On Tuesday, October 15, 2019 at 6:02:15 AM UTC-5, Philip Thrift wrote: > > > > On Tuesday, October 15, 2019 at 5:48:58 AM UTC-5, Lawrence Crowell wrote: >> >> On Tuesday, October 15, 2019 at 2:24:10 AM UTC-5, Philip Thrift wrote: >>> >>> >>> >>> On Monday, October 14, 2019 at 6:52:24 PM UTC-5, Lawrence Crowell wrote: >>>> >>>> On Monday, October 14, 2019 at 4:44:42 PM UTC-5, Bruce wrote: >>>>> >>>>> On Tue, Oct 15, 2019 at 5:38 AM Philip Thrift <[email protected]> >>>>> wrote: >>>>> >>>>>> On Monday, October 14, 2019 at 1:20:39 PM UTC-5, Brent wrote: >>>>>>> >>>>>>> Part of the dislike of the MWI is that its proponents assume a >>>>>>> purity that is not an evident virtue of the intepretation. For >>>>>>> example, >>>>>>> interpreting the squared amplitudes as probabilities seems to be >>>>>>> assumed, >>>>>>> along with the existence of the preferred basis in which the amplitudes >>>>>>> are >>>>>>> defined. Together these are almost the same as CI. If you ask >>>>>>> "probabilities of what?" in MWI the answer can't be probability of >>>>>>> existing >>>>>>> because MWI has committed to all solutions, however improbable, >>>>>>> existing. >>>>>>> So it becomes probability of finding yourself in a particular >>>>>>> world...which >>>>>>> depends on a theory of consciousness and seems to regress to von >>>>>>> Neumann >>>>>>> and Wigner. >>>>>>> >>>>>>> Zurek's envariance attempts to answer these questions and provide a >>>>>>> justification for preferred bases and what probability refers to. But >>>>>>> notice that to the extent he succeeds he is justifying taking a simple >>>>>>> probabilistic view and saying one of those preferred states happens and >>>>>>> the >>>>>>> others don't. >>>>>>> >>>>>>> Brent >>>>>>> >>>>>>> >>>>>>> >>>>>> In the single-particle double-slit experiment*, an observer could see >>>>>> a dot appear anywhere on a screen where path interference does not >>>>>> reduce >>>>>> the probability to zero. So with the literal many-world-branching >>>>>> theory, >>>>>> how many different worlds are produced, each on with its own observer >>>>>> seeing a dot on the screen? >>>>>> >>>>> >>>>> According to MWI, an infinite number. Each world will have the dot at >>>>> a different place on the screen. >>>>> >>>>> Bruce >>>>> >>>> >>>> What you say may open up a bit of a hole or snag in MWI. This is >>>> something I have been pondering some since Carroll's popularization. If >>>> MWI >>>> fundamentally preserves unitarity by splitting off worlds then >>>> localization >>>> of a measurement is an illusion.Consider a particle measured somewhere on >>>> a >>>> path from x and x'. The path integral and the nonlocality of paths is a >>>> sum over all possible measurements in all space containing x and x', then >>>> there must be a continuum of possible worlds splitting off. If the >>>> operator >>>> has a continuum of eigenvalues *x*|x> = x|x> there must then be a >>>> continuum of possible worlds if there is indeed no fundamental >>>> localization >>>> with a measurement. This is not just infinite, but uncountably infinite. >>>> >>>> This is different from how decoherence maintains unitarity and >>>> conserves qubits. There a local interaction occurs that induces quantum >>>> phase to enter into a set of ancillary states or reservoir of states. Then >>>> we can consider quantum states as finite, but unbounded from above, so >>>> that >>>> local observations and measurements are possible. >>>> >>>> This does seem to run into some oddities that either need to be worked >>>> out or that might indicate some gap in MWI. The persistence of nonlocality >>>> in MWI is interesting for possible quantum gravitation work. In that case >>>> I >>>> can think of maybe a way around this, where this uncountably infinite set >>>> of g_{ij} configurations, or Ψ[g_{ij}], can be identified with "exotic" >>>> manifolds that are removed. It is less clear how this can happen with >>>> ordinary quantum fields that have local realizations. >>>> >>>> LC >>>> >>> >>> >>> >>> To mix an analysis (or a theory) of the path integral with an analysis >>> (or a theory) of MWI is mixing two fundamentally contradictory frameworks >>> that only leads to confusion. >>> >>> @philipthrift >>> >> >> I am thinking of a path integral as most physicists do, which is an >> action principle that is a sum over amplitudes or histories. You are >> thinking according to the quantum interpretation of Dowker and others, >> which has auxiliary postulates or assumptions. >> >> LC >> > > Path integrals or histories are not eve brought up in Sean Carroll's book > (a search of the text shows). > > So they not present in any way in MWI. > > MWI (in Sean's mathematical formulation) is contrary to the path integral, > because histories (as you mention above) are simply not worlds (in Sean's > formulation). > > @philipthrift >
Path integrals are just methods. Three is nothing any different from QM or QFT without them other than a methodology. Dowker et al are jumping off into an interpretation based on path integrals. LC -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/5462422b-789d-4b59-a881-117bd8e0b2af%40googlegroups.com.
