On 10/15/2019 1:46 PM, John Clark wrote:
On Mon, Oct 14, 2019 at 6:22 PM 'Brent Meeker'
<everything-list@googlegroups.com
<mailto:everything-list@googlegroups.com>> wrote:
>>This is physics not mathematics, the Born rule isn't derived
it's observed, and it's observed to work.
/> But then MWI can't claim to be simpler and "purer" than CI. /
CI says the laws of physics work one way if a system is not observed
and another way if it is observed, and it never makes clear what
observed means. The MWI says the laws of physics only work one way and
it makes crystal clear what observed means. And I don't know about
purer but MWI is certainly simpler than interpretations that are
compelled to add extra terms to Schrodinger's Equation that, other
than get rid of other worlds, do nothing but complicate a already
hideously complicated calculation.
>> I like Many Worlds because it gives me a little intuitive
understanding why we can only make probabilistic predictions
even though the underlying mathematics is completely
deterministic, and I like it because it gives a precise
definition of "measurement".
/> That your consciousness becomes correlated with an eigenvalue
of some Hermitean operator?/
No.
> Does MWI define when a measurement has taken place or not?
It does.
> /What is this precise definition of which you write? /
Oh for christ sake! As I've said over and over, in Many Worlds a
change, any change, is equivalent to a measurement and it doesn't make
the slightest difference if that change involves consciousness or not.
If Brent Meeker flips a coin and it comes out heads then obviously
that Brent Meeker is not living in the world where it came out tails.
Any change?? What about the world in which a K40 atom in JKC's blood
stream decayed compared to one in which it didn't? What about the one
were this N2 molecule bounced left instead of right on colliding with
that CO2 molecule?
In the same way if you do the two slit experiment and the photon goes
through slit A then you are not living in the world where it went
through slot B, but the 2 slit experiment can be a little different from
the simple coin toss example.
If after the photon makes its decision on which of the 2 slits to go
through it then hits a photographic plate then both photons in both
universes are destroyed and thus there is no longer any difference
between the two, so the universes will merge back together. So in that
newly re-merged universe there will be ambiguity about which slit the
photon actually went through which is why that photon will contribute
to the interference pattern that shows up on the photographic plate.
The important thing is that the photographic plate destroys the photon
in both universes so you could replace the plate with a brick wall and
the same thing would happen, it would just be harder to tell that
something funny was going on.
However if you had a detector next to each slit and sent information
on which slit the photon went through to your computer then there
would still be a physical difference between universes even though the
photon no longer exists in either, one universe would have computer in
it with a few magnetic spots on its disk drive indicating the photon
went through slot A but in the other universe the magnetic spots would
be in a slightly different place indicating slot B, so the universes
remain different, so they don't remerge, so there is no ambiguity in
either universe, so neither universe will see a interference pattern.
Universes don't usually merge back together because the differences
between them usually accelerates so it's astronomically unlikely they
will ever become identical again, however a skilled experimenter can
make the change to be very small and then can gently nudge them back
together.
Well in practice he has to measure them in an orthogonal basis in order
to erase the welcher weg.
Brent
If you got rid of the film (or the brick wall) and let the photon head
out into infinite space after it passed the slits then the universes,
and you, will split and never recombine, and so of course you will see
no interference effect. The beautiful part of the theory is that it
doesn't have to explain what an observer is and that's why a brick
wall will work just as well as a photographic plate.
John K Clark
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