> On 27 Jan 2021, at 23:28, Bruce Kellett <[email protected]> wrote: > > On Thu, Jan 28, 2021 at 3:08 AM Bruno Marchal <[email protected] > <mailto:[email protected]>> 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 [email protected] > <mailto:[email protected]>. > 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/C18F63B5-08D2-42A2-92C4-63E09E8E7675%40ulb.ac.be.
