The typical and the exceptional in physics

[ddd123]

But we have to talk about ontology, because it's everywhere. etc

Well, quantum suicide isn't science because you can't publish your results!

If you want to talk people out of suicide it's great but it isn't science, it's social aid. Or, more to the point, what you're talking about is philosophy. In that context I start talking about ontology and discussing this topic in much more detail than this. But concerning hard science I stop at what I've said above.

I am saying that religion is the proper sphere for ontology whenever the ontology is taken seriously

No, philosophy is.

 

[Ken G]

No, philosophy is.

Fair enough, but it is not important to me to parse between religion and philosophy, it is only important to parse between science and non-science. The crux of my argument is that science is always pure epistemology, and taking an ontology seriously is always a brand of philosophy that is not science. I mentioned religion purely as an example that most people would agree is not science, but if that example raises flags, ignore it-- the important point is that we leave science when we do ontology (in the serious sense, not the sense of "picture this to help you understand"). What is so ironic about this point is that it is popular to characterize science as a path to arrive at ontology! That's wrong, and I don't think the history of science could possibly be much clearer on that.

 

[ddd123]

Fair enough, but it is not important to me to parse between religion and philosophy, it is only important to parse between science and non-science. The crux of my argument is that science is always pure epistemology, and taking an ontology seriously is always a brand of philosophy that is not science. I mentioned religion purely as an example that most people would agree is not science, but if that example raises flags, ignore it-- the important point is that we leave science when we do ontology (in the serious sense, not the sense of "picture this to help you understand"). What is so ironic about this point is that it is popular to characterize science as a path to arrive at ontology! That's wrong, and I don't think the history of science could possibly be much clearer on that.

Well, this I think as well, but I don't want to impose my view on science, if anything because some ideas may come to you only if you really believe in them.

But I cannot argue on this because I'm not a proponent of ontology, and it would be awkward to take that side. A pro-ontology user should answer you on this.

 

[Simon Phoenix]

Epistemic means how your mind interacts with its stimulus

That's not how I understand the onto/epi distinction within the context of physics. An ontic state is one that has some objective existence in the world - as Matt Leifer puts it if all the conscious beings in the world suddenly vanished an ontic state would still exist. An epistemic state is one that describes our current knowledge of a system; it is not something that exists in the external physical world.

So when we talk of a phase space point in classical physics this is an ontic state - it's a description that assumes a given particle has a specified position and momentum. If we suddenly ceased to exist those particles would still have a position and a momentum in this perspective.

In QM the ontic/epi argument is really about whether the wavefunction is one of these ontic states - or put more crudely "is the wavefunction real?" or is it just some mathematical device that encodes our knowledge? If we ceased to exist would objects still be 'in' quantum states?

If we hadn't needed QM to actually describe physical processes (in an ontic or epistemic fashion, whichever takes your fancy) then we wouldn't even be having this discussion since it's clear that classical physics deals with ontic states - or assigns probabilities to those states.

If you're going to suggest that the phase space point (p,q) of classical physics is an example of an epistemic state, then we'll just have to agree to disagree :-)

 

[Ken G]

That's not how I understand the onto/epi distinction within the context of physics. An ontic state is one that has some objective existence in the world - as Matt Leifer puts it if all the conscious beings in the world suddenly vanished an ontic state would still exist. An epistemic state is one that describes our current knowledge of a system; it is not something that exists in the external physical world.

What I mean by how the mind reacts to stimulus is the internal experience of having knowledge of that stimulus. I don't mean how someone else would invoke ontological pictures to be able to get an epistemic understanding of how my mind reacts to stimulus, I mean how my mind experiences stimulus. This is the whole point of the "collapse" in QT-- you never have any collapse until you look at how the mind experiences the sensation of a given experimental outcome. The origin of collapse is someone saying "hey, how come I got a single outcome from a theory that talks about a mixed state of outcomes?" You never get that at all until you include the experience of a single outcome.

So when we talk of a phase space point in classical physics this is an ontic state - it's a description that assumes a given particle has a specified position and momentum.

Not necessarily. A phase space can easily be turned into an epistemic tool, you simply say "let us treat this system as though it were a point in an abstract space with the following intellectual properties". The properties are then properties of the epistemology, not properties of the system. That subtle transformation completely escapes all the ontological quagmires of various interpretations of both classical and quantum physics, in one fell swoop.

If we suddenly ceased to exist those particles would still have a position and a momentum in this perspective.

Not in the way I just framed it-- yet I lost nothing in my power to do physics, I merely escaped making an assumption I never needed and never used (that the abstract space corresponded to something that would continue to exist if no mind conceived of it).

In QM the ontic/epi argument is really about whether the wavefunction is one of these ontic states - or put more crudely "is the wavefunction real?" or is it just some mathematical device that encodes our knowledge? If we ceased to exist would objects still be 'in' quantum states?

Yes, precisely. Notice how silly the entire question becomes if you simply stir in a dose of skepticism that quantum mechanics won't be replaced in a few hundred years by something almost completely different, as is the typical pattern in science.

If you're going to suggest that the phase space point (p,q) of classical physics is an example of an epistemic state, then we'll just have to agree to disagree :-)

Saying that it either is or isn't is ontological thinking. Saying that we can regard it either way is epistemic thinking. The latter is clearly correct though-- we clearly can regard a phase space as either an ontological or an epistemic entity, just like with a wavefunction! I'm saying you get all the problems one way, that you don't get the other way.

 

[secur]

In QM the ontic/epi argument is really about whether the wavefunction is one of these ontic states - or put more crudely "is the wavefunction real?" or is it just some mathematical device that encodes our knowledge? If we ceased to exist would objects still be 'in' quantum states?

To be careful, instead of "wavefunction" we should say "something corresponding to the wavefunction, which is basically equivalent to it". Otherwise hair-splitters will deny wavefunction and talk instead of Hermitian operators, or Bohmian beables, or whatever. The point (I believe) you want to make is: the ontic/epi argument asks whether "something basically equivalent to" the wavefunction must be ontic.

By the way,

I was walking across the golf course the other day and then suddenly this golf ball hit me right between the eyes. My doctor told me not to worry about the huge lump on my forehead as it was only epistemic

No doubt the doctor actually said it was only epidermic, i.e. didn't break the skin. But when you replied "Of course, nothing is real. No lump, no golf ball, no doctor. Only quantitative measurement!" he realized the brain damage was a lot worse than he thought :-)

 

[Simon Phoenix]

Notice how silly the entire question becomes if you simply stir in a dose of skepticism that quantum mechanics won't be replaced in a few hundred years by something almost completely different, as is the typical pattern in science.

Yes - but the question is really whether there is anything about the structure of QM that forces us to ascribe an ontic character to the state (and that's independent of whether QM is replaced some way down the line) - but if you don't accept that the phase space point (p,q) of classical physics is an ontic state - then the whole discussion is somewhat irrelevant, because that's an example of what the quantum foundation people mean when they use the term 'ontic state'. If you think that the whole concept of an 'ontic state' can be transformed using your terminology into an 'epistemic state' then you're probably wondering what on Earth all these foundation people are wasting their time on :-)

What we're looking for is some kind of theorem that can settle the issue (or at least bound things) with the same kind of power and clarity that Bell used in his assassination of locally realistic hidden variable theories. And in the context of this discussion, Bell's treatment using hidden variables would definitely be described as an ontological model.

 

[ddd123]

but if you don't accept that the phase space point (p,q) of classical physics is an ontic state - then the whole discussion is somewhat irrelevant, because that's an example of what the quantum foundation people mean when they use the term 'ontic state'. If you think that the whole concept of an 'ontic state' can be transformed using your terminology into an 'epistemic state' then you're probably wondering what on Earth all these foundation people are wasting their time on :-)

I have explained this earlier:

When, for example, we talk about falsification, or even more radically, like in this thread, about ontic vs. epistemic interpretations, we are using concepts directly borrowed from philosophy which come with a baggage that isn't necessarily carried along with them properly across the border.

Ontic and epistemic are concepts borrowed from philosophy, possibly without understanding philosophy: this can be an issue. They lose their originary meaning.

Ken G is using "ontic" in the philosophical sense, not in the foundations of physics sense. If he is onto something, it means that the assumption behind all these talks, that there is a distinction between epistemic and ontic states in physics, is void, and thus also the discussions and theorems are based upon a meaningless premise.

The basic philosophical idea is that our senses are turned by our brain into intelligible experience as a representation, which not necessarily (and most likely not) corresponds to "what is out there". A point in space is an idea within our minds: space itself is an idea within our minds. What is out there, if there is such a thing at all, is outside the scope of our mind's objectification, it's intangible. So, for Ken G, devising this strange distinction within our minds of "what's really there" vs "a mental picture of what's really there" is kind of absurd. My answer to him is that, subtly, he's still trying to rein in science in a way that's not proved is justified, if the scope is advancing in science, developing new and successful theories: maybe such an absurdity works in that sense. Let me post an illustration from the official site of the 2df Galaxy Redshift Survey experiment, which shows that also scientists can be aware of this issue:

 

[secur]

@Ken G's point is, indeed, philosophical. But if you're going to get just one idea from philosophy, this is the one to get. For my taste Bishop Berkeley said it best in "A Treatise Concerning the Principles of Human Knowledge", whence his famous aphorism "Esse est Percipi". His take on it was called "Subjective Idealism". However moderns might find him incomprehensible (like Shakespeare). The 2dFGRS cartoon above might be more appropriate. Also movie "The Matrix". After all it's simple enough.

Since all our information comes very indirectly through the senses, we don't know what's out there (if anything) and never will. That's it. Something so obvious is impossible to "prove", although @Ken G's persistent defense of it has done some good.

Modern concepts like atoms, statistical thermodynamics, EM radiation, relativity and especially QM have made it very relevant to science. Once you get it, simply do the following. There are a lot of things we think of as ontically real, like people, rocks and wavefunctions. Continue calling them "real" but translate, in your thoughts, to "appears real to me, based on the persistent and convincing data of my senses, but of course there's no way to tell if it's really real." No further adjustment is needed. This paradigm shift can never reveal any new scientific facts, but it automatically ends a common type of endless debate.

If everybody accepts this fact you never need mention it again. We can happily continue to use words like "real", "ontic", and "epistemic", mutatis mutandis. However if you, or anyone, won't accept it, that's alright. We'll just translate your concept of "real" as described above, and move on. Unfortunately you'll continue to hunt down blind alleys, vainly seeking a through passage. Have fun.

 

[Simon Phoenix]

Continue calling them "real" but translate, in your thoughts, to "appears real to me, based on the persistent and convincing data of my senses, but of course there's no way to tell if it's really real."

Eh? This is supposed to be the sharp pointy thing that cuts through the Gordian knot?

All we have to do here is to play with words to get back to the issue at hand - "I must interpret the quantum state as if it were describing something real, even though I can never prove that anything is real" would then be something like the ontic position and "I must interpret the quantum state as being descriptive of my knowledge about some reality that only appears real" would be something like the epistemic position. OK I could probably phrase those better, but I fail to see how the rather obvious and trivial assertion that we can never prove anything to be real solves anything as far as the epi/onto problem in foundations physics is concerned.

So given the assumption that there is an external reality independent of our senses and consciousness do we have to take an ontic or epistemic view of the quantum state, according to the structure of QM? That's the issue - and it isn't in any sense resolved by merely saying the initial assumption is unprovable or false.

 

[secur]

Eh? This is supposed to be the sharp pointy thing that cuts through the Gordian knot?

it automatically ends a common type of endless debate.

I fail to see how the rather obvious and trivial assertion that we can never prove anything to be real ...

Something so obvious is impossible to "prove".

... solves anything as far as the epi/onto problem in foundations physics is concerned.

This paradigm shift can never reveal any new scientific facts.

So given the assumption that there is an external reality independent of our senses and consciousness do we have to take an ontic or epistemic view of the quantum state, according to the structure of QM? That's the issue - ...

That is the question:

... and it isn't in any sense resolved by merely saying the initial assumption is unprovable or false.

This paradigm shift can never reveal any new scientific facts.

 

[Simon Phoenix]

@secur

Lol - I can't work out whether you're agreeing with me that Ken G's position is utterly irrelevant to the ontic/epistemic debate in the context of quantum foundations, and solves precisely nothing, or conversely whether you think it renders the whole foundations debate irrelevant, as Ken G appears to suggest.

I think on a physics forum we probably shouldn't spend too much time debating the fruitless philosophical frippery of whether there is an objective reality that exists independent of our senses (I wouldn't really describe this amusing diversion that we all went through sometime before high school as a 'paradigm' shift though).

I don't want this thread to get closed down because it's been pretty cool so far. So I'll shut up (and calculate)

 

[andrew s 1905]

How many ontic angels can dance on the head of a epistemic pin ?

Regards Andrew

 

[ddd123]

I think on a physics forum we probably shouldn't spend too much time debating the fruitless philosophical frippery of whether there is an objective reality that exists independent of our senses (I wouldn't really describe this amusing diversion that we all went through sometime before high school as a 'paradigm' shift though).

It's because it's not quite like this. I think few would take on the position that there is nothingness apart from our senses. The point is that being beyond the senses is inaccessible - it's different. The usual idea people have is this:

But it would be preposterous to say that the stuff outside the head is like that: the stuff inside is a representation extrapolated from the senses, that has evolved for millions of years to fulfill certain survival functions. I think
a) it's not hard to understand;
b) it's not trivial (not a high school existential moment, it's serious business);
c) it may be relevant at some point in the history of science.

 

[secur]

Lol - I can't work out whether you're agreeing with me that Ken G's position is utterly irrelevant to the ontic/epistemic debate in the context of quantum foundations, and solves precisely nothing, or conversely whether you think it renders the whole foundations debate irrelevant, as Ken G appears to suggest.

Well, I have said twice before in this thread that it does NOT solve the ontic/epi debate. Ken G does, indeed, seem to think otherwise. But it's not "utterly irrelevant" - it clears away some of the underbrush. This "trivial" point can extremely get in the way when discussing ontological issues more directly related to physics, because it's not accepted by everyone.

How many ontic angels can dance on the head of a epistemic pin ?

Case in point :-)

I think on a physics forum we probably shouldn't spend too much time debating [philosophy] ...

That's right. But half of this thread, and about half of PF and foundational physics in general, does exactly that. People keep getting sidetracked by this and a couple other equally obvious philosophical facts. BTW I didn't bring it up and have been avoiding it. As my kids used to say "It wasn't me! He did it."

... the fruitless philosophical frippery of whether there is an objective reality that exists independent of our senses (I wouldn't really describe this amusing diversion that we all went through sometime before high school as a 'paradigm' shift though).

You don't get it. You think you do - that's half the battle, I suppose. It's not a dormitory diversion but a fundamental fact of existence which can't - I mean, shouldn't - be forgotten in serious contexts such as foundational physics.

I don't want this thread to get closed down because it's been pretty cool so far.

Yes, let's drop it before Dale takes notice :-) And yet if ever there was a place that would benefit from understanding it, this is that place.

Re. ontic/epi issue, I'm ontic. Still working out how to defend my stance. Believe it or not there are some new things to say about it.

 

[A. Neumaier]

How many ontic angels can dance on the head of a epistemic pin ?

http://arnold-neumaier.at/physfaq/topics/needle

 

[Simon Phoenix]

You don't get it. You think you do

Well both you and ddd123 have now suggested that the fact that our brain constructs a representation of 'reality' which may, or may not, have some substantial overlap with 'reality' (assuming we have taken the blue pill, or was it the red pill?) - is some tremendously important fact. I think it's kind of obvious and of complete irrelevance to physics (or pretty much anything else, for that matter).

So what am I not getting?

 

[ddd123]

Well both you and ddd123 have now suggested that the fact that our brain constructs a representation of 'reality' which may, or may not, have some substantial overlap with 'reality' (assuming we have taken the blue pill, or was it the red pill?) - is some tremendously important fact. I think it's kind of obvious and of complete irrelevance to physics (or pretty much anything else, for that matter).

Tell that to the foundations guys

 

[ddd123]

To think of it, you are among them! You have said the exact opposite just a little earlier:

So given the assumption that there is an external reality independent of our senses and consciousness do we have to take an ontic or epistemic view of the quantum state, according to the structure of QM? That's the issue

So is it an issue, or is it completely irrelevant?

 

[Simon Phoenix]

So is it an issue, or is it completely irrelevant?

The issue, as I see it anyway, isn't anything at all about how our conscious brains perceive reality, or construct that reality from our sensory inputs, or whether there is such a thing as an external reality (you could just be some part of the computer simulation that is responsible for what I perceive as consciousness, and so on, and so forth). These are all red herrings.

Let us assume there is such a thing as an external reality and that our consciousness constructs a reasonably faithful and consistent representation of that for us. Since we can't really say one way or the other we may as well assume the simplest explanation. If we wanted to be more sophisticated we could couch everything in terms of perceptions of reality - but then all we'd be doing is to have to add a zillion qualifiers to everything when we talked about reality and our models of it - and we wouldn't have changed the basic problem one iota - just nested it within a quagmire of qualification.

We can all agree, I think, that the mathematical models we write down, the squiggles on the paper are not 'reality' themselves, but are (at best) merely representations of some underlying reality. The underlying reality doesn't change if we use a different notation, for example. This is the ontic view. When we describe a particle with a p and a q we are saying that the particle has some position and some momentum which we label with the symbols p and q. The concepts of position and momentum have some objective meaning and are not just mental constructs. Certainly the transfer of momentum of a golf ball as it hits our heads is far from being simply a mental construct - the particle has objective properties (we use mental constructs to reason about those properties but the properties themselves are more than merely mental constructs). This is the ontic view.

Yes in some sense momentum is a 'mental construct' but it maps onto a real property in the real world in the ontic view - and I would describe classical physics as ontic in this sense.

The question is whether the quantum state also maps onto some real property of the real world - is it describing some objective reality, or is it just a convenient mathematical tool to describe what we can know about something?

This issue is not resolved or sidestepped or brushed away if we adopt some notion of perceived reality constructed by our consciousness. We'd just have to qualify everything in terms of a model of the perceived reality (perceived ontic) or what we can perceive we can know about this perceived reality (perceived epistemic). So in my view trying to emphasize that we can never know whether there is an external reality and, if there is, whether our evolved consciousness constructs a faithful representation of that for us, does not help us in any way whatsoever with the ontic/epistemic debate.

 

[ddd123]

how our conscious brains perceive reality, or construct that reality from our sensory inputs

The concepts of position and momentum have some objective meaning and are not just mental constructs. [...] Yes in some sense momentum is a 'mental construct' but it maps onto a real property in the real world in the ontic view - and I would describe classical physics as ontic in this sense. [...] The question is whether the quantum state also maps onto some real property of the real world - is it describing some objective reality, or is it just a convenient mathematical tool to describe what we can know about something?

I think these two quotes address essentially the same issue. Don't we perceive position, in the sense that that's what the brain does?

We can all agree, I think, that the mathematical models we write down, the squiggles on the paper are not 'reality' themselves, but are (at best) merely representations of some underlying reality. The underlying reality doesn't change if we use a different notation, for example. This is the ontic view.

I think I'm lost here. The epistemic view holds that the underlying reality changes instead?

This issue is not resolved or sidestepped or brushed away if we adopt some notion of perceived reality constructed by our consciousness. We'd just have to qualify everything in terms of a model of the perceived reality (perceived ontic) or what we can perceive we can know about this perceived reality (perceived epistemic). So in my view trying to emphasize that we can never know whether there is an external reality and, if there is, whether our evolved consciousness constructs a faithful representation of that for us, does not help us in any way whatsoever with the ontic/epistemic debate.

I'm lost again. Haven't you simply redefined the problem, and now you are asserting that THAT is what we care about, eventually perceived ontic vs perceived epistemic and not just simply ontic vs epistemic? So of course if that's the nature of the problem, and I wasn't informed, then it is a red herring, but it seems to me even more "irrelevant" than the actual ontic vs epistemic debate: why would we care about such a thing?

 

[Simon Phoenix]

why would we care about such a thing?

That's a very good question :-)

Since we get the same results in QM if we adopt an ontic picture or an epistemic picture then many people would suggest that it doesn't really matter.

I tend to think of the quantum state as a real thing and think of measurements projecting into a new state - so broadly speaking a collapse picture. That's just the view that helps me get the right answers in calculations. Is it what's actually happening? Buggered if I know.

I would like to have a clearer 'physical' picture of what's 'really' happening - but that's more of an emotional response on my part than any rational requirement. I just see part of the job of physics as explaining the 'why' as much as it can - as well as the 'how'. We need to be able to predict stuff because we want to test our ideas of the why and how as best we can.

 

[ddd123]

In any case, when physicists say, to use exactly your own words:

"momentum is a 'mental construct' but it maps onto a real property in the real world"

or

"no, momentum is only a 'mental construct' and it doesn't map onto a real property in the real world",

they are talking exactly about the issue I was talking about above, with the colorful cartoon I posted. Or if they aren't, how can I tell?

 

[ddd123]

IMHO it seems that exactly the same problem, for you, is once irrelevant for physics (and for everything else!) and another an interesting issue, depending on whether you put on it the philosophy badge or the foundations badge respectively.

 

[Simon Phoenix]

"no, momentum is only a 'mental construct' and it doesn't map onto a real property in the real world",

I think this is all part of the dissociative personality disorder induced by QM. I don't think this kind of thinking would have made any sense before the advent of QM - and as has been mentioned I believe there has been some attempt to redefine what 'science' is about because of the difficulties introduced by QM. Some in this thread have posited that this is a more correct view of science, but I am not convinced.

I am not aware of any textbook dealing with classical physics that would not implicitly (or explicitly) adopt an ontic view. There may be some I suppose, but in my experience classical physics is almost never introduced, taught or thought about as an epistemic theory (that is a theory that describes what we know, rather than a theory that describes some reality). Maybe I've just read the wrong stuff :-)

I have never read any description of a (purely) classical process that does not talk about position, momentum, energy, electric field, etc as if they were anything but descriptive of something objectively real. Again - this doesn't mean that epistemic descriptions don't exist - but I think it would be fair to say that from the perspective of classical physics it would be a bit weird to say that momentum doesn't map onto some real world property.

But clearly, when QM came along, something went disastrously wrong with this way of looking at things - and this I think is why there were so many struggles to get to grips with it in the early days. This disconnect with previous classical ways of thinking is beautifully illustrated by Dirac in the introduction to his textbook (which I think should be required reading for anyone studying QM). He describes the problem of figuring out specific heat capacities for atoms. Assuming there were classical variables which contributed, as any classical degree of freedom would, to the specific heat capacity gave the wrong answer. So it was clear from the early days that something different than 'classical variables' was required. In one way we can see this as a very persuasive early argument against the existence of classical-like hidden variables.

 

[ddd123]

So you simply disagree with this foundations debate, the epistemic view within foundations is disastrous, and the interesting aspect is how to get back to the ontic?

That's different, though, than calling my explanation completely irrelevant to physics or to anything else.

 

[Simon Phoenix]

So you simply disagree with this foundations debate, the epistemic view within foundations is disastrous, and the interesting aspect is how to get back to the ontic?

Well if I've given you these impressions from what I've written - then I apologise.

I think the foundations debate is interesting - is the wavefunction describing something real, or is it just a device to describe our knowledge? I think if this question could be answered definitively then it would be a wonderful thing (either way). I would certainly prefer it if the answer came out on the ontic side - but either way it would represent a very significant advance.

At the moment we can't tell - the predictions from all of the various interpretations/formulations of QM are the same. It would be nice to have some experimental way to rule out some of these.

I just don't see how delving into an appreciation that our consciousness constructs a perception of reality for us helps us to progress towards an answer to these questions. If I've missed the point of your argument I apologize and would appreciate being corrected.

 

[Nugatory]

I don't want this thread to get closed down because it's been pretty cool so far.

Speaking for myself here... I don't worry overmuch about what consenting adults are doing in the privacy of the 20th page of an interpretations thread. Just be sure that the children aren't watching.

 

[ddd123]

I just don't see how delving into an appreciation that our consciousness constructs a perception of reality for us helps us to progress towards an answer to these questions. If I've missed the point of your argument I apologize and would appreciate being corrected.

No problem, I don't say it helps us progress, I say it's just a rephrasing of the same question. From our perception of reality (i.e. mental construct) comes the concept of point in space for example, and thus classical mechanics is just taking that on. Along these lines, even if we construct a completely counterintuitive "ontic" model (say, holographic principle) and say THAT is what is outside our heads, it simply means that our mental constructs have refined themselves enough to somewhat depart from the old intuition, but we are still debating on: our mental constructs have a correspondence outside or not. Which is exactly the foundations debate we're talking about.

 

[Simon Phoenix]

Just be sure that the children aren't watching.

lol

whenever my kids were playing up I'd threaten them with a lecture on interpretations of QM - worked a treat :-)

 

[Simon Phoenix]

our mental constructs have a correspondence outside or not. Which is exactly the foundations debate we're talking about.

OK - that's a nice way of putting it. My issue with going into detail about perceptions of reality and so forth is that we end up talking about mental constructs of mental constructs (our mentally constructed models of a perceived reality which is itself a mental construct) and so we end up with this tortuous nesting of mental constructs.

So I like to keep things simpler and just assume that there is an external reality, that our mental construct of that reality, derived from sensory inputs, is pretty faithful. So the question then becomes one of whether the models we adopt to explain things have a mapping to some external reality or whether those models merely describe what we can know about that reality.

Although I would prefer an ontic answer and despite the fact that when doing QM I think in ontic and collapse terms I actually can't help but think that the epistemic approach is actually more logically cohesive. Problem is I find it more difficult to actually do calculations if I try to think in terms of epistemology

 

[atyy]

Although I would prefer an ontic answer and despite the fact that when doing QM I think in ontic and collapse terms I actually can't help but think that the epistemic approach is actually more logically cohesive. Problem is I find it more difficult to actually do calculations if I try to think in terms of epistemology

That is the beauty of Copenhagen. Ontology is a means to epistemology.

 

[atyy]

In this sense, of course the Heisenberg cut is there. The only thing I see no justification for is to claim that on a fundamental level there is a "quantum world" and a "classical world" governed by different dynamical laws. I think the classical behavior of macrocopic objects under usual conditions is a phenomenon that can be understood from QT, using the standard ("coarse-graining") techniques of many-body theory.

There is no absolute cut. The cut is subjective and observer dependent. In the standard interpretation, anything can be quantum, but not everything can be quantum.

However, I sense that you believe that in principle there is a quantum state of the universe, including the observer, and the measuring apparatus can be obtained by coarse graining. This is not the standard or minimal interpretation. It is true that classical mechanics is a limit of quantum mechanics. However, that does not mean we can do away with postulating a a "classical world" on one side of the cut that is in fact more fundamental than the "quantum world" on the other side of the cut.

 

[RockyMarciano]

The way I usually try to frame this ontic/epistemic duality so it doesn't lead me to a stalemate is by trying to concentrate on the physics, and to me this means observations, specifically observations that can be translated into physical measurements.
Now if you look at it from the classical mindframe(wich we all tend to do by habit even after the quantum revolution since the formalism has been basically inherited from classical physics-Hamitonians, linearity, Hilbert spaces from symplectic,...etc- and the observables are classical), and since classically there was a clear cut between measurement and measured system, we tend to hang on intuitively to the separation between the ontic and the epistemic that reflects that cut.

But if you concentrate on the quantum phenomenology and let go of the inertia that holds you back to the classical thinking, you can dissolve the antinomy because it really is not relevant if all you care about is measurements. You are led to a natural fusion. Noone will deny their existence("onticity") since they are all we have in physics in the end and they can also be regarded as purely "informational" or epistemic.

Of course the problem here is we don't yet have a quantum measurements-only theory in this sense, we have an operationally efficient theory for predicting quantum measurements probabisitically that ironically leaves measurements out of the mathematical formalism.
This already happened in classical physics, where the phenomenology didn't require to fuse measurement and system measured, they were independent, but it is a problem with the quantum phenomenology where it is very difficult to maintain that measurement and measured system are independent. If the formalism doesn't reflect this dependency that actually contradicts its mathematical premises there are going to be interpretational issues for sure.

From this point of view it is easy for me to be understanding both with those that don't see any problem in quantum foundations or any measurement problem whatsoever(i.e. vanhees71 or Neumaier) and those that really feel there are deep problems(i.e. stevendaryl and others). It all depends on how attached(most likely unaware of it) you are to the classical perspective.

 

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1. Subjective Reality Principle

... our senses are turned by our brain into intelligible experience as a representation, which not necessarily (and most likely not) corresponds to "what is out there".

Since all our information comes very indirectly through the senses, we don't know what's out there (if anything) and never will.

I take it we all agree on this fundamental fact: "Reality" is (when you get right down to it) subjective. This principle needs a name, how about "Subjective Reality Principle" (SRP).

The way I usually try to frame this ontic/epistemic duality so it doesn't lead me to a stalemate is by trying to concentrate on the physics, and to me this means observations, specifically observations that can be translated into physical measurements.

Yes, the scientific version of SRP is something like "we know only physical observations or measurements, not any 'reality' we might imagine was responsible for them".

2. What good is it?

It's not a dormitory diversion but a fundamental fact of existence which can't - I mean, shouldn't - be forgotten in serious contexts such as foundational physics.

I just don't see how delving into an appreciation that our consciousness constructs a perception of reality for us helps us to progress towards an answer to these questions.

I'll try to explain what good it is in a later post. If I get to it.

There are a lot of things we think of as ontically real, like people, rocks and wavefunctions. Continue calling them "real" but translate, in your thoughts, to "appears real to me, based on the persistent and convincing data of my senses, but of course there's no way to tell if it's really real."

We have to keep the SRP in mind and deal with it, for foundational issues.

Let us assume there is such a thing as an external reality and that our consciousness constructs a reasonably faithful and consistent representation of that for us. Since we can't really say one way or the other we may as well assume the simplest explanation.

With this over-simplifying assumption, SRP is "resolved or sidestepped or brushed away" entirely. Given this approach, of course SRP has no impact on foundational issues. That's why you don't "get" its importance IMHO.

I fail to see how the rather obvious and trivial assertion that we can never prove anything to be real solves anything as far as the epi/onto problem in foundations physics is concerned.

So given the assumption that there is an external reality independent of our senses and consciousness do we have to take an ontic or epistemic view of the quantum state, according to the structure of QM?

SRP is relevant to all foundations physics, particularly QM wavefunction ontology question. It doesn't "solve" anything by itself but is a vital principle for analysis. IMHO.

3. QM Interpretations

I tend to think of the quantum state as a real thing and think of measurements projecting into a new state - so broadly speaking a collapse picture.

Me too. It's simple and intuitive, and accounts for all experimental data. The collapse interpretation has always been the most popular way of looking at it.

Since we get the same results in QM if we adopt an ontic picture or an epistemic picture ...

I actually can't help but think that the epistemic approach is actually more logically cohesive.

I haven't seen an epistemic approach that actually works to reproduce QM phenomena although some people claim such exists. At the moment, I don't think it's more logical, either. Admittedly there's a lot I don't know about the subject.

4. Miscellaneous

We need to be able to predict stuff because we want to test our ideas of the why and how as best we can.

Practical people would instead say that we want to predict how things will behave under given conditions so we can build cars, cell phones and bombs instead of relying on horses, letters and clubs. That it's not about testing ideas but making a product.

I have never read any description of a (purely) classical process that does not talk about position, momentum, energy, electric field, etc as if they were anything but descriptive of something objectively real.

This sort of debate has occurred often in history of science. GR says that absolute position doesn't exist. Zeno argued that velocity (momentum, motion) wasn't real. Ontological status of energy was questioned by many. Read "On Action At A Distance" by Maxwell http://www.informationphilosopher.com/solutions/scientists/maxwell/action_at_a_distance.html where he argues that the electric field is objectively real, against the majority opinion of the day (led by Ampere). It sounds a lot like this thread, in places.