On Wed, Nov 15, 2017 at 10:54:51PM +1100, Bruce Kellett wrote: > On 15/11/2017 5:02 pm, Russell Standish wrote: > > On Wed, Nov 15, 2017 at 02:46:21PM +1100, Bruce Kellett wrote:
> > > I said "one of the strongest"! I know that you want to define QM from the > > > idea of observer moments. I don't think that this will work, and the usual > > > consensus is that one of the strengths of MWI is the elimination of the > > > conscious observer. > > Where's your evidence that this is the usual concensus? Who argues for it? > > Most people, indirectly if not directly. I am thinking of MWI proponents > such as Deutsch and Wallace. Wallace puts it like this "Some have argued > that he measurement problem of quantum mechanics gives us reason to abandon > the picture of science as describing an observer-independent world....". He > does not accept this view. The general view of scientific realism consists > in the belief that the objective external world is independent of the > observer. The thinking is related to Bell's assertion that: "Measurement > should never be introduced as a primitive process in a fundamental > mechanical theory like classical or quantum mechanics..." Measurement, > observation, observers are all related concepts in this context. > Deutsch, I could believe would argue that. But Wheeler would be a counter to that. I'm not that familiar with Wallace. > > > > A conscious observer (or rather just observer, really) is still > > > > required to define the branches of the MWI, be that mediated by Zeh's > > > > decoherence process, or otherwise. To eliminate observers entirely > > > > requires solving the preferred basis problem without reference to an > > > > observer or observation. > > > That is not true. The basis problem is solved by Zurek's einselection -- > > > the > > > preferred basis is the one that is stable against further > > > decoherence. > > I understand that the idea of einselection is still rather > > controversial, > > Not really. See Schlosshauer's paper and book. > I haven't really followed the literature, but it strikes me that problem is that ultimately einselection is not a unitary process, so it has to be considered as the result of some sort of coarse graining (which is, of course, due to the actions of the observer discretising a continuous world), in much the same way as the second law of thermodynamics emerges from a strictly reversible microscopic dynamics. I find it intriguing that the recent critique of Einselection by Kastner is entitled "`Einselection' of Pointer Observables: the new H-Theorem". The H-Theorem, as I'm sure you know, but for the benefit of other lurkers is Bolzmann's mechanism of deriving the second law from coarse graining the revrsible microscopic dynamics. > > but be that as it may, I can't see how it solves the > > preferred basis problem. Consider an experiment where the experimenter > > may choose between inserting a circularly polarised file, or a > > linearly polarised one. The preferred basis (selected by einselection) > > will depend on that choice. > > That is a common misconception, but the angle selected for the polarizer, or > the S-G magnet in a spin measurement, is not a selection of a measurement > basis. The measurement is actually the observation whether or not the > photon/particle passes the filter. It is then an inference from the > observation of a point on a screen, or the firing (or failing to fire) of a > detector of some sort, that the polarization/spin-component was such and > such. You don't actually measure anything in the selected orientation, you > only ever measure whether the particle passed the filter or not. So the > actual measurement is just a position measurement (position on a screen), > and the measurement basis is the position (pointer) basis. > But not all measurements are measurements of the position of something. What about measuring the voltage of a circuit using an A->D converter? Or the measurement of the momentum of a charged particle in an electron multier? > > In MWI, we normally assume that there are > > two branches of the universe with different choices made by the > > experimenter. > > That is really an oversimplification. It is done because it is simpler to > work with two-state systems, and position measurements are of a continuous > variable, so are not neatly two-valued. > The choice between circularly polarised filter and linear polarised filters is binary. Obviously, there follows the choice of orientation, which is continuous... > > Unless there is some sort of superdeterminism in play, > > where the experimenter does not have the freedom to choose. But > > superdeterminism is certainly not a popular idea. > > No, superdeterminism does not have many advocates. > > > > Observers have nothing to do with it. In Zurek's account, it is the fact > > > that the results of interactions, be they measurements or not, are > > > recorded > > > multiple times in the environment via decoherence, that is the mark of an > > > irreversible quantum event. > > If you put a system in contact with a completely symmetric heat bath, > > there will be no preferred basis selected by einselection. > > The environment of a measurement or an interaction is not generally a > symmetric heat bath. If there is no experimenter, just an environment, then we must consider all possible environments in superposition. That will have maximal symmetry. > If you measure a spin component (space quantization) > you get one of two spots on a screen downstream of the S-G magnet. These are > not symmetric wrt the rest of the environment. That is because we're considering an SG experiment, with an SG experimenter. That breaks the symmetry. > In one world the irreversible > record is of an upper spot. In the other world it is of the lower spot. The > distinction is not lost because of symmetry. The basis for the measurement > is the position basis, because that is stable against further decoherence. > The angle of the S-G magnet is not the measurement basis. > > > The only > > way for a basis to emerge is if there are system constraints of some > > sort. I would argue that the only way these constraints could arise in > > a Multiverse (which is symmetric by construction) is by considering > > the environment from the point of view of some observer, ie the basic > > symmetry breaking mechanism. > > The observer is not a general symmetry breaking mechanism. I would argue that observation in a multiverse is a symmetry breaking mechanism. In the multiverse, all possible outcomes of a measurement exist as separate branches, and if all outcomes are equally likely, there is a fundamental symmetry along that measurement axis. But the action of observation fixes the outcome for a particular observer, breaking that symmetry. > The many worlds > in QM are not symmetric anyway. > Not completely, but far more symmetric that the world we inhabit. -- ---------------------------------------------------------------------------- Dr Russell Standish Phone 0425 253119 (mobile) Principal, High Performance Coders Visiting Senior Research Fellow hpco...@hpcoders.com.au Economics, Kingston University http://www.hpcoders.com.au ---------------------------------------------------------------------------- -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. 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