## Interpretations of Quantum Mechanics (is there a general consensus?)

 Quote by jambaugh ... reading further. Ah!, Ballentine is a realist! He wants to preserve reality ... near the end of p361 "...in contract the statistical interpretation considers the a particle to always be at some position in space, each position being realized with relative frequency $|\psi(r)|^2$ in an ensemble of similarly prepared experiments." I'll digest it and Ballentine's paper and get back to you.
Very perceptive. Yes indeed he is a realist, as am I. The ensemble interpretation is not a realist interpretation - it is strictly silent on it - you simply consider any observation as consisting of a preparation procedure then an observation with a very large number of preparations having the different possible observations associated with a preparation. You use the law of large numbers to ensure it is large enough so the proportion has reached a stable limit and what you observe is simply considered as selecting one of them. I hasten to add this does not make it a physical interpretation as someone tried to assert on philosophical grounds - that ensemble resides in one place only - the head of the theorist - the very large number you would need to guarantee the law of large numbers can not be replicated out there in reality.

The thing though with this interpretation is it whispers in your ear - there is more to this - there is some other factors at work that causes a particular element of that ensemble to be chosen and that would be a realist interpretation. Personally I believe some sub-quantum process does that (one candidate would be Primary State Diffusion advocated by Ian Percival although I don't think that's it - QM's secrets are probably not that easily won) but there are issues with the KS theorem that means that process is a theory that has QM as a limit but can't be QM. IMHO that's the reason Einstein liked it because he did not believe QM was fundamental - but Bohr did.

Anyway when you have finished it I would be really interested in what you think.

Oh - one thing I want to mention is I do not agree with Ballentine that other interpretations as bad as he makes out. I know Consistent Histories pretty well and a smattering of others - IMHO they all suck (including the Ensemble interpretation) in their own way and leave you dissatisfied - its just the way they suck is different for each interpretation. The way the Ensemble interpretation sucks is how does it chose the element from the ensemble - the way consistent histories sucks is it looks like you are defining you way out of the problem by saying you can't ask certain types of questions.

Thanks
Bill

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 Quote by Ken G Dense student: "So what is gravity exactly?" Professor: "Physics doesn't tell us that." Dense student: "I don't understand, isn't physics where we get the notion of gravity? Experiment, hypothesis, theory, that whole scientific method business? So why can't it tell us what gravity is exactly, if it is responsible for the word?" Professor: "Physics can tell us exactly what our approximate models are." Dense student: "So gravity is a collection of approximate models, that physics tells us exactly what each particular model is?" Professor: "Yes." Dense student: "So gravity is a construct of our minds?" Professor: "Um, well, er..."
I sorta follow this and yet I don't understand it. I mean there's a difference between unicorns and gravity. Unlike the former, "gravity" (the stuff/something that our model is refering to) affects rocks, humans, squirrels, planets, stars, galaxies, etc. I understand that our present model/theory of gravity is likely not final as we cannot foresee what a future theory of quantum gravity, etc. will be like, but our model is talking about some aspect of an observer independent reality; that is, the mathematical structure of the theory refers to or represents something that there is in the world independently of our theories.

 Quote by bohm2 I sorta follow this and yet I don't understand it. I mean there's a difference between unicorns and gravity. Unlike the former, "gravity" (the stuff/something that our model is refering to) affects rocks, humans, squirrels, planets, stars, galaxies, etc. I understand that our present model/theory of gravity is likely not final as we cannot foresee what a future theory of quantum gravity, etc. will be like, but our model is talking about some aspect of an observer independent reality; that is, the mathematical structure of the theory refers to or represents something that there is in the world independently of our theories.
I would say that Ken G considers the mind to be the fundamental framework that encompasses our reality and provides a logical limit to what we can know through science (how can we step outside of the mind to examine its scientific place in “something”?)

So theories do not tell us anything scientific about mind independent reality, rather they can only tell us about consistencies within mind dependent reality. But I believe Ken takes this further – that even the elementary observation that excludes any kind of cognitive analysis of a rock falling to the ground is a product of the mind, the event has no scientific place within mind independent reality only a philosophical one.

I agree with all of that, but I stop short of what seems to me to be a stance of radical idealism. I’m not at all sure that this is a philosophically satisfactory stance; certainly Bernard d’Espagnat (his book “Veiled Reality”) puts forward philosophical arguments that suggest there is an external “something” to phenomena than just constructs of the mind. In this sense I find intersubjective agreement to be perplexing in terms of radical idealism along with the notion that within this stance knowledge comes before existence.

But the basic statement of Ken that says, the only thing we will ever have in our reality in which to establish “knowledge” is the mind, is quite stark and surely true. There appears no means, even in principle, of stepping outside of our minds, ever.

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 Quote by bohm2 I sorta follow this and yet I don't understand it. I mean there's a difference between unicorns and gravity. Unlike the former, "gravity" (the stuff/something that our model is refering to) affects rocks, humans, squirrels, planets, stars, galaxies, etc. I understand that our present model/theory of gravity is likely not final as we cannot foresee what a future theory of quantum gravity, etc. will be like, but our model is talking about some aspect of an observer independent reality; that is, the mathematical structure of the theory refers to or represents something that there is in the world independently of our theories.
It sounds like your definition of gravity would be something like "whatever it is that exists independently of our theories that makes our theories work." I'm fine with that, but note that this is not the way gravity gets used in physics. Gravity, in physics, is not whatever makes the theories work, it's just the theories, period. This is demonstrable-- we never test what makes the theories work, we test the theories.

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 Quote by Len M So theories do not tell us anything scientific about mind independent reality, rather they can only tell us about consistencies within mind dependent reality.
Yes, I couldn't have said it better.
 But I believe Ken takes this further – that even the elementary observation that excludes any kind of cognitive analysis of a rock falling to the ground is a product of the mind, the event has no scientific place within mind independent reality only a philosophical one.
Yes, the "scientific place" is just what mind-dependent reality is, because the purpose of science is to replace (or represent) a mind-independent reality (if it is believed to exist) with a mind-dependent one (which is not a matter of belief, it is demonstrable).
 I agree with all of that, but I stop short of what seems to me to be a stance of radical idealism. I’m not at all sure that this is a philosophically satisfactory stance; certainly Bernard d’Espagnat (his book “Veiled Reality”) puts forward philosophical arguments that suggest there is an external “something” to phenomena than just constructs of the mind.
I actually have no issue with the philosophical stance that there is some reality "out there" that we are interacting with when we form the scientific image of mind-dependent reality. I just don't think it matters to science whether or not such a thing exists, and none of the language of science refers to it. The confusion that comes up is that invariably people ask, "so you think there was no universe out there before humans came along?", but to that I simply say "you cannot make any sense of the phrase 'before humans came along' until you think like a human. So yes, I do think there was a universe out there before humans came along, and the reason I think that is because I think like a human, and so clearly everything I am talking about is the universe that humans think about, not some mind-independent version for which I cannot even define the words I'm using."

 In this sense I find intersubjective agreement to be perplexing in terms of radical idealism along with the notion that within this stance knowledge comes before existence.
Yes, physics always leaves us with the question "why does this work at all?", including "why is there any such thing as objectivity or intersubjective agreement?" We don't know the answers to these, they might not even be questions that physics is capable of answering (just as no mathematical structure can be used to understand why its axioms are held to be true). I would say that all we can really say is that we know it does work, for what it works at, and we have no idea why, and even if we ever did get some idea why, it would not be a glimpse into mind-independent reality-- it would just be a deeper glimpse into mind-dependent reality, we would get some insight into how our minds work such that physics works, but we never escape the fact that all we get to know about reality is always the mind-dependent version. This is virtually tautologically true.
 But the basic statement of Ken that says, the only thing we will ever have in our reality in which to establish “knowledge” is the mind, is quite stark and surely true. There appears no means, even in principle, of stepping outside of our minds, ever.
Exactly the issue. So instead of bemoaning that we cannot step outside our minds, or pretend that we can, we should simply embrace this truth, stop claiming physics is something it never was, and start accepting what it really is-- as Bohr said, it is what we can say about nature (using our minds).
 I think what you both (Ken G and Len M) are saying is obvious, as I said in other thread about this. But the thing is that many people don't understand what you are saying at all. I have seen here people criticizing Ken G but showing that they did not understand what he is saying at all.

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 Quote by Ken G Exactly the issue. So instead of bemoaning that we cannot step outside our minds, or pretend that we can, we should simply embrace this truth, stop claiming physics is something it never was, and start accepting what it really is-- as Bohr said, it is what we can say about nature (using our minds).
I don't think a scientific realist will deny that our cognitive structures puts a limit on how we interpret the world and they do not deny the limitations of our mathematical models available to us to describe the world but I think there is disagreement with respect to this point below:
 However, it is important to recognise that there is a very obvious difficulty with the thought that what can be said provides a constitutive contribution to what can be real and that physics correspondingly concerns what we can say about nature. Simply reflect that some explanation needs to be given of where the relevant constraints on what can be said come from. Surely there could be no other source for these constraints than the way the world actually is-it can't merely be a matter of language. It is because of the unbending nature of the world that we find the need to move, for example, from classical to quantum physics; that we find the need to revise our theories in the face of recalcitrant experience. Zeilinger and Bohr (in the quotation above) would thus seem to be putting the cart before the horse, to at least some degree. Schematically, it's the way the world is (independently of our attempted description or systematisation of it) that determines what can usefully be said about it, and that ultimately determines what sets of concepts will prove most appropriate in our scientific theorising. It is failure to recognise this simple truth that accounts, I suggest, for the otherwise glaring nonsequitur in the proposed answer to Why the quantum?'...Of course, what statements can be made depends on what concepts we possess; and, trivially, in order to succeed in making a statement, one needs to obey the appropriate linguistic rules. But the point at issue is what can make one set of concepts more fit for our scientific theorising than another? For example, why do we have to replace commuting classical physical quantities with non-commuting quantum observables?
Information, Immaterialism, Instrumentalism: Old and New in Quantum Information
http://users.ox.ac.uk/~bras2317/iii_2.pdf

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 Quote by mattt I think what you both (Ken G and Len M) are saying is obvious, as I said in other thread about this. But the thing is that many people don't understand what you are saying at all. I have seen here people criticizing Ken G but showing that they did not understand what he is saying at all.
Yes, I think that's all true. The point itself is obvious, but its ramifications are not. Some complain about the point because they reject the ramifications, but it is often because they leap too far into thinking what it implies. Two examples are, the common claims that if all physics language is mind-dependent, then we shouldn't be able to talk about the universe before there were minds (we are only now making sense of what came before), or that we could not all agree on the laws if they weren't independent of us (we are all quite similar, so why wouldn't we agree on laws that come from how we look at things?). So it is the objections based on false ramifications that fall through, not the claims themselves.

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 Quote by bohm2 I don't think a scientific realist will deny that our cognitive structures puts a limit on how we interpret the world and they do not deny the limitations of our mathematical models available to us to describe the world but I think there is disagreement with respect to this point below:
That argument is a classic example of what I am talking about. They claim to be refuting the idea that physics is entirely 100% what we can say about nature and nothing more, even though it is, by saying that if physics wasn't about something else, it couldn't work. There is no basis for that argument at all. We have no idea why physics works, and hence we also have no idea when it wouldn't work.

 Quote by Vectronix Hi :) I recently read a book that states that most scientists believe the wave function represents a real field (i.e., one that possesses energy and momentum). I think this is part of the transactional interpretation of QM but not sure... can anyone confirm whether the book I read is right about this or not?
Afaik, the conventional/mainstream interpretation of QM is that it's a probabilty calculus. That is, it's a mathematical system designed to calculate the probabilities of instrumental results. It's not a description of reality. And doesn't necessarily inform wrt what's going on wrt the behavior in realms that aren't amenable to our normal sensory apprehension.

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 Quote by ThomasT Afaik, the conventional/mainstream interpretation of QM is that it's a probabilty calculus. That is, it's a mathematical system designed to calculate the probabilities of instrumental results. It's not a description of reality. And doesn't necessarily inform wrt what's going on wrt the behavior in realms that aren't amenable to our normal sensory apprehension.
What's more, the same statement can be made about all of physics-- there's nothing about quantum mechanics that makes it more true than it always was. Quantum mechanics is simply the place where we are forced to part with our illusions to the contrary. What gets me is, I simply don't see any reason why anyone would hesitate to see physics for exactly what it is, what it does, and what is demonstrable about it. From where comes the need for pretense it is something else? Do the equations work differently if we pretend they correspond to some reality that physics is probing, other than the reality that emerges when we use our minds and senses? What is mind-independent, or sensory-independent, about that interaction? What is mind-independent, or sensory-independent, about anything in physics at all?

What's more, I don't see it as some kind of "bitter pill" to recognize that physics is something we humans participate in. Indeed, quite the contrary-- I think it is quite freeing to recognize that, and I suspect it will be more and more important, going forward into future theories, to continue to bear this in mind. The naivete of the "fly on the wall" physicist is gone forever from our most fundamental theories, vive la difference.

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 Quote by Ken G What's more, the same statement can be made about all of physics-- there's nothing about quantum mechanics that makes it more true than it always was. Quantum mechanics is simply the place where we are forced to part with our illusions to the contrary. What gets me is, I simply don't see any reason why anyone would hesitate to see physics for exactly what it is, what it does, and what is demonstrable about it. From where comes the need for pretense it is something else? Do the equations work differently if we pretend they correspond to some reality that physics is probing, other than the reality that emerges when we use our minds and senses? What is mind-independent, or sensory-independent, about that interaction? What is mind-independent, or sensory-independent, about anything in physics at all? What's more, I don't see it as some kind of "bitter pill" to recognize that physics is something we humans participate in. Indeed, quite the contrary-- I think it is quite freeing to recognize that, and I suspect it will be more and more important, going forward into future theories, to continue to bear this in mind. The naivete of the "fly on the wall" physicist is gone forever from our most fundamental theories, vive la difference.
One (social) concern is to clearly make this point in a way that it cannot be confused by persons not appreciating the issues of the question, who would highjack the authority of science to rationalize their wish-fulfilling mystical beliefs. In short we don't want the magicians saying "See this proves ESP and 'mind over matter' "!!!!

Of course this is an absurd misinterpretation but there are no limits to human absurdity, e.g. http://www.churchofquantumconsciousness.com

 Quote by apeiron What's more, the same statement can be made about all of physics-- there's nothing about quantum mechanics that makes it more true than it always was. Quantum mechanics is simply the place where we are forced to part with our illusions to the contrary.
I hadn't ever thought of it like that. But it makes sense. Ie., due to QM we're forced to face the apparent fact that the mathematical theories aren't precisely corresponding to the qualitative characteristics of an underlying reality. And this goes for classical as well as quantum physics.

 Quote by apeiron What gets me is, I simply don't see any reason why anyone would hesitate to see physics for exactly what it is, what it does, and what is demonstrable about it. From where comes the need for pretense it is something else?
I suppose that's attributable to some scale/regime specific stuff that QM isn't designed to deal with. That is, human nature.

 Quote by jambaugh One (social) concern is to clearly make this point in a way that it cannot be confused by persons not appreciating the issues of the question, who would highjack the authority of science to rationalize their wish-fulfilling mystical beliefs. In short we don't want the magicians saying "See this proves ESP and 'mind over matter' "!!!! Of course this is an absurd misinterpretation but there are no limits to human absurdity, e.g. http://www.churchofquantumconsciousness.com
This is a good point also, imho. Because people do sometimes, quite incorrectly, misinterpret and adopt stuff from quantum theory to support their social agendas.

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 Quote by ThomasT I hadn't ever thought of it like that. But it makes sense. Ie., due to QM we're forced to face the apparent fact that the mathematical theories aren't precisely corresponding to the qualitative characteristics of an underlying reality. And this goes for classical as well as quantum physics.
By qualitative, I'm guessing here you mean intrinsic? If you are, I think I agree but was it any different in classical physics? I think an argument can be given that we were always ignorant of the intrinsic properties of matter. I think this is the point that Russell, Eddington and Stoljar, more recently, has argued; that is, physics can tell us only about the dispositional or relational properties of matter, but since dispositions ultimately require categorical properties as bases, and relations ultimately require intrinsic properties as relata, there must also be categorical or intrinsic properties about which physics is silent. Or so goes the argument. As Van Fraassen points out:
 If all the ‘observable’ (in the physicist’s sense) properties of an object can be represented in structural terms, then what is the nature of the ontological residuum?...If there is something to nature besides its structure, but structure is all that science describes or can describe, then what is that something, that undescribed and indescribable something...? But what sense does it make to try and conceive of structure that is not structure of something? Structure of nothing is nothing, isn’t that so?
Structuralism(s) about science: some common problems.
http://onlinelibrary.wiley.com/doi/1...07.00150.x/pdf

So our model of "electrons" presumably is not be based on any sort of direct access to the particle’s intrinsic nature, but rather must be based on information about the particle’s behavior, reflected in the overall configuration of the particles (Jeremy Butterfield). But I still don't think this necessitates an anti-realist view (e.g. that the world does not exist independently of the human mind). For example, chemical facts that were not necessitated by physical facts in the past turned out later to be frustrated by then unknown physical facts (e.g. unification of chemistry with physics didnt happen until the physics changed via quantum mechanics and then everything made more sense).

 Quote by jambaugh ... reading further. Ah!, Ballentine is a realist! He wants to preserve reality ... near the end of p361 "...in contract the statistical interpretation considers the a particle to always be at some position in space, each position being realized with relative frequency $|\psi(r)|^2$ in an ensemble of similarly prepared experiments."
Well, it seems to me that one of the points of Bell's analysis of the twin-particle version of the EPR experiment is that a realistic interpretation of that kind is not so easy to make coherent. In the case of position, you can consistently believe that a particle has a position at every moment, but you just don't know what it is. But in the case of spin, is it consistent to believe that the particle simultaneously has a spin in the x-direction, the y-direction and the z-direction, but you just don't know what it is? It seems to me that Bell's argument shows that it's not consistent to believe that (and also believe in locality).

 Quote by bohm2 By qualitative, I'm guessing here you mean intrinsic?
By qualitative I mean an apprehension of what's happening wrt our sensory capabilities (this is what understanding refers to). I'm not sure what intrinsic means.

 Quote by bohm2 If you are, I think I agree but was it any different in classical physics?
No, but it was the disparity between quantum experimental phenomena and the visualizability of the mathematics that accounted for it that made us realize that we really don't, and perhaps can't, maybe ever, have an accurate qualitative apprehension of the reality underlying instrumental behavior.

 Quote by bohm2 I think an argument can be given that we were always ignorant of the intrinsic properties of matter.
I don't think in terms of intrinsic properties of matter.

 Quote by bohm2 I think this is the point that Russell, Eddington and Stoljar, more recently, has argued; that is, physics can tell us only about the dispositional or relational properties of matter, but since dispositions ultimately require categorical properties as bases, and relations ultimately require intrinsic properties as relata, there must also be categorical or intrinsic properties about which physics is silent. Or so goes the argument. As Van Fraassen points out: Structuralism(s) about science: some common problems. http://onlinelibrary.wiley.com/doi/1...07.00150.x/pdf So our model of "electrons" presumably is not be based on any sort of direct access to the particle’s intrinsic nature, but rather must be based on information about the particle’s behavior, reflected in the overall configuration of the particles (Jeremy Butterfield). But I still don't think this necessitates an anti-realist view (e.g. that the world does not exist independently of the human mind). For example, chemical facts that were not necessitated by physical facts in the past turned out later to be frustrated by then unknown physical facts (e.g. unification of chemistry with physics didn`t happen until the physics changed via quantum mechanics and then everything made more sense).
I wouldn't say that thinking that the world exists independently of the human mind characterizes the realist view. It seems to me that all physical sciences, including quantum physics, assume that the world exists independently of the human mind. But standard quantum theory is certainly not realistic. Is it?