An observer is a point of view, but not necessarily something at that point observing, and not something that has an effect. — noAxioms

I hope you realize that an observer, without something observing is contradictory.

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. — noAxioms

A measurement is a comparison, between something observed, and a scale (an ideal). A table lamp does not measure.

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

The problem is that anything within that "system" needs to be interpreted according to standards before the system has any observational value. The "system" has no observational value without those human standards.

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". — Janus

Since "observer", as commonly used, requires that one notices what occurs, the notion that something other than an intentional being could be an observer needs to be supported. Suppose a machine records, as in wayfarer's example, or an object is changed by an event. How does this qualify as noticing what occurs? When that information in the machine, or the changes in the object, are interpreted, the interpretation requires basic assumptions about the relationship between the machine or object doing the recording, and the event being documented. The "observation" of the event is not complete without those assumptions. So the machine or object, on its own, is just changing, it is not observing.

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'. — Wayfarer

I agree that 'observer' is a poor choice of words in Rovelli's interpretation. That's why in some of my former posts I preferred the more general word 'perspective'.

Anyway, note that there is a problem of self-reference even in Relational approach(es). I suggest you to read section four of the SEP article about 'Relational Quantum Mechanics': https://plato.stanford.edu/entries/qm-relational/#SelRefSelMea. It is a discussion about the possibility of self-measurement. (Maybe @Andrew M and @noAxioms will find it intriguing too!)

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’. — Wayfarer

Well, I think that I agree in part with this. But as you say, it's not by definition a scientific issue :smile:
So, I do not think that your reasoning here is really affected by what interpretation of QM is 'right'. (After all, Kant and Schopenhauer did not knew QM)
At the same time, what I find fascinating is that with the advent of QM and with the introduction of interpretations like the Von Neumann-Wheeler a.k.a 'consciousness causes collapse', Bitbol's (and d'Espagnat) etc and also Many Minds, this issue has become of interest of scientists themselves.

I agree that knowledge is perspectival and since we are conscious, it is at least in some but very deep sense, 'subjective'. But at the same time, my fear is that, if we embrace this kind of reasoning completely, we end up to deny 'reality' completely.

In terms of the noted parable of the blind men and an elephant (here the Wikipedia article), the risk is to deny the 'elephant' instead of denying the 'perspectival' (in this case 'subjective') character of knowledge. In other words, my fear is that we fall into the other extreme, so to speak :smile:

How does this work? Do you think the observer's intention somehow acts on a superposition to constrain it - tightening the distribution of states or collapsing it to a single one?

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. — noAxioms

Yes, you are right. That's one difference between Wigner's original proposal and Bitbol's take (other than a less 'ontological' take on what the 'collapse' is) and possibly also QBism (but I admit that I do not understand it very well). Here an article by Bitbol about the Wigner's friend scenario: https://core.ac.uk/download/pdf/148348264.pdf. An excerpt:

Now, what happens if WE open the door of the lab. to see what happened in it? As previously, we see a well-defined chain of characters on the screen of the computer, we see that the cat is either dead or alive, and we hear a colleague saying that he had already seen (well before our arrival) what we are now discovering. And as previously, we must modify suddenly our tool of probabilistic prediction in order to account for our certainty of finding everything in the same configuration, if we come back in the lab. some time later. In the same way as we had to reduce the probability function of the whole measurement chain, we now have to reduce its wave function. There is a big difference between the two cases, however: whereas the ordinary probability functions could be considered as the expression of our ignorance about what effectively occurred in the lab., this is not true for the wave functions of quantum mechanics. The wave function of the measurement chain just provides a probabilistic prediction of the result of a possible (uncontrollable) interaction between it and something else. And this manifests itself through the persistent presence of a term W (for “wavering” or “wavelike effects”), in the probabilities calculated from the wave function.
...
Let me show how this indexical “solution” (or “dissolution”) of the measurement problem of quantum mechanics works. It is based on the far-reaching, and already documented, difference between a property and an observable. A property of an object is defined in the absolute, whereas an observable refers to a possible relation between the object and something else. Each time one wishes to make the relation explicit, one has to introduce the “something else” into the field of description. But then, the characterization of this something else is itself relative to a possible interaction with a third element, and so on and so forth. Isn't there a natural end to this chain of relations? Yes, there is. WE are this end. Of course, I am not trying to say that WE are unique or privileged beings in nature (this would be collective solipsism of an absurd sort), but only that WE are privileged beings for US! As soon as we establish a relation with an element of the measurement chain, this element acquires a determination relative to US. Nothing has thus to be changed in the physical description, since determinations of the measurement chain are still relative to something. But everything is different for US, since the determinations of the measurement chain are now relative to US. And a relation of which WE are one term is something quite peculiar, even if it is only peculiar ... from OUR point of view.

Oddly, I think that Bitbol's view seems a mixture of CI and RQM, but in fact I think it is still a form of CI. In usual formulations of CI, there is only a 'classical world'. Yet, Bitbol's point is that Wigner still has to consider his friend in superposition. In other words, just like in the case of Rovelli, in Bitbol's take of CI, there is no single 'history', so to speak. As Bitbol points out in the other article I linked before (i.e. this: http://www.bourbaphy.fr/bitbol.pdf):

This is not to deny that quantum mechanics, as one of the most accomplished realizations of the ideal of universal description pursued by the natural sciences, could indeed describe any phenomena.
Yet, in doing so, it could not avoid leaving the preconditions for description outside its scope. As a well-known article about the measurement problem of quantum mechanics puts it: the quantum theory can describe anything, but not everything [Peres1982][Fuchs2000].

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. — noAxioms

Yes, I agree with you on the ambiguity of CI. But some proposals to resolve it, involve that registering devices 'collapse' the wave-function. If true, I believe you need the physical interaction and the act of registration.

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. — noAxioms

Yes, that's my concern too. Regarding consciousness, I believe that science can give us some knowledge of it. But it cannot give us the full story.

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. — noAxioms

I see. Me too, actually. So do not trust my word :wink:

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

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

Me too. And unfortunately, I do not know if it is really self-consistent (honestly, I do have a similar concern for RQM).

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. — noAxioms

According to Bitbol, collapse is due to an increase of knowledge. It is not a physical process. The wave-function is regarded as a tool.
Of course, it becomes more problematic if a minimalist take on the wave-function is untenable.

Regarding your question how is possible that matter can host a 'non-physical mind', I just do not know how to answer. And that's one of the reason why giving a special role to consciousness in a scientific theory is for me problematic.

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? — noAxioms

Well, yes and I also believe in free-will. [But I am a bit unwilling to explain why I think so here... :smile: Anyway, in brief, for example, I believe that this is a consequence to both the so-called 'hard problem of consciousness' and my acceptance of free-will (because I do not believe that free-will, if is real as I think it is, can be explained in purely physical terms...).]

At the same time even if I have this belief, I am not so sure that giving consciousness a so special role in a scientific theory is a very good idea. But, oddly, the fact that this has been done in various ways fascinates me.

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. — noAxioms

Ok...Yes, I agree that inter-subjectivity and objectivity in the usual sense are different. What moral relativism denies, however, is that there are no universal ethical truths. I find it somewhat irrational, actually. In a sense, it is somewhat dogmatic: 'perspectivism' does not entail that it is impossible to find something that is considered 'good' for everyone. Also, it has absurd consequences: I believe that, indeed, there are actions that can be considered good/bad by everyone. And I do not believe that rejecting 'objectivity' in the usual sense denies that. (I referred to a discussion on ethics when I referred to 'off-topic')

Regarding the example of the Moon, I am a bit perplexed however. If the Moon is completely non-existent for anybody that has not measured it, how can I say that measurement is an interaction?

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. — noAxioms

Intuitively I would agree with you! But look at the link I gave to Wayfarer of the SEP article on RQM :smile:

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. — noAxioms

Ok!

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. — noAxioms

Ok thanks, I see. But it seems that this kind of definition of 'S' (or whatever physical object you have in mind) presupposes that can be used to all perspectives.

Take for instance even an electron. Its state might be different for the various 'perspectives'. But for all physical systems it is indeed an 'electron'. So, you need something invariant, after all. Can we still have invariants if we do not have something perspective-independent? I am struggling with this point and I am not arrived to a solution.

I would love to talk philosophy with a sentient amoeba. — noAxioms

Well, me too! But as Wittgenstein remarked, we might not be able to understand a lion, let alone an amoeba :sad:

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

Thanks!

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. — Andrew M

Mmm, I see!

Also, both she and Shimony are in fact clear that 'potentialities' for them are in some sense non-local.

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. — Andrew M

Agreed!

Let me, however, ask you the same question that I asked to noAxioms.

Consider an electron. According to RQM, its state is 'perspective'-dependent. But all of them are in agreement that it is an 'electron'. So, is 'out there' something identifiable as an 'electron' even when is not measured? What I am saying is that it seems we need after all something invariant, equal to all perspectives. Is this compatible with RQM? :smile:

,

Just a curiosity...

Interestingly, it seems that RQM agrees with the Consistent Histories interpretation about the lack of a 'single history'. From the SEP article on Consistent Histories, section 11.4:

In a probabilistic theory the limiting cases of a probability equal to 1 or 0 are equivalent to asserting that the corresponding proposition (e.g., “the system has property P”) is, respectively, true or false. In the histories approach probabilities are linked to frameworks, and for this reason the notions of “true” and “false” are also framework dependent. This cannot lead to inconsistencies, a proposition being both true and false, because of the single framework rule. But it is contrary to a deeply rooted faith or intuition, shared by philosophers, physicists, and the proverbial man in the street, that at any point in time there is one and only one state of the universe which is “true”, and with which every true statement about the world must be consistent. In Sec. 27.3 of Griffiths (2002a) this belief is referred to as unicity, and it is what must be abandoned if the histories interpretation of quantum theory is on the right track.

Well, I really find this interpretation (at least as it is presented there) somewhat difficult to understand. So, I still have not formed an idea about it. In fact, I somehow have a problem to really distinguish it from MWI.

What do you think of Consistent Histories?

Since "observer", as commonly used, requires that one notices what occurs, the notion that something other than an intentional being could be an observer needs to be supported. — Metaphysician Undercover

As far as I can tell the notion of an observer in QM is a specialized one; so 'observer' would be a metaphor, not a literal definition in strict accordance with everyday.usage.

An observer is simply a scientist making the observation. It’s not specialised. The whole controversy is because of the requirement to consider the observer at all, because it threatens the notion of ‘mind-independence’.

Do you think the observer's intention somehow acts on a superposition to constrain it - tightening the distribution of states or collapsing it to a single one? — fdrake

Isn’t that the very kind of question that the article in the OP addresses? That two observers observing what ought to be the same event each see something different?

Physicists have long suspected that quantum mechanics allows two observers to experience different, conflicting realities. Now they’ve performed the first experiment that proves it.

Recall Figure 7 in the Wheeler article again - that what we call ‘reality’ is in part a construction (‘between the ‘iron posts’ of observations). That is what I take Schopenhauer to mean by ‘Vorstellung’ and Buddhist philosophers by ‘vikalpa’ or ‘Vijñāna’. This is *not* to say that ‘everything is in the mind’ but, as Wheeler is saying, that the mind has an inextricable role in ‘constructing’ reality, and that we can’t see without it (hence, also, Kant).

Naturalism starts with the perspective ‘I - it’, the division of subject and object. But that is part of the construction, it is a learned cognition that is acquired in early childhood. That’s what I mean by saying that naturalism ‘assumes the world’ - it assumes that the division of subject and object is fundamentally real, but in actuality, reality is not something we’re outside of, or apart from. That sense of being apart from, or outside of, reality, is what I refer to as ‘the illusion of otherness’. In modern thought, generally, that is one of the base assumptions, but here we are beginning to see it break down. And that really is an epochal shift, make no mistake.

That still leaves a vast domain of phenomena about which there can be objective agreement (‘iron posts’). But the objective domain is not (in Buddhist terms) ‘self-existent’. Perception or cognition is a foundational aspect, but it is never a ‘that’, it only ever appears as the subject, as the ‘unknown knower’.

Note this encyclopaedia snippet on ‘objective idealism’:

It accepts common sense Realism (the view that independent material objects exist), but rejects Naturalism (the view that the mind and spiritual values have emerged from material things).

Plato is regarded as one of the earliest representatives of Objective Idealism (although it can be argued that Plato's worldview was actually dualistic and not truly Idealistic). The definitive formulation of the doctrine came from the German Idealist Friedrich Schelling, and later adapted by G. W. F. Hegel in his Absolute Idealism theory. More recent advocates have included C. S. Peirce and Josiah Royce (1855 - 1916).

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. — Andrew M

Sort of. Tegmark takes the MWI position that the structure (the universal wave function) exists, and thus he has to explain its 'being'. I don't buy into Platonic existence of numbers, and to both of us, the universal wave function is a mathematical thing, so same category.

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.

It is very physical if you consider the physical universe to be a mathematical thing. The answer is still lousy, but I find it to be a very physical 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.

Does RQM have branches? That is more an MWI thing. Prior to that measurement, there is no collapse, so the wave function puts the photon on both paths, not on 'either' path. The photon in this state can interfere with itself on both paths (to detector 1 and to detector 2) after the final beam splitter resulting in one wave function that yields almost all of the probability of measurement on detector 1 and none on detector 2.
That's not so much a description of RQM as it is a description of QM. I don't know where you might suggest locality comes into play. Nothing is being affected faster than light or anything, unlike what apparently goes on in some delayed choice experiments.

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'. — Wayfarer

He's not saying that the lamp is taking note of the hand motion. He's just saying that the motion is relative to the motion of the lamp, be it noticed or not. The word 'observer' is being used in place of reference frame.

An inertial reference frame doesn't even need an origin. 20 things can all have identical velocity in some inertial frame and some other thing will have identical velocity relative to any of them, so in this sense they're all the same 'observer' as Rovelli uses the term. It doesn't work for accelerating frames, so 20 things can all be different parts (let's say rivets of a ship) of some rigid accelerating object and those 20 parts will have different velocities in any frame in which they are moving. So an 'observer' in an accelerating situation like that needs to be a specific point like one of those 20 objects or any other coordinate in that accelerating frame.

In which case, how does this address the 'observer problem'? The observer might occupy a particular reference frame, but without an observer, then what is being measured/observed? I guess I will have to find time to go back and look at those resources that @boundless provided in more detail.

I hope you realize that an observer, without something observing is contradictory. — Metaphysician Undercover

Not the way Rovelli is defining the word. I personally dislike such usage because it encourages exactly such misinterpretations.

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.
— noAxioms

A measurement is a comparison, between something observed, and a scale (an ideal). A table lamp does not measure.

It is warmer than the same lamp measuring colder air. The air temperature has had an effect on the lamp. One system has effected the 2nd, and that's the second definition of measurement that @boundless gave.

Anyway, note that there is a problem of self-reference even in Relational approach(es). I suggest you to read section four of the SEP article about 'Relational Quantum Mechanics': https://plato.stanford.edu/entries/qm-relational/#SelRefSelMea . It is a discussion about the possibility of self-measurement. (Maybe Andrew M and @noAxioms will find it intriguing too!) — boundless

OK, that's what you meant by the self reference issue. Theorem aside, it seems quite intuitive that an aparatus cannot measure all of its own states since the taking of that measurement changes those states. This seems a little analogous to Heisenberg uncertainty where the more you know about one aspect of yourself, the less the can be known about some other aspect.
None of this means I cannot collapse my own state in sufficient hindsight, which is sort of what I meant with my first reply to this issue.

As far as I can tell the notion of an observer in QM is a specialized one; so 'observer' would be a metaphor, not a literal definition in strict accordance with everyday.usage. — Janus

Not the way Rovelli is defining the word. I personally dislike such usage because it encourages exactly such misinterpretations. — noAxioms

The problem is that the definition of "observer' is not consistent with what the observer really is, in practise. The reference frame, which is supposed as the "observer", is inherently a human perspective. Any reference frame is. So to define "observer" in such a way that the observer might be something independent from a human perspective is to falsely define "observer", i.e. to define "observer" in a way which is inconsistent with what an observer really is in practise.

It is warmer than the same lamp measuring colder air. The air temperature has had an effect on the lamp. One system has effected the 2nd, and that's the second definition of measurement that boundless gave. — noAxioms

You cannot say that the lamp is warmer, unless you, or some other human being actually measures to see that it is warmer. Even if you conclude deductively that the lamp was exposed to warm air, therefore it is warmer, this still requires certain premises, and a human being to observe that it was exposed to the warm air, and apply the premises to make the deductive conclusion. You cannot get away from the need of human presence to make an observation, simply by asserting that an object can make an observation without a human presence. Even if the object did make the observation in that way, such an observation would be absolutely useless to any human being. We can't simply assume that an object made a specific observation without confirming that it did, but then it's a human observation. The only observations which are useful to us are the ones which we interpret using our assumptions and logical principles, but then the observation is not made by an object, it is made by the human being which makes the interpretation.

I have a hard time keeping up with you guys :)

Here an article by Bitbol about the Wigner's friend scenario:
An excerpt:
" ... In the same way as we had to reduce the probability function of the whole measurement chain, we now have to reduce its wave function. There is a big difference between the two cases, however: whereas the ordinary probability functions could be considered as the expression of our ignorance about what effectively occurred in the lab., this is not true for the wave functions of quantum mechanics." — boundless

This isn't the QM I know. There is no 'big difference' between the two cases. The cat is both dead and alive (superposition), not either dead or alive (result of an unobserved coin toss). The latter probability function is said expression of ignorace about how the coin toss turned out, but the probability function of the cat is not ignorance. It really is dead and alive until measured, else it could not interfere with itself. Of course, being a classic object, it is not easily going to interfere with itself, but quantum states very much do, so it seems to be a mistake to qualify the probability function as a mere expression of ignorance.

Maybe the colleague (Wigner's friend) changed that (being a conscious being that the cat apparently isn't), and that explains this assertion above. This I suppose cannot be disproved since there is no way to prevent the decoherence of something as classic as a human, but it also goes for the cat of course. They seem to allow the inconsistency of having a cat in superposition but not a lab assistant.

"The wave function of the measurement chain just provides a probabilistic prediction of the result of a possible (uncontrollable) interaction between it and something else."

What does the measurement chain have to do with it? I shoot a photon through the slits and it makes a mark on the screen. That's a measurement even though it might be a minute before the operator bothers to look and learn of the result. The result is not being kept hidden in a box to prevent decoherence. If consciousness causes collapse, it doesn't imply that knowledge causes it. The conscious guy is in the room, ignorant of the result of the measurement, but nevertheless present. The collapse occurs because of that presence, no? If it is awareness, then I should be able to measure a thing but not take note of the result, and find the thing still in superposition later on. But that doesn't happen. It seems a falsification for the 'conscious knowledge' causing collapse idea.

I'm just trying to shoot holes in what I think might be being described in these quotes.
More of that quote:

"...
Let me show how this indexical “solution” (or “dissolution”) of the measurement problem of quantum mechanics works. It is based on the far-reaching, and already documented, difference between a property and an observable. A property of an object is defined in the absolute, whereas an observable refers to a possible relation between the object and something else. Each time one wishes to make the relation explicit, one has to introduce the “something else” into the field of description. But then, the characterization of this something else is itself relative to a possible interaction with a third element, and so on and so forth. Isn't there a natural end to this chain of relations? Yes, there is. WE are this end. Of course, I am not trying to say that WE are unique or privileged beings in nature (this would be collective solipsism of an absurd sort), but only that WE are privileged beings for US!"

So what? Only the table lamp is the privileged object for the table lamp. We are no more a natural end to the chain of reactions than is the table lamp. The reactions continue right on through us to affect other things. I have a hard time thinking of any causal chain that is initiated (rather than propagated) and cannot think of any that can end ever (per conservation of information). Radioactive decay might be an example of a new causal chain. Depends on interpretation.

"As soon as we establish a relation with an element of the measurement chain, this element acquires a determination relative to US. Nothing has thus to be changed in the physical description, since determinations of the measurement chain are still relative to something. But everything is different for US, since the determinations of the measurement chain are now relative to US. And a relation of which WE are one term is something quite peculiar, even if it is only peculiar ... from OUR point of view."

OK, but I can substitute "table lamp" for "US" everywhere in that bit and it still holds. If "WE" are not special, why bring US up all the time like that?

Oddly, I think that Bitbol's view seems a mixture of CI and RQM, but in fact I think it is still a form of CI. In usual formulations of CI, there is only a 'classical world'. Yet, Bitbol's point is that Wigner still has to consider his friend in superposition.

I didn't get that from reading that bit.

I don't formally know what Wheeler means by 'registration'.
— noAxioms

I see. Me too, actually. So do not trust my word :wink:

OK, so take caution when the term is used below:

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.
— noAxioms

Yes, I agree with you on the ambiguity of CI. But some proposals to resolve it, involve that registering devices 'collapse' the wave-function. If true, I believe you need the physical interaction and the act of registration.

Without a description of what constitutes that registration act then, I have no idea what he's talking about.

According to Bitbol, collapse is due to an increase of knowledge. It is not a physical process. The wave-function is regarded as a tool."

If CI is taken as an epistemological interpretation, I suppose this is true in a way, but it seems trivial to falsify. Alice (a simple device) measures the spin on one of an entangled pair, and prints the result of that measurement on a little paper that ejects face down on the table. Human Bob sees the paper but has gained no knowledge of the result, only knowledge that the measurement has taken place. He now measures the other particle of that pair and is is no longer in superposition. His lack of knowledge did not prevent the collapse of the wave function of his sample The device (Alice) has no knowledge since it retains no state of the incident after finishing its little printout. Does the unseen paper have the knowledge? It certainly contains the (hidden) information, but does it have 'knowledge'? If it does, why that anthropocentric choice of words?

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?
— noAxioms

Well, yes and I also believe in free-will.

Well, so do I, but my definition might be different than yours, so it isn't saying much. I will to be on the other side of these jail bars, so physics, deterministic or otherwise, very much does get in my way on that account, but few consider such restriction to be an example of lack of free will.

[But I am a bit unwilling to explain why I think so here... :smile:.]Agree, this would be too far off topic. There are always other threads about such things.

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.
— noAxioms

Ok...Yes, I agree that inter-subjectivity and objectivity in the usual sense are different. What moral relativism denies, however, is that there are no universal ethical truths.

Double negative. It denies that there are universal ethical truths. I'm sure you meant that.

I find it somewhat irrational, actually. In a sense, it is somewhat dogmatic: 'perspectivism' does not entail that it is impossible to find something that is considered 'good' for everyone.

Actually, I find that any particular rule is probably meaningless for most situations. 'Torture of babies is bad' has no application to the vast majority of things where 'torture' and 'babies' are both meaningless or at least poorly defined. Note my use of 'things' instead of the already restrictive word 'everybody' which detracts from the universality of the rule. A universal rule should not only apply to things that are member of 'everybody'.

I believe that, indeed, there are actions that can be considered good/bad by everyone. And I do not believe that rejecting 'objectivity' in the usual sense denies that.

Same here. I don't necessarily deny objective morality, just playing devil's advocate.

Regarding the example of the Moon, I am a bit perplexed however. If the Moon is completely non-existent for anybody that has not measured it, how can I say that measurement is an interaction?

Don't understand your, um, misunderstanding. How can it exist unmeasured? I've not measured the 2nd even larger moon, so it doesn't exist, and that seems not a problem to you. Nobody can be on this Earth (can exist relative to me say) and not have measured the moon. We have an inter-subjective agreement about that. Similarly, if one has not measured the moon (or has measured that bigger one), then that person cannot establish any inter-subjective relationship with me. It would be a contradiction.

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.
— noAxioms

Intuitively I would agree with you! But look at the link I gave to Wayfarer of the SEP article on RQM :smile:

The article says a complete measurement of ones self cannot be taken, not that you can't measure yourself. My pants size is a measurement of myself. :sad:

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.
— noAxioms

Ok thanks, I see. But it seems that this kind of definition of 'S' (or whatever physical object you have in mind) presupposes that can be used to all perspectives.

I don't have a definition of S. It seems arbitrary. It is fairly easy to do for a human, but less so for other things. The ease of defining human X (and equating that definition to the same X at some other time) allows the existence of a legal identity of X. You can't do that with amoebas and flames.

Take for instance even an electron. Its state might be different for the various 'perspectives'. But for all physical systems it is indeed an 'electron'.

I think there are interactions between two electrons (like both being part of the same Helium) that ambiguates which one is which when one of the two changes state (like exits the atom). So yes, an electron departed, but it wasn't necessarily a particular electron. This is not a measurement thing. Of course there is no way to measure which one stayed and which one left. I'm just saying that metaphysically, it seems that electrons don't have identities, and thus act like a distinct 'system S'.

So, you need something invariant, after all. Can we still have invariants if we do not have something perspective-independent? I am struggling with this point and I am not arrived to a solution.

Not sure if we're talking about the same thing here. Most of my relation with the electron is 'it is there', and relative to some other observer, it isn't there, or anywhere, just like the moon. To any two intersubective observers, they should agree on the electron being there or not, even if viewed from different frames. Isn't 'it is there' an invariant between said intersubjective perspectives? One says it is northbound and the other says eastbound, but both say it is there. That relation is not invariant between perspectives that are not intersubjective.

I would love to talk philosophy with a sentient amoeba.
— noAxioms

Well, me too! But as Wittgenstein remarked, we might not be able to understand a lion, let alone an amoeba :sad:

We should if it is sentient. I just want to talk to an alien that reproduces by suddenly falling into two halves. There is so much stuff that we find intuitive only because we don't do that, and talking to such a being would drive out all those inbred biases in not just us, but the amoeba as well. It would learn from us. The flame is even worse, because two flames can merge into one. Even the amoeba can't do that. We may well be able to talk to the flame some day soon because any AI entity (say an intelligent virtual being) would benefit from working that way


Appreciate the good discussion. Been a while for me.

Consider an electron. According to RQM, its state is 'perspective'-dependent. But all of them are in agreement that it is an 'electron'. — boundless

From some (most) perspectives, there is no 'it' to be an electron. To consider an electron is to have already assumed a perspective where it exists. It is a measurement already taken.

Just a curiosity...

Interestingly, it seems that RQM agrees with the Consistent Histories interpretation about the lack of a 'single history'

Well, I really find this interpretation (at least as it is presented there) somewhat difficult to understand. So, I still have not formed an idea about it. In fact, I somehow have a problem to really distinguish it from MWI.

What do you think of Consistent Histories? — boundless

Hard to understand is my current state of affairs. I don't get a clear statement about how it differs from the others.

From the SEP article on Consistent Histories, section 11.4:

"... This cannot lead to inconsistencies, a proposition being both true and false, because of the single framework rule. But it is contrary to a deeply rooted faith or intuition, shared by philosophers, physicists, and the proverbial man in the street, that at any point in time there is one and only one state of the universe which is “true”, and with which every true statement about the world must be consistent."

The man on the street, sure, but to philosophers and physicists who know their QM, that faith in there being an actual state of affairs is not very deeply rooted at all. Those roots were discarded a century ago. There are interpretations that support it and interpretations that do not. That this interpretation lists itself among the latter is hardly contrary to established belief. Yes, it seems a lot like MWI and I'd like to see a thing that spells out where the two differ in metaphysics, and not just terminology.

From a quick glance at the wiki chart, both have universal wave function, but only MWI considers that wave function to be real. MWI is deterministic and CHI is not, but it isn't clear from the linked article why not.

I have a problem with worlds of non-equal weights in MWI, and I'm not sure if the interpretation addresses that, or if CHI has a similar problem.

In which case, how does this address the 'observer problem'? The observer might occupy a particular reference frame, but without an observer, then what is being measured/observed? — Wayfarer

I think this was addressed to me. An observer occupies all reference frames, but is stationary in only one of them. Without an actual observer doing an act of observing, relative velocities of rocks and table lamps and such are still defined, just not noticed in any conscious way. You seem to continue the classic definition of 'observer' here rather than the one being described by, Rovelli was it?

None of this means I cannot collapse my own state in sufficient hindsight, which is sort of what I meant with my first reply to this issue. — noAxioms

Ah, ok! I see. S can have a 'partial knowledge' of its own state, but not complete. This makes sense.

I have a hard time keeping up with you guys :) — noAxioms

No worries!

This isn't the QM I know. There is no 'big difference' between the two cases. The cat is both dead and alive (superposition), not either dead or alive (result of an unobserved coin toss). The latter probability function is said expression of ignorace about how the coin toss turned out, but the probability function of the cat is not ignorance. It really is dead and alive until measured, else it could not interfere with itself. — noAxioms

Well, I think that you actually pointed to the 'big difference': quantum probabilities are not explainable in terms of ignorance :smile:

Maybe the colleague (Wigner's friend) changed that (being a conscious being that the cat apparently isn't), and that explains this assertion above. This I suppose cannot be disproved since there is no way to prevent the decoherence of something as classic as a human, but it also goes for the cat of course. They seem to allow the inconsistency of having a cat in superposition but not a lab assistant. — noAxioms

I see. Maybe I misunderstood.

But, I still believe instead that here for Wigner also his friend is in superposition. That's why I referred to Bitbol's take as a sort of middle ground between CI and RQM.

What does the measurement chain have to do with it? I shoot a photon through the slits and it makes a mark on the screen. That's a measurement even though it might be a minute before the operator bothers to look and learn of the result. The result is not being kept hidden in a box to prevent decoherence. If consciousness causes collapse, it doesn't imply that knowledge causes it. The conscious guy is in the room, ignorant of the result of the measurement, but nevertheless present. The collapse occurs because of that presence, no? If it is awareness, then I should be able to measure a thing but not take note of the result, and find the thing still in superposition later on. But that doesn't happen. It seems a falsification for the 'conscious knowledge' causing collapse idea. — noAxioms

This is a very good point and I'll think about it :smile:

So what? Only the table lamp is the privileged object for the table lamp. We are no more a natural end to the chain of reactions than is the table lamp. The reactions continue right on through us to affect other things. I have a hard time thinking of any causal chain that is initiated (rather than propagated) and cannot think of any that can end ever (per conservation of information). Radioactive decay might be an example of a new causal chain. Depends on interpretation. — noAxioms

Yes, that's the reasoning of RQM. According to RQM all physical systems are good 'end points'. Bitbol, however, notes that 'our' knowledge is always made from 'our' perspective. So, for 'us' there is a special 'end point': us. According to him, this reflects an intrinsic limitation of our knowledge: we cannot know, in principle, what is 'seen' from other perspective. The 'starting point' for our knowledge is lived experience. We cannot totally 'disregard' this and, therefore, we should not speak of how the world is 'for an experimental apparatus'. On the other hand, we can have knowledge of other human (at least) perspectives because they are qualitatively (very) akin to ours.

As you say, however, at the level of practice this does not make any difference. After all, in RQM it is still true that for 'our' perspective, 'we' are 'special'. And our knowledge is perspectival. In a 'Kantian-like' philosophy it is impossible to know 'things as they are' because phenomena (in our immediate experience) are conditioned by a-priori categories of our mind. So, for Bitbol, we can only be (almost) sure about our perspective.

Note however, that I do not believe that accepting a 'Kantian-like' philosophy requires that you have to choose a determinate interpretation of QM. (After all, Kant himself did not know QM)

Without a description of what constitutes that registration act then, I have no idea what he's talking about. — noAxioms

I believe that the registration act involves 'something' that is able to store information. E.g., a computer that stores '0' ('1') for spin 'up' ('down') when the spin of an electron is measured. But anyway, if one follows Rovelli in saying that everything can store information in that way, I believe that Wheeler's CI becomes RQM.

If CI is taken as an epistemological interpretation, I suppose this is true in a way, but it seems trivial to falsify. Alice (a simple device) measures the spin on one of an entangled pair, and prints the result of that measurement on a little paper that ejects face down on the table. Human Bob sees the paper but has gained no knowledge of the result, only knowledge that the measurement has taken place. He now measures the other particle of that pair and is is no longer in superposition. His lack of knowledge did not prevent the collapse of the wave function of his sample The device (Alice) has no knowledge since it retains no state of the incident after finishing its little printout. Does the unseen paper have the knowledge? It certainly contains the (hidden) information, but does it have 'knowledge'? If it does, why that anthropocentric choice of words? — noAxioms

Another excellent point. This in fact seems to go against Bitbol's interpretation. Maybe the 'counter-objection' is that when Bob sees the piece of paper at that point he knows that there is no superposition and, therefore, the situation is now more or less like the unseen coin. I don't know if this makes sense, though.

I agree that claiming that the piece of paper has knowledge is an anthropocentric choice.

Well, so do I, but my definition might be different than yours, so it isn't saying much. I will to be on the other side of these jail bars, so physics, deterministic or otherwise, very much does get in my way on that account, but few consider such restriction to be an example of lack of free will.

[But I am a bit unwilling to explain why I think so here... :smile:.]Agree, this would be too far off topic. There are always other threads about such things. — noAxioms

Agreed! I agree that 'free will' is not 'complete free-will'. But in my opinion, it is not just an 'effective free will' a la what's is required in Bell's theorem to avoid superdeterminism, for instance. I believe that we have some autonomy - our actions cannot be (entirely) explained via physical processes (after all, I believe that neither determinism nor randomness nor some combination of the two are compatible with a 'real free will'). But as you say, it is O.T. :smile:

Ok...Yes, I agree that inter-subjectivity and objectivity in the usual sense are different. What moral relativism denies, however, is that there are no universal ethical truths. — boundless

Double negative. It denies that there are universal ethical truths. I'm sure you meant that. — noAxioms

Yes, sorry.

Actually, I find that any particular rule is probably meaningless for most situations. 'Torture of babies is bad' has no application to the vast majority of things where 'torture' and 'babies' are both meaningless or at least poorly defined. Note my use of 'things' instead of the already restrictive word 'everybody' which detracts from the universality of the rule. A universal rule should not only apply to things that are member of 'everybody'. — noAxioms

Ok. I think I see what you mean. Ethical statements are contextual. If there were no human beings (or more generally 'sentient beings' if one accepts that there are non-human sentient beings and those beings have some kind of 'ethics'), there would probably be no ethical truths.

Same here. I don't necessarily deny objective morality, just playing devil's advocate. — noAxioms

Ok!

Don't understand your, um, misunderstanding. How can it exist unmeasured? I've not measured the 2nd even larger moon, so it doesn't exist, and that seems not a problem to you. Nobody can be on this Earth (can exist relative to me say) and not have measured the moon. We have an inter-subjective agreement about that. Similarly, if one has not measured the moon (or has measured that bigger one), then that person cannot establish any inter-subjective relationship with me. It would be a contradiction. — noAxioms

Yes, I agree that everybody on this Earth measure the Moon and, therefore, we all agree on its existence. But let's consider an alien who never measured it. Suppose that he visits our Solar System and 'measures' the Moon. So, at this point he agrees with us about the existence of the Moon. But before that, is it right to say that for him the Moon is simply non-existent?

The article says a complete measurement of ones self cannot be taken, not that you can't measure yourself. My pants size is a measurement of myself. :sad: — noAxioms

LOL. You are right! :smile:

I don't have a definition of S. It seems arbitrary. It is fairly easy to do for a human, but less so for other things. The ease of defining human X (and equating that definition to the same X at some other time) allows the existence of a legal identity of X. You can't do that with amoebas and flames. — noAxioms

Ok, I see. Good point!

Oddly, this point might be made by Bitbol himself. Since we cannot define S but it is very easy to define our own 'perspective', then it is not very natural to define the the perspective of a pen.

I think there are interactions between two electrons (like both being part of the same Helium) that ambiguates which one is which when one of the two changes state (like exits the atom). So yes, an electron departed, but it wasn't necessarily a particular electron. This is not a measurement thing. Of course there is no way to measure which one stayed and which one left. I'm just saying that metaphysically, it seems that electrons don't have identities, and thus act like a distinct 'system S'. — noAxioms

I think I agree!

Not sure if we're talking about the same thing here. Most of my relation with the electron is 'it is there', and relative to some other observer, it isn't there, or anywhere, just like the moon. To any two intersubective observers, they should agree on the electron being there or not, even if viewed from different frames. Isn't 'it is there' an invariant between said intersubjective perspectives? One says it is northbound and the other says eastbound, but both say it is there. That relation is not invariant between perspectives that are not intersubjective. — noAxioms

Right, I agree.

But I am not sure that we can say that the unobserved electron does not exist.

In other words, let O be an 'observer'. What is the ontological status of unobserved systems according to O? :smile:

We should if it is sentient. I just want to talk to an alien that reproduces by suddenly falling into two halves. There is so much stuff that we find intuitive only because we don't do that, and talking to such a being would drive out all those inbred biases in not just us, but the amoeba as well. It would learn from us. The flame is even worse, because two flames can merge into one. Even the amoeba can't do that. We may well be able to talk to the flame some day soon because any AI entity (say an intelligent virtual being) would benefit from working that way — noAxioms

:up:

Yeah, I actually agree with you that a (partial) understanding of other sentient beings. I was a bit joking. Wittgenstein was far too extreme. Language, culture etc are not such an insurmountable barrier.

Appreciate the good discussion. Been a while for me. — noAxioms

Ditto :wink:

In which case, how does this address the 'observer problem'? The observer might occupy a particular reference frame, but without an observer, then what is being measured/observed? I guess I will have to find time to go back and look at those resources that boundless provided in more detail. — Wayfarer

Well, according to Rovelli there is no 'observer problem' in the sense of CI. According to his interpretation, 'observer' is actually an excessively anthropomorphic expression to denote whatever physical system. Rovelli tries to do that in order to overcome the ambiguity present in CI about what an 'observer' is (in CI it is strictly speaking unspecified...).

But maybe even Rovelli's solution is problematic. After all (as it came up in my discussion with noAxioms) defining a 'physical system' is arbitrary. Let's take the example of the pen on my table. It can be argued that I can define my 'physical system' as both the pen and the 'pen + my table'. But also the 'pen tip' can define a 'physical system'. In other words, it might be argued that there is an undesirable explosion of the number of 'perspectives'. (Maybe it is more like an 'inelegance' rather than a problem, however...)

From some (most) perspectives, there is no 'it' to be an electron. To consider an electron is to have already assumed a perspective where it exists. It is a measurement already taken. — noAxioms

Sorry, I can understand this but only in part. But I am just not sure that this is satisfactory. I mean, according to RQM, measurement involves an interaction. Are you saying that according to RQM the measurement process 'creates' the 'electron' 'out of nothing'? (this is actually a problem that can be raised to any form of CI)

Hard to understand is my current state of affairs. I don't get a clear statement about how it differs from the others. — noAxioms

Ok, same here. As far as I understand it, the main difference between MWI and CH is that the universal wave-function is unreal and that CH is indeterministic (as you pointed out). My problem is with the first part, in fact. I think I'll have to re-read that article.

The man on the street, sure, but to philosophers and physicists who know their QM, that faith in there being an actual state of affairs is not very deeply rooted at all. Those roots were discarded a century ago. There are interpretations that support it and interpretations that do not. That this interpretation lists itself among the latter is hardly contrary to established belief. Yes, it seems a lot like MWI and I'd like to see a thing that spells out where the two differ in metaphysics, and not just terminology. — noAxioms

Agreed!

From a quick glance at the wiki chart, both have universal wave function, but only MWI considers that wave function to be real. MWI is deterministic and CHI is not, but it isn't clear from the linked article why not. — noAxioms

I believe that in CH is more or less like MWI + Born Rule. In MWI, all results are equally 'real'. In CH, apparently there is the additional axiom that a particular result is 'selected' with a probability given by the Born Rule. I just do not get the unreality of the universal wave-function. I can appreciate the philosophical reason behind considering it 'unreal' (i.e. do not consider unrealized experimental results as 'real') but IMO this makes somewhat questionable its introduction in the first place.

I have a problem with worlds of non-equal weights in MWI, and I'm not sure if the interpretation addresses that, or if CHI has a similar problem. — noAxioms

Well, yeah that is one of the problems of MWI. In the case of CH, it seems that 'histories' have non-equal weight and you consider only the 'history' that you observe as 'real'. Not sure that this is really tenable, though.

Ah, ok! I see. S can have a 'partial knowledge' of its own state, but not complete. This makes sense. — boundless

The article says that an external system can take this more 'full measurement' of some system, but not any system containing the system being measured. I don't understand this since Heisenberg's uncertainty says that even an external system can't do that. So they must mean something else when discussing the sort of information they expect from this 'self measurement'.

But, I still believe instead that here for Wigner also his friend is in superposition. That's why I referred to Bitbol's take as a sort of middle ground between CI and RQM.

Under any 'consciousness causes collapse' or other anthropocentric take, the friend, being conscious, cannot be in superposition. In any other interpretation, the friend very much can be.
The view cannot be falsified given that they've never put anything more complex than a barely visible dust mote in local superposition. Until they can put a human in a box, the interpretation remains valid.

Radioactive decay might be an example of a new causal chain. Depends on interpretation.
— noAxioms

Just thought of this: Per time symmetry, is there such a thing as radioactive un-decay, and would such an event constitute an end to a causal chain? If not, I don't think the decay can constitute an uncaused event.

According to RQM all physical systems are good 'end points'. Bitbol, however, notes that 'our' knowledge is always made from 'our' perspective. So, for 'us' there is a special 'end point': us. According to him, this reflects an intrinsic limitation of our knowledge: we cannot know, in principle, what is 'seen' from other perspective. The 'starting point' for our knowledge is lived experience. We cannot totally 'disregard' this and, therefore, we should not speak of how the world is 'for an experimental apparatus'. On the other hand, we can have knowledge of other human (at least) perspectives because they are qualitatively (very) akin to ours.

I have a hard time figuring out what Bitbol finds special about us. I am special to me, but everything has a relationship like that with itself. Another human ('us' but not 'me') measuring something gives me no more or less knowledge of that measurement than a dot on an unseen paper, and the wave function collapses either way. Wigner's friend just doesn't change that, so there is no 'us', just 'me', which is solipsism if you posit any QM significance to that.
Sorry. You can see I have little patience for anthropocentrism. I'm biased all to hell.

As you say, however, at the level of practice this does not make any difference. After all, in RQM it is still true that for 'our' perspective, 'we' are 'special'.

I see no such thing in any way that QM changed.

Without a description of what constitutes that registration act then, I have no idea what he's talking about.
— noAxioms
I believe that the registration act involves 'something' that is able to store information. E.g., a computer that stores '0' ('1') for spin 'up' ('down') when the spin of an electron is measured. But anyway, if one follows Rovelli in saying that everything can store information in that way, I believe that Wheeler's CI becomes RQM.

I was going to make Rovelli's point. If something changes state at all, it stores that information in its changed state. A prism is an example of something that sort of interacts with a photon without a state change (storage of the information). The photon is absorbed and immediately a new one is emitted in the same direction, leaving no state change to the prism and a change to the photon for the tiny delay in its journey. The prism does not store the information, and thus does not collapse the wave function of the photon. Objects that do change state don't seem to need to perform an act of registration to be affected like that, so that wording is still a bit unclear to me.

If CI is taken as an epistemological interpretation, I suppose this is true in a way, but it seems trivial to falsify. Alice (a simple device) measures the spin on one of an entangled pair, and prints the result of that measurement on a little paper that ejects face down on the table. Human Bob sees the paper but has gained no knowledge of the result, only knowledge that the measurement has taken place. He now measures the other particle of that pair and is is no longer in superposition. His lack of knowledge did not prevent the collapse of the wave function of his sample The device (Alice) has no knowledge since it retains no state of the incident after finishing its little printout. Does the unseen paper have the knowledge? It certainly contains the (hidden) information, but does it have 'knowledge'? If it does, why that anthropocentric choice of words?
— noAxioms

Another excellent point. This in fact seems to go against Bitbol's interpretation. Maybe the 'counter-objection' is that when Bob sees the piece of paper at that point he knows that there is no superposition and, therefore, the situation is now more or less like the unseen coin. I don't know if this makes sense, though.

Bob's knowledge of the paper means nothing: The device may have randomly declined to take a measurement and emit a blank paper. Bob can tell if it happened by measuring superposition or not. So the device taking the measurement, and not Bob's knowledge of that action is what collapses the wave function.

I agree that claiming that the piece of paper has knowledge is an anthropocentric choice.

Yes, I agree that everybody on this Earth measures the Moon and, therefore, we all agree on its existence. But let's consider an alien who never measured it. Suppose that he visits our Solar System and 'measures' the Moon. So, at this point he agrees with us about the existence of the Moon. But before that, is it right to say that for him the Moon is simply non-existent?

For the alien not to measure the moon, he'd have to put the moon (and everything else) in Schrodinger's box, which is best achieved by making a ship that is one, inside out. Zero information can penetrate from outside to inside the box. He opens the box randomly at some location which happens to be here, and there is some vast wave function of what he might find here that collapses quite improbably to us and our moon. Far more likely it collapses to empty space. Depend on from what distance he came, but it would have to be from over 5 billion light years away because the moon (or the whole solar system) needs to be unmeasured from the start. He'd have to come from a helluva longer distance to find no galaxy here. How far must I travel now to find a place where I have zero information about what is there? A lot further than the event horizon. It cannot be done. We see stuff that is 22 BLY away, which is not possible to reach ever. But the moon is young enough that it can be done.

But before that, is it right to say that for him the Moon is simply non-existent?

Before that there is no moon to be nonexistent. He can equally declare torrid-planet Vulcan to not exist. In both cases, he's just making stuff up.

Oddly, this point might be made by Bitbol himself. Since we cannot define S but it is very easy to define our own 'perspective', then it is not very natural to define the the perspective of a pen.

I don't follow. The perspective of the pen seems the same as that of a human being there. The pen just pays a lot less attention. I honestly give humans or any living thing no special regard in this topic.

I think there are interactions between two electrons (like both being part of the same Helium) that ambiguates which one is which when one of the two changes state (like exits the atom). So yes, an electron departed, but it wasn't necessarily a particular electron. This is not a measurement thing. Of course there is no way to measure which one stayed and which one left. I'm just saying that metaphysically, it seems that electrons don't have identities, and thus act like a distinct 'system S'.
— noAxioms
I think I agree!

Cool. Few agree with that. It is controversial.

But I am not sure that we can say that the unobserved electron does not exist.

Kind of hard not to observe an electron. Its state might be hidden if put in a box, but we put it there so we know its there. If not in the box, it interacts with other things and that makes it exist. I cannot escape that interaction.

In other words, let O be an 'observer'. What is the ontological status of unobserved systems according to O?

An unobserved system is in superposition of possible states that follow from the last observed state of the system. The real trick is how to go about not observing it for any length of time. Hence our alien showing up in an inside-out Schrodinger's space ship.

From some (most) perspectives, there is no 'it' to be an electron. To consider an electron is to have already assumed a perspective where it exists. It is a measurement already taken.
— noAxioms

Sorry, I can understand this but only in part. But I am just not sure that this is satisfactory. I mean, according to RQM, measurement involves an interaction. Are you saying that according to RQM the measurement process 'creates' the 'electron' 'out of nothing'? (this is actually a problem that can be raised to any form of CI) — boundless

Suppose you wanted to measure the diameter of a pizza. The way to do that is to put the pizza in front of you and hold a tape measure up to it, but the act of putting the pizza in front of you already performed the pizza/not-pizza measurement. I could in theory walk into a dark room, hold out the tape, have the lights turned on and hope by improbable chance that a pizza appears directly under that tape, but that is not likely to happen if I had zero knowledge of the presence of a pizza in that dark room.

So the electron is like that. Maybe I shot it and want to measure where it goes, or any other property of it, but to do that, I'm not taking a measurement of a random volume of space and hoping an electron appears in it. I probably already have a specific one in mind, meaning the measurement of its mere existence has already been done.

As far as I understand it, the main difference between MWI and CH is that the universal wave-function is unreal and that CH is indeterministic (as you pointed out). My problem is with the first part, in fact. I think I'll have to re-read that article.

I have more of a problem with MWI having a real wave function because it makes for a weighted reality of each of the worlds. One world seems to exist more than the other, but existence seems not to be anything but a True/False state. How cat X exist twice as hard as Y? So maybe CH resolves that problem for me.
I don't see why it needs to posit indeterminism or not.

I believe that in CH is more or less like MWI + Born Rule. In MWI, all results are equally 'real'.

Equally weighted then, but why do we find ourselves in a world where far more 'likely' collapses occur than the 'unlikely' ones? If all results are equally real, why are the probabilities of measuring those results unequal?

Well, yeah that is one of the problems of MWI.

In the case of CH, it seems that 'histories' have non-equal weight and you consider only the 'history' that you observe as 'real'. Not sure that this is really tenable, though.

Sounds like RQM. My history is real to me. My future is not, thus 'I' am defined as this endpoint event along with its history, plus an arbitrary designation of which events are 'me' and which ones are 'other stuff'. There's nothing in physics to make that designation.

Information preservation seems to prevent multiple histories from culminating in the same state

Isn’t that the very kind of question that the article in the OP addresses? That two observers observing what ought to be the same event each see something different? — Wayfarer

It depends, I think you keep reading it that an observer is required to be a human and measurement
is a form of conceptualisation. I also think you believe that conceptualisation is how a human consciousness intervenes in quantum processes. You also seem to argue for 'X exists requires that X is conceptualised' through a largely transcendental idealist perspective - even though the point you're seeking to demonstrate is much closer to subjective idealism, and you're using an empirically realist conception of scientific methodology to do all this.

This is a self reinforcing collection of equivocations. For example, one moment of it is that evidence for only humans being observers is read into the supporting articles you provide by your interpretation of the word 'subjective' being necessarily associated with consciousness. This is even rejected in the paper discussed by the OP (as well as all the other articles we've discussed).

Before we describe our experiment in which we test and indeed violate inequality (2), let us first clarify our notion of an observer. Formally, an observation is the act of extracting and storing information about an observed system. Accordingly, we define as observer any physical system that can extract information from another system by means of some interaction, and store that information in a physical memory. Such an observer can establish “facts”, to which we assign the value recorded in their memory. Notably, the formalism of quantum mechanics does not make a distinction between large (even conscious) and small physical system, which is sometimes referred to as universality. Hence, our definition covers human observers, as well as more commonly used nonconscious observers such as (classical or quantum) computers and other measurement devices—even the simplest possible ones, as long as they satisfy the above requirements.(not uniquely human - me)

We both agree on the data, I don't agree with your equivocations, and I don't agree with the strategy you use that paints me as disagreeing with the data (or that the arche-fossil argument is refuted through it) while substituting your idiosyncratic interpretation of the terms in the data for its results; all the while reserving a primordial realm of meaning for philosophical contemplation which isn't touched by the 'mechanistic', merely empirical, inquiry of science. Can't have it both ways.

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. — Wayfarer

What human beings and table lamps have in common is that they are substantial and have form. What RQM says is that that form is relative to the observer, not intrinsic, so a point-of-view is explicitly recognized.

But RQM also says that an observer is internal to the universe. As a consequence, RQM allows an observer to be part of a system that is itself being observed by another observer. That is the scenario that the Wigner's friend thought experiment presents.

But we don't need RQM in order to recognize that. We observe others in everyday life and they can observe us. The principle is the same.

The problem is that anything within that "system" needs to be interpreted according to standards before the system has any observational value. The "system" has no observational value without those human standards. — Metaphysician Undercover

Which is fine. The point is only that QM is an abstract theory about the mechanics of physical systems generally, regardless of the specific systems one is interested in modelling (which will include context-specific information).

Anyway, note that there is a problem of self-reference even in Relational approach(es). I suggest you to read section four of the SEP article about 'Relational Quantum Mechanics': https://plato.stanford.edu/entries/qm-relational/#SelRefSelMea . It is a discussion about the possibility of self-measurement. (Maybe Andrew M and @noAxioms will find it intriguing too!) — boundless

Yes, it alludes to the self-referential problems associated with predicting what oneself is going to do in the future. Fortunately, you can usually just choose!

Also, both she and Shimony are in fact clear that 'potentialities' for them are in some sense non-local. — boundless

Yes. Whereas, in my view, potential just means that the value has not been actualized yet for the observer (which would require a local interaction).

It's like the problem of non-referring sentences. The sentence "The King of France is wise" has a potential use but not an actual use until the appropriate physical conditions occur (i.e., a King of France is installed). As a consequence, you have to be careful about the logic applied to such statements.

Let me, however, ask you the same question that I asked to noAxioms.

Consider an electron. According to RQM, its state is 'perspective'-dependent. But all of them are in agreement that it is an 'electron'. So, is 'out there' something identifiable as an 'electron' even when is not measured? What I am saying is that it seems we need after all something invariant, equal to all perspectives. Is this compatible with RQM? :smile: — boundless

My own view is that there is a universal quantum state that is invariant, but RQM seems to reject that. Though perhaps another invariant is that we are all human beings with similar physical structures so we should always be able to agree that there are electrons and on the form of an electron.

Interestingly, it seems that RQM agrees with the Consistent Histories interpretation about the lack of a 'single history'.
...
Well, I really find this interpretation (at least as it is presented there) somewhat difficult to understand. So, I still have not formed an idea about it. In fact, I somehow have a problem to really distinguish it from MWI.

What do you think of Consistent Histories? — boundless

Basically the same as you. I think almost all of these views can end up looking like Many Worlds when you dig into them. It makes sense in a way since they all depend on unitary QM. Though I think RQM would say that a history can be indefinite rather than there being multiple histories.

Prior to that measurement, there is no collapse, so the wave function puts the photon on both paths, not on 'either' path. — noAxioms

The problem is that the above doesn't really make sense on a single-world interpretation, at least in my view. What I'm interested in is whether there is a way for the photon to travel on only one path but yet have physical interference still occur. And also while avoiding hidden variables.

One thought here is the idea of reflection. When Alice looks in the mirror and raises her left arm, it appears in the mirror that she is raising her right arm. Now Alice's action and her reflection are both the results of local physical processes. Bob, observing from afar, might receive light signals directly from Alice and indirectly via the mirror that end up superimposing for him, so it seems that Alice is raising both her left and right arms at the same time. That would be a physical interference effect. However when Bob and Alice interact, he discovers and they agree that she was raising her left arm.

Prior to that measurement, there is no collapse, so the wave function puts the photon on both paths, not on 'either' path.
— noAxioms

The problem is that the above doesn't really make sense on a single-world interpretation, at least in my view. What I'm interested in is whether there is a way for the photon to travel on only one path but yet have physical interference still occur. And also while avoiding hidden variables. — Andrew M

It makes perfect sense. The photon cannot take one path, unmeasured. That would be the counterfactual definiteness that any local interpretation denies.

One thought here is the idea of reflection. When Alice looks in the mirror and raises her left arm, it appears in the mirror that she is raising her right arm.

That's your brain interpreting it that way. The reflection very much still appears to raise the arm on the same side, but appears to have switched front to back. This doesn't seem to change the point you're making.

Now Alice's action and her reflection are both the results of local physical processes. Bob, observing from afar, might receive light signals directly from Alice and indirectly via the mirror that end up superimposing for him, so it seems that Alice is raising both her left and right arms at the same time.
That would be a physical interference effect.

I don't see that as superimposing or interference. Bob perhaps sees two images facing in different directions, but not one image facing in both directions. Bob cannot tell which is the reflection, and technically they're both images, modified by mirrors and lenses and such, so none of those images is Alice.

I didn't think my analogy was very good either. I like that we're both trying. I suspect there isn't a classic analogy.

The problem is that the definition of "observer' is not consistent with what the observer really is, in practise. The reference frame, which is supposed as the "observer", is inherently a human perspective. Any reference frame is. So to define "observer" in such a way that the observer might be something independent from a human perspective is to falsely define "observer", i.e. to define "observer" in a way which is inconsistent with what an observer really is in practise. — Metaphysician Undercover

"Observer" does seem to imply a studied separation or distance form what is observed, and that seems inappropriate in the context of lived experience. I don't know much about QM, but I have tended to think of reality as virtual or potential until the advent of experience, in the sense of underlying or providing the conditions for actual experience.

I have somewhat of a taste for Whitehead's notion of pan-experientialism; the idea that experience or relation appertains to all entities and is thus the 'substance' of reality. Another way Whitehead expresses this is with his notion of concrescence. So, it might be better to say that experience rather than observation collapses the wave function. Experience can be a very broad term even in ordinary usage: as when we say things like "The cliff face experienced the erosive effects of the wind and rain".

An observer is simply a scientist making the observation. It’s not specialised. The whole controversy is because of the requirement to consider the observer at all, because it threatens the notion of ‘mind-independence’. — Wayfarer

I can't see how the question of "mind-independence' really has anything to do with QM. If you want to say that 'having a perspective' is what collapses the wave function, and if to have a perspective is to be in relation, then in accordance with what I wrote above about the ubiquitous nature of experience it is fine to say that a particular cliff being eroded by the wind and rain has a unique particular perspective on the world. No other cliff erodes the way each cliff does.

I also think you believe that conceptualisation is how a human consciousness intervenes in quantum processes. You also seem to argue for 'X exists requires that X is conceptualised' through a largely transcendental idealist perspective - even though the point you're seeking to demonstrate is much closer to subjective idealism, and you're using an empirically realist conception of scientific methodology to do all this. — fdrake

I really believe that you don't see the problem. One of the things Bohr said, and it's a bona fide quotation, is that 'Anyone who is not shocked by quantum theory has not understood it.' And I don't think you see anything shocking about it - ergo ...

Another Bohr quote is that 'a thing does not exist until it's measured'. The Wheeler 'Law without Law' article draws on the same point, where it says 'a phenomenon is not a phenomenon until it has been brought to a close by an irreversible act of amplification'. OK, this might be a photographic plate or some other device, but in all cases, the act of measurement or observation is intrinsic to it.

we define as observer any physical system that can extract information from another system by means of some interaction, and store that information in a physical memory.

But look at the definition of 'device': "a thing made or adapted for a particular purpose, especially a piece of mechanical or electronic equipment". Devices are made by an observer, to complement or supplement the natural senses, and their operation and raison d'être are entirely dependent on the observer. And, as I noted already, 'data' does not become 'information' until it is interpreted in a context - until someone is informed by it. An automatic weather station contains only data, which do not become information until they're observed.

the point you're seeking to demonstrate is much closer to subjective idealism, and you're using an empirically realist conception of scientific methodology to do all this. — fdrake

Yes, quantum physics does suggest 'subjective idealism'. Hence the controversy! But that is not exactly news - Sir James Jeans and Arthur Eddington both wrote books on it between the wars ('the universe seems more a great mind than a great machine'). Paul Davies and other science writers have been commenting on it for decades - I read 'The Matter Myth' in, oh, about 1989.

All of the arguments that are being deployed here are specifically to avoid the implication of the role of the observer which seems the unavoidable inference. But many think it's solved, or that it's a non-problem, because of 'presumptive realism', which is that 'common sense simply insists that the Universe exists when we're not observing it. Everyone know this is true.' But this is precisely why Bohr said that 'quantum mechanics is shocking'. This is why Einstein felt compelled to ask the question about 'does the moon continue to exist when we're not looking at it?', and why Einstein and Bohr went on to debate the point for 30 years.

The initial philosophical problem has never been solved, it's simply been continually obfuscated. What I'm arguing is that there is an irreducible subjective element to all science and all observation, which is the constructive (in the Kantian sense) activities of the mind. 'Modern thought' believes that it has bracketed this out by arriving at a purely quantitative and completely impersonal description of the Universe - the so-called 'view from nowhere'. However physics shows us that even the view from nowhere is still a view, and that a view requires a viewer. But people would rather believe in an infinite number of parallel universes than face up to it.

What human beings and table lamps have in common is that they are substantial and have form. — Andrew M

And what they DON'T share is 'the ability to form a perspective'.