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

[timmdeeg]

How is it in conflict with GR?

My reasoning is that a non-existing particle can't feel gravity e.g. while its path is deflected by a mass.

 

[martinbn]

My reasoning is that a non-existing particle can't feel gravity e.g. while its path is deflected by a mass.

What has that to do with RQM?

 

[PeroK]

My reasoning is that a non-existing particle can't feel gravity e.g. while its path is deflected by a mass.

Note that the Rovelli paper above does not consider the question of the existence of an electron, as we have been discussing it here. As far as I can tell, it is fundamentally an information-theoretic approach that attempts to avoid the problems of other interpretations. And, in particular, to explain things like the Wigner's friend paradox.

I suspect that in his popular science presentations of the interpretation, Rovelli has resorted to more provocative statements about the non-existence of a particle between measurements. To some extent, therefore, we have been dragged into a debate not about RQM but about the popularized version of it.

 

[timmdeeg]

What has that to do with RQM?

Mentioning GR I refer to "doesn't exist" in the quote in #59 obviously wrongly thinking that this relates to RQM.

 

[Sambuco]

Why not include General Relativity in these considerations? The wave-function doesn't feel gravity but a quantum object does as long as it exist. Isn't RQM in conflict with GR?

In fact, Rovelli developed the relational interpretation inspired by his work in loop quantum gravity. He discusses this in section 4(c) of this paper.

Lucas.

 

[Sambuco]

A very clear explanation of what constitues the ontology of RQM, taken from this paper:

"The standard objection to the epistemic interpretation of the wave function is that instrumentalism about it (i.e. treating it as a bookkeeping device) is simply giving up on physics. But if quantum events are all there is, there is nothing in physics to give up on. As shown in [7], restricting the ontology to the instantaneous quantum events is possible, if we take these to be relational. Thus, the alternative to wave function realism is not to give up on physics, it is just to make the ontology more sparse. Which, at the end, is precisely Heisenberg’s original intuition that started quantum mechanics. An example of a fully developed interpretation of quantum theory based on this ontology is relational quantum mechanics (RQM) [7].
What does produce the events we observe, in RQM? The answer is “nothing”: they are the primitive ontology of the theory. Asking what produces them is like asking what produces the particles or the fields of the Standard Model. In the theory, these are not tot to be explained: they are the ingredients to explain the rest. On this point, see [11]."

The consultation is needed if you want to claim that Rovelli says that entities don't exist between measurments. I don't see it in either of these two papers.

I don't see the point in asking Rovelli if when he said that "instantaneous quantum events" are "the primitive ontology of the theory," he really meant that. Of course, feel free to write to him if you wish.

In any case, as I mentioned in post #57, Rovelli recently published a paper where he discusses the possibility of analyzing events continuously, avoiding these discontinuities, i.e. this issue is still being debated, despite all the quotes I have given before.

Lucas.

 

[jedishrfu]

I guess I'm late to the party. I struggled with this as an undergrad until I read somewhere that there is no connection between math and physics. We intrinsically use our math, define some axioms, and apply them to a problem. When difficulties arise, we adjust our math to cover them. When the theory doesn't match reality, we adapt our math in careful ways soo as not to break other predictions.

NOVA did a great episode on this called: The Great Math Mystery



Watching this episode never gets boring.

 

[timmdeeg]

That means that what we call a particle may not exist beyond measurements/observations/interactions. What is "real" are the detection events. Of course, it's a matter of interpretation, but in my opinion, thinking in terms of "permanent entities," as Schrödinger called them, is a step in the wrong direction.

I'm still not clear with this. Wouldn't the assumption that "a particle may not exist beyond measurements/observations/interactions" be disproved in case the particle feels gravity beyond measurements ... what in principle should be measurable in case it isn't obviously true anyway?

 

[PeroK]

I'm still not clear with this. Wouldn't the assumption that "a particle may not exist beyond measurements/observations/interactions" be disproved in case the particle feels gravity beyond measurements ... what in principle should be measurable in case it isn't obviously true anyway?

Imagine that we were living in a simulation. Everything would look the same, but there would be no force of gravity, as such. A particle would start at point A and be detected at point B, consistent with the laws of gravity. Between the two measurements, there would be nothing physical, as such.

Another example is a game of chess played on a computer. On a real board, the pieces have to be physically moved. But, on a computer, there is only the position before a move and the position after a move. With literally nothing in between. As long as the rules of chess are codified in terms of allowable moves, the game is simulated without continuous physical movement.

RQM, as it is being presented here, has a similar structure. The only things we have are the measurement results. Nothing is to be said about how those measurement results are produced.

In some interpretations of QM, a real, physical particle would interact continuously with a real, physical magnetic field (say) and that particle would be described at all times by an evolving wave-function. Whereas, in RQM (as presented here), we are not to assume that a real particle and real magnetic field interact. The interaction is codified in the QM calculations and is purely a calculation that does not represent a real physical process.

The debate is whether Rovelli himself would agree or disagree with that analysis!

 

[martinbn]

Here is a quote from Rovelli. Taken from here https://plato.stanford.edu/entries/qm-relational/

There is nothing in RQM that contradicts the assumption that the world is “out there”, irrespectively of our mental states, or perceptions. In this weak sense RQM is consistent with realism. But RQM questions the assumption that each variables of each subsystem of the world has a single value at each and every time. In this stronger sense, realism is questioned by RQM.

To me this is clear. The existence of the world and its subsystems is not questioned. The existence of values of the variables of the subsystems at each and every time is.

 

[timmdeeg]

Imagine that we were living in a simulation. Everything would look the same, but there would be no force of gravity, as such. A particle would start at point A and be detected at point B, consistent with the laws of gravity. Between the two measurements, there would be nothing physical, as such.

Another example is a game of chess played on a computer. On a real board, the pieces have to be physically moved. But, on a computer, there is only the position before a move and the position after a move. With literally nothing in between. As long as the rules of chess are codified in terms of allowable moves, the game is simulated without continuous physical movement.

Thanks for clarifying, this I've been missing even though I'm watching chess games online sometimes.

 

[Sambuco]

I'm still not clear with this. Wouldn't the assumption that "a particle may not exist beyond measurements/observations/interactions" be disproved in case the particle feels gravity beyond measurements ... what in principle should be measurable in case it isn't obviously true anyway?

In RQM, what matters is the transition probability between two events involving the particle. If there is a gravitational field, it is included in the Hamiltonian.

Lucas.

 

[Fra]

Let's take the Stern-Gerlach experiment. There is a source of silver atoms. Those atoms pass through an inhomogeneous magnetic field and impact a detector screen in one of two (in practice fuzzy) locations.

At what times in that experiment do the silver atoms exist? The evolution of a silver atom's wave function depends on the magnetic field (the field strength and the duration for which the atom is subject to the field). That doesn't appear to be a discrete or sparse interaction. The obvious formulation is that the silver atom itself exists throughout.

If you say the silver atoms only exist when they hit the detector screen, then that (IMO) is simply redefining the word "exists" to mean "is subject to a measurement". There is an evolving wave-function (an evolving expectation in your terms). To say that the evolving expectation applies to a "non-existent" particle seems like playing with words to me. In QM "particle" generally refers to the system, whatever its state. This also avoids the popular concept of wave-particle duality.

My main point was just a conceptual comment to "I don't see what it means for something that doesn't exist to interact" suggesting that I dont see that prejudices about existence of something with particular structure is required to interact. An agent/observer could conceptaully simply interact perhaps randomly with its own environment. From such an interaction history perhaps the illusion of a silver atom fits perfectly. And this picture will evolve, wether "true" in some metaphysically unverifiable sense or not. The notion of wether the illusion corresponds to some thing real persisten, does not seem to matter, it cancels out doesn't it?

(This is just a conceptual perspective, in a real experiment, under human control, obviously the source of the silver atom exists in the macroscopi sense etc, this is not what i question. But then in that picture we are mixing perspectives and separate measurement device from the whole observing context. )

/Fredrik

 

[Fra]

???
How can the observer's brain solve the Schrödinger equation in real time?

It wasn't what i had in mind.

There are no brains. I entertain a more holographic picture where the microstate of the agent/observer (not brains or human), might self-evolve, perhaps loosely like Baranders stochastic process from the perspective of a local system.. this stochastic process might then conceptaully be the analog of a computation in real time that holographically mirrors the environment. And in some limiting cases (big macr observer) considering a small subsystem, maybe that random process would be as per barandes correspondence is corresponding to schrödinger dynamics.

My only point was that the questions asked, is interpretation dependent, and i put forwards one defense where the existence of the atoms between measurements, might not be important. Ie. it does not necessarily mean that evolution isnt possible.

/Fredrik

 

[Sambuco]

Here is a quote from Rovelli. Taken from here https://plato.stanford.edu/entries/qm-relational/


To me this is clear. The existence of the world and its subsystems is not questioned. The existence of values of the variables of the subsystems at each and every time is.

Thanks for the reference @martinbn!

I've been reading a bit about all this and I'd like to add something that I think is interesting... and confusing. In the paper I refer to in post #66, Rovelli states that the ontology of RQM consists of the instantaneous quantum events. Furthermore, he mentions Dorato's paper, which discusses the ontology of the theory (Dorato even thanks Rovelli for his comments on draft versions). It says "it should be stressed that the “beables” of RQM, its fundamental or primitive ontological posits, are those quantum events that are the manifestation of the propensity of isolated systems to reveal certain values, relative to other well-identified systems." In one sense, ontology is said to be formed only by events, which might suggest that systems emerge from these. That's the interpretation I was considering. However, he also says "Rovelli need not deny with the instrumentalists the existence of isolated quantum system: qua carriers of dispositions, such systems can be regarded as real as the table on which I am typing. “Going dispositionalist” as the second slogan recommends ensures both the reality of the isolated systems and the lack of definiteness of state-dependent properties. In a word, and summarizing the second slogan, I will regard isolated quantum systems as endowed with an intrinsic propensity (a probabilistic disposition) to reveal certain definite values of physical magnitudes by interacting with any kind of physical system." That aligns with your interpretation, @martinbn.

Not so fast! I can add some confusion to this matter. In the review paper you shared, Rovelli says "Laura Candiotto (2017) argues that the best philosophical framework for RQM is Ontic Structural Realism (OSR) (Ladyman& Ross 2007; French & Ladyman 2011). Ontic structural realism is meant to be a defensible form of scientific realism (Ladyman 2019); it argues for the priority of relations over substances, as self-subsistent individual objects (Morganti 2011). For Candiotto, RQM is a realistic theory that assumes the notion of relation (the physical interaction between systems and instruments) as primitive; objects emerge as relational “nodes” (French 2006), or intersections of processes." Although this interpretation is very close to the one I mentioned earlier, Rovelli clarifies that it is Candiotto's opinion. What I find a little confusing is that, immediately afterwards, Rovelli adds "The relation between RQM and ontic structural realism has been emphasized also by Mauro Dorato (2016)." But Dorato seemed to be saying that isolated systems do, in some way, exist!

In short, I'm not sure what Rovelli thinks. There's some "interfence" between both philosophical "branches". Perhaps Rovelli's opinion doesn't exist until we interact with him!

It's worth adding that, personally, I believe both philosophical positions are consistent with RQM. After all, it's not called the "non-existence-between-interactions interpretation," but rather the "relational interpretation". That's the core of the theory!

Lucas.

 

[physika]

The existence of values of the variables of the subsystems at each and every time is

Right
counterfactual definiteness (CFD) of values.


........

 

[javisot]

Thanks for the reference @martinbn!

I've been reading a bit about all this and I'd like to add something that I think is interesting... and confusing. In the paper I refer to in post #66, Rovelli states that the ontology of RQM consists of the instantaneous quantum events. Furthermore, he mentions Dorato's paper, which discusses the ontology of the theory (Dorato even thanks Rovelli for his comments on draft versions). It says "it should be stressed that the “beables” of RQM, its fundamental or primitive ontological posits, are those quantum events that are the manifestation of the propensity of isolated systems to reveal certain values, relative to other well-identified systems." In one sense, ontology is said to be formed only by events, which might suggest that systems emerge from these. That's the interpretation I was considering. However, he also says "Rovelli need not deny with the instrumentalists the existence of isolated quantum system: qua carriers of dispositions, such systems can be regarded as real as the table on which I am typing. “Going dispositionalist” as the second slogan recommends ensures both the reality of the isolated systems and the lack of definiteness of state-dependent properties. In a word, and summarizing the second slogan, I will regard isolated quantum systems as endowed with an intrinsic propensity (a probabilistic disposition) to reveal certain definite values of physical magnitudes by interacting with any kind of physical system." That aligns with your interpretation, @martinbn.

Not so fast! I can add some confusion to this matter. In the review paper you shared, Rovelli says "Laura Candiotto (2017) argues that the best philosophical framework for RQM is Ontic Structural Realism (OSR) (Ladyman& Ross 2007; French & Ladyman 2011). Ontic structural realism is meant to be a defensible form of scientific realism (Ladyman 2019); it argues for the priority of relations over substances, as self-subsistent individual objects (Morganti 2011). For Candiotto, RQM is a realistic theory that assumes the notion of relation (the physical interaction between systems and instruments) as primitive; objects emerge as relational “nodes” (French 2006), or intersections of processes." Although this interpretation is very close to the one I mentioned earlier, Rovelli clarifies that it is Candiotto's opinion. What I find a little confusing is that, immediately afterwards, Rovelli adds "The relation between RQM and ontic structural realism has been emphasized also by Mauro Dorato (2016)." But Dorato seemed to be saying that isolated systems do, in some way, exist!

In short, I'm not sure what Rovelli thinks. There's some "interfence" between both philosophical "branches". Perhaps Rovelli's opinion doesn't exist until we interact with him!

It's worth adding that, personally, I believe both philosophical positions are consistent with RQM. After all, it's not called the "non-existence-between-interactions interpretation," but rather the "relational interpretation". That's the core of the theory!

Lucas.

This seems like a reasonable stance, since what happens between measurements is conflict and a source of interpretations; let's stick with what's important, what we should all agree on: quantum events. (Do we all really agree on this?)

But I don't understand the difference between Candiotto and Rovelli. Both assume, with equal importance, that the fundamental element is quantum events, not what happens between them. On that point, Candiotto asserts that these relationships demonstrate the existence of an object when measuring, while Rovelli, on the other hand, only analyzes the relationships without considering the existence of any object. Is that essentially what they're proposing?