Problems with Many Worlds Interpretation

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  • #651
Ken G
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Yes, in order for a conceptual model to qualify as an interpretation of a theory, we must establish a clear correspondence between the elements and features of the model and the empirical content of the theory, which is generally expressed in mathematical terms. I wouldn’t have thought this was controversial.
What is controversial is what you mean by a "clear link." Who decides what forms this link must take, and when is it clear versus murky? I would say that MWI does have a clear link-- they say closed systems (and systems whose only external interactions can be treated as specified rather than self-consistently evolving, as with a potential function) evolve by the Schroedinger equation, and that when an observer (or apparatus) becomes part of that system in ways that are not being tracked in detail, the Born rule applies for attributing the measure of the various outcomes the apparatus might be considered to follow when all that missing information is not being tracked. That seems like a clear link to me, even though it doesn't explain the Born rule any better than CI does. If MWI users want a better explanation of the Born rule, it's not because they have to have one to make MWI a valid interpretation, it's that they need one to make MWI a new theory that could potentially make different predictions and guide us into seeing how to test those differences. Successful testing would then make MWI a clearly superior theory, rather than just an alternate interpretation.

The point is, only better predictions are demonstrable, not better interpretations. I would argue that anyone who sees a link, and uses it when they write down the equations, is following their interpretation without any need to demonstrate that their interpretation leads to those equations because interpretations always fall short of doing that. Interpretations are fundamentally subjective, and fundamentally ad hoc.
For example, there is no difficulty translating between a force/vector formulation of mechanics to a Lagrangian formulation. This is a perfectly well defined correspondence. No problem at all.
Sure, but those are formulations, meaning they are equations. We can all agree on the equations of quantum mechanics, they're in the textbooks. What you are saying is that a valid interpretation of a given formulation must demonstrate a correspondence with that formulation. You are in effect asking for the postulates of the formulation to follow from the interpretation! That never happens, it would be backward. We don't interpret Newton's laws as forces on particles, and that gives us F=ma, we start with the formulation (F=ma) and interpret the meaning of the letters. The interpretation gives us a sense of cognitive resonance when we write those letters down, that's all it does. People who use the MWI interpretation get that sense of cognitive resonance when they write the equations of quantum mechanics, so they are using an interpretation-- they can no longer demonstrate that the equations they are writing down somehow follow from that interpretation than you can demonstrate that F=ma follows from the concept of pushing on particles.

To elaborate, let's say I am a strict "shut up and calculate" empiricist. I say that F=ma is just some mathematical symbols used to translate between the outcomes of experiments. I have my initial data, and my calculated prediction, and I compare that to some final data. That's it, no forces, no particles, nothing-- just letters and data. Further, I claim that this is all anyone can ever demonstrate that the physicist is actually doing. The rest is just some kind of self-delusion they carry in their minds, a bunch of interpretations that fail the very test you have put to them-- that they must establish a clear correspondence to the letters in the formulae. If I say that no such clear correspondence is possible because there's no such thing as any of those make-believe notions like forces or electrons, there is not a single thing you can do to demonstrate that I am wrong. If physics really stuck to what is demonstrable, then it would involve no interpretations of any kind. That's what "shut up and calculate" really means-- all interpretations are invalid at the level of demonstrability. So we either stick to that, or we take the alternate approach of recognizing from the start that interpretations are not demonstrable, and use them to get that sense of cognitive resonance that we crave.
So hopefully we agree that an advocate of MWI is entitled to make that kind of calculation. But they never do. Instead, they use the von Neumann recipe, and they justify this use by claiming that the mathematics associated with their model reduces to the von Neumann recipe (at least for all practical purposes). But does it?
There is no other mathematics associated with their model-- they don't have a model. They have an interpretation of the exact same mathematics. If they had any different mathematics, or anything that was demonstrably a different model, then it would be a different theory. If it makes all the same testable predictions, then it is the same theory, and any differences in how it is imagined is just an ontological difference, a purely philosophical difference. This is the only way to enforce a line between science and philosophy.
We have two mathematical formalisms, and a claim that one entails the other. This is easy to confirm in the case of force/vectors versus Lagrangian, but not nearly so easy to confirm for the mathematics of MWI and CI.
If those mathematics are different, then what is the difference? I think we agree that if you look over the shoulder of an MWI proponent as they solve some problem on a quantum mechanics final exam, you are not going to have the slightest idea if they are an MWI proponent or a CI proponent. So I reject the idea that there is a "mathematics of MWI", if there were you could point out on their paper "that's where they used the mathematics of MWI." There won't be such a place.

So you are claiming that the reason for this is they were really using CI, not MWI, they only deluded themself into thinking they were using MWI, but in fact the mathematics they did use is only consistent with CI. CI has now claimed the quantum mechanics theory, from your perspective, so of course MWI must be wrong if it isn't allowed to use quantum mechanics. But then you have to point to the place where they used an equation that was not consistent with MWI. That would have to be the Born rule-- you are claiming MWI has no Born rule. But it does-- it just uses the Born rule postulate to determine the measure of the probabilities that associate with the fragmented "worlds."

Note that is just exactly what CI would do, and for no better reason, the only difference would be that the CI user would be imagining in their head, when they write down the Born rule, that this corresponds to the entire reality. The MWI user imagines it corresponds to a "world." The answer to the final exam question, the "empirical content", is exactly the same either way-- nowhere in that correct solution will we ever see what is going on in the imagination of the testtaker, we just don't get to see the interpretation because it was never anything but a source of cognitive resonance that might have helped them imagine what the letters they were writing down mean. Since the letters are the same, they translate immediately across interpretations, and no one is the wiser. Much like the word "red" we use when we are describing our experience of color.
We lack any demonstration that the axioms of MWI (whichever version you prefer) actually do lead to the von Neumann recipe, even just "for all practical purposes".
The von Neumann recipe is a postulate of MWI just like it is a postulate of CI, all that is different is what that is imagined to mean. The MWI user thinks the Born rule means something different, and might someday yield to some deeper derivation as a result, but they still use it all the same-- begrudgingly. Just like how someone might use F=ma begrudgingly even if they believe the real ontology is least action-- they know that F=ma makes equivalent predictions to any approach that would fit in their ontology, so they use it, even though it is not in their ontology. Same for the Born rule.
This is why so many volumes have been filled by people striving to establish that correspondence, or at least to make it more plausible. I get the impression that you would advise them to stop wasting their time, because you think it has already been sufficiently established. But I suspect that even most advocates of MWI would not agree with that, and certainly the critics would not agree.
I believe that is because they are talking about something different from what you are. They want something more from MWI than just another valid interpretation of QM! They want it to guide them to some deeper message that QM is trying to tell them, something CI is not hearing, but there's no way to demonstrate it is really doing that, until MWI (or CI) inspires some new theory that is actually different from QM and makes some testable prediction that has been verified.
Actually I agree with your standard, i.e., an interpretation needs to "give us a sense that we understand the meanings of the operations we are carrying out". That's essentially a paraphrase of my criterion.
It includes a very important change-- I have stricken out your objective requirement for "demonstrably clear connection" in favor of the purely subjective criterion that it "uses the same mathematics but imagines that it means something different." Sort of like how, if you watch someone solve an F=ma problem, you never have any idea what they imagine that "F" means.
I think we differ only in having different ideas about what it takes to "give us a sense that we understand" something. For me, I don't have that sense unless I can see how the terms of my equations correspond to the features of the conceptual model in some definite way.
Yes, we differ on what requirements we need to satisfy to claim we have an understanding. Let me give an example. Let's say someone back in the day of Newton, let's call him Jim, was told about F=ma and how great it works, and Jim said he will be happy to use F=ma, but he just can't interpret it as forces that are pushing on things. Jim has a philosophical objection to the idea that objects can really have that kind of power over each other, they are just dumb inanimate objects. Instead, all agency must stem from nature herself, and nature must create in some sense the "best of possible worlds". So Jim imagines that objects follow F=ma not because there really are forces on them, but because nature is finding some kind of extremum in some quantity that has not yet been discovered. Jim interprets the "F" as just an illusion of the presence of a force, he feels the F is emergent from some effort by nature to find an extremum. It doesn't matter that Jim cannot say what that extremum is, it's just an interpretation of the meaning of F, based on his philosophical priority that everything that happens must trickle down from nature herself, nothing can be what one object is doing to another because objects don't have that ability.

So then, you come along and say Jim's interpretation is not valid because he can't say what is being minimized. But he says he doesn't need to, it's just what he's imagining when he writes down "F". All the same, he's motivated to try and figure out an extremum principle that could generate the same equation, and he eventually finds action, and then he goes on to use that in deriving relativity and quantum mechanics-- which actually are new theories in which minimizing action has some greater importance than just F=ma. You can say that only then has his interpretation become valid, but he says no, that was only when it became powerful. That's what MWI proponents are trying to do (and similarly for some CI proponents, like Fra)-- they are trying to make the interpretation powerful instead of just passively valid. Power is the only thing that is demonstrable.
Yes, I only mention it to emphasize that the task of reconciling the MWI model with our actual computational physics is even more challenging than just the non-relativistic version might suggest, so we are very far from being able to really justify MWI as a viable model.
MWI isn't really a model, but I agree that these are obstacles for MWI to become powerful. Still, shouldn't we look under every stone? You don't need to put your own stock in that avenue, but it's best if someone tries it.
So if v does not interact with anything in a way that leaves a signature or trace, is that a strong enough condition to say that v(t) evolves in accord with Schrodinger’s equation? If not, wouldn’t the deviation itself constitute a signature?
Yes, the deviation does constitute a signature, collapse constitutes a signature that the observer (or his proxies) have become part of the system and the Schroedinger equation only applies when no measurement is occuring (in CI, where the truth must result from that interaction, rather than preside in spite of it).
Well, if someone like William Kingdon Clifford, who vaguely imagined that gravity might be interpreted as curvature of space, had written F=mg and claimed that this equation was consistent with his conceptual model of gravity, he would indeed have been lying, because he could not establish that correspondence.
You are asking Clifford to have a new theory of gravity, not an interpretation of Newton's gravity. An interpretation would go like "the reason all objects follow the same paths in space and time under gravity is because gravity is nothing but a redefinition of the meaning of an inertial path." That's it, that's all one would need to say, it's an interpretation of mg = ma by cancelling the m's and writing it a-g=0. There is no requirement to provide any equation to support that interpretation other than that.
It was Einstein’s great achievement to show – explicitly – precisely how the 4-dimensional tensor equations of his metrical theory of spacetime curvature actually do reduce to the simple Newtonian scalar equations in the lowest order approximation.
True, but Einstein was not credited with finding a new interpretation, he found a new theory. I would say a better analogy to a new interpretation was D'Alembert's. He replaced F=ma by F-ma=0 and interpreted ma as some kind of inertial force, then he said that the principle is that all forces always balance. He never provided any reason that there ought to be some inertial force called ma, he just asserted that one could look at Newton's laws that way.

That's all MWI is doing-- saying you can look a different way at the postulates of QM, and even though you still use the same postulates, you think they carry a different message (like D'Alembert thinking the message is that forces are always in balance, we live in a balanced universe). It is only the ontology that is different, not the mathematics. When the mathematics is demonstrably different, you have a new theory.
You need to start with the wave function and Hamiltonian and initial conditions of the entire universe (none of which are knowable), and then show how the Schrodinger evolution of this wave function, taking decoherence into account, leads (at least approximately) to the time-asymmetrical behavior and empirical content represented by the von Neumann recipe.
Then why doesn't CI have to start with the observer and show how making an observation collapses into an eigenstate? If CI is allowed to assert the Born rule by fiat and interpret what is real is what happens on the observer end of that mathematical description, then MWI is allowed to assert the Born rule by fiat and interpret whas is real is what happens on the wavefunction end of that mathematical description. It is only if someone wants to argue that MWI is a different theory, or a superior interpretation at least, that they would need to do what you ask. They would like to do it, no doubt, but failing to do so does not render the interpretation invalid, and more than failing to account for why the Schroedinger equation applies to unobserved wave functions if it is their collapse that is real renders CI invalid (which anti-CI people claim all the time).
If I tell you I can parse the equations of quantum mechanics from contemplation of my dog Smithers, you would dismiss my claim out of hand – and rightly so.
Not quite, what I would do is say that I see no personal value for me in the interpretation that you suggest. But if a thousand theoretical physicists interpreted quantum mechanics the way you were describing, and achieved some cognitive resonance by doing so, I would probably have to conclude I couldn't find any value because I simply didn't understand the interpretation you were suggesting.

So you can’t maintain the position that you will accept any claim that any model represents a legitimate interpretation of any theory. You do have standards, i.e., you require some rational basis for thinking the model really is a representation of the theory.
I have to to use it myself, but I don't have to convince others. One can point to a problem with an interpretation without concluding that the interpretation is invalid, because validity of an interpretation is not demonstrable, it is highly subjective.
You are convinced that if someone actually could make sense of the Hilbert space and Hamiltonian of the entire universe, and if they could somehow divine the initial conditions of a universal wavefunction, such that, subject to the Hamiltonian under the Schrodinger equation (or, better, it’s relativistic counterpart) it leads to suitable time-asymmetric evolution, and that the result, taking decoherence into account, would yield something whose components or projections into some suitable sub-spaces, selected, combined, and arranged in some suitable order, would reduce in some approximation to the usual equations of quantum mechanics. To you this is sufficiently self-evident that you’re willing to take it as given. It isn’t that self-evident to me.
That means the interpretation doesn't work for you-- you see those conditions as a stretch. Others don't think quantum mechanics could work as well as it does if those things weren't true. Myself, I'm agnostic about it-- I don't see the point in building a world view that involves those things being true, but I don't think interpretations are for building world views. I think an interpretation is nothing other than a way of thinking about a theory, a way to get the theory to show you a different angle of itself.
 
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  • #652
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I would like to make a few comments regarding Samshorn’s position from my philosophical perspective. They don’t add anything at all of substance to the discussion between Samshorn and Ken G, but it is a topic that I find very interesting and I do often wonder (and puzzle) about the relationship between a descriptive model (or interpretation) and a corresponding mathematical predictive model.

I do wonder if Samshorn perhaps places too much emphasis on the validity of an interpretation, (what I would describe as a descriptive model). As far as I can understand, Samshorn considers a descriptive model should have a “scientific linkage” to a mathematical predictive model in order for that interpretation to have some “proper” scientific validity. I would tend to say this linkage happens because generally it is essential to the thought process of the physicists – physicists could not possibly construct predictive mathematical models without the pictures of interpretation (the descriptive models). But I would place no more “proper” scientific validity other than that process of the physicist to the descriptive models, the real physics (for me) is the verified predictive mathematical model which represents our attempts at discerning objective patterns within our reality, not that which lay outside of our mindset and our reality – the ultimate “real thing” if you like. I can actually readily foresee a time (way in the future) when our mathematical models are generated by computers crunching massive amounts of empirical data – then there will be no descriptive models (interpretation) involved.

But I obviously make the above statement from a philosophical perspective of idealism (though with a hint of a scientifically unknowable realism). From the philosophical perspective of strong realism, the above is unpalatable – from a strongly realist perspective, the descriptive model is describing nature as it exists outside of our involvement (at least that’s the intended inference) provided the mathematical predictive model of that descriptive model is verified. Thus a realist would place much more emphasis on the descriptive model than I ever would. For them, if there were no “scientific linkage” (and from my perspective, I question the usage of the word science here because I don’t see descriptive models as being science, but realists would disagree with me here) of an interpretation to a mathematical model, then that is not science. But note that this stance is a philosophical stance with a philosophical premise that states our descriptive models and predictive mathematical models correspond closely to mind independent reality (or will get closer and closer, if not actually reaching that goal). Whatever access we may have to mind independent reality, it is not through the scientific method because we have no means in which to scientifically prove that we can step outside of our involvement, thus rendering an objective investigation of mind independent reality impossible. Any exploration of mind independent reality is going to be philosophical in nature, not scientific. I’m not at all suggesting that Samshorn is a realist in this sense; I only mention it because I think the issue of philosophical perspectives is at the heart of topics like this.

From my perspective, all descriptive models (and hence interpretations) are philosophical, even those most macroscopic of models involving (say) a trajectory of an object. The involvement of space and time that we link to a trajectory of a ball is intuitive, but I consider it to be an interpretation of an underlying “explanation”. That underlying “explanation” I consider to lie outside of our involvement and outside of space and time (which I consider to be constructs of our minds) – it resides within mind independent reality. We have no means in which to step outside of our minds, consciousness, and anything else deemed to be part of us, therefore the scientific premise of objectivity fails when attempting to extrapolate to mind independent reality. The fundamental “explanation” (for want of a better word) that “explains” the trajectory of the ball lay within mind independent reality – all we can do is to interpret the descriptive model of a trajectory as a moving ball, (that interpretation tells us nothing about what a moving ball really is) and construct a mathematical predictive model. The success of the latter within our reality does not give any kind of firm “scientific” validity to our interpretation and does not signify that an interpretation with no mathematical predictive model is invalid. Rather we should remove the word “science” from this context and say that interpretations (and I emphasise that I consider descriptive models to be interpretations) are philosophical, and if looked at in that light, gives a clear distinction between the actual science (which are the predictive mathematical models) and the interpretations. I would have no qualms in accepting a verified mathematical model derived by a physicist via a very ad hoc descriptive model that didn’t make any sense or have any kind of “proper” linkage to the mathematical model. I would instead see it as a physicist making use of pictures in a way that helps their creative process in deriving a very powerful predictive mathematical statement about our reality, not of a reality that lay outside of our involvement.

Of course this is open to ridicule if I say my dog is a descriptive model of the mathematical model of gravitational attraction – the argument that my dog is as valid a descriptive model as an imaginary force between objects is obviously ridiculous. But that is not really my point, my point is that I question the emphasis placed on descriptive models as being science – I would rather describe them as purely philosophical with a hierarchy of “validity”. My dog would be out of sight on this hierarchal scale, but the MWI would certainly be on the list.
 
  • #653
kith
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Yes, I'm afraid it does. According to the "many worlds interpretation", the overall universal wave function is continually evolving into more and more proliferating self-consistent "worlds".
A "world" in the MWI doesn't refer to the universe as a whole but rather to a "world of our experience" (see for example Everett's first paper). To allow for experience, the universe must be divided at least into two interacting parts: observer + rest. In a typical measurement situation, it is divided into observer + subsystem of interest + measuring apparatus + uninteresting rest.

So a "world" in the MWI is always a subsystem of the universe. In the theory of open quantum systems, interactions with an environment (like the one given by the measurement apparatus) typically cause decoherence, which leads an initial superposition state of the subsystem to an incoherent mixture. This is interpreted as "splitting of worlds" in the MWI.

Since we agree on the "splitting"-part but not on the mechanism, again the question: what do you think does cause decoherence? This really seems to be the crucial point in the discussion, which is why I asked you some related questions in my last post.
 
  • #654
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If those mathematics are different, then what is the difference?

The projection postulate. According to ordinary non-relativistic quantum mechanics, a system in isolation (subject to a specified potential, etc) evolves according to the Schrodinger equation with a suitable Hamiltonian, and then a measurement of the system by an observer (say) yields an eigenvalue of the measurement operator, and the measured system jumps [projection postulate] to the corresponding eigenstate of that operator, and the probabilities of the various possible eigenvalues are given by the Born rule. Now, according to MWI, approximately this same behavior would appear to an observer if we combine the original system and the observer into a single isolated system (with suitable initial conditions, subject to specified constraints, and with the appropriate Hamiltonian) and this combined system evolves according to the Schrodinger equation, plus some form of the Born rule. But please note the word approximately, or, as Bell put it, “for all practical purposes” (FAPP). Decoherence is never complete or perfect in the unitary evolution of a wave function, whereas the von Neumann projection postulate doesn’t entail any fuzziness; it says the state after the measurement is nothing but one of the eigenstates of the measurement operator, and hence the Born rule has sharp applicability to just those precise eigenstates. This is not true in MWI, so the mathematics of MWI are not literally the same as the mathematics of ordinary quantum mechanics. The advocate of MWI just says it is close enough for all practical purposes. In other words, he is arguing that his mathematical model, consisting of applying Schrodinger’s equation to the combined system of observer & observed with suitable Hamiltonian and initial conditions, taking decoherence into account, etc., leads to predictions for the expectations of an observer that are sufficiently similar to the predictions yielded by the von Neuman recipe and the projection postulate so that we wouldn’t expect to be able to tell the difference – at least not in normal circumstances. On this basis, the believer in MWI claims the right to use the mathematical recipe of von Neumann rather than the recipe actually prescribed by MWI (which is convenient, because the latter is utterly impossible to apply in any realistic circumstance).

But there are obvious problems with the claim that the mathematics arising from the MWI model really are (even approximately) consistent with observation and ordinary quantum mechanics. It is only supported by rather vague and incomplete plausibility arguments, and references to putatuve isolated systems involving observers, even though any such system can hardly be smaller than the entire universe, which then leads to its own set of ambiguities. It’s far from clear that the MWI calculational prescription (the one that is actually manifest in the interpretation) could ever be carried out, even in principle. The plausibility arguments depend on viewing things within the context of some definite conditions, and then considering one little incremental (and time-asymmetrical) step being carried out according to the Schrodinger equation, and arguing that over this incremental step the divergence from ordinary quantum mechanics evident to some conception of an observer is too small to be noticed. This is already debatable, but even if one accepts this, it doesn't come close to substantiating the viability of the MWI model as a whole, because that ultimately involves the wave function of the entire universe, and needs to address all the ambiguities arising from that.

As I understand it, you deny that MWI entails any mathematical formulation distinct from ordinary quantum mechanics, but I don’t think that position is tenable (and I don’t think even the advocates of MWI would agree with you). The mathematics of MWI are clearly stated to be nothing but unitary evolution of the universal wave function, augmented if you like with something approximating the Born rule (it can’t be exactly the Born rule, for the reason explained above), but it definitely does NOT include the projection postulate, as explained above. Hence the mathematics of MWI are fundamentally different... but it is argued that, if we correctly account for decoherence, something closely approximating (but not identical to) the projection postulate emerges (for some suitable model of a conscious observer) from the unitary evolution of the universal wave function. But the mathematics are definitely not the same.

It really is very similar to the case of general relativity, where the metrical spacetime curvature interpretation of gravity consists of the proposition that isolated systems simply undergo geodesic motion through the spacetime manifold. People could ask “How can simple unforced geodesic motion possibly be consistent with anything resembling the observed phenomena of forced trajectories described by Newton’s laws!?”, and the task was to show that, in fact, Newton’s laws and all the observed behavior that they describe really do emerge [approximately enough for empirical viability] from the four-dimensional tensor equations describing the curved spacetime representation of events. The empirically accessible differences are so small as to be almost imperceptible in normal circumstances, so GR is deemed consistent with all the empirical success of Newton’s theory. The same task faces MWI. It needs to show that the ordinary equations of quantum mechanics really do emerge [approximately enough for empirical viability] from the Schrodinger equation description of the unitary evolution of the universal wave function. But this has never been shown, so MWI doesn’t really (at present) qualify as an interpretation of quantum mechanics. At best, it is an idea for an interpretation of quantum mechanics.
 
  • #655
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Since we agree on the "splitting"-part...

I'm still not following. You began by objecting to one of my statements on the grounds that you believe there can be no "splitting" in an isolated system. Now you seem to be saying that splitting does occur within an isolated system (e.g., the universe), and yet you still seem to be maintaining the objection that was based on the opposite view. So I'm still not understanding you.
 
  • #656
kith
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You began by objecting to one of my statements on the grounds that you believe there can be no "splitting" in an isolated system.
Not "in" but "of". The isolated system as a whole doesn't split. Let's return to your original phrasing. Saying that an isolated system v splits into v1, v2, v3... remains wrong. What does split are open subsystems of isolated systems.

/edit: Probably it's time to use a more precise language. Initially, the isolated system is in state |ψ(0)>. For every time t>0, you can express it's state as U(t)|ψ(0)>. So where's the splitting?
 
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  • #657
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The way I see it, CI is a recipe for calculating what observer (a big, highly complicated system) will see.
MWI (potentially) provides a derivation of such recipe from basic laws by considering evolution of the big, highly complicated system that is observer.
The CI is shut up and calculate, then midway just square the amplitudes and stop calculating, the MWI is shut up and calculate all the way into observer itself. The value of trying to calculate things about observer is that: if we indeed fail to derive Born probability in MWI we will know there is some extra fundamental physics leading up to Born's probability. The approach of sticking to CI is just a case of giving up, using a magical formula for magical 'observer' without ever figuring out how it works. It's like having the gas law and not trying to figure out kinetic theory or thermodynamics.

Regarding a single photon hitting you on forehead, even a single photon will over time fork you into a very huge number of yous due to how thermodynamics works and due to how thermal noise influences the thought. One has to wonder if a digital observer may see different probability laws.
Anyhow, what I believe is that the thermodynamics should be reworked for quantum mechanics, and then from that thermodynamics the Born probability will naturally arise for systems like brains where the thermal noise affects what you think (and what you will think). It may also turn out that the probabilities arise in repeat experiments due to effect on the e.g. source of the photons.
 
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  • #658
Ken G
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The CI is shut up and calculate, then midway just square the amplitudes and stop calculating, the MWI is shut up and calculate all the way into observer itself.
Here's the problem though. Physics is not a purely rationalistic endeavor-- we don't just introspect the mathematical aesthetics that we like. Instead, we must check our theories against experiment, and MWI simply provides no accounting for the nonunitarity of what we actually perceive. MWI in effect subjugates the action of the observer to the theory about the observer, rather than using the action of the observer to substantiate the theory. The result is that MWI only requires itself to not contradict observations, but physics is built on something deeper than just not contradicting observations, it is built on receiving evidence from observations. Any number of pseudoscientific claims from ghost stories to UFO landings are based on the weak requirement of merely not contradicting observations, and while MWI certainly has a much more scientific footprint than these, it shares this fundamental problem.
The value of trying to calculate things about observer is that: if we indeed fail to derive Born probability in MWI we will know there is some extra fundamental physics leading up to Born's probability.
But we always know that, it is the default assumption. The sticky problem is how to use the approaches of science to get at a principle that underlies the whole structure of how science is done. Some reworking of what we even mean by science is going to be needed to do that, and it must be done so as not to throw out what is good about science, and what separates it from pseudoscience. Faith that MWI will lead us to that principle is fine for an individual to have, but it is hardly some kind of arguable benefit of MWI.
The approach of sticking to CI is just a case of giving up, using a magical formula for magical 'observer' without ever figuring out how it works.
I think this stems from a common misconception about CI. When Bohr says "there is no quantum world", he means "there is no need to continue to advance physics to try to go deeper than quantum mechanics." I don't think Bohr would ever have suggested such a non-scientific idea. What he really meant, I believe, is that the problem of using physics to describe the observer/system interaction encounters a fundamental difficulty that is independent of quantum mechanics or any particular theory-- the act of observation is a kind of filter, and whatever does not come through that filter is not going to be able to be put into a physics theory. This problem was with us all along, but quantum mechanics is the place where we smacked right into it. MWI is essentially what you get when you try to ignore this problem and hope that it will go away, but the bizarre and almost mystical elements of MWI are the consequence of that attitude. It is really the place where science meets pseudoscience, and all Bohr was trying to do was retain the firewall between them.
 
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  • #659
kith
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Instead, we must check our theories against experiment, and MWI simply provides no accounting for the nonunitarity of what we actually perceive.
We can explicitly see how nonunitary dynamics emerges from unitary dynamics for certain model systems. So if one agress, that there is no good reason to assume that measurement devices obey different laws than electrons (which is based on the fact that the classical laws can be derived from QM), the assumption that collapse could be explained in principle by decoherence seems reasonable. Don't you agree?

This doens't lead directly to MWI, however.
 
  • #660
Ken G
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We can explicitly see how nonunitary dynamics emerges from unitary dynamics for certain model systems. So if one agress, that there is no good reason to assume that measurement devices obey different laws than electrons (which is based on the fact that the classical laws can be derived from QM), the assumption that collapse could be explained in principle by decoherence seems reasonable. Don't you agree?
No, I don't think collapse will ever be explained in an unambiguous way by decoherence, but we need to distinguish two very different types of collapse that are easily confused. Decoherence is very good at getting a superposition state involving a subsystem to "collapse" that subsystem into a mixed state of eigenvectors of the decoherence. That's just exactly what decoherence does. But that type of collapse never presented any problems, because it is still perfectly unitary on the whole system, and projections onto subspaces never had to be unitary, even in formal Schroedinger evolution.

The collapse that is at the heart of "the measurement problem" is something different-- it is the nonunitary collapse that occurs when you interpret a mixed state as not a projection from a decohered superposition, but as a particular outcome that has occured even if you don't know it yet. Scientific predictions are moot on that difference, but interpretations of quantum mechanics are not. Since the predictions are moot on the issue, no experimental test can ever distinguish them, and so no theory that leads to predictions (like decoherence) can suggest how to test that difference either. It is a purely philosophical difference, but what is clear is that the experience of a particular outcome is nonunitary.
 
  • #661
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This is way too long of a thread to go through all of it and a quick search of the first author of the paper below didn't bring up anything...here is a fairly recent paper arguing against Everett interpretation:

In other words: POD (Parallel Occurrence of Decoherence) points out the existence of not only one, but two mutually independent and irreducible Brownian particles that are subsystems of the same composite system. As long as this is a consistent quantum mechanical picture, we show that this makes for the apparent inconsistency in the very foundations of the Everett Interpretation. In Section 5 we show that the inconsistency can be removed if there is a privileged spatial structure of the model-universe (only one Brownian particle is physically realistic). The absence of a particular rule/prescription or a criteria for choosing the preferred structure forces us to conclude that the highlighted inconsistency is not removed.

We demonstrate that the Everett Interpretation is not consistent with the universally valid quantum mechanics, as long as the Everett-worlds are considered physically realistic. This inconsistency follows from the recent results of Entanglement Relativity and the Parallel occurrence of decoherence (provided for the Quantum Brownian Motion-like models) as corollaries of the universally valid quantum mechanics. In simplified terms: the Everett worlds splitting (branching) is not allowed for the realistic Everett worlds. Thus, we conclude: Unless there is a privileged, spatial structure (decomposition into subsystems) of the model-universe, Everett Interpretation appears either to be not correct or the Everett-worlds (the Everett ”branches”) are not physically real. The interpretational consequences as well as some ramifications of our findings are yet to be explored.

http://arxiv.org/PS_cache/arxiv/pdf/1109/1109.6424v1.pdf
 
  • #662
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We can explicitly see how nonunitary dynamics emerges from unitary dynamics for certain model systems. So if one agress, that there is no good reason to assume that measurement devices obey different laws than electrons (which is based on the fact that the classical laws can be derived from QM), the assumption that collapse could be explained in principle by decoherence seems reasonable. Don't you agree?

This doens't lead directly to MWI, however.

Collapse is not derivable from decoherence. Neither decoherence has solved the measurement problem

http://arxiv.org/abs/quant-ph/0112095

The key point is that nonunitary dynamics are irreducible (i.e., are not derivable from) unitary dynamics.
 
  • #663
kith
Science Advisor
1,395
481
But that type of collapse never presented any problems, because it is still perfectly unitary on the whole system, and projections onto subspaces never had to be unitary, even in formal Schroedinger evolution.
For me, the important point is that decoherence shifts the measurement problem from pure states to mixed states. Decoherence explains how a system with a well-defined property (beeing the eigenstate of an observable) evolves into a system about which we can make only statistical statements. This can be interpreted in the way that the state of the system doesn't contain enough information to determine a unique outcome. And this is a something classical.

Maybe the crucial point is that the CI assumes reductionism?

The collapse that is at the heart of "the measurement problem" is something different-- it is the nonunitary collapse that occurs when you interpret a mixed state as not a projection from a decohered superposition, but as a particular outcome that has occured even if you don't know it yet.
How can a mixed state be a particular outcome? Do you use outcome in a different meaning than outcome of a single experiment?

It is a purely philosophical difference, [...]
Yes, I agree. But a proponent of the Lorentz ether theory can use the same argument to claim that his view should be treated equal to SRT. Yet the overwhelming majority of physicists thinks SRT is the better interpretation. We agree that interpretations can't be proven, but still some are more plausible than others. And if there's an unambiguous reasonable way to motivate the appearance of collapse from the other axioms, most people are probably willing to adopt this view.
 
  • #664
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This is way too long of a thread to go through all of it and a quick search of the first author of the paper below didn't bring up anything...here is a fairly recent paper arguing against Everett interpretation:





http://arxiv.org/PS_cache/arxiv/pdf/1109/1109.6424v1.pdf

Thanks by the link.

What I do not understand is why it is needed to show that the Everett interpretation is internally inconsistent and does not agree with experiments when this has been done in the past in many occasions.

That is so weird for me as if it was needed to prove today that the ancient Weber electrodynamics suffers from the same kind of defects. If you look to Goldstein textbook, in some footnote page he merely says that Weber electrodynamics is inconsistent but he does not need to prove this (neither its failure to explain experiments) because it was already done in the past.
 
  • #665
kith
Science Advisor
1,395
481
juanrga, I think our views are quite incompatible when it comes to interpretations of QM, because you don't seem to acknowledge any other interpretation than the orthodox one. So I don't see the point in discussing with you here.

However, thanks for the paper. I have saved it, but there are other decoherence-related paper's I am going to read first.
 
  • #666
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juanrga, I think our views are quite incompatible when it comes to interpretations of QM, because you don't seem to acknowledge any other interpretation than the orthodox one. So I don't see the point in discussing with you here.

However, thanks for the paper. I have saved it, but there are other decoherence-related paper's I am going to read first.

I know a physicist who does not accept Maxwell electrodynamics, neither SR or GR; affirms that are nonsensical theories, that would be abandoned by 'rational' minds; and promotes the outdated, inconsistent, and falsified weber electrodynamics (see also #664) as the 'rational' theory that every physicist would embrace.

He has been shown to be completely wrong in many occasions, but he cannot accept this and ignoring any criticism he has extended this kind of wrong theory to gravity as well. His theory of gravity is even poor and, as today, it cannot explain simple stuff as Mercury perihelion anomaly and light bending at once (although his theory contains a free parameter) unless you abandon energy conservation principle

http://arxiv.org/abs/gr-qc/9708047

I have discussed with him in the past and showed many mistakes in his papers and books, but he ignores any criticism, because he has philosophical prejudices about how nature reveals itself in experiments.

I find the same kind of attitude regarding QM.

Some few people has philosophical prejudices about how nature reveals itself in experiments and want to substitute QM by some other pseudo-theory satisfying their philosophical beliefs/credo because do not accept QM: the theory developed by Bohr, Heisenberg, vonNeumann, Schrödinger... using scientific methods.

This same people is also blind to any experiment disproving their 'theory', do not read the criticism done, neither care about the inconsistencies found in their 'theories'.

This people reveals their own inconsistency when sometimes they claim that MWI is just another interpretation of QM (although the contrary has been shown in literature), whereas sometimes they claim that is a theory that does different predictions than QM (although none of their new predictions have been verified).

Decoherence community is very related to MWI community and make bold claims about deriving nonunitary dynamics from unitary one, about solving the measurement problem and so on. However, all those bold claims are shown to be plain false (when one checks the details on the papers and preprints) again and again.

I have no problem with the possible existence of other 'interpretations' of QM different from that found in main textbooks. I have a problem when some few people claims that MWI (Everett, Deutsch, and friends), ensemble (Ballentine), Bohmian (Broglie, Bohm)... are merely another interpretations of the QM that one finds in textbooks, when none of them is even close.

I am sorry by saying what some people here want to ignore, but well, guys this is the post #666 here :devil:
 
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  • #667
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I thought this French physicist's (Gisin) reasons for being against MWI were kinda of cool:

I won't try to present the many-worlds view any further; from the little above it should already be clear that I am not sympathetic with this view. Two reasons.

First, all the assumptions presented in the previous section have an explanatory power. Moreover they could even be experimentally tested (and - even better for me - using technologies available in my lab!). On the contrary, I do not see any explanatory power in the many worlds: it seems to be made just to prevent one from asking (possibly provocative) questions. Moreover, it has built in it the impossibility of any test: all its predictions are identical to those of quantum theory. For me, it looks like a "cushion for laziness" (un coussin de paresse in French).

And there is a second, decisive, reason to reject the many-worlds view: it leaves no space for free will. I know that I enjoy free will much more than I know anything about physics. Hence, physics will never be able to convince me that free will is an illusion. Quite the contrary, any physical hypothesis incompatible with free will is falsified by the most profound experience I have about free will.

Are There Quantum Effects Coming from Outside Space-time? Nonlocality, free will and "no many-worlds"
http://lanl.arxiv.org/PS_cache/arxiv/pdf/1011/1011.3440v1.pdf

And the video version [the latter part (~16:35) discusses his criticism of MWI]. Even if one doesn't agree with him, you gotta like this guy's spunk:

https://www.youtube.com/watch?v=9WnV7zUR9UA
 
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  • #668
Ken G
Gold Member
4,462
333
For me, the important point is that decoherence shifts the measurement problem from pure states to mixed states.
But this holds in every interpretation of QM, it does not single out many-worlds in any way. What you need an interpretation to do is to interpret the meaning of a mixed state. Many worlds says that any mixed state is a set of real states that we are only going to be able to perceive one, whereas Copenhagen says that any mixed state is a condition of lack of knowledge (only one state actually occured, we just don't have knowledge of it yet). Hence, the many-worlds version is still unitary, but has no accounting for why we perceive only one, whereas the Copenhagen version is nonunitary, but easily accounts for why we perceive only one. Choose your poison.
Maybe the crucial point is that the CI assumes reductionism?
I think one could either hold to, or drop, reductionism with either CI or MWI. Here's how it might look:
CI, drop reductionism: the "collapse" is controlled by holistic factors we have no scientific access to.
CI, keep reductionism: the "collapse" is fundamentally random in character, so there is nothing missing from the reduced perspective-- random is just random.
MWI, drop reductionism: there is no "collapse", but we perceive a collapse because of some holistic connection between all the minds in the many worlds, which somehow "mete out" experiences between them all.
MWI, keep reductionism: there is no "collapse", but we perceive one because each thread of the many-worlds splitting contains the bare ingredients to create a mind within that branch.
How can a mixed state be a particular outcome? Do you use outcome in a different meaning than outcome of a single experiment?
A mixed state is always conceived of as a particular outcome in CI, or indeed any interpretation other than MWI. But by "outcome", I just mean what actually happened, independently of our knowledge of it. If one uses the more restricted meaning that an "outcome" is only what I know happened, then my outcomes can be different ones from yours, so that isn't the kind of meaning I have in mind for the term. MWI, on the other hand, does not recognize our perceptions as being definitive of what actually happens, so in MWI a mixed state comprises a whole bunch of outcomes in a whole bunch of independent (mutually incoherent) worlds. So in MWI, the entries of a density matrix are interpreted as weighting the worlds, whereas in CI, the entries are interpreted as giving the probabilities of what actually occurs.
Yes, I agree. But a proponent of the Lorentz ether theory can use the same argument to claim that his view should be treated equal to SRT. Yet the overwhelming majority of physicists thinks SRT is the better interpretation.
But I have see no contradiction there. Yes, a proponent of LET can definitely make that argument, and be perfectly corrct, and yes, most physicists think SRT is a better interpretation. Those are both facts, no contradiction there at all. Indeed, a century from now something might happen and the majority of physicists will shift over to LET, so it's important to realize that LET is perfectly viable-- it's just not preferred at present. So it is with MWI or any other QM interpretation.
We agree that interpretations can't be proven, but still some are more plausible than others. And if there's an unambiguous reasonable way to motivate the appearance of collapse from the other axioms, most people are probably willing to adopt this view.
Yes, if the theory changes in some way, it might become clear which interpretation was superior, but in the mean time, it's always just going to be a matter of personal opinion-- and some might not care what the majority think, they might still hold to their own view and be perfectly successful in doing so.
 
  • #669
Ken G
Gold Member
4,462
333
I thought this French physicist's (Gisin) reasons for being against MWI were kinda of cool:
And those are perfectly valid reasons for him. But I don't see anything in them that are compelling in general, and indeed it seems to me that he makes the common mistake of confusing an interpretation of a theory for some kind of authoritative world view-- a practice we should have dispensed with centuries ago.

My only objection to MWI is that I feel it is unscientific to take it as a world view, like some kind of true ontology, instead of what it actually is-- an interpretation of the unitarity postulate of QM. But the same can be said for any of the other interpretations as well-- they are each a way of thinking about a theory, that's what an interpretation of a theory is. So it is not a problem that it doesn't make predictions, and it's not a problem that it rules out free will. Interpretations don't make their own predictions, they give you a way to think about the predictions of some theory. And no physical theory rules out free will, any more than Newtonian gravity ruled out black holes. Theories don't rule things out, they make successful predictions. The predictions of QM have really nothing to do with free will, we have no idea how to connect those two things. Thus no interpretations of QM can say the least thing about free will, given our current understanding (or lack thereof) of the latter.

Thus, I claim it is certainly not true that MWI "rules out" free will while CI allows for it-- neither have anything to say on the matter, because the predictions of QM stand squarely between any of these interpretations and free will, so the real question is, what do the predictions of QM say about free will? I believe the answer to that is "nothing at all at present", but even if someone does think they have something to say, it will be the same statement that all the interpretations make-- at least as long as the interpretations are treated as what they should be (ways to think about the predictions of a theory, not demands on how what is currently unknown will have to work out). I could easily imagine some "next theory" that allowed for both many worlds and free will, the obvious example being the will to choose among the worlds.
 
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  • #670
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0
I thought this French physicist's (Gisin) reasons for being against MWI were kinda of cool:



Are There Quantum Effects Coming from Outside Space-time? Nonlocality, free will and "no many-worlds"
http://lanl.arxiv.org/PS_cache/arxiv/pdf/1011/1011.3440v1.pdf

And the video version [the latter part (~16:35) discusses his criticism of MWI]. Even if one doesn't agree with him, you gotta like this guy's spunk:

https://www.youtube.com/watch?v=9WnV7zUR9UA

It is not needed to appeal to some kind of personal experience for disproving determinism. A simple analysis of the scope of science and a review of the available theories would be enough.

When cosmologists as Sean Caroll state

http://blogs.discovermagazine.com/cosmicvariance/2011/12/05/on-determinism/

My personal suspicion is that the ultimate laws of physics will embody something like the many-worlds philosophy

them fail to consider the simplest technical details of the theories (classical mechanics, chaos, QM...) that he is naming

http://blogs.discovermagazine.com/c...on-determinism/comment-page-1/#comment-202663

and fails to consider even the most direct philosophical consequences derived from these details

http://blogs.discovermagazine.com/c...on-determinism/comment-page-1/#comment-203643
 
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  • #671
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It is not needed to appeal to some kind of personal experience for disproving determinism.

If I'm understanding you, I agree. I think the issue of determininsm/indeterminism has very little to do with the issue of free will. Even if the universe is non-deterministic, I can't see how that would help the "free will" position anymore than a deterministic universe. Wouldn't that just lead to some sort of "random will" versus truly "free will"? In my opinion, the strongest argument put forth for the possibility of "free will" is positions that are able to challenge the following premise by Carl Hoefer:

For reasons that Kant first realized, indeterminism at the microphysical level does not seem to help. The randomness, if any, in microscopic phenomena does not seem to “make room” for free will, but rather only replaces a sufficient physical cause with (at least in part) blind chance. The presumption in favor of upward causation and explanation (from microphysical to macrophysical) that comes with causal completeness is what cuts free agency out of the picture, whether this causation is deterministic or partly random.

Some have argued Bell's theorem and violations does do this by allowing some type of bi-directional causality, etc. but I'm not sure?

The classical picture offered a compelling presumption in favour of the claim that causation is strictly bottom up-that the causal powers of whole systems reside entirely in the causal powers of parts. This thesis is central to most arguments for reductionism. It contends that all physically significant processes are due to causal powers of the smallest parts acting individually on one another. If this were right, then any emergent or systemic properties must either be powerless epiphenomena or else violate basic microphysical laws. But the way in which the classical picture breaks down undermines this connection and the reductionist argument that employs it. If microphysical systems can have properties not possessed by individual parts, then so might any system composed of such parts...

Were the physical world completely governed by local processes, the reductionist might well argue that each biological system is made up of the microphysical parts that interact, perhaps stochastically, but with things that exist in microscopic local regions; so the biological can only be epiphenomena of local microphysical processes occurring in tiny regions. Biology reduces to molecular biology, which reduces in turn to microphysics. But the Bell arguments completely overturn this conception.

For Whom the Bell Arguments Toll
http://faculty-staff.ou.edu/H/James.A.Hawthorne-1/Hawthorne--For_Whom_the_Bell_Arguments_Toll.pdf
 
  • #672
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1
Here's the problem though. Physics is not a purely rationalistic endeavor-- we don't just introspect the mathematical aesthetics that we like. Instead, we must check our theories against experiment, and MWI simply provides no accounting for the nonunitarity of what we actually perceive. MWI in effect subjugates the action of the observer to the theory about the observer, rather than using the action of the observer to substantiate the theory. The result is that MWI only requires itself to not contradict observations, but physics is built on something deeper than just not contradicting observations, it is built on receiving evidence from observations. Any number of pseudoscientific claims from ghost stories to UFO landings are based on the weak requirement of merely not contradicting observations, and while MWI certainly has a much more scientific footprint than these, it shares this fundamental problem. But we always know that, it is the default assumption. The sticky problem is how to use the approaches of science to get at a principle that underlies the whole structure of how science is done. Some reworking of what we even mean by science is going to be needed to do that, and it must be done so as not to throw out what is good about science, and what separates it from pseudoscience. Faith that MWI will lead us to that principle is fine for an individual to have, but it is hardly some kind of arguable benefit of MWI.
I think this stems from a common misconception about CI. When Bohr says "there is no quantum world", he means "there is no need to continue to advance physics to try to go deeper than quantum mechanics." I don't think Bohr would ever have suggested such a non-scientific idea. What he really meant, I believe, is that the problem of using physics to describe the observer/system interaction encounters a fundamental difficulty that is independent of quantum mechanics or any particular theory-- the act of observation is a kind of filter, and whatever does not come through that filter is not going to be able to be put into a physics theory. This problem was with us all along, but quantum mechanics is the place where we smacked right into it. MWI is essentially what you get when you try to ignore this problem and hope that it will go away, but the bizarre and almost mystical elements of MWI are the consequence of that attitude. It is really the place where science meets pseudoscience, and all Bohr was trying to do was retain the firewall between them.
Sounds like a very bad argument in favour of retaining non-unitary behaviour rather than trying to derive it from the unitary theory. Yes, the observer effects are fundamental but we didn't try to introduce human eye into the optics, we predict what happens in the human eye.

With regards to 'evidence based' research, there is presently no evidence of wavefunction collapse and other FTL stuff. None whatsoever.

The problem with MWI really is that people can't shut up their useless philosophical nonsense (which has never been shown to be useful in science in the first place, the free will being a great example), and consider a theory that is more compact and doesn't make use of concepts with immense hidden complexity, like that of 'observer'. The best parallel I can find is the 'god' concept, whereby you replace the complexity of the world with complexity hidden into the word 'god'. Likewise, in CI, you replace the complexity of the system that is observer, and the complexity that arises from the Schrodinger's equation, with the verbal concept of 'observer' that seems very simple at the surface.
 
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  • #673
Ken G
Gold Member
4,462
333
Sounds like a very bad argument in favour of retaining non-unitary behaviour rather than trying to derive it from the unitary theory.
The problem in your claim here is your use of the implication that we "derive behaviors from theory." Physics does not work that way, instead, it works the opposite way: it derives theories from behavior. Your expressed bias is very common for MWI enthusiasts, it is a starkly rationlistic framing of what physics is: the theory is right, the behavior happens because of the theory. That has never been true in the entire history of science. Instead, theories attempt to explain behaviors, we don't start trying to reinterpret behaviors to fit our theories. But that's just exactly what MWI does when it is taken to the extreme beyond what it actually is: what it actually is is a way to think about the theory, not a way to think about the behavior. The behavior is highly non-unitary, that's how we perceive it. Nothing in MWI changes this fact, it merely gives us a way to rationalize the behavior that we actually perceive. Rampant rationalization is not good science-- but there is certainly a role for rationalization, which is in the generation of new theories. If someone wants to use MWI to create a new theory that is not just quantum mechanics, more power to them, but no one has actually done that yet, so there is no actual demonstrable benefit of the rationalization exhibited by MWI.

Yes, the observer effects are fundamental but we didn't try to introduce human eye into the optics, we predict what happens in the human eye.
What we are talking about actually has nothing to do with the human eye, it has to do with what the human eye is even capable of interacting with, recording, or perceiving in any way at all. That's quite a different matter, and is fundamental to any empirical endeavor-- like physics. That's what Bohr was saying.
With regards to 'evidence based' research, there is presently no evidence of wavefunction collapse and other FTL stuff. None whatsoever.
No, that is incorrect. There is nothing "FTL" about wavefunction collapse, you are again mistaking the behavior for the explanations of the behavior within some theory. That is a very typical problem for rationalists. But collapse is not a theory, it is an observed behavior-- outcomes are eigenvalues of the observables (and that means the theory labels the outcomes as eigenvalues and goes from there). MWI then takes this observed fact and weaves it into a theory that builds onto it whatever scaffolding is necessary to retain the concept of unitarity. It certainly does not act in the opposite direction, in the way it is oversold to do.
The problem with MWI really is that people can't shut up their useless philosophical nonsense (which has never been shown to be useful in science in the first place, the free will being a great example), and consider a theory that is more compact and doesn't make use of concepts with immense hidden complexity, like that of 'observer'.
Again you are missing the crux of the issue. For most physicists, it is MWI itself that represents the useless philosophical nonsense. I don't go that far-- I say it is simply a valid interpretation of a theory, it only becomes useless philosophical nonsense when it is mistaken for a world view of how some behavior actually happens. What is certainly demonstrable is that MWI is "useless" (at the moment-- it certainly has no uses) and it is philosophical (that's obvious to anyone who knows what philosophy is). Whether or not it is "nonsense" depends on whether or not it is important for deriving the next theory. I would say the same for any interpretation of QM that is elevated to the level of a world view-- the world views are useless and philosophical, but might become real science depending on the next theory, or how they can be used to motivate observations that current QM cannot predict.
The best parallel I can find is the 'god' concept, whereby you replace the complexity of the world with complexity hidden into the word 'god'. Likewise, in CI, you replace the complexity of the system that is observer, and the complexity that arises from the Schrodinger's equation, with the verbal concept of 'observer' that seems very simple at the surface.
Yet to me, it is MWI that is the classic example of "god perspective" thinking. The real world rarely works out the way we want to imagine it does, whenever we have tried to take the "god perspective" in the past.
 
  • #674
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If I'm understanding you, I agree. I think the issue of determininsm/indeterminism has very little to do with the issue of free will. Even if the universe is non-deterministic, I can't see how that would help the "free will" position anymore than a deterministic universe. Wouldn't that just lead to some sort of "random will" versus truly "free will"? In my opinion, the strongest argument put forth for the possibility of "free will" is positions that are able to challenge the following premise by Carl Hoefer:
I think the core of issue is that the determinism does not imply that everything is 'predetermined' or 'predeterminable'. The issue is with 'pre' prefixes.

Free will is a pair of dangling references: free from what? Will of who?
Predetermined is a pair of dangling references too: pre, before what? determined by whom? Philosophy is full of concepts that contain dangling references and are thus undefined, but are argued as if they were well defined concepts on par with those in sciences.

If what you decide could have been determined by something different than you before you make your decision, then indeed that would exclude free will.
However, outcomes of even very simple 'deterministic' processes capable of universal computation (cellular automata, Turing machines) can not be calculated other than by running those exact processes. If such process was to make a decision, this decision is made by that process, and by nothing else. Furthermore that process would make that particular decision, and no other decision. If someone had to make an exact copy of you to predict your choice, they aren't predicting your choice, they're just letting you choose it yourself.
Sounds free enough to me; indeed such deterministic automations are more free than living human brains that would make decision either way depending to the thermal noise at the synaptic junctions; all your reasoning is only able to bias the probability.

I think the 'but we have free will' resistance to determinism arises from some sort of reversal of above reasoning. You start with the notion of system that evolves by deterministic steps, then you slip up a little and say that everything is predetermined, and it happens to be true that if outcome of a process really is prerunning of that processdeterminedby someone, then intuitively, this process would be very simple and uninteresting; definitely not intelligent.
 
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  • #675
510
1
The problem in your claim here is your use of the implication that we "derive behaviors from theory." Physics does not work that way, instead, it works the opposite way: it derives theories from behavior. Your expressed bias is very common for MWI enthusiasts, it is a starkly rationlistic framing of what physics is: the theory is right, the behavior happens because of the theory.

Sorry, but you're just incorrect. The theory is designed so that all the observed behaviours result from the theory. Indeed, the theory is derived from behaviour, but it is derived using highly informal process of human reasoning, involving hunches, guesses, and mental visualization, while the observed behaviours must be produced by theory via a very direct and straightforward calculation (otherwise the theory is demonstrably incorrect or incomplete).
Furthermore a more compact theory is chosen over a less compact theory (for example, Einstein's general relativity would be chosen over someone dull who would be simply fitting polynomial curve to observations, edit: even though former is based on a hunch and a belief that there's something to the equivalence of inertial and gravitational mass, whereas latter was straightforwardly derived from behaviour).
 
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