Relational Quantum Mechanics

[Steve Esser]

I throw this out to see if any forum participants have come across this idea or have opinions on it:

A while back I was pleasantly surprised to find a reference to an interpretation of QM which I had not seen before. Due to physicist Carlo Rovelli (of loop quantum gravity fame), I found it to be very thought-provoking and philosophically appealing.

Called relational quantum mechanics, it interprets QM by rejecting the idea that quantum systems really exist in isolation absolutely, and says instead that they really only exist as they relate to another system. The interaction between systems is the “real” entity. By taking this approach, a consistent quantum description of an entire world is possible which seems to avoid the problems of other interpretations. The world is a network of interactions. The slogan for how this addresses the measurement problem might be “Everything measures everything else”. I refer you to the Stanford Philosophy Encyclopedia entry for a fuller description.

 

[Marek Domanski]

It seems that Rovelli doesn't distinguish between the microscopic world and the macropscopic world. Do I understand correctly?

In this case why do his examples aways start in the microscopic world and then end up in the macropscopic world? Eg Schrodinger' Cat and non-locality.
Why doesn't he give a straight example from the macropscopic world? For example, I open a door to see if my wife is in the room. Before I open the door is there a superposition between her being there and not being there?

In saying that facts are relative to specific objects or observers, he is just changing the meaning of the word 'fact' from its common use to done which suits him. We normally mean by a fact something that is true for all observers, whether they yet know it or not. What has just happened in Beijing is a fact for me, whether I know it or not. We might say . When we say that we have belatedly learned something from Beijing, we don't think that it became a fact only because we got the information from Beijing.

It is probably that he is explicating the word 'fact' to fit astronomical distances. Just like there is no universal 'now', so there are no universal facts. However, he he should acknowledge that he is using the word differently from the usual sense.

Finally what problems of interpretation has RQM solved?

It is a very interesting book, but annoyingly for me there are many loose ends.

 

[Marek Domanski]

It seems I may have been a somewhat pedantic in my discussion of facts.

 

[PeterDonis]

Moderator's note: Thread moved to the quantum interpretations forum.

 

[Fra]

I throw this out to see if any forum participants have come across this idea or have opinions on it:

Many years ago I started to read Rovellis QG book in order to evaluate the idea, and soon come across his RQM interpretation. Up to a certain point Rovellis reasoning is sound and appealing, but it has (from my perspetive) som flaws that I can not let pass.

There is an old thread on this

https://www.physicsforums.com/threa...able-in-classical-and-quantum-gravity.220841/

Starting from post #19 I wrote about my first impressions on his reasoning. I am seeking for a reconstruction in terms of an agent centered inference, that should explain why agents make use of non-commutative information. Rovelli seems to embrace the relational perspective (good) but at some point simply assumes that, the relations are given by QM; whithout demanding that there is a physical process that can infer it. That is fine if you seek an interpretation, but if you are seeking an reconstruction, I don't find Rovelli's view satisfactory.

/Fredrik

 

[Demystifier]

It seems that Rovelli doesn't distinguish between the microscopic world and the macropscopic world. Do I understand correctly?

I wouldn't say that he does not distinguish them, it's rather that he assumes that the same fundamental principles should be valid for both. I think it's a reasonable assumption, shared by most other interpretations of QM.

 

[Demystifier]

It is a very interesting book

What book?

 

[Marek Domanski]

Helgoland. Sorry I did not make this clear. A previous poster referred to a book and I assumed it was Helgoland.

 

[Marek Domanski]

I wouldn't say that he does not distinguish them, it's rather that he assumes that the same fundamental principles should be valid for both. I think it's a reasonable assumption, shared by most other interpretations of QM.

1. Yes he states that probability drives the macro-world also. I don't think this is orthodox. It is a commonly held position that in any experiment, such as the double slit experiment, the wave function is said to collapse when a detector is encountered. And RQM doesn't require a conscious observer.

It would be funny if the same fundamental principles applied to the macro-world. Firstly, it would seem that we can't actually quantify psi in the macro-world.- Also, that the macro-world is not deterministic would be very counter intuitive.

If I open the door of a room to see whether my wife is inside, would you say that there was a quantum superposition before I opened the door, and that there is another superposition when a second observer arrives.

2. Dealing with quantum entanglement, Rovelli seems to think that he has solved some problem with regard to it. I see no problem that an experimenter in Vienna has to check by phone with the other in Beijing. Can you clarify what problem has been solved by RQM?

I find that in Helgoland there are so many things that are not clear. Maybe my problem, but it is very frustrating.

 

[Demystifier]

Can you clarify what problem has been solved by RQM?

Not really, I am not a fan of RQM.

 

[Fra]

Finally what problems of interpretation has RQM solved?

Many interpretations don't solve any open problems at all I would say. They are just a more or less comfortable way to digesting something weird.

I personally don't see RQM from my perspecive as one of those interpretations that aim to solve any big problems (which by defintion then are not pure interpretations, but comes mixed with conjectures or speculations that you may or may not constructive).

As far as I see, Rovelli seems to accept QM as universally valid, and just tried to find an interpretation. Any such attempt is bound to never be quite satisfactory.

If any, RQM manages to "remove the observer", by treating the observer as effectively a choice, and the QM probability is thus a conditional one. But RQM also discards important keys in the inference process, which is my it does not please me. For example Rovellis holds high that there are no outside observers, yet the ontological status of symmetry (*) is swallowed with uncritically. I insist the symmetry should follow from a similarly physical inside inference. Rovellis doesn't raise this, but seems to except laws of physics (ie the tranasformations rules that makes observer equivalence manifest) from the inferrability requirements. This is what sticks out to be as inconsistent reasoning in RQM.

/Fredrik

 

[*now*]

1. Yes he states that probability drives the macro-world also. I don't think this is orthodox. It is a commonly held position that in any experiment, such as the double slit experiment, the wave function is said to collapse when a detector is encountered. And RQM doesn't require a conscious observer.

It would be funny if the same fundamental principles applied to the macro-world. Firstly, it would seem that we can't actually quantify psi in the macro-world.- Also, that the macro-world is not deterministic would be very counter intuitive.

If I open the door of a room to see whether my wife is inside, would you say that there was a quantum superposition before I opened the door, and that there is another superposition when a second observer arrives.

2. Dealing with quantum entanglement, Rovelli seems to think that he has solved some problem with regard to it. I see no problem that an experimenter in Vienna has to check by phone with the other in Beijing. Can you clarify what problem has been solved by RQM?

I find that in Helgoland there are so many things that are not clear. Maybe my problem, but it is very frustrating.

This recent paper could help with your questions

Di Biagio, A., Rovelli, C. Stable Facts, Relative Facts. Found Phys 51, 30 (2021). https://doi.org/10.1007/s10701-021-00429-w

Abstract

Facts happen at every interaction, but they are not absolute: they are relative to the systems involved in the interaction. Stable facts are those whose relativity can effectively be ignored. In this work, we describe how stable facts emerge in a world of relative facts and discuss their respective roles in connecting quantum theory and the world. The distinction between relative and stable facts resolves the difficulties pointed out by the no-go theorem of Frauchiger and Renner, and is consistent with the experimental violation of the Local Friendliness inequalities of Bong et al.. Basing the ontology of the theory on relative facts clarifies the role of decoherence in bringing about the classical world and solves the apparent incompatibility between the ‘linear evolution’ and ‘projection’ postulates.

----
For example, the final remark-
"As a final remark, observe that if the quantum state has no ontic interpretation, the only meaning of ‘being in a quantum superposition’ is that interference effects are to be expected. Saying “Friend is in a quantum superposition” does not mean anything more than saying that Wigner would be mistaken in using (3). It has no implications on how Friend would “feel” while being in a superposition. Friend sees a definite result of her measurement, a fact, and this does not prevent Wigner from having the chance to see an interference effect in his facts. Wigner’s friend does not stop being an observer simply because Wigner has a chance to detect interference effects in his facts. Schrödinger’s cat has no reason to feel ‘superposed’.

 

[Marek Domanski]

Not really, I am not a fan of RQM.

Good. Please let us know why you are not a fan of RQM.

 

[Marek Domanski]

I wouldn't say that he does not distinguish them, it's rather that he assumes that the same fundamental principles should be valid for both. I think it's a reasonable assumption, shared by most other interpretations of QM.

My question still stands. If he assumes that the same fundamental principles should be valid for both then he he must be able to identify examples of interference in the macro-word. He has actually said in Helgoland that the macro-word is also probabalistic. And this probability is not one based on ignorance.
I quote him: "The solidity of the classical vision of the world is nothing other than our own myopia. The certainties of classical physics are just probabilities."
This goes against all our experience. We would not have been able to send people to the moon if we were just relying on probability, unless of course we embrace the many worlds interpretation.
I am waiting for serious criticism of "Helgoland", not just shining reviews which say how stimulating it is.
Please let me know your thoughts.

1. Yes he states that probability drives the macro-world also. I don't think this is orthodox. It is a commonly held position that in any experiment, such as the double slit experiment, the wave function is said to collapse when a detector is encountered. And RQM doesn't require a conscious observer.

It would be funny if the same fundamental principles applied to the macro-world. Firstly, it would seem that we can't actually quantify psi in the macro-world.- Also, that the macro-world is not deterministic would be very counter intuitive.

If I open the door of a room to see whether my wife is inside, would you say that there was a quantum superposition before I opened the door, and that there is another superposition when a second observer arrives.

2. Dealing with quantum entanglement, Rovelli seems to think that he has solved some problem with regard to it. I see no problem that an experimenter in Vienna has to check by phone with the other in Beijing. Can you clarify what problem has been solved by RQM?

I find that in Helgoland there are so many things that are not clear. Maybe my problem, but it is very frustrating

 

[Fra]

This goes against all our experience. We would not have been able to send people to the moon if we were just relying on probability

A very peaked probability distribution (even one not depending on ignorance) should in the FAPP sense be sufficent to reproduce classical certainty? So THIS part in Rovellis reasoning is not my main issue.

/Fredrik

 

[Marek Domanski]

Ok Frederik (probably from Denmark - irrelevant of course) - a very peaked probability distribution might just do it. But this cannot be empirically be verified, or more importantly, be falsified. Also he should say that the probability distribution is peaked.
What please tell me what aspects of Rovelli's reasoning are your main issue.
He just does not anticipate objections, as a good philosopher should.

 

[Marek Domanski]

Sorry Frederik, you already have given your objections to Rovelli in terms of symmetry.
But there are many simpler objections such as his treatment of Shrodingers cat. Are we to say that the superposition continues in an infinite sequence. And how does this differ from an every day world where you just look into a room to see if your dog is inside? Our every day world does not begin in a quantum experiment.
Shrodinger's cat is a red herring. It had a special reason for Schrodinger. Most people would say that the geiger counter was the detector.
It is better to look at the double split experiment. Would you say that the position of the dot a single photon makes on the screen has no reality until someone has seen it.
There is absolutely, absolutely no reason why the quantum world has to continue into our every day world. It is just not necessary.
Also we cannot detect interference in our every day world.

 

[PeterDonis]

we cannot detect interference in our every day world

Yes, we can. For example, when we see an interference pattern in the double slit experiment.

 

[EPR]

Staying within the classical framework of how the world was thought to operate(with immutable objects that behave according to deterministic causality) and trying to adjust QT to fit in will produce all kinds of nonsensical theories and misunderstandings ala Schroedingers cat and Wigner's friend.

Enjoy your personal experience. This is all there is to how the world operates. Some of the fathers of QT leaned in that direction when they warned that the task of science is not to explain how the world works, but what we can say about this reality.
There is no going back to the Stone age conception of the world where solid objects disobey relativity and qm.

The world is both quantum and relative. And still quite foreign to mundane pedestrian perception.
The issues raised will not be resolved soon without some really major breakthrough in the foundations.

 

[Marek Domanski]

Yes, we can. For example, when we see an interference pattern in the double slit experiment.

Yes of course, but I was talking about the macro-world.
We do not for example see interference when I go into a room to see if my dog is there.
I have great respect for the double slit experiment, but only here do we see interference.
Thanks for you reply Peter.

 

[EPR]

Yes of course, but I was talking about the macro-world.
We do not for example see interference when I go into a room to see if my dog is there.
I have great respect for the double slit experiment, but only here do we see interference.
Thanks for you reply Peter.

This could be due to a cut-off scale where the small size 'particles' tend to interfere with themselves while the 'classical' apparatus does not( due to size and scale).

EDIT: actually this is wrong. All of the 'particles' of the apparatus must be in definite state the entire time the apparatus(or cat/dog) is perceived as 'classical'. Even when the cat moves, all of its particles are in a definite state the entire time. It's only when the electron travels unobserved in the double slit experiment(between emission and detection) that it seems to be in a superposition of states. Unobserved events are not definite/classical - it kind of implies that unobserved(unmeasured) cats are also not classical.

 

[*now*]

My question still stands. If he assumes that the same fundamental principles should be valid for both then he he must be able to identify examples of interference in the macro-word. He has actually said in Helgoland...

I haven’t read the book yet but the paper linked earlier discusses suppression of interference, e.g.,

“Various characterisations of a classical or semiclassical situation can be found in the literature: large quantum numbers, semiclassical wavepackets or coherent states, macroscopic systems, large or infinite number of degrees of freedom...All these features play a role in characterising classical systems in specific situations. But the key phenomenon that makes facts stable is decoherence [36, 39, 40]: the suppression of interference that happens when some information becomes inaccessible”.
Stable Facts, Relative Facts | SpringerLink

 

[EPR]

So theoretical states lose their coherence(their relatives phases no longer overlap) and this brings up 'particles' from the field at the detector screen!?

No wonder decoherence is not accepted as a measurement problem solver by any credible source. Losing the coherence phase of theoretical wavefunctions does not produce outcomes. It may shift slightly the interference pattern left or right in the double slit experiment but that's about it. The MWI does not depend on de-coherence and was invented decades before this theory was proposed. I do not believe it has any bearing on how theoretical quantum states become actual outcomes.

 

[PeterDonis]

I have great respect for the double slit experiment, but only here do we see interference.

Not just in the double slit experiment, no. We see interference whenever we have a system for which we can maintain quantum coherence long enough to run an experiment. There are many, many systems and experiments for which this is true, and experimentalists continue to expand the boundaries for such systems and experiments.

 

[EPR]

If I could dis-entangle myself from the environment, the famous Einstein-Bohr debate about the Moon would be pretty much settled right now.
We get entangled with everything in our way - be it photons bounced off the surface of the Moon or photons from the QLED TV screen in the living room or photons from an apparatus reading. After entanglement with an observer, quantum systems display classical behavior. This apparent classical behavior is sometimes known as decoherent classicality(Newtonian world). It happens almost instantly when information about a quantum system can be known or becomes available. This is highlighted in the extension of the double slit experiment with delayed choice and eraser.

 

[Marek Domanski]

This could be due to a cut-off scale where the small size 'particles' tend to interfere with themselves while the 'classical' apparatus does not( due to size and scale).

EDIT: actually this is wrong. All of the 'particles' of the apparatus must be in definite state the entire time the apparatus(or cat/dog) is perceived as 'classical'. Even when the cat moves, all of its particles are in a definite state the entire time. It's only when the electron travels unobserved in the double slit experiment(between emission and detection) that it seems to be in a superposition of states. Unobserved events are not definite/classical - it kind of implies that unobserved(unmeasured) cats are also not classical.

 

[Marek Domanski]

I don't know if you have read Covelli's book Helgoland. It is very confusing that he uses the example of Schrodinger's cat.
The simplest way of approaching SC is to hold that collapse occurs in the geiger counter (and Rovelli emphasises that a conscious observer is not required).
In this case it would be simplest to hold than the cat is not in a superposition at all, and thus neither is the person who is going to open the box. He is just ignorant.
I wonder if Rovelli would actually hold that if you are about to open the door of the bedroom to see if your wife is inside, in situation not originating in a laboratory quantum setup, that you are in a superposition. A yes or no here would clarify things a lot.
I agree with you about the double slit. It is the best example possible. I'm just trying to get at what Rovelli means.

 

[Marek Domanski]

If I could dis-entangle myself from the environment, the famous Einstein-Bohr debate about the Moon would be pretty much settled right now.
We get entangled with everything in our way - be it photons bounced off the surface of the Moon or photons from the QLED TV screen in the living room or photons from an apparatus reading. After entanglement with an observer, quantum systems display classical behavior. This apparent classical behavior is sometimes known as decoherent classicality(Newtonian world). It happens almost instantly when information about a quantum system can be known or becomes available. This is highlighted in the extension of the double slit experiment with delayed choice and eraser.

Yes, we can. For example, when we see an interference pattern in the double slit experiment.

Yes, of course, but apart from such situations. Is there interference and superposition when I am about to open the door of the bedroom to see if my wife is inside, or in any other situations that might be described as classical. I do not think so, but after reading Rovelli's Helgoland, I am not sure.

 

[Marek Domanski]

If I could dis-entangle myself from the environment, the famous Einstein-Bohr debate about the Moon would be pretty much settled right now.
We get entangled with everything in our way - be it photons bounced off the surface of the Moon or photons from the QLED TV screen in the living room or photons from an apparatus reading. After entanglement with an observer, quantum systems display classical behavior. This apparent classical behavior is sometimes known as decoherent classicality(Newtonian world). It happens almost instantly when information about a quantum system can be known or becomes available. This is highlighted in the extension of the double slit experiment with delayed choice and eraser.

I agree, but in regards to the temperature of a cake, Rovelli maintains that the there is entanglement between the cake and a thermometer stuck in it. This is a classical situation. He is very confusing.

 

[EPR]

Yes, of course, but apart from such situations. Is there interference and superposition when I am about to open the door of the bedroom to see if my wife is inside, or in any other situations that might be described as classical. I do not think so, but after reading Rovelli's Helgoland, I am not sure.

The interference is inferred. It cannot be measured as when it's measured, it disappears.

I can only speculate about your wife but I would be walking on thin ice.
We cannot infer either the interference of your wife and hence her potential superposition, as it would be to small to leave a trace. Maybe it could, if someone could devise a proper setup and its technical parameters allow.

As far as I can remember, the biggest object in superposition that has been indirectly "observed" is half millimeter in size

 

[EPR]

Big objects have vanishingly small interference traces due to scale and average probabilities. My guess is we have to go small, lower than 1mm to have a noticeable pattern. Classicality is a law of this reality. If it was possible or easy to avoid it, billions of people before us would have noticed it and the quantum nature of the Universe would have been known earlier.

 

[Marek Domanski]

Big objects have vanishingly small interference traces due to scale and average probabilities. My guess is we have to go small, lower than 1mm to have a noticeable pattern. Classicality is a law of this reality. If it was possible or easy to avoid it, billions of people before us would have noticed it and the quantum nature of the Universe would have been known earlier.

That is roughly what I thought, but Rovelli in his popular books is very confusing. I am waiting for a negative review.
You could of course have quantum effects have a real purely objective probabalistic effect on the world by putting the likes of Donald Trump in Schrodinger's box instead of a cat.

 

[AlexCaledin]

...quantum systems... really only exist as they relate to another system. The interaction between systems is the “real” entity.

- do we then come to the Process Philosophy as opposed to the Substance metaphysics?

https://plato.stanford.edu/entries/process-philosophy/

Indeed, then the fundamental entities are psychophysical events as interactions between the psychical and physical side of reality.

 

[PeterDonis]

do we then come to the Process Philosophy as opposed to the Substance metaphysics?

Philosophy is off topic in this forum. Please keep discussion focused on RQM considered as a QM interpretation.

 

[Sunil]

Please let us know why you are not a fan of RQM.

Such relativization is cheap and gives nothing new. Whenever you have some reasonable realistic interpretation, you can relativize it without having to add something new at all. All you have to do is to relativize all the absolute things. So all what is reached is that we have, after relativization, less valuable information than before.