EPR paradox revisited, again. hehehe

[ttn]

hmmm so all wavefunctions in QM are beables?

That's the only way I know of to make sense of Bohr's claim that QM was "complete." I'm sure there are some people who would deny that, for OQM, the wf is a beable. They'd say: no, it's just some meaningless abstract thing in our heads that we use to calculate probabilities. The problem is, they then don't have a theory at all -- just some meaningless abstract formal rules in their heads that refer *only* to measurement outcomes. And then any questions like "Is the theory complete?" or "Is the theory local?" become meaningless. If your "theory" doesn't actually say anything about anything, there's no answer to these questions because, really, you don't have a theory.

So, in my opinion, yes, wavefunctions in QM are beables for QM. And that is precisely why OQM violates Bell Locality: what you decide to do over here can affect what is real (the wf) over there, and the effect is instantaneous. Nonlocal action at a distance. This repulsed Einstein, who thus argued that we ought to reject the completeness doctrine and construct a hidden variable theory to replace/supplement OQM.

 

[ttn]

I have at no point talked about locality in any of my arguments. What is your definition of locality please?

Maybe vanesch wants to answer, but... you have too talked about locality! You talked all about violating (or not) the "speed of light limit." Well, that's all "locality" means. A local theory is one that doesn't violate relativity's speed of light limit. The problem is: what exactly is this limit a limit *on*? Do we require no particles moving faster than light? No information transfer faster than light? No signalling faster than light? No causal influences faster than light? Or what?

I already noted/explained Bell Locality as one particular answer here. Bell Locality means "no causal influences faster than light." What more are you looking for from poor old vanesch?

 

[alfredblase]

reply to ttn post 71:

this is what i suspected. It seems that beable is not a clearly and well defined word... And that therefore neither is Bell Locality. Indeed I have read this elsewhere; I have even read that no physical significance is attached to Bell Locality...

that is why I have avoided using the word "locality" because it was never clear.

So it seems you cannot definitely and inequivocably (not sure if i spelt that right :P, I am a bit tipsy at the mo :P ) define what you mean by locality. Therefore I will not consider that any post so far has demonstrated that QM doesn't violate something that really shouldn't be violated. I hesitate to say the speed of light limit now since bizzarely this doesn't seem to be a problem for most of you, even when arguably reality is changing; since I'm tipsy and reckless right now I'm going to put my chips on the table, (not literarly [i'm sure i spelt THAT wrong]; I am actually eating an omellete) and state that if one adopts a QM description of reality in EPR type experiments, causality is violated... (i'm a bit scared of the responses I might get after this post... :s heheh :P )

 

[vanesch]

this is what i suspected. It seems that beable is not a clearly and well defined word...

It is a clearly defined concept, but is dependent on the particular interpretation. The interpretation is exactly that: saying which elements of a formalism of a physical theory have ontological existence (= are beables).

And that therefore neither is Bell Locality. Indeed I have read this elsewhere; I have even read that no physical significance is attached to Bell Locality...

Bell locality is a clear concept, because it deals with OUTCOMES of experiment (or the empirical predictions of the outcomes of experiment of a physical theory). As such, quantum theory, and all other theories that are empirically equivalent to it, are Bell-non-local. They violate the conditions which define Bell locality. Bell locality is independent of any interpretation of the formalism, because it deals only with experimental outcomes.
Even without any theory, a list of observations can be judged to be Bell local or not.

So it seems you cannot definitely and inequivocably (not sure if i spelt that right :P, I am a bit tipsy at the mo :P ) define what you mean by locality. Therefore I will not consider that any post so far has demonstrated that QM doesn't violate something that really shouldn't be violated.

It's difficult to give a proof of a statement of which you yourself claim that it cannot be defined correctly

What's the relationship between locality and speed of light ? Locality means, essentially, that "things happening at an event (x,y,z,t)" should only depend directly on all beables that are related to the event (x,y,z,t), and not to any other event (x',y',z',t) (same t). As such, locality is "beable-dependent" - it is dependent on the interpretation.
However, if there is no upper limit to the speed of anything, then it doesn't make sense to say that the event at (x,y,z,t) did depend on the a beable at (x',y',z',t) because there might be a small error on the last t, and with high enough speed, this can arrive at (x,y,z,t). So the concept of locality would depend upon an infinite precision of the time variable.
However, with a finite speed limit, it DOES make sense (even with finite measurement errors on x,y,z,t) to say that something happening on a beable at (x,y,z,t) should only depend upon other beables in its neighbourhood, and hence should NOT depend upon the beables at (x',y',z',t) if (x',y',z') is spatially remote enough from (x,y,z).

So it is thanks to the speed of light limit for beables, that the locality concept has ueberhaupt a meaning.

But you see that it also depends on what is taken to be a beable (= what is taken to be ontologically there). If you assign "beable" status to measurement results, then locality implies Bell locality. If you DON'T assign ontological status to measurement results (such as MWI does), then Bell locality has nothing to say about locality (beable locality). It is of course objectionable to NOT assign beable-status to measurement outcomes - this is only possible if outcomes are an effect of the relationship between observer and ontology. Many people object to this, understandably, and hence do not consider MWI.

Now, if your ontology has to have any sense what so ever, then SIGNALS should have some or other beable status. So a theory that does not satisfy SIGNAL LOCALITY will have a hard time having "beable"-locality. Signal non-locality leads to paradoxes in relativity.
Signal locality is ANOTHER condition on experimental outcomes (less severe than Bell locality). Quantum theory (and empirically equivalent theories) are signal-local (that was my proof with the reduced density matrix).
As such, the gate is still OPEN for (beable) locality.

 

[ttn]

Bell locality is a clear concept, because it deals with OUTCOMES of experiment (or the empirical predictions of the outcomes of experiment of a physical theory). As such, quantum theory, and all other theories that are empirically equivalent to it, are Bell-non-local. They violate the conditions which define Bell locality. Bell locality is independent of any interpretation of the formalism, because it deals only with experimental outcomes.
Even without any theory, a list of observations can be judged to be Bell local or not.

vanesch, perhaps you are also tipsy? This is completely wrong.

Bell Locality does not pertain exclusively to experimental outcomes. It is a statement about the probabilities for such outcomes *as assigned by some particular theory*. You *can't* just look at some outcomes and say yes/no Bell Locality was/wasn't violated.

Here's a simple example. Say there's a game where you put two balls into two little boxes so you can't see the balls' colors. Then Alice and Bob each carry a box with a ball to some distant location. Then they simultaneously open them and observe the color. And say that they always see opposite colors: whenever Alice sees green Bob sees red, and vice versa. OK? That's what we know from observation. Is Bell Locality respected? It depends:

Theory1: Balls are neither green nor red until someone looks at them; they're, say, grey. Whoever (Alice or Bob) opens their box first (relative to some preferred frame) *causes* their own ball to switch from grey to one or the other of the observed colors, with 50/50 probability each. And this same act of observation also causes the *distant* ball to pick a definite color which is always opposite to her own. So: alice looks in her box, which causes her initially grey particle to turn green and also causes bob's distant as-yet-unobserved particle to turn red. Or maybe the other way round. Anyway, clearly this theory can account for the observations described above, yes?

Theory2: Balls are either green or red regardless of whether anyone has looked. Either a red ball goes into Alice's box and a green into Bob's, or vice versa, and nothing funny is going on at all when they carry the boxes apart and then look in them. Alice sees green if/when her particle has been green all along, etc. So the correlations are explained by the fact that there is always one green and one red put into the boxes. OK? So this theory too can explain the observations perfectly well.

Here's the rub: Theory1 violates Bell Locality, while Theory2 respects it. So it is just wrong to say that you can tell from the predictions alone whether Bell Locality is violated. Bell Locality is not about the outcomes, it's about the theories which predict those outcomes. It's particular theories which are or are not Bell Local.

That said, I agree with you that any theory making the same prediction as QM will not be Bell Local. But I think it's very misleading to argue for this claim the way you did.

 

[ttn]

Now, if your ontology has to have any sense what so ever, then SIGNALS should have some or other beable status. So a theory that does not satisfy SIGNAL LOCALITY will have a hard time having "beable"-locality. Signal non-locality leads to paradoxes in relativity.
Signal locality is ANOTHER condition on experimental outcomes (less severe than Bell locality). Quantum theory (and empirically equivalent theories) are signal-local (that was my proof with the reduced density matrix).
As such, the gate is still OPEN for (beable) locality.

This is a cheap shot that I don't intend all that seriously, but...

Does MWI respect signal locality? Or rather, does the claim that MWI is signal local have any meaning? The reason I wonder is that, according to MWI, all of the other "people" in the universe are actually mindless hulks. So if I transmit a signal to them, it is never really consciously received, i.e., it wasn't really a signal. So not only is superluminal signalling impossible, all signalling is impossible, and the idea of signal locality has no meaning.

If a tree falls in the forest and crushes a mindless hulk, ...?

 

[alfredblase]

I'm sorry but I can't test more than one theory at a time. I thought QM was a widely accepted theory and that there was only one QM theory! I thought it was ironclad; the most proven theory in the history of science... please tell me which theory I was thinking of so that I can test it... please? But don't tell me there are a few of them and so making my test impossible.

 

[Sherlock]

sherlock you also refer to locality as being the violated principle. Is your definition of locality that given by Bell Locality or do you use another one? If another please give this definition.

I think I said something like that you can infer that quantum theory and nature are nonlocal depending on how you interpret the theory.

Bell Locality is a straightforward mathematical criterion for evaluating whether or not a theory is locally causal. Bell Locality requires that the sort of nonseparable quantum states that are used in Bell tests be factorizable. But in quantum theory these states are not factorizable, so the theory is evaluated as not being a locally causal theory according to the Bell Locality test.

This doesn't automatically mean that quantum theory is a nonlocally causal theory. Depending on how you interpret the formalism of the theory, it might be said that it's not a causal theory --- in which case it's also not a nonlocally causal theory.

There are parts of the qm algorithm that are deterministic, but their relationship to (an underlying) reality isn't quite clear.

If the whole of quantum theory is interpreted as being an acausal theory (which is the standard interpretation), then an evaluation of some part(s) of its formal structure wrt the Bell Locality criterion is meaningless.

One way of reading orthodox QM is to take wave functions as beables. If we do that, the theory violates Bell Locality. On the other hand, if we don't do that -- and hence say that the theory has no beables at all, then the question of the theory's locality becomes meaningless because, really, it isn't even a theory unless it asserts *something* about the way the world works.

The only thing that the theory is asserting unambiguously about reality is the calculation of probability distributions of instrumental output. That's what it does, that's what it's for. It's a theory about quantum phenomena. Quantum phenomena are instrumental phenomena. Even if that's all the formalism is about, it's nevertheless telling us *something* about the way the world works.

I like to think that it's telling us more than that --- something about an underlying reality. But exactly what it's telling us about an underlying reality is still a matter of speculation.

 

[alfredblase]

A theory must be testable on all counts.

It seems you all agree that whether or not QM violates causality depends upon interpretation.

But you must understand that an interpratation that does not violate causality is essential to QM, and that it must be found before we can accept QM as a a physical theory.

 

[vanesch]

vanesch, perhaps you are also tipsy? This is completely wrong.

Bell Locality does not pertain exclusively to experimental outcomes. It is a statement about the probabilities for such outcomes *as assigned by some particular theory*. You *can't* just look at some outcomes and say yes/no Bell Locality was/wasn't violated.

I thought that Bell locality came down to requiring that all observed (or empirically predicted) correlations respected all thinkable Bell inequalities. In other words, that they CAN be produced by a theory that you call "Bell local".

Your theory 1 is a theory that is Bell local, but is not beable local (and as such a very strange theory!), that is, the outcomes do not violate the Bell inequalities (and hence CAN be generated by a theory that is, according to your wordings, Bell local). However, the inner gears and workings of the theory do involve non-local actions, but which are such, that this compensates entirely any potential signal or Bell non-locality (my definition).

If Bell locality were a property of a theoretical construction, one could not test it in a lab! I think you're mixing up Bell locality and "beable locality".
(and then, it is maybe just a matter of semantics, but I prefer to keep Bell locality for that typical requirement of respecting Bell inequalities, something that is entirely independent of any theory behind it).

 

[vanesch]

But you must understand that an interpratation that does not violate causality is essential to QM, and that it must be found before we can accept QM as a a physical theory.

Hence my insistance upon MWI as the preferred view on QM...

 

[vanesch]

The reason I wonder is that, according to MWI, all of the other "people" in the universe are actually mindless hulks. So if I transmit a signal to them, it is never really consciously received, i.e., it wasn't really a signal.

The "mindless hulk" has to come to you with his notebook. If you notice a correlation that depends upon your CHOICE of experiment (and not on your OUTCOME) then you know you signalled something.
It is like an EPR experiment, except that you now look for the correlation between your SETTING, and his results, and not your RESULTS and his RESULTS.

 

[alfredblase]

you forgot to quote my first sentence vanesch...

"a theory must be testable on all counts"

since MWI predicts many worlds and since these many worlds can never be observed, MWQM is not a physical theory either.

 

[ttn]

I thought that Bell locality came down to requiring that all observed (or empirically predicted) correlations respected all thinkable Bell inequalities.

No, Bell Locality doesn't just mean "respects Bell inequalities." See the discussion in section 2 of quant-ph/0601205 for more info about Bell Locality.

The problem is, to derive the inequality you have to assume that there exist "hidden variables" of a certain type which determine the outcomes. So what kind of theory is required to respect those inequalities? Only that type of hidden variable theory. So it wouldn't even make sense to say something like "OQM is nonlocal because it violates a Bell inequality." It does violate the inequality, yes, but that doesn't prove squat about whether it's local or not, because it isn't the kind of theory (namely, the kind of hidden variable theory) to which the inequalities are supposed to apply.

Your theory 1 is a theory that is Bell local, but is not beable local (and as such a very strange theory!), that is, the outcomes do not violate the Bell inequalities (and hence CAN be generated by a theory that is, according to your wordings, Bell local). However, the inner gears and workings of the theory do involve non-local actions, but which are such, that this compensates entirely any potential signal or Bell non-locality (my definition).

Well maybe we're just using words differently. I have no idea what you mean by "beable local." But what *I* mean by "Bell Local" is what Bell meant, as explained in several of his papers and in the paper I mentioned above. And my theory1 from that previous post is definitely not Bell Local -- even though, as you point out, the theory doesn't predict any violation of bell inequalities.

Your talk of the "inner gears and workings" is more along the lines of what I (and Bell) mean by Bell Locality.

By the way, my toy theory1 is, in all relevant respects, exactly like orthodox QM. Theory1 and OQM violate Bell Locality for exactly the same reasons (and are signal local for exactly the same reasons too).

If Bell locality were a property of a theoretical construction, one could not test it in a lab! I think you're mixing up Bell locality and "beable locality". (and then, it is maybe just a matter of semantics, but I prefer to keep Bell locality for that typical requirement of respecting Bell inequalities, something that is entirely independent of any theory behind it).

Can you define "beable locality"?

BTW, you're absolutely right that you can't *directly* test Bell Locality in a lab. That's why Bell's two part argument is so important. The first part shows that the only way to Bell-Locally explain a certain set of the observed correlations is for certain kinds of hidden variables to exist. Then the second part (the derivation of the inequality) shows that that kind of hidden variable theory can't account for some of the other observed correlations. So it's only at the end of that whole chain of reasoning that one is entitled to conclude that Bell Locality fails (in the sense that no Bell Local theory can be consistent with the observed facts).

 

[vanesch]

you forgot to quote my first sentence vanesch...

"a theory must be testable on all counts"

since MWI predicts many worlds and since these many worlds can never be observed, MWQM is not a physical theory either.

The effects of the "worlds" can be observed, in principle, by quantum interference experiments. Now, of course, from a certain entanglement on, the experiment is not feasible anymore. I could devise an "in principle" experiment for each statement where one says that a "parallel world" (a term in the wavefunction) has disappeared. Of course it would be technically totally unfeasable: it would be quantum erasure experiments on the scale of macroscopic items.

Also the extreme empiricist idea that a theory must be testable on all counts would simply imply that every theory which is more than a simple catalog of past observations would not satisfy the requirement. Try to account testability of the concept of "force" in Newtonian physics...

 

[vanesch]

So it wouldn't even make sense to say something like "OQM is nonlocal because it violates a Bell inequality." It does violate the inequality, yes, but that doesn't prove squat about whether it's local or not, because it isn't the kind of theory (namely, the kind of hidden variable theory) to which the inequalities are supposed to apply.

Right. In the Copenhagen view, where the wavefunction does not represent any physical quantity (where it is even left open as to whether nature exists on the microscopic level ) it would then be silly to say that the theory is not "Bell local" according to this definition.

Well maybe we're just using words differently. I have no idea what you mean by "beable local." But what *I* mean by "Bell Local" is what Bell meant, as explained in several of his papers and in the paper I mentioned above.

I admit not really knowing what Bell meant with the word (I even think he simply called it "local", no ?), and I have to say that historical prerogatives are not my strongest point. The essence of Bell's work is, I'd say, the derivation of his inequalities, and the particularity of quantum theory is that it violates _IN ITS PREDICTIONS OF OBSERVABLE MEASUREMENTS_ these inequalities. So I'd say that THIS property is what captures most what Bell meant with his concept of "locality".

And my theory1 from that previous post is definitely not Bell Local -- even though, as you point out, the theory doesn't predict any violation of bell inequalities.

Your talk of the "inner gears and workings" is more along the lines of what I (and Bell) mean by Bell Locality.

By the way, my toy theory1 is, in all relevant respects, exactly like orthodox QM. Theory1 and OQM violate Bell Locality for exactly the same reasons (and are signal local for exactly the same reasons too).

"Orthodox" quantum theory does not even assign *ANY* inner gears and workings to its formalism (according to the Copenhagen view - maybe less according to the von Neumann view), so saying that there is a violation of "Bell locality" according to gears and wheels would mean nothing in that respect.

Can you define "beable locality"?

I think it is exactly what you mean by "Bell locality": that the beables (the inner parts of the formalism that are supposed to correspond to something real out there) have only interactions (changes in their nature dictated by) with things they are in local spatial contact with.

BTW, you're absolutely right that you can't *directly* test Bell Locality in a lab. That's why Bell's two part argument is so important. The first part shows that the only way to Bell-Locally explain a certain set of the observed correlations is for certain kinds of hidden variables to exist. Then the second part (the derivation of the inequality) shows that that kind of hidden variable theory can't account for some of the other observed correlations. So it's only at the end of that whole chain of reasoning that one is entitled to conclude that Bell Locality fails (in the sense that no Bell Local theory can be consistent with the observed facts).

That's why I found it more logical to call THIS aspect, Bell locality. You may be right in the historical definition, I don't really know.

 

[ttn]

Right. In the Copenhagen view, where the wavefunction does not represent any physical quantity (where it is even left open as to whether nature exists on the microscopic level ) it would then be silly to say that the theory is not "Bell local" according to this definition.

Well, it's true that Bohr once said "there is no quantum world" or whatever. But he (and generations of followers) also insisted that the wave function alone provides a *complete* description of... [something]. I can only assume that something is the relevant aspect of the quantum world. What else could the completeness doctrine mean? The whole anti-hidden-variables attitude of the orthodoxy is precisely against the idea of *supplementing* the wf's description of the quantum world with something else.

So, I guess I think you shouldn't accept so easily something that is often said but is not actually accepted in practice. Plus, as I've said before, if there is some interpretation in which the wf does not refer to anything actually real (any gears and wheels) then that interpretation is not a theory, and there is therefore no way to apply terms like complete/incomplete/local/nonlocal to it. Those terms refer to gears and wheels, period. So if the copenhagen/orthodox people don't believe their theory provides any gears and wheels, what the heck are they talking about when they keep on insisting decade after decade that OQM is both complete and local?

The essence of Bell's work is, I'd say, the derivation of his inequalities, and the particularity of quantum theory is that it violates _IN ITS PREDICTIONS OF OBSERVABLE MEASUREMENTS_ these inequalities. So I'd say that THIS property is what captures most what Bell meant with his concept of "locality".

Yes, Bell's main achievement is indeed the derivation of his inequalities. But he also understood very clearly that the inequality is only the second part of a two part argument. See, for example, the section "QM is not locally causal" in la nouvelle cuisine (I think), where he notes that EPR pointed out years ago that QM (if taken as complete) is not local. Bell considered the EPR argument to be the first half of the argument. OQM is not local and (as EPR suggested) we need a certain kind of hv's to reinstate locality. Then enter Bell's inequality, which shows that no hv theory of that type can agree with experiment. Conclusion: the locality criterion (on which was based our belief in the kind of hv theory that the inequality further constrains) cannot be maintained in the face of experiment.

So... the point is, the first half of this argument is *crucial*. Without it, your left with the muddle-headed view that is so widely held today: Bell proved not that there is any problem with QM itself, but only with attempts to add hidden variables -- i.e., Bell proved that Bohr was right and Einstein was wrong. This view is complete BS.

And it is based, in part, on the confusion between Bell Locality (which is a basic requirement for theories) and the Bell Inequalities (which is merely a consequence for a certain class of Bell Local theories).

 

[selfAdjoint]

But he (and generations of followers) also insisted that the wave function alone provides a *complete* description of... [something]. I can only assume that something is the relevant aspect of the quantum world.

No in Copenhagen it's a complete description of anything we might find if we did an experiment. So it's not ontological, at least in the traditional sense, but kind of meta-epistomological. It's not "knowledge" exactly, because it's complete, and knowledge for Bohr can only be knowledge of the familiar macroworld; it's the prior necessity for knowledge.

If this sounds like pop Kant, you're right. All that generation of German-influenced physicists studied Kant as teenagers; this was the peak of the German educational tradition, before the deluge. It informed their thinking.

 

[ttn]

No in Copenhagen it's a complete description of anything we might find if we did an experiment. So it's not ontological, at least in the traditional sense, but kind of meta-epistomological. It's not "knowledge" exactly, because it's complete, and knowledge for Bohr can only be knowledge of the familiar macroworld; it's the prior necessity for knowledge.

Perhaps you are right about what Bohr or some other particular person actually intended. But to me it's clear that this philosophy is a muddled and contradictory hash. It doesn't actually form a coherent position. So I am more concerned with finding some definite (if wrong) position that at least captures some aspect of what Bohr was aiming for.

Now, specifically, what you say in the first sentence doesn't make sense. The wave function in QM is *not* a description of measurement outcomes. It just isn't. That isn't the role it plays in the theory. Rather, you *use* the wave function to compute the possible measurement outcomes. So a statement like "the wave function is a complete description of possible measurement outcomes (or their probabilities or whatever)" is incoherent. Or, if coherent, it has nothing to do with how orthodox QM actually works as a theory. So I'm unwilling to accept that position as what Copenhagen really means.

Don't get me wrong. I don't necessarily insist that, according to Copenhagen, the wf is ontological. My claim is weaker: *if* Copenhagen is interpreted as positing any ontology at all, it can *only* be in terms of the wave function. Or put it this way: forgetting about traditional terminology, there exists a reasonably coherent interpretation which takes the wave function as a literally true and complete description of the actual state of quantum systems, i.e., which takes the wf as a "beable". And that interpretation (whatever you want to call it) violates Bell Locality.

Now there is of course the alternative of treating the wave function as a mere calculation instrument that has nothing whatever to do with ontology. Well, the "completeness" claim is then totally meaningless as I've said before, so I don't know why anyone would want to identify this interpretation with Copenhagen. But whatever; leaving aside all the mere terminology issues, let's just look at this interpretation. Well, since there is no candidate for "beable status" *other* than the wf, it is clear that this interpretation provides no ontology at all. It says literally nothing about any reality "behind" measurement outcomes. It is exclusively a formal recipe for calculating probabilities of certain outcomes. There are then several points to make about this. First, it is *meaningless* to say that this "theory" is local or nonlocal. Those terms denote certain features of the ontology posited by a theory, namely, whether or not it includes faster-than-light causation; but this "theory" posits no ontology, so there is simply no way to apply such terms to it. Second, I think it is a stretch of terminology to even call this a theory. Blind formalisms for predicting measurement outcomes are precisely what one resorts to in the *absense* of a theory, when one has no idea whatsoever what's going on "behind" the measurement processes to produce outcomes. Of course, advocates of this approach will resist the claim that their approach isn't a theory, because it is usually part of their approach that we shouldn't look for a theory (in the traditional sense). But that simply unveils how philosophical and stupid this view is. It is one thing to play it safe and not commit to any definite ontology when there is not yet suffiicient evidence; it is another entirely to enshrine that normally-temporary state of ignorance and insist not only that we don't have a clear physical picture of what's going on, but that (paraphrasing Bell) "it is immoral to look for one." This is made even more ridiculous because we're talking after all about physicists! Imagine it! *Physicists* saying, in effect, we don't now have -- and *never should look for* -- a coherent physical picture to go along with the calculation formalism. That is so preposterous it shouldn't be taken seriously by anyone who calls themself a physicist!

...and it is precisely why I prefer to be generous and interpret Copenhagen as defining the wf as a complete ontology (for, at least, quantum systems).

If this sounds like pop Kant, you're right. All that generation of German-influenced physicists studied Kant as teenagers; this was the peak of the German educational tradition, before the deluge. It informed their thinking.

I agree 100%. But I would add that Kant is anti-scientific trash. To say that orthodox QM is based on Kant (and his stupid phenomenal/noumenal distinction, etc...) is to confess that the theory is completely arbitrary (from a *physics* standpoint) and we shouldn't bat an eye if we're going to reject it -- or, as I prefer, give it as much benefit of the doubt as possible by tweaking it into a coherent position, and then rejecting that for sound scientific reasons (such as that the resulting theory suffers from the measurement problem, unlike alternatives such as Bohmian Mechanics).

 

[selfAdjoint]

Now, specifically, what you say in the first sentence doesn't make sense. The wave function in QM is *not* a description of measurement outcomes. It just isn't. That isn't the role it plays in the theory. Rather, you *use* the wave function to compute the possible measurement outcomes. So a statement like "the wave function is a complete description of possible measurement outcomes (or their probabilities or whatever)" is incoherent. Or, if coherent, it has nothing to do with how orthodox QM actually works as a theory. So I'm unwilling to accept that position as what Copenhagen really means.

You keep saying "not coherent" but you don't justify it. Consider the giant's line in "Jack and the Beanstalk": "Fee Fi Fo Fum! I smell the blood of an Englishman! Be he alive or be he dead, I'll grind his bones to make my bread!". That is a complete description of the hypothetical life-states of a hypothetical Englishman (cf. cat).

The wavefunction's eigenvalues when acted on by the operator representing a particular experiment give a complete description of the possible outcomes of the experiment. Complete in the sense that if you actualize the experiment correctly, you WILL observe one of the indicated outcomes. The wave function it self is even more complete in that it contains the partial information suitable to determine the possible outcomes of any hypothetical (properly set up) experiment.

That seems coherent enough to me. I may or may not agree with it, but coherent? Yes.

 

[ttn]

You keep saying "not coherent" but you don't justify it. Consider the giant's line in "Jack and the Beanstalk": "Fee Fi Fo Fum! I smell the blood of an Englishman! Be he alive or be he dead, I'll grind his bones to make my bread!". That is a complete description of the hypothetical life-states of a hypothetical Englishman (cf. cat).

You mean: he's either alive or dead? This makes me think you don't understand QM very well. Take a nice 2-state quantum analogue: a measurement of the z-axis-spin of some electron will either result in "up" or "down." So "up" and "down" are the only two possible states? Not according to QM! "up" and "down" merely form a *basis* for a whole infinity of possible states, all of which are surely supposed to be in some sense *different* according to the completeness doctrine, yes? What you're saying (if I understand correctly) makes it sound like the completeness doctrine (combined with a purely epistemic attitude toward the wf) implies the old "ignorance interpretation" -- namely, what it means to be in a superposition is, really, to be in one or the other of the states but we're not sure which. But to say that is precisely to confess that the wave function is *not* a complete description of the real state!

The wavefunction's eigenvalues when acted on by the operator representing a particular experiment give a complete description of the possible outcomes of the experiment. Complete in the sense that if you actualize the experiment correctly, you WILL observe one of the indicated outcomes. The wave function it self is even more complete in that it contains the partial information suitable to determine the possible outcomes of any hypothetical (properly set up) experiment.

The wf doesn't have eigenvalues; the operator does.

This is actually an important point. A list of possible measurement outcomes can be produced without specifying the wf. So if that's what you mean by a "complete description" then you don't even need to specify the wave function to have a complete description. Maybe you want to be able to specify not only the possible outcomes, but also the probabilities for each outcome? But then |+x> and |+y> become "the same state" so long as you're about to measure the z-spin. And that again seems to conflict with any rational meaning of completeness.

But let's come to the fundamental: you say that the wf "contains the ... information suitable to determine the possible outcomes..." Look at the word "information". What do you mean by this? What is this "information" information *about*? Is it information about the really-existing quantum system? If so, then either that information is or isn't complete (in the usual ontological sense) and we just have to argue about whether or not there's some good reason to add additional variables. (I will argue that there is a good reason -- namely, to solve the measurement problem.) But if the "information" you speak of is information about something else, you'd better tell me what the something else is.

That seems coherent enough to me. I may or may not agree with it, but coherent? Yes.

Maybe we've just misunderstood each other. I didn't say that the purely epistemic interpretation wasn't coherent. It is. I said that this interpretation rendered the completeness doctrine (as well as claims about the locality of the "theory") incoherent. One is free to deny that one's calculation recipe is telling us anything about the gears and wheels. But then one cannot go on to claim that one's description of the gears and wheels is complete, nor that the gears and wheels don't affect each other superluminally. That's the point.

 

[selfAdjoint]

"up" and "down" merely form a *basis* for a whole infinity of possible states, all of which are surely supposed to be in some sense *different* according to the completeness doctrine, yes?

Yes. And from the point of view of the giant, the hypothetical englishman is in a superposition of the states alive or dead. But the coefficient field in his case (he is a stupid, classical giant) is $$Z_2$$ not C.

The wf doesn't have eigenvalues; the operator does.

True, I should have phrased it differently. But the operator's eigenvalues don't have any issue in reality unless it acts on the wavefunction. The Copenhagen view is that the whole operator-wavefunction apparatus is just a formalism for predicting outcomes; the wave function is like a database of hypothetical conditions, and the operator is like a program that reads the database and instantiates them. Neither amounts to anything without the other, but it is meaningful to say that the database contains what any well set-up program will need to instantiate outcomes of a well-prepared experiment.

If you don't like the term information for what the wave function comprises, and want to avoid the weasel word state, I suggest quantum hypothetical.

 

[ttn]

The Copenhagen view is that the whole operator-wavefunction apparatus is just a formalism for predicting outcomes; the wave function is like a database of hypothetical conditions, and the operator is like a program that reads the database and instantiates them. Neither amounts to anything without the other, but it is meaningful to say that the database contains what any well set-up program will need to instantiate outcomes of a well-prepared experiment.

If you don't like the term information for what the wave function comprises, and want to avoid the weasel word state, I suggest quantum hypothetical.

To avoid historical confusion over terminology, let's call the above view the self-adjoint-interpretation. Then let me ask you: according to this interpretation, does the wave function provide a complete description? And then I hope you can clarify: a complete description *of what*? And also this: does the theory respect relativity's prohibition on superluminal causation?

I still don't see how you can address either of these questions unless you accept that the wave function is a description *of* *something*, i.e., unless you accept that the wf is supposed to be a beable. But since it's you who is apparently making this claim, I'll let you clarify things (i.e., discharge the burden of proof).

BTW, here's why the burden of proof is on you: if you interpret the wf as a beable (and as the only beable, i.e., as providing a complete specification of the real state of things) then there is an absolutely clear meaning to the "completeness" and "locality" claims (though, as proved by EPR, both claims can't be simultaneously true!). I don't see how you can say the wf provides a complete description, and also deny that it describes anything. Same sort of problem with the locality question. But prove me wrong if you can!

 

[alfredblase]

the extreme empiricist idea that a theory must be testable on all counts would simply imply that every theory which is more than a simple catalog of past observations would not satisfy the requirement. Try to account testability of the concept of "force" in Newtonian physics...

[the above quote was from vanesch]

Newton's second law states that:

The rate of change of momentum of a body is equal to the resultant force acting on the body and is in the same direction.

You prove this statement every day vanesch [within well defined limits of course]. Newtonian physics makes no other definition of force.

Next point:

The effects of the "worlds" can be observed, in principle, by quantum interference experiments.

No no no. "in principle" is certainly not good enough. You must first define the term "world" and all other terms involved in this definition. Then you must prove inequivocably that there are "many" of them. Either that or I denounce you as a crackpot physicist for claiming that MWQM [meaning "Many Worlds Quantum Theory" ] is an undeniable physical theory.

Ok; I'm going to going to present my argument fully as I can:

1. Causality must hold in all physical theories [I can provide arguments for this if needed]

2. In view of point 1: QM must have a provable physical interpretation that ensures causality is not violated in order to be accepted as a physical theory.

I ask for a brief description [if there is one] of such an interpretation please

 

[DrChinese]

So... the point is, the first half of this argument is *crucial*. Without it, your left with the muddle-headed view that is so widely held today: Bell proved not that there is any problem with QM itself, but only with attempts to add hidden variables -- i.e., Bell proved that Bohr was right and Einstein was wrong. This view is complete BS.

Well, you have an opinion on that... but the facts are a bit short and hinge on your interpretation of EPR and Bell (that not all of us agree upon).

First, let's agree that there is nothing in particular "wrong" with the current oQM formalism.

Second, Einstein - EPR - *was* wrong - at least in some ways. EPR absolutely felt that experiments would show that the Heisenberg Uncertainty Relations could be beaten. They never knew about Bell or Aspect. They contended that if oQM were complete, that there could not be simultaneous reality to non-commuting observables - a position they considered unreasonable. Of course, they too recognized that if locality were violated, this would provide an escape route. But that too was considered at least as unreasonable.

Third, I would cast doubt that Bohr's position that oQM is complete has not been successfully defended. And of course, by completeness I mean that the WF is complete.

I would agree with you that there is a sense in which oQM is non-local, that being the collapse of the WF. (And I don't mean to step on MWI in that statement because that is not my intention.) However, I do not agree that causality is violated by such non-local collapse; and we already agree there is no non-local signal mechanisms. So the only real disagreement is whether we now call oQM non-local. I don't (because local causality is not violated in the sense that Alice's choice of setting does not affect Bob's result); you do (because WF collapse is FTL).

 

[DrChinese]

1. Causality must hold in all physical theories [I can provide arguments for this if needed]

2. In view of point 1: QM must have a provable physical interpretation that ensures causality is not violated in order to be accepted as a physical theory.

I ask for a brief description [if there is one] of such an interpretation please

1. Causality is not a requirement of all physical theories. QM is a counter-example to that idea. See for instance a paper I wrote: Determinism Refuted[/url].

2. QM *is* generally accepted, and subsequent to Bell I doubt it is considered causal universally.

A theory could consist of voodoo if it worked - and by "worked" I mean: it is useful. Please do not confuse theories with "the truth".

 

[vanesch]

[the above quote was from vanesch]

Newton's second law states that:

The rate of change of momentum of a body is equal to the resultant force acting on the body and is in the same direction.

You prove this statement every day vanesch [within well defined limits of course]. Newtonian physics makes no other definition of force.

The concepts of "momentum", "force" and so on are only helpful quantities in order to EXPLAIN, conceptually, observations (which are usually visual impressions of pointers on a dial, or spots on a photograph or whatever tool you decide to use as experimental apparatus). You cannot observe DIRECTLY a force, you can only observe its pretended consequences. As such it is an organizing principle of your observations.

The "many worlds" (in other words, the wavefunction!) is exactly that too.

No no no. "in principle" is certainly not good enough. You must first define the term "world" and all other terms involved in this definition.

world = term in the wavefunction, when written in a particular basis (usually the one that corresponds to the Schmidt-decomposition between the Hilbert space of the observer and the rest of the world).

I protest against the rejection of "in principle": it is the essence of any theory, to be able to say what would happen in principle, without limitation by the state of experimental technology (as long as that limitation is also not a matter of principle of course, that's the danger...).

Then you must prove inequivocably that there are "many" of them. Either that or I denounce you as a crackpot physicist for claiming that MWQM [meaning "Many Worlds Quantum Theory" ] is an undeniable physical theory.

You can say the same about Newton, then. Or any other person who has set up a physical theory. You can NEVER PROVE the existence of all the theoretical concepts that appear in the theory, you can only argue about its empirical validity or not. Because if what you claim is right, then it would be sufficient to reformulate a theory in an empirically equivalent one to show the "crackpottishness" of both. Newtonian physics (with forces) can be reformulated as a stationarity principle (Lagrange, ...). So both are clearly crackpottish theories according to your criterium (because in the Lagrangian formulation, no concept of "force" appears explicitly).

 

[vanesch]

I can only assume that something is the relevant aspect of the quantum world. What else could the completeness doctrine mean? The whole anti-hidden-variables attitude of the orthodoxy is precisely against the idea of *supplementing* the wf's description of the quantum world with something else.

I think that what's meant is that the WF contains ALL POSSIBLE information that one could ever extract from the system by any conceivable experiment (in other words, that the statistical predictions by quantum theory of the outcomes of experiment contain already the MAXIMUM amount of information (in the information-theoretic sense) about these outcomes, and that no theoretical refinement ever is going to do any better.

Now, of course I share your problems with this view which vehemently refuses to consider the ontology of the microworld and nevertheless claims to know all about it that can be known, but I think that this IS the view that is proposed in the Copenhagen interpretation.

So, I guess I think you shouldn't accept so easily something that is often said but is not actually accepted in practice. Plus, as I've said before, if there is some interpretation in which the wf does not refer to anything actually real (any gears and wheels) then that interpretation is not a theory, and there is therefore no way to apply terms like complete/incomplete/local/nonlocal to it.

I agree with your statement concerning locality ; however, "completeness" in the above sense would make sense.

I also agree with your claim about the schizophreny of its practicians: when they do physics with the wavefunction (when they write out interaction terms and so on, and say they can neglect certain contributions and so on) I have a hard time imagining that they do not give it some kind of ontological status (I don't know how you devellop an intuition for something to which you assign no ontological status at all).

And it is based, in part, on the confusion between Bell Locality (which is a basic requirement for theories) and the Bell Inequalities (which is merely a consequence for a certain class of Bell Local theories).

Probably, but given that everybody already confuses Bell locality with Bell inequalities, why don't we just tag the word "Bell locality" to just that, and we tag the word beable locality to the "locality of interaction by the beables of the theory".

Or otherwise we call it "Bell inequalities induced locality"...

Now we clearly have that, when measurement outcomes are seen as beables (which they are NOT in the MWI view!), then beable locality is equivalent to Bell locality (and that was in fact Bell's reasoning, right ?). So probably because Bell took this statement as so very obvious (that observations are "real", hence, beables) that he didn't even gave it further thought, he could reason the way he did.

 

[ttn]

I think that what's meant is that the WF contains ALL POSSIBLE information that one could ever extract from the system by any conceivable experiment (in other words, that the statistical predictions by quantum theory of the outcomes of experiment contain already the MAXIMUM amount of information (in the information-theoretic sense) about these outcomes, and that no theoretical refinement ever is going to do any better.

But (to repeat an earlier question) what is this "information" information *about*? There is no such thing as free-floating information that isn't information about something. The very concept "information" is literally meaningless without some object (like other concepts such as "awareness").

As I've said, it is possible to deny any micro-ontology and regard the whole QM formalism as simply being about measurement outcomes and nothing else. But then, as I keep arguing, all talk about "completeness" or "locality" becomes meaningless.

Now, of course I share your problems with this view which vehemently refuses to consider the ontology of the microworld and nevertheless claims to know all about it that can be known, but I think that this IS the view that is proposed in the Copenhagen interpretation.

It's one of the views, but the advocates aren't consistent. They go back and forth between the common-sense ontological interpretation of wf-as-complete, and the completely epistemic version. When they want to rail against Bohmian mechanics, they deride the hidden variables as cumbersome metaphysics (or whatever) and insist that the wf alone provides a complete description of quantum states. Then when they want to avoid the charge that their theory (like Bohm's) is nonlocal, they switch to the epistemic version. Well, we shouldn't let them so easily have it both ways. There *are* two ways to think about it, but they're not the same. Each has a virtue and a vice, and it's just not reasonable to let people fuzz up the issue and pick and choose the virtues from mutually inconsistent theories as it suits them.

I agree with your statement concerning locality ; however, "completeness" in the above sense would make sense.

Only if what the "complete" description is a complete description *of* is measurement outcomes. But (a) this claim doesn't really make any sense and (b) it is not at all the same thing that is claimed or denied in the context of debates about "hidden variables".

I also agree with your claim about the schizophreny of its practicians: when they do physics with the wavefunction (when they write out interaction terms and so on, and say they can neglect certain contributions and so on) I have a hard time imagining that they do not give it some kind of ontological status (I don't know how you devellop an intuition for something to which you assign no ontological status at all).

Right, I totally agree.

Probably, but given that everybody already confuses Bell locality with Bell inequalities, why don't we just tag the word "Bell locality" to just that, and we tag the word beable locality to the "locality of interaction by the beables of the theory".

I personally think this confusion over terminology reflects a much deeper and more important/fundamental confusion over what Bell's theorem proves in the first place. So I think it's worth fighting to clarify this terminology, rather than just accepting the confusion and introducing new terminology.

Now we clearly have that, when measurement outcomes are seen as beables (which they are NOT in the MWI view!),

Aren't they as much beables as anything else in MWI? I mean, the measuring appratuses are made out of electrons and whatnot, and hence described by wave functions. It's just that, usually, the apparatus isn't in a definite pointer state. But the formal entities that MWI uses to refer to the apparatuses (namely, wave functions!) are not only beables -- they're the only (kind of) beables. Well, except for those pesky "consciousness tokens"...

then beable locality is equivalent to Bell locality (and that was in fact Bell's reasoning, right ?). So probably because Bell took this statement as so very obvious (that observations are "real", hence, beables) that he didn't even gave it further thought, he could reason the way he did.

That's right. But I object to your making it sound like it was some kind of dubious, uncareful "leap" to just assume (without "giving it further thought") that pointers actually point. I mean, if you can't believe what you see, how the heck are you going to believe anything? Even your precious quantum formalism is ultimately -- historically -- based on putting together a whole bunch of things that a whole bunch of people literally saw!

 

[Sherlock]

Well, it's true that Bohr once said "there is no quantum world" or whatever. But he (and generations of followers) also insisted that the wave function alone provides a *complete* description of... [something]. I can only assume that something is the relevant aspect of the quantum world. What else could the completeness doctrine mean?

... as I've said before, if there is some interpretation in which the wf does not refer to anything actually real (any gears and wheels) then that interpretation is not a theory, and there is therefore no way to apply terms like complete/incomplete/local/nonlocal to it. Those terms refer to gears and wheels, period. So if the copenhagen/orthodox people don't believe their theory provides any gears and wheels, what the heck are they talking about when they keep on insisting decade after decade that OQM is both complete and local?

If assumptions about quantum theory's relationship with an underlying quantum world are avoided, then the expansion theorem-postulate doesn't say anything about nonlocality. The theory is then interpreted as being acausal, and as such makes no statement about the existence, or not, of nonlocal causality in nature. In this view it isn't a locally causal theory either. So, it wouldn't, strictly speaking, be correct to call it a local theory. If OQM is thought of that way (as a local theory), then I would guess that it just has to do with it not violating the principle of local causality (which it doesn't as long as it's not being taken as mirroring an underlying quantum world).

What they are talking about wrt completeness is that the wavefunction is regarded as a complete description of what can be quantitatively determined about a quantum experimental preparation --- that the instrumental output will correspond to the probabilities assigned by the wavefunction for the setup.

The orthodox interpretation is about what the theory is, not what it might be. The theory is a mathematical scheme that assigns probabilities to qualitative instrumental behavior. Attributing some speculative significance (in terms of a correspondence to an underlying quantum world) to the qm algorithm or any part thereof is beyond the scope of the theory itself (and apparently beyond the scope of physics, at least for the foreseeable future).

So, the only interpretation of quantum theory that is clearly meaningful is the orthodox, probabilistic (or Copenhagen) interpretation. Specifying what quantum theory is known to be about (assigning probabilities to experimental results), while avoiding speculation about the theory's relationship to an underlying reality, doesn't make it any less a physical theory. It just can't necessarily be taken as a description of an underlying reality --- and this is maybe the most confounding way in which quantum theory differs from its classical predecessors.

Your two-part argument for nonlocality in nature, ttn, seems solid enough given the assumption that the mathematical gears and wheels of quantum theory are a 1-1 mapping, or at least in very close approximation to, the relevant (to the experimental results) qualitative aspects of an underlying quantum world. However, it seems just as reasonable to assume that they aren't, but rather are just charting the evolution of the instrumental probabilities. Seen from the latter point of view, the gaps in the quantum theoretical picture aren't surprising and don't imply nonlocal causality.

 

[ttn]

If assumptions about quantum theory's relationship with an underlying quantum world are avoided, then the expansion theorem-postulate doesn't say anything about nonlocality. The theory is then interpreted as being acausal, and as such makes no statement about the existence, or not, of nonlocal causality in nature. In this view it isn't a locally causal theory either. So, it wouldn't, strictly speaking, be correct to call it a local theory.

That is exactly the point I keep trying to make. If one's response to the assertion "your theory, if interpreted ontologically, is nonlocal" is to say "oh, well then I guess I won't interpret it ontologically" -- then one is *not entitled* to claim that one's theory is local! The very thing that prevents the accuser from saying it's *nonlocal* -- the very thing that makes people want to take this strategy to avoid what is otherwise an unavoidable accusation -- *also* prevents the advocate from saying it's *local*! That's the whole key point. It's not that it's not nonlocal and therefore local. It's not nonlocal in a different sense. It's not nonlocal in the sense that the whole idea of "nonlocality" is now inapplicable. But guess what? The whole idea of "locality" is also now also inapplicable, for exactly the same reason.

To "go epistemic" as a way of eluding the charge of nonlocality is *not* to defend the locality of one's theory. It's to remove one's theory from the class of things to which concepts like locality/nonlocality are applicable.

If OQM is thought of that way (as a local theory), then I would guess that it just has to do with it not violating the principle of local causality (which it doesn't as long as it's not being taken as mirroring an underlying quantum world).

It's the same issue. It neither violates nor fails to violate "the principle of local causality." It no longer *says* anything causal.

What they are talking about wrt completeness is that the wavefunction is regarded as a complete description of what can be quantitatively determined about a quantum experimental preparation --- that the instrumental output will correspond to the probabilities assigned by the wavefunction for the setup.

On that premise, what should/do they say about something like Bohmian mechanics?

The orthodox interpretation is about what the theory is, not what it might be. The theory is a mathematical scheme that assigns probabilities to qualitative instrumental behavior. Attributing some speculative significance (in terms of a correspondence to an underlying quantum world) to the qm algorithm or any part thereof is beyond the scope of the theory itself (and apparently beyond the scope of physics, at least for the foreseeable future).

What about Bohmian Mechanics? You can't just arbitrarily say it's "beyond the scope of physics for the foreseeable future" when there already exists an empirically viable theory that does precisely this.

So, the only interpretation of quantum theory that is clearly meaningful is the orthodox, probabilistic (or Copenhagen) interpretation.

Bohmian Mechanics is not meaningful?

You'll have to explain what you mean by "meaningful".

Specifying what quantum theory is known to be about (assigning probabilities to experimental results), while avoiding speculation about the theory's relationship to an underlying reality, doesn't make it any less a physical theory.

Refusing on principle to provide a theoretical account of physical reality doesn't make it any less a physical theory? I thought providing some such account was what a physical theory *was*?

It just can't necessarily be taken as a description of an underlying reality --- and this is maybe the most confounding way in which quantum theory differs from its classical predecessors.

It *isn't* taken as a description... But it *can* be.

Your two-part argument for nonlocality in nature, ttn, seems solid enough given the assumption that the mathematical gears and wheels of quantum theory are a 1-1 mapping, or at least in very close approximation to, the relevant (to the experimental results) qualitative aspects of an underlying quantum world. However, it seems just as reasonable to assume that they aren't, but rather are just charting the evolution of the instrumental probabilities.

As I keep saying, it's fine to take them that way. But then you just don't have a theory anymore. If a theory is something that provides an account of the state of the quantum system, then no Bell Local theory can agree with experiment. Of course someone can refuse to put forth a theory, or can put forth a calculation recipe that they *call* a theory but which is not a theory in the sense I've just defined it. That doesn't magically count as a "local theory" though. It's just a calculation recipe, and doesn't effect one whit the two part argument. No theory can be Bell Local and still agree with experiment.

Seen from the latter point of view, the gaps in the quantum theoretical picture aren't surprising and don't imply nonlocal causality.

Sure, in the same sense that if I only say "I like peanut butter" I don't imply any nonlocal causality. But who cares? What we're talking about is not all the possible ways of avoiding making a certain kind of false statement. What we're talking about is whether one can have a *theory* that respects Bell Locality and still agrees with experiment. I claim Bell proved (with the 2 part argument) that we can't. And you don't refute this proof by pointing out that there are other things one could utter (things which aren't theories) which "don't imply nonlocal causality." All sorts of things don't imply it -- by virtue of their not making any causal claims in the first place. But citing a bunch of such things isn't a good strategy for refuting Bell's argument -- it's just a distraction technique! As if I said "all men are mortal" and you tried to refute me by pointing to a rock and saying "that thing isn't mortal". Or really it's more like you point to a rock and say "I like peanut butter".

 

[alfredblase]

1. Causality is not a requirement of all physical theories. QM is a counter-example to that idea. See for instance a paper I wrote: Determinism Refuted[/url].

I looked at your paper but... I disagree. I don't see anything wrong in doing the following: I will define causality [how about calling it Blase Causality? :P ] and from that definition it will be evident that it is inviolate. The definition is merely a description of what can be observed every day.

A_d is a description of reality of A and B_d is a description of B. If when an action is performed on A so that A_d changes, B_d also changes, and if this has been observed to happen every time this action occurs, then I hold that the change in A_d causes the change in B_d. Blase Causality is the principle stating that the causing change should always occur before the resulting change, and always with enough time for the causing change to affect the resulting change. “Enough time” depends upon the mechanism via which the change or causality occurs.

In the case of EPR type experiments I must confess I am ignorant of the actual mechanism [according to QM] via which the evident change in Alice'selectron_d causes the evident change in Bob'selectron_d. Is there an identified mechanism? And if there is I would very much appreciate someone enlightening me on this.

2. QM *is* generally accepted, and subsequent to Bell I doubt it is considered causal universally.

I’m very well aware that QM *is* generally accepted ; This thread began in an effort to find a way of accepting it myself, but in my view has raised many questions that must be answered and which I havn't seen answers to.

A theory could consist of voodoo if it worked - and by "worked" I mean: it is useful. Please do not confuse theories with "the truth".

Yes, you are absolutely right; I was struggling with how to phrase my second point, thanks for finding the words for me. I rephrase the second point as follows:

2. In view of point 1: QM must have a provable physical interpretation that ensures Blase Causality is not violated in order to be accepted as a physical theory describing reality in wholly acceptable way.

 

[alfredblase]

lol, this is hard work interesting tho

The concepts of "momentum", "force" and so on are only helpful quantities in order to EXPLAIN, conceptually, observations (which are usually visual impressions of pointers on a dial, or spots on a photograph or whatever tool you decide to use as experimental apparatus). You cannot observe DIRECTLY a force, you can only observe its pretended consequences. As such it is an organizing principle of your observations.

Ok we express ourselves differently but I see now that we agree about this.

The "many worlds" (in other words, the wavefunction!) is exactly that too.

world = term in the wavefunction, when written in a particular basis (usually the one that corresponds to the Schmidt-decomposition between the Hilbert space of the observer and the rest of the world).

Ok, I must confess I don’t really know what that means, but I am willing to assume that your definition is sound.

I protest against the rejection of "in principle": it is the essence of any theory, to be able to say what would happen in principle, without limitation by the state of experimental technology

we agree on this but...

(as long as that limitation is also not a matter of principle of course, that's the danger...).

is there an actual experiment, that can actually be carried out, that can prove that there are “many worlds”?

You can say the same about Newton, then.

not at all; there are many actual experiments which prove, without a doubt, Newton’s laws within its well defined limits.

You can NEVER PROVE the existence of all the theoretical concepts that appear in the theory, you can only argue about its empirical validity or not.

You have misunderstood what makes a theory. A theory makes a statement such as Newton’s second law. Perfectly valid in my view and merely defines a force as the measurable quantity “rate of change of momentum”; nothing more, nothing less. It does not suggest an unseen thing that can never be observed, just rate of change of momentum, simple enough and more than adequate vanesch.

Because if what you claim is right, then it would be sufficient to reformulat.e a theory in an empirically equivalent one to show the "crackpottishness" of both. Newtonian physics (with forces) can be reformulated as a stationarity principle (Lagrange, ...). So both are clearly crackpottish theories according to your criterium (because in the Lagrangian formulation, no concept of "force" appears explicitly).

Again no! The Lagrangian approach is equivalent to the Newtonian approach but instead of force we talk about the gradient of the potential energy.

You are misunderstanding me Vanesch and you have still to come up with an experiment that can actually be carried out that proves that MWQM is acceptable. Again I repeat: is there one?

 

[vanesch]

is there an actual experiment, that can actually be carried out, that can prove that there are “many worlds”?

Personally, I consider the EPR experiments a good indication, but then there are other interpretations of the same. So no, you cannot *prove* that there are many worlds (in the same way that you cannot prove that there are forces).

You have misunderstood what makes a theory. A theory makes a statement such as Newton’s second law. Perfectly valid in my view and merely defines a force as the measurable quantity “rate of change of momentum”; nothing more, nothing less. It does not suggest an unseen thing that can never be observed, just rate of change of momentum, simple enough and more than adequate vanesch.

I've never seen a momentum. Momentum is a conceptual tool to arrive at predictions of measurements. So is force. After all, in Einsteins GR, there IS no force of gravity! It's geometry. So you see, no matter how "real" force seems to be to you, it is a conceptual entity which is not directly observable (but whose consequences, WITHIN THE FRAMEWORK OF THE THEORY, are observable ; agreement with such observations then strengthens the belief in the reality of the concept).

Again no! The Lagrangian approach is equivalent to the Newtonian approach but instead of force we talk about the gradient of the potential energy.

Well, "many worlds" are then equivalent to standard quantum theory in its observable predictions too. And note that the Lagrangian approach is conceptually TOTALLY DIFFERENT than Newton's. In the Lagrangian approach, there is a holistic COST FUNCTION which is minimised (or extremalized), and things move (a bit magically) in such a way as to minimize their "Lagrangian taxes". Nothing pulling and pushing. You can then DERIVE that thinking this way will give you the same results AS IF there were forces acting. But there are no forces, just "lagrangian taxes". In the same way, from these "many worlds" you can derive that everything will happen AS IF there were a projection.

You are misunderstanding me Vanesch and you have still to come up with an experiment that can actually be carried out that proves that MWQM is acceptable. Again I repeat: is there one?

MWQM has only one reason of existence: giving a coherent and ontological picture of the formalism of quantum theory, where no distinction is made between "interaction physics" and "measurement physics".

 

[alfredblase]

Personally, I consider the EPR experiments a good

I don't understand the MWI so I guess I can't really judge. Is it generally accepted that EPR experimental experiments are proof that MWQM is a wholy acceptable theory? Perhaps you could point me to an online introductory paper/article on MWI so that I may understand a bit more.

indication, but then there are other interpretations of the same. So no, you cannot *prove* that there are many worlds (in the same way that you cannot prove that there are forces).

In the case of Newtonian force all that is needed is proof that his second law is valid, I maintain you expect too much from the concept of force.

I've never seen a momentum. Momentum is a conceptual tool to arrive at predictions of measurements.

Momentum is mass times velocity. You can measure the mass of an object by directly comparing its weight with other well defined masses. I'm very happy with that measurable defintion, I don't see why you have a problem with it. The metre and the second also have measurable definitions. So you have seen a momentum.

Well, "many worlds" are then equivalent to standard quantum theory in its observable predictions too.

I don't know... I direct you to my reply to Dr Chinese's post [post 102] MWQM presumably has an identified mechanism in EPR experiments which ensures Blase Causality is not violated, I have yet to hear about OQM's such mechanism. Also OQM is generally accepted, is MWQM generally accepted?

And note that the Lagrangian approach is conceptually TOTALLY DIFFERENT than Newton's. In the Lagrangian approach, there is a holistic COST FUNCTION which is minimised (or extremalized), and things move (a bit magically) in such a way as to minimize their "Lagrangian taxes". Nothing pulling and pushing. You can then DERIVE that thinking this way will give you the same results AS IF there were forces acting. But there are no forces, just "lagrangian taxes".

Both are valid interpretations of the same law. Nothing wrong with that.

In the same way, from these "many worlds" you can derive that everything will happen AS IF there were a projection.

again I don't know enough I repeat:

I direct you to my reply to Dr Chinese's post [post 102]. MWQM presumably has an identified mechanism in EPR experiments which ensures Blase Causality is not violated, I have yet to hear about OQM's such mechanism. Also OQM is generally accepted, is MWQM generally accepted?

MWQM has only one reason of existence: giving a coherent and ontological picture of the formalism of quantum theory, where no distinction is made between "interaction physics" and "measurement physics".

If it is generally accepted that MQWM provides such a picture, then being the only such interpretation I have heard of I will adopt it myself =) But I repeat: is MWQM generally accepted?