Exploring the Bohmian Interpretation: Why Study It?

[jambaugh]

If you want it very strict : - say - the preferred spaces in a static universe; you can carefully relax this condition furthermore. Moreover, in line of my argument it is irrelevant how to determine such frame operationally; but I guess you can retrieve the metric in free space by studying deviations in light paths (and reflection times) between different free falling mirrors (and by defining your units).

W.r.t. recovering the metric, it doesn't uniquely define an inertial frame. The local Lorentz group IS the invariance group of the local metric.

W.r.t. the operational meaning being irrelevant, then if this is necessarily so then by the same failure of operational distinction then the point made if requiring this argument is also operationally meaningless.

Yeh, so what ? Is that against observation ? :uhh: What if special relativity is only valid for elementary particles with velocity almost up to c (but not quite) in almost empty space ?

I don't know what you mean about "velocity almost up to c" unless you are selecting a specific inertial frame. Either the 4-velocity is a unit vector or a null vector.

Let's see if I can reproduce your reasoning:
a) There's a preferred inertial frame.
b) The relativity group is approximately the Lorentz group (or has a Lorentz subgroup).
c) The action of the relativity group is approximately linear on local space-time coordinates and 4-momenta.
d) These "approximations" loose precision the farther one gets from the preferred inertial frame.
e) These divergence from SR is sufficient to imply FTL signals in the preferred frame never result in backward in time signals in any inertial frames.

Is this a good summary or have I misunderstood?

Of course one does.

Let us see...

Euh that doesn't make any sense to me. The retarded field exists without any acceleration. Moreover, if no external force is used, there is no acceleration at all for a single electron (there is enough discussion on that point in the literature concerning the Lorentz Dirac equation).

Yes, I used the accelerated case as an example because the advanced and retarded solutions are distinct... see below.

Euh, for an electron at rest (or uniform motion), the Coulomb field = Field strength arising from the RETARDED propagator.

And also the field strength arising equivalently from the ADVANCED propagator. The situation is time symmetric.

Gravitons are plane wave solutions of the linearized field equations around a flat background metric; hence the local causality principle simply follows from the well known causality theorems for hyperbolic partial differential equations. If I linearize around de Sitter, I get different null geodesics (expanding congruences) and hence different causality properties.

I would rather you said, Gravitons are as yet not well defined hypothesized quanta which may be approximately resolved in terms of plane-wave solutions around...

Firstly let's stick to classical gravitational waves until such time as a reasonable QG theory is presented. Secondly even photons do not uniquely correspond to plane wave phenomena. That is just one of the many bases into which they may be resolved.

Thirdly, your linearization around de Sitter has the same well known causality theorems for hy. p.d.e.s when you look at them in terms of equivalent pdes in the 1+4 dimensional flat space in which the de Sitter manifold is a unit pseudo-sphere. The characteristics of the equations may project onto curves on the pseudo-sphere rather than "straight lines" but they have the same local topology and no qualitative distinction in the global setting w.r.t. causality. Asymptotically they are the same and hence they are the same with regard to local causal structure.

That doesn't make any sense to me (and denying the reality of the measurement of Alice, being Bob, doesn't really help in making progress IMO).

Let me make it clear. Say you are observing that "the electron" within a one particle system to be in a specific region of space. You are not making a local observation when you couple this with the "one particle system" assumption because there is an implicit rejection of cases where you observe an electron as stated and additionally do not observe an electron elsewhere.

It is not that the measurement (a local action) causes a global effect, but rather your system definition causes you to reject those cases or globally prevent those cases where distant electron counts correlate to the count of 1 or 0 at the given local.

The restriction to outcomes where only one particle is ever detected globally (globally in the sense of a larger region then you are resolving locales) is a non-local conceptual constraint when you consider the idealized system with fixed total=1 particle number.

The physical locality of the situation is seen when you consider two subsequent such global measurements of particle counts at all locals.
You will never see physically observable quantities causally propagate FTL (according to the current theory).

For the rest, you basically say : nothing real can correspond to the quantum waves -->> what is the use of BM ? Again, why do you think the first thing is true at all ?? Some people would say particles are not reall at all, but merely localized field exitations, and that it is the wave which is fundamental (Einstein was one of them).

I would phrase it differently:
Nothing observable can correspond to the quantum waves -->>...

As to why I believe this beyond the causality arguments I've made...
I look most often to Bell inequality violation in QM and EPR experiments.
There is in my opinion a much simpler derivation of Bell's inequality which doesn't require any locality issues be brought up per se, but rather only that you can actually find commuting observables. Bell's inequality is simply the triangle inequality when you assume:
a) An objective state of reality prior to measurement.
b) That the probabilities of outcomes derive from a probability measure over the set of states of reality.
c) That two measurements can be made without the outcome of one affecting the other (usually handled by spatially separating them and using locality arguments but not necessarily done this way).

I believe (c) and that (b) necessarily follows from (a) and the assertion that the measurement is causally determined by the prior state.

(a) seems to be the most intuitively obvious but so to was the assumption of absolute time pre SR. Parse the classical notion of "state" more closely and note that it had an operational meaning since it is classically assumed that all properties can be independently measured and thus the state of reality can in principle be empirically determined. Once you invalidate this classical assumption you find that "objective reality" is not quite physically meaningful. In quantum theory you start with measurements and forget about states. The "wave functions" "state vectors" "kets" etc which are best labeled "mode vectors" are representatives of classes of systems which have been measured with respect to a certain maximal observable. Maximal no longer being "complete" in the classical sense of defining a state.

BTW I am also one of those people who say "particles are not real" (rather I would say they are actual pheonmena as opposed to e.g. the conceptual status of the wave functions representing them.)
But I also give the same status to the "fields". They are all pheomena, out there but not reducible to "transitions between states of reality". Ultimately "an electron" is the causal correlation between "electron emitters" and "electron detectors". Similarly for photons et al.

What then are the wave functions? They are representations of equivalence classes of such emitters or detectors, said representations giving also information about partial correlations between inequivalent emitter-detectors. When you propagate a wave-function you are simply specifying how under the given dynamics earlier and later acts of emission yield equivalent behavior with respect to measurements in the future of both acts. All is expressed in terms of the actual empirical elements, the measurements (provided you don't additionally tack on an ontological interpretation of the wave function).

Given then that this operational interpretation by its formulation addresses any and all questions of what can be observed (given the theory itself specifies limits via the uncertainty principle), then adding another level of ontological interpretation can at "best", add nothing or at "worst" predict deviations from the predictions of QM. Even so said deviations can still be recast in purely operational terms.

I assert that this is a great virtue in physics. Sticking to the operational language forces one to ask the right questions (those which can be empirically tested) an not to waste time on artificial distinctions.

With regard to Bohmian interpretation I'll ask Mammy to summarize my position:
http://www.obcgs.com/firstwomen/mammy.jpg
"It just ain't physics! It ain't PhysICS! It ain't PHYsics!"

 

[Careful]

Jambaugh, you miss the first two points entirely although I have explained how GR allows you to speak in those terms, so I am not going to come back to this again. Of course, the Lorentz group is a local symmetry group of GR, but then on the natural bundle of orthonormal frames or as a subgroup of the Diff_0.
About the accelerated case, your original ``point'' was that the distinction between the retarded and advanced propagator doesn't matter which is false in case you include background radiation (which is what I did in the first place) or more than one particle. Concerning your de Sitter argument, of course this theorem remains valid (but then with respect to the de Sitter metric) which of course differs locally from the Minkowskian one. May I ask you what your definition of locally causal is anyway ?

 

[ueit]

This mental picture of all past and future as a fixed state is a useless arguing point.

Nevertheless, this is the picture BM (and any deterministic theory) gives us. If you disagree with it there is no point to object to the theory on other grounds, as all your arguments are bound to be circular (sooner or later you'll make an appeal to "free choice" or something of that sort which is the logical opposite of determinism).

I can argue that I can flap my arms and fly. You can't disprove it because I am predetermined to never actualize this ability. It redefines the word "can" and "ability" to be meaningless.

That's not exactly true. I can disprove it because it is against the physical law.

It is the same problem moral philosophers have with ethics and (quasi)deterministic models of human behavior. It is pardoxically used to justify relaxing punishment for criminal behavior rather than more consistently being used to say that the choice of punishment we make is just as predetermined.

This doesn't mean the argument is not sound. We may not like it but it may still be true.

In short the use of such argument in context is self contradictory in that choice is a priori assumed in the very foundation of the argument. You can't say the value of the observable you choose to measure is predetermined because everything is predetermined (implicitly including your choice). The "because" here is meaningless because you must change contexts from this hypothesized globally determined states in the very semantics of the language in which you express the physics.

I disagree. Even if I am not able to "choose" to do a measurement, I can observe it unfolding. I still can notice correlations between what I do (freely or not) and what the outcome is and do science.

There is in fact a subtle category error built into such arguments. Even asserting metaphysically such a globally deterministic state, one recasts the concept of choosing to execute an experiment in terms of metachoice of circumstances where such an experiment is determined to occur. It then just as certainly leads to questions about whether the metachoice exists which will find in the deterministic clockwork of the universe the appearance of backward in time causality.

The very notion of cause and effect and hence determinism is premised on external free choices in the operational verification of cause and effect. Determinism must always be relative to a system epi-system cut and is meaningless in a universal context (except as "religious" dogma).

Without it all you get semantically is correlation and the ordering of cause and effect is all together meaningless. You can adopt such a world picture but it doesn't fit into quantum theory. The "bras" in quantum theory correspond to an experimenter causing e.g. an electron to be emitted which he knows from past experience will always affect one type of detector (the dual "ket") and never affect specific others (the dual "kets" of orthogonal "bras").

For calculating experimental results one have to use the wave function of a subsystem. This has all the required properties including the experimenter's "free choice" so no contradiction with QM exists. However, I see no reason why BM cannot be applied to the experimenter himself. It is a logical step to make regardless of what philosophical questions it may produce.

Now your point is well taken that this does appear resolve the objection I have to the Bohm pilot waves propagating back in time, i.e. that it is only partial resolutions of this universal system which appear to have this behavior due to the nature of how the piece of the whole is resolved. But then again this relativizes the "objective reality" one is trying to latch onto.

If it makes you sleep better to imagine this universal wave function is "out there" instead of just an imaginary construct then great. I've no real problem with other people's belief systems be they this or say "intelligent design" just so long as they don't try to call it science.

You have a really strange position here. You tell me to go to the "intelligent design" camp because I pointed an error in your line of reasoning. In BM the future is fixed, period. This has nothing to do with my "belief system". If you think that the deterministic nature of BM is contrary to science then say so. If you have a reason to believe that BM cannot be applied to a human brain/mind then please state clearly what that reason is. If not, stop using the "free choice" assumption when dealing with a deterministic theory. At most, you could argue for some type of statistical independence between various parts of an experiment (like detectors' settings in an EPR experiment), but never for the possibility of multiple outcomes from the same initial state.

 

[jambaugh]

Nevertheless, this is the picture BM (and any deterministic theory) gives us. If you disagree with it there is no point to object to the theory on other grounds, as all your arguments are bound to be circular (sooner or later you'll make an appeal to "free choice" or something of that sort which is the logical opposite of determinism).

The problem is that the determinism of the "theory" which then in principle means the deterministic outcome of say the z-spin measurement of an electron which has just previously been measured with x-spin -1/2, disallows any actual prior experiment which would observe the variables determining this event. It is a "theory" about empirically invisible entities. Which is why I keep comparing it to e.g. theology.

Now "determinism" can be defined in two contexts. They way you're using it is in the sense that the universe as a whole is a clockwork. QM (in its purely operational form) can be also defined as "deterministic" in a weaker form in that any (possible) outcome of any measurement may be assured by suitable prior actions. You can cause any effect you choose given enough prior warning.

I bring up this distinction because this weak determinism can be empirically tested and is operationally meaningful. But your sort of clockwork determinism cannot be given such meaning because it is asserting that the outcome of any possible measurement of a given instance of a system is a priori determined. You can't actually measure prior variables which will predict all outcomes of any measurement. You can at best actualize a prediction of one of the measurements as via measuring a second system totally entangled with the one in question.

Thus specifically you measuring the half of an entangled pair, or any other prior systems going all the way back to the big bang, cannot tell me the outcome of a specific measurement I will choose to make without me first telling you which measurement I will make. You can't send me a complete list of "if you measure A you will see a, if you measure B you will see b..."

You seem to be arguing that there is an invisible version of such a list "out there" in the form of a universal wave function. I can't see such an assertion as other than "mystic belief".

That's not exactly true. I can disprove it because it is against the physical law.

But you must understand. In reality I can fly but when I do so I will be invisible and you see only projection of my body which just appears to be standing there. The projection is so perfect it even will affect both light and material particles. But the real me... my pilot wave... is flying.

Pardon my facetiousness... but you can only prove that a hypothesized physical law's predictions disallow what I described. I, to be intentionally difficult, will just hypothesize a physical law which doesn't. How do we weigh and compare such laws? By empirical test if we wish to call our methods science. If such a law as you invoke has been confirmed by empirical data that confirmation is only about the observable predictions of that law, namely the empirical meaning of "me flapping my arms and flying" and NOT my assertions about reality behind what is empirically visible.

Granted this example didn't fit well the point I was making. You have the weak form of determinism I mentioned which allows you to disprove my claim without being invalidated by my resistance to the test. (And if the weak form I stated is inconsistent with the strong form it may yet be modified and still allow this example's invalidation.)

This doesn't mean the argument is not sound. We may not like it but it may still be true.

It is not its truth I criticize, rather its inconsistent application of the premise. The person is arguing that the relevant decision maker should make a reasoned choice based on the premise that people cannot make reasoned choices but rather only react to their environment. It also fails to consider that part of that environment is the social judicial policy.

I was implying your determinism argument is similarly inconsistent. But now upon consideration I think I must back-peddle.

I disagree. Even if I am not able to "choose" to do a measurement, I can observe it unfolding. I still can notice correlations between what I do (freely or not) and what the outcome is and do science.

But you can't choose what you observe, its predetermined. For all you know there is a strong correlation between what you will be predetermined to observe and the behavior of that observation. I'm trying to say that invoking this determinism doesn't tell you anything about what you aren't actually observing, unless you assume an independence of choice in contradiction to the assumed determinism. It is either self contradictory or it again all reverts back to operationalism. You only talk about what is observed and "the reality" component is outside the domain of science.

[addendum] On a more conciliatory note, I offer a weaker statement. I can say rather that it is sufficient for any empirical predictions to stick to descriptions of what the outcomes of measurements we choose (or are predestined) to make and thus the rest extends outside the domain of science. By its sufficiency nothing is added by reality hypotheses.

For calculating experimental results one have to use the wave function of a subsystem. This has all the required properties including the experimenter's "free choice" so no contradiction with QM exists. [...

The point is that those predictions for the subsystem (which is the QM theory, not just consistent with it) are all causally local and self consistent. I asserted that the wave function itself when given ontological status is not. You say this is "cured" by viewing the wave-function as part of a global deterministic ontological model. I asserted that you can't invoke this choice negating "cure" while still allowing the choice. However I back-peddle here as well and concede the issue.

You I take it would argue that there is sufficient "randomness" between the variables determining the property to be measured which variation is uncorrelated with those subsystem variables determining the outcome of the measurement so as to allow a statistical inference over many isomorphic trials.

I concede then that my "determinism invalidates implicit choice in defining experimental measurement" doesn't hold up. It is after all the circumstance we see in astrophysics. We can make statistical inferences in looking at many astronomical objects without the need to "choose" from where in the universe we watch or "choose" via active preparation the initial conditions of e.g. two colliding galaxies.

Very well. I will henceforth restrict my objections to ("strong") determinism to only the issue of operational meaning.

...] However, I see no reason why BM cannot be applied to the experimenter himself. It is a logical step to make regardless of what philosophical questions it may produce.

Yes. But I see no distinction between giving the wave functions ontological status and calling it BM vs treating the wave functions as mathematical constructs and calling it e.g. (Copenhagen) QM.

You have a really strange position here. You tell me to go to the "intelligent design" camp because I pointed an error in your line of reasoning.

Firstly I didn't tell you to go to the "intelligent design" camp, nor did I bring up "intelligent design" out of malice for loosing an argument. I brought up intelligent design as another example of a belief system insisting on being granted status as a scientific theory when it is in fact based on beliefs about reality beyond what can be observed.

In BM the future is fixed, period. This has nothing to do with my "belief system".

BM is not a belief system? It doesn't posit metaphysical assertions? Does it not in fact posit metaphysical assertions outside the domain of what may be empirically tested? Is not this "fixed future, period." assertion just such an example?

If you think that the deterministic nature of BM is contrary to science then say so.

Right. I so say...or rather said above with regard to its lack of operational meaning of some of its assertions.

If you have a reason to believe that BM cannot be applied to a human brain/mind then please state clearly what that reason is.

In so far as BM doesn't disagree with operationally interpreted QM I see no reason to distinguish it as particularly inapplicable to the human brain/mind.
[deleted a long meaningless speech.]
I just don't see any fruitful results from any quantum analysis of the brain.[deleted second long tangential speech.] We can discuss my opinions about applying quantum methods to psychology in another setting if you wish.

If not, stop using the "free choice" assumption when dealing with a deterministic theory.

I shall as I think you've quite well countered it in the context I was trying to apply it. I would go so far as to say I may have been guilty of sophistry.

At most, you could argue for some type of statistical independence between various parts of an experiment (like detectors' settings in an EPR experiment), but never for the possibility of multiple outcomes from the same initial state.

On this last I'm not quite clear what you mean. I at least must try to rephrase it so as to remove implicit assumptions I deny. You say "initial state" I say initial mode of preparation. (Our distinct meanings given to the wave function) Given that mode (a class of instances) you can have (across many instances) multiple outcomes of identical modes provided the outcome is a measurement for an observable for which that mode is not an eigen-mode. Clearly in a single instance you can only measure one observable and see only one outcome of that measurement. If that's what you mean I can't see how I led you to believe I would think otherwise.

Well I can't imagine that you fail to understand my points about operational meaning and I've conceded the point about "choice" so I don't think, as much as I like "hearing" myself "speak" that I can add any more to the discussion.
You're probably weary of me as well so I'll read your replies and endeavor only respond to append brief clarifications. Thanks for the debate and especially for revealing a weakness in my arguments.

Regards,
James Baugh

 

[ueit]

The problem is that the determinism of the "theory" which then in principle means the deterministic outcome of say the z-spin measurement of an electron which has just previously been measured with x-spin -1/2, disallows any actual prior experiment which would observe the variables determining this event. It is a "theory" about empirically invisible entities. Which is why I keep comparing it to e.g. theology.

So, what interpretation of QM is free from "empirically invisible entities"?

Now "determinism" can be defined in two contexts. They way you're using it is in the sense that the universe as a whole is a clockwork. QM (in its purely operational form) can be also defined as "deterministic" in a weaker form in that any (possible) outcome of any measurement may be assured by suitable prior actions. You can cause any effect you choose given enough prior warning.

My issue with this "weak determinism" is that its logical consistency is questionable. We are ourselves quantum systems, part of the environment and we obey the same constraints as the system under study. It has to be proven from inside the studied theory, not assumed, that a certain action is possible. For example, if you study gravity by orbiting around earth, you cannot just assume that you can change orbit at will. If you have no massive object at hand you are bound to deterministically follow the same orbit for ever.

Or consider an EPR experiment. Say that one proposes a theory stipulating that an entangled pair is only emitted when a signal from the would-be absorbers is recieved. Now, you cannot just assume that the detector orientations are free parameters because the spin of the entangled particles is a function of the detector's state.

I bring up this distinction because this weak determinism can be empirically tested and is operationally meaningful. But your sort of clockwork determinism cannot be given such meaning because it is asserting that the outcome of any possible measurement of a given instance of a system is a priori determined. You can't actually measure prior variables which will predict all outcomes of any measurement. You can at best actualize a prediction of one of the measurements as via measuring a second system totally entangled with the one in question.

Thus specifically you measuring the half of an entangled pair, or any other prior systems going all the way back to the big bang, cannot tell me the outcome of a specific measurement I will choose to make without me first telling you which measurement I will make. You can't send me a complete list of "if you measure A you will see a, if you measure B you will see b..."

You seem to be arguing that there is an invisible version of such a list "out there" in the form of a universal wave function. I can't see such an assertion as other than "mystic belief".

I actually agree with you that assuming hard determinism (HD) is useless from a scientific stand point. However, I did not assume HD but I pointed out that it is inescapable if BM is true. One cannot have BM and not have HD. So, if one wants to do an internal critique of BM one has to agree, for the sake of the argument, with HD.

[addendum] On a more conciliatory note, I offer a weaker statement. I can say rather that it is sufficient for any empirical predictions to stick to descriptions of what the outcomes of measurements we choose (or are predestined) to make and thus the rest extends outside the domain of science. By its sufficiency nothing is added by reality hypotheses.

It depends on what you mean by sufficient. Science evolves and models that propose unobservable mechanisms can be useful in the long run. There are also entities that could be required for logical/mathematical consistency.

Very well. I will henceforth restrict my objections to ("strong") determinism to only the issue of operational meaning.

See my objections to weak determinism above.

Firstly I didn't tell you to go to the "intelligent design" camp, nor did I bring up "intelligent design" out of malice for loosing an argument. I brought up intelligent design as another example of a belief system insisting on being granted status as a scientific theory when it is in fact based on beliefs about reality beyond what can be observed.

OK, I'm sorry for misunderstanding what you were saying and giving a hasty answer. The difference between ID and HD is that ID-ers make a set of very unparsimonious assumptions (that a omnimax god exists and the bible is his word and it is absolutely true) while BM makes a pretty simple assumption, that the quantum particles move from place to place on a deterministic trajectory. This hypothesis in turn implies HD as a logical conclusion.

BM is not a belief system? It doesn't posit metaphysical assertions? Does it not in fact posit metaphysical assertions outside the domain of what may be empirically tested? Is not this "fixed future, period." assertion just such an example?

As I said before, I just assume, for the sake of the argument that BM is true. My point is that you cannot criticize BM by denying that the future is fixed, because the later is implied by the former.

Right. I so say...or rather said above with regard to its lack of operational meaning of some of its assertions.

OK.

In so far as BM doesn't disagree with operationally interpreted QM I see no reason to distinguish it as particularly inapplicable to the human brain/mind.
[deleted a long meaningless speech.]
I just don't see any fruitful results from any quantum analysis of the brain.[deleted second long tangential speech.] We can discuss my opinions about applying quantum methods to psychology in another setting if you wish.

I agree with you on this. I only pointed out that we are part of this universe and subject to the same laws. If these laws are deterministic, so are we. You cannot have a deterministic interpretation of QM and free choice unless that choice comes from somewhere else (soul?)

On this last I'm not quite clear what you mean. I at least must try to rephrase it so as to remove implicit assumptions I deny. You say "initial state" I say initial mode of preparation. (Our distinct meanings given to the wave function) Given that mode (a class of instances) you can have (across many instances) multiple outcomes of identical modes provided the outcome is a measurement for an observable for which that mode is not an eigen-mode. Clearly in a single instance you can only measure one observable and see only one outcome of that measurement. If that's what you mean I can't see how I led you to believe I would think otherwise.

I meant that, an initial bohmian state (wave function + configuration) "fixes" the future, a rephrasing of my previous point.

Well I can't imagine that you fail to understand my points about operational meaning and I've conceded the point about "choice" so I don't think, as much as I like "hearing" myself "speak" that I can add any more to the discussion.
You're probably weary of me as well so I'll read your replies and endeavor only respond to append brief clarifications. Thanks for the debate and especially for revealing a weakness in my arguments.

I thank you for your answers as well. My only remaining question is related to the logical consistency of weak determinism.

Regards,
Andrei Bocan

 

[jambaugh]

So, what interpretation of QM is free from "empirically invisible entities"?

Basically the "operational interpretation" I much earlier described which I believe is the same as the Copenhagen. What mathematical objects which do not directly correspond to laboratory actions of preparation/measurement/selective detection are not granted status other than as mathematical objects.

My issue with this "weak determinism" is that its logical consistency is questionable. We are ourselves quantum systems, part of the environment and we obey the same constraints as the system under study. It has to be proven from inside the studied theory, not assumed, that a certain action is possible. For example, if you study gravity by orbiting around earth, you cannot just assume that you can change orbit at will. If you have no massive object at hand you are bound to deterministically follow the same orbit for ever.

Hmmm... I'm not sure I see your point here. My thought was that if you give me an early enough head's-up on e.g. your future plan to measure the z-spin of an electron, I can make sure the electron is there with a specific momentum and z-spin value. I didn't see any special logical issues in this.
The ability to prepare a system in a given mode was I though a foundational assumption in QM.

Or consider an EPR experiment. Say that one proposes a theory stipulating that an entangled pair is only emitted when a signal from the would-be absorbers is recieved. Now, you cannot just assume that the detector orientations are free parameters because the spin of the entangled particles is a function of the detector's state.

Huh? As I was thinking of the definition the orientation of the detectors would have to be give to me before I prepared the pair of particles. I would then be able to assure a given pair of spin measurements. Whether the particles are entangled would be a secondary condition which is possibly (most probably) inconsistent with the type of assured outcome you are describing.

I actually agree with you that assuming hard determinism (HD) is useless from a scientific stand point. However, I did not assume HD but I pointed out that it is inescapable if BM is true. One cannot have BM and not have HD. So, if one wants to do an internal critique of BM one has to agree, for the sake of the argument, with HD.

Yes, You've convinced me I can't get an "internal" contradiction, and the desire for this HD is after all one of the main reasons given for considering BM.

It depends on what you mean by sufficient. Science evolves and models that propose unobservable mechanisms can be useful in the long run. There are also entities that could be required for logical/mathematical consistency.

Yes that is a weak piece of my argument. I can't really argue any case except certain basic preferred heuristics, dictating the conceptual path one might best take to get to a new and improved theory. The path that insight takes isn't predictable enough for the level of insistence I expressed.

OK, I'm sorry for misunderstanding what you were saying and giving a hasty answer. The difference between ID and HD is that ID-ers make a set of very unparsimonious assumptions (that a omnimax god exists and the bible is his word and it is absolutely true) while BM makes a pretty simple assumption, that the quantum particles move from place to place on a deterministic trajectory. This hypothesis in turn implies HD as a logical conclusion.

Yes, I used and exaggerated parallel of ID to really push the point.

As I said before, I just assume, for the sake of the argument that BM is true. My point is that you cannot criticize BM by denying that the future is fixed, because the later is implied by the former.

Right, I think we've now consensus between us on this.

I agree with you on this. I only pointed out that we are part of this universe and subject to the same laws. If these laws are deterministic, so are we. You cannot have a deterministic interpretation of QM and free choice unless that choice comes from somewhere else (soul?)

Yes. I think my invocation of "weak determinism" (in possibly modified form) does allow room for (even requires) free choice. (And I still believe much of the formulation of physics implicitly invokes choice in its language.)

Hmmm... I may see what you're getting at. Does the formulation imply that a a third party can prepare my intent and the system so that the outcome is different from my expectations. This brings up a big issue as to what concerning the person is really an observable. It's Schrodinger's cat all over again. I've some canned arguments but let's not start that here. Possibly another thread?

I meant that, an initial bohmian state (wave function + configuration) "fixes" the future, a rephrasing of my previous point.

OK.

I thank you for your answers as well. My only remaining question is related to the logical consistency of weak determinism.

I defined it on the spur of the moment so it may need some modification if there is a consistency issue. My main thought was any measurement or sequence of measurements of commuting observables could be a priori assured provided one is not appending additional constraints equivalent to specifying values of observables not commuting with those in question. (Such as requiring specific pairs of measurements and that the pair of systems be entangled.)

It is really nothing more than the assumption in QM that any given mode vector can be actualized.

If I understand your issue correctly, (that logical inconsistency could occur when you include the intending experimenter within the system of a second experimenter) is your objection any different than in a classical setting, saying you can tie my hands to prevent me from actualizing my intent to e.g. put the eight ball in the corner pocket? Thus the classical physics of pool is not weakly deterministic?

Regards,
James

 

[Demystifier]

For the most recent contribution to the program of answering the question "Why Bohm?" see
http://lanl.arxiv.org/abs/0706.2522

 

[jambaugh]

For the most recent contribution to the program of answering the question "Why Bohm?" see
http://lanl.arxiv.org/abs/0706.2522

I note in reading this paper that it promulgates the same misinterpretation of Orthodox (Copenhagen) QM, al la Bell's arguments.

However Bell’s theorem[4,2]showed that this problem
is inescapable for any interpretation of QM that admits the reality of measurement outcomes for space-like separated observers.

There is a grave distinction between the "reality of outcomes" and the dependence of outcomes on an underlying reality.

The distinction is in the totality of the reality assertion. A measurement is "real" in the exact meaning of "measurement" i.e. an amplification of a specific quantum variable to the scale at which its value can be described classically e.g. as a record on a measuring device. It is not the same as identifying that measurement with the totality of reality implicit in the state of reality picture for the physical system.

Bell showed that given a series of assumptions one can derive his famous inequality which contradicts the predictions of QM. One of those assumptions is local causality between acts of measurement. But another is that the a priori probabilities of the outcomes of these causally separated measurements derives from local objective states whether these states be observable or no. In essence He then showed that:

QM + Local Causality + Local Objective Reality, are incompatible. The author is making a grave mischaracterization in that in the Copenhagen interpretation it is the objective reality which is rejected (replaced with subjective actuality if you will) and hence local causality is not incompatible with QM.

See e.g. http://arxiv.org/html/quant-ph/9907027"
for a semantic analysis of the argument.

Indeed the no signaling theorem (see Eberhard 1978, Ghirardi, Rimini and Weber 1980, Jordan 1983, Shimony 1984, Redhead 1987, pp. 113-116 and 118) explicitly demonstrates that in so far as local causality is operationally defined it is a consequence of QM.

Any causality arguments in the context of "interpretations" of QM which still abide by the predictions of QM are like arguing "how many angels can dance on the head of a pin". (Something I let myself fall into earlier to my regret.)

So are there any "Why" 's out there which correctly characterize Copenhagen?

So far all that I've seen which is valid is either
I. "Personal philosophical preference" and
II. "It might somehow provide insight into new physics".
I assert the same is true vis versa with a stronger argument w.r.t. insight given operationalism is a powerful heuristic principle in physics. It helps one avoid hysteresis in ones conceptualization (which, I might add, Einstein used to great effect.)

Regards,
James Baugh

[Edit] P.S. This paper, by the way, is a very nice piece of work, or would be if (in my characterization) the BM "nonsense" were excised. But I don't see it as saying anything terribly ground breaking. Taking an operational approach it is clear that an ensemble average of his weakly observed normalized currents, for many systems by the very nature of the correspondence principle must approach the presented classical limit particle velocities. His assertion that an ensemble average must conform to the reality of an individual instance is predicated on the assertions of BM which he rightly qualifies. But absent these assertions the operational meaning is the same. One is taking an ensemble average and getting in the limit a classical description. Pushing the Bohmian part of it is to my mind no different than say ascribing a pressure to each particle of a (classical) gas because you can give the pressure of the ensemble operational meaning.
R., J. B.