Ken G said:In any event, I disagree with your "point". All I notice is you chose not to provide any of the support I requested that you provide.
Feynman was a terrific physicist, but his knowledge of, and appreciation for, anything else was not so legendary. In particular, he had nothing but disdain for both psychology and philosophy, but was never considered a master of either, indeed he was positively ignorant of both. I think we'll just have to give him a pass for his closedmindedness on both those counts. All I can say is, among those who don't know much about philosophy, there is a very clear tendency to adopt the attitude that philosophy is counted as anything that other people think.
Actually, it is your answer that is simply not in keeping with the facts. The comment from Feynman that I reacted to was not at all a technical point of physics. To quote you:juanrga said:Well, since that (i) I cited the excellent technical remarks on physics by Feynman, the physicist, since (ii) I emphasized that we are not discussing about philosophy, and since (iii) he was correctly criticizing philosophers when they try to discuss the nature and properties of physical objects, your repetitive answer has very little to see with the points that I was making.
Now, it is not at all surprising that physics is superior "when dealing with physical objects", that's what it is for. The real question is, why do you think Feynman is expert enough to critique philosophers? Philosophers don't even ask the same questions that physicists do, and indeed it is quite apparent from the history of both that physics was invented by philosophers to answer certain types of questions. This is why physics was originally called natural philosophy. It expanded into its own field, but it still has the same charge originally given to it by natural philosophy. Feynman is critiquing the gun on grounds that the bullet is more effective.If you read what he wrote, you will discover, with irony, that he starts his lecture with a critic of philosophers and of how the point of view of physics is superior when dealing with physical objects.
juanrga said:I think that all of this was answered before:
The preprint correctly states that none of the different MWI formulations found in the literature contains an internally consistent and complete set of axioms that reproduces the known physics. Either the axioms are contradictory or the predictions do not agree with what we observe in labs or both.
You already asked me about if MWI is an interpretation of QM or another theory, and you received at least two answers, one from mine.
Ken G said:One doesn't "disagree" with an interpretation, one cites reasons for "preferring" a different one, which largely amounts to identifying philosophical priorities. Or one criticizes elevating an interpretation to something more than an interpretation...
Ken G said:The real question is, why do you think Feynman is expert enough to critique philosophers?
BruceW said:Well, the preprint says that if we formulate an MWI with different mathematical axioms to standard QM, then we get inconsistent answers. So if we formulate an MWI with the same mathematical axioms as standard QM, then we don't necessarily get inconsistent answers.
So this is equivalent to saying that MWI as a separate theory to QM is inconsistent, but MWI as an interpretation of QM is not inconsistent.
And the author of that paper argues that the proponents of MWI were using it as a separate theory to QM. And I think he is probably right. So I'd probably agree that the proponents of MWI did not achieve what they were hoping for. (But we'd only really know by asking them).
But just because I don't agree with some of the possible MWI's (i.e. the MWI's that are effectively new theories), it doesn't mean I disagree with MWI's that are simply interpretations of standard QM.
Sure, but that's much more difficult, and must be held to a higher standard of proof. For example, that's just what the "lost causes" article did not successfully do. All too often, a criticism of an interpretation gets intermingled with implicit philosophical priorities that go unnoticed, rather than a logical proof that some interpretation is incorrect. How can an interpretation be incorrect if a physicist is not led to doing incorrect calculations by employing that interpretation to motivate those calculations? What incorrect calculation does MWI motivate?Samshorn said:There's another possibility: One points out that what is claimed to be an interpretation of a given theory is really no such thing.
I suspect Bell was referring, as usual, to certain philosophical priorities. The basic idea behind MWI is completely simple-- it merely asserts that all closed systems, including closed systems that include observers and physicists (and even including open systems where the external constraints are fixed and not self-consistently updated with the system), must evolve according to the Schroedinger equation. That's it, that's MWI as an interpretation of quantum mechanics (and not as a new theory like the way BruceW was talking about). I'm always surprised how many people think that closed systems do evolve that way, in the sense that it should provide a complete description of their evolution, yet they reject MWI. That's an internally inconsistent stance, because if evolution by the Schroedinger equation provides a complete description of closed systems, then closed systems evolve completely unitarily. MWI is the sole interpretation which allows that to be a complete description. That doesn't mean we should all adopt it, but it does mean that to say MWI is an invalid interpretation is identical with claiming that it is invalid to imagine that a complete description of closed systems evolution could be given by the Schroedinger equation without any additional bells and whistles like pilot waves or empirical perceptions of collapse.This is the situation with MWI. On its face, it does not give an intelligible account of the world of our experience. As John Bell said, when you examine it closely, you find that it is not coherent (so to speak).
I think the problem is that MWI users try to go farther than simply saying that closed systems, even those including observers, are described completely by the Schroedinger equation. They further build a kind of world view that can make additional predictions, along the lines of what the multiverse is used for with the anthropic principle. That goes beyond an interpretation of quantum mechanics, it is something closer to the creation of a new theory that makes new predictions, and this is the place where all the stumbling occurs, because no such new theory really exists at present. There are no clear new predictions made by MWI that could justify imagining those "other worlds" really exist, and whether Weinberg's cosmological constant prediction counts as a new prediction of anthropic thinking is clearly a debatable issue (one that I would be dubious of, but that's another thread).So, although I think you've expressed some valid views about the tension between rationalism and empiricism, and about the hazards of thinking our current rationalizations are the ultimate ones, etc., I would say that to some extent they are wasted on a consideration of MWI, because the real problem with MWI is that it isn't really an interpretation of quantum mechanics; at best it is just an idea for an interpretation - and not a successful one. That's what forces its believers to continue modifying it, trying to somehow shape it into something that could genuinely be called an interpretation of quantum mechanics. And that's why its critics continue to point out that, at the very least, something more would be needed before one could even claim that MWI is an interpretation of quantum mechanics.
Ken G said:Sure, but that's much more difficult, and must be held to a higher standard of proof. For example, that's just what the "lost causes" article did not successfully do. All too often, a criticism of an interpretation gets intermingled with implicit philosophical priorities that go unnoticed, rather than a logical proof that some interpretation is incorrect. How can an interpretation be incorrect if a physicist is not led to doing incorrect calculations by employing that interpretation to motivate those calculations? What incorrect calculation does MWI motivate?I suspect Bell was referring, as usual, to certain philosophical priorities. The basic idea behind MWI is completely simple-- it merely asserts that all closed systems, including closed systems that include observers and physicists (and even including open systems where the external constraints are fixed and not self-consistently updated with the system), must evolve according to the Schroedinger equation. That's it, that's MWI as an interpretation of quantum mechanics (and not as a new theory like the way BruceW was talking about). I'm always surprised how many people think that closed systems do evolve that way, in the sense that it should provide a complete description of their evolution, yet they reject MWI. That's an internally inconsistent stance, because if evolution by the Schroedinger equation provides a complete description of closed systems, then closed systems evolve completely unitarily. MWI is the sole interpretation which allows that to be a complete description. That doesn't mean we should all adopt it, but it does mean that to say MWI is an invalid interpretation is identical with claiming that it is invalid to imagine that a complete description of closed systems evolution could be given by the Schroedinger equation without any additional bells and whistles like pilot waves or empirical perceptions of collapse.
I think the problem is that MWI users try to go farther than simply saying that closed systems, even those including observers, are described completely by the Schroedinger equation. They further build a kind of world view that can make additional predictions, along the lines of what the multiverse is used for with the anthropic principle. That goes beyond an interpretation of quantum mechanics, it is something closer to the creation of a new theory that makes new predictions, and this is the place where all the stumbling occurs, because no such new theory really exists at present. There are no clear new predictions made by MWI that could justify imagining those "other worlds" really exist, and whether Weinberg's cosmological constant prediction counts as a new prediction of anthropic thinking is clearly a debatable issue (one that I would be dubious of, but that's another thread).
Let's look at a simple question. Do you, or do you not, think that closed systems always evolve according to the Schoedinger equation?juanrga said:All known MWIs are internally inconsistent and do not agree with observations.
Ken G said:Sure [i.e., one obviously CAN argue that a purported interpretation is incorrect, meaning it is not a valid or viable interpretation of the theory it claims to represent], but that's much more difficult, and must be held to a higher standard of proof.
Ken G said:How can an interpretation be incorrect if a physicist is not led to doing incorrect calculations by employing that interpretation to motivate those calculations? What incorrect calculation does MWI motivate?
Ken G said:…MWI merely asserts that all closed systems… must evolve according to the Schroedinger equation… MWI is the sole interpretation which allows that to be a complete description.
Ken G said:To say MWI is an invalid interpretation is identical with claiming that it is invalid to imagine that a complete description of closed systems evolution could be given by the Schroedinger equation without any additional bells and whistles like pilot waves or empirical perceptions of collapse.
Ken G said:Let's look at a simple question. Do you, or do you not, think that closed systems always evolve according to the Schoedinger equation?
Samshorn said:No proponent of any of the mutually exclusive versions of MWI has ever succeeded in showing this - at least not to the satisfaction of anyone other than himself.
Anyone who espouses anyone of the mutually exclusive versions of MWI can explain to you why each of the other versions “motivates incorrect calculations”. For example, read Deutsch on why he believes Everett was wrong to think unitary evolution of the wave function, all by itself, represents a viable interpretation of quantum mechanics.
But you have not supported your claim here. Your claim is that Deutsch is saying Everett would make wrong calculations, but the evidence you cite is a quote that is not saying anything about calculations at all. This is the widespread problem-- an inability to tell the difference between a scientific difference and a difference in philosophical priorities. Give me a quote by Deutsch in which he is saying that Everett does wrong quantum mechanics, not a quote where Deutsch is quite clearly saying that he demands some ontological "connection" between the wave function and the universes. That looks to me like Deutsch is simply raising a philosophical objection, which I claim is exactly where all the debates about interpretations are held.Samshorn said:For example, read Deutsch on why he believes Everett was wrong to think unitary evolution of the wave function, all by itself, represents a viable interpretation of quantum mechanics, i.e., it cannot serve as a legitimate basis for correct calculations. He says MWI needs something more, an additional mathematical structure to “provide the connection between the wave function and the concept of the many parallel universes.”
Remind me-- what extra mathematical structure are you talking about? The main proponent of MWI, early in this thread, was Hurkyl, and I am aware of the writings of Max Tegmark, and neither of them ever refer to any "extra mathematical structures", indeed their support of MWI invariably rests on what they perceive as an absence of extra mathematical structures (like the deBB pilot waves, or the Copenhagen manual postulate about wavefunction collapse). In my view, they are right about that-- MWI is clearly the mathematically minimalist description, it is just not the empirically minimalist description (that's CI) or the most neoclassical (that's deBB).Note, however, that when, earlier in this thread, I outlined for you the extra mathematical structure that this particular advocate of MWI thinks is necessary to turn MWI into a viable interpretation that motivates correct calculations, you responded with something like “Well, that is obviously not a viable interpretation of quantum mechanics!”.
That will come as a big surprise to Hurkyl, he seems to have no trouble making correct calculations. The grandiose claims made about the failings of MWI as a viable interpretation seem highly unresponsive to the facts of the matter. All I see are objections that are ontological and philosophical in nature, and a bunch of empty claims that they are more than that. I think the real problem is that MWI proponents are trying to arm their interpretation with more completeness than has been demonstrated by either deBB or CI, and that's where they have not succeeded-- because that would make MWI more than just a different interpretation, it would make it a different theory (as it invariably comes with suggestions for different predictions it would make, like if influences from "other worlds" could actually be measured).There is no interpretation of MWI that motivates correct calculations.
Says you, but that very clearly is a question that must be answered by the person using that motivation. An interpretation is just not anything more than whatever the physicist is imagining is happening when he/she thinks about the result they are calculating. Why don't we see people claiming that Newtonians "may be capable of performing correct calculations, but those calculations are not warranted" by imagining that forces are real, rather than that action is minimized or some such equivalent interpretation of what is really happening there? Why do people argue about this in quantum mechanics, but not classical mechanics, even though saying that action is minimized is just as ontologically vastly different from saying that there are real forces, as is saying that there are many worlds is different from there being pilot waves. For some reason, when we get to quantum mechanics, everyone seems to suddenly forget what an equivalent interpretation means any more.Of course, those who advocate some version of MWI may be capable of performing correct calculations, but those calculations are not warranted (“motivated”) by their version of MWI.
That just doesn't make sense to me. No one "adheres to" an interpretation when they do quantum mechanics (that's why some people claim they only "shut up and calculate"), they apply the postulates of quantum mechanics, which you can read in any textbook on quantum mechanics (some of which make no mention at all of any interpretation whatsoever). No one uses an interpretation to do quantum mechanics, they use an interpretation to give them something to picture in their minds when they do quantum mechanics. The interpretation motivates the equations they are using, it does not provide the equations they are using. Indeed, quantum mechanical interpretations are often even less important than interpretations of classical mechanics, because in classical mechanics the equations can start out being different (as in minimizing action vs. Newton's laws), even though they end up being the same before the motion is solved. That's more akin to deBB, which starts out with a different equation before it ends up solving Schroedinger, but MWI and CI don't even do that-- the equations are never different one iota. Often, interpretations in QM, like MWI and CI, appear after the fact of the calculation-- they tend to be a priori types of interpretations, which is the least significant type.If they adhered strictly to MWI, they would be unable to correctly calculate anything connected with the observables of our experience in accord with quantum mechanics.
Let's look at an example. You can easily solve for the motion of the Earth around the Sun by treating the Earth-Sun system as closed and applying the Schroedinger equation, we just approximate the Earth as having a pure-state wavefunction when we know if we had more precision we'd have to treat is as a mixed-state subsystem.The problem is that, above a certain complexity, there are no effectively closed systems smaller than the entire universe, and no MWI advocate can tell you the Hamiltonian of the universe, nor even what such a thing could possibly look like, even in principle, since a Hamiltonian is sui generis an external constraint of some kind.
CI does not escape this problem either, it just makes different philosophical choices about how to deal with it. CI says that effectively closed systems evolve by the Schroedinger equation until you open them up, and the mixed states that appear when one considers open subsystems should be interpreted as definite outcomes that there is a lack of information about until the definite result is recorded. There is no evidence of any time-symmetry breaking there in anything that is happening independently of how we do physics, it is merely by fiat that the arrow of time is applied. It has our fingerprints all over it, just as does the second law of thermodynamics. So CI is pretty much standing up and saying "physics is done by physicists, and is all about what we can say about nature and nothing more." It is all the things so many on this thread reject, in the same breath that they reject MWI, even though MWI provides a way to avoid having a very clear role of the mind of the physicist in the ontology of the interpretation.And even if they could provide the Hamiltonian of the universe (of a form that doesn’t violate their own premises), and even if they could provide plausible initial conditions, they would face the problem Deutsch mentioned, about not having the structure to actually define how “any individual universe in the vast stack of cosmic alternatives fits into the stack”, which immediately leads to problems like temporal symmetry – how can we maintain that unitary evolution (under the unknown and unknowable Hamiltonian of the universe from some unknown and unknowable initial conditions) leads to “splitting” or “differentiating” or “re-shuffling” of self-consistent universes in one time direction but not in the other?
I did balk at that point, but my way of balking was not to say MWI is invalid, I merely used the example to point out how radically rationalistic MWI is-- it represents the complete denial of the role of the mind of the physicist in physics (rationalists view mathematics as existing outside the mind of the mathematician). I don't think it's invalid to do that, I think it's invalid to do that and claim that a fairly narrow set of philosophical priorities is not being invoked in the process. The rationalistic MWI proponent thinks that the arrow of time is an illusion, as is the whole concept of a definite unique outcome of an experiment. MWI is a symmetry principle-- the symmetry that any outcome that can occur cannot be distinguished in the full reality from any other outcome that can occur, so the distinctions we perceive are illusory. It is the culmination of the Parmenides philosophy that A cannot become B unless A and B are the same thing.Or if we accept that unitary evolution must be time-symmetrical, how can we reconcile with our experience and with quantum mechanics the re-converging of universes that this entails? (This is the point that led you to baulk previously.)
Not so, MWI proponents have no trouble applying the Born rule. It is as though you think they are schizophrenic, as if their interpretation forces them to reject the Born rule postulate, so whenever they do a QM calculation they enter an unconscious state when they apply the Born rule, and wake up seconds later with no memory of having used it!And of course the Born rule is external to unitary evolution, etc. The point is that MWI is very far from being an intelligible interpretation of quantum mechanics, and it certainly doesn’t warrant any correct calculations at all.
Sure, MWI requires the Born rule postulate too. It is not something demonstrably better than CI.Unitary evolution according to the Schrodinger equation does not, by itself, constitute an interpretation of quantum mechanics. At the very least, some additional structure would be needed in order to establish a viable mapping from the wave function to the measures of our experience in accord with quantum mechanics – and it is far from clear that any such approach could ever work.
I think he is very clearly talking about philosophical priorities-- he is talking about MWI as providing the ontological completeness that CI lacks. He is saying that MWI does not in fact achieve that completeness-- it is not better than CI. But if he would criticize MWI for not being coherent, then he would have to explain how the CI collapse postulate is "coherent." It works, it is empirically borne out, but it is completely ad hoc. The CI user is not bothered by this, but only because empiricists always think theories are ontologically incomplete.As John Bell said “the many universes interpretation is a kind of heuristic, simplified theory, which people have done on the backs of envelopes but haven’t really thought through. When you do try to think it though it is not coherent.” He was not talking about philosophical priorities, he was saying MWI does not represent a coherent interpretation on a technical level.
This is the key point that we agree on. This is the only basis that MWI can be criticized as an interpretation of QM, because it makes a different claim about what QM is saying, but then one must be able to offer proof that closed systems are not completely described that way, and that is lacking here (that's the "higher standard" I alluded to above).Right. It is invalid to imagine that a complete description of closed systems evolution – consistent with the quantum mechanical account - could be given by the Schroedinger equation without any additional bells and whistles.
The absence of completely closed systems is a bugbear for all of physics, not just MWI interpretations of quantum mechanics. It is the reason we have empiricists in the first place-- people who are skeptical that physical theories can ever describe the true reality, because theories always make idealizations to work at all. But rationalists have been over that terrain many times-- they know they are making idealizations, but like Plato, they see the ideal as the true reality. They don't think messy reality is the truth and idealizations are some simplified version that fits in our heads, they think idealized principles are the truth and messy reality is a reflection of how poorly our five senses are able to penetrate to the underlying truth of what reality actually is. That's why they say things like "God is a mathematician". We don't have to agree with rationalism, but we do have to recognize this is the fundamental debate we are entering.Even most advocates of MWI (who have thought about it carefully) agree with this. And of course it’s also invalid to imagine any closed systems containing a physicist and smaller than the entire universe. (I choose the measurement angle of my Stern-Gerlach device today based on my memory of a constellation my grandfather pointed out to me in the night sky when I was a little boy.)
Ken G said:But you have not supported your claim here. Your claim is that Deutsch is saying Everett would make wrong calculations, but the evidence you cite is a quote that is not saying anything about calculations at all. This is the widespread problem-- an inability to tell the difference between a scientific difference and a difference in philosophical priorities. Give me a quote by Deutsch in which he is saying that Everett does wrong quantum mechanics, not a quote where Deutsch is quite clearly saying that he demands some ontological "connection" between the wave function and the universes. That looks to me like Deutsch is simply raising a philosophical objection, which I claim is exactly where all the debates about interpretations are held.
Remind me-- what extra mathematical structure are you talking about? The main proponent of MWI, early in this thread, was Hurkyl, and I am aware of the writings of Max Tegmark, and neither of them ever refer to any "extra mathematical structures", indeed their support of MWI invariably rests on what they perceive as an absence of extra mathematical structures (like the deBB pilot waves, or the Copenhagen manual postulate about wavefunction collapse). In my view, they are right about that-- MWI is clearly the mathematically minimalist description, it is just not the empirically minimalist description (that's CI) or the most neoclassical (that's deBB).
That will come as a big surprise to Hurkyl, he seems to have no trouble making correct calculations. The grandiose claims made about the failings of MWI as a viable interpretation seem highly unresponsive to the facts of the matter. All I see are objections that are ontological and philosophical in nature, and a bunch of empty claims that they are more than that. I think the real problem is that MWI proponents are trying to arm their interpretation with more completeness than has been demonstrated by either deBB or CI, and that's where they have not succeeded-- because that would make MWI more than just a different interpretation, it would make it a different theory (as it invariably comes with suggestions for different predictions it would make, like if influences from "other worlds" could actually be measured).
Says you, but that very clearly is a question that must be answered by the person using that motivation. An interpretation is just not anything more than whatever the physicist is imagining is happening when he/she thinks about the result they are calculating. Why don't we see people claiming that Newtonians "may be capable of performing correct calculations, but those calculations are not warranted" by imagining that forces are real, rather than that action is minimized or some such equivalent interpretation of what is really happening there? Why do people argue about this in quantum mechanics, but not classical mechanics, even though saying that action is minimized is just as ontologically vastly different from saying that there are real forces, as is saying that there are many worlds is different from there being pilot waves. For some reason, when we get to quantum mechanics, everyone seems to suddenly forget what an equivalent interpretation means any more.
That just doesn't make sense to me. No one "adheres to" an interpretation when they do quantum mechanics (that's why some people claim they only "shut up and calculate"), they apply the postulates of quantum mechanics, which you can read in any textbook on quantum mechanics (some of which make no mention at all of any interpretation whatsoever). No one uses an interpretation to do quantum mechanics, they use an interpretation to give them something to picture in their minds when they do quantum mechanics. The interpretation motivates the equations they are using, it does not provide the equations they are using. Indeed, quantum mechanical interpretations are often even less important than interpretations of classical mechanics, because in classical mechanics the equations can start out being different (as in minimizing action vs. Newton's laws), even though they end up being the same before the motion is solved. That's more akin to deBB, which starts out with a different equation before it ends up solving Schroedinger, but MWI and CI don't even do that-- the equations are never different one iota. Often, interpretations in QM, like MWI and CI, appear after the fact of the calculation-- they tend to be a priori types of interpretations, which is the least significant type.
Let's look at an example. You can easily solve for the motion of the Earth around the Sun by treating the Earth-Sun system as closed and applying the Schroedinger equation, we just approximate the Earth as having a pure-state wavefunction when we know if we had more precision we'd have to treat is as a mixed-state subsystem.
No one knows if large suitably closed systems have pure-state wavefunctions or if they have to be treated as mixed states, it has never been put to the test. The expectation from quantum mechanics is that the more closed the system is, the less of a mixed-state description it requires, leading ultimately to a pure state in the limit of complete closure. So the MWI proponent holds that if we had truly closed systems, they would evolve unitarily, but we always actually have mixed-state subsystems projected from larger systems that we are not treating. By "large" I don't necessarily mean spatially large, I just mean there is a way larger amount of information in that system than we would ever be able to use our intelligence and senses to analyze or track, so we instead track a remotely tiny subset of that full complexity. The MWI proponent sees that fact as the reason that we do not perceive the full "unity" of the effectively closed systems we participate in.
CI does not escape this problem either, it just makes different philosophical choices about how to deal with it. CI says that effectively closed systems evolve by the Schroedinger equation until you open them up, and the mixed states that appear when one considers open subsystems should be interpreted as definite outcomes that there is a lack of information about until the definite result is recorded. There is no evidence of any time-symmetry breaking there in anything that is happening independently of how we do physics, it is merely by fiat that the arrow of time is applied. It has our fingerprints all over it, just as does the second law of thermodynamics. So CI is pretty much standing up and saying "physics is done by physicists, and is all about what we can say about nature and nothing more." It is all the things so many on this thread reject, in the same breath that they reject MWI, even though MWI provides a way to avoid having a very clear role of the mind of the physicist in the ontology of the interpretation.
I did balk at that point, but my way of balking was not to say MWI is invalid, I merely used the example to point out how radically rationalistic MWI is-- it represents the complete denial of the role of the mind of the physicist in physics (rationalists view mathematics as existing outside the mind of the mathematician). I don't think it's invalid to do that, I think it's invalid to do that and claim that a fairly narrow set of philosophical priorities is not being invoked in the process. The rationalistic MWI proponent thinks that the arrow of time is an illusion, as is the whole concept of a definite unique outcome of an experiment. MWI is a symmetry principle-- the symmetry that any outcome that can occur cannot be distinguished in the full reality from any other outcome that can occur, so the distinctions we perceive are illusory. It is the culmination of the Parmenides philosophy that A cannot become B unless A and B are the same thing.
Not so, MWI proponents have no trouble applying the Born rule. It is as though you think they are schizophrenic, as if their interpretation forces them to reject the Born rule postulate, so whenever they do a QM calculation they enter an unconscious state when they apply the Born rule, and wake up seconds later with no memory of having used it!
That's not what they do, they simply apply the Born rule when they determine the weights of the mixed state they get when they consider a subsystem (like a measured object). MWI has no problem at all with the Born rule, they simply view it as the weights of a mixed state, rather then as probabilities of what "really happens." They only get into trouble when they are unwilling to think of the Born rule as an additional postulate to the wavefunction evolution, they, being lovers of unification, would rather see it as stemming from something more fundamental. But that's asking MWI to be more ontologically complete than CI is, to be something demonstrably better-- that's where it has not succeeded, not in its own internal viability. It has failed to be something better than CI, and it is die-hard rationalism, rather than embracing the empiricism of CI.
Sure, MWI requires the Born rule postulate too. It is not something demonstrably better than CI.
I think he is very clearly talking about philosophical priorities-- he is talking about MWI as providing the ontological completeness that CI lacks. He is saying that MWI does not in fact achieve that completeness-- it is not better than CI. But if he would criticize MWI for not being coherent, then he would have to explain how the CI collapse postulate is "coherent." It works, it is empirically borne out, but it is completely ad hoc. The CI user is not bothered by this, but only because empiricists always think theories are ontologically incomplete.
So the only problem the MWI rationalists face is they cannot accept ontological incompleteness, they want to have an answer for why the Born rule holds. They are trying to be more ontologically complete than CI, and that's where they fail. I believe that is also what Bell is saying-- the MWI camp has set an unreachable goal for themselves, and that unreachable goal is the thing that cannot be coherently addressed. But if they simply relax that goal, and allow MWI to simply assert the Born rule as a postulate, then they still have many worlds as long as they still have closed systems evolving solely by the Schroedinger equation, and if the meaning of that evolving wavefunction is given by the Born rule as the means of calculating the weights of the mixed state when the effectively closed system becomes effectively open. The defining characteristic of MWI, despite its various flavors and failed efforts to be something more than this, is the interpretation of a mixed state as a projection from something unitary, rather than as an expression of a definite outcome that we the physicists simply don't have full information about.
This is the key point that we agree on. This is the only basis that MWI can be criticized as an interpretation of QM, because it makes a different claim about what QM is saying, but then one must be able to offer proof that closed systems are not completely described that way, and that is lacking here (that's the "higher standard" I alluded to above).
Also, given the absence of evidence to the contrary, a lot of people do think that a complete account of closed systems that don't contain observers or macroscopic measuring devices can be given by the Schroedinger equation, so they effectively assert that the Schroedinger equation "doesn't work" for the larger "self-measuring" systems. The problem with that view is that an understanding of decoherence has clarified that the Schroedinger equation never actually breaks down when you go to larger systems-- it still provides us with the correct mixed state that happens when you decohere a subsystem by coupling it to a macrosystem. So QM is quite clear on the mixed state you get, that is interpretation independent. The interpretation, then, doesn't even appear until you go to interpret what the mixed state means physically. But that's pure philosophy-- all the physics is over with once you have the mixed-state outcome. You're done with doing calculations and making predictions even before the interpretation, be it MWI or CI, even appears. So none of the interpretations can be "wrong" when the science is already over before you get to them. Instead, they merely reflect different philosophical priorities.
The absence of completely closed systems is a bugbear for all of physics, not just MWI interpretations of quantum mechanics. It is the reason we have empiricists in the first place-- people who are skeptical that physical theories can ever describe the true reality, because theories always make idealizations to work at all. But rationalists have been over that terrain many times-- they know they are making idealizations, but like Plato, they see the ideal as the true reality. They don't think messy reality is the truth and idealizations are some simplified version that fits in our heads, they think idealized principles are the truth and messy reality is a reflection of how poorly our five senses are able to penetrate to the underlying truth of what reality actually is. That's why they say things like "God is a mathematician". We don't have to agree with rationalism, but we do have to recognize this is the fundamental debate we are entering.
Yes, we agree that is the experimental fact. But the Bohmian perspective has an account for that which is entirely deterministic. The trajectories the particles follow is altered by the presence of the experiment that determines the which-way information-- it has an effect on the pilot wave, and the pilot wave shepherds all the possible particle trajectories into doing what the Schroedinger equation says it should do, subject also to the informational constraints. It is "one stop shopping" for Bohm, you just say "the pilot wave did it". Unfortunately the pilot wave has no requirement to be there, so many view it as superfluous, but for those who like determinism, they are welcome to hold that it is actually there and their belief cannot be falsified by experiments of the kind you describe (or any other known).dreamland37 said:In my opinion, as far as simple English is concerned, I think the double slit experiment confirmed that an electron has an interference pattern when it passes through both the slits. Meaning that it behaves as a wave when left unobserved. However, when you try to measure which slit it goes through, the interference pattern vanishes and merely the particle behavior arises.
The two ways to hold that, MWI and consciousness-based collapsed, both seem rather mystical to a lot of physicists. I know you hold to the latter of those, and just like the Bohmians, if you are inclined to believe that there is no known experiment that can falsify your belief.In other words, the wave function is not only a mathematical tool, but a real description of reality.
That isn't really a theory because it doesn't make any new predictions. However, it is a perfectly valid interpretation, albeit somewhat mystical and inclined to lean on Cartesian mind/body dualism. Is that a strength or a weakness? I have no idea, it depends on one's philosophical priorities, and the next big theory that none of us know yet.That is why I posed a new interpretation of MWI, one that unifies all the theories and ascribes a physical reality to the equations. It is the only explanation that fits the math, but if the theory is correct than it implies that on a fundamental level, all quantum possibilities are inherent realities possessing a hint of the true essence of things but reside only within the Mind.
Yes, I see no flaw in that position, I place it squarely amid all the other interpretations! One would associate it with either dualism or idealism, depending on whether or not you believe there really is a physical reality that the mind is in contact with.Since matter is nothing more than the manifestation of the Mind as the collective data via our senses, it means that the collapse of the wave function is nothing more than the most probable state of these quantum possibilities. It is the act of measuring (something that can make a judgement) which collapses the wave function.
Personally I would prefer that to many worlds, if I had to hold that the wavefunction is something real, but I tend to favor the empiricism of saying that the wavefunction isn't real and the next big theory probably won't even use it.Therefore the difference between the Mind and Matter, possibility and probability is nothing other than the collapse of the wave function. This is the best interpretation I have found for the Many worlds
Ken G said:But you have not supported your claim here...
My take on this is that MWI should never claim to yield all the empirical content of quantum mechanics with just the unitarity postulate, it should claim to hold all the ontological content of quantum mechanics that way. MWI is an interpretation of what is really happening, we already know it does not gibe with our empirical experience. It claims that our empirical experience is not the complete story (as it is nonunitary), so we need the Born rule to describe our empirical experience. However, the Born rule is then seen as a description of the incompleteness of our experience-- the "full reality" has no Born rule, it is just the wavefunction evolution. One might then say that the Born rule controls some kind of measure of the "worlds" that split off into different experiential coherent islands that are mutually incoherent. So yes, it will always take an additional postulate to get the measure of that splitting (or fragmenting and re-merging, these aspects of MWI are not clear because they don't deal with what is "really happening" to the whole system but rather with the vagaries of coherent experiences of subsystems).Samshorn said:Let me try to explain more succinctly what I mean. At issue is the claim that every isolated system can be modeled as nothing but a quantum wave function represented by a state vector in some suitable Hilbert space, evolving in accord with Schrodinger’s equation for some suitable Hamiltonian and initial conditions, and that this model, with no additional axioms, yields all the empirical content of quantum mechanics.
Yes, but we should not expect MWI to circumvent the Born postulate, it's still quantum mechanics. It is just a way to interpret quantum mechanics where the Born rule appears at the level of how physicists experience the reality, the piece they get to experience. It's too much to ask that they would have any better insight into that than the CI does (except for those who ask MWI to be better than CI)-- it's just the ad hoc way that the wavefunction passes into predictions about our experience. Of course, CI maintains that the latter is all that physics is ever about, so saying anything more is entering into a kind of rationalistic fantasy.I say this claim is false, because (among other reasons) all the measurement correlations predicted by quantum mechanics correspond to one particlar definition of the “measure” of a state, but there is nothing in the single axiom of Schrodinger evolution that warrants any physical meaning for this particular measure. So, at the very least, some further axiom or principle is needed in order to actually have a viable interpretation of quantum mechanics.
I actually do think it is just a philosophical preference-- it is the preference that a physics theory should describe a true mathematical ontology, rather than the "empirical content" of that same theory. To a rationalist, empirical content is of secondary importance, which you can tell when you see them use phrases like "the experiments test the theory, to determine which theory is true" rather than just "experiments determine truth." The key difference is that the theory survives if the observations don't falsify it, rather than establish it. To them it is the theory that is the truth, or at least the approximation to the truth if the theory is only "converging on" the truth. So if the theory says we have a wavefunction that evolves unitarily, then that's the truth as long as observations can be interpreted as not falsifying it, and the nonunitary experiences described by the Born rule are nothing more than trying to understand why people see mirages in the desert. Yes it's important to the progress of science to be able to explain why people see mirages in the desert, but it's not so critical to the ontology of what a desert "really is." When you look at MWI that way, you see that they can have a self-consistent ontology without the Born postulate, and no observations falsify the many worlds description, but they just can't use it for science until they tack on the Born rule. That doesn't make it less than CI, it makes it equivalent to CI, from the scientific perspective-- the end of the equivalence comes only in the ontology.Now, you may agree or disagree with this objection, but hopefully you at least agree that it isn’t a question of philosophical preferences (except in the sense that reason itself is a philosophical preference).
I don't think it is sufficient to constitute an interpretation of quantum mechanics, it is sufficient to constitute an interpretation of the ontology of quantum mechanics used by MWI. To actually get an interpretation of quantum mechanics, you have to be able to interpret the Born rule somehow. So you have to be able to say that the Born rule gives the measures of the many worlds, and that is always going to be ad hoc-- because it is the part of the ontology that deals with physicists' perceptions, and no one has any kind of model for that.It is an objection to the validity of the claim that the single axiom of Schrodinger evolution of a wave function for isolated systems is sufficient to constitute an interpretation of quantum mechanics.
What is your objection to MWI simply saying that the true ontology of the universe is the unitary evolution of the wave function, and the Born rule is just a rule about how the wavefunction controls the creation of "coherent islands" of analytical intelligent agents? Certainly MWI cannot say why the Born rule does that, nor can CI, nor can Einstein say why mass curves spacetime. It just isn't different physics, it's still quantum mechanics-- and that's why debates about interpretations have to involve nothing more than philosophical priorities (until someone claims MWI is demonstrably better than CI, in which case they need to be able to explain the Born rule better than CI does-- I agree that I have never seen that pulled off, but that only supports my contention that the differences are all philosophical).You can explain why you disagree with the objection, or you can agree with the objection and offer some additional axiom(s) in the hopes of arriving at a genuine interpretation of quantum mechanics, but in the latter case you commit yourself to defending the additional axiom(s). (The are problems with all such supplementary axioms that I’ve ever seen.) But what you can’t do, I think, is claim that this is all just arguing about philosophical priorities.
Yes, I suspected yours was essentially the "idealist" interpretation of quantum mechanics. I don't dispute that interpretation is fully available if one is inclined to idealism, Berkeley would probably have liked quantum mechanics a lot. One thing I will personally agree with you is that quantum mechanics may be the first time that we are seeing, in our physics, the reflections of our own minds. I'm not sure that the role of the mind is neatly or clearly laid out in quantum mechanics, but I do get the sense we are seeing through that glass darkly. That's why I think the next big advance in physics might come from neuroscience or artificial intelligence-- we may be at the point where we need to understand our own minds to progress further in physics. Or maybe we're not at that place yet, and string theory is the next place to go. Only time will tell!dreamland37 said:On the other hand, quite contrary to Cartesian mind/body dualism which Spinoza was not able to unify, my theory or extension of probability theory unifies the mind/body dualism via the collapse of the wave function which incorporates George Berkeley's "esse est percipi" (to exist is to be perceived) which is more or less the philosophical reality behind the collapse of the wave function.
Yes, but pilot waves are not local hidden variables. The purpose of the pilot wave is to get the same behavior that the Schroedinger equation gets, so any experiment (like those of Bell type) that quantum mechanics gets right is just fine with Bohmian mechanics.The development of Bells theorem does not incline the notion of hidden variable theories such as the Pilot wave theory. Bell's theorem suggests in the opinion of most physicists and contrary to Einstein's assertion that local hidden variables are impossible.
Determinism is not incompatible with action at a distance. Champions of Bohmian mechanics might revel in the holistic character of Bell's theorem-- they'd say "see, we told you there was a nonlocal pilot wave there."Therefore the Pilot wave theory can't be seen as a complete interpretation because it is deterministic which doesn't allow action at a distance contrary to Bell's theory and Classical Quantum mechanics.
That's the great thing about quantum mechanics-- it admits to a host of wildly differing interpretations about what it all means. However, we must recognize that there is no appeal to authority when choosing an interpretation-- for there are "authorities" on every side of the issue. All we can do is say "gee isn't it grand that such a seemingly dry and impartial endeavor as physics can be so vibrantly alive with vastly differing interpretations."Max Planck said,
"There is no matter as such. All matter
originates and exists only by virtue of a force which brings the particle
of an atom to vibration and holds this most minute solar system of the
atom together. We must assume behind this force the existence of a
conscious and intelligent mind. This mind is the matrix of all matter. "
I certainly agree that it is meaningless to talk about anything in physics without an observer, for the simple reason that physics is an empirical science, and also there wouldn't be anyone to do the talking.So I feel that without an observer to single out the reality of possibilities we live in, it is meaningless to even talk about many worlds.
The metaphor is poetic, and certainly apt to some interpretations, but I point out that others would see in that metaphor the basic flaw: physics is supposed to be the description we get when we are awake, not when we are asleep. But I personally agree with the complementarity of observer and reality, as I believe would Bohr.For an observer and reality are complementary to each other, just as the dream and the dreamer.
Ken G said:I actually do think it is just a philosophical preference-- it is the preference that a physics theory should describe a true mathematical ontology, rather than the "empirical content" of that same theory.
I'm not very familiar with the MWI, but this doesn't sound right. Decoherence only occurs, when there are interactions with the environment. Since MWI uses decoherence to explain collapse, it certainly doesn't assume the subsystem of "the world of our experience" to be isolated.Samshorn said:The MWI tells us that at any given time t, our sub-world vector v is some kind of projection of V into a certain sub-space s, and it also tells us that the system described by v is perfectly isolated (going forward in time), so it's future evolution is, by hypothesis, also governed by the Schrodinger equation, as is the future evolution of V.
kith said:...note that in general, the state of a subsystem can't be written as a vector in Hilbert space but only as a density operator.
kith said:I'm not very familiar with the MWI, but this doesn't sound right. Decoherence only occurs, when there are interactions with the environment. Since MWI uses decoherence to explain collapse, it certainly doesn't assume the subsystem of "the world of our experience" to be isolated.
Ok. But this is the case in the CI as well as in the MWI. Collapse occurs only in measurements and in order to perform a measurement, you have to interact with your system. Thus it is not isolated anymore.Samshorn said:The hypothesis in question is that every isolated system (which may be a sub-system of some larger system) undergoes unitary evolution in accord with Schrodinger's equation - and nothing else.
dreamland37 said:Dear Ken G,
You make very valid points and thank you for providing a more wholesome view Bohemian mechanics. You draw out your arguments in a clear and concise way, but I fail to see how pilot waves are not local hidden variables.
Even according to the wiki, the Pilot wave description is listed as
"Principles
The Pilot Wave theory is a hidden variable theory...
The position and momentum of every particle are considered hidden variables; they are defined at all times, but not known by the observer; the initial conditions of the particles are not known accurately, so that from the point of view of the observer, there are uncertainties in the particles' states which conform to Heisenberg's Uncertainty Principle." http://en.wikipedia.org/wiki/Pilot_wave
In other words, if it is not a hidden variable theory it will break Heisenberg's Uncertainty Principle.
kith said:Collapse occurs only in measurements and in order to perform a measurement, you have to interact with your system. Thus it is not isolated anymore.
Yes, BM is a hidden variable theory. But it's not a local hidden variable theory.dreamland37 said:You draw out your arguments in a clear and concise way, but I fail to see how pilot waves are not local hidden variables.
...
The Pilot Wave theory is a hidden variable theory...
...
In other words, if it is not a hidden variable theory
Right. So it is an alternative to local realism. In local realism, each piece "carries with it" all its own reality, so assembling the pieces is assembling the reality. But QM has many holistic elements, including the related issues of joint wave functions that are not separable, entanglement, and identical particles.BruceW said:Ken G - Can I ask about the word holistic? I see it being used a lot but I'm not totally sure what it means..
Holism means something like 'the whole is more than just the parts together' right?
That isn't necessarily what I would call holistic, more like a meta-theory (a theory about theories). But there is a holistic element of relativity-- it's the idea that motion is a relationship between objects, rather than something any of the objects are doing by themselves. But by holistic I generally mean something more physical-- the system is not just the particles and the fields they generate, there is a kind of connection between the particles that you don't get if you just look at the parts independently.So a 'holistic theory' is a theory that can be applied to many different questions? And as an example, Einstein's general theory of relativity is holistic because it tells us that the laws of physics are the same for any observer. So this one theory tells us something about all other theories that obey relativity. Is all this roughly correct?
How can it be unrelated? You talked about what you think to be the basic hypothesis of the MWI and I expressed the view that this hypothesis also holds in the CI. If this is true, one can't "disprove" the MWI without disproving the CI as well.Samshorn said:What you're saying is unrelated to what I described.
There are certainly some subtle points here. If you look at a MWI-favoring physicist doing a quantum mechanics calculation, you are not going to be able to tell they hold to MWI. The mechanics are all the same, leading to predictions of experiments that are all the same, so if predictions are what is meant by "empirical content," then it is the same with MWI. This is because MWI proponents don't shun the Born rule, they use it just like everyone else.Samshorn said:I think we've isolated the basic difference in our views. I differ with your above statement on two counts. First, essentially as a matter of definition, I think that in order for a conceptual model to qualify as an interpretation of a physical theory, it must establish an explicit and unambiguous mapping from the elements/features of the model to the empirical content of the theory. Your definition of "interpretation" is based just on the ontological elements, which I'll discuss below, but I really don't think that's a valid definition of a physical interpretation, because models could have the same ontology but different empirical behavior, and we surely wouldn't say they were interpretations of the same theory.
The "worlds" of MWI are not evolving unitarily. If they did, we wouldn't need MWI at all! The worlds are subspaces, and it is in them that the nonunitariness of our experiences occurs. They are projections, yes, but they only evolve unitarily so long as they are not splitting into new worlds, which as I understand it is basically when there are no apparent collapses. When there are apparent collapses, unitarity is broken in the fragments-- it is only recovered by restitching the fragments back into their whole, but that whole isn't the space s.Let V(t) denote the state vector of the overall universe, existing within the Hilbert space S, and let v(t) denote the state of the sub-world that we experience. The MWI tells us that at any given time t, our sub-world vector v is some kind of projection of V into a certain sub-space s, and it also tells us that the system described by v is perfectly isolated (going forward in time), so it's future evolution is, by hypothesis, also governed by the Schrodinger equation, as is the future evolution of V. The problem is that s cannot be constant if v is going to consistently represent the world of our experience over time, and if both V and v are evolving unitarily according to Schrodinger's equation.
I would say the rules for the evolution of s are just the same in CI or MWI, what is different is whether or not s is considered to be the whole reality. In CI, it is, but it is nonunitary. In MWI, it isn't, the reality stitches together the various s to restore unitarity. Yes MWI must use a CI-like rule for evolving s, but it claims that is a rule about our limited ability to perceive the full reality. It is like a rule for how a telescope blurs an image, which it distinguishes from the rules that govern what is being imaged. There is no difference in what is seen in the telescope of empirical verification, the difference is in the idea of what is being empirically verified. An empiricist knows that a blurry telescope image is a technological limitation that should not be confused with the "true" image, but the collapse is a fundamental limitation so we don't know what to make of that distinction any more. CI and MWI make something different of that distinction-- to CI, any image that is inescapably and fundamentally blurred is the reality of the image, but to MWI, it is still viewed as a blurred version of the reality.And the rule for the evolution of s is essentially none other than the CI or something similar. So the axioms of a viable MWI, augmented to the point of actually being a genuine interpretation, are not a SUBset of the axioms of CI, they are a SUPERset.
That's the key point right there. You are saying that you don't know of any MWI versions that are actually different theories from quantum mechanics, because everything that you can find in a quantum mechanics textbook you are calling CI. I agree, MWI is not mechanically different from CI, even if some practitioners hoped to find a way to make it so. It's just a different ontology, a very rationalistic one-- so although you may regard that difference as trivial scientifically, it isn't if one takes the ontology of a theory seriously. Shall we view things like "electrons" as real members of our universe, taking our ontologies seriously, or should we regard "electrons" as just pictures that physicists conjure while they do some calculation? That is the same issue as the differences between CI and MWI.That's why I say I'm not aware of any viable MWI - aside from the trivial one that postulates CI and then advises us to embedd all possible outcomes into a superstructure whose overall shape (unitary) we find more pleasing.
Ken G said:The trajectories the particles follow is altered by the presence of the experiment that determines the which-way information-- it has an effect on the pilot wave, and the pilot wave shepherds all the possible particle trajectories into doing what the Schroedinger equation says it should do, subject also to the informational constraints...
The two ways to hold that, MWI and consciousness-based collapsed, both seem rather mystical to a lot of physicists.
Someone who is more of a deBB proponent might wish to correct me, but I don't think that's the way the Bohmians think about it. I believe they treat every quantum state as if it was already collapsed, we just didn't have enough information to know which state it was. But the collapsed state in some sense takes into account the entire physical environment-- that's why the hidden variables are nonlocal. So the "informational constraints" I was referring to simply winnow down the possible trajectories, they don't "change" the trajectory from one to another. Which-way information means you have a different pilot wave, and a different bunch of potential trajectories any of which could be the "real one". Think of them as "virtual" trajectories, meaning only that they are possibilities we have to entertain, until we find otherwise, but the Bohmians think individual particles always follow definite predetermined trajectories.dreamland37 said:So the more I am learning the deeper characteristics of the debb the more I am fascinated by it. It seems so very mystical to me that I want to hold that both theories are correct. Because the environment registering the detection effectively alters the course of particles which can otherwise be viewed as the collapse of the WF. All the theory seems to do is transfer the role of the observer (collapsing the wave ect.) to the environment (a quantum conscious environment aware of all non local variables).
Right, the pilot wave takes into account the full situation.Therefore in the case of the double slit experiment, the environment is aware that there is a measuring apparatus placed by one of the slits. This has also been confirmed in experiments where the measuring device was placed after the photon was released to see if the photon would notice so to speak.
But in deBB, there is no more role for mind in quantum mechanics than there is in classical mechanics-- both QM and CM describe a fully predetermined future, from the deBB perspective (personally I don't think the effectiveness of either QM or CM imply that). But I suppose within the context of complete determinism, there is still the possibility for associating the pilot wave with some sort of mindlike function, for those who tend toward idealism.Basically Debb leads to the sublime notion that Nature is aware of itself which conforms to the semi-conscious behavior of particles which act as if they also are aware of their surroundings.
I believe that will be a key element, but I still haven't seen anything that I regarded as a different theory that guides new observations to test it-- I just see a lot of philosophical priorities in conflict. I think our philosophical priorities are important to us, but I also think history is quite clear that philosophical priorities show no tendency to converge.The basic assumption is to fully understand the role of the observer to unify these theories. Because we are apart of nature and therefore complementary to it.
dreamland37 said:what does it mean that the Bohmain interpretation is causal but not local? Also as in the case of the two slit experiment I fail to see how the interference pattern of the wave function vanishes when a measuring device is put next to one of the two slits.
Otherwise it seems a very valid interpretation and also inline with the new E8 theory of everything posed by Garrett Lisi
Ken G said:I still haven't seen anything that I regarded as a different theory that guides new observations to test it-- I just see a lot of philosophical priorities in conflict. I think our philosophical priorities are important to us, but I also think history is quite clear that philosophical priorities show no tendency to converge.
Ken G said:There are certainly some subtle points here. If you look at a MWI-favoring physicist doing a quantum mechanics calculation, you are not going to be able to tell they hold to MWI... because MWI proponents don't shun the Born rule, they use it just like everyone else.
Ken G said:The "worlds" of MWI are not evolving unitarily. If they did, we wouldn't need MWI at all!
Ken G said:I agree, MWI is not mechanically different from CI, even if some practitioners hoped to find a way to make it so.
I don't think that's right. How does v split? By decoherence. What is the cause of decoherence? Interactions with the environment. Thus in isolation, there is no splitting. If v splits it is not isolated.Samshorn said:I hoped it wouldn't be necessary to fill in so many details, but to clarify, what I mean is that at some instant t there is a self-consistent subworld described by v that branches off into isolation from all the rest of the universe. Now, v immediately can be regarded as splitting into sub-sub-worlds v1, v2, v3..., and each of those splits into sub-sub-sub-worlds such as v2a, v2b, v2c,..., and each of those splits into worlds such as v2b1, v2b2, v2b3,... But the point is that these are all constituents of the isolated system v, which does not interact with anything else.
Well, I wouldn't base your argument on that. What you're describing sounds like water being frozen in random ways that give rise to the well-known symmetry-breaking properties of frozen snowflakes, which are not molecules but are structures of molecules (that is not what is normally meant by "molecular structure"), and freeze in different but random ways. If I "bless" five different random number generators with five different blessings, and get five different numbers out, I'm not going to conclude that the numbers were different because of differences in my blessing until I can show with a double-blind test that the blessings repeatably correlated with the outcomes of multiple trials. It really doesn't sound like anything like that was done in the movie, it sounds more like the way parlor magic tricks can fool non-magicians.dreamland37 said:One so-called example is listed in a movie, What the Bleep Do We Know?, where a Buddhist monk blesses a number of different bottles of water with different blessings. Before the experiment, each bottle of water had a random molecular structure but after the blessings, each one changed differently into a beautiful snowflake-like shape.
That's the rub-- philosophical ideas can give us a sense of mental satisfaction, but they are not science until they motivate a mathematical description that makes testable predictions that are different from the ones we already have.Are there any mathematical models are predictions you can think of? Or are there any arguments you know of that might work against such a theory. For even Einstein's theory of relativity wasn't complete until he added his mathematical framework to it. Until than it was just a philosophy which many scientists disagreed with.
So it is as I said above-- you simply equate the mathematical machinery that can be found in any quantum mechanics textbook with CI, and say that MWI has to use some other currently nonexistent mathematical machinery or it isn't MWI. That just doesn't seem like a realistic requirement to call something MWI to me, and I don't think the proponents of MWI need to disallow themselves to use quantum mechanics textbooks when they do calculations.Samshorn said:But by dealing with apparently classical outcomes and using the Born rule to compute the probabilities of those outcomes they are not holding to MWI, because according to MWI they should really be making decoherence calculations on the wavefunction of an entire isolated system including both the experimental subject and the observer, with the suitable Hamiltonian for this whole isolated system (which, for the reasons explained before, can hardly be smaller than the entire universe), and at best this will lead only to approximately classical outcomes, so the application of the Born rule to the results of this hypothetical calculation, even if it could be carried out, would be inherently ambiguous... But of course no one has ever made such a calculation, and of course no one ever will, and they have never offered more than hand-wavy plausibility arguments that they ever could do such a calculation, even in principle.
I would be careful about that requirement-- you are saying that anyone who claims to have an interpretation must make a demonstrable link from their interpretation to the equations they are using the interpretation to understand. I actually don't think any interpretation in the history of physics can satisfy that demand, for the simple reason that mathematics is just one thing-- mathematics. No one can ever prove that an interpretation really does "establish the consistency" of the interpretation with the mathematics. If I interpret forces as real but action as a mathematical trick, according to your stated criteria, I could never use a Lagrangian approach to calculate a constraint force-- I'm being inconsistent with my interpretation that says forces are real and Lagrangians are just mathematical tricks. I'd be turning my back on my philosophical beliefs as soon as I wrote down the Lagrangian, because it isn't something accepted in the ontology of my interpretation.The point is that just because someone who espouses (some version of) MWI avails himself of the calculational recipes of ordinary quantum mechanics, it doesn't follow that his calculations really are consistent with his philosophical beliefs. This consistency needs to be established.
But it certainly isn't fair to drop any of those things on the doorstep of MWI, because they all fall on the doorstep of any interpretation of nonrelativistic quantum mechanics. No one ever said physics had to be exact or perfectly internally consistent, and so no interpretation has to be those things either. We cannot hold interpretations of physical theories to higher standards then we would ever hold the theory itself to! But I do agree that this is the very reason that we should take neither our theories, nor their interpretations, as seriously as some seem to. I don't believe in building "world views" based on interpretations of physical theories, because of the limitations in both the interpretations, and in the theories themselves. Indeed, exactly how I look at interpretations is as a way to see a theory from a different philosophical angle, and nothing more or less than that.Much ink has been spent by people trying to establish this, and making adjustments to their conceptions of MWI in order to help establish this, but there are deep and subtle issues involving the concept of a wave function and Hamiltonian of the entire universe (for example), the arrow of time, etc., not to mention the fact that we know Schrodinger's equation is wrong, because it isn't relativistic, so we're led to consider quantum field theory, which has its own issues.
Actually, I don't think there is a requirement for the subsystem v to not interact with anything else, the sole requirement is that it not interact with anything else in a way that leaves a signature or trace. That is essentially the definition of an "other world" (when it is not true, we use the term superposition instead). This means that if "other worlds" affect v, they do so in ways that look completely unpredictable and nondeterministic.I hoped it wouldn't be necessary to fill in so many details, but to clarify, what I mean is that at some instant t there is a self-consistent subworld described by v that branches off into isolation from all the rest of the universe. Now, v immediately can be regarded as splitting into sub-sub-worlds v1, v2, v3..., and each of those splits into sub-sub-sub-worlds such as v2a, v2b, v2c,..., and each of those splits into worlds such as v2b1, v2b2, v2b3,... But the point is that these are all constituents of the isolated system v, which does not interact with anything else.
I don't see where MWI is missing that, it uses the projection postulate just like it uses the Born rule, just like someone who doesn't think gravity is really a force can still write F=mg without making themselves some kind of liar! All they are doing is parsing between what they know is an effective theory, and what they think is "actually happening", and that is almost always a purely philosophical distinction.But of course the world we experience at a sequence of times t1, t2, t3, t4... is not v(t1), v(t2), v(t3), v(t4)..., it is something like v(t1), v2(t2), v2b(t3), v2b1(t4),... and so on. Obviously this sequence of worlds is not evolving in a unitary way (viewed by itself), but the point is that the projections from the universal wave function V(t) (which IS evolving in a unitary way) down to each of these instantaneous worlds cannot be going to the same subspace s, they must be projections to a sequence of sub-spaces s, s2, s2b, s2b1,... so in order to place the terms of the MWI model into explicit correspondence with the measures of our experience in accord with quantum mechanics, we need more than just the Schrodinger rule for evolving isolated systems, we also need the rule for evolving the projection subspaces... and this is MUCH more than just the Born rule for assigning probailities, we need the rule to define the (approximate) subspaces to which the Born rule is applied. Explicitly defining this sequence of subspaces is what the projection postulate in ordinary quantum mechanics does, on a piece-meal basis.
That is also why I prefer CI. Note where you have identified your own philosophical priority in making that statement of why you consider CI to be "more legitimate"-- that it is closer to shutting up and calculating. Note that someone who really does prefer shutting up and calculating (I've met many who claimed that, none who ever actually did) could easily claim CI is not legitimate either, on grounds that it is not close enough to shutting up and calculating!Now, I personally don't think CI is free of conceptual difficulties either. But I would say that CI comes closer to being a legitimate interpretation of quantum mechanics than does MWI, probably because CI is really not too far removed from just shutting up and calculating.
kith said:What is the cause of decoherence? Interactions with the environment.
kith said:Thus in isolation, there is no splitting. If v splits it is not isolated.
kith said:Also note that Schrödinger's equation does hold in QFT. See for example this wikipedia entry, where the free-field Hamiltonian is given.
Ken G said:You are saying that anyone who claims to have an interpretation must make a demonstrable link from their interpretation to the equations they are using...
Ken G said:I actually don't think any interpretation in the history of physics can satisfy that demand... If I interpret forces as real but action as a mathematical trick, according to your stated criteria, I could never use a Lagrangian approach to calculate a constraint force...
Ken G said:I feel the actual standard we should hold interpretations to needs to be much looser-- they need to give us a sense that we understand the meaning of the operations we are carrying out.
Ken G said:But it certainly isn't fair to drop any of those things on the doorstep of MWI, because they all fall on the doorstep of any interpretation of nonrelativistic quantum mechanics.
Ken G said:Actually, I don't think there is a requirement for the subsystem v to not interact with anything else, the sole requirement is that it not interact with anything else in a way that leaves a signature or trace.
Ken G said:The fundamental connection between the worlds is the maintenance of unitarity of the whole, and that might require all kinds of "interactions" between the systems, much like entanglements in the EPR paradox.
Ken G said:I don't see where MWI is missing that, it uses the projection postulate just like it uses the Born rule, just like someone who doesn't think gravity is really a force can still write F=mg without making themselves some kind of liar!
Ken G said:All they are doing is parsing between what they know is an effective theory, and what they think is "actually happening"…
If you omit the "and MWI is impossible" yes, this is one of the points I'm trying to make. Maybe this seems nonsensical to you, but we should really finish the decoherence discussion first.Samshorn said:That's completely wrong. The unvierse is an isolated system, so according to you there is no splitting, and MWI is impossible. Is this the point you are trying to make?
kith said:If you omit the "and MWI is impossible" yes, this is one of the points I'm trying to make. Maybe this seems nonsensical to you...
