Is QM interpretation a matter of knowledge and probability?

[reilly]

One of my goals in participating in this forum, is to get my physics chops back, after a long period in the hinterlands of commerce. I've learned a great deal from many bright and interesting people here.

My introduction to QM happened almost 50 years ago, at which point I became fascinated with the issues of interpretation. Nobody then worried much about interpretation, because the heyday of particle and solid state was in full swing by the late 50s -- Schwinger's Radiative Corrections Paper came out in 1949. There was more opportunity for theoreticians than there were theoreticans -- many of us found working with experimentalists fascinating and rewarding -- dealing with Nature face-to-face if you will. QM interpretation was not on the A-list; too many other things to do.

After reading many posts about interpretation, some clear and straight forward, some logically and factually challenged, some that are over the top, I feel comfortable in laying down my views on interpretation, many of which I owe to Sir Rudolf Peierls' writings.
.................
To be direct: QM probabilities represent states of knowledge, just as classical probabilities do. When I do a measurement, indeed the wave function collapses to provide the knowledge of the particular outcome. The collapse is a physical phenomena, as the brain goes from knowledge of probabilities to knowledge of the outcome.

This approach has many advantages, and requires no mysticism nor methodological hand-waving. And it recognizes that, at the probability level, classical and quantum physics are very similar. That is, probability is probability, whether applied to electrons or football games. Why? The formal measure-theoretic approach is applicable to both flavors of physics. The probabilities at issue are often governed by similar differential equations for the systems probability density. In physics we use the evolution of the density matrix, in classical cases we use some form of a stochastic differential equation. (See An Introdution to Stochastic Processes by M.S. Bartlett. This is a tough book.But, if you can get through it, you'll have a better understanding of why probability is probability -- QM and CM just use different dynamics and assumptions. )

It's relevant to note that classical and quantum meet in Rutherford's experiment. The alpha-nucleus cross section can be computed classically or quantumly (sorry 'bout that) with identical results.

This means, of course, that there are many wave functions, one for each observer if you will. Naturally, when doing a scattering experiiment, all observers will agree on the outcome probabilities. It's crucial at this point to reinforce the almost obvious: the outcome probabilities of the various observers must be the same: they are all observing the same event. And, Einstein is our authority. He says that events are invariant. (I'm assuming all the observers are in the same inertial frame. But unitary transformations are around to help any referehnce frame generalization required.

There's another way to view this interpretation, based in the Shannon-Weiner Theory of Communication(or Information) -- discussed in Bartlett's book --. Roughly speaking, a measurement generates a signal, which ultimately one or more of the experimenters receive. If you push through, you can identify the transmitter and the receiver, the channel(s), the aplphabet, and the error patterns. One of the coolest results is that it is always possible to discern a message from noise -- but it may take a long time. The basics are simple: Shannon, sort of in so many words, uses the law of Large Numbers to average out the errors, which may require lots of repititions.

(I'm fairly convinced that all of physics, at the minimum. can be fully described as a communication system -- nature speaks to us through experiments and observations. What I'm less than clear about, is the value of such an enterprise. if it has not been done, it might well be a great thesis topic for a budding theorist.)

A look at EPR, and then we're done. EPR is probably unparalleled in physics for the amount of nonsense generated, the amount of profoundity generated, and the amount of passion generated. Let's look at EPR from the knowledge perspective. Let's do the simplest experiment-- electrons or photons, each with opposite helicities. and each traveling down a tube toward a detector, which will measure helicities. We'll make a configuration that precludes quick communication between Mr. A, and Ms. B -- there is no chance they can compare notes afer one measurement.

Mr. A finds helicity UP. He knows from appropriate theory, that Ms. B, measuring after Mr. A will measure spin down. he is projecting by means of established theory, that the second measure ment MUST be spin down. (We do this sort of thing all the time.) He knows that a single helicity measurement is sufficient to determine the spin state of the two particle system.

Ms. B knows zip about Mr. A. As far as she is concerned, there's an equal chance for UP or DOWN. However, she does know that if she gets UP, then he got DOWN, and vice versa. Again, this is aplication of fundamental theory.

Everything is local, and there is no need to invoke faster-than-light communication. Also note, that this experiment can be done with numerous classical systems. The difference beteween QM and CM show up when, for example, we measure spin in a direction other than that of the particle's momentum, the outcomes of which are controlled by Clebsch-Gordan coefficients. (The closest classical situation I can imagine is a pair of spinning tops with nutation and precession somehow paired.)

If there is any magic here, it has to do with physics itself. Physics tells Mr. A about things outside his immediate environment, by inference rather than by direct observation. It is our cumulative knowledge that allows Mr. A to transcend space and time with his knowledge.


Regards,
Reilly Atkinson

What about simultaneous measurements with Mr. A and Ms. B? Anybody know anything about this issue?

 

[vanesch]

This is the positivist viewpoint. It takes that there is only a "state of knowledge". But the problem I have with it, is:
knowledge about WHAT ? If there is no state of nature, what does it mean for me to have "the knowledge that the electron is in position x" ? If there is no "position of the electron" in the state of nature ? There *is* then no nature (or at least not the possibility of a mathematical description of the state of it) ?
And from the moment you DO introduce a (classically-like) state of nature of which we learn stuff, you run into troubles, no ?

 

[reilly]

This is the positivist viewpoint. It takes that there is only a "state of knowledge". But the problem I have with it, is:
knowledge about WHAT ? If there is no state of nature, what does it mean for me to have "the knowledge that the electron is in position x" ? If there is no "position of the electron" in the state of nature ? There *is* then no nature (or at least not the possibility of a mathematical description of the state of it) ?
And from the moment you DO introduce a (classically-like) state of nature of which we learn stuff, you run into troubles, no ?

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>..
I view myself, as do, I think, many scientists as a pragmatist. At the minimum, this pushes us toward less than perfection in the big picture, and modest comfort in the day-to-day picture. Said directly: I assume there's a world out there, it provides the signals we perceive. As a physicist, I'm cautious in making inferences, so I say, "It is as if Nature is out there." Looks like a "State of Nature", sounds like a "state of nature", walks ...

So, outside of my scientific perspective, I say, "It's a duck" -- like my grandkids are real, my piano is real, ..." God bless Occam.

As a matter of fact, this Peirels - Knowledge approach to QM really parallels our day-to-day encounters with reality -- you "see", you know, you don't see, you don't know, of course, unless ...'" What is more practically real than our knowledge?

I think, I might have been a positivist once -- but then I enountered Theloneous Sphere Monk, ee cummings, and Paul Klee, and decided, as. pointed out by Archibald MacLeish, "A poem should not mean but be."


That's a rather oblique answer to your question about knowledge. But it is indeed an answer. You truly know what you know.


Regards,
Reilly Atkinson

 

[leandros_p]

That's a rather oblique answer to your question about knowledge. But it is indeed an answer. You truly know what you know.
Regards,
Reilly Atkinson

Dear sir,

I am Greek and there is an ancient greek scientific rule that says: "I know only one thing, that I know nothing".

This phrase belongs to Socrates. While the contemporary wisdom names the ancient Greek scientists as philosophers, actually they were scientists. So was Socrates too.

Maybe, this could be the answer to your question: Science always proves the ignorance of the scientists. This is the essence of science. QM does this in a more profound way, neverthelles it is "science".

 

[reilly]

leandros-p -- What you say makes sense to me, with, however, one exception. My family and I have greatly benefited from modern medical practice, which is permeated by what might be called, at least by some, scientific knowledge. (In fact, as I think about it, without something to know, there can be no ignorance. )

And, I think the essence of science is courage: to seek order in the face of ignorance and stuff going every which way. Perhaps another take, courage to follow one's curiousity. And, to do all of this with a respectable level of humility.

Regards,
Reilly Atkinson

 

[Sherlock]

One of my goals in participating in this forum, is to get my physics chops back, after a long period in the hinterlands of commerce. I've learned a great deal from many bright and interesting people here.

So have I, and that includes from you, and the other mentors, and some unofficial mentors as well. My comments below are just my current thoughts on this stuff ... and are, as always, amenable to modification.
Any corrections or alternative perspectives are appreciated.

To be direct: QM probabilities represent states of knowledge, just as classical probabilities do. When I do a measurement, indeed the wave function collapses to provide the knowledge of the particular outcome. The collapse is a physical phenomena, as the brain goes from knowledge of probabilities to knowledge of the outcome.

This is sort of the way I've learned to think about it. Whatever else the wave equations and wave functions might be conjectured to represent wrt an underlying quantum world, it can at least be said that they represent our quantitative apprehension of events that occur at the level of our sensory perception.

The probabilities, and our knowledge of quantum systems, refer to the formalism(s) and the frequencies of occurance of certain specific qualitative (macroscopic) phenomena at the detector end of a setup --- things that anyone with normal sensory capabilities can observe directly.

The detector outputs might be assumed to be amplifications of phenomena occurring at the level of an underlying quantum world not amenable to our sensory perception. This assumption of an underlying realm seems to be a reasonable one given what has actually been observed by physicists. Nevertheless, it is a metaphysical assumption --- and because the definition of this assumption entails that the underlying quantum world isn't amenable to our sensory perception, then the precise relationship between an underlying quantum reality (whatever it might be and however it might be behaving) and the detector outputs that the formalism of the theory quantitatively describe is, and must remain, a matter of speculation.

Thus arises the quantum measurement problem.

It's difficult to sort out exactly what quantum theory, being an assemblage of mathematical abstractions (some of which correspond to our ordinary experience and some of which don't), corresponds to in the real world (which, presumably, includes an underlying quantum world as well as the worlds of microscopic, macroscopic and telescopic phenomena) --- except that it seems clear enough that it contains symbolic elements that correspond to the data, the instrumental outputs, that you or I or anyone can perceive.

We ascribe meaning to statements about the world of our sensory experience by pointing to the objects and events that those statements correspond to. But we don't, by its definition, perceive an underlying quantum world. So, there's no way to ascertain how closely, or to verify even if this or that qualitative or quantitative symbolic construction corresponds to an underlying reality that is precipitating the causal chain of amplifications that eventually results in the data. We can only ascertain how closely the quantitative predictions correspond to the instrumental output.

This means, of course, that there are many wave functions, one for each observer if you will.

This seems like it might be an unnecessary complication. The basis of empirical science is that we are (us humans) essentially the same (sort of) detector. So, for a given instrumental setup, you don't need to have different wave functions for professors Smith and Jones' brainstates. The instrumental setup is the observer of (or perhaps more precisely, the producer of --- or perhaps more precisely, as far as we can know, it is) the quantum system, and what is observed by us is the instrumental setup's output (via data tapes, screens, clicks, cloud chambers or whatever).

What about simultaneous measurements with Mr. A and Ms. B? Anybody know anything about this issue?

The order of detection of an AB pair doesn't matter in the optical EPR-Bell situations you're considering, afaik. The pairings are made via coincidence intervals as well as time to amplitude conversion. There is one joint polarizer setting associated with a pair. In practice, again afaik, simultaneous detection doesn't actually occur.

 

[Sherlock]

This is the positivist viewpoint. It takes that there is only a "state of knowledge".

The positivist viewpoint is the basis of empirical science. It's all about meaning. The basis of meaning is our sensory perception. Any statement that purports to describe something in the physical world elicits two questions: 1) what do you mean?, and 2) how do you know? If the answer to the first question has no physical referent other than a set of symbols and the manipulation of these symbols, then the statement is said to be metaphysical. The world-branching of the MWI is, by its definition, a metaphysical construct.

The photons and electrons of quantum theory are, by contrast, labels that correspond to specific experimental preparations and results, as well as symbols and symbolic operations.

But the problem I have with it, is:
knowledge about WHAT ? If there is no state of nature, what does it mean for me to have "the knowledge that the electron is in position x" ? If there is no "position of the electron" in the state of nature ? There *is* then no nature (or at least not the possibility of a mathematical description of the state of it) ?

"The electron is in position x" corresponds to a specific instrumental result. QM assigns probabilties to the various possible instrumental results. The "state of nature" pertaining to some preparation prior to an experimental run is a statement regarding the possible and probable instrumental results of the run. The "state of nature" pertaining to the preparation following the run is the raw data (which might of course require some post-processing to make theoretical sense of).

And from the moment you DO introduce a (classically-like) state of nature of which we learn stuff, you run into troubles, no ?

No. The "(classically-like) state of nature of which we learn stuff" is the stuff that we perceive --- from the results of quantum experiments to observations of the world at large. Using this as the evaluational basis for statements about the world provides an unambiguous criterion for deciding which statements about the world are more or less accurate --- the positivist approach is the one that characterizes science precisely because it avoids the troubles that accompany metaphysical statements.

The troubles that accompany the MWI interpretation are unavoidable given the two assumptions on which it seems to be based: 1) there is an underlying quantum world wrt which we're necessarily perceptually ignorant, and 2) the formalism of qm is in 1-1 correspondence with the makeup and behavior of this underlying quantum world.

Even though assumption 1) seems reasonable and arguable enough, it isn't necessary.
Wrt assumption 2), you could just as well say that the formalism of qm isn't in 1-1 correspondence with an underlying quantum world. Either way, it's just metaphysical speculation.

On the other hand, the minimalist probabilistic interpretation makes no such assumptions and is therefore consistent with the tenets of empirical science. It concerns what we know to be true (ie., even if assumptions 1) and 2) are true, which we don't know, it is still also true that qm is a mathematical algorithm for predicting the probable results of experiments.

Anyway, let's assume that assumption 1) is true. Then any troubles that might accompany qm (or any theory of quantum phenomena) have to do primarily with our perceptual ignorance of an underlying quantum world. That is, it's primarily a hardware (biological as well as instrumental) problem rather than one of merely interpreting the formalism (since our perceptual ignorance of an underlying quantum world entails that we have no basis on which to evaluate how closely the qm formalism corresponds to it).

I've been reading over your recent replies to me regarding MWI, as well as some other stuff. At this time the main thing that I'm getting from them is that MWI advocates want quantum theory to be more than it actually (at least the way I see it so far) is.

 

[vanesch]

Warning: highly philosophical content. If this continues, I think I'll move the thread to the philosophy forum.

If the answer to the first question has no physical referent other than a set of symbols and the manipulation of these symbols, then the statement is said to be metaphysical. The world-branching of the MWI is, by its definition, a metaphysical construct.

Of course it is metaphysical! But so it the hypothesis of the existence of an objective world. Even the phrase "the voltmeter reads 7V" is metaphysical because it includes in it, an implicit assumption of an objective existence of a voltmeter and of its reading. The only phrase that is not metaphysical is "I perceive a voltmeter reading 7V". But we are so very used to making this identification that we don't even bother.

The photons and electrons of quantum theory are, by contrast, labels that correspond to specific experimental preparations and results, as well as symbols and symbolic operations.
"The electron is in position x" corresponds to a specific instrumental result.

That's my point: this is just as well metaphysical. The only thing you really know is that you perceive a specific instrumental result. You have extrapolated here the "I perceive an instrumental result" into "there IS a specific instrumental result" ; but we're so used to do so this metaphysical interpretation, that you don't even notice.

No. The "(classically-like) state of nature of which we learn stuff" is the stuff that we perceive --- from the results of quantum experiments to observations of the world at large. Using this as the evaluational basis for statements about the world provides an unambiguous criterion for deciding which statements about the world are more or less accurate --- the positivist approach is the one that characterizes science precisely because it avoids the troubles that accompany metaphysical statements.

Entirely, but as such, it is a viewpoint which is "minimalistic" (and compatible with solipsism in fact! You equate the "state of the world" to the "state of your subjective perception" - the difference with solipsism is that you do not postulate the non-existance of a real world, you simply don't want to consider it). So a positivist interpretation denies the possibility of a description of an objective world. Although this is possible, I find it too early to deny the very well working hypothesis of a real, objective world.

The troubles that accompany the MWI interpretation are unavoidable given the two assumptions on which it seems to be based: 1) there is an underlying quantum world wrt which we're necessarily perceptually ignorant, and 2) the formalism of qm is in 1-1 correspondence with the makeup and behavior of this underlying quantum world.

YES! That's the very meaning, to me, of a physical theory: you ASSUME for the sake of interpretation, that the theory is describing correctly an objectively existing world, and then you point out what are the relationships between the formal elements of the theory, and the (metaphysically postulated) external objective world.

There are 2 possible denials of an interpretation:
1) there IS no objectively existing world
2) the theory at hand is NOT describing it

Now, if we take 1) (which is the solipsist viewpoint), I think we can stop right away. If we take 2) then, by definition, we are not going to interpret a (wrong) theory, are we ? So in our quest to interpret a theory we must assume that there *IS* an objective world, and we must also assume that the theory describing it *IS* going to be describing it correctly. So of course, for the sake of interpreting quantum theory as a description of an objective world, we have to assume 1) and 2). Any denial of this starting hypothesis puts into jeopardy the very exercise of an interpretation.

Even though assumption 1) seems reasonable and arguable enough, it isn't necessary.

The only way out is solipsism! However, the hypothesis of an existing external world IS possible, and it has always been a very fruitful hypothesis, so there's no reason to drop it now.

This is what I don't understand, btw. People arguing against an MWI interpretation of the quantum formalism often do this because they "find this assumption of parallel worlds in which copies of themselves wander around too weird to be true" ; but then they have no difficulties of kicking out ENTIRELY the assumption that there *IS* an objective world!

Wrt assumption 2), you could just as well say that the formalism of qm isn't in 1-1 correspondence with an underlying quantum world. Either way, it's just metaphysical speculation.

Well, as I tried to point out, this statement is simply that QM could be the WRONG theory, which has a WRONG description of the objective world. I ALWAYS POINTED OUT THAT THAT WAS A POSSIBILITY, but then you should come up with a better theory! But this is NOT the starting point of an interpretation of a theory.
Take Ptolomy's epicycles. It is empirically CORRECT. It is, however, a WRONG description of the solar system (with its spheres and so on), and Newton's theory does better. Once we have Newton's theory, we can UNDERSTAND how it came about that Ptolomy's epicycles gave good empirical results, and we also can re-interpret them as terms in a perturbation expansion in Newtonian dynamics. However, as long as you didn't have Newton's theory, there was no point in viewing Ptolomy's theory as a perturbation expansion of an unknown dynamics. That was not a helpful way to work with Ptolomy's theory, was it. If you wanted to interpret Ptolomy's theory, you had to stick to the spheres. It would have been difficult to reason physically in Ptolomy's theory without the spheres thing. So the *right* thing to do was to accept the hypothesis of reality of the spheres. This can, one day, happen to quantum theory. Maybe we'll find an underlying theory which will explain the formal success of quantum theory. Then we will not have to worry anymore about interpretational problems of the quantum formalism, because they will now be interpreted in function of the new theory. At that point, MWI will be of no use anymore. I never claimed anything else. But, there's no other such theory around ! (at least, that doesn't bump into other problems)

On the other hand, the minimalist probabilistic interpretation makes no such assumptions and is therefore consistent with the tenets of empirical science. It concerns what we know to be true (ie., even if assumptions 1) and 2) are true, which we don't know, it is still also true that qm is a mathematical algorithm for predicting the probable results of experiments.

The problem I have with seeing QM as "just a mathematical algorithm" is that you do not know anymore what the different parts in the calculational procedure are supposed to mean. It is not unthinkable that 1) and 2) are false, and as you point out, the assumption of their correctness is essentially a metaphysical hypothesis. But WHY SHOULD WE NOT CONTINUE TO ACCEPT THOSE METAPHYSICAL HYPOTHESES, IF THIS IS SOMEHOW POSSIBLE ?
I mean, we never did that with classical physics, did we ? We always assumed that the state description of classical physics corresponded to an objective world outside, and it helped us in using classical physics, and we saw it as having a strong explanatory power. The moon really was there, and was not just "a construct of our knowledge", right ? It was a strong intuition builder to take the material points in classical physics are "really out there". Why deny this faculty to QM ?

Anyway, let's assume that assumption 1) is true. Then any troubles that might accompany qm (or any theory of quantum phenomena) have to do primarily with our perceptual ignorance of an underlying quantum world.

But I fail to see WHAT troubles. If I offer you a view in which the theory to be interpreted can:
1) accept the existence of an objective world (a metaphysical hypothesis)
2) assume that the formalism of the theory we're trying to interprete is a correct description of an objective reality (the correctness of the theoretical framework)
3) be in accordance of how we should deduce from it, our subjective experiences

isn't that better than an "interpretation" that is based upon:

1) the assumption that there is no objective world (but only our subjective experiences, organized around some principles of knowledge)
OR
2) that the formalism of the theory is in fact fundamentally misguided but results nevertheless in correct empirical predictions ?

Isn't 1) far more outlandish than the claims MWI makes and isn't 2) a priori denying the theory you're trying to interpret ? Of course all these considerations are metaphysical, but isn't a priori taking 1) and 2) as working hypotheses, a far more reasonable POV, which will pay off in a much better intuitive understanding of the theory at hand ?

I've been reading over your recent replies to me regarding MWI, as well as some other stuff. At this time the main thing that I'm getting from them is that MWI advocates want quantum theory to be more than it actually (at least the way I see it so far) is.

The point is: why can't we assume that quantum theory is more than you think it is, as a working hypothesis, to construct a view on it ? You can only *know* that quantum theory is less than it claims if you have a better theory, no ? Must we necessarily start by assuming it is WRONG, even before thinking about it ? Is that the best way to interpret it ?

 

[Schrodinger's Dog]

This is just my opinion so feel free to disagree.

Is anyone surprised that when you start looking at things that are smaller than we can percieve, that we no longer have a means to absolutely prove anything, therefore QM is always going to be a hypothesis driven science that leads to theory rather than what we see we interpret as with most other sciences, until we can absolutely say that whatever maths and evidence we come up with is inference rather than stated fact.

With the advent of QM theory there was a move away from experimentation into speculation that has continued unchecked to this day, when you can't see directly what it is your looking at then what do you expect? Yes QM has a more than a few bewildering concepts to get your head round, but for now I see it as the best fit theory, and until someone comes up with some proofs for the other theories floating around I'll be looking at that not dreaming of membranes or strings. Fascinating though they are.

 

[leandros_p]

What you say makes sense to me, with, however, one exception. My family and I have greatly benefited from modern medical practice, which is permeated by what might be called, at least by some, scientific knowledge. (In fact, as I think about it, without something to know, there can be no ignorance. )

Dear Reilly,

We all have the same experience of medical treatment, but let me say that this is not the effect of "scientific knowledge". Science works with "information".

Both Physics and Medical sciences are conducting their function by processing "information". It is a common misunderstanding that a pill, or a medical operation, produces a result in a deterministic way, but every scientific medical effort to cure is just an attempt to provide the best treatment. "Best medical treatment” is that which has the best probability to provide cure, therefore the "medical practice" is an attempt for treatment.

So, like any other science does, medical science just makes "attempts", just offers a "prospect", just measures the "odds". Medical practice just handles information. There is no "knowledge" in science.

It is human custom to reckon the information with the best uncertainty factor as knowledge. But this is a mistake. Knowledge should have no element of uncertainty.

If you study a medical publication, it becomes evident that medical practice is about statistics and probabilities. Certainty and absolute knowledge is not there at all. Any well defined medical therapy, which has the best probability to cure, is always proven to fail to provide the remedy in certain instances. These “certain instances”, in which cure fails, are undefined until the moment they are being observed and it is possible to define them only by a statistical definition. This makes Physicians to “look” like non-scientists. But they are Scientists; they do not know the cure, they calculate the cure.

Quantum Physics constantly reminds to us this axiom: Science is the mathematical/logical process of information.

The scientific “peculiarity” of Quantum Physics was expressed by the ancient Greek scientist Heraclitus: “You cannot step twice into the same river, for other waters and yet others go ever flowing on”.

And a final comment for vanesch: let me say that this is not "highly philosophical content". This is the most physical scientific content. It is the empathy within ourselves towards a specific classification that makes the content to "look" metaphysical or physical. And it seems to me that the forum is using a specific classification, although this is what Quantum Physics is trying to prevent us from doing. It is all about scientific methodology and philosophy has nothing to do with that.

Leandros

 

[vanesch]

Yes QM has a more than a few bewildering concepts to get your head round, but for now I see it as the best fit theory, and until someone comes up with some proofs for the other theories floating around I'll be looking at that not dreaming of membranes or strings. Fascinating though they are.

Just for the sake of it: string theory and variants ARE quantum theories which do not touch upon the general axiomatic structure of quantum theory.

 

[vanesch]

And a final comment for vanesch: let me say that this is not "highly philosophical content". This is the most physical sientific content. It is the empathy within ourselves towards a specific classification that makes the content to "look" metaphysical or physical.

Just as a general remark: when I say that something is "philosophical" in content, I do not mean this in any kind of negative way. I know that in the culture of some physicists, "philosophy" is another word for mystical, meaningless blathering ("it is nothing but philosophy" Feynman style of talking), but I am not one of them. I simply mean that the discussion goes towards the more conceptual or primordial viewpoints, and goes away from the discussion of actual scientific practice, which is the discussions of the mathematical technicalities of the formalism and/or the operational technicalities of experimental work.

I really think that I'm going to move this thread to the metaphysics forum...

 

[selfAdjoint]

knowledge about WHAT ? If there is no state of nature, what does it mean for me to have "the knowledge that the electron is in position x" ? If there is no "position of the electron" in the state of nature ? There *is* then no nature (or at least not the possibility of a mathematical description of the state of it) ?

I read this before I went away, and I have been turning over in my mind. The knowledge interpretation doesn't say anything silly like there is no state of nature. It just denies that quantum mechanics has anything to say on the subject. And why should QM do that? If you consider its history, beginning with Planck and going through Bohr and Heisenberg and Schroedinger and so on, none of them were concerned to erect an ontology, they were trying to explain how subatomic particle could behave in the apparently paradoxical way they did; how electrons seemd to orbit but without radiating. How X-rays could behave now like waves and then like little bullets.

And the theory these founders erected DOES that! It accounts for our observation of these subatomic events (and of course nowadays of macroscopic events as well). Why does it have to carry an ontological burden too?

Knowledge of what? Of the outcome of the experiment. As Bohr maintained, there is always an experiment in the discussion because QM is not a theory about the world but a theory about how we see the world.

 

[vanesch]

I read this before I went away, and I have been turning over in my mind. The knowledge interpretation doesn't say anything silly like there is no state of nature. It just denies that quantum mechanics has anything to say on the subject. And why should QM do that?

The problem with that POV, is that it doesn't allow you to posit it as a universal theory of nature. In other words, it is not fundamental physics.
I repeat the 3 possibilities we have:
1) There is no objective reality
2) There is an objective reality, but it is somehow not logical (in that there is no mathematical structure that can model it entirely, that you will always run into contradictions)
3) There is an objective reality, and it is logical (in that there exists a mathematical object that models it perfectly).

I would say that physics takes as its basic hypothesis, (3). (1) is solipsism, and (2) is illogical and as such, not open to rational inquiry on a deep level (this is often the hypothesis of religious world views, where a kind of deity decides, in an unfathomable way).

So once we accept (3), all physical theories are supposed to be approximations of that ultimate mathematical model (the correct laws of physics). As such, they need elements in them that are supposed to at least try to come close to the mathematical model of nature. Now, in certain cases, we have found good models, just to find totally different, and better models afterwards. We can understand the good models as aspects of the better models. But when we "reach the bottom" of our theoretical constructs, in the sense that we arrive at our currently most fundamental description, we have no choice but to seek in them the things that are supposed to correspond to the mathematical object that is supposed to represent nature. For the moment, QM is our "bottom" theory. We have no underlying theory. If we want to interpret it (in the sense of turning the mathematical machinery into a physical theory) we have no choice but to take certain theoretical constructs in the formalism of QM as corresponding to that sought-for mathematical object that describes nature. Maybe it does this in a clumsy way, but it is always better than to simply give up on it, because if we do that, we LOOSE THE LINK BETWEEN experiment and theory.

Bohr can only pretend to escape this necessary interpretation by assuming
that QM is not a universal theory, nor is classical physics, but that there is some kind of barrier between both. He takes it that classical physics can pretend to a description of "macroscopic nature" (and he NEEDS this description to associate to a measurement apparatus, a certain operational meaning) WITHOUT having an ontological description of any microscopic nature. For instance, a light flash coming off a screen is probably seen as having a classically ontologically correct description (using classical EM). An electron, however, is to have such an ontological description (it hit the screen) when we want to make sense of the light flash in the first place, but is NOT to have such an ontological description without the screen. This is inconsistent. The electron WAS there and DID produce a flash, or it doesn't make sense to talk about the electron as being somewhere. But you can't have it both ways. You cannot have it that "an electron was ontologically responsible for the emission of a flash", and "we're not supposed to talk about the position of an electron, or even of an electron in the first place". Bohr seems to take the first view when it suits him (in order to be able to give a meaning to the quantum formalism, and to define the relationship between his observables and an apparatus), and take the second view when confronted with the consequences of his first view.

1) "is there a flash ?" (yes, because macroscopic and thus classical, which has an ontology).

2) "is the flash caused by an electron ?" (yes, because otherwise I loose my link between my quantum description (position operator of electron) and my experimental reality) :shy:

3) "was the electron at the screen then ?" (eh... yes, we saw the flash) :uhh:

4) "was an electron emitted from the electron gun ?" (yes, otherwise it wouldn't have arrived at the screen, would it ?)

5) "was there an electron between the electron gun and the screen ?" (sure, but we cannot talk about its properties, it is now described by a wavefunction, which is simply supposed to be a tool to link our knowledge from the emission of the electron to the flash seen on the screen)

5) "is an electron an excitation of the Dirac field ?" (the Dirac field is a construction in our theory structurising our knowledge about the different ways of preparing and observing experiments, and we should not attach any reality to it, nor to its excitations)

6) "so finally, there was no electron, because it is only a concept in our theoretical construction of our knowledge organization, namely "excitation of the Dirac field" ?" (indeed, the electron, as a excitation of the dirac field, is not supposed to correspond to a certain ontology, but just an explanatory concept in the organization of our knowledge, as proposed by quantum theory)

7) "But if the electron doesn't correspond to anything, why do you say that it was causing the flash ?" (eh... an electron is nothing else but a "flash causing entity" in our theory) :grumpy:

8) "Are atoms made up of flash causing entities then ?"

In Bohr's view, we then have: a classical current heats somehow a classical wire in a classical electron gun, "magic happens" and then a classical flash is emitted by a classical screen. The "magic happens" is the quantum description of the wavefunction of the electron (which is not supposed to correspond to anything real) evolving through the setup, which is not, in any way, supposed to correspond to any ontological description. But it needs suddenly to come into ontological existence when it activates the measurement apparatus, because otherwise, there is no link between the outcome of the measurement apparatus and the quantum mechanical description. This is where Bohr is cheating. He DOES give an ontological existence to his quantum chimera, but only when it suits him (as the proper activation of the measurement apparatus), and then denies it when it doesn't suit him. That's what I call "inconsistent".

Also, I find this view highly incompatible in the framework of (3), because NO consistent mathematical description of nature is proposed. There is a dancing left and right between classical and not classical, real and "just formal"...
Nevertheless it is not consistent with (1) either, because SOME ontology is given to macroscopic descriptions in classical theory. It's closer to (2): an illogical universe. An inconsistent world view is probably a suitable description of such a universe :yuck:

 

[selfAdjoint]

The problem with that POV, is that it doesn't allow you to posit it as a universal theory of nature. In other words, it is not fundamental physics.

Sure. And so what? Maybe some other physics will do the job or maybe not.

Do you really characterize your work with MWI as "fundamental physics"? How about careful's backward causation or the transactional interpretation? They all sound like sci fi bafflegab to me. "Built up logically" yes, but based on wild and crazy (i.e. implausible to me) premises.


(added) One of the constant features of the history of physics is the temptation to reify. From Descartes' vortices to Kelvin's and Maxwell's mechanical ethers, this is something a prudent physicst (like Newton!) will do well to avoid. Let your theory do what it does, explain what it explains, and don't try to push it into being a fundamental account of reality.

(second add) For the rest of your argument, my sense is somewhere between your options 2 and 3. I would plump for 3 except for that intrusive word "perfectly". But assuming that 3 is true and there is a perfect mathematical model of reality, why would you assume that quantum mechanics is it? Notice that QM is subsumed in field theory, that field theory has only shaky localization and problems representing interaction, and that "thingness" seems not to be preserved very well by the proposed physics of the standard model. You can't REALLY fillet non relativistic QM out of all this melange and treat it as a standalone philosophical construction can you?

 

[leandros_p]

Also, I find this view highly incompatible in the framework of (3), because NO consistent mathematical description of nature is proposed. There is a dancing left and right between classical and not classical, real and "just formal"...
…An inconsistent world view is probably a suitable description of such a universe

You are right, if you are accepting that science is about the "description of nature".

But science is about the "information about nature".

It is the difference between the phrases "description of an object" and "information about an object" that makes the difference in forming a conclusion about the "knowledge" of the object. Science is a common language that is used to share information. It is impossible to share knowledge about something, because knowledge is non-communicable.

The failure in descrying the difference between “description” and “information” produces the confusion. Let me use an analogy: if I will describe to you the whether of tomorrow I am providing knowledge, I am sharing my knowledge with you. If I will give you a forecast for the whether of tomorrow I am sharing with you scientific information. This example seems obvious, because we are talking about the future and it is impossible to know the future, while it is only possible to calculate the future based on information with calculated uncertainty.

This uncertainty is not based on our weakness to gather the proper scientific information. Whether forecasting depends on many physical elements, each one being distinct information, interacting with each other and the problem of describing the future whether is a problem of making the proper measurements and the proper calculations of an object that does not have one “picture”. We can not calculate the whether by seeing a single “picture” of information.

Bohr said about quantum theory: “Evidence obtained under different experimental conditions cannot be comprehended within a single picture, but must be regarded as complementary in the sense that only the totality of the phenomena exhausts the possible information about the objects”. ( http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Bohr_Niels.html )

It is important that Bohr was talking about “the possible INFORMATION about the objects”. He was NOT talking about the “the possible description of the objects”. In Science, there can only one “description” of an object; while there can be a number of possible information about it. The “totality” off the possible information constitutes the “picture” of the physical object as a multi-folded description.

Regarding the description of a physical object as the “evidence obtained under different experimental conditions”, according to Bohr, it “cannot be comprehended within a single picture, but must be regarded as complementary in the sense that only the totality of the phenomena exhausts the possible information about the objects”.

So, Bohr said that the totality of information about “the flash”, “the electron on a screen”, “the electron between the screen and the gun”, “the emission of electrons”, “the excitation of the Dirac field”, “the flash causing entity”, “the electron as atomic particle”, which you enumerate in your post, in the extent that they “exhaust the possible information about the electron” must be regarded as “complementary pictures” in order to comprehend the “evidence obtained under different experimental conditions”.

Quantum theory makes clear that a physical object, like an electron, is not possible to be comprehended/described by a single picture/information. The picture of physical objects is not univocal. Physical objects are “realities” that produce different information, which are being expressed by Science discretely because information/evidence is obtained under discrete different experimental conditions.

The “inconsistent world view” is valid only if you assume a single pictured view.

But it seems that the “World view” should not be comprehended as a single picture, but each “world view” must be regarded as complementary picture of a multi-pictured view.

Leandros

 

[reilly]

Well, when this thread got moved, I got lost.

Pragmatic and practical (ex)physicist that I am, I have litle clue about most of the discussion that has emerged from my initial post -- way above my pay grade. And, for me the knowledge interpretation is practical, simple, consistent with actual practice in the physics community -- and it is totally consistent with the way most people operate on a day-to-day basis. (I'll leave that idea as it is. I tend to avoid statements like, "It is clear,..." "It is obvious,... But in this case, to me it is obvious and clear. To me wave functions that physically collapse, MWI-type interpretations, make no sense, and seem overly complex, non-Occam if you will.

I will say that much of the impetus for this statement comes from my experience as a business man and consultant working with probability and statistics, simulation models, market and survey research, and from my experience as a research economist "bringing physics methods" to housing and urban economics. Probability is probability is probabiliy; it's all the same.

This is just my opinion so feel free to disagree.

Is anyone surprised that when you start looking at things that are smaller than we can percieve, that we no longer have a means to absolutely prove anything, therefore QM is always going to be a hypothesis driven science that leads to theory rather than what we see we interpret as with most other sciences, until we can absolutely say that whatever maths and evidence we come up with is inference rather than stated fact.

With the advent of QM theory there was a move away from experimentation into speculation that has continued unchecked to this day, when you can't see directly what it is your looking at then what do you expect? Yes QM has a more than a few bewildering concepts to get your head round, but for now I see it as the best fit theory, and until someone comes up with some proofs for the other theories floating around I'll be looking at that not dreaming of membranes or strings. Fascinating though they are.

What sciences are not hypothesis driven?

In fact with the advent of QM theory, experimentalists went nuts, behaved as if they were in a candy store. QM is based on experiment. My terribly biased view is that physicists go into massive speculation when they don't have enough to do, when they can't interpret or design experiments.


leandros_p -- What's the difference between information and knowledge? Funny, as a parent, a teacher, a manager, I always thought I was communicating my knowledge -- still do, for that matter.

To me, knowledge is what you know. Information is that which informs, unless you want to reevisit Shannon and Wiener. Info and knowledge can be the same, or different.

As far as I'm concerned, for example, my Doc's knowledge about the efficacy of various medications is exactly that. And, of course, he is highly aware of the problems and uncertainties. But, I pay him because he knows the ins-and-outs of treatments and medications.

For example, we know that left untreated, an infection can and will kill you. We know that a bi-polar individual who does not take Lithium (or equivelent) wiil start climbing the walls in a manic episosde. If you drink no liquids for long enough you will die. So, in my humble, simple-minded way, I conclude we know a lot about medicine, including some certainties.

Back to physics. But thanks for the discussion, even if much of it is way over my head.
Regards,
Reilly Atkinson

 

[leandros_p]

leandros_p -- What's the difference between information and knowledge? Funny, as a parent, a teacher, a manager, I always thought I was communicating my knowledge -- still do, for that matter.

To me, knowledge is what you know. Information is that which informs, unless you want to reevisit Shannon and Wiener. Info and knowledge can be the same, or different.

Dear Sir,

Let me present a schema of information and knowledge; doing that I will try to use your "language".

The process of "knowing" is the following:

Source -- Transmitter -------- Receiver -- Destination

Between source and destination travels a Message – this message is called knowledge. Between the Transmitter and Receiver there is “noise”, always.

The reception of message and the possession of the message thereafter are called knowledge status, at the destination.

This is a general logical schema. The absolute “knowledge”, in the way that you understand the term, is when in the above procedure the destination accepts the message in the original, unchanged and complete form, which had at the source.

Unfortunately, the intermediate stages of transmitter and of receiver, in being imperfect, combined with the noise that exists through the propagation media introduce alteration to the message, either by addition, or by subtraction. Therefore, the original message arrives at the destination modified, that is, the message at the destination is true but has a degree of uncertainty, while the original message at the source had no degree of uncertainty. The message at the destination is not the same as the message at the source. There is an uncertainty factor introduced in the message at the destination, during the process, which was not present at the source. This uncertain knowledge is called “information”.

You say that you are communicating your knowledge, which in a similar way was communicated to you in the first place. Because you do that according to the above logical schema, your "audience" does not get knowledge; it gets information, that is, a message with a degree of uncertainty. This is not a metaphysical interpretation of knowledge or of information. This is a scientific way to describe physical communication and physical understanding.

But then, don't we ever possesses knowledge at all? Well, not in an absolute way. We possesses knowledge in a relative way: First, we calculate the degree of uncertainty for the information we posses and we classify them accordingly. Then we accept the convention that knowledge is the least uncertain information.

This process of transmitting a message between a source and a destination is the way we process the reality of our everyday life, which is full of continuous messages which have their source in the outside world and their destination is “within” us.

So, scientists used the same methodology to get to know the messages that were transmitted by the physical objects and phenomena, which were being received by the proper receivers, either in the lab by instruments, or mentally by our logic. In the process, the message becomes information, in the context that it is modified compared to the original message, acquiring a degree of uncertainty.

While it is perfectly normal to suggest that we “know” and that we transmit/communicate our “knowledge” to others, the words “know” and “knowledge” have only conventional meaning, in defining the least uncertain possessed information by us.

There was a time, when Science also used such conventions. Today, Science of physics can not accept these conventions. It has to use literal terms in defining the “message” that physical objects transmit to our “receivers” as information, because the physical sources that are being examined, such as the atomic and subatomic particles and phenomena, send inconsistent messages.

The objects of classic physics are sending messages to our scientific receivers that during the above process are altered by the imperfection of the stages of the system and by the noise. Scientists have learned how to overcome these problems, which are called measurement problems. BUT, the objects of quantum physics are sending messages to our scientific receivers that are inconsistent, not just altered or modified. So scientists felt obligated to treat these messages in their “true” form, that is, as information. This is the “truth” of physical reality that we refused to face in classic physics, in the past: We can not know physical reality; we can only be informed about physical reality.

This is hard to accept, because for some strange reason it makes us feel like second class beings. Our certainty of “being” is staggered.

Leandros

 

[vanesch]

BUT, the objects of quantum physics are sending messages to our scientific receivers that are inconsistent, not just altered or modified.

And given the fact that ALL objects are "objects of quantum physics" in a certain way, this simply means that our universe is inconsistent...
I think that that step is slightly too fast, and I have difficulties seeing why people want to accept so very easily that the universe is INCONSISTENT (can you figure that ?), simply because the obvious view is "too wild and crazy" . So quantum theory, in this view, is a mathematical algorithm that allows us to find the statistics of inconsistency ?

I mean, quantum theory forces us in a certain way, to led go some of our preconceived ideas. That always happens with a new physical paradigm. Relativity had us let go the idea of absolute time, for instance. (To me, quantum theory just learns us something else: the relativity of perception.)

But I think there is a hierarchy amongst our preconceived ideas:

1) there exists an objective world
2) that objective world is logically build up
3) our subjective world is defined by the objective world
4) physical theories try to model the objective world
5) relativity is a principle (time is relative)
6) time is absolute
7) Newtonian physics works
8) Ptolomean system works
9) the Earth is flat

We've been changing a few times our view of the world through physical theories, and had to let go some of our previously cherished ideas. But I think that there is a difference between letting go "the Earth is flat" and "there is no objective world", or "the objective world is inconsistent".

I think that letting go things like "the objective world is logically build up" is a far greater step, than to say "the relationship between my subjective experience and the objective world became relative, and is not 1-1". This goes in the same direction as the "relativity of simultaneity". And it goes in the same way as a long tradition: the Earth is not the center of the universe, the sun isn't, our galaxy isn't, even your perceived universe is not THE universe, but just one amongst many.
As such, we can keep all the rest of our hypotheses. Is that not much simpler, more consistent and elegant way of viewing things than "the universe is inconsistent", or "quantum objects are not described by quantum theory" or so ?

As to the remark that QM is maybe NOT containing the final principles of nature, I say: SURE! The day that we know more, we'll change again our world view. Maybe we'll have to take a step back. Maybe, after all, time IS absolute and relativity WAS wrong in its conceptual framework too. (Hey, maybe the Earth IS flat too! :tongue2:) But what I don't understand is that people go all out of their way in order NOT to have to face the simple interpretation of the QM formalism: that (as all physical theories have always done) it *describes* nature, up to a point. That its mathematical structure *comes close* to what really happens out there. Ok, it takes on a very peculiar description of nature we are not used to (namely a difference between an objective reality and what we perceive of it, which is only one small part). But is that not conceptually simpler to swallow, than to go and claim that nature is *inconsistent* or that we don't have the ability to *describe* nature ?

 

[vanesch]

And, for me the knowledge interpretation is practical, simple, consistent with actual practice in the physics community -- and it is totally consistent with the way most people operate on a day-to-day basis.

I think I understand what you say. You say that people using quantum theory, only use it in a limited way, and then apply the Born rule, get out results (which can be the starting point for a classical calculation) and that's it. As such, QM was a tool to delve into some microscopic aspects, why not.

What I want to say is that there IS a possibility to view the entire quantum mechanical theory as a genuine, real description of the world and that it is *conceptually helpful* to do so when you are working with it, especially in tricky cases such as EPR. I do not find it conceptually helpful to say that the mathematical concepts I'm manipulating are NOT related to anything "real" out there: it kills all intuition one can potentially have about it. The electron as a flash-causing conceptual entity in an electrongun-screen setup without any reality attached to it, not very helpful, is it. Why not little spaghetti monsters throwing light balls at the screen ?

Same with EM: you could somehow claim that the EM field is "not really out there", and is just a calculational tool to find the correct cause and effect relationships between moving charged particles. But that is not the right mindset when you are doing classical EM calculations. When you DO accept that there's a arrow attached to each position (for instance), you get a much better view on what is happening.

It is in the same spirit that I'm pushing the MWI view. I'm not pushing it as "being ultimately true" ; rather I say that it is a view (IMO, the ONLY view) that goes naturally with the formalism of quantum theory, and which allows us to stick to some more fundamental hypotheses, such as the existence of a logically consistent objective reality, and the idea that we are somehow describing that objective reality. If the price I have to pay is that I have to accept the working hypothesis that I subjectively experience only PART of that objective reality, I do not find that so disturbing (many people do, apparently). If this is what *really* happens, I don't know, and up to a point, I don't care. I just want to have a coherent conceptual description of nature, that's all, and do so with what we have at hand. It does not need to be "ultimately right", as long as it is consistent, logically, and with observation.

I find all other alternatives too pricy: "the universe is inconsistent", go figure. "we are unable to describe nature, just to know relationships between an experimental setup and measurement apparatus", what a defeat !

The only one that is potentially acceptable, is: "QM is simply a wrong theory, but empirically accurate in those domains where it has been tested". But then one should put one's money where one's mouth is, and consider all efforts of a unitary quantum gravity and related to it, all quantum cosmology and so on, as a total waste of time. One should then look for the better theory right away! I'm however, rather pessimistic that a more modern theory will give us a SIMPLER conceptual picture. Usually, things get conceptually farther and farther from our intuitive ideas (the very argument to refute MWI). So I'm not sure that, if ever we find out that QM is wrong, the replacement will be easier to interpret, and closer to our intuition.

 

[vanesch]

(added) One of the constant features of the history of physics is the temptation to reify. From Descartes' vortices to Kelvin's and Maxwell's mechanical ethers, this is something a prudent physicst (like Newton!) will do well to avoid.

Well, my impression is the opposite. Often the formal results have NOT been taken to their full meaning, people clinging to the interpretational aspects of the former paradigm. Maxwell's equations clearly SCREAMED for the existence of an EM field, but people were so much used to have fields only as apparent quantities in material media, that they needed to invent such a medium. It was only after decades of struggle that it was finally recognized that the "formal quantities" in the Maxwell equations corresponded to a genuine DESCRIPTION of nature and not to some derived property of a hypothetical substance.

Notice that QM is subsumed in field theory, that field theory has only shaky localization and problems representing interaction, and that "thingness" seems not to be preserved very well by the proposed physics of the standard model. You can't REALLY fillet non relativistic QM out of all this melange and treat it as a standalone philosophical construction can you?

The aspects of quantum theory that give rise to a body state to occur in several states (which is the basis for MWI) are just as present in QFT than they are in non-relativistic quantum theory - unless I'm mistaking. The two aspects are: the state of nature is an element of a Hilbert space (consequence of the superposition principle), and the relationship between an initial state and a final state (before and after interaction) is given by a unitary operator describing the interaction.
In NR QM, we know how to do all this in detail, while in QFT, we only know some aspects: we have to take "initial" and "final" states towards t -> - infinity and + infinity respectively, and we can only find some matrix elements of the unitary operator (the S-matrix) through some mathematical procedure or other (canonical, path integral,...). So we master the formalism much less. But I would think (correct me if I'm wrong) that the two basic hypotheses of a quantum theory (superposition principle, and hence Hilbert space ; and unitarity) are just as well satisfied in QFT as in NR QM ; as such, QFT is simply "another" quantum theory, with "another" model. Is that wrong ?
It was my understanding that string theory is acting along exactly the same scheme, respecting superposition and unitarity. Is that wrong ?

 

[selfAdjoint]

Maxwell's equations clearly SCREAMED for the existence of an EM field, but people were so much used to have fields only as apparent quantities in material media, that they needed to invent such a medium. It was only after decades of struggle that it was finally recognized that the "formal quantities" in the Maxwell equations corresponded to a genuine DESCRIPTION of nature and not to some derived property of a hypothetical substance.

Excuse me but I think this illustrates my point about reification, rather than refutes it.

But I would think (correct me if I'm wrong) that the two basic hypotheses of a quantum theory (superposition principle, and hence Hilbert space ; and unitarity) are just as well satisfied in QFT as in NR QM

OK, I'll give you superposition (experimentallay demonstrated at macroscopic scale) and unitarity is essential for meaningful probabilities. But I'm not too sure that the probability interpretation, the basis of your MWI derivation of the Born rule, is god-given. We do not really have thousands of repetitions of identically prepared experiments to verify it. I'd call it a useful hypothesis, but not something to hang your philosophical hat on.

 

[Sherlock]

The world-branching of the MWI is, by its definition, a metaphysical construct.

Of course it is metaphysical! But so it the hypothesis of the existence of an objective world.

We assign the label metaphysical to objects and events that have only a symbolic existence. Symbolic objects, such as gods and non-interfering world branches, that have no physical referents, no physical existence other than as symbolic objects, are metaphysical. There's nothing in the world of our sensory perception that corresponds to those symbols other than the symbols themselves. Electron and photon wave functions, on the other hand, are not metaphysical. They exist as collections of materials and instruments and operations on those materials and instruments as well being symbols and operations on those symbols.

The existence of an objective world is definitional not hypothetical.

Even the phrase "the voltmeter reads 7V" is metaphysical because it includes in it, an implicit assumption of an objective existence of a voltmeter and of its reading. The only phrase that is not metaphysical is "I perceive a voltmeter reading 7V". But we are so very used to making this identification that we don't even bother.

The physical existence of an object or an event is defined by our sensory experience of it. "The voltmeter reads 7V" might be associated with some set of operations wrt which you predict a reading of 7V can be perceived, or it might mean that you have perceived a voltmeter reading of 7V. Either way, it's not a metaphysical statement because the criterion of physicality is our sensory perception. Objectivity just means that you aren't the only one seeing this --- that all observers agree that their sensory perception of the voltmeter is that it reads 7V. Since this sort of behavior is a fact of our existence, then we say that an objective world exists. The existence of an objective world isn't a question or a conundrum or a hypothesis in the physical sciences --- it's simply the way that things are talked about. It's what our collective behavior means. Whether we're all in some sort of dreamworld, or hallucinating in the same way, or whatever --- by definition, these are nonsensical considerations and aren't considerations of the physical sciences.

The photons and electrons of quantum theory are, by contrast, labels that correspond to specific experimental preparations and results, as well as symbols and symbolic operations.
"The electron is in position x" corresponds to a specific instrumental result.

That's my point: this is just as well metaphysical. The only thing you really know is that you perceive a specific instrumental result. You have extrapolated here the "I perceive an instrumental result" into "there IS a specific instrumental result" ; but we're so used to do so this metaphysical interpretation, that you don't even notice.

Putting labels on our sensory perceptions isn't metaphysics. Putting labels on abstractions of our sensory perceptions isn't metaphysics.

The "(classically-like) state of nature of which we learn stuff" is the stuff that we perceive --- from the results of quantum experiments to observations of the world at large. Using this as the evaluational basis for statements about the world provides an unambiguous criterion for deciding which statements about the world are more or less accurate --- the positivist approach is the one that characterizes science precisely because it avoids the troubles that accompany metaphysical statements.
[

Entirely, but as such, it is a viewpoint which is "minimalistic" (and compatible with solipsism in fact! You equate the "state of the world" to the "state of your subjective perception" - the difference with solipsism is that you do not postulate the non-existance of a real world, you simply don't want to consider it). So a positivist interpretation denies the possibility of a description of an objective world. Although this is possible, I find it too early to deny the very well working hypothesis of a real, objective world.

A positivist interpretation is all about describing an objective world. Positivism asks what is the meaning of the terms and statements. Meaning is defined by our collective sensory experience (that is, communication of and agreement on what each of us subjectively experience wrt objects and events that each of us perceive as external to ourselves and others).

The troubles that accompany the MWI interpretation are unavoidable given the two assumptions on which it seems to be based: 1) there is an underlying quantum world wrt which we're necessarily perceptually ignorant, and 2) the formalism of qm is in 1-1 correspondence with the makeup and behavior of this underlying quantum world.

YES! That's the very meaning, to me, of a physical theory: you ASSUME for the sake of interpretation, that the theory is describing correctly an objectively existing world, and then you point out what are the relationships between the formal elements of the theory, and the (metaphysically postulated) external objective world.

But there are reasons to believe that assumption 2) is wrong, and they seem to outweigh the reasons for assuming that it's correct. MWI is constructing a metaphysical ontology (the existence of worlds that can't be verified) based on an assumption that can't be verified. This is why MWI isn't physics in any sense of the word. Or even natural philosophy.

There are 2 possible denials of an interpretation:
1) there IS no objectively existing world
2) the theory at hand is NOT describing it

Now, if we take 1) (which is the solipsist viewpoint), I think we can stop right away. If we take 2) then, by definition, we are not going to interpret a (wrong) theory, are we ? So in our quest to interpret a theory we must assume that there *IS* an objective world, and we must also assume that the theory describing it *IS* going to be describing it correctly. So of course, for the sake of interpreting quantum theory as a description of an objective world, we have to assume 1) and 2). Any denial of this starting hypothesis puts into jeopardy the very exercise of an interpretation.

There is, by definition, an objectively existing world. It's the world of our collective sensory experience.

By way of interpretation, the positivist asks what the components of quantum theory mean wrt this objectively existing world of our collective sensory experience. It's noted that the quantum theory is a probabilistic accounting of certain phenomena in this objectively existing world of our collective sensory experience.

It might be asked what is the meaning of the components of quantum theory wrt an underlying quantum world. The positivist asks, what underlying quantum world?
It's noted that there are, because of the quantum experimental phenomena, reasons to think that the world of our collective sensory experience is but one level of the whole of physical reality. The positivist says, ok, it makes sense to think that, but since neither we nor the instruments that we use to augment our senses can reliably track the behavior of such an underlying world or discern the media in which such behavior is taking place, then perhaps science should concern itself with what can be objectified and verified via our collective sensory experience.

So, we're left with an interpretation of the meaning of quantum theory that's based on how the theory relates to the objects and events of our collective sensory experience (microscopic, macroscopic, and telescopic --- but not submicroscopic or supertelescopic).

Maybe there is some meaning of quantum theory wrt some visualization of an underlying quantum world, but in order to ascertain this it's necessary to have some idea of what the developers of quantum theory were thinking (in terms of describing an underlying reality by way of analogy to the world of our sensory experience) as they formulated the theory.

And, if we do this, I think we would find that the world-branching of MWI was not part of those visualizations. In fact, such world-branching isn't in any way visualizable and prima facie makes no sense at all wrt what is known about the world of our sensory experience and what might be taken from that experience and applied to some conceptualization of an underlying quantum world. That is, even if you take the wave equation and wave functions of the theory as being very close to the way an underlying quantum reality actually behaves, this doesn't lead to the world-branching of MWI.

The only way out is solipsism! However, the hypothesis of an existing external world IS possible, and it has always been a very fruitful hypothesis, so there's no reason to drop it now.

The positivistic viewpoint is that solipsism makes as little sense as MWI. The positivistic (the scientific) viewpoint is that of course there's an objective world. It's established by definition, not hypothesis.

This is what I don't understand, btw. People arguing against an MWI interpretation of the quantum formalism often do this because they "find this assumption of parallel worlds in which copies of themselves wander around too weird to be true" ; but then they have no difficulties of kicking out ENTIRELY the assumption that there *IS* an objective world!

I don't understand that either.

Well, as I tried to point out, this statement is simply that QM could be the WRONG theory, which has a WRONG description of the objective world. I ALWAYS POINTED OUT THAT THAT WAS A POSSIBILITY, but then you should come up with a better theory! But this is NOT the starting point of an interpretation of a theory.

Noting that quantum theory is a good approximation of instrumental behavior, that it is a probabilistic accounting of quantum experimental phenomena, is the starting point. What isn't a good starting point is to simply assume that it is in 1-1 correspondence with all of reality --- because we can see that it isn't even in 1-1 correspondence with events at the level of our sensory experience.

Take Ptolomy's epicycles. It is empirically CORRECT.
It is, however, a WRONG description of the solar system (with its spheres and so on), and Newton's theory does better. Once we have Newton's theory, we can UNDERSTAND how it came about that Ptolomy's epicycles gave good empirical results, and we also can re-interpret them as terms in a perturbation expansion in Newtonian dynamics. However, as long as you didn't have Newton's theory, there was no point in viewing Ptolomy's theory as a perturbation expansion of an unknown dynamics. That was not a helpful way to work with Ptolomy's theory, was it. If you wanted to interpret Ptolomy's theory, you had to stick to the spheres. It would have been difficult to reason physically in Ptolomy's theory without the spheres thing. So the *right* thing to do was to accept the hypothesis of reality of the spheres. This can, one day, happen to quantum theory. Maybe we'll find an underlying theory which will explain the formal success of quantum theory. Then we will not have to worry anymore about interpretational problems of the quantum formalism, because they will now be interpreted in function of the new theory. At that point, MWI will be of no use anymore. I never claimed anything else. But, there's no other such theory around ! (at least, that doesn't bump into other problems)

But the MWI isn't of any use now. It's just a bad way to interpret the meaning of quantum theory.

The problem I have with seeing QM as "just a mathematical algorithm" is that you do not know anymore what the different parts in the calculational procedure are supposed to mean.

You can say something about what the different parts in the calculational procedure mean. It's just that there's no way to know how they correspond to an underlying quantum reality. By the way, I believe in the existence of an underlying quantum reality --- but I haven't worked out yet (don't know enough about the level of reality that I actually experience) just how I want to visualize it.

It is not unthinkable that 1) and 2) are false, and as you point out, the assumption of their correctness is essentially a metaphysical hypothesis. But WHY SHOULD WE NOT CONTINUE TO ACCEPT THOSE METAPHYSICAL HYPOTHESES, IF THIS IS SOMEHOW POSSIBLE ?

To me, it is unthinkable that 1) is false --- at least at this moment that I'm writing this.

I mean, we never did that with classical physics, did we ? We always assumed that the state description of classical physics corresponded to an objective world outside, and it helped us in using classical physics, and we saw it as having a strong explanatory power. The moon really was there, and was not just "a construct of our knowledge", right ? It was a strong intuition builder to take the material points in classical physics are "really out there". Why deny this faculty to QM ?

One can accept the probabilistic interpretation, and deny solipsism and MWI, without denying this faculty to QM. The positivistic approach (my version) does allow some analogizing and visualization of an underlying quantum world as long as it makes sense wrt what our senses tell us. But mainly it's about the meaning of statements, and meaning can only be unambiguously evaluated wrt the objective world or our collective sensory perceptions.

... why can't we assume that quantum theory is more than you think it is, as a working hypothesis, to construct a view on it ? You can only *know* that quantum theory is less than it claims if you have a better theory, no ? Must we necessarily start by assuming it is WRONG, even before thinking about it ? Is that the best way to interpret it ?

Saying that quantum theory probably isn't, or that it can't be said for sure that it is, in 1-1 correspondence with an underlying quantum world isn't saying it's wrong or that an underlying quantum world definitely doesn't behave that way. Quantum theory itself doesn't claim to be in 1-1 correspondence with an underlying quantum world. In fact, quantum theory has very little to say about an underlying quantum world. I've got a few different presentations of the theory here. In the newest, purely mathematical one, there's absolutely no mention of an underlying quantum world --- the probabilistic interpretation is just assumed. In the 1950 text by David Bohm, there is a lot of discussion about the physical meaning of the theory. Bohm concludes that the theory should be interpreted as not in 1-1 correspondence with an underlying quantum world. Heisenberg wrote a small book, The Physical Meaning of the Quantum Theory, where he discusses these issues. None of these say that there isn't an underlying quantum world. The only question is, what can be said about it --- and that isn't known for sure.

What does seem clear to me is that the MWI isn't even in the running as a serious way to evaluate the meaning of quantum theory.

 

[vanesch]

We assign the label metaphysical to objects and events that have only a symbolic existence. Symbolic objects, such as gods and non-interfering world branches, that have no physical referents, no physical existence other than as symbolic objects, are metaphysical.

That's not the usual definition of "metaphysical".
http://en.wikipedia.org/wiki/Metaphysics
http://pespmc1.vub.ac.be/METAPHYS.html

Metaphysics tries to describe what is "real". What is "existing out there". It is not a matter of convention, but of hypothesis.

The existence of an objective world is definitional not hypothetical.

The physical existence of an object or an event is defined by our sensory experience of it.

Sorry, but you are now re-defining the concept of ontological existence, and in fact your definition coincides with what is usually called "subjective experience".

The existence of an objective world isn't a question or a conundrum or a hypothesis in the physical sciences --- it's simply the way that things are talked about. It's what our collective behavior means. Whether we're all in some sort of dreamworld, or hallucinating in the same way, or whatever --- by definition, these are nonsensical considerations and aren't considerations of the physical sciences.

Well, they are exactly the subject of metaphysics. And metaphysics is also the defining frame of physical science: the theoretical description of an ontology. In other words, the starting hypothesis of physical science is that we are going to model reality (well knowing that this will always be on the level of a working hypothesis), and our guiding principle is empirical observation: empirical observation and its confrontation with what is deduced from our model of reality as a prediction for that observation is the judge by which we establish - or not - the quality of our model of reality. As such, agreement with observation is of course not a proof for the validity of our model. It is only a necessary condition. But the interpretation of our formal model is always that it describes objective reality. This is the defining frame of physics.

Now, positivism tries to get rid of that part which is "model of reality" and sees the theory just as a relationship between observations. I think that as such, it misses the essence of physical science, because it reduces physics as a "curve fitting activity" that "fits curves" upon our subjective experiences. Any "curve fitting algorithm" works, in that case ; and there is no room for "general physical principles". THIS is what I think is the loss in the positivist attitude.

Now, it wouldn't occur to you to do the same with classical physics, would it ? I mean, in Newtonian physics, matter points are supposed to be "really there" where the mathematical model says they are, and gravity is "really pulling" on planets. It wouldn't occur to you to say that the moon is a coherent set of descriptions which make visual observations of the sky agree with ocean tides, through a symbolic model of a matter ball and gravitational interactions which is needed in the formalism to explain the light we see from the moon and the water that rises at the shore, right ? You associate to the concept of a matter ball which we call Moon, an ontological reality even though we can't touch it, and so on.
In the same way, I'm simply proposing that we do the same with quantum theory: that the wave function is describing something that is "really there". And that's sufficient to arrive at MWI, at least if you do not think that "your observation" is going to change what "is really there" (what is NOT the case with the definition you gave of "objective reality" in the positivist viewpoint - and which corresponds to (collective) subjective experience: for instance, the neutrino was only "really there" since it has been detected and observed ; before it "was not really there").

If you think that observation is NOT going to change the entire ontology of the world, then there is NO basis for the projection postulate as a physical action which somehow happens during "measurement" and which is different from a physical interaction. As such, only the unitary evolution of the state of the universe is a possibility, and as such, "parallel worlds" arrize unavoidably.

Putting labels on our sensory perceptions isn't metaphysics. Putting labels on abstractions of our sensory perceptions isn't metaphysics.

Except if that label is "objective reality" because that is the subject matter of metaphysics.

A positivist interpretation is all about describing an objective world. Positivism asks what is the meaning of the terms and statements. Meaning is defined by our collective sensory experience (that is, communication of and agreement on what each of us subjectively experience wrt objects and events that each of us perceive as external to ourselves and others).

As I said before, this redefines the word "objective" by what is usually taken to be "subjective experience". Even the "collective" part is an illusion of course: you can only subjectively observe other (?) entities to agree with you. You don't know if they "really" exist and if they "really" agree with you. All that is metaphysical considerations.

MWI is constructing a metaphysical ontology (the existence of worlds that can't be verified) based on an assumption that can't be verified. This is why MWI isn't physics in any sense of the word. Or even natural philosophy.

Well, I claim that it is the core of physics, as defined by the frame set by natural philosophy, in the sense that every physical theory is supposed to describe, by its mathematical formalism, the ontology of the physical world.
(note that "a metaphysical ontology" is a tautology).

There is, by definition, an objectively existing world. It's the world of our collective sensory experience.

Which is usually called the world of our subjective experience...

It's noted that there are, because of the quantum experimental phenomena, reasons to think that the world of our collective sensory experience is but one level of the whole of physical reality. The positivist says, ok, it makes sense to think that, but since neither we nor the instruments that we use to augment our senses can reliably track the behavior of such an underlying world or discern the media in which such behavior is taking place, then perhaps science should concern itself with what can be objectified and verified via our collective sensory experience.

Ok, and the natural philosopher says: science should concern itself with trying to model the ontology of the world, well knowing that the only empirical evidence it has at its disposal is one's subjective experience (which you call collective (?) sensory experience) of empirical observations.

Maybe there is some meaning of quantum theory wrt some visualization of an underlying quantum world, but in order to ascertain this it's necessary to have some idea of what the developers of quantum theory were thinking

The devellopers of quantum theory do not have any exclusivity as to its interpretation ; I'd rather say that we are in a better position than they to do so, because they had to fight a battle on many fields, and did not have the advantage of hindsight as we do, today. A physical theory is not some religious writing where one has to go back to the "master" to learn the true meaning. Newton knew less about his mechanics than did, say, Landau.

And, if we do this, I think we would find that the world-branching of MWI was not part of those visualizations. In fact, such world-branching isn't in any way visualizable and prima facie makes no sense at all wrt what is known about the world of our sensory experience and what might be taken from that experience and applied to some conceptualization of an underlying quantum world.

Well, that's entirely not true. I find it, for instance, a highly enlightening viewpoint wrt to "riddles" such as EPR situations. I mean, apart from some weirdness, it gives you an *almost classical* view of quantum theory: you have a DETERMINISTIC physics, and you, as an observer, see this physics from a certain viewpoint. A bit as in relativity. The only difference is that you do not have access to ALL of objective reality. In relativity, you have a "scewed" view on reality depending on your world line, but you nevertheless see ALL of it. The difference with quantum theory in the MWI view is just this: you only have access to PART of it, and that's randomly decided (which introduces the probabilistic aspect of observations). But in all other matters, you're back in a classical picture, with a genuine "state of nature", and a deterministic evolution law (Schroedinger's equation).

That is, even if you take the wave equation and wave functions of the theory as being very close to the way an underlying quantum reality actually behaves, this doesn't lead to the world-branching of MWI.

Eh, sorry, it does. But maybe the word "world branching" is oversold. It means simply "several components in your "brain state basis"".

The positivistic viewpoint is that solipsism makes as little sense as MWI. The positivistic (the scientific) viewpoint is that of course there's an objective world. It's established by definition, not hypothesis.

And that definition is the same as the usual one for the "world of your subjective experience"...

Noting that quantum theory is a good approximation of instrumental behavior, that it is a probabilistic accounting of quantum experimental phenomena, is the starting point.

It is in not such a good agreement. You have to postulate non-physical interactions in every measurement apparatus to arrive at this conclusion.

What isn't a good starting point is to simply assume that it is in 1-1 correspondence with all of reality

Well, but that is the metaphysical frame of all physical theories given by natural philosophy. And moreover, it is possible. So I don't see why we should kick it out...

You can say something about what the different parts in the calculational procedure mean. It's just that there's no way to know how they correspond to an underlying quantum reality. By the way, I believe in the existence of an underlying quantum reality

I would like to hear about ...

One can accept the probabilistic interpretation, and deny solipsism and MWI, without denying this faculty to QM.

I would like to see this...

For instance, I would like to see how you could, in principle of course, describe the physics of your own brain in the framework of quantum theory, without running into something like MWI.
Imagine that you have a superduper computer to run any computation on, and that I give you all you can know about the matter state of your brain (say, the wavefunction of it, containing all its particles, which corresponds to your actual "state of experience" of course). How would you use quantum theory to calculate what's going to happen to your own brain ?

Are you going to use Schroedinger's equation to evolve the state ? And when do you observe something ? When are you going to "measure" the state of your brain ? When do we use collapse ? When do probabilities arise ?

Quantum theory itself doesn't claim to be in 1-1 correspondence with an underlying quantum world. In fact, quantum theory has very little to say about an underlying quantum world.

Eh, it does: it says in its first axiom: the state of the system is given by a vector in hilbert space...

None of these say that there isn't an underlying quantum world. The only question is, what can be said about it --- and that isn't known for sure.

Of course, because the MWI view was only invented in the 50ies !

What does seem clear to me is that the MWI isn't even in the running as a serious way to evaluate the meaning of quantum theory.

You might be surprised...

 

[reilly]

For instance, I would like to see how you could, in principle of course, describe the physics of your own brain in the framework of quantum theory, without running into something like MWI.
Imagine that you have a superduper computer to run any computation on, and that I give you all you can know about the matter state of your brain (say, the wavefunction of it, containing all its particles, which corresponds to your actual "state of experience" of course). How would you use quantum theory to calculate what's going to happen to your own brain ?

Are you going to use Schroedinger's equation to evolve the state ? And when do you observe something ? When are you going to "measure" the state of your brain ? When do we use collapse ? When do probabilities arise ?

That's the beauty of the knowledge approach. That I have knowledge about myself is a no-brainer; that I can make probabilistic statements about myself is certainly true; that my mind can tolerate 'yes it is' and 'no it isn't' at the same time is a fact of Nature. (That's really what the Schrodinger Cat false-paradox is about.)

The plain fact is that in the neurosciances, and associated engineering disciplines, people are building models of brain functioning that are probabilitstic, all the time. I used to build neural network models of certain kinds of perceptions, some of which could have been perfectly applicable to me. Aldous Huxley fell into the trap you are engaging: in his view, the human mind would be forever a mystery, because we can't study ourselves with any objectivity. He's wrong.

If it hasn't happened yet, the day will come when some ambitious researcher will stick probes in his brain, and watch what happens -- and, most likely, his observations will agree with others. Check out Sir Francis Crick's book, The Amazing Hypothesis, in which he discusses the standard neuroscience approach to the mind and brain-- it all stems from the brain's neural networks

Don't forget that, while vision, for sure, and smell and taste, I think start with quantum phenomena, the brain operates at a virtually classical level. Another thing to remember is that our perceptual systems operate with huge sample; and all that we experience is the result of our mental innards executing sophisticated averaging over time and space. Quantum fluctuations don't have enough "oomph" to trigger neural discharges with any regularity. Even if the fluctuations hit a period of big fluctuations, the noise surpressing circuitry of the brain would tend to damp them out.

That's to say, with a density matrix approach to the QM of any brain, the drivers and processes will largely operated in the large-sample, classical domain. And then, classical? Quantum? it's all the same.

But there's no reason why you could not simulate the brain -- other than actually understanding enough detail to foster writing the code and getting the cycles --. It is a physical system, about which we know a very great deal, so people do simulate specific areas and/or functions of the brain. It's just another system.

Regards,
Reilly Atkinson

 

[vanesch]

That's to say, with a density matrix approach to the QM of any brain, the drivers and processes will largely operated in the large-sample, classical domain. And then, classical? Quantum? it's all the same.

Density matrix... in what basis ? Because depending on the answer, the density matrix will describe something that 1) looks like a statistical distribution in classical phase space (what you imply), or 2) will look completely different !

Write the density matrix in the basis (|dead cat> + |live cat>) and (|dead cat> - |live cat>) for instance... Now, you can say that one OBVIOUSLY has to use the basis {|dead cat>, |live cat>} but I hope that you see the circularity of that argument...

Again, you seem to think that I fight the potentially probabilistic aspect of quantum theory. I'm not.

I'm pointing out that, along the chain, you need to say WHAT it is that you consider classical, because it is in THAT basis that you have to write your density matrix and to put the non-diagonal elements to 0, and that is a matter of convention (except in decoherence schemes, but these are inherently MWI). How do you get out your "classical" basis of your brain, when you have your Schroedinger equation ? And if you use projection, in what basis do you project, in order to get out probabilities (or for that matter, the density matrix) ?

The density matrix is the singly most abused quantity to "solve" the measurement problem (because it always leads to a circular reasoning), because of the easy sneaking in of the "classical basis".

I went to the observer's brain, because for all other apparatus, it is "obvious" that a measurement instrument is going to measure in the basis it is designed for (which is in fact absolutely not obvious... except, again, if you go to a decoherence approach, which is part of an MWI view). Tell me, what "basis" is our brain supposed to measure ? The "classical" states ? Why ?

 

[Sherlock]

I only replied to part of your last reply to me. I'll do the rest tomorrow. Anyway, the discussion you and Reilly are having seems more interesting. The sense of smell, for example, seems to operate in some sort of vibrational basis ... matching of resonant frequencies. More support for the notion that nature is fundamentally wavelike?

Metaphysics tries to describe what is "real". What is "existing out there". It is not a matter of convention, but of hypothesis.

If we use the word real to refer to anything that we can imagine, then it becomes absurdly ambiguous. The criterion that we use to separate fact from fiction is our collective sensory perception of the world outside our skins. We include as real, those objects and events reported to us by people we trust even though we haven't actually sensed the objects and events themselves. But, clearly there is a difference between saying that reality is composed of an infinite number of non-interacting brain-state branches and that a voltmeter reads 7V. Physical science is concerned with the latter sort of statement (the meaning of which is quite clear), while metaphysics is concerned with the former sort of statement (whatever it might mean).

I agree that metaphysics describes what MIGHT be out there. Physics describes what IS out there.

The following passage is from one of the places you linked to:
A more nuanced view is that metaphysical statements are not meaningless statements, but rather that they are generally not fallible, testable or provable statements. That is to say, there is no valid set of empirical observations nor a valid set of logical arguments which could definitively prove metaphysical statements to be true or false. Hence, a metaphysical statement usually implies a belief about the world or about the universe which may seem reasonable but is ultimately not provable. That belief could be changed in a non-arbitrary way, based on experience or argument, yet there exists no evidence or argument so compelling that it could rationally force a change in that belief, in the sense of definitely proving it false. Yet this does not mean that science can be altogether freed from metaphysical assumptions or beliefs, since scientific thought is based on axiomatic systems, which by definition operate with unprovable assumptions. One reason for that is that, typically, there are always more theories, than valid data that could corroborate or falsify those theories (Cf. also Stefan Amsterdamski's reflections on this topic). But whereas the metaphysician is likely to say, "this is how it is", the physician (i.e. natural scientist) is likely to say "this is how it is, though I could be proven wrong".

The existence of an objective world is definitional not hypothetical.
The physical existence of an object or an event is defined by our sensory experience of it.

Sorry, but you are now re-defining the concept of ontological existence, and in fact your definition coincides with what is usually called "subjective experience".

All experience is subjective. When we can communicate our subjective experience unambiguously, then we call it objective. We can communicate unambiguously when we are talking about sensory perceptions of objects and events that are defined as existing outside ourselves. Objects and events in the external world. The external world of our collective sensory perceptions isn't a hypothetical world. This world, as well as the internal world of our thoughts, dreams, and emotions is what we say exists. I see a computer screen in front of me. This isn't a hypothetical statement. It's simply what I call the thing that I'm seeing. To ascertain whether what I'm seeing is actually part of the external, objective world, I corroborate my perception with what others say they see when they're looking at my computer screen. This is reality, because we call it reality. This perception I'm experiencing is called a computer screen. On this computer screen are symbols and collections of symbols which either refer to objects and events that are either amenable in some way or other to our collective sensory perceptions, or they aren't --- and if they aren't, then we call them metaphysical. The BRANCHING world or brain states of MWI which, by definition, aren't amenable to our collective sensory perceptions are metaphysical. Voltmeters and voltmeter readings are not metaphysical.

The existence of an objective world isn't a question or a conundrum or a hypothesis in the physical sciences --- it's simply the way that things are talked about. It's what our collective behavior means. Whether we're all in some sort of dreamworld, or hallucinating in the same way, or whatever --- by definition, these are nonsensical considerations and aren't considerations of the physical sciences.

Well, they are exactly the subject of metaphysics.

I agree. But metaphysics isn't physics. That's why they tacked that META onto the beginning of it.

And metaphysics is also the defining frame of physical science: the theoretical description of an ontology. In other words, the starting hypothesis of physical science is that we are going to model reality (well knowing that this will always be on the level of a working hypothesis), and our guiding principle is empirical observation: empirical observation and its confrontation with what is deduced from our model of reality as a prediction for that observation is the judge by which we establish - or not - the quality of our model of reality. As such, agreement with observation is of course not a proof for the validity of our model. It is only a necessary condition. But the interpretation of our formal model is always that it describes objective reality. This is the defining frame of physics.

The defining frame of physics is our collective sensory perceptions. The guiding principles might be metaphysical, but they don't necessarily have to be.

Now, positivism tries to get rid of that part which is "model of reality" and sees the theory just as a relationship between observations. I think that as such, it misses the essence of physical science, because it reduces physics as a "curve fitting activity" that "fits curves" upon our subjective experiences. Any "curve fitting algorithm" works, in that case ; and there is no room for "general physical principles". THIS is what I think is the loss in the positivist attitude.

Positivism is about the meaning of statements, and the criterion of meaningfulness is, as you stated above, empirical observation. Is a statement that purports to describe reality but which is by definition not amenable to empirical observation really of any use if the goal is to describe physical reality?

Now, it wouldn't occur to you to do the same with classical physics, would it ? I mean, in Newtonian physics, matter points are supposed to be "really there" where the mathematical model says they are, and gravity is "really pulling" on planets.

I've learned to NOT think of 'point particles' and gravitational 'forces' that way. They are simplifications ... convenient mathematical conventions.

It wouldn't occur to you to say that the moon is a coherent set of descriptions which make visual observations of the sky agree with ocean tides, through a symbolic model of a matter ball and gravitational interactions which is needed in the formalism to explain the light we see from the moon and the water that rises at the shore, right ? You associate to the concept of a matter ball which we call Moon, an ontological reality even though we can't touch it, and so on.

We can SEE the moon. Men have walked on and taken samples of the moon.

In the same way, I'm simply proposing that we do the same with quantum theory: that the wave function is describing something that is "really there".

I agree. But it is an unfounded stretch to say that whatever the wave function is describing in the underlying reality is in 1-1 correspondence with the wave function. The success of the Schroedinger formulation is one good reason in support of the idea that the underlying quantum reality is essentially wavelike in its composition and behavior. But that's all that can be said for now.

And that's sufficient to arrive at MWI, at least if you do not think that "your observation" is going to change what "is really there" (what is NOT the case with the definition you gave of "objective reality" in the positivist viewpoint - and which corresponds to (collective) subjective experience: for instance, the neutrino was only "really there" since it has been detected and observed ; before it "was not really there").

The assumption that the wave function is in 1-1 correspondence with an underlying quantum world might be sufficient to arrive at MWI, but it doesn't NECESSARILY lead to MWI. And anyway, as I said, the assumption itself is an unnecessary stretch.

The neutrino, like all the particles of the standard model, is a creation of the experimental procedures which define and produce it. We have to talk about it this way because, unlike the moon, we have no other sensory apprehension of neutrinos. We have no way of knowing if they exist in nature in the absence of the structures that we've imposed to produce them.

If you think that observation is NOT going to change the entire ontology of the world, then there is NO basis for the projection postulate as a physical action which somehow happens during "measurement" and which is different from a physical interaction.

Even though it's an apparently underivable assertion, the projection postulate is an extension of the wave model of reality. If it didn't work, then we wouldn't be considering that model as a reasonable approximation of what is happening in the underlying quantum world, and quantum theory would have to be rethought and reformulated. But it does work (at least to a reasonably good approximation).

As such, only the unitary evolution of the state of the universe is a possibility, and as such, "parallel worlds" arrize unavoidably.

Parallel worlds arise if you deny the unique reality of irreversible data. And when you do that then all sorts of silly problems ensue ... the solving of which will not in any way either enhance the applicability or the efficacy of QM calculations.

Putting labels on our sensory perceptions isn't metaphysics. Putting labels on abstractions of our sensory perceptions isn't metaphysics.

Except if that label is "objective reality" because that is the subject matter of metaphysics.

No, that's exactly the problem with metaphysical statements. There's no way to objectify them. The subject matter of physics is objective reality. The subject matter of metaphysics is whatever subjective vision you or I might have wrt the way we think reality ought to be on presumed scales of interaction that are not amenable to our collective sensory perceptions.

MWI is constructing a metaphysical ontology (the existence of worlds that can't be verified) based on an assumption that can't be verified. This is why MWI isn't physics in any sense of the word. Or even natural philosophy.

Well, I claim that it is the core of physics, as defined by the frame set by natural philosophy, in the sense that every physical theory is supposed to describe, by its mathematical formalism, the ontology of the physical world.
(note that "a metaphysical ontology" is a tautology).

It's the behavior of the world of our collective sensory perceptions that we seek to explain. With the advent of quantum experimental phenomena (which are part of the world of our collective sensory perceptions, not the underlying reality), the classical metaphysical underlying reality was put to explanatory tests that it couldn't pass. So, a new theory emerged which was a combination of two, apparently mutually exclusive, apprehensions of the reality underlying what was observed at the instrumental level.

The core of quantum theory is the mathematical formalism and the algorithmic steps that one goes through to apply the formalism in order to correctly predict experimental results. MWI is something that got associated with it much after the fact of its basic development. To be sure, the developers of the theory, in using the mathematical formulations that they did, had some ideas about the composition and behavior of an underlying quantum world and how it might be related to the phenomena of our ordinary experience, and how the formulas that correctly describe behavior at the level of our sensory perceptions might be related to behavior at levels fundamental to and encompassing our sensory perceptions.

Then of course there's Heisenberg. I haven't learned his formulation yet.

There is, by definition, an objectively existing world. It's the world of our collective sensory experience.

Which is usually called the world of our subjective experience...

All sensory experience is, first, subjective. But all subjective experience isn't the apprehension of objects and events outside ourselves, and all subjective experience isn't objective. Objective experience (the objectively existing world) is the proper subset of all subjective experience that corresponds with objects and events that can be unambiguously communicated (ie., fapp, the stuff that we perceive as be external to us, the stuff that is not just thoughts, or dreams, or emotions, etc.). If I taste something sweet (say, a doughnut) and you try it and say that it tastes sweet to you also, then we've communicated a more or less objective qualitative property of doughnuts. Still somewhat ambiguous though. If I look at a group of doughnuts and count 10 of them, and you count the same number, then we've communicated an unambiguous fact about the objective world.

 

[vanesch]

The criterion that we use to separate fact from fiction is our collective sensory perception of the world outside our skins. We include as real, those objects and events reported to us by people we trust even though we haven't actually sensed the objects and events themselves.

Well, that viewpoint is, in itself, a metaphysical assumption, and goes under the name of "naive realism". It assigns reality to what "is perceived to be real". http://en.wikipedia.org/wiki/Naive_realism

But, clearly there is a difference between saying that reality is composed of an infinite number of non-interacting brain-state branches and that a voltmeter reads 7V.

I don't know. It depends upon your metaphysical assumptions, no ? In a naive realism view, you are right. In a positivist view, we don't talk metaphysics ("perceptions happen" and are supposed to be all we have to care about).

Physical science is concerned with the latter sort of statement (the meaning of which is quite clear), while metaphysics is concerned with the former sort of statement (whatever it might mean).

I agree that metaphysics describes what MIGHT be out there. Physics describes what IS out there.

Hehe, rather the opposite, no ? The fundamental assumption behind the idea of physics, is that there is a mathematical description of reality (metaphysical) from which it is possible to DEDUCE our perceptions. As such, in physics we make suppositions of what MIGHT be out there (in the form of a mathematical formalism representing nature) and we try to deduce from that, what we might perceive (what we call: experimental observation). If there is agreement, we say that our physical theory MIGHT be true (in the sense that its mathematical structure MIGHT correctly describe reality). But we know that we will never know for sure. Now, metaphysics is the reflection on all these concepts, and thus talks about what IS out there, because that is its very subject.

So the statement "this physical theory describes nature" is a metaphysical statement. IMO, it doesn't even make sense to talk about a certain physical theory without having made this previous, metaphysical statement about it. So when we talk about a physical theory (and its interpretation), we ALREADY are supposed to have made the metaphysical statement "this theory describes nature".

The following passage is from one of the places you linked to:
A more nuanced view is that metaphysical statements are not meaningless statements, but rather that they are generally not fallible, testable or provable statements. That is to say, there is no valid set of empirical observations nor a valid set of logical arguments which could definitively prove metaphysical statements to be true or false. Hence, a metaphysical statement usually implies a belief about the world or about the universe which may seem reasonable but is ultimately not provable. That belief could be changed in a non-arbitrary way, based on experience or argument, yet there exists no evidence or argument so compelling that it could rationally force a change in that belief, in the sense of definitely proving it false. Yet this does not mean that science can be altogether freed from metaphysical assumptions or beliefs, since scientific thought is based on axiomatic systems, which by definition operate with unprovable assumptions. One reason for that is that, typically, there are always more theories, than valid data that could corroborate or falsify those theories (Cf. also Stefan Amsterdamski's reflections on this topic). But whereas the metaphysician is likely to say, "this is how it is", the physician (i.e. natural scientist) is likely to say "this is how it is, though I could be proven wrong".

See... metaphysics says "how it is" and the physicist says "this is (according to theory X) how things are, but of course theory X could be wrong (although empirically correct)".

All experience is subjective. When we can communicate our subjective experience unambiguously, then we call it objective. We can communicate unambiguously when we are talking about sensory perceptions of objects and events that are defined as existing outside ourselves. Objects and events in the external world. The external world of our collective sensory perceptions isn't a hypothetical world.

Sorry, but it is. The proof of that is the unfalsifiability of solipsism. Now, I think that the HYPOTHESIS of an objective world (which is a metaphysical hypothesis, which can hence never be proved - hence the unfalsifiability of solipsism which is its negation) is a very useful one, and a FUNDAMENTAL metaphysical assumption to even start to do physics.

This world, as well as the internal world of our thoughts, dreams, and emotions is what we say exists. I see a computer screen in front of me. This isn't a hypothetical statement.

That is correct, you SEE a computer screen in front of you is a correct assesment of your subjective experience "seeing a computer screen". However, DEDUCING that there is such a thing as a computer screen, out there, is BASED UPON THE ASSUMPTION of the existence of an external world. The IDENTIFICATION of subjective experience with an external world (namely the assumption that all our perceptions correspond 1-1 with "things out there") is the metaphysical assumption of naive realism.

It's simply what I call the thing that I'm seeing. To ascertain whether what I'm seeing is actually part of the external, objective world, I corroborate my perception with what others say they see when they're looking at my computer screen.

Yes, but the fallacy in this reasoning is of course, that you don't KNOW FOR SURE that there are OTHERS confirming their perception of a computer screen. All YOU know, it that _you perceive them to do so_, and as such, you are using ONE subjective experience (perceiving others to confirm your computer screen) which you take tacitly to be real (hypothesis !), to deduce that your other subjective experience (seeing a computer screen) is to be taken as real. So you USE the conclusion of your reasoning (my perceptions correspond to reality) in the argumentation of your conclusion. That's circular reasoning.

The BRANCHING world or brain states of MWI which, by definition, aren't amenable to our collective sensory perceptions are metaphysical. Voltmeters and voltmeter readings are not metaphysical.

That's a metaphysical statement as any other. You just decided what is real, and what is not.

I agree. But metaphysics isn't physics. That's why they tacked that META onto the beginning of it.

That is because metaphysics is the philosophical DEFINING FRAME of physics.

The defining frame of physics is our collective sensory perceptions. The guiding principles might be metaphysical, but they don't necessarily have to be.

I think I've shown that, while you think you can do away with it, you are making your own metaphysical assumptions (but as hidden hypotheses).

Positivism is about the meaning of statements, and the criterion of meaningfulness is, as you stated above, empirical observation. Is a statement that purports to describe reality but which is by definition not amenable to empirical observation really of any use if the goal is to describe physical reality?

Of course it is useful, because it is an organizing principle from which our observations can be deduced. What is probably less useful, is to have TWO different statements which lead to the same empirical observations. (that is: two different physical theories with different formalism, but which are empirically equivalent). Then, you take your pick and all discussion about which one to take is a matter of taste.
But it is always better to have ONE such statement than ZERO, because (as do positivists) with ZERO metaphysical statements, you've LOST your organizing principle. You've lost the logical structure from which empirical observation can be deduced.

I've learned to NOT think of 'point particles' and gravitational 'forces' that way. They are simplifications ... convenient mathematical conventions.

Then, how do you think of it ? (without of course saying, curved spacetime! We now "know" that Newtonian gravity is an approximation to general relativity, but that has simply displaced the interpretational issue to GR - let's assume for the sake of simplicity that you don't know of GR, and you don't know that Newtonian gravity is not ultimately the correct description of gravity).
Is repeating in your head "everything in the formalism LOOKS AS IF the sun is pulling on the earth, but that's NOT what I should think of it" the best way to devellop an intuition for doing Newtonian gravity ?

We can SEE the moon. Men have walked on and taken samples of the moon.

Well, you've heard stories and saw movies about men who walked on the moon (= subjective perception).

I agree. But it is an unfounded stretch to say that whatever the wave function is describing in the underlying reality is in 1-1 correspondence with the wave function. The success of the Schroedinger formulation is one good reason in support of the idea that the underlying quantum reality is essentially wavelike in its composition and behavior. But that's all that can be said for now.

Well, it is not an unfounded stretch, in the following way. Contrary to the case of Newtonian gravity, were you can now easily say "hey, look, we KNOW that the sun is not pulling on the earth, it is only deforming the spacetime continuum, look at GR", we DO NOT HAVE SUCH AN UNDERLYING theory for QM. So *we do not know* if the quantum mechanical structure is there to stay or not. Making the assumption that it is NOT is a less founded assumption, than making the assumption that it IS going to stay. This assumption can be wrong, but we have less indications for it being wrong than for it being right. So, given the metaphysical frame of every physical theory, we START by stating that quantum theory DOES DESCRIBE REALITY WITH ITS FORMALISM. As a metaphysical starting assumption, well knowing that this is ALWAYS going to be hypothetical.
You can take on another metaphysical starting assumption, which is naive realism. But it is JUST AS WELL AN ASSUMPTION. So take your pick. I'm only saying that *if we are going to do an interpretation of a physical theory, we are supposed to make the metaphysical assumption that its formalism is going to describe nature*.

And ONCE you do that, you arrive at MWI. You can avoid arriving at MWI by introducing 2 possible things:
1) you can introduce "unknown measurement interactions" which only happen in physical constructions called "measurement instruments", and which collapse the wavefunction - which moreover introduce non-locality as a physical process, and as such screw up Lorentz invariance, or:

2) you can say that there IS no physical reality, take on the strictly solipsist viewpoint, and as such say that the wavefunction is what guides your subjective experience. The "collapse" is then simply "you perceiving". The wavefunction describes your dream.

The assumption that the wave function is in 1-1 correspondence with an underlying quantum world might be sufficient to arrive at MWI, but it doesn't NECESSARILY lead to MWI.

Let's look at the logic of this statement:
proposition (1) : "the wavefunction is in 1-1 correspondence with quantum world"
proposition (2): "MWI"

statement 1: (1) is sufficient to arrive at (2)
statement 2: (1) does not necessary lead to (2)

Hummm...

The neutrino, like all the particles of the standard model, is a creation of the experimental procedures which define and produce it. We have to talk about it this way because, unlike the moon, we have no other sensory apprehension of neutrinos. We have no way of knowing if they exist in nature in the absence of the structures that we've imposed to produce them.

Well, I don't know if the president of the United States is a guy called Bush. In fact, I think that the world is a flat disk, and that there is no such thing as the united states, as I've never been there. So the US, to me, is a "creation of the experimental procedure of taking an airplane and go and see" ? Come on... :rofl:

Even though it's an apparently underivable assertion, the projection postulate is an extension of the wave model of reality.

The projection postulate, as presented in the Copenhagen view, is simply an INCONSISTENT operation, because the theory presents TWO CONTRADICTORY WAYS of arriving at the state of the measurement apparatus: one is the unitary way, which is build up by all elementary interactions of the constituents of the apparatus, which gives you RESULT A, and the OTHER is the projection postulate, which gives you result B.
A and B are NOT equal. So you have now to decide - in a totally arbitrary way - what things are suddenly NOT to be described by the interactions of their constituents, and are to be labelled "measurement apparatus", and what things are NOT a measurement apparatus, and hence are to be described by the normal unitary laws followed by their constituents.

If it didn't work, then we wouldn't be considering that model as a reasonable approximation of what is happening in the underlying quantum world, and quantum theory would have to be rethought and reformulated. But it does work (at least to a reasonably good approximation).

It works only because we happen to have an intuitive "list of measurement apparatus" in our head, and we switch to the 'right rule' when it suits us. But quantum theory, by itself CANNOT TELL US WHEN A SYSTEM IS A MEASUREMENT APPARATUS OR NOT. We have to do so, intuitively, in order not to be inconsistent. We have to split the world into two different kinds of systems: those that are build up of elementary constituents and follow unitary evolution, and those OF WHICH WE'RE NOT SUPPOSED TO SAY THAT THEY ARE BUILD UP OF ELEMENTARY CONSTITUENTS, and which we call "measurement apparatus". In order to be consistent, there should be a general rule for when a system is build up from constituents, and when it is a holistic measurement apparatus. And then try to find a physical explication of why systems behave differently if they are, or not, a measurement system.

Parallel worlds arise if you deny the unique reality of irreversible data.

No, parallel worlds arise when we deny certain systems to NOT FOLLOW the laws of physics of their constituents.

And when you do that then all sorts of silly problems ensue ... the solving of which will not in any way either enhance the applicability or the efficacy of QM calculations.

No, that's exactly the problem with metaphysical statements. There's no way to objectify them. The subject matter of physics is objective reality.

No, that's the subject matter of metaphysics. There is a metaphysical assumption, called "physics" which says that objective reality is describable by a mathematical theory, and that subjective experiences (experimental observation) is to be deducible from that theory.

The subject matter of metaphysics is whatever subjective vision you or I might have wrt the way we think reality ought to be on presumed scales of interaction that are not amenable to our collective sensory perceptions.

Of course, and one of those visions is that there ought to be a mathematical theory describing objective reality. That vision is called "physics".

It's the behavior of the world of our collective sensory perceptions that we seek to explain. With the advent of quantum experimental phenomena (which are part of the world of our collective sensory perceptions, not the underlying reality), the classical metaphysical underlying reality was put to explanatory tests that it couldn't pass. So, a new theory emerged which was a combination of two, apparently mutually exclusive, apprehensions of the reality underlying what was observed at the instrumental level.

That was the crazy assumption of Bohr, but we're not obliged to follow him. The classical metaphysical underlying reality was simply that there was that naive realism helt, up to a point, in that objective reality corresponded more or less to our perception of it (like you try to push here). Indeed, this could not be brought in accordance with quantum theory (but also not with general relativity, which has no special treatment of "now", contrary to Newtonian physics).
So IN ORDER TO CLING TO NAIVE REALISM, Bohr kicked out the fundamental metaphysical frame that physical theories describe objective nature, and as such, introduced a lot of inconsistency.

However, if you take the opposite step, which is, to consider that physical theory DOES describe objective nature, and you let go naive realism, you can do fine (that's MWI). You have 1) a mathematical description of objective nature and 2) a rule how to deduce your perceptions (given that they now do not correspond anymore 1-1).

To be sure, the developers of the theory, in using the mathematical formulations that they did, had some ideas about the composition and behavior of an underlying quantum world and how it might be related to the phenomena of our ordinary experience, and how the formulas that correctly describe behavior at the level of our sensory perceptions might be related to behavior at levels fundamental to and encompassing our sensory perceptions.

Of course they did, and they did so by playing a schizophrenic game. When they were reasoning about the physics, they were in fact taking the wavefunction for more or less real, and when they switched to interpretational problems, they said we didn't have to take it for real.
You cannot require, for instance, that interaction terms written as operators on wavefunctions, should obey certain principles such as locality, or charge conservation or momentum conservation, and then claim that the items on which they work are not really describing the physics that is going on "for real".

Still somewhat ambiguous though. If I look at a group of doughnuts and count 10 of them, and you count the same number, then we've communicated an unambiguous fact about the objective world.

Except of course, that you will never know if *I* counted them or whether you only perceived me counting them...

 

[vanesch]

An interesting read about the viewpoint I'm defending (called scientific realism, as opposed to Logical positivism) can be found here:

http://en.wikipedia.org/wiki/Scientific_realism


http://en.wikipedia.org/wiki/Logical_positivism

 

[selfAdjoint]

An interesting read about the viewpoint I'm defending (called scientific realism, as opposed to Logical positivism) can be found here:

http://en.wikipedia.org/wiki/Scientific_realism

http://en.wikipedia.org/wiki/Logical_positivism

I think from the descriptions in the article I would describe myself as a pessimistic inductionist. Not that I assert that physical theories of the past have failed; they have succeeded in sometimes quite spectacular ways, but at the cost of employing unobservable entities (epicycles, elastic ether) that were later shown not to exist. Young's elastic ether theory accurately and quantitatively predicted the two slit interference of light, for example, and Young actually developed his modulus, still in use, to describe the mechanical elasticity of his supposed ether.

And I don't assert either that multiple worlds don't or can't exist; just that they seem very unlikely to me and that the success of quantum mechanics in predicting experimental behavior is not really an argument in favor of them.

 

[Sherlock]

... it doesn't even make sense to talk about a certain physical theory without having made this previous, metaphysical statement about it. So when we talk about a physical theory (and its interpretation), we ALREADY are supposed to have made the metaphysical statement "this theory describes nature".

What doesn't make sense is to talk about the constructs of a theory as being in 1-1 correspondence with an underlying reality that we have no sensory apprehension of.

The external world of our collective sensory perceptions isn't a hypothetical world.

Sorry, but it is. The proof of that is the unfalsifiability of solipsism.

Objective reality is just a term that refers to collective sensory perceptions meeting certain criteria. It's definitional. It's a convention.

We just DEFINE terms like knowing and knowledge, objective reality, etc. and then proceed.

... you SEE a computer screen in front of you is a correct assesment of your subjective experience "seeing a computer screen". However, DEDUCING that there is such a thing as a computer screen, out there, is BASED UPON THE ASSUMPTION of the existence of an external world.

If I can't know that what I AM seeing is part of the objective physical world, then why should I assume that something that I CAN'T see is part of the objective physical world? What do terms like objective reality, and really out there MEAN then?

It's simply what I call the thing that I'm seeing. To ascertain whether what I'm seeing is actually part of the external, objective world, I corroborate my perception with what others say they see when they're looking at my computer screen.

Yes, but the fallacy in this reasoning is of course, that you don't KNOW FOR SURE that there are OTHERS confirming their perception of a computer screen. All YOU know, is that _you perceive them to do so_, and as such, you are using ONE subjective experience (perceiving others to confirm your computer screen) which you take tacitly to be real (hypothesis !) ...

... So you USE the conclusion of your reasoning (my perceptions correspond to reality) in the argumentation of your conclusion. That's circular reasoning.

It's not reasoning, per se. It's how we DEFINE reality. Our collective (communicated) perceptions ARE reality. This is the basis that the physical sciences use to evaluate statements about the world.

Now, if you have some other idea about what reality IS, then what is it?

The BRANCHING world or brain states of MWI which, by definition, aren't amenable to our collective sensory perceptions are metaphysical. Voltmeters and voltmeter readings are not metaphysical.

That's a metaphysical statement as any other. You just decided what is real, and what is not.

Real is a four-letter word. If you don't assign some meaning to it (ie., if you have no criterion for discerning what is real from what isn't) then the word has no utility.

So yes, we DECIDE what is real and what is not based on some definition or other of the term, real.

I agree. But metaphysics isn't physics. That's why they tacked that META onto the beginning of it.

That is because metaphysics is the philosophical DEFINING FRAME of physics.

I agree (to the extent that the formulation of physical theories does involve a certain amount of metaphysical speculation), but metaphysics isn't the physical defining frame of physics. The physical defining frame is our collective sensory perceptions. Metaphysical HYPOTHESES aren't physical hypotheses, and are therefore excluded from the actual SCIENCE of physics. That is, the metaphysical part or interpretation of a physical theory isn't amenable to scientific investigation. So, for example, nothing definitive can be said about the veracity of the claim of MWI world-branching. It just seems like a silly way to think about things. But how can one possibly KNOW whether MWI actually is silly or if it actually is the way things are? So, the MWI interpretation does have that going for it.

The defining frame of physics is our collective sensory perceptions. The guiding principles might be metaphysical, but they don't necessarily have to be.

I think I've shown that, while you think you can do away with it, you are making your own metaphysical assumptions (but as hidden hypotheses).

So, in your view, everything is metaphysical? Or what? I would suppose not, but I'm not even sure what we're talking about any more. It seems like you're taking an unnecessarily circuitous route to get to a place where physics already was. This is the same thing that the MWI interpretation itself does. You're trying to recover the Born rule in MWI, but quantum theory already includes that. Ok, so nobody understands exactly why it works as well as it does. Then that's what the problem is, and that's what is to be investigated --- rather than trying to find how it can be derived from an interpretation of quantum theory that really doesn't seem to fit with what is known about our universe. I do, by the way, believe that the idea of other universes makes sense, but not in the MWI sense. It follows from contemplating the (yes, metaphysical) implications of the Big Bang theory.

The MWI and it's associated problems come back to the assumption that the constructs of quantum theory are in 1-1 correspondence with an underlying quantum world. But, with or without that assumption quantum theory will be making the same predictions --- and with that assumption (and all the fussing over the MWI) you might be overlooking some very important clues.

The general problem, as I see it, is that physics hasn't come up with a definitive formulation of the first principles of nature yet. I believe that the Schroedinger approach of quantum theory is on the right track, in that it hints that nature is fundamentally waves and wave complexes in various media. But quantum theory, just as special relativity (and ordinary experience for that matter) tells me that what you see depends on how you look at something. We don't SEE the evolutions and interactions on the quantum scale. But if they are actually evolutions and interactions of wave structures of varying complexity, then the Born rule makes sense. It applies to macroscopic and irreversible measurement results because this is the context in which we're observing the underlying quantum world.

Have you ever contemplated the movements of a drum head after you hit it? Standing waves, harmonic resonances. You can't actually see them. Put some powder or sand on the drum head and you get more or less static geometric patterns corresponding to these wave motions and interactions. This is one way to think about the difference between the underlying quantum world and our macroscopic apprehension of it.

Or is this not a good analogy. I don't know. Remember I'm still just a novice at this stuff.

 

[Sherlock]

But it is always better to have ONE such (metaphysical) statement than ZERO, because (as do positivists) with ZERO metaphysical statements, you've LOST your organizing principle. You've lost the logical structure from which empirical observation can be deduced.

Positivism (physical science) is just a way to sort out which statements make more sense, or any sense. There's lots of metaphysical speculation going on, both conceptual and mathematical. Some speculations make more sense than others. MWI makes very little sense, imo.

I've learned to NOT think of 'point particles' and gravitational 'forces' that way. They are simplifications ... convenient mathematical conventions.

Then, how do you think of it ? (without of course saying, curved spacetime! We now "know" that Newtonian gravity is an approximation to general relativity, but that has simply displaced the interpretational issue to GR - let's assume for the sake of simplicity that you don't know of GR, and you don't know that Newtonian gravity is not ultimately the correct description of gravity).
Is repeating in your head "everything in the formalism LOOKS AS IF the sun is pulling on the earth, but that's NOT what I should think of it" the best way to devellop an intuition for doing Newtonian gravity ?

My intuition, such that it is, tells me that everything is a matter of wave mechanics. GR and Newtonian gravity are simplifications of the underlying wave mechanics that actually determines gravitational behavior. The standard model, with it's particles and forces and exchange particles, is a simplification of the underlying wave mechanics.

... it is an unfounded stretch to say that whatever the wave function is describing in the underlying reality is in 1-1 correspondence with the wave function. The success of the Schroedinger formulation is one good reason in support of the idea that the underlying quantum reality is essentially wavelike in its composition and behavior. But that's all that can be said for now.

... *we do not know* if the quantum mechanical structure is there to stay or not.

Isn't that what I said?

Making the assumption that it is NOT is a less founded assumption, than making the assumption that it IS going to stay.

I'm not making either assumption. I'm saying it's too early to make either assumption about the qm structure , but that its success indicates that the wave APPROACH is the right one, conceptually.

This assumption can be wrong, but we have less indications for it being wrong than for it being right. So, given the metaphysical frame of every physical theory, we START by stating that quantum theory DOES DESCRIBE REALITY WITH ITS FORMALISM. As a metaphysical starting assumption, well knowing that this is ALWAYS going to be hypothetical.
You can take on another metaphysical starting assumption, which is naive realism. But it is JUST AS WELL AN ASSUMPTION. So take your pick. I'm only saying that *if we are going to do an interpretation of a physical theory, we are supposed to make the metaphysical assumption that its formalism is going to describe nature*.

This is where I think you're making a mistake. The history of physics theories indicates that we should regard current quantum theory as a simplification of what is actually happening in the underlying quantum world.

Your starting metaphysical hypothesis should be that nature is fundamentally waves and wave interactions.

And ONCE you do that, you arrive at MWI. You can avoid arriving at MWI by introducing 2 possible things:
1) you can introduce "unknown measurement interactions" which only happen in physical constructions called "measurement instruments", and which collapse the wavefunction - which moreover introduce non-locality as a physical process, and as such screw up Lorentz invariance, or:

2) you can say that there IS no physical reality, take on the strictly solipsist viewpoint, and as such say that the wavefunction is what guides your subjective experience. The "collapse" is then simply "you perceiving". The wavefunction describes your dream.

It's reasonable to assume that there are some unknown interactions going on, and it's reasonable to assume that nature is fundamentally waves and wave interactions. And from this it's reasonable to assume that quantum theory is a simplification of what is happening, fundamentally, in nature. And this doesn't lead to MWI.

The assumption that the wave function is in 1-1 correspondence with an underlying quantum world might be sufficient to arrive at MWI, but it doesn't NECESSARILY lead to MWI.

Let's look at the logic of this statement:
proposition (1) : "the wavefunction is in 1-1 correspondence with quantum world"
proposition (2): "MWI"

statement 1: (1) is sufficient to arrive at (2)
statement 2: (1) does not necessary lead to (2)

Hummm...

You forgot the part about interpreting what the wavefunction means. You say that it means that two or more mutually exclusive measurement possibilities exist simultaneously in nature. I say it doesn't mean that at all. What I think it means is that the principle of linear superposition in wave mechanics seems to apply in the underlying quantum world as well as it does in the macroscopic world. Thinking of it this way does not lead to the world-branching of MWI.

The neutrino, like all the particles of the standard model, is a creation of the experimental procedures which define and produce it. We have to talk about it this way because, unlike the moon, we have no other sensory apprehension of neutrinos. We have no way of knowing if they exist in nature in the absence of the structures that we've imposed to produce them.

Well, I don't know if the president of the United States is a guy called Bush. In fact, I think that the world is a flat disk, and that there is no such thing as the united states, as I've never been there. So the US, to me, is a "creation of the experimental procedure of taking an airplane and go and see" ? Come on...

Bush is undoubtedly a pinhead, but to equate him with a neutrino is going too far. Anyway, neutrinos and photons and electrons, etc. are creations of experimental procedures. If they exist in nature independent of these experiments, then show me just one.

It would be nice if Bush didn't actually exist in nature independent of our observations of him.

But I see your point. If I don't actually do a certain set of operations that allows me to see Bush, then I won't see him.

The difference of course is that the composition and behavior of the macroscopic world in which I might see Bush is the world that I actually SEE, whereas the composition and behavior of the underlying quantum world can ONLY be inferred from macroscopic instrumental behavior.

The projection postulate, as presented in the Copenhagen view, is simply an INCONSISTENT operation, because the theory presents TWO CONTRADICTORY WAYS of arriving at the state of the measurement apparatus: one is the unitary way, which is build up by all elementary interactions of the constituents of the apparatus, which gives you RESULT A, and the OTHER is the projection postulate, which gives you result B.
A and B are NOT equal. So you have now to decide - in a totally arbitrary way - what things are suddenly NOT to be described by the interactions of their constituents, and are to be labelled "measurement apparatus", and what things are NOT a measurement apparatus, and hence are to be described by the normal unitary laws followed by their constituents.

I don't think it's a totally arbitrary decision. If it was, then physicists would be getting about as many wrong predictions as correct ones by using quantum theory. Obviously, once you get a sufficient detector output, then the unitary evolution(s) involved in predicting that output no longer applies.

In his Quantum Theory (the chapter on the quantum theory of the measurement process, page 622), Bohm says:
Finally, it is perhaps interesting to consider in a new light the fact that the mathematical description provided by the wave function is not in a one-to-one correspondence with the actual behavior of matter. From this fact, we are led to conclude that, contrary to general opinion, quantum theory is less mathematical in its philosophical basis than is classical theory, for, as we have seen, it does not assume that the world is constructed according to a precisely defined mathematical plan. Instead, we have come to the point of view that the wave function is an abstraction, providing a mathematical reflection of certain aspects of reality, but not a one-to-one mapping. To obtain a description of all aspects of the world, one must, in fact, supplement the mathematical description with a physical interpretation in terms of incompletely defined potentialities. Moreover, the present form of quantum theory implies that the world cannot be put into a one-to-one correspondence with any conceivable kind of precisely defined mathematical quantities, and that a complete theory will always require concepts that are more general than that of analysis into precisely defined elements. We may probably expect that even the more general types of concepts provided by the present quantum theory will also ultimately be found to provide only a partial reflection of the infinitely complex and subtle structure of the world. As science develops, we may therefore look forward to the appearance of still newer concepts, which are only faintly foreshadowed at present, but there is no strong reason to suppose that these new concepts are likely to lead to a return to the comparatively simple idea of a one-to-one correspondence between the real world and precisely defined mathematical abstractions.

It works only because we happen to have an intuitive "list of measurement apparatus" in our head, and we switch to the 'right rule' when it suits us. But quantum theory, by itself CANNOT TELL US WHEN A SYSTEM IS A MEASUREMENT APPARATUS OR NOT. We have to do so, intuitively, in order not to be inconsistent. We have to split the world into two different kinds of systems: those that are build up of elementary constituents and follow unitary evolution, and those OF WHICH WE'RE NOT SUPPOSED TO SAY THAT THEY ARE BUILD UP OF ELEMENTARY CONSTITUENTS, and which we call "measurement apparatus". In order to be consistent, there should be a general rule for when a system is build up from constituents, and when it is a holistic measurement apparatus. And then try to find a physical explication of why systems behave differently if they are, or not, a measurement system.

This is what Bohm's chapter on the quantum theory of the measurement process is about..
I've only scanned it so far.

It's the behavior of the world of our collective sensory perceptions that we seek to explain. With the advent of quantum experimental phenomena (which are part of the world of our collective sensory perceptions, not the underlying reality), the classical metaphysical underlying reality was put to explanatory tests that it couldn't pass. So, a new theory emerged which was a combination of two, apparently mutually exclusive, apprehensions of the reality underlying what was observed at the instrumental level.

That was the crazy assumption of Bohr, but we're not obliged to follow him. The classical metaphysical underlying reality was simply that there was that naive realism held, up to a point, in that objective reality corresponded more or less to our perception of it (like you try to push here). Indeed, this could not be brought in accordance with quantum theory (but also not with general relativity, which has no special treatment of "now", contrary to Newtonian physics).
So IN ORDER TO CLING TO NAIVE REALISM, Bohr kicked out the fundamental metaphysical frame that physical theories describe objective nature, and as such, introduced a lot of inconsistency.

However, if you take the opposite step, which is, to consider that physical theory DOES describe objective nature, and you let go naive realism, you can do fine (that's MWI). You have 1) a mathematical description of objective nature and 2) a rule how to deduce your perceptions (given that they now do not correspond anymore 1-1).

At this point in my education I can only say that, so far, Bohr's ideas make sense to me (and they are the ideas pushed by Bohm in his textbook), and that your's don't.

I think that Bohr might say that your MWI is giving you consistency at the expense of truth.

To be sure, the developers of the theory, in using the mathematical formulations that they did, had some ideas about the composition and behavior of an underlying quantum world and how it might be related to the phenomena of our ordinary experience, and how the formulas that correctly describe behavior at the level of our sensory perceptions might be related to behavior at levels fundamental to and encompassing our sensory perceptions.

Of course they did, and they did so by playing a schizophrenic game. When they were reasoning about the physics, they were in fact taking the wavefunction for more or less real, and when they switched to interpretational problems, they said we didn't have to take it for real.
You cannot require, for instance, that interaction terms written as operators on wavefunctions, should obey certain principles such as locality, or charge conservation or momentum conservation, and then claim that the items on which they work are not really describing the physics that is going on "for real".

The idea that the "... wave function is an abstraction, providing a mathematical reflection of certain aspects of reality, but not a one-to-one mapping" seems to me like a much better way to consider it --- wrt both calculation and interpretation.

 

[vanesch]

I think from the descriptions in the article I would describe myself as a pessimistic inductionist.

I'm aware of that (likely) possibility. That's why I ALWAYS put as a *working hypothesis* that we take it that the theory we are going to interpret, is correct. I find it not helpful to start with the opposite working hypothesis, namely that the theory we're going to interpret, is wrong. The reason for that is simply that you tend to sweep many nagging little problems in your theory under the rug of "well, anyway there will be an underlying theory which can change all of this, so don't worry". I mean, imagine you write software, and you start from the principle that anyway, the real firmware of your computer does not correspond to the documentation and your understanding of it. Are you going to write great software that way ? I guess every silly bug you encounter (which is your fault) will be put on the shoulders of the "bad documentation" or even of the bad functioning of the computer. So EVEN if you take the viewpoint that there might be a much better documentation coming along, one day, explaining the functioning of your hardware and firmware using totally different concepts, *in order to use it with your current set of documentation* you better assume that it is correct, no ? Because, hey, it MIGHT even be correct!

As to these "parallel worlds", I really have not so much difficulty with it. For most of what's happening, it doesn't really matter. You really get used to the weirdness. What, finally, can it matter to you whether, or not, there are invisible copies of you that run around in "other worlds" you'll never hear about ? Does that change your "view of the world" ? No, I wouldn't think so, because for YOU, it doesn't make any difference.
Do you have difficulties, in relativity, to consider that "yesterday" and "tomorrow" are just as well "statically there" as "today", while you only experience "today" ?

Look at all the people trying to "look for what is propagating faster than light" in EPR situations, while a many-worlds view on it solves the issue without invoking non-locality or something propagating. It is an amazing and simple solution to the riddle. No need to invoke *inconsistencies*, or "unknown interactions" or concepts such as the "inpossibility to say what really happens on micro scale", or "inexploitable non-localities" or whatever. It all fits together nicely: Bob's in a superposition wrt to Alice, and when she meets him, she will be in one of the branches, and hence find the right correlations. I find this, by itself, the most interesting application of the MWI view. It gives you a clear physical picture of what's going on, and why there is NOTHING propagating from Alice to Bob, and why there is NOTHING special happening during a measurement process.

Look at to what extend people are ready to sacrifice such fundamental things as CONSISTENCY in order to have to avoid an MWI picture. Do they have such a difficulty too with the existence, or not, of "yesterday" and "tomorrow" ? Nevertheless, if you ask them about "spacetime" do they think it "exists" ?

That's again, why I think that, *when interpreting a quantum mechanical situation*, taking on an MWI viewpoint is often the cleanest, most logical viewpoint. In the same way as taking on the viewpoint that the sun pulls on Jupiter is the cleanest, most logical viewpoint when doing Newtonian physics, and supposing that there is a 4-dim spacetime manifold is the most logical viewpoint when doing relativity, and assuming that dinosaurs really ran around on Earth are the most logical viewpoint when doing paleontology. I find it always as the most productive viewpoint that one takes the theory one is working with, seriously.

If you ask me now: ARE THERE REALLY parallel worlds, according to me ? My answer is simply: I don't know. Quantum theory suggests it. But then, quantum theory might be wrong on that (but then, tell me what is right...). It might be right on it. *the best information I have* is that they are there, but I know that that information is still rather uncertain (mainly given the problems with unification with GR). I'm even more pessimistic than you are: I think I'll never get an update on the information in my lifetime. So this is the viewpoint I'll have to deal with, until I'm dead (unless a good surprise comes along).

Again, I'm fully aware that another theory might come along which will put the entire quantum framework down, just to replace it with some other framework. A world vision is tied to the knowledge one has, in one's time. But even with all its imperfections, I think it is still better to HAVE a consistent world vision (knowing it might be wrong) than REFUSING to have one, or to accept an INCONSISTENT world vision.

 

[vanesch]

You say:

What doesn't make sense is to talk about the constructs of a theory as being in 1-1 correspondence with an underlying reality that we have no sensory apprehension of.

Objective reality is just a term that refers to collective sensory perceptions meeting certain criteria. It's definitional. It's a convention.

Ok, then, I told you that that is not the standard view, and that it is a branch of philosophy, called metaphysics, which is supposed to ponder on these issues. But let's accept your point of view, namely that "objective reality" is a matter of convention. Well, I'm proposing the convention that "objective reality" is nothing else but the mathematical structure of the best physical theory that is around at a certain moment. There :tongue2:

If I can't know that what I AM seeing is part of the objective physical world, then why should I assume that something that I CAN'T see is part of the objective physical world? What do terms like objective reality, and really out there MEAN then?

Right, you're now doing a metaphysical reflection. Good

It's not reasoning, per se. It's how we DEFINE reality. Our collective (communicated) perceptions ARE reality. This is the basis that the physical sciences use to evaluate statements about the world.

Not really. Did dinosaurs really exist, or are they just "bones in the ground" ?

Now, if you have some other idea about what reality IS, then what is it?

The mathematical structure of our best physical theory.

So yes, we DECIDE what is real and what is not based on some definition or other of the term, real.

Ok, then I have the same liberty

I agree (to the extent that the formulation of physical theories does involve a certain amount of metaphysical speculation), but metaphysics isn't the physical defining frame of physics. The physical defining frame is our collective sensory perceptions. Metaphysical HYPOTHESES aren't physical hypotheses, and are therefore excluded from the actual SCIENCE of physics. That is, the metaphysical part or interpretation of a physical theory isn't amenable to scientific investigation. So, for example, nothing definitive can be said about the veracity of the claim of MWI world-branching. It just seems like a silly way to think about things. But how can one possibly KNOW whether MWI actually is silly or if it actually is the way things are? So, the MWI interpretation does have that going for it.

The problem with your view is the circularity of it: this is the main critique of positivism. WITHOUT a metaphysical frame, there is NO LINK between any formalism and any empirical observation. You *always* sneak in some metaphysical hypothesis when doing so. At a certain point, you ALWAYS identify certain aspects of the formalism with a reality. But you do so intuitively, in order to make things come out right, without any logics behind it.

See, you first say that "reality" is a matter of convention. And then you wonder how you can KNOW whether or not the other branches in MWI are real. If it is a matter of convention, we can decide about it by, say, voting ! You cannot IGNORE a convention you decided upon!
But if you decide, by convention, to call only your collective experiences as real, then I can decide to call the theoretical elements of quantum theory and the parallel worlds "hyporeal".
And if we now REDEFINE the words "real" into "subjectively experienced" and "hyporeal" into "objectively real", we arrive at MWI.
If we keep the words as we have them, then, the wavefunction has a hyporeal meaning, and locality is a hyporeal concept about hyporeal worlds. Ok. So in this hyporeal meaning, dynamics is given by unitary time evolution. And now that I have hyporeal operators, corresponding to hyporeal interactions, how can I link them to "real" apparatus ?
At what point does a hyporeal structure of particles that looks like a hyporeal voltmeter, become a real voltmeter ?

You're trying to recover the Born rule in MWI, but quantum theory already includes that. Ok, so nobody understands exactly why it works as well as it does.

No, I'm not. I think it is the error many MWI proponents make. One shouldn't try to derive the Born rule, it is the rule that gives the relationship between the MWI ontology (the hyporeal world) and the subjective experience (the conventional "real" world). As such, it is an axiom of the theory, related to perception.

But, with or without that assumption quantum theory will be making the same predictions --- and with that assumption (and all the fussing over the MWI) you might be overlooking some very important clues.

Quantum theory (without MWI) does not make predictions, without you sneaking in some extra hypothesis. You cannot say that the wavefunction is NOT in correspondence with physical reality and then 2 minutes later, find it obvious how we can extract measurement results from it, because in order to do so, you have to find a link between the physical operation of your measurement apparatus, and your non-physical quantum state. That's where most people say the most schizophrenic things.

Look at a photomultiplier, with a single atom as a photocathode. The EM quantum field is in an excited state, described by a wavefunction in Fock space (but that's not real of course). We know how to calculate the interaction of an atom in the ground state with the EM field state, through unitary evolution. So now the atom's wavefunction becomes partly in a state that corresponds to an ionized atom, and partly in its ground state, entangled with the EM wavefunction (which did the opposite thing). But all this is not real of course. In the state with the ionized atom, the electron will accelerate towards the dynodes (in the other state, not, of course) through a unitary evolution. On the dynodes, it will interact (unitarily) with the metal and entangle with other electronstates, until we get an appreciable amount of electrons coming down on the anode. In the other state, no such thing will happen. But remember, that all this is just hyporeal mathematical manoeuvring on a wavefunction which has no physical meaning. So now we end with a wavefunction which is a superposition of the state where no charge arrives on the anode, and where a lot of charge arrives on the anode. We could continue that way, and we'd find that the amplifier and the light bulb attached to it, in their wavefunction are written as a superposition of a lightbulb that doesn't light up, and one that does light up. But all this is hyporeal of course (and the two branches are hyporeal). At what point did they become "real" ? At what point can I say that THIS corresponds to a genuine real effect, predicted by quantum theory ? BTW, have you noticed that we could reason in each branch, as if it were a world of its own, and that, in doing so, we took the implicit assumption that there was "something real" to them ? While nevertheless each individual operation was described by a UNITARY operator ? If I don't do that, how am I going to link the above wavefunction to my lightbulb lighting up or not ? How am I going to describe the unitary operator that describes the physics of the electrons within the apparatus ?

The general problem, as I see it, is that physics hasn't come up with a definitive formulation of the first principles of nature yet.

But you will be able to make that statement along the entire history and future of humankind. What do we do in the mean time ?

I believe that the Schroedinger approach of quantum theory is on the right track, in that it hints that nature is fundamentally waves and wave complexes in various media.

There's a theorem against that statement, which is Bell's theorem. No local realist field theory can have the same empirical predictions as quantum theory. Now, as I said, experimentally there are strong indications, but no proof, that quantum theory is right. There is still room to wiggle in such a theory. Only, I don't know of any. And it will make in any case different predictions than quantum theory. So, in order to "interpret" quantum theory this way, you must make the assumption that quantum theory will make empirically WRONG predictions in certain respects, and you'll need to invent a realistic wave theory that DOES give you all the right other predictions. Some people (local realists) do try to do so. But you see that you are also TRYING to find a physical theory that is in 1-1 correspondence with a physical reality behind the scenes. You have 3 possibilities (if you accept a physical reality that can be mathematically described, and on which your mind has no physical influence on cosmic scales):

1) let go certain empirical predictions of QM and try to find a correct field theory that does all that, and that wins from QM (local realist approach, good luck). It's main prediction is that the EPR effect doesn't exist.

2) let go locality (and hence relativity, both SR and GR). Bohm's theory does exactly that (and still has some conceptual problems). Good luck with quantum field theory! And back to ether theory.

3) accept the reality of the wavefunction, and hence MWI.

These are the directions that people have explored since 80 years. The other possibilities are to DENY a possibility of mathematical description of nature (like Bohr proposes) - hence accepting an inconsistent behaviour of nature, to deny reality all together, or to speculate other things, like backwards causation (although I have yet to see a working model that works as well as current theory).

But quantum theory, just as special relativity (and ordinary experience for that matter) tells me that what you see depends on how you look at something.

Yes. Or even classical physics.

 

[reilly]

leandros_p Small world. Some years ago I wrote a paper, for a neural network conference, about using Shannon's Information Theory as a framework for describing mental and perceptual processing. We agree quite substantially on our basic models. The differences lie in our words and meanings.

Dear Sir,

Let me present a schema of information and knowledge; doing that I will try to use your "language".

The process of "knowing" is the following:

Source -- Transmitter -------- Receiver -- Destination

Between source and destination travels a Message – this message is called knowledge.

Leandros

More often than not, the message is just called a message. Not that it means that much, but,the earnest folks in the Knowledge Mangement field, have been greatly hampered by the fact that they can't fully agree on a definition of knowledge. Although there is a often used heirarchy, which goes: data -> information -> knowledge ( and, yes, some say -> wisdom). It is true, I've checked, that, all three, data, information, knowledge, are used interchangeably in many but not all circumstances.
For many of us, knowledge is what you know -- if you think about the limitations of language and human logic, your estimation of the worth of that seemingly trivial statement might strengthen.

And note, that Shannon and Weaver and Weiner didn't touch the issue of meaning. So, in my opinion, your definition of knowledge is unusual. What does it buy you?

Between the Transmitter and Receiver there is “noise”, always.

The reception of message and the possession of the message thereafter are called knowledge status, at the destination.

This is a general logical schema. The absolute “knowledge”, in the way that you understand the term, is when in the above procedure the destination accepts the message in the original, unchanged and complete form, which had at the source.

Unfortunately, the intermediate stages of transmitter and of receiver, in being imperfect, combined with the noise that exists through the propagation media introduce alteration to the message, either by addition, or by subtraction. Therefore, the original message arrives at the destination modified, that is, the message at the destination is true but has a degree of uncertainty, while the original message at the source had no degree of uncertainty. The message at the destination is not the same as the message at the source. There is an uncertainty factor introduced in the message at the destination, during the process, which was not present at the source.

This uncertain knowledge is called “information”.


Leandros

Not quite. Information refers to the message as a whole, and is, in a crude sense, a measure of surprises -- improbable messages, submessages, etc carry high information content.

Information, in communication theory, is a purely technical, probability based, property of messages -- often measured in bits. This is not quite the same as the more colloquial notions of information.As in any computer seup, you need to know how to translate "binary' to human -- so, with action, there's a whole new set of comunication channels to transmit orders from the brain to the hand, foot, ...

There was a time, when Science also used such conventions. Today, Science of physics can not accept these conventions. It has to use literal terms in defining the “message” that physical objects transmit to our “receivers” as information, because the physical sources that are being examined, such as the atomic and subatomic particles and phenomena, send inconsistent messages.

The objects of classic physics are sending messages to our scientific receivers that during the above process are altered by the imperfection of the stages of the system and by the noise. Scientists have learned how to overcome these problems, which are called measurement problems. BUT, the objects of quantum physics are sending messages to our scientific receivers that are inconsistent, not just altered or modified. So scientists felt obligated to treat these messages in their “true” form, that is, as information. This is the “truth” of physical reality that we refused to face in classic physics, in the past: We can not know physical reality; we can only be informed about physical reality.

Leandros

I do not at all understand the so-called quantum message inconsistencies -- what are they? (I hope you are not thinking waves and particles and interference,... These clearly happen. The inconsistencies come from our inability to describe quantum phenomena in ordinary language.) I'm curious.

Yes, messages can be distorted, But, as Shannon and followers showed, virtually any noise from most any system can be filtered out, so that the probability of extracting the sent message is very high -- the cost might be high also. For pracical purposes, I suspect that the major human communication problems aren't so much noise based, but rather tranaslation based -- like we have some badly coded, biased receivers for certain messages, or message types.



That we can, in your language, only be informed about physical reality has been around for a while -- at least since Plato -- and, in fact, makes very good practical sense -- circumstantial evidence and all that.
Interesting.

Regards,
Reilly Atkinson