On Fri, Mar 4, 2022 at 1:04 AM John Clark <[email protected]> wrote:
> On Wed, Mar 2, 2022 at 7:05 PM Bruce Kellett <[email protected]> > wrote: > > >> Many worlds can explain all known experimental results without >>> resorting to non-local influences because many worlds is not a >>> realistic theory. >>> >> >> > *In that case, if you believe that MWI is local, give me the local >> account of Bell-type correlations of spin measurements at spacelike >> separations.* >> > > OK, the key is understanding what "the collapse of the wave function" > means physically. Many Worlds says everything that is not forbidden is > mandatory so everything Schrodinger's wave equation does not rule out > does physically happen, so "collapse" just means that different solutions > to Schrodinger's equation are ... well... different. And the great virtue > of tautologies is that they're always true. Richard Feynman said all the > weirdness in quantum mechanics can be found in the 2 slit experiment, so I > will use that to illustrate the point. This is how I think Many Worlds > would describe the two-slit experiment and several variations of it. > I take the fact that you have changed the subject to a many worlds account of the two-slit experiment as clear evidence that you do not have a local many worlds account of the question at issue, namely, a local account of Bell-type correlations. Don't worry. No one else has such a local account either. Saibal's account below is every bit as non-local as the original quantum account. Many Worlds says that in the usual experiment the universe splits after the > photon passes the two slits because the 2 worlds are different, a photon in > one world went through the right slit and a photon in another world went > through the left slit. But when the photons hit the film they no longer > exist in either world, so the 2 worlds are identical once more, so the > universes fuse back together again. Looking back from that fused world we > find evidence that the photon went through slit X only and evidence it went > through slit Y only and this causes an interference pattern. There is > nothing special about an observer in any of this, the same thing would > happen if nobody looked at the film, or even if you used a brick wall > instead of film, because the important thing is not that the photon makes a > record (whatever that is) but simply that it is destroyed. Mind has > nothing to do with any of this so unlike the Copenhagen interpretation Many > Worlds doesn't need to explain it, or explain what “measurement" means, or > “record", or “observation", or “consciousness". That is a gargantuan > advantage! The key point is that worlds split when they become different > and merge when they become the same again. > You equivocate on the word "world". What you are really talking about here are just components of a superposed wave function. Such superposed components can interfere, whereas separate worlds (or branches) are disjoint and cannot interfere. Now do the two-slit experiment again but instead of using film to stop the > photon after it passes the slits let the photon head out into infinite > space. If Many Worlds is correct then the entire universe splits into 2 > when the photon hit's the 2 slits and never recombines. There is nothing > special about you the observer, you split just like everything else, you > know that the photon went through one and only one slit, but you don't know > which one. The 2 slit experiment can be set up in such a way that you can > tell which slit the photon went through, but if you do that then the > photons will not produce an interference pattern on the film. This is > because even after the photon hits the film in both worlds and is destroyed > the worlds remain different because in one the physical memory pattern in > your brain encodes that the photon went through slot right and in the > other slot left, so the different worlds don’t merge back together, and so > no interference pattern is seen in either world. > > Many Worlds predicts that even if you could devise an experiment that > could detect which slit the photon went through without changing the photon > in any way (it would pose enormous technical challenges but I think that > might be possible, perhaps by using Stimulated Emission) there still would > be no interference pattern because although the photons are identical the > universes would still be different because your brain has different memory > patterns which means the physical structure of your brain is still > different in the two universes. Separate worlds only emerge if there is a > difference between them, if the worlds evolve in such a way that the > difference disappears then re-coherence occurs. For obvious reasons > re-coherence can only occur if the 2 worlds are only very very slightly > different and have only been separated for a short time, and that's why > experiments of this sort are difficult and it explains why in our everyday > world we don’t see macro objects becoming entangled, and even atoms aren’t > usually entangled for long at room temperature. > > *> I will salute you if you can do this, because no one else has ever >> managed in the past* > > > As much as I'd like to take the credit for it nothing I said is original > with me, I just used my own words to describe what other people have > done. > No, it is not original. And it is not a local account of the correlations under discussion either -- so no lollipops from me!. Bruce > > *Realism is completely beside the point.* > > > Nope. If Many Worlds was a realistic theory and thus a photon always > remained in one and only one definite state both before and after passing > a slit and before and after a measurement is made then none of the above could > possibly work. > -- 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/CAFxXSLT_uiazcjXm7089RVy_8xP7S%2BThtaY4x4gS4TAWQ-sT_w%40mail.gmail.com.
