Russell Standish writes:

[quoting Norman Samish]
> Suppose we take ten apparently identical ball bearings and put stickers on
> each with the identifiers "1" through "10."  We leave the room where the
> balls with stickers are, and a robot removes the stickers and mixes the
> balls up so that we don't which ball is which. However, the robot remembers > which sticker belongs on which ball. We come back into the room and pick > one ball at random to destroy by melting it in an electric furnace. If at > this point we ask "What is the probability that the destroyed ball is ball > '3'?" we can truthfully answer "My memory tells me that the destroyed ball
> has a one in ten probability of being '3.' "
>
> However, by reviewing the robot's record we can see that "6" was, in fact,
> the one destroyed.
>
> Does this mean that the quantum wave functions of all ten balls collapsed at > the moment we viewed the record and observed what happened to "6"? Or did > the wave function never exist, since the robot's record always showed the
> identity of the destroyed ball, irrespective of whether a human observed
> this identity or not?

Yes and no. In a 3rd person description of the situation, the
Multiverse has decohered into 10 distinct universes at the moment the
robot decides which ball it picks up. What about the 1st person
description? According to the interpretation I follow, the observer is
in fact superposed over all 10 branches, and only collapses into a
single branch the moment the observer becomes aware of the robot's
record.

A more conventional physics interpretation would have the conscious
observer as belonging to a definite branch since the Multiverse
decohered, but not knowing which. I understand that David Deutsch
holds this interpretation, for example.

There is certainly no 3rd person experiment that can be done to
distinguish between these two interpretations, and the only 1st person
experiment I can think of relates to tests of quantum immortality. I
find it hard to believe the "no cul-de-sac" conjecture would hold in
the latter case.

If you accept that it makes no first person difference whether there is one or many instantiations of the same observer moment - that it is all one observer moment - then it becomes meaningless to ask whether the observer belongs to just one or to a superposition of all of the instantiations. How would QTI distinguish between the two interpretations?

--Stathis Papaioannou

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