You haven't attempted to answer any of the question posed in the post you are responding to here. If you won't engage directly with what your co-discussants write, how can the discussion progress?
So, there's is not much incentive for me to make an effort to respond to the few allusions that what you wrote here consists in, when I have little confidence that you will respond in kind, and particularly considering that you apparently now intend to "log out" of the discussion.

The issue here is how to interpret the wave-function. If you interpret it as 'real' (or 'representational'), then you are right, there is no selection and the 'other branches' are still 'real' after the measurement.

If, instead, the wave-function is not treated as real/representational (as I think Rovelli does), it does not give a description of reality. — boundless

I have a rough time with this distinction. Something not real can still be used to describe a real thing. It just isn't the actual thing. I think more on the lines of what is more fundamental. So I exist, but I'm made of more fundamental matter. Matter exists, but the mathematics underneath seem more fundamental. Below that is what, law of form? None of this stuff 'is real' under RQM, but one part really does relate to others.

There is a single outcome given by a probabilistic law.

That doesn't follow from either interpretation of the wave function. It seems to require an additional postulate. A unreal wave function can still describe a multi-state system, and in fact must in order to describe superposition.

Everett was forced to reign in his views in order to gain acceptance. — noAxioms

Reign... Brain fart. :yikes:

I see. [Everett's] proposal was certainly revolutionary (regardless whether one agrees with him or not).

He was shunned by the physics community after his PHD and went into the defense industry instead, but was asked to present his work 5 years after the paper was published. Somewhere around that time DeWitt coined the MWI term from Everett's original "relative state formulation" which sounds an awful lot like RQM.

I say it isn't selected at all.
— noAxioms

If one sees the wave-function as real then there is no selection, I agree. Otherwise, there is a 'selection'.

That works given a postulate of such selection going on. My statement was an opinion, not an assertion.

RQM indeed does not claim anything about what path is taken. Any statement about the path taken (such as it taking one or the other) would be a counterfactual one, and RQM is not a counterfactual interpretation. — noAxioms

Yes, that's a good way to put it.

Right, that's the point, there are epistemic issues with "observations" no matter how you define the term. Sometimes the "observer" might be focused so as to miss many possibly relevant factors. In a human observer, this is one's attention. The person might observe with eyes and not ears, or vise versa, and miss some relevant information. In the case of an observing machine, its capabilities are limited by the intent of the design. — Metaphysician Undercover

Agreed. A human observer and an artifact will interact differently with their environment based on their physical characteristics. And no observer will pick up all the information available during an interaction. However since whether or not there is a hole in the dish is a physical characteristic then a subsequent observation could detect it (either because the human observer directs their attention to it or because the machine is modified to detect it).

Just a curiosity: has anyone ever suggested an interpretation where the 'universal wavefunction' is real (like in MWI) and a single branch is 'selected' by a probabilistic rule (as in Consistent Histories as I understand it)?

This would be similar to the 'unreal' interpretation of MWI referenced in the Wikipedia article about MWI where only one branch is 'real' and the others are not. The only difference is that here there is an explicit axiom of a probabilistic selection. — boundless

It seems that some objective collapse interpretations might fit the bill:

On the other hand, it is shown that dynamical collapse models, of the type originally proposed by Ghirardi-Rimini-Weber, can be re-interpreted as set selection criteria within a quantum histories framework, in which context they appear as candidate solutions to the set selection problem. — Quantum Histories - Adrian Kent

Agreed. A human observer and an artifact will interact differently with their environment based on their physical characteristics. And no observer will pick up all the information available during an interaction. However since whether or not there is a hole in the dish is a physical characteristic then a subsequent observation could detect it (either because the human observer directs their attention to it or because the machine is modified to detect it). — Andrew M

The problem is that in QM we are dealing with the boundaries of "physical characteristics". If having "physical characteristics" is defined as having spatial-temporal presence, then special relativity places electromagnetic energy (light) as the boundary of physical existence. Now we cannot talk about the physical characteristics of the boundary of physical existence. The spatial-temporal presence of light (physical properties) is nonsensical in the context of relativity, that's why it's like a wave (physical property) without an ether.

So, back to the analogy. The dish in this instance, now the boundary, has no physical characteristics. What type of observation could be used to detect holes in the "dish", which has no physical properties? What is necessary is to either release the confines of special relativity, allowing light to have physical properties, and describe those properties, or devise a way of observing non-physical properties.

The quarry - atomic particles in this case - were found not to have an independent reality, and they were supposed to be the fundamental building blocks of nature. — Wayfarer

Just because something has an indeterminate state from an epistomological point, up to when it's observed, does not mean it does not exist "independently". (Also, quantum particles, not atomic). You're confused about the implications of QM experimental results if you think a particle requires an observer to exist. It's a shitty article with an even shittier headline.

Is a particle really there when there's no one to observe it? Yes, otherwise experimental physicists would be out of a job or wouldn't bother to share the results with us.

Or as Dustin Lazarovici reacted to the paper: "A group of physicists claims to have found experimental evidence that there are no objective facts observed in quantum experiments. For some reason, they have still chosen to share the observations from their quantum experiment with the outside world.

...

In particular, it doesn’t mean that measurement outcomes, once obtained, are not objective. It rather reminds us that a measurement is not a purely passive perception but an active interaction that “brings about” a particular outcome and can affect the state of the measured system in the process."

Basically, the only way we would have to let go the assumption of an objective reality is if we were to insist on locality (against this and other experimental results) in which case nothing really exists but thank God it's local! (pace Tim Maudlin)

Also, quantum particles, not atomic — Benkei

Could you explain the difference?

Just because something has an indeterminate state from an epistomological point, up to when it's observed, does not mean it does not exist "independently". ( — Benkei

What do you mean "from an epistomological point up to when it's observed"?

Are you saying the particles have location and momentum and so forth prior to observation, it's just that the information is unavailable to us?

If so, does that quantum theory have a name? What is it?

What is an indeterminate state from an epistemilogical point of view?

What does that mean?

I'm no expert on this matter as an English language understanding can only get you so far without an understanding of the underlying mathematics (which I do not understand at all) but I'm not going to preface everything with "as far as I know" as that is now a given. I might state something with conviction and it might be wrong but I'm sure that will be picked up by more knowledgeable posters. That said, I'd answer your questions as follows.

Quantum particles are even smaller, aka subatomic particles, and not properly described as particles but that's language for you.

What do you mean "from an epistomological point up to when it's observed"? — frank

An electron orbiting a nucleus is in a superposition around it. It doesn't come into existence because of a quantum measurement establishing its position, it has a position independent of the measurement that we cannot predict but we can probabilistically describe it. Hence we know we do not have to put a measuring device on the moon to establish the position of an electron for an atom in a lab in San Francisco. Epistomologically its position was indeterminate until we measured it.

Are you saying the particles have location and momentum and so forth prior to observation, it's just that the information is unavailable to us? — frank

I'm saying that wave function collapse is a matter of knowledge. The information isn't entirely unavailable to us, we know it has location and momentum and we know the possible states, we just don't know which one until we measure.

If so, does that quantum theory have a name? What is it? — frank

I'm confused by this as I'm under the impression I'm describing something the various theories agree on.

I'm starting to think you're not just asking questions to get to know more. And the line of questioning feels like there's an underlying reason to it. Is my use of language at issue here?

I'm saying that wave function collapse is a matter of knowledge. — Benkei

There are a lot of quantum theories. Some involve a wave function collapse, some don't. The ones that do usually say that it's not appropriate to talk about location prior to the collapse. Waves don't have specific locations the way particles do.

It's definitely not a matter of knowledge.

Is a particle really there when there's no one to observe it? Yes, otherwise experimental physicists would be out of a job or wouldn't bother to share the results with us. — Benkei

You're not seeing the problem, again. You're simply asserting that it isn't real.

The attitude of the Copenhagen group is pretty succinct on this: the particle doesn't exist until it's measured. That's the whole problem in a nutshell. Asking 'where is it' or 'what is it' before it's been measured is pointless, because all there is, is probabilities. It's not as if it's there somewhere waiting to be discovered. It's described by the wave function (hence the talk of it being 'smeared out'.)

Almost everyone assumes that there is a real, objective atomic particle which is there whether you observe it or not. But if you read the account of the debates between Einstein-Bohr-Heisenberg and others, this is precisely what is at issue. Bohr explicitly questions whether atoms exist (in any sense other than an explanatory model.) As I've said, this is why Einstein asked (in an exasperated way) 'doesn't the moon continue to exist when we're not looking at it?'

The answer seems obvious, because humans have only been around for less than a million years and the moon is demonstrably millions of years older than that. So it seems an absurd question, asked for polemical reasons, to elicit the answer 'of course it is!' But the question still had to be asked! And again if you read the accounts of the debates in the 20's and 30's, the answer is not nearly so clear-cut as common sense entails. This is why it is a 'revolution' (not that you would know from many of the comments here.)

I think this is why this issue elicits such a heated response. It's because we have a temperamental attachment to the reality of the domain of sensory perception, what is demonstrably and measurably 'out there'. (Isn't that shorthand for what we think is real? 'Out there somewhere'?) After all this is one of the implications of empiricism - that only what can be validated against sensory perception (augmented by scientific instruments) is real. But quantum theory challenges that, precisely because the elements examined by physics have a kind of ambiguous existence. They do not really exist, but they're not non-existent.

Heisenberg wrote in his well-known 1958 book Physics and Philosophy. “It [quantum physics] introduced something standing in the middle between the idea of an event and the actual event, a strange kind of physical reality just in the middle between possibility and reality.”

In their paper, titled “Taking Heisenberg’s Potentia Seriously,” Ruth Kastner and colleagues elaborate on this idea, drawing a parallel to the philosophy of René Descartes. Descartes, in the 17th century, proposed a strict division between material and mental “substance.” Material stuff (res extensa, or extended things) existed entirely independently of mental reality (res cogitans, things that think) except in the brain’s pineal gland. There res cogitans could influence the body. Modern science has, of course, rejected res cogitans: The material world is all that reality requires. Mental activity is the outcome of material processes, such as electrical impulses and biochemical interactions.

Kastner and colleagues also reject Descartes’ res cogitans. But they think reality should not be restricted to res extensa; rather it should be complemented by “res potentia” — in particular, quantum res potentia, not just any old list of possibilities. Quantum potentia can be quantitatively defined; a quantum measurement will, with certainty, always produce one of the possibilities it describes. In the large-scale world, all sorts of possibilities can be imagined (Browns win Super Bowl, Indians win 22 straight games) which may or may not ever come to pass.

If quantum potentia are in some sense real, Kastner and colleagues say, then the mysterious weirdness of quantum mechanics becomes instantly explicable. You just have to realize that changes in actual things reset the list of potential things. 1

.

But I would take issue with this in one particular. Again, it's the role that the act of measurement plays in eliciting a response, which discovers 'the electron' in a particular position. That can be seen as the role of the observer. As Bohr says, this 'seeing' might take place via an instrument or device, but the act of observation is central to it. It 'makes manifest' something which is only 'potentially existent'. And that is arguably the doing of 'res cogitans' (although it not and can never be an object of cognition, for which see Bitbol.)

There are schools of philosophy that accomodate this attitude quite comfortably, although they're usually denigrated on this forum as 'idealist'.

That's only a realism-- the presence of a distinct entity measured at that instance-- it doesn't suppose anything about the rest of reality, particularly unobserved instances which might be present.

Your whole approach of trying to use the appearance experience as a measure of which things can be aid to exist does not work for unobserved presence-- in that situation, we cannot use a standard of observation or not precisely because the state in question is not object to observation.

If we are to propose an unobserved quantum events, atom, person, universe, etc., are knowledge of must be given without observation of it, for our concepts are referring to the unobserved instance in that case. As such, we cannot use our observations to dismiss those instances because they are states present prior to our act of measurement. The addition of us and any measurement device changes what we are dealing with, an instance of an unobserved object to an observed one.

The reason you are degraded as "idealist" is because you are taking exactly the opposite conclusion about the limits of our observation. You try to use it as a measure of things we have not observed: an oxymoron if there ever was one.

When we are dealing with unobserved events, we are dealing with what we haven't seen. A question not of empirical observation of an instance, but a conceptual grasp of something we've not yet seen or measured, much like correctly imagining who is standing behind you in a room, even though you haven't looked or made any other empirical observation of who it is.

You're making the same mistake Benkei did.

The Copenhagen interpretation says that prior to measurement, stuff doesnt have the properties we associate with particles.

I was just talking about Wayfarer's metaphysical error.

There is nothing wrong with suggesting instances of things we don't obsevre have the same properties as instances we do. Indeed, this is how we make commentary on things we don't observe with descriptions like those we have: the unobserved stuff behaves similarly.

But Wayfarer won't get this point until he stops equating things of the world with our experiences and our knowledge of things with empirical observation-- it amuses he complains so much about "scientism," when his own position reduces knowledge of things to purely when they are empirically observed.

Well, but we weren't talking about common sense. We were talking about quantum theory.

The ones that do usually say that it's not appropriate to talk about location prior to the collapse. Waves don't have specific locations the way particles do. — frank

But they all do. The particle is somewhere within the range of possibilities provided by the probability field. It is true that by measuring position the thing measured behaves as a particle and not a wave for that measurement but this is a result of it really being neither a wave nor a particle and a limit of language.

You're not seeing the problem, again. You're simply asserting that it isn't real. — Wayfarer

This is my first reply with a position. I asked a question previously so that seems an odd start is your reply.

They do not really exist, but they're not non-existent. — Wayfarer

This just violates the law of non-contradiction.

Why measure for position to begin with if the theory does not predict it will be there? They all, even the Copenhagen interpretation, assume when measuring position it will return a result.

It's definitely not a matter of knowledge. — frank

Heisenberg agreed with me by the way, which is why he uses the term reduction and not collapse.

I asked a question previously so that seems an odd start is your reply. — Benkei

You asked a question - and then answered it yourself, in the affirmative. ‘Is the particle there when there’s nobody there to observe it?’ is the crux of the problem. So just casually saying ‘yes it is’ indicates you’re not seeing what the issue is - because that is the issue.

They do not really exist, but they're not non-existent.
— Wayfarer

This just violates the law of non-contradiction. — Benkei

That's kind of the point! See the beginning of the forward to Heisenberg’s Philosophy and Physics which specifically mentions Heisenberg's re-introduction of 'potentia' into physics (as per the quote in my earlier post). One interpretation is that this implies there are 'degrees of reality', that what is being predicted by the 'wave function' is a pattern of probabilities, but the probabilities don't pertain to some individual thing which might or might not be there. It's pure potentiality.

It's worth having a read of Heisenberg's 'Debate between Plato and Democritus', given as a conference keynote speech. In that, he talks about the meaning of the word 'exists' in relation to sub-atomic particles:

This difficulty relates to the question whether the smallest units are ordinary physical objects, whether they exist in the same way as stones or flowers. Here, the development of quantum theory some forty years ago has created a complete change in the situation. The mathematically formulated laws of quantum theory show clearly that our ordinary intuitive concepts cannot be unambiguously applied to the smallest particles. All the words or concepts we use to describe ordinary physical objects, such as position, velocity, color, size, and so on, become indefinite and problematic if we try to use then of elementary particles. I cannot enter here into the details of this problem, which has been discussed so frequently in recent years. But it is important to realize that, while the behavior of the smallest particles cannot be unambiguously described in ordinary language, the language of mathematics is still adequate for a clear-cut account of what is going on.

I think the suggestion that sub-atomic particles don't exist 'in the same way' as stones and flowers is pretty significant - because we would generally assume that something either exists or it doesn't, don't we? Democritus certainly thought so: atoms 1, void 0.

The particle is somewhere within the range of possibilities provided by the probability field. — Benkei

But it's not, otherwise, again, there would be no problem.

Why measure for position to begin with if the theory does not predict it will be there? They all, even the Copenhagen interpretation, assume when measuring position it will return a result. — Benkei

It predicts according to statistical probabilities, very accurately. But according to the Copenhagen stance, you can't go behind the observations and say anything about what is really there; you can't assume that there is a real X apart from the observation. (This is why Bohr is sometimes (incorrectly) said to be positivist.)

Heisenberg agreed with me by the way, which is why he uses the term reduction and not collapse. — Benkei

We may be having a translation problem, but it sounds like you're saying that superposition can be understood as a classical physical state, the particulars of which are only known to us by probability.

If that's what you're saying, you're wrong, but you have a mind-bending journey ahead of you in discovering how bizarre quantum theories really are. I envy you.

We may be having a translation problem, but it sounds like you're saying that superposition can be understood as a classical physical state, the particulars of which are only known to us by probability. — frank

Not what I meant. The probability describes the possible outcomes of measurement not that at any given moment before measurement it is accurate to say it has a singular position that we just don't know and will discover through measurement. The measurement just brings out a specific property of the object at the expense of all other possible properties "disappearing".

Which object would that be?

Not what I meant. The probability describes the possible outcomes of measurement not that at any given moment before measurement it is accurate to say it has a singular position that we just don't know and will discover through measurement. The measurement just brings out a specific property of the object at the expense of all other possible properties "disappearing". — Benkei

Yeah, that's true. So your point was that measurement doesn't create anything. It just brings about an alteration. Therefore we shouldn't think of quantum experiments as undermining objectivity.

I agree. Although there is a sense (or two) of "objectivity" that is damaged by quantum experiment and quantum theory.

But they all do. The particle is somewhere within the range of possibilities provided by the probability field. It is true that by measuring position the thing measured behaves as a particle and not a wave for that measurement but this is a result of it really being neither a wave nor a particle and a limit of language. — Benkei

It's not a limit of language, it's a limit of the principles employed toward understanding the thing. In other words, if the thing cannot be understood, it is because inadequate principles are being employed toward understanding it. Language doesn't have limits in that way. We just make up new words for new things, physicists have no problem making up new words. When you're talking about a thing which you cannot identify (point to), it's very hard to describe that thing. This is not a limit of language, because the thing (just like imaginary things) can be named. Its a limit of the method of observation.

Which object would that be? — Wayfarer

So you aren't suggesting that measurement creates something ex nihilo, You're just saying it creates the type of thing we usually think of as a physical object in the same way an artist creates a statue out of clay. And to the extent that an objective view is populated with regular stuff that does not shift or change by virtue of being measured, quantum theory screws up what we usually think of as objectivity.

Is that true?

You're just saying it creates the type of thing we usually think of as a physical object in the same way an artist creates a statue out of clay. — frank

Sort of. Wheeler uses the metaphor of paper mache. In any case there isn’t ‘a particle’ lurking there undetected. What is there, is a distribution of possibilities - degrees of potential existence, you might say. Measurement or observation then ‘collapses’ the domain of possibilities - hence the ‘wave-function collapse’. Realists.couldn’t accept that, because they naturally assumed that there had to a real object. But this is why Bohr said of such things that ‘they don’t exist until they’re measured’. That’s the basis of the controversy as laid out in Manjit Kumar's book Quantum.

It all hinges on the fact that, for scientific realism, ‘real’ means ‘mind-independent’. That is what has been called into question, and it’s clear from this thread that it’s a very controversial issue.

It all hinges on the fact that, for scientific realism, ‘real’ means ‘mind-independent’. That is what has been called into question, and it’s clear from this thread that it’s a very controversial issue. — Wayfarer

Quantum physics doesn't give a subjective idealist any leverage. It might have seemed so early on, but not anymore.

What is necessary is to either release the confines of special relativity, allowing light to have physical properties, and describe those properties, or devise a way of observing non-physical properties. — Metaphysician Undercover

There is no implication of non-physical properties. In QM, light quanta (photons) have physical properties. And QM is consistent with special relativity.