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 -- 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/9a6d5bbf-a214-45ef-9cff-4b6eeb8764eb%40googlegroups.com.
