More evidence that the wavefunction is ontologically real?

[bhobba]

Microworld is very different in approaches from the macroworld. Quantum nonlocality disappears as things get bigger. My monitor doesn't appear to be in places at the same time or jittery. It looks different to me?

That's exactly my issue. QM says none of those things - it is silent on it. If QM is non-local or not is interpretation dependant - the same with things being in two places at once (although I don't know any interpretations that says that - but there may be some).

Thanks
Bill

 

[Quantumental]

You are mixing concepts from interpretations as if they were the same interpretation. That is, and very obviously so, flawed logic.

No. If you want an ontological wavefunction and you accept functionalism you do not get to say that by magic the worlds do not occur in the wavefunction

 

[bhobba]

No. If you want an ontological wavefunction and you accept functionalism you do not get to say that by magic the worlds do not occur in the wavefunction

You logic is flawed. BM is an ontological interpretation that does not involve worlds - QED - your argument is wrong.

Thanks
Bill

 

[Quantumental]

You logic is flawed. BM is an ontological interpretation that does not involve worlds - QED - your argument is wrong.

Thanks
Bill

This is what happens when otherwise very smart people decide to ignore philosophy. Saying that the worlds aren't in the wavefunction doesn't actually remove them. As has been argued in the litterature before: http://philsci-archive.pitt.edu/1659/1/Cushing.pdf

 

[julcab12]

That's exactly my issue. QM says none of those things - it is silent on it. If QM is non-local or not is interpretation dependant - the same with things being in two places at once .

Thanks
Bill

... I'm just saying it is different by behavior but not solely disconnected(post#23). If your saying that QM is only constrained to a certain formalism -- certain formalism or statistic or probabilty simply because things doesn't behave or obey at what we usually expect (classical). What about quantum observables or observed quantities.. Are observed behavior interpretation dependent too? If say, when particle are observed to be in multiple places at the same time. QM is out of the picture? I'm confused.

 

[ephen wilb]

No. There are many interpretations of QM besides Copenhagen and MW - some have collapse, some don't, some have many worlds, some even have many minds, there are all sorts out there.

Thanks
Bill

Ensembles or Copenhagen smell of Newtonians.. because in Newtonian classical world is the primary.. and you treat the wave functions as just ensembles or subjective or just probabilistic tools in a primary Newtonian world... with definite outcome as the primitive of the axiom. But isn't this Newtonian biased? You know Newtonians are just illusions. Newtonians is just smoke and mirrors.. so is not ensembles interpretation going backwards (in thinking)?

 

[bhobba]

But isn't this Newtonian biased?

Its got nothing to do with Newtonian mechanics. I have zero idea how you would form such a view. Its simply an interpretation of probability - frequentest vs bayesian:
http://jakevdp.github.io/blog/2014/03/11/frequentism-and-bayesianism-a-practical-intro/

The ensemble interpretation is frequentest in that it views the possible outcomes of an observation as a large ensemble determined by the state and observation. Copenhagen is Bayesian in that it views the state as subjective knowledge.

Unfortunately Copenhagen sometimes isn't explained well - the following fixes that:
http://motls.blogspot.com.au/2011/05/copenhagen-interpretation-of-quantum.html

Thanks
Bill

 

[carllooper]

Microworld is very different in approaches from the macroworld. Quantum nonlocality disappears as things get bigger. My monitor doesn't appear to be in places at the same time or jittery. It looks different to me?

Non-locality isn't quite the same thing as superposition. And neither disappear at macro-scales. A particle in so-called super-position can occupy a wave that is miles across. The EPR mind experiment involved galactic distances.

The non-local refers to relationships between things or events, and measurable ones as much as any unmeasurable ones. For example, the concept of distance (a measurable attribute) is one of the simplest measurable conceptions of the non-local. The distance between a couple of apples sitting on a table is not localised in anyone of the apples. The distance between the apples represents a relationship between the apples rather than anything specific to the apples themselves. In this case the relationship is a spatial relationship. And if we were to move one of the apples, while not touching the other apple, this spatial relationship (ie. the distance between the apples) would change. And this change in distance would demonstrate that a local change (moving one of the apples) altered a non-local attribute (the distance between them). Or equally: that altering the distance between them, altered one or both of the apples!

Understood in this way, non-locality isn't that strange, nor new. However it's had a very troubled history due to it's early association with the supernatural.

C

 

[ephen wilb]

Its got nothing to do with Newtonian mechanics. I have zero idea how you would form such a view. Its simply an interpretation of probability - frequentest vs bayesian:
http://jakevdp.github.io/blog/2014/03/11/frequentism-and-bayesianism-a-practical-intro/

The ensemble interpretation is frequentest in that it views the possible outcomes of an observation as a large ensemble determined by the state and observation. Copenhagen is Bayesian in that it views the state as subjective knowledge.

Unfortunately Copenhagen sometimes isn't explained well - the following fixes that:
http://motls.blogspot.com.au/2011/05/copenhagen-interpretation-of-quantum.html

Thanks
Bill

When one mentions "Newtonian".. it is automatically "Newtonian mechanics"? I was thinking Newtonian refers to nuts and bolts and macroscopic classicality. Special relativity and quantum mechanics are supposed to be saying things are not what they seem. Newtonian mechanics being just classical limits and coarse grain limit of a universe where things were supposed to expand, dilate in SR and vanish and in two places at once in QM. In your view. SR and QM are just for calculations and not really objectively there creating matter, space and time?

 

[carllooper]

Ensembles or Copenhagen smell of Newtonians.. because in Newtonian classical world is the primary.. and you treat the wave functions as just ensembles or subjective or just probabilistic tools in a primary Newtonian world... with definite outcome as the primitive of the axiom. But isn't this Newtonian biased? You know Newtonians are just illusions. Newtonians is just smoke and mirrors.. so is not ensembles interpretation going backwards (in thinking)?

Ensemble theory isn't necessarily Newtonian, although there are Newtonian (or classical) conceptions of the ensemble. If you were to treat the ensemble as a function of otherwise independent effects (or causes) then you might be entertaining a classical version of such theory. But in an alternative version of such, (and not necessarily modern for that matter) the collective operation (the ensemble) of otherwise individual effects (or causes) can be treated as the fundamental "reality" being studied. The events as individual and independant of each other become the "illusion" (so called).

But these terms "reality and "illusion" are just historically loaded terms. It doesn't really matter which is called which, or what you study. The so-called "illusions" are just as interesting, from the point of view of science, as the so-called "realities".

C

 

[bhobba]

and in two places at once in QM.

QM doesn't say that.

In your view. SR and QM are just for calculations and not really objectively there creating matter, space and time?

That depends on what you mean by objectively there. I consider 'objectively there' to be what out theories describe, so obviously its 'objectively there' in my view. However philosophers argue incessantly what things like that mean, and never reach any conclusion, so my view won't resolve anything.

Thanks
Bill

 

[carllooper]

It seems to me that I have, in the past, been professorially chastised for questioning what quantum physics implies about "reality" at the fundamental level, as well as when I suggested that it seems in many ways that the only thing "real" about the quantum state of a physical system is the information that describes it. Despite that, it appears that this thread demands that those issues to be addressed.

First off, what does it mean for something to be "ontologically real"? The definition of "ontological" (according to i.word.com) is :"relating to or based upon being or existence." I interpret that to mean that it's something that actually "exists", in a substantive manner.

But, to what do the values correspond? What is it that actually "exists" that the values describe?

Yet, negative numbers don't actually "exist", in a substantive manner. For that matter, neither do positive numbers, nor arithmetic functions. They are mathematical constructs... abstract ideas. They have no substantive form.

So, this leaves me with the question... Is the information content of the quantum state what is objectively "real". Is it, in fact, all that is "real"?

A mathematical model represents what otherwise "exists". To the extent that there are things that exist, which can be represented with a negative number, one will use such numbers to represent such things. Bhobba's example of a debt is just such an example. If one regards a debt as real (ie. that you are not a thief and intend to pay back the debt) then you can represent this debt (in your ledger) with a negative number.

Although a mathematical model represents something other than itself that doesn't mean it's not in itself a "reality". Indeed I imagine most mathematicians would treat mathematics as a "reality" in itself. But in the context of physics a mathematical model (also) represents something other than just itself. It refers us back to, at the very least, some observable phenomena: the results of an experiment (or just fortuitous observations). But models tend to go a bit further than just what is observable. After all, if it's only the observations one is interested in then one can just do the experiments and not trouble oneself with any models.

A model tends to treat the observations (ie. the results of experiments) as a function of something more "real" behind such observations. One speaks of the "reality" behind an observation. One models this "reality". Now a model will produce it's own results, and any agreement between the model's results, and otherwise experimental results will typically be treated as a good thing. What one is after. The model is effectively a substitute for what is otherwise not immediately obvious in an experimental observation - be it the notion of some invisible "reality" behind such observations, or simply some unobvious pattern (or signal) in the observations itself: drawing our attention back to the observation and what we might have overlooked but is otherwise entirely visible in the observation.

The question of "reality" will always be a vexed one because most conceptions of such treat it as being something different to what is observable - as that which is "behind" the observable, rather than equal to it. An invisible reality. As if what we observe was some sort of illusion, or was subjective. At best a representation. As if observations were in themselves something not real. As if we were all living in The Matrix, or Plato's cave. Its a particularly ancient idea but also a very compelling one. But how does one emperically prove this concept of reality (of that which would be outside of the cave)? By definition one can't. It's invisible! As troubling as this notion of "reality" is (as something invisible and fundamentally different from observation) it has nevertheless proved a very useful concept. However it is still just another model.

The simplest approach, I find, is to treat that which is observable, as one's starting concept of reality. Whenever you run into trouble with a model, you just return to this reality (rather than the idea of some reality behind such). There is something extremely simple about this approach. Myself I find it even easier to treat observations, not only as a starting reality (and a reality to which one might return when in trouble) but as the only reality there is: that there is no reality behind an observation - that observations themselves are the fundamental reality about which we are otherwise creating models. The models become a way of expressing, in more formal terms, what would otherwise be visible (or can be made visible) - rather than expressing the invisible.

C

 

[Nick666]

carllooper , I opened a thread in General Discussion, if you want we can continue there .

 

[Feeble Wonk]

I hope my post (#26) didn't drop us into the philosophical abyss. I'm sincerely attempting to comply with the PF convention to refrain from that. But, again, this subject matter by its very nature requires that we at least tread carefully toward the slippery slope without sliding over the precipice.

A mathematical model represents what otherwise "exists".
...
Although a mathematical model represents something other than itself that doesn't mean it's not in itself a "reality".
...
The question of "reality" will always be a vexed one...

C

As Carl suggests, any reference to an ethereal and/or abstract reality is "vexing", because that concept of "reality" allows for a confounding degree of ambiguity. Yet, the ONTOLOGICAL designation should alleviate a great deal of that ambiguity. In an effort to get back on topic, and make my point more clearly, I'd like to return to the money analogy for just a moment. What the concept of money "represents", in terms of its relative value, might be "real" in some respects, but it is not ontologically real. The aspect of money that is ontologically real is the paper of the currency, and the metal of the coin. Ontological reality is tangible and substantive. It is what it is, not what it represents.

Its interpretation dependant - the formalism is silent on the issue of the reality of a quantum state.

Formally QM is a generalised probability model - in fact the simplest that allows continuous transformations between pure states. States are a generalisation of probability. Is the probability you assign to the face of a coin real?

I suppose this is precisely the issue that I'm trying to clarify. Regardless of the QT interpretation, as Bill reminds us, the wave function itself is a "probability model". It's not a "thing", in the sense that you can hold it in your hand. And, it doesn't represent the observable. It represents the "probability" of how you will observe the observable when you look. It is, by its very nature, information, and only information. I don't understand how this mathematical entity can be, or represent, something that is "ontologically" real.

Here is a free link:
http://arxiv.org/pdf/1412.6213v2.pdf

Note what it says:
'Assuming that some underlying reality exists, our results strengthen the view that the entire wavefunction should be real'

So, if this paper is claiming that it has demonstrated that the wave function is as equally "real" as is the "pure" quantum state of a physical system... as "real" as any underlying reality that exists... is it arguing that "reality" in general is fundamentally informational?

 

[carllooper]

There's nothing to suggest that what is observable isn't also that which some position (such as mine) would mean by "ontologically real".

An observation is both tangible and substantive.

And if not why not?

If by the phrase "ontologically real" one means something other than an observation, then one is left with either the model (a representation) and/or some non-observable reality (represented by the model).

Neither of which seem to me to be any more tangible and substantive than an observation. But on the other hand no less tangible and substantive.

A non-observable reality needs some way of being expressed in terms that do not depend on observation - for obvious reasons. A model is precisely the means by which such a reality can be expressed. For that reason such a model, and what it represents, are 'entangled' with each other. They become, in a sense, the 'same' thing. An observable reality doesn't depend on a model in quite the same way since the reality being established is already expressed by a given observation.

A model, as mentioned, seeks to go beyond what is simply given as raw data. The concept of raw data invokes for example, a list of numbers. For obvious reasons a list of numbers can look pretty meaningless and offer not much insight into what one might be wanting to do with such numbers. And so models are made to sort of put all these numbers into some sort of more manageable form. And by assuming there is some sort of more ordered "reality" producing these numbers in the first place, really effective models have been made. There's no denying this. Models are really really effective things.

Whether we call them real, or a representation, or ontologically real, or not ontologically real, or merely "adequate" as Bohr once said is really beside the point. Who cares? Who cares are those who need the models rather than the philosophical trajectories that such models might invoke or contest. They need the models in the work they do - be it to manage raw data or design some new technology. There are all sorts of reasons.

For example, I'm currently building an optical printer for 16mm and Super8 film. I need a model of light transmission in terms that will allow the computer control system to dynamically adjust the exposure time as a function of dynamic changes in magnification. I don't necessarily need the full quantum mechanical picture for this, but it doesn't hurt factoring such in since it can then handle some of the more subtle operations the system might be expected to handle - to do with holographic encodings. What matters in this context is not whether the models correctly represent some notion of an ontological reality but that the model gives the correct value to set the exposure time (amongst other things) - which one assumes it would do if the model represented reality - but needn't do so - as long as the result is effectively the same.

Be that as it may, the philosophical trajectory is still interesting. One is in a sense always doing philosophy anyway. Model makers use philosophy all the time - not classical philosophy, but versions thereof - adapted to the problems at hand and the way nature expresses herself, rather than some fantasy of complete "philosophical" closure on the nature of the universe.

The concept of reality as fundamentally information is, I think, quite a good one. I've found it a productive angle to take.

C

 

[Ilja]

Sorry - but I don't get that at all eg why even the concept of 'prepared' is applicable to wave-function needs detailing before you can even introduce it in that context. In modern times state and preparation procedure are pretty much synonymous but that requires detailing of what it is in the first place - which is very interpretation dependant.

The point is that in some interpretations, like dBB, the measurement process is covered by the theory. And the essential point of preparing the wave function of a system is to put the trajectory of the measurement device into the wave function of system + device. (In this sense, the argument is indeed interpretation-dependent - which is natural, because I don't know how to make arguments which would make sense in interpretations I reject as nonsensical, like many worlds.)

But in this case, if you want to apply this to the preparation itself, and not just to a measurement, which, then, leads to a subsequent preparation of the system after the measurment, you have to start with some assumptions about the unprepared wave function.

Fortunately, this is not as problematic as it looks like, because in this case you can use epistemic considerations to define the initial wave function. You know nothing, thus, can try to find out which wave function or state accurately describes this knowledge.

The point of the argument is that after the preparation measurement, the effective wave function depends on the trajectory of the measurement device, which is something really existing even in the Copenhagen interpretation.

 

[Ilja]

But, to what do the values correspond? What is it that actually "exists" that the values describe?

In dBB theory it is simply the trajectory of the measurement device used during the preparation procedure.

 

[bhobba]

So, if this paper is claiming that it has demonstrated that the wave function is as equally "real" as is the "pure" quantum state of a physical system... as "real" as any underlying reality that exists... is it arguing that "reality" in general is fundamentally informational?

No. Its quite simple really. All its doing, assuming its valid of course, is, similar to PBR, showing that if its real in a weak sort of wishy washy sense it must be real in a stronger sense.

If its not real in any sense at all, such as for example its simply a state of knowledge like in Copenhagen, then it says nothing.

Thanks
Bill

 

[carllooper]

No. Its quite simple really. All its doing, assuming its valid of course, is, similar to PBR, showing that if its real in a weak sort of wishy washy sense it must be real in a stronger sense.

If its not real in any sense at all, such as for example its simply a state of knowledge like in Copenhagen, then it says nothing.

Thanks
Bill

Why is that a "state of knowledge" be considered as not real? Or why would such a state (whether its be called real or not) not say anything?

Copenhagen can be regarded as a kind of user interface to quantum physics, but for users with an otherwise classical disposition. If one is not classically predisposed to begin with (as many now are), the Copenhagen user interface may not work.

Every now and then Bohr let's out a little frustrated squeal in his otherwise measured responses to Einstein. For Bohr, it is obvious that one can not entertain any classical interpretation of the experimental data. But almost as immediately as this is uttered it is withdrawn. Bohr's main approach is to frame the situation from the point of view of a classical user. Bohr adopts what is called a "quasi-classical" interpretation.

In this approach, the reality or otherwise of what is happening (that which classical thought entertains as comprehensible), is put to one side. Instead of talking in terms of an invisible reality behind observations, Bohr will talk in terms of what is visible instead - the actual detections taking place. Bohr is an empiricist in this regard.

Bohr's effort seems to be aimed at a kind of an awareness that should become obvious - that the more you look at those dots in an interference pattern - that whatever "reality" is behind such a pattern must be a "reality" impossible to reconcile with notions of reality as entertained by classical physics. Bohr is often genuinely perplexed as to why Einstein isn't getting with the program.

But instead of proposing some alternative reality to classical notions of reality Bohr will stick with empericism. He sticks with the user (the classical user) and how the situation can be managed from that perspective. Bohr introduces a dividing line between the classical user and whatever "reality" (be it classical or quantum) might be entertained as behind such. From the point of view of the classical user there are classical assumptions in operation, many of which can actually be employed. For example, in classical physics there is nothing wrong with collecting data and doing a statistical analysis on such. There's nothing wrong with using probability theory to determine where a classical particle might be. He knows full well that the particle in question can't possibly be a classical particle but he allows the classical user to entertain that fiction.

He will speak in terms of (quasi) classical particles. He will frame an interpretation that, as far as possible, maintains classical assumptions. It will be up to the user to realize that there really is a limit on how far you can actually push such assumptions. He wants the user to discover for themselves the truly astonishing nature of the physical world.

Is this a trick?

No. It is simply respect for the history of physics - and the current framework of such (at that time) - that physics progresses in a very conservative way - ie. by not introducing radical changes if there is not any need to do so. But he and Heisenberg were many times tempted to do just that. They refrained.

It is often said that Bohr is not a realist - but it entirely depends on what one means by realism. In Bohr there is an emphasis on what is visible (empiricism) and in empiricism, what is visible is real - it is the primary reality. Bohr is a realist. Just not in the sense that others mean by such.

This is not subjectivism. It is not some mind over matter model. It would only be subjectivism if you maintained that the visible was subjective. But in empiricism the visible is not subjective. On the contrary the visible is treated as an objective thing. It is photography, invented 50 odd years earlier, that makes this understandable. The visible as an objective thing. As a real thing. Realism.

C

 

[bhobba]

Why is that a "state of knowledge" be considered as not real?

BTW that's 'subjective knowledge'. Because it resides in the head of a theorist.

If you think that's real - go ahead - we don't argue philosophy here - but I doubt most would agree.

Thanks
Bill

 

[jfizzix]

So, this leaves me with the question... Is the information content of the quantum state what is objectively "real". Is it, in fact, all that is "real"?

Caution: Metaphysics is not my forte'.

I don't know what is truly objectively "real"; nobody does.
I do know what over time has become a set of concepts useful for reckoning with what I experience through my senses.
Over time, I have come to believe that there are aspects of the physical world that I experience through my senses that are independent of anyone's particular sensory experience (i.e., objectively determined).
In that sense, I believe the Moon is objectively "real", though it's not something that can truly be "proven" in the mathematical/logical sense.

With that in mind, I think that if there is an objective "reality",
then the information determining physical "reality" is objectively defined,
and anything uniquely defined from that information is objectively "real" as well.

That's really all I'm prepared to say without being forced to define what "reality" is.

 

[Feeble Wonk]

No. Its quite simple really. All its doing, assuming its valid of course, is, similar to PBR, showing that if its real in a weak sort of wishy washy sense it must be real in a stronger sense.

Thanks for the direction to PBR as a reference. I hadn't read much about it previously. It's giving me a different way to think about things. Very interesting.

 

[craigi]

So let's assume the wave function is real. does that mean that qm needs no further interpretations? (consciousness, many worlds, etc)

No.

If the wavefunction is real then we exclude the Copenhagen, Ensemble and Rovelli's Relational interpretation. The differences in other interpretations still address other foundational issues.

The MWI would have to be considered the most natural interpretation, but I think most (about half) of the leading theorists and cosmologists have already come round to that anyway.

Those who still cling to the Copenhagen or Ensemble interpretations, because they find the parallel universes conclusion of the MWI too troubling, would probably seek solace in Consistent Histories.

 

[carllooper]

BTW that's 'subjective knowledge'. Because it resides in the head of a theorist.

If you think that's real - go ahead - we don't argue philosophy here - but I doubt most would agree.

Thanks
Bill

Hmmm, where did I suggest knowledge is subjective?

Oh, that's right. I didn't.

Quite the contrary.

While knowledge can certainly occupy the head of a theorist, that doesn't mean it necessarily originates there. And there is nothing in Copenhagen to suggest it does.

But otherwise, if what we're talking about is "subjective knowledge" then yes, of course, by definition it would not be real (and somewhat irrelevant in a physics forum).

However I wasn't addressing subjective knowledge, even if Bhobba was. I was addressing the suggestion that Copenhagen would be proposing such a thing. It doesn't. Nor do I.

Indeed, in what I said, I explicitly rejected a subjectivist interpretation of knowledge, and I quote what I said:

This is not subjectivism. It is not some mind over matter model. It would only be subjectivism if you maintained that the visible was subjective. But in empiricism the visible is not subjective. On the contrary the visible is treated as an objective thing. It is photography, invented 50 odd years earlier, that makes this understandable. The visible as an objective thing. As a real thing. Realism.

So when discussing a photograph, for example, the emphasis from a physics point of view would not be on what a photograph might represent (be it classical reality or some other reality) but on the photograph in itself (as a visible material reality thing in itself). And one can describe this visible material thing in terms of concepts such as particles of light. And one can elaborate those concepts using the photograph (the visible/material thing) as a constraint on such elaborations. If we remove this constraint the elaborations could very well become that 'dreaded' thing we otherwise call "philosophy" (I'd suggest).

C

 

[bhobba]

Hmmm, where did I suggest knowledge is subjective?

I never claimed you did. I claimed I did in reply to the assertion:

Why is that a "state of knowledge" be considered as not real?

Thanks
Bill

 

[carllooper]

I never claimed you did. I claimed I did in reply to the assertion

I don't quite follow. Here is the post in question:

BTW that's 'subjective knowledge'. Because it resides in the head of a theorist.
If you think that's real - go ahead - we don't argue philosophy here - but I doubt most would agree.

On the one hand this post is a clarification of what Bhobba meant by 'knowledge', ie. he meant subjective knowledge:

BTW that's 'subjective knowledge'. Because it resides in the head of a theorist..

And that's fair enough. So the clarification means we're really talking about two different things. Subjective knowledge on the one hand (Bhobba) and objective knowledge on the other (me).

But then Bhobba goes on to clearly suggest that I might like to think 'subjective knowledge' (what he is talking about) is real, and challenges me to go ahead and argue that case:

If you think that's real - go ahead - we don't argue philosophy here - but I doubt most would agree.

In response to this obvious barb I am merely saying that there is no indication, whatsoever, in my post, that I would hold such a position, or would be even remotely interested in arguing such a position. If we're talking about two different things, then that is what we're doing. There is no need to re-conflate the two.

What I go on to pursue in my post is an objection to the populist idea that Copenhagen be understood as a subjectivist interpretation (regardless of who may, or may not, hold such an idea).

C

 

[zonde]

He will speak in terms of (quasi) classical particles. He will frame an interpretation that, as far as possible, maintains classical assumptions. It will be up to the user to realize that there really is a limit on how far you can actually push such assumptions.

Copenhagen attributes wavefunction to single particle. And Einstein's answer was ensemble interpretation.

He wants the user to discover for themselves the truly astonishing nature of the physical world.

So you have discovered "the truly astonishing nature of the physical world" and think that that was as intended by Bohr? Maybe cool down?

 

[carllooper]

Copenhagen attributes wavefunction to single particle. And Einstein's answer was ensemble interpretation.

So you have discovered "the truly astonishing nature of the physical world" and think that that was as intended by Bohr? Maybe cool down?

I entirely agree with what is said about Copenhagen and Einstein.

As for the second part, Bohr's intentions come nowhere near what I think.

C

 

[carllooper]

Einstein treats the wave function (or psi-function as he calls it) as an "ensemble" description of something more detailed to be found or inferred. By an ensemble description, Einstein means by such a description that such a description is incomplete, meaning that the description is more like some sort of average than characteristic of any reality underlying such.

Bohr treats the wave function as describing a single particle. But this does not in any way stop an ensemble of such particles producing a composite wave function no different from a single one. If the experimental setup remains a static one there will be no difference between a wave function representing individual particles and one representing heaps of them. The obvious benefit with associating the wave function with a single particle is that it becomes a lot easier to model dynamic experimental setups, where there is only a trickle of detections.

Another ensemble approach, which Bohr does not pursue, but is compatible with Bohr's empiricism, is to treat the distribution of particle detections as no less a "phenomena" as each individual particle detection.

This would differ from Einstein's ensemble in the sense that there is no more detailed information to be found by subdividing such up - on the contrary it would lead to a loss of information. By analogy, a digital photograph can be regarded as an ensemble of pixels, but if you subdivide the photograph up you just end up with unrelated pixels. The information we might have otherwise assigned the ensemble is lost. There are relationships between the pixels that are not to be found in any particular pixel - that are not a function of the pixels. On the contrary, the pixels are a function of the ensemble (so called).

Carl

 

[bhobba]

Einstein treats the wave function (or psi-function as he calls it) as an "ensemble" description of something more detailed to be found or inferred.

Its exactly the same as Ballentine and its a standard interpretation - in fact its the one I hold to:
http://en.wikipedia.org/wiki/Ensemble_interpretation

Its actually quite similar to Copenhagen:
http://en.wikipedia.org/wiki/Copenhagen_interpretation
The subjective view, that the wave function is merely a mathematical tool for calculating the probabilities in a specific experiment, has some similarities to the ensemble interpretation in that it takes probabilities to be the essence of the quantum state, but unlike the ensemble interpretation, it takes these probabilities to be perfectly applicable to single experimental outcomes, as it interprets them in terms of subjective probability.

Its basically the difference between Bayesian and Frequentest view of probability.

Einstein's and Bohr's interpretations were in fact not that dissimilar - the key difference was Bohr considered the state a complete description - Einstein most definitely did not.

Thanks
Bill

 

[andresB]

Unfortunately Copenhagen sometimes isn't explained well - the following fixes that:
http://motls.blogspot.com.au/2011/05/copenhagen-interpretation-of-quantum.html

Thanks
Bill

From the text"In practice, everyone can use pretty much the same wave function. But in principle, the wave function is subjective. If the observer A looks at a quantum system S in the lab, he will use a wave function where S has a well-defined sharp spin eigenstate as soon as the spin of S is measured by A. However, B who studies the whole system A+S confined in a lab won't "make" any collapse, and he evolves both S and A into linear superpositions until B measures the system. So A and B will have different wave functions during much of the experiment. It's consistent for B to imagine that A had seen a well-defined property of S before it was measured by B - but B won't increase his knowledge in any way by this assumption, so it is useless. If he applied this "collapsed" assumption to purely coherent quantum systems, he would obtain totally wrong predictions."So, where I can read more bout that?

 

[carllooper]

Its exactly the same as Ballentine and its a standard interpretation - in fact its the one I hold to:
http://en.wikipedia.org/wiki/Ensemble_interpretation

Its actually quite similar to Copenhagen:
http://en.wikipedia.org/wiki/Copenhagen_interpretation
The subjective view, that the wave function is merely a mathematical tool for calculating the probabilities in a specific experiment, has some similarities to the ensemble interpretation in that it takes probabilities to be the essence of the quantum state, but unlike the ensemble interpretation, it takes these probabilities to be perfectly applicable to single experimental outcomes, as it interprets them in terms of subjective probability.

Its basically the difference between Bayesian and Frequentest view of probability.

Einstein's and Bohr's interpretations were in fact not that dissimilar - the key difference was Bohr considered the state a complete description - Einstein most definitely did not.

Thanks
Bill

Thanks Bhobba, that's well summarised.

The only point I'd disagree with is the idea that Bohr would hold either the wave function (the mathematical formalism) to be subjective, or what it represents to be subjective. In Copenhagen (as much as other interpretations) the wave function still represents (or encodes) what is understood as physically taking place.

If we otherwise characterise Copenhagen as a "subjectivist" interpretation we would have to demonstrate in what way that would be the case, either independently of any claims Copenhagen makes, or conversely where in Copenhagen it characterises itself in that way.

I guess what is really at issue is this term "subjective". What is it's function or purpose? How does it enter the language? If it's sole purpose is to suggest that the wave function itself is a representation, then by that definition all interpretations of the wave function would probably call it "subjective" - not just Copenhagen. It is a representation, be it a complete one, or an incomplete one. But the issue isn't (or shouldn't be) the internal reality or otherwise of the wave function itself, but in what it represents. Is what it represents, subjective? Therein we are on firmer ground. In Copenhagen I'd argue that what it (the wave function) represents is not being interpreted or proposed as subjective - or at least not intended to be interpreted that way.

That all said, I do get Motl's take on this. Heisenberg, if not Bohr, employs the term "subjective". Heisenberg's use of the term is in a way that will be agreeable to classical thought and classical realism. To not buck the system (as one might say). To speak in terms that can be understood (at that time, or even now). But it is certainly not in any way meant to suggest that the wave function represents some sort of fantasy. Bohr is quite clear about this. What becomes a fantasy for Bohr is just classical realism. Not realism full stop.

While Bohr might think the wave function (and/or what it represents) is the last word in the matter, that doesn't (of course) mean it is, but nor does it mean that any other word in the matter would look anything like that which a post-Einstein conception might propose.

Carl

 

[bhobba]

So, where I can read more bout that?

I am not quite sure what you want to read more about, but these days Copenhagen, as indicated in the linked article, is a bit dated. Consistent Histories is the more modern take:
http://quantum.phys.cmu.edu/CHS/histories.html

Its generally accepted decoherent and consistent histories are basically the same - but there are a few differences in approach. Interestingly decoherent histories is rather like many worlds without the many worlds.

Thanks
Bill

 

[bhobba]

I guess what is really at issue is this term "subjective".

You and me both.

It's the same thing as Frequentest vs Bayesian probability - you find heated arguments on both sides. Bayesian is subjective - in fact I can't really tell the difference between Copenhagen and the Bayesian interpretation of QM:
http://math.ucr.edu/home/baez/bayes.html

John Baez, who often penetrates to the heart of issues, says it well:
'It turns out that a lot of arguments about the interpretation of quantum theory are at least partially arguments about the meaning of the probability!'

Here is the actual Bayseayn interpretation of QM:
http://en.wikipedia.org/wiki/Quantum_Bayesianism

Thanks
Bill

 

[andresB]

I am not quite sure what you want to read more about,

I was asking about that example that I quoted above, basically the subjectivity of the wave function proved by comparing the measurement of two different observers.