On Tuesday, October 15, 2019 at 10:26:15 AM UTC-5, Lawrence Crowell wrote: > > 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 >
There is no interpretation outside of methods. Physicists who pursue "interpretations" without method (without useful application) are wasting their time in fantasyland, as Sean Carroll is doing. See: https://arxiv.org/abs/1807.10749 : *Quantum Supremacy Is Both Closer and Farther than It Appears* Our algorithms can be characterized as *Schrödinger-Feynman hybrids*. Our simulator combines highly-optimized Schrödinger-style simulation within each qubit block and simulates xCZ gates with Feynman-style path summation, to limit memory use. Unlike in Feynman-style simulation, runtime scales with the number of xCZ gates, which is very limited in planar qubitarray architectures with nearest-neighbor gates. Unlike traditional Schrödinger-style simulation, the resulting algorithms are depth-limited, and supercomputer simulations may hold some advantage for very deep circuits. However, near-term quantum computers rely on noisy gates that also limit circuit depth. @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/fecfb1d6-f2c7-4b26-9e1d-cf6a1950a613%40googlegroups.com.
