Is there an assumption that there are no separate yet correlated properties in nature?

 

[Killtech]

This is a tricky one, because those equivalence classes risk to reduce the usefulness of an ontology. On the other hand, sometimes equivalence classes are unavoidable in a strong sense. But one point of studying ontology is actually to identify such situations.

Just asking because if you cannot separate representation from the object being represented, you risk rendering making the the representation the real thing rather what the object it represents. I would find that weird.

 

[Killtech]

Is there to be an assumption that there are no separate yet correlated properties in the nature?

Sounds like you are talking QT. If a quantity is uniquely determined by another, this question isn't relevant. Correlation on the other hand always implies a certain type of dependence. If you assume something is sepererable, then you have to specify what that means and Bell's factorization is one type of separation. And it yields his inequality. Strongest separation is that of independence which implies null correlation.

 

[Jarvis323]

Just asking because if you cannot separate representation from the object being represented, you risk rendering making the the representation the real thing rather what the object it represents. I would find that weird.

Not necessarily. In a more macroscopic picture at least, we can think of lots of physical objects in which we can know some properties of some object from observing another, even though those different properties are different real things.

 

[Jarvis323]

Sounds like you are talking QT. If a quantity is uniquely determined by another, this question isn't relevant. Correlation on the other hand always implies a certain type of dependence. If you assume something is sepererable, then you have to specify what that means and Bell's factorization is one type of separation. And it yields his inequality. Strongest separation is that of independence which implies null correlation.

We can have a reduced description of something based on correlation in the information we obtain about it and calculations exploiting those correlations. It doesn't mean that the reduced description represents less real stuff. The theory is about prediction. It is only necessary that we have sufficient information to make predictions. We even seek simplified models as preferable. It doesn't mean nature is simple and reduces in reality to the shortest description as we like our models to.

 

[Killtech]

We can have a reduced description of something based on correlation in the information we obtain about it and calculations exploiting those correlations. It doesn't mean that the reduced description represents less real stuff. The theory is about prediction. It is only necessary that we have sufficient information to make predictions. We even seek simplified models as preferable. It doesn't mean nature is simple and reduces in reality to the shortest description as we like our models to.

entirely different motivation. Don't think it makes sense to talk about ontology of an approximation. Approximations may work with various things like averages over many original values and you would be forced to declare such as ontic since the originals aren't available but then you can more or less declare anything as ontic since you could derive very different effective quantities and use those instead. But when you could declare almost any quantity as ontic, it makes the word loses all meaning.

Alternatively you could declare most quantities as non-ontic making some of the information a theory uses having no ontic source inside the theory.

 

[Morbert]

Continuing the ontology discussion from the many-worlds thread here as it's probably more approrpriate

In classical physics, the finest possible graining is unique. CH, on the other hand, says that the finest possible graining is not unique. A Bohmian would say that the finest possible graining corresponds to primitive ontology, so in this language one would say that in CH primitive ontology is not unique. A classical analogy would be using the fact that a classical field $\phi(x)$ can equivalently be represented by its Fourier transform $\tilde{\phi}(k)$ and saying that $\tilde{\phi}(k)$ is not any less real than $\phi(x)$. The claim that, in classical physics, $\tilde{\phi}(k)$ is as real as $\phi(x)$ is very seducing mathematically, but at the same time it's very hard to swallow it from an intuitive physical point of view. CH interpretation of QM is hard to swallow for exactly the same reason.

"Finest possible graining" might have two interpretations. If, by a finest possible graining, we mean for example alternative field configurations $\phi(x)$, CH would fail to ascribe any ontological meaning to them, primitive or otherwise, since these histories (four-dimensional configurations) would fail to decohere for general circumstances. We would have to introduce a coarse-graining that satisfies a decoherence criterion. E.g. Instead of alternative field configurations, we would take alternative averages of field configurations over causally consistent spacetime regions. Once we have these as our finest possible grainings, CH can offer an ontic meaning to them, in the sense that we can interpret measurement outcomes as revealing pre-rexisting properties that these averages represent. The necessity of coarse-graining means we would struggle to say these properties are primitive. It would therefore be hard to interpret CH as offering multiple representations of a primitive ontology. The ontic contribution of CH only extends to the interpretation of measurements as revealing pre-existing properties, regardless of the status of those properties as primitive. Using the example from the other thread: CH won't tell you if your airplane is a primitive element of reality, it will just tell you if it will crash.

There is an adjascent interpretation "Extended Probability Ensemble Decoherent Histories" which does try to ascribe an ontic meaning to maximally fine-grained histories. This interpretation selects a preferred set of histories, and if we are talking about a field theory, they would indeed be field configurations $\phi(x)$.

 

[physika]

the particle position and its mass we have all information we need so we can derive the force from there. Thus the force field itself merely holds redundant information.

Without field there is no particle.

 

[Demystifier]

You would still have to claim that "kinematics" only includes position, which is debatable. And then you would have to claim that, while things that change are "ontic" (kinematics), the things that cause them to change are not (dynamics). Which, again, does not seem to be a "basic intuition" that an ordinary person in the street would have.

I had a different idea in mind. I was suggesting to completely remove "ontic" from the vocabulary and talk about "kinematics" instead. Here is an example:
- What's wrong with Copenhagen interpretation?
- The problem is that it doesn't clearly specify what is its kinematics.
- But it does, it's wave function $\psi(x,t)$.
- But $\psi(x,t)$ is similar to $S(x,t)$ in Hamilton-Jacobi formulation of classical mechanics. And we know that $S(x,t)$ is not kinematics, but one of ways to formulate the dynamics. By analogy, it's possible that $\psi(x,t)$ in QM is also one of ways to formulate dynamics. If so, then it's not clear what in Copenhagen QM is kinematics.
- I think you are just trying to justify Bohmian mechanics, according to which quantum kinematics is $x(t)$.
- Not necessarily, for example MWI and GRW say clearly what the kinematics is, but they don't say that it's $x(t)$. Copenhagen, on the other hand, does not say clearly what's kinematics.

 

[PeterDonis]

I was suggesting to completely remove "ontic" from the vocabulary and talk about "kinematics" instead.

How does that help? Why should I just care about "kinematics" and not about "dynamics"? Or why should I care about making a precise distinction between them?

 

[Demystifier]

$E$ is force on unit charge. So forces are ontic after all.

Unless you believe that $E$ exists even when it does not act on a charge, for example during a propagation in EM wave.

 

[Demystifier]

Continuing the ontology discussion from the many-worlds thread here as it's probably more approrpriate
"Finest possible graining" might have two interpretations. If, by a finest possible graining, we mean for example alternative field configurations $\phi(x)$, CH would fail to ascribe any ontological meaning to them, primitive or otherwise, since these histories (four-dimensional configurations) would fail to decohere for general circumstances. We would have to introduce a coarse-graining that satisfies a decoherence criterion. E.g. Instead of alternative field configurations, we would take alternative averages of field configurations over causally consistent spacetime regions. Once we have these as our finest possible grainings, CH can offer an ontic meaning to them, in the sense that we can interpret measurement outcomes as revealing pre-rexisting properties that these averages represent. The necessity of coarse-graining means we would struggle to say these properties are primitive. It would therefore be hard to interpret CH as offering multiple representations of a primitive ontology. The ontic contribution of CH only extends to the interpretation of measurements as revealing pre-existing properties, regardless of the status of those properties as primitive. Using the example from the other thread: CH won't tell you if your airplane is a primitive element of reality, it will just tell you if it will crash.

There is an adjascent interpretation "Extended Probability Ensemble Decoherent Histories" which does try to ascribe an ontic meaning to maximally fine-grained histories. This interpretation selects a preferred set of histories, and if we are talking about a field theory, they would indeed be field configurations $\phi(x)$.

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.

 

[Demystifier]

Or why should I care about making a precise distinction between them?

I don't know why should you care, but in the context of classical mechanics many physicists care. In elementary school (7th grade) that was one of the first things we were taught in physics class.

Or for Copenhagenians, it can be a way to explain the difference between classical and quantum mechanics: classical physics treats kinematics and dynamics separately, while QM doesn't. From that point of view, BM, MWI and GRW are attempts to restore their separation in QM too.

Isn't it at least a bit less vague than a talk about ontic?

 

[PeterDonis]

In elementary school (7th grade) that was one of the first things we were taught in physics class.

I guess it depends on the school system and the curriculum. I took physics in high school and again in several classes in college and nobody ever mentioned kinematics vs. dynamics. I don't feel like I missed anything.

 

[Demystifier]

I guess it depends on the school system and the curriculum. I took physics in high school and again in several classes in college and nobody ever mentioned kinematics vs. dynamics. I don't feel like I missed anything.

I'm not saying that physics cannot be taught without that distinction. I'm just saying that kinematics vs. dynamics is less vague and less philosophic than ontic vs. non-ontic. So if we want to discuss quantum foundations at all (and it seems that we do), it makes a step forward by removing ontic and non-ontic from the vocabulary and replacing them with kinematics and dynamics. In fact, I plan to do exactly that in the future discussions. We shall see how that will work.

 

[martinbn]

$E$ being ontic is less problematic than force being ontic, because $E$ exists in space and time. The force resulting from Newton's law of gravity on the other hand does not have an independent existence in space and time, but can only exist where the particle position already exists. Therefore the particle position is the primary ontology in that case, and force is only one of many possible secondary variables.

I don't see the difference. You place a test object and it experiences a force. Same in both cases.

This existence in space and time is precisely one of the reasons why ontology with respect to "physical existence" has a slightly different character from ontology with respect to "mathematical existence". The "intuitive notion" of something which exists physically normally implies that it exists at some time and at some point, or at least in some region of space and time. This is one reason why the wavefunction should better not be ontic.

I agree with this. This is why for me it is strange to shift the ontology from the particles to the mathematical object $x(t)$.

 

[martinbn]

I don't know why should you care, but in the context of classical mechanics many physicists care. In elementary school (7th grade) that was one of the first things we were taught in physics class.

Or for Copenhagenians, it can be a way to explain the difference between classical and quantum mechanics: classical physics treats kinematics and dynamics separately, while QM doesn't. From that point of view, BM, MWI and GRW are attempts to restore their separation in QM too.

Isn't it at least a bit less vague than a talk about ontic?

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.

 

[vanhees71]

Sorry,
Treated, but not ontic...

Ontic (from the Greek ὄν, genitive ὄντος: "of that which is") is physical, real, or factual existence.
Maybe both, particles as excitations of the fields.

.

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.

 

[vanhees71]

$E$ being ontic is less problematic than force being ontic, because $E$ exists in space and time. The force resulting from Newton's law of gravity on the other hand does not have an independent existence in space and time, but can only exist where the particle position already exists. Therefore the particle position is the primary ontology in that case, and force is only one of many possible secondary variables.

This existence in space and time is precisely one of the reasons why ontology with respect to "physical existence" has a slightly different character from ontology with respect to "mathematical existence". The "intuitive notion" of something which exists physically normally implies that it exists at some time and at some point, or at least in some region of space and time. This is one reason why the wavefunction should better not be ontic.

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 here we also have to distinguish between the physical and the physiological meaning. Physically what's observable is an electric signal which we describe to be due to the photoelectric effect, i.e., the interaction of the em. wave field with the charged matter particles making up our retina, which already starts to process the signal, which then is propgated to our brain where it's further processed and so on until we preceive the phenomenon "light".