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 [email protected] 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 [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
