On Fri, Mar 4, 2022 at 1:04 AM John Clark <johnkcl...@gmail.com> wrote:

> On Wed, Mar 2, 2022 at 7:05 PM Bruce Kellett <bhkellet...@gmail.com>
> 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!.


> > *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.

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