So? This does not imply an internal inconsistency.
I’m not sure what the argument is you’re making here; neither of these have anything to do with vacuum fluctuations or their decohering effects…?
Well, I’m just saying that I don’t get where that radical departure lies. You can still propose a perfectly sensible ‘relative state’-description of physics even in a world populated by zombies. The ‘awareness’ of anything of a measurement outcome does not have to go beyond a pointer pointing somewhere—you just need a correlation between two systems, one of which you consider the object, and the other the measurement apparatus.
I didn’t necessarily mean you with the uncharitability, but simply the way the discussion is generally framed, which I see as much too simplistic. Everyone argues that (their favorite interpretation) is better than the Copenhagen one, while simultaneously, nobody seems to be able to agree what exactly the Copenhagen interpretation is, and very little of what then is attributed to the Copenhageners does seem to be in good accord with what they actually proposed.
Well, I can’t really point you to any good references (I haven’t read the article on the Stanford Encyclopedia of Philosophy, but they’re usually pretty good), but as I said, many think of consistent histories as a continuation of the spirit of Copenhagen theory, mainly giving an explicit formulation for the different complementary viewpoints—namely the histories; also, I’ve sometimes heard a more subjectivist take on things, in which quantum states simply encapsulate our knowledge about a system, where the wave function collapse as such is no more problematic than the Bayesian updating of a probability distribution upon learning new information (and does not require a ‘suspension’ of the usual laws of quantum mechanics anymore than the analogous process in a classical stochastic theory requires a suspension of its laws). The modern offshoot of this is probably quantum Bayesianism (QBism) by Fuchs, Caves, Schack et al. (and also David Mermin of late). Though such a subjective viewpoint would probably be associated more with Heisenberg than with Bohr. (I think I remember Heisenberg discussing something like this in an essay somewhere in “Quantum Theory and Philosophy”.)
Well, I’m not sure about that since I would have to go back and see if they’ve pinned down the precise mechanism that creates the entangled state that permits magnetic field detection in some birds and coherent propagation (?) in photosynthesis. I suspect that vacuum fluctuations do play some role, but that might be above my pay grade.
Either way, it wasn’t essential to the point I wanted to make. The idea was much simpler. It was just that biological systems can actively manipulate quantum effects of various kinds and therefore it’s premature to reject out of hand an entire class of possible phenomena - even if some of their leading proponents happen to skew to truly alternate realities.
Having now read the article, I indeed heartily recommend it. It does a very good job at clarifying the notion of complementarity and Bohr’s views on wave functions, resp. any purported ‘collapses’ thereof.
Any interaction creates entanglement. In the case of the birds, a photon interacts with two electrons, which then are entangled; in the photosynthesis case, I don’t think entanglement is involved at all, it’s just that the quantized vibrations of complex proteins remain coherent much longer than naive models would have indicated. There’s nothing about vacuum fluctuations.
I’m not sure what you mean by ‘manipulating quantum effects’; they make use of quantum effects that one would generally not think to persist at the relevant scales (the wet, warm and wild environment of biology), in order to accomplish tasks more efficiently than would perhaps be possible classically—similar to how present-day or near-future applications of quantum communication or computation use quantum effects to accomplish classically difficult (or even impossible) tasks. But there’s, in a sense, nothing ‘new’ there: the quantum effects that are being used are perfectly ordinary.
And I’m also not sure what ‘entire class of possible phenomena’ you think is being rejected, and by whom…
In fact, any inference about the interpretation of fundamental quantum behavior, even by physicists whose research area is in quantum mechanics, is worthless unless that interpretation can be experimentally distinguished from other interpretations. The sum total of all interpretations gives precisely the same indistinguishable result from a given starting condition.
It should also be understood that the entire “waveform collapse” action is (as far as we can tell) nothing but a mathematical formalism to give a starting point from which to begin simulating the behavior of the system, analagous to beginning a steam cycle calculation with the working fluid already at a state elevated pressure and temperature without any prior history. It treats the quantum system as a completely isolated system from the beginning of all time up to the moment of calculation, and then initiates the action by allowing this “collapse” from a stocahstic state to an explicitly deterministic one. However, unless you are a solipsist, it is difficult to conceive that the entire world is awaiting your particular consciousness before congealing from a superposition of all possible permutations of states. The “Wigner’s Friend” experiment highlights the absurdity of this line of thinking, and when conceived ad infinitum requires that the particular observer is necessary in order to collapse the global superposition of all waveforms.
At the level of the macroscopic world, all of this business about collapsing waveforms and other individual actions are completely hidden. We don’t observe any kind of collapse, only a result that is consistent with the mathematical description of such an interaction, but this is not a unique intrepretation as it can also result from any number of hidden variable or relative state intrepretations. None of these requie consciousness or free will to occur; these conditions are tacked on in order to give consciousness, which itself is a very nebulously defined and poorly understood process, some special place in the universe and is ultimately just a modern manifestation of the assumption that human beings are in some way particularly special in the universe.
Here are a couple of previous threads on decoherence and measurement/observation in quantum mechanics:
[POST=9054751]How well defined is the size boundry between quantum and macroscopic objects?[/POST]
[THREAD=597846]What does the term “measurement” mean in quantum mechanics?[/THREAD]
That is not to say that we understand everything, or indeed, hardly anything about the fundamental behavior at the quantum level. We can describe the interactions in a way that is consistent with observation of the resulting states, but that just means that the math works at describing the beginning and end states, and does not give insight into what occurs “in-between” (or indeed, if there is any intermediate condition between quantum states). In other words, it is like watching a train entering one side of a tunnel and exiting on the other side; we can infer what may have gone on inside the tunnel, and we certainly assume that it will come out the other side with momentum and length conserved, but we have no way of observing or measuring what goes on inside the tunnel.
The reality is that our difficulty in understanding quantum mechanical behavior–such as the so-called particle/wave duality–stems from trying to force our conception of the world based upon macroscopic behavior onto the quantum level. The reality is that behavior on the quantum level is neither quite like classical particle or wave mechanics, and instead has its own rules of interaction tha we can only roughly approximate in conventional terms.
While consciousness is not required to explain quantum mechanics (or vice versa, insofar as we can explain consciousness at all), it is not at all surprising to find that some macroscopic phenomena may involve systematic interactions at the quantum level such as entanglement. This isn’t flaketastic pseudoscience; a perusal of technical hard science journals, including Nature and the Journal of Biological Physics, indicates papers on that particular topic from UC Berkeley, Cambridge University, and Okinawa Institute of Science and Technology. We may not be able to model these types of system-level interactions with the relatively crude discrete mechanical rules that we currently employ with individual interactions, but that just means that we know so little about the real nature of behavior at the quantum level that we are as fumbling in the dark as the occupants of Plato’s cave. If quantum entanglement is involved in consciousness, it is unquestionably not some special or exclusive mechanic, but just an extension of basic quantum inteactions at the electrochemical level.
Stranger
All I can do is ask that you take a look at the links I gave, if that’s possible. I know a lot of the ones I use tend to require a subscription.
I can’t tell if you’re trivializing what’s going on in the examples I gave or not. To the extent that quantum effects exist all around us, yes. That is barely worth mentioning. Using them to amplify a signal or find the most efficient transfer of energy though, I’m not sure that you’re really seeing how significant that is or that you realize just how recently that has even been considered plausible.
As to the lunatic fringe, I was going back to the article I referenced on time-like entanglement as to which you also seemed to be nonplussed. So since I’m batting a solid 0.000 at this point, I’m more inclined to just assume I’m not going anywhere with this.
Many worlds asserts that universal wave function is the reality, but empirical physical reality, nevertheless is still described by a projection of that wave function and that is where the many worlds class of interpretations run into their biggest problem: relating the ontology to the empirical reality, which why for example it has a hard time explaining observed probabilities (of course the numbers relating to probabilistic are still contained with the wave function, but why on Earth they should relate to observed probabilities is not clear at all).
Not that many worlds isn’t rightly one of the leading interpretations, just that it is not necessarily a cornucopia for quantum mechanics conceptual problems.
This is shifting the argument. The MWI has its own problems, but it is not internally inconsistent, and it would be a pretty miraculous coincidence that the most parsimonious assumption of only Schrodinger evolution being true should also happen to itself contain the explanation for the appearance of wave function collapse. Also please be aware that how the wave function should relate to observed probabilities is not “not clear at all.” It is certainly not any less clear than in other interpretations. It’s only deficit is that so far, no one has been able to unequivocally go further than the others in explaining the origin of the Borne rule. The fact that the potential even exists in the MWI should be interpreted as a feather in its cap rather than a conceptual problem when comparing it to interpretations for which it is merely an axiom.
The classical theory does not contain superposition. The point of the measurement problem is to explain why measurements cause the collapse of superposition. In Everettian QM, the apparent collapse of superposition is the end result of the assumption (in addition to unitary QM) that consciousness is not in a macroscopic superposition. If it were otherwise, then Everettian anthropic selection would include consciousnesses in superpositions with macroscopic objects, and the appearance of collapse could not be explained.
[ETA] Note that this is not internally inconsistent; it is the whole point of MWI: each consciousness is a trace over delta functions that are part of the wave function, and each trace is mathematically equivalent to a separate “universe.”
I can’t remember saying it was inconsistent. How parsimonious it is depends on how you look at it. The universal wave function, by its nature, is completely unconstructable and like I’ve said it is only projections of that wave function that actually describe empirical reality. The difference between many worlds and other interpretations is that many worlds needs to derive the Born rule as it doesn’t assume it. So far though attempts to derive the Born rule in many worlds theory haven’t been entirely convincing.
The bolded part confuses me, surely in the many worlds interpretation ‘consciousness’, if exists in a way that makes sense for it to be in a superposition of states or not, IS in a superposition of states which leads to an extension of many worlds theory like many minds theory.
Well, masturbating on a beach does tend to leave you contemplative…
I don’t follow. In MWI (and also in Many Minds, I think), each consciousness is assumed to correspond to a classical (“delta function”) subset of the wave function. Since the wave function is continuous, it represents the evolution of a collection of an infinite number of such subsets. Each subset is by definition not in superposition. This fact is what allows the appearance of decoherence to happen. To take it to an extreme, if a consciousness existed across the entire universal wave function, then trivially it would not observe collapse.
You didn’t. But you did respond to my saying that Copenhagen is inconsistent with the assertion that the MWI had similar conceptual difficulties. My point is that no, it does not have similar conceptual difficulties. Like any theory, however, there are still things that need to be fleshed out. You could validly call them “difficulties”. But they are not similar conceptual difficulties to what plagues Copenhagen, which is just logically inconsistent (and further, unnecessarily so). You seem to be trying to put these interpretations on equal standing. I’m saying they should not be. First and foremost logically inconsistent interpretations can be demoted, and after that you can argue about things like parsimony.
Well, the part of it that is scientifically relevant is constructable given a projection as a starting point. From that starting point, it is the utmost of parsimony: all that is assumed is Schrodinger evolution.
But MWI certaintly can derive Born rule using any number of assumptions which are no less arbitrary than the Born rule that is taken as an axiom in Copenhagen. The hope is that it can be derived using a less arbitrary assumption, perhaps one that is intuitive and enlightening. There have already been such arguments made which come close, in my opinion.
In ordinary quantum mechanics, the Born rule follows straightforwardly from Gleason’s theorem, which states roughly that the only viable probability measures in complex Hilbert spaces are the density operators. The problem for many worlds is that there seems to be no reason that these probabilities should relate at all to the likelihood of finding oneself in one branch or another.
Or put differently, any sequence of measurement results occurs in some branch or another; why those branches in which the results obey the quantum statistics should be preferred over those in which they don’t is not at all clear. In fact, since there are more ways for the frequencies to disagree with quantum theory than to agree with it, on the harshest reading, many worlds actually predicts the wrong statistics and is thus empirically inadequate. (This however assumes that the ‘counting measure’ is a good measure for worlds, which seems equally unjustified.)
Why is conscious awareness of some experiment outcome more special than a pointer pointing somewhere, indicating the measurement outcome? If you have to make the extra assumption (which of course ruins the parsimony argument) that consciousness is not in a macroscopic superposition, then you could just as well make the assumption that pointer observables are not in a macroscopic superposition.
(It’s also not at all clear to me that Everett actually makes such an assumption. In fact, it seems to me that on the most conservative reading of his works, he’s just fine with one and the same physical object having more than one physical state, and that every state of any other object is simply assigned relative to one particular of these states. I don’t recall consciousness being excluded from this anywhere.)
And besides, the fact whether a given observer’s consciousness is in superposition is not accessible to that observer: if he believes himself to be in a definite state upon observing any of a given set of alternatives, then, by the linearity of the dynamics, he believes himself to be in a definite state upon observing a superposition of these alternatives (consequently being in a superposition himself). This forms the basis of what’s sometimes called the ‘bare theory’ reading of Everett.
First of all, I think that the way our minds work here sufficiently different that we are talking past each other. The way I see it, Gleason’s theorem obviously must also apply to MWI. The only “problem” is that the equivalence has yet to be explicitly shown. The fact that it has shown to be true for “ordinary” QM is due to the implicit assumption that the wave functions have anything to do with probability at all. This mind sound silly to you, but I think it is not. The big difference here between “ordinary QM” and MWI is that in MWI you do not have to make such an assumption. The anthropic selection out of the larger wave function clearly motivates the existence of a probability measure, without first assuming that the wave function must have anything to do with probability. This, I think, is deep. The details of showing that the specific Born rule is bourne from the Everettian view of the wave function must be worked out, to be sure, but then again hardly anyone seems to be working seriously on this problem, and it’s not an easy one. But the fact that it is hard should not be a reflection on the theory itself. Solving the 3-body problem is hard, but that does not reflect a problem with Newtonian mechanics. The fact that intuitively it makes sense that some probability measure at all should come of MWI is itself an extraordinary fact that I think you may not be appreciating.
No, it does not ruin the parsimony argument (although you saying that is already annoyingly unfair because even assuming the extra assumption the theory is still more parsimonious than alternatives). The assumption is not necessary because without the assumption, the theory predicts that if the most fecund consciousness is able to exist in superposition, then there would be no collapse. The fact that we see collapse is simply evidence that our consciousnesses are not existing in macroscopic superposition.
I don’t follow your point about pointer observables (I think because you are not following my point). The a reason conscious awareness is more special than a pointer observable is because conscious awareness is not in superposition, whereas if you don’t consider consciousness at all you have no way of preferencing pointer observables that are in a macroscopic superposition from those that aren’t, and therefore you don’t predict collapse.
I don’t follow you here. If his consciousness is in a macroscopic superposition, then by definition he is consciously aware of, for example, the electron being both spin up and spin down. This is not something observed in nature by conscious humans.
It does, there’s just no reason that it should give the probabilities of finding yourself in a given branch. As I said, all sequences of measurement outcomes are realized in certain branches; that we only observe those agreeing with QM is an extra fact that needs explaining. And you don’t need to assume any probabilistic interpretation of the wave function in order to get Gleason’s theorem and hence Born probabilities; all you need is the event structure of quantum mechanics, that is, that propositions about a system are represented by the closed subspaces of Hilbert space.
This is pretty much orthogonal to the common view, at least as far as I am aware of it. Many worlds after all is a deterministic theory; to get anything probabilistic out of it, you already have to confront some deep interpretational troubles, since the only kind of probability left in a deterministic theory is an ignorance probability. On the most immediate reading, it’s absolutely meaningless to ask questions like: “what is the probability that I observe A instead of B?” in the many worlds interpretation, because you won’t observe A instead of B; you’ll observe both.
You say that because we never observe consciousness to be in superposition; but we also never observe pointer observables in superposition.
But he would not be consciously aware of being in a superposition. Let’s say I am a faithful observer for the states |0> and |1>, such that from an initial |ready> state, the evolution of the system consisting of me and the electron (say) is the following:
|ready>|0> –> |“0”>|0>
|ready>|1> –> |“1”>|1>,
where |“1”> and |“0”> are the states of me being ‘aware’ (in whatever sense) of the electron’s state being |1> or |0>. Let’s also say I can check whether I have made some definite observation, i.e. I will be in an eigenstate |Def!> of believing to have made a definite observation whenever it is the case that I have, in fact, made a definite observation. Then the evolution is:
|Def?>|ready>|0> –> |Def?>|“0”>|0> –> |Def!>|“0”>|0>
|Def?>|ready>|1> –> |Def?>|“1”>|1> –> |Def!>|“1”>|1>,
such that after each observation, I can check and faithfully discover that I have made some definite observation (otherwise, I could not know that I indeed have done so).
But what happens if we start with a general (unnormalized) state |0> + |1>? Well, as I said, by the linearity of the dynamics:
|Def?>|ready>(|0> + |1>) –> |Def?>(|“0”>|0> + |“1”>|1>) –> |Def!>|“0”>|0> + |Def!>|“1”>|1>
=|Def!>(|“0”>|0> + |“1”>|1>),
such that I again find myself in an eigenstate of believing to have made a definite observation. Thus, even if I were in a superposition, I could never discover the fact, i.e. never form any belief according to it.
I’m not sure that many worlds does say this, but this view is highly problematic. When you say each consciousness corresponds to a delta function, you mean it corresponds to an idealized measurement. Obviously no measurement is idealized, actual measurements never give precise results, but far worse than that it is only a useful fiction to say that a Dirac delta function [i.e. a function of the form δ(x-x’) where δ(x) is the Dirac delta function] corresponds to the state of the wave function after an idealized measurement on an observable with a continuous spectrum. A Dirac delta function is not an eigenstate of any observable and it is not a solution to the Schrodinger equation.
Also the HUP tells that for example that if something has sharply defined position, it’s momentum cannot be defined at all, so even if we allow the fiction of Dirac delta functions as actual states they are completely unlike classical states where position and momentum are both reasonably well-defined.
In many worlds’ 'no collapse view, the inability to observe interference effects associated with a superposition, does not mean that something is not a superposition of states, just that there’s been a branching of the universal wave function.
No, I do not mean that.
The point is that you have a wave function written in some basis. Let’s say the x-basis. You can always write that wave function as a linear combination of multiple wave functions. If you want, you can write your wave function as an infinite number of sharply peaked, non-overlapping wave functions. The MWI simply reinterprets each of these wave functions as being separately ontic. There is indeed a difficulty in trying to change this “preferred” basis once you have started this process in one basis. However this is just a complicated book-keeping problem. You can stay in the basis you started with and that’s fine. You can also start in a different basis, and show that the predictions are the same.
Huh? This is just wrong.
Of course they are unlike classical states. They are quantum states. The MWI is QM, remember. I think you haven’t shifted your intuition into the MWI view. Let’s take an example. In the x basis we have a delta function for the position. In the p basis it’s a plane-wave. In the MWI we choose a basis. Let’s choose the x basis. We can time evolve the x-basis wave function without having to check-in on the p-basis wave function. This means that despite the HUP, we can start in a universe that is delta-peaked in x, that’s fine. It’s just that as the worlds split (ie the wave function diffuses and we reinterpret the diffused wave function as being a sum of pieces) many of the pieces will find their x-position changing as though they had some initial momentum. It is all perfectly consistent. And if you want you can start in the p-basis. Here there are infinitely many pieces of the wave function, each with different momenta. This is completely consistent with the infinitely many wave functions in the x-basis as the wave function diffuses in response to the uncertainty in momenta as seen from the p-basis.
Why not? There are densities of branches. It seems natural that branch density would correspond to probability density.
This I don’t understand. Decoherence! Consistent Histories!
Again I don’t understand. You have an abstract theory in which a wave function evolves according to a differential equation. This has nothing to do with physics, events, or probabilities. There is a big jump to Gleason’s theorem from what is a purely mathematical structure. There is an assumption hidden in there.
One copy of you observes A, another copy observes B. There is an anthropic selection such that there is a 50% probability of finding yourself to be the copy that observes A or B. This is not confronting deep interpretational troubles. This, as I see it, is the very point of the MWI.
Huh? Pointer variables can be in superposition.
Your interpretation of your last line is incorrect: |Def!>(|“0”>|0> + |“1”>|1>) shows that you find yourself in a state of having made a definite observation: of both outcomes happening simultaneously. In other words you are consciously aware of quantum superposition, which is what I have been saying.