> On 27 Jan 2021, at 23:28, Bruce Kellett <bhkellet...@gmail.com> wrote: > > On Thu, Jan 28, 2021 at 3:08 AM Bruno Marchal <marc...@ulb.ac.be > <mailto:marc...@ulb.ac.be>> wrote: > > Also, worlds interfere statistically, by do not interact at all. A term in a > superposition cannot interact with any other terms, but we can make them > interfering, like with the two slits. > > > Your grasp of the relevant physics is rather tenuous, I'm afraid Bruno.The > idea of "worlds interfering statistically without interacting" is just a > nonsense. There can only be interference if there is an interaction.
See Weinstein for good explanation on this, and a proof that if we allow interaction between, the “Everett world”, we violate thermodynamic and GR. > And there certainly is an interaction between the photons on the two possible > paths in the two slit experiment. The two paths arrive at the screen with > different amplitudes and phases -- if the signs are the same, they add. But > if the signs are different they cancel -- partially or completely depending > on the relative amplitudes. That is not a physical interaction between the photon(s). The amplitude concerne the wave, which describes the worlds/histories. > > The trouble is that David Deutsch has really screwed up the understanding of > "worlds" for a lot of people. I got the "Many-Words Interpretation” from Mechanism, and this for any physical reality compatible with mechanism, well before I knew anything on quantum mechanics. Only later I got the formalism. If you believe in 2+2=4 & Co, and in the Indexical Digital Mechanist hypothesis, the “many-worlds”, or better “the many histories” are unavoidable (where an history is a computation as seen from universal+ machine supported by that computation). Then, if the founders dod not realise the MW aspect of quantum mechanics, they would not have invented a wave-collapse, which is trick to make them disappear. Everett showed just that we don’t need that trick, which is nice as it lead to many difficulties. > He has talked as though each path in the two slit case is a separate "world", > and then has to resort to magic to reproduce the interference. The Everett > concept of a "world" is a "relative state", in which an "observer" sees a > definite result. This idea was made more precise with the introduction of the > idea of decoherence, and generalized entanglement with the environment. If > "worlds" are defined as the result of decoherent histories, then Deutsch's > confusion should not arise. A "world" is the result of (FAPP irreversible) > decoherence. OK. Thanks to the quote for “world”. > There is no decoherence at the slits in the two slit experiment, so no > separate "worlds" are formed. But locally you do have a superposition of an history (going to this slit + going through the other slits), like in a quantum computer you can superpose different computations (and then make the result interning in a way such that a minimum of realism entails that you can understand that all computations have been performed. > If you induce decoherence by measuring at the slits, then the interference > pattern disappears -- you have certainly created a separate "world" for each > path, but these can no longer interfere. That is part of the definition of > the "worlds" that are created by irreversible decoherence. No problem. > > So the concept of "world" is, indeed, well-defined in physics. By giving a magic role to the observer, or its consciousness, or of measurement. The observer can no more be a machine in that picture. > It might not be defined in logic or metaphysics, but this is of no concern to > the working physicist -- we know perfectly well what we mean by "a world”. FAPP. OK. The goal here is to try to understand what happens. > And we can readily tell when someone is talking nonsense by claiming that > "worlds interfere statistically without interacting”. ? (That is rather standard, and pretty obvious, I would say). > The superposition of the paths in the two slit case extends right to the > screen: that is what produces the interference -- superposition means that > the two components are added together with their intrinsic phases intact. If > you destroy the superposition at any point, such as by interacting with the > paths at the slits, Nothing in the SWE allows anyone to destroy a superposition. We can only entangle the state with an unknown complex environment making the observation irreversible, but no superposition is physically destroyed. Even Bohr admitted this in his EPR answer to EPR. > there is no more interference -- you have produced separate "worlds" that can > no longer interact so there is no interference. As Scott Aaronson is fond of > saying: quantum computers work by interference, so the computations must all > occur in one "world”. But then that “one world” becomes a multiverse realising the many-histories. > As Scott recently posted: "BREAKING: President Biden signs executive order > banning people from saying "Quantum computers solve problems by just trying > all possible solutions in parallel”." Lol Bruno > > Bruce > > -- > 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 > <mailto:everything-list+unsubscr...@googlegroups.com>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/everything-list/CAFxXSLQfi1Ximm14BrP659fyrt5O3GH%3DLXH6ntt6GMkUaRbB-g%40mail.gmail.com > > <https://groups.google.com/d/msgid/everything-list/CAFxXSLQfi1Ximm14BrP659fyrt5O3GH%3DLXH6ntt6GMkUaRbB-g%40mail.gmail.com?utm_medium=email&utm_source=footer>. -- 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. 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