Undergrad One does not “prove” the basic principles of Quantum Mechanics

[javisot]

Your words

Please don't create confusion. The paragraph you mentioned and tried to correct is by Rovelli, not me.

My words don't confirm anything; I don't understand what interpretation you're referring to.

 

[physika]

My words don't confirm anything; I don't understand what interpretation you're referring to.

recommend read:
https://plato.stanford.edu/entries/qm-relational/

..."There is nothing in RQM that contradicts the assumption that the world is “out there”
"In this weak sense RQM is consistent with realism. RQM questions the assumption that each variables of each subsystem of the world has a single value at each and every time"...


.....

 

[Lord Jestocost]

Well, since this has touched on Realism, I suggest reading Fields and their Quanta by Art Hobson.
https://www.amazon.com.au/Fields-Their-Quanta-Quantum-Foundations-ebook/dp/B0DLNLLG7Y

It gives a very compelling case for Realism.

Thanks
Bill

Quantum field theory is a useful computational model, but there is no need to identify quantum fields as an ‘ontological reality’. Claims concerning merely the existence or reality of something to which a theory may refer, without actually describing how that something exists, i.e., how that something can be represented, constitute to my opinion no form of scientific realism.

 

[martinbn]

I insist that in Rovelli's RQM vision, objects don't even exist, he says in the article that martinbn shared:

I don't see how you reached that conclusion! Here is the quote you gave.

"Dorato observes that the relativisation of values implies a relativisation of the very notion of object or entity, if (i) having some intrinsic, non-purely dispositional properties is essential to the identity of an object, and (ii) no entity can exist if it does not have an intrinsic identity (see Nāgārjuna 1995). The only reality in RQM is given by events, which are the result of interactions between distinct quantum systems, but even these events can be described in a different way by different physical systems. The interaction cannot be described in a more precise way by a constructive theory in Einstein’s sense (Einstein 1919) that can explain the coming into being of a definite outcome without just assuming it as a fundamental fact. Dorato concludes that there is no measurement problem in RQM because RQM is implicitly formulated as a theory of principle."

He says "The only reality in RQM is given by events, which are the result of interactions between distinct quantum systems", if the quantum systems don't exist, then what interacts?! To me it is clear that the quantum systems exist according to Rovelli.

 

[martinbn]

Quantum field theory is a useful computational model, but there is no need to identify quantum fields as an ‘ontological reality’.

I don't know if there is a need, but that is how it is in quantum field theory, isn't it?

 

[PeterDonis]

if the quantum systems don't exist, then what interacts?!

You missed this part: "even these events can be described in a different way by different physical systems".

This is the part I would want to see concrete examples of--a given interaction being describable in different ways by different sets of quantum systems. If this can be done, that is indeed an argument for not giving ontological status to the quantum systems themselves, but viewing them as model artifacts with no actual existence. But so far I don't see anything in the references given that shows that it can be done.

 

[PeterDonis]

that is how it is in quantum field theory, isn't it?

Just as with the wave function in ordinary non-relativistic QM, the ontological status one assigns to quantum fields in QFT is interpretation dependent.

 

[PeterDonis]

Moderator's note: Thread moved to the interpretations subforum.

 

[javisot]

I don't see how you reached that conclusion! Here is the quote you gave.

"In this way, RQM succeeds in making sense of a fully quantum world without requiring hidden variables, many worlds, physical collapse mechanisms, or a special role for mind, agents, or similar."

"For instance, a real fact is the position of a particle having a certain value x at a certain time t. Facts as this one (“the particle is at x at time t”) are called “events”, or “quantum events”."

"Relative’ does not mean subjective. Subjects, or agents play no special role in RQM. When we say that our speed is 11km/second with respect to the Sun, we are not attributing subjectivity to the Sun. When we say that the distance between a signpost and a road intersection is 100 meters, we are not thinking that a road’s intersection is an agent. In a naturalistic perspective, a person, an agent, a subject, are physical systems; the world they relate to is described by the value of the variables with respect to them. A person dwelling on the Earth sees the Cosmos rotating because the Earth is spinning; but the Cosmos rotates with respect to the frame defined by Earth irrespectively from the existence of persons on the Earth. To say that RQM requires subjects or agents is the same mistake as saying that our explanation of the daily rotation of sun moon and stars around the Earth requires to take agency or subjectivity into account: a nonsense. There is nothing subjective, idealistic, or mentalistic, in RQM."

"Quantum mechanics can be formulated without reference to the quantum state, as a theory of probabilities for sequences of events. The state ψ is a convenient tool, not a necessary one."

"Second, quantum mechanics describes the world in terms of values of variables at specific discrete times. This second aspect of discreteness is directly accounted for by the sparse ontology of RQM. The history of a quantum particle, for instance, is neither a continuous line in spacetime (as in classical mechanics), nor a continuous wave function on spacetime. Rather, with respect to any other system it is a discrete set of interactions, each localized in spacetime."

"Dorato observes that the relativisation of values implies a relativisation of the very notion of object or entity, if (i) having some intrinsic, non-purely dispositional properties is essential to the identity of an object, and (ii) no entity can exist if it does not have an intrinsic identity (see Nāgārjuna 1995). The only reality in RQM is given by events, which are the result of interactions between distinct quantum systems, but even these events can be described in a different way by different physical systems. The interaction cannot be described in a more precise way by a constructive theory in Einstein’s sense (Einstein 1919) that can explain the coming into being of a definite outcome without just assuming it as a fundamental fact. Dorato concludes that there is no measurement problem in RQM because RQM is implicitly formulated as a theory of principle."


It's true that there isn't a paragraph that literally says "in RQM there are no objects, only relationships", but...it seems like it

 

[bhobba]

but there is no need to identify quantum fields as an ‘ontological reality’.

That's why I used the word compelling. One can still maintain the fields of QFT as just a calculational aid. Indeed, the Effective Field Theory view of QFT can be used as evidence for such a view. But then we are faced with the reality of particles themselves. Sure, all we have and can predict are measurements, observations, interaction outcomes, detections, whatever you want to call them; there is nothing that can be said for sure beyond that. The day-to-day macro world can 'emerge' from such a view.

My issue is this. Take the first QFT, the quantisation of the EM field by Dirac (and for those that have not seen such before, see the following:
https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3211&context=physics_facpub)

EM fields are usually considered real (they have energy, for example). If the Quantum EM field is not real, exactly at what point does it become real? That, with work, could probably be answered, but I don't understand what would be gained. In the final analysis, it is perhaps a matter of taste.

Thanks
Bill

 

[martinbn]

You missed this part: "even these events can be described in a different way by different physical systems".

This is the part I would want to see concrete examples of--a given interaction being describable in different ways by different sets of quantum systems. If this can be done, that is indeed an argument for not giving ontological status to the quantum systems themselves, but viewing them as model artifacts with no actual existence. But so far I don't see anything in the references given that shows that it can be done.

Isn't the relativity of the state such an example? A half spin particle sent to the measuring device will interact with it, and then the state of the particle relative to the device is either spin up or spin down. But there isn't an absolute state of the particle. For someone who has not interacted with the particle and device system yet, the particle is in a mixed state. But all the systems here, particle, device and the someine, exist. The state of a system is not absolute, it is relative.

 

[martinbn]

Just as with the wave function in ordinary non-relativistic QM, the ontological status one assigns to quantum fields in QFT is interpretation dependent.

By quantum field i didn't mean the operators, i meant the thing that is out there. I thought that there are no interpretational differences for this. Just like it is in classical electrodynamics. The elecrromagnetic filed exists, it can propagate and affect things. And here I don't mean the mathatical fields E and D (or any other choice).

 

[martinbn]

It's true that there isn't a paragraph that literally says "in RQM there are no objects, only relationships", but...it seems like it

It doesn't seem to me like that at all. But it may be that I don't understand it, and I am projecting my own philisophical prejudices. May be some one should ask Rovelli, or we just leave it at this point without an agreement.

 

[PeterDonis]

By quantum field i didn't mean the operators, i meant the thing that is out there.

What in the math of QFT corresponds to "the thing that is out there"?

 

[martinbn]

That's why I used the word compelling. One can still maintain the fields of QFT as just a calculational aid. Indeed, the Effective Field Theory view of QFT can be used as evidence for such a view. But then we are faced with the reality of particles themselves. Sure, all we have and can predict are measurements, observations, interaction outcomes, detections, whatever you want to call them; there is nothing that can be said for sure beyond that. The day-to-day macro world can 'emerge' from such a view.

My issue is this. Take the first QFT, the quantisation of the EM field by Dirac (and for those that have not seen such before, see the following:
https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3211&context=physics_facpub)

EM fields are usually considered real (they have energy, for example). If the Quantum EM field is not real, exactly at what point does it become real? That, with work, could probably be answered, but I don't understand what would be gained. In the final analysis, it is perhaps a matter of taste.

Thanks
Bill

My view is a bit stronger. I think that the fields are real and the oposite view is inconsistent.

 

[PeterDonis]

Isn't the relativity of the state such an example?

No. You have a system consisting of a particle and a measuring device. That's true regardless of what outcome you measure.

The sentence I quoted implies that there are cases where there are multiple different ways of describing an interaction, in terms of different quantum systems interacting.

 

[PeterDonis]

the oposite view is inconsistent

How is the opposite view inconsistent? It makes all of the same experimental predictions.

 

[martinbn]

What in the math of QFT corresponds to "the thing that is out there"?

Well, the operators (or operator valued distributions, or whatever the strict maths obects are).

 

[martinbn]

No. You have a system consisting of a particle and a measuring device. That's true regardless of what outcome you measure.

The sentence I quoted implies that there are cases where there are multiple different ways of describing an interaction, in terms of different quantum systems interacting.

I see, i cannot give you and example like that. But vaguely remember Rovelli discibing such.

 

[martinbn]

How is the opposite view inconsistent? It makes all of the same experimental predictions.

That is just my opinion, nothing more. I also thing the existence of god(s) is inconsistent.

 

[PeterDonis]

Well, the operators (or operator valued distributions, or whatever the strict maths obects are).

But you said that by "the quantum field", you didn't mean the operators, you meant "the thing that is out there". If "the thing that is out there" is the operators, then I can't make sense of your previous statement.

 

[PeterDonis]

That is just my opinion, nothing more. I also thing the existence of god(s) is inconsistent.

Then please keep these opinions out of this discussion. They're off topic.

 

[martinbn]

But you said that by "the quantum field", you didn't mean the operators, you meant "the thing that is out there". If "the thing that is out there" is the operators, then I can't make sense of your previous statement.

No, you asked me what in the math corresponds to what is out there. The fields are out there, and the operators correspond to them in the theory.

 

[PeterDonis]

No, you asked me what in the math corresponds to what is out there. The fields are out there, and the operators correspond to them in the theory.

Ah, ok. Then my question would be: which operators? The quantum field operators aren't the ones we actually measure; they aren't observables. And whether those field operators do indeed represent "what is out there" is, as I said, interpretation dependent.