Or one might argue that, for instance, you cannot have a well-defined concept of information without relating it to some form of consciousness (not necessarily human, in fact). — boundless

I am definitely very ignorant about Information Theory, but I believe that the status of 'Shannon information' is somewhat controversial. The point is that there is a disagreement e.g. whether it is objective or subjective etc.

On this issue, maybe some might find interesting this paper by Basil Hiley (who collaborated with Bohm for many time): https://pdfs.semanticscholar.org/bb05/2740074f3e6b19f685315c9ddb994b563e29.pdf.

Obective collapse theories (such as GRW and Penrose's) are physically different theories to standard QM. I don't know what specific explanations they would give for this particular experiment. But they make predictions for Wigner's friend-style experiments that make them experimentally differentiable from standard QM. — Andrew M

OK, my comment assumed it was an interpretation. But if the the different theory is experimentally differentiable from standard QM, then by all means let's devise the experiment.

As Brukner says in that link (my italics):
In my eyes, outcomes 1 and 2 would indicate fundamentally new physics. I will not consider these cases further and regard quantum theory to be a universal physical theory. This leaves us with situation 3 as the only possible outcome of Deutsch's thought experiment. The outcome is compatible with the Everett interpretation: each copy of the observer observes a definite but different outcome in different branches of the (multi)universe. The outcome is compatible with the Copenhagen interpretation too, but it is rarely discussed what the implications of this claim are for our understanding of physical reality within the interpretation. The rest of the current manuscript is devoted to this problem.
— On the quantum measurement problem - Caslav Brukner

My comment on that is about how Copenhagen deals with those implications, but since I understand that 'interpretation' to be an epistemological one, it doesn't really have implications for physical reality, only about what one observer might know vs another.

I'd be curious to know your thoughts about the RQM questions from my earlier exchange with boundless here.

From that exchange then:

Thanks boundless - they're excellent videos and well worth watching for anyone with an interest in the philosophical aspects of QM. Fun quote from Rovelli at 36 mins: "When I told Max (Tegmark) that he was a relationist, he told me that he is going to convince me that I'm, without knowing, a Many World believer." — Andrew M

They're almost the same thing, with different definitions of 'is real'. RQM says this world is real to me and a different world is real to anything else (the cat say), so they're both talking about different worlds. MWI says they're all equally real, and RQM says none are real, only that there are relations between worlds and observers. Neither requires an observer to by anything more sentient than a speck of dust, and I find any interpretation that requires otherwise to border on religion. Even Copenhagen, an epistemological interpretation, can be applied to the dust speck. It 'knows' about the wind because it reacts to it, and thus has a relationship with it. It is real in a way that something unmeasured isn't.

Still, there are very 'real' differences between MWI and RQM, and I don't see how either Rovelli and Tegmark are going to convince the other that they hold the opposite view. I have yet to view the video since I tend not to get my information from such sources.

Anyway, Rovelli has a slide at 40:15 that says:

The price to pay for RQM:
We need to get rid of the notion of:
- absolute (observer-independent) state of a system
- absolute (observer-independent) value of a physical quantity
- absolute (observer-independent) fact

I don't consider it a price to discard these things. Quite the opposite. All the threads on forums such as this one discussing some form of "why is there something, not nothing" take for a premise that there is something, and then run into all sorts of valid contradictions that follow from it. So it appears that the notion, however intuitive, of there being something is the thing with the price to pay. My answer to the above question is that perhaps there isn't anything, and thus there is no need to have to explain its being.

But as I mentioned before I find (among other things) this 'oddness' as an indication that some kind of 'paradigm change' is required. Also, it seems that, in general, there is a trend to more and more 'counter-intuitiveness' in physics... — boundless

Boundless echoes my mistrust of such intuitions. My username carries an implication of not taking any of them as a premise, at least not without explicitly calling them out. I'm always on the search for assumptions I don't even know I'm making and are thus unseen biases.

The claim of RQM is that if you take this step, everything becomes simpler (cfr: special relativity, and the need of getting rid of absolute simultaneity.)
— RQM - Rovelli

A lot of people had no trouble getting rid of absolute simultaneity when relativity came into acceptance a century ago. Some still cling to it religiously.

My questions are:
1. Is this just a semantic difference with Many Worlds? (That is, there are nonetheless many physical branches, but there are only deemed to be facts relative to an observer's branch.)
2. If not, then what is the substantial physical difference and what explains physical interference effects? (Many Worlds would explain it as physical interference between branches.)

Well it seems a real difference. There 'are' no branches at all in RQM, and they are 'are' in MWI. That's the huge difference such that I doubt an adherent to either interpretation can be convinced that they also hold to the other. Even the relations don't exist.
I always reach for integers and the simplest cases for many of my examples. I claim that 7 is indeed 2 less than 9, but I don't claim that that particular relation between 7 and 9 exists as a real fact. Is it still counterfactually definite if I word the claim that way?

What is interference? It seems to be 'maybe' as an answer to a question not yet asked, a measurement not yet taken. So X = square root of 2 is 1.414 but also -1.414 and both those values can work through my equation until a choice must be make before the mathematics can continue. That's a measurement, and now there are two equations that proceed in different directions using a now real value for X instead of one in superposition.
That's a cheesy description of superposition, but I feel it fails as an analogy of interference since the two values never seem to interact with each other. I like the question and it deserves a better answer than that.
It seems too simple since they are discreet values, which a wave function really does describe a wave that yields an interference pattern when the wave for path-A is added to wave for path-B, which yields an interference pattern in 2D but only a flat scalar in 1D. So my X probably needs to be more complex than a simple scalar with two discreet values that satisfy a polynomial.

@Andrew M@boundless@noAxioms, note of appreciation for such a good sustained discussion. :clap:

thanks for the clarification of what constitutes ‘an observer’, for the purpose of this discussion. Helpful.

I can understand the unease with Bitbol's approach. But note that consciousness in his interpretation does not 'do' anything, in fact. It does not affect physical reality. It simply define the 'perspective' of the 'observer'. In a way analogous to Kant, Bitbol in fact IMO says that the 'quantum world' is indeterminate. But it is not a denial of it and neither he claims that it is 'modified' by consciousness. — boundless

Bitbol is interesting to me because I’m more interested in philosophy than physics.

All the threads on forums such as this one discussing some form of "why is there something, not nothing" take for a premise that there is something, and then run into all sorts of valid contradictions that follow from it. So it appears that the notion, however intuitive, of there being something is the thing with the price to pay. My answer to the above question is that perhaps there isn't anything, and thus there is no need to have to explain its being. — noAxioms

The price to pay for that is subjectivism/relativism/nihilism.

My view is that naturalism as a stance assumes the reality of the world (or rather, the sensory domain). There is nothing the matter with so doing, in fact, it's an essential methodological step. The problems start when the fact that it's a methodological step is forgotten, and it is mistaken for a metaphysical principle, or a statement about the real nature of things. In other words, methodological naturalism is interpreted as a metaphysical principle, which it is not. That is the whole issue, in a nutshell. (One way to avoid that is positivism, which says that only statements made on the basis of methodological naturalism are meaningful - but as has become evident, this too results in self-contradiction.) But the net result is, that the primacy of metaphysics has once again asserted itself through these conundrums posed by physics.

easy to demonstrate with a football

the QB throws the foot ball to his reciever who turns around at the last second to catch it .

the QB throws the ball and it spins clockwise direction as he sees it get further and further away

the receiver sees it coming but its spinning counter clockwise.NOT clockwise

the ball never stopped or changed directions between the two players

BOTH see opposite directions at the same time and both are correct.
both see the ball but the QB sees it get smaller as it gets further away and the receiver sees it get bigger as it gets closer

bigger and smaller
closer and further

If the QB hands the ball to his receiver , at the same time, then both are doing opposite actions at the same time in the same motion

one hands it over and the other takes it over at the same time

this can be construed as opposite or complimentary AT THE SAME TIME

black comes from white
white makes black
white reflects and black absorbs at the same time and they also oppose at the same time they complement by the way of contrast
white is an absolute and so is black
you cant get whiter than white or blacker than black

https://cdn-images-1.medium.com/max/1600/1*V377-3x7cHjr9HCebFGHJw.png

the wave and matter are at two poles of same item wave starts at blue and ends solid at black . It starts as emphty space and positive potential at WHITE with no density

the number 1 is both a positive number and a neg at the same time
1x1=1
1/1=1

multiplication is a positive and its opposite negative is division at the same time

white is a positive and black its negative

Forget about looking into a mirror, that might get real complicated.

use water , mirrors violate occams razor. its simple .

the reflection of the sun setting across the ocean always goes from the sun, to the water and towards your POV

If the 2nd person stands 25 feet away on the same beach at the same time , BOTH will observe the lights reflection on the water at he same time and it only leads to the person who is observing it . It doesnt go to both place and it does go to both places AT THE SAME TIME but the lights reflection will not be at both places at the same time .in the same relative locations.

opposites are both subjective and objective based only on ones SUBJECTIVE POV

if two people shine the sun light into each others eyes with a mirror at 25 feet apart , both will be in conflict with each other objective reality .You can use a garden hose and spray each other too . same difference

The price to pay for that is subjectivism/relativism/nihilism.

My view is that naturalism as a stance assumes the reality of the world (or rather, the sensory domain). There is nothing the matter with so doing, in fact, it's an essential methodological step. The problems start when the fact that it's a methodological step is forgotten, and it is mistaken for a metaphysical principle, or a statement about the real nature of things. In other words, methodological naturalism is interpreted as a metaphysical principle, which it is not. That is the whole issue, in a nutshell. (One way to avoid that is positivism, which says that only statements made on the basis of methodological naturalism are meaningful - but as has become evident, this too results in self-contradiction.) But the net result is, that the primacy of metaphysics has once again asserted itself through these conundrums posed by physics. — Wayfarer

Why should the acknowledgement of absolute nothing (more aptly no-thing) entail "subjectivism/relativism/nihilism"?

Naturalism is not merely a 'methodological step"; it is the step from the dead to the living; it is a phenomenological step. There is no phenomenological nothing just as there is no absolute something!

'So what?' I say; the absolute is nothing to us except an unthinkable thought rife with every paradox that both afflicts and invigorates the mind. Affliction or invigoration? Fallacy of misplaced concreteness or the principled placement of phenomenal ashlar?

Physics, being a phenomenology, knows no metaphysics beyond its own bounds. not all walls are prisons; there is no boundless freedom.

There are no metaphysical principles; can you name one? If metaphysics is not phenomenology informed by science (itself a phenomenology) then what can it be but thought tying its own Gordian Knot?

Legend has it that Alexander circumvented the common afflictions of delusory puzzlement and cut the seminal Gordian Knot with a single blow of his sword.

There is a time to remember and a time to forget; but beyond that it is always time to remember to forget false hope.

You're welcome.

Anyway, I am not @noAxioms, but I believe that his point was not 'nihilistic'.

Basically, according to RQM you can only define a state of a system S in relation to something else. In other words, when you speak of the state of S you always need to specify the 'perspective' according to which you are making such a description. You can't avoid that.

So, RQM seems to imply that while there are 'individual' systems like S, their states are meaningfully defined only in relation to something else.

In other words, RQM threatens the view that physical objects have some intrinsic properties. If true, the very concept of 'object' becomes problematic for it seems difficult to speak of objects that do not have any intrinsic properties. But if S does not have any intrinsic properties, what does S, S?

I do not believe that RQM per se goes as far as denying that we can speak of individual objects, i.e. a 'no-thing' view, so to speak. After all, perspectives here are defined in relation to these objects. But it certainly comes close to this idea: ultimately there are no 'objects' (which should not be taken as saying that 'there is no reality'). Rather objects are useful abstractions or approximations :smile:

Thank you :blush:

In CI, measurements are explained via the 'collapse' of the wave-function. The problem is, however, that CI is simply ambiguous on it. In fact, I would say that there is no 'Copenaghen Interpretation' at all. It is rather a 'class' of very different views that are, so to speak, 'grouped' together. — boundless

With this I agree. I often characterize it the way Bohr did: as a description of what can be known, and not at all a description of what is. It is rather a jumping board by which a description of what is might be bounded. Others take their interpretation of what is and label it Copenhagen because it fits within these bounds.

But where is the ambiguity? The problem is that the formalism of the theory alone does not identify what is the 'observer'. Yet, in order to explain the wave-function collapse you need to posit an 'observer'. If not, we cannot explain why our 'everyday world' looks classical, so to speak.

I thought the difference between the various interpretations often focuses on the treatment of the Heisenburg Cut. The Wigner's friend scenario basically puts one observer on either side of that cut, and drives out many of the differences between the interpretations.

Anyway, let's see the proposed solutions to this intrinsic ambiguity of CI.

Firstly, one might try to say that, indeed, there are physical objects that count as 'observers'. For instance, objects that are able to store and process 'information', like e.g. computers, registering devices, brains etc. If I am not mistaken this is the view of Wheeler. The 'universe' is 'participatory' in this view because each of these 'observers' can 'modify' reality by 'collapsing' the wave-function.

Isn't there a problem with this view in that without earlier collapse, none of these registered devices could possibly exist in the first place? If understanding of a measurement is what causes the collapse, how could the thing doing the understanding come about to do it? A chicken/egg problem.

Secondly, another possible way to deal with this is to go with RQM (Relational Quantum Mechanics) as Rovelli et al do. Here, all physical systems can be 'observers' and the 'measurement' is simply a physical interaction.

That definition of 'measurement' is hardly confined in RQM. With the exception of anthropocentric Wigner interpretation, I think all the interpretations assume something along these lines, and even Wigner backed down from his own interpretation due to it reducing to solipsism.

This is because, according to Rovelli, there is nothing special about computers, etc:
"By using the word “observer” I do not make any reference to conscious, animate, or computing, or in any other manner special, system. I use the word “observer” in the sense in which it is con- ventionally used in Galilean relativity when we say that an object has a velocity “with respect to a certain ob- server”.
...
We do not need a human being, a cat, or a computer, to make use of this notion of information."
But Rovelli's RQM is, in fact, not classified as 'CI'. Why? Rovelli claims that QM is complete, whereas for CI you still need to consider something as classical.

OK, that is a point about CI. To know something about system X, I must exist, and I am classical, thus something needs to exist in a classic sense. MWI falls under CI then?

Or one might argue that, for instance, you cannot have a well-defined concept of information without relating it to some form of consciousness (not necessarily human, in fact). And you end up with the 'Consciousness causes collapse' interpretation

The Wigner interpretation I referenced.

Or a Kantian-like interpretation like the one proposed by Bitbol and others (and possibly of Bohr at least for some parts of his life, if Bitbol is right...) if you do not like the idea that consciousness really 'modifies' reality (but it is nevertheless necessary to have an 'observer').

How does this interpretation get around the chicken/egg problem if an observer is necessary for an observer to collapse out of a system? I presume Bitbol does not consider a dust mote to be an observer?

The price to pay for that is subjectivism/relativism/nihilism. — Wayfarer

Existential nihilism perhaps. Life still has meaning, even if that meaning isn't objective. Even a typical theist doesn't really consider say morality to be objective. Don't kill because God says it's wrong. 'Don't do it because I said so' is relative to the thing saying so, not objective.
This is as opposed to objective morality where God tells you not to do wrong things, and a good god doesn't do them either. The morality is a higher authority than God if it is objective, which makes for a weaker god if it answers to this higher objectivity.

Yes, it seems something along the lines of those 3 views is a price paid. If a view you find distasteful is more sound than one you'd like to be the case, does comfort trump logic?
Surely you have a spin on the whole 'why is there something' debate, else you'd have to face the subjectivism yourself.
Is time a property of the universe or does the universe, like any other object, exist in time? Only with the latter does it make sense for it to have come into being, in which case one has to posit a way that came about. Is there a first cause? RQM doesn't posit this 'being', so it doesn't have to answer to the conundrum.

Anyway, I am not noAxioms, but I believe that his point was not 'nihilistic'. — boundless

My post above sort of indicates that while I don't mean to be nihilistic, I'm not sure the view doesn't lead necessarily to that camp.

if two people shine the sun light into each others eyes with a mirror at 25 feet apart , both will be in conflict with each other objective reality .You can use a garden hose and spray each other too . same difference — TRUE

I'm talking about what one individual observer sees when looking into the mirror. My right arm appears to be my left arm.

Basically, according to RQM you can only define a state of a system S in relation to something else. In other words, when you speak of the state of S you always need to specify the 'perspective' according to which you are making such a description. You can't avoid that.

So, RQM seems to imply that while there are 'individual' systems like S, their states are meaningfully defined only in relation to something else. — boundless

It is meaningful to say that there are individual systems like S? That sounds an awful lot like counterfactual definiteness. A system with states still in complete superposition is still an existing system. There was no description of S existing in relation to R. Just 'there is a system S', which sounds more like MWI and not RQM.
I tend to go whole-hog on the implications of the interpretation, so I found less reason than you did to counter the suggestion of a sort of nihilism.

But if S does not have any intrinsic properties, what does S, S?

S does have intrinsic properties. I'm just balking at the suggestion that there is S, unqualified.

I do not believe that RQM per se goes as far as denying that we can speak of individual objects, i.e. a 'no-thing' view, so to speak.

? I would say we can only speak of objects. There is no 'no thing' view. That would be the objective view, things that exist without the relation, or with only an objective relation.

With this I agree. I often characterize it the way Bohr did: as a description of what can be known, and not at all a description of what is. It is rather a jumping board by which a description of what is might be bounded. Others take their interpretation of what is and label it Copenhagen because it fits within these bounds. — noAxioms

Yeah! Bohr's IMO was not an ontological position. And yet, 'Copenaghen Interpretation' is often used to denote one.

But where is the ambiguity? The problem is that the formalism of the theory alone does not identify what is the 'observer'. Yet, in order to explain the wave-function collapse you need to posit an 'observer'. If not, we cannot explain why our 'everyday world' looks classical, so to speak. — boundless

I thought the difference between the various interpretations often focuses on the treatment of the Heisenburg Cut. The Wigner's friend scenario basically puts one observer on either side of that cut, and drives out many of the differences between the interpretations. — noAxioms

I agree with this. Maybe Wigner himself however thought that all conscious observers are 'classical', i.e. according to him in the thought experiment Wigner's friend causes the collapse also with the respect to Wigner.

Firstly, one might try to say that, indeed, there are physical objects that count as 'observers'. For instance, objects that are able to store and process 'information', like e.g. computers, registering devices, brains etc. If I am not mistaken this is the view of Wheeler. The 'universe' is 'participatory' in this view because each of these 'observers' can 'modify' reality by 'collapsing' the wave-function. — boundless

Isn't there a problem with this view in that without earlier collapse, none of these registered devices could possibly exist in the first place? If understanding of a measurement is what causes the collapse, how could the thing doing the understanding come about to do it? A chicken/egg problem. — noAxioms

Bingo! That's IMO the billion dollar question for all versions of CI. Classicality is both the result of collapse and the necessary condition of it.

Note, though, that if you accept the versions of CI where consciousness has a special role and you do not have a physicalist theory of consciousness the argument you are making does not really apply. Why? Because, consciousness is not a result of a physical process. That's the point that, for instance, Bitbol makes (also @Wayfarer makes this point in my understanding).

Secondly, another possible way to deal with this is to go with RQM (Relational Quantum Mechanics) as Rovelli et al do. Here, all physical systems can be 'observers' and the 'measurement' is simply a physical interaction. — boundless

That definition of 'measurement' is hardly confined in RQM. — noAxioms

I am not completely sure. Take Wheeler's view for instance. While not giving a special role to consciousness, he nevertheless gives a special role to the act of registration. So, it seems that in CI 'measurement' is at least given by both the interaction and the act of registration. Does this make sense to you?

OK, that is a point about CI. To know something about system X, I must exist, and I am classical, thus something needs to exist in a classic sense. MWI falls under CI then? — noAxioms

I agree on the first part. Regarding the question, instead, I would say that MWI is CI plus universal wave-function.

Or one might argue that, for instance, you cannot have a well-defined concept of information without relating it to some form of consciousness (not necessarily human, in fact). And you end up with the 'Consciousness causes collapse' interpretation — boundless

The Wigner interpretation I referenced. — noAxioms

Yep!

Or a Kantian-like interpretation like the one proposed by Bitbol and others (and possibly of Bohr at least for some parts of his life, if Bitbol is right...) if you do not like the idea that consciousness really 'modifies' reality (but it is nevertheless necessary to have an 'observer'). — boundless

How does this interpretation get around the chicken/egg problem if an observer is necessary for an observer to collapse out of a system? I presume Bitbol does not consider a dust mote to be an observer? — noAxioms

Yes, Bitbol does not consider a dust mote to be an observer. In my understanding, Bitbol thinks that only conscious beings can be observers.

FWIW, I am not a 'physicalist' myself but I am not convinced that consciousness has a special role in QM.

Anyway, I am not noAxioms, but I believe that his point was not 'nihilistic'. — boundless

My post above sort of indicates that while I don't mean to be nihilistic, I'm not sure the view doesn't lead necessarily to that camp. — noAxioms

Oh, I see. I believe that it does not necessary lead to nihilism or relativism. After all, there is still the possibility of inter-subjective agreement on ethical matters (so in some sense we can still talk about 'objective ethics') in a similar way that there is inter-subjective agreement on scientific matters. [Maybe this is too off-topic, though]

It is meaningful to say that there are individual systems like S? That sounds an awful lot like counterfactual definiteness. A system with states still in complete superposition is still an existing system. There was no description of S existing in relation to R. Just 'there is a system S', which sounds more like MWI and not RQM. — noAxioms

So S defines a perspective and everything (i.e. all its properties) about it is defined in relation to other systems? Is there something about S that is not defined in relation to other systems?

Another question, maybe problematic: How is S in relation to itself?

S does have intrinsic properties. I'm just balking at the suggestion that there is S, unqualified. — noAxioms

I'd agree with you if by 'intrinsic properties' you mean properties that distinguish S from other systems.

? I would say we can only speak of objects. There is no 'no thing' view. That would be the objective view, things that exist without the relation, or with only an objective relation. — noAxioms

In this case, we would have that both S is associated with a perspective and everything about it is defined in relation to other objects. I am not sure if this position is fully consistent but it is very fascinating! :smile:

Basically, according to RQM you can only define a state of a system S in relation to something else. In other words, when you speak of the state of S you always need to specify the 'perspective' according to which you are making such a description. You can't avoid that. — boundless

Actually I read your account of Rovelli's 'observer' again, and there's something about it I can't buy. It says "I use the word “observer” in the sense in which it is conventionally used in Galilean relativity when we say that an object has a velocity “with respect to a certain observer”. The observer can be any physical object having a definite state of motion'.

But this simply means, anything that moves with respect to anything else is 'an observer'. And I don't see how 'an observer' can be 'a table lamp' or a rock or dust mote or whatever.. I think this must be mistaken. I think what this is trying to do, is preserve a sense of scientific realism in the absence of observers - which is precisely the problem! It is one thing to say that "all motion is relative motion" but another thing to say that "all objects are observers". It seems to me to deny the issue rather than solve it.

I’ll spell out my bottom line - that all measurement or observation has a subjective aspect, i.e. it is undertaken by a subject, and the subject is (obviously) never disclosed in the act of observation, because observation is always of objects or at least of the objective domain. As Bitbol says, the inability to recognise the ubiquitous presence of the subject is precisely the blind spot of modern science. Philosophers (including Kant and Schopenhauer) understand this but many scientists do not, because it’s not, by definition, a scientific issue. But the fact that it becomes a subject of discussion here is because scientists are perhaps operating at ‘the limit of objectivity’.

If a view you find distasteful is more sound than one you'd like to be the case, does comfort trump logic?

Surely you have a spin on the whole 'why is there something' debate, else you'd have to face the subjectivism yourself.

Is time a property of the universe or does the universe, like any other object, exist in time? Only with the latter does it make sense for it to have come into being, in which case one has to posit a way that came about. Is there a first cause? RQM doesn't posit this 'being', so it doesn't have to answer to the conundrum. — noAxioms

I think there's little understanding of the idea of 'first cause' nowadays. Because science has habituated us to thinking of causality in terms of material and efficient causation, then we can only conceive of 'first cause' as something at the temporal beginning of the sequence. But I think the original notion of the first cause is of a different order or kind to material and efficient causes.

I thought the difference between the various interpretations often focuses on the treatment of the Heisenburg Cut. The Wigner's friend scenario basically puts one observer on either side of that cut, and drives out many of the differences between the interpretations.
— noAxioms
I agree with this. Maybe Wigner himself however thought that all conscious observers are 'classical', i.e. according to him in the thought experiment Wigner's friend causes the collapse also with the respect to Wigner. — boundless

Don't think there is such a cut with Wigner's interpretation. Consciousness causes collapse, period. If the cat is conscious, then it can't be in superposition of dead/alive. If not, then it can. There is no way to disprove this since there is no way to isolate a human in Schrodinger's box except by distance. I cannot take a human Alice and measure superposition on her. In principle I can, but there is just no practical way to prevent decoherence of a human. Alice is just not going to interfere with herself, even though I thought of a way for her to do it.

Bingo! That's IMO the billion dollar question for all versions of CI. Classicality is both the result of collapse and the necessary condition of it.

Does CI explicitly define measurement far enough to classify it in general as a 'registered device'? I thought it left measurement fairly undefined, allowing all sorts of interpretations on the spectrum from interaction through information processing and full on has-a-soul.

Note, though, that if you accept the versions of CI where consciousness has a special role and you do not have a physicalist theory of consciousness the argument you are making does not really apply. Why? Because, consciousness is not a result of a physical process. That's the point that, for instance, Bitbol makes (also Wayfarer makes this point in my understanding).

Yes, that's the full-on definition. It is outside methodological naturalism, but not outside science. Wigner concluded that the interpretation led to solipsism partly because other consciousnesses will collapse waves functions differently, and that puts each of these consciousnesses in different physical worlds. If that's not the view, then you don't exist until I collapse you, and that again makes for solipsism.

That definition of 'measurement' is hardly confined in RQM.
— noAxioms

I am not completely sure. Take Wheeler's view for instance. While not giving a special role to consciousness, he nevertheless gives a special role to the act of registration. So, it seems that in CI 'measurement' is at least given by both the interaction and the act of registration. Does this make sense to you?

Not really. I don't formally know what Wheeler means by 'registration'. I tried to look it up but found the term only fairly well buried in papers beyond my ability to absorb. I used the word above, but only to echo the notion of a system that meets some unstated qualification of processing the information of measurement.

Or a Kantian-like interpretation like the one proposed by Bitbol and others (and possibly of Bohr at least for some parts of his life, if Bitbol is right...) if you do not like the idea that consciousness really 'modifies' reality (but it is nevertheless necessary to have an 'observer').

What I like has little to do with it. I'm interested in what works: is self consistent.

Yes, Bitbol does not consider a dust mote to be an observer. In my understanding, Bitbol thinks that only conscious beings can be observers.

Well it works I suppose. If consciousness is not a classical physical thing, then there's no chicken/egg problem. Still, how does it manage to collapse a state of total superposition into a state with matter present, let alone matter that can host consciousness? Collapse seems not to be in any way a function of will. I cannot will a measurement of vertical polarization, yet I would seem to need to do that to find my physical host.

FWIW, I am not a 'physicalist' myself but I am not convinced that consciousness has a special role in QM.

Oh good, then you might take a stab at my questions, even though they're geared towards a Wigner sort of setup. Are you saying that consciousness is not physical?

Anyway, I am not noAxioms, but I believe that his point was not 'nihilistic'.
— boundless
My post above sort of indicates that while I don't mean to be nihilistic, I'm not sure the view doesn't lead necessarily to that camp.
— noAxioms

Oh, I see. I believe that it does not necessary lead to nihilism or relativism. After all, there is still the possibility of inter-subjective agreement on ethical matters (so in some sense we can still talk about 'objective ethics') in a similar way that there is inter-subjective agreement on scientific matters. [Maybe this is too off-topic, though]

If there's not another topic to discuss it, then why not here? I'm in no way against inter-subjective agreements. I just don't think that makes things objective. We both see the same moon, sort of, but the moon's existence is still relative. It totally doesn't exist to something that has taken no measurement of it, but it also doesn't stop existing to us if everybody looks away for a moment. It cannot be un-measured.

A system with states still in complete superposition is still an existing system. There was no description of S existing in relation to R. Just 'there is a system S', which sounds more like MWI and not RQM.
— noAxioms

So S defines a perspective and everything (i.e. all its properties) about it is defined in relation to other systems? Is there something about S that is not defined in relation to other systems?

Another question, maybe problematic: How is S in relation to itself?

S can define a perspective, yes. S is perhaps a collapsed state at some event say. Doesn't matter what the system is. The collapsed state here might be the two of us looking at a moon, and might be a moonless Earth without either of us, or it might be empty space between galaxies. In MWI speak, those are all existing worlds, and the we only exist in the first one, so the moon exists relative to that S and not to other potential states for the same collapsed S at that event.

S always exists to itself it would seem. The live cat measures a live cat, never the dead one, let alone no-cat. I don't see how that is problematic.

Since I am not really an event, I'm also not a defined measured state S. Relative to parts of me, other parts are in superposition. This does not in any way impede my classic functionality, but it does mean that lacking a defined state, I lack a defined state and thus a defined identity, which was never a problem to my view, so I don't care. But one has to be careful when trying to pinpoint an intersubjectivity between two systems. So each of us measures a past state of the other, not a current one. These are nitpicks since the parts in superposition are trivial differences.

S does have intrinsic properties. I'm just balking at the suggestion that there is S, unqualified.
— noAxioms

I'd agree with you if by 'intrinsic properties' you mean properties that distinguish S from other systems.

You need to define S. This collection of atoms currently has an arbitrary box drawn around them and is designated as S or 'noAxioms' for the moment, even though many of those atoms come and go continuously. You may have a different idea if you have a different philosophy of mind and identity. For me, at best, my identity is the stuff in that abstract box drawn around a bunch of matter near a certain event, and the entire worldline that led to that event. That definition only works because I cannot subjectively split or merge. It wouldn't work for an amoeba, starfish, or a candle flame.
I would love to talk philosophy with a sentient amoeba.

In this case, we would have that both S is associated with a perspective and everything about it is defined in relation to other objects. I am not sure if this position is fully consistent but it is very fascinating! :smile:

Maybe it isn't consistent. Hence the appreciated cage rattling.

An observer is one who takes notice of (and this means pays attention to) the thing which is observed.

Right. And by my reckoning table lamps can’t do that.

Actually I read your [boundless's] account of Rovelli's 'observer' again, and there's something about it I can't buy. It says "I use the word “observer” in the sense in which it is conventionally used in Galilean relativity when we say that an object has a velocity “with respect to a certain observer”. The observer can be any physical object having a definite state of motion'. — Wayfarer

That sounds like a reference frame, which A) doesn't require an object stationary in that frame to define it, and B) has nothing to do with what causes a wave function to collapse. Rovelli says this in the context of equating that 'observer' to the mechanism that collapses/splits a wave function? I think not the latter. An observer is a point of view, but not necessarily something at that point observing, and not something that has an effect.. Just a point from which a description can be made. It does imply a partially collapsed state, so it isn't really defined without the table lamp, stationary or otherwise.

I’ll spell out my bottom line - that all measurement or observation has a subjective aspect, i.e. it is undertaken by a subject, and the subject is (obviously) never disclosed in the act of observation, because observation is always of objects or at least of the objective domain.

I kind of agree with this terminology being ambiguous, which is why I hesitate to use the word observation. Wave function collapse has presumably been going on long before any object has been capable of being this sort of 'observer'. So if I claim the table lamp takes a measurement of the air heating it, I'm not laying claim that it has subjective experience.

Surely you have a spin on the whole 'why is there something' debate, else you'd have to face the subjectivism yourself.
— noAxioms

I think there's little understanding of the idea of 'first cause' nowadays. Because science has habituated us to thinking of causality in terms of material and efficient causation, then we can only conceive of 'first cause' as something at the temporal beginning of the sequence. But I think the original notion of the first cause is of a different order or kind to material and efficient causes.

Is that an answer? It is a of a different order or kind. OK, I can agree with that, but it isn't a specific answer. Indeed, I think it is a category error to treat the universe as an object, which, like all objects, doesn't exist, comes into being, and then exists (for a duration). 'Exists' means something different than how we use it for objects. But what does it mean actually? I find it to hold no distinction. An existing object is distinct from a non-existing one, but that is the object category. It seems not to apply to a universe category. That's just me and my relativist mindset. I'm sure you see a distinction, but you haven't really identified what 'order or kind' we're talking about here.

Thanks !

Regarding Kaster's approach I am not sure to call it 'non-local'. — boundless

Yes, it seems she is simply talking about a logical consequence there. If the cafe closes then no-one can eat there. But her characterizing a logical consequence as an instantaneous and acausal effect, or a form of global non-locality, is a category mistake.

All that is physically going on are systems interacting locally with other systems. The time of closure of the cafe is system-dependent and is determined by physical interactions.

To be more complete, in fact I lean towards RQM and CI. The problem I have with RQM is that 'information' maybe is not something well-defined in relation to all physical systems. But as I said in my previous post, this is a quite controversial point. If 'information' is something that can be defined in relation to all physical system, then RQM is IMO the best choice.

If not, maybe something like Bitbol's interpretation (with maybe some elements of 'actuality/potentiality' dualism) would be best.

I am simply undecided. — boundless

Fair enough! As it happens, I also find Aristotle's form/matter distinction useful for considering information. A physical system, being substantial, can be abstracted in terms of its matter and form (or state). Which provides a natural isomorphism between a physical system and a point in state space.

They're almost the same thing, with different definitions of 'is real'. RQM says this world is real to me and a different world is real to anything else (the cat say), so they're both talking about different worlds. MWI says they're all equally real, and RQM says none are real, only that there are relations between worlds and observers.
...
Still, there are very 'real' differences between MWI and RQM, and I don't see how either Rovelli and Tegmark are going to convince the other that they hold the opposite view. — noAxioms

Thanks! My own reading of RQM for a while was as a relational semantics abstracting over a Many Worlds dynamics. But as boundless also suggested, I think Rovelli would reject an underlying Many Worlds dynamics.

My answer to the above question is that perhaps there isn't anything, and thus there is no need to have to explain its being. — noAxioms

I recall that you accept Tegmark's mathematical universe hypothesis, so that would seem to follow. :-)

What is interference? It seems to be 'maybe' as an answer to a question not yet asked, a measurement not yet taken. So X = square root of 2 is 1.414 but also -1.414 and both those values can work through my equation until a choice must be make before the mathematics can continue. That's a measurement, and now there are two equations that proceed in different directions using a now real value for X instead of one in superposition. — noAxioms

OK, but that seems like a nonphysical answer. Just to follow up a bit further, suppose we have an equal path-length Mach-Zehnder interferometer that sends every emitted photon to detector 1.

Now since RQM respects locality, it raises a question of what is physically going on in the interferometer prior to detection of the photon. MWI says there is amplitude for a photon on each path which results in subsequent interference at the final beam splitter. But it seems that RQM can't explain it that way since it raises the prospect of branches.

An observer is one who takes notice of (and this means pays attention to) the thing which is observed. — Metaphysician Undercover

Right. And by my reckoning table lamps can’t do that. — Wayfarer

Simply substitute system for observer if that helps. That is how Rovelli is using the term.

Observers are not systems, but intentional beings.

That's why I don't get this:

For instance, I say that my hand moves at a velocity v with respect to the lamp on my table. Velocity is a relational notion (in Galilean as well as in special relativistic physics), and thus it is always (explicitly or implicitly) referred to something; it is traditional to denote this something as the observer, but it is important in the following discussion to keep in mind that the observer can be a table lamp. — Carlos Rovelli

I think I understand what a reference frame is. But I don't understand how an inanimate object can be regarded as equivalent to 'an observer'.

Ask yourself this: NASA sends out a probe, as it often does, which whizzes by Saturn, all the while recording data, but then its radio link with Earth fails. It keeps registering data for an indefinite period of time - years, perhaps - but does that any of that data comprise an observation, without it having been sent to, and interpreted by, the scientists who sent the probe? I say not.

There's a distinction between 'data' and 'information'. Until data is organised and contextualised, it doesn't become information. That is the difference between them, and I think it's being obfuscated by these arguments.

For similar reasons, I'm dubious of the following:

a pen on my table has information because it points in this or that direction. We do not need a human being, a cat, or a computer, to make use of this notion of information.

I mean, according to this definition, every single thing that is arrayed in respect of some other object (for example, any atom) has, or conveys, information. I think this definition is so broad as to be meaningless. I don't believe 'information' has a single definition. Shannon's definition of information was specifically given in the context of transmission of electronic information through a physical medium, so that definition has certain boundary conditions, so to speak. To generalise from that to information in such an amorphous sense, seems illegitimate to me.

The whole problem in this debate is "what is the role of the observer", is it not? And the paradox is that science knows that "the observer" - h. sapiens - is a latecomer on the scene, we're the proverbial lighting of a match at the end of a vast aeon of time. So it doesn't make any sense, from that point of view, that "the observer" should have such a central role in any physical observation.

But the problem is simply that when you make such a statement, you're looking at "the observer" from the outside - in other words, treating "the observer" as another object - here, the solar system, or whatever, and there, h. sapiens.

But how can you assume that perspective? Because we never get outside of the perspective of being an observer. "Observation" in the broader sense, includes everything, not because lamps and rocks and atoms are conscious (which is nonsense), but because everything we know is ultimately and irrevocably a cognitive act. We're knowing beings, and everything we know is based on observation (and reasoning based on observation). Then, as Bitbol points out, we overlook or forget the "role of the observer" in all of this, assuming that we're viewing the world as if from no perspective or no point of view. Seeing that requires a gestalt shift, an aha moment, which some get, and some don't.

Observers are not systems, but intentional beings. — Wayfarer

I can't see any evidence in the article you cited that the notion of "observer'' in QM is thought as having anything to do with being "an intentional being".

Right. That’s why I am taking issue with it. I’m saying observers are intentional beings, and not simply objects or systems.