On 13 Apr 2015, at 07:16, Bruce Kellett wrote:
LizR wrote:
<mailto:[email protected]>> wrote:
If we compare this to FPI in the MW Interpretation of quantum
mechanics we see that this is just a branch counting account of
quantum probabilities. Now it is well-known that this fails to
reproduce the correct quantum probabilities in MWI. So FPI as via
Step 3 and FPI as in MWI are intrinsically different.
Does the MWI predict an infinite number of branches from any given
measurement? I'm not sure (from FOR) that the MWI predicts branches
at all, so much as differentiation within a continuum? Maybe you
could expand on this. Why (to keep it simple) would a quantum
experiment with two possible outcomes not reproduce the correct
probabilities in the MWI? (Or is that a special case where it would?)
No, MWI does not predict an infinite number of branches for any
measurement. It predicts a number of branches equal to the number of
possible distinct outcomes for the measurement. The classical
duplication model of step 3 cannot reproduce quantum probabilities
because it relies on branch counting. There are only ever two
branches for a measurement in a 2-dim Hilberst space, but the
probabilities can take on any real values between 0 and 1. Foe a
spin measurement with the appropriate magnet orientation you can
have a probability of 1/pi for Up (and 1 - 1/pi for Down). This
cannot be reproduced by observer duplication as in step 3.
David Deutsh has his own peculiar take on many worlds. Most people
would consider his isea of a 'world' to be premature. In the
developed MWI, with decoherence, eiselection and the rest, a worl
emerges only after decoherence and orthogonalization. In this
picture, worlds are disjoint and can never interfere or recombine.
When we go to the full dovetailer stage we get multiple copies of
the same conscious instant. If we interpret these as repetitions
of
the same quantum experiment (say a Stern-Gerlach spin
measurement),
we get some sequences of Up and Down results. I'm not sure I
understand this. Why do we need to interpret these copies (an
infinite number, if the UD is able to run for an infinite time) as
repetitions of the experiment? Personally, I have only compared the
MWI with step 3 for John Clark's benefit, since he insists there is
some problem with pronouns in step 3, but not in the MWI. The
extent to which they are the same is that they produce both FPI
from splitting or differentiation of fungible observers. But at
this stage there is no need to take this any further. I'm just
trying to help Mr Clark get his head around this particular point,
and since comp assumes classical computation I wouldn't expect it
to reproduce quantum probabilities "simplistically" - if it's going
to work, it needs to produce them as an end result, not be expected
to produce them until the entire logic of the argument has been
examined. (Bruno claims to have produced some sort of quantum
results at the far end of the comp argument, but I haven't got that
far myself.)
But in so far as the duplication ideas of Step 3 are involved, the
Born Rule of quantum probabilities will not be reproduced, since
that cannot be obtained by branch counting in the MWI.
OK. I believe that this is not the intention of step 3. It's only a
metaphorical comparison for people who suffer from pronoun trouble,
or only an exact comparison to the extent that both give a form of
FPI. To assume this is the final result is to be "too quick".
But it is introduced as an illustration of FPI, and the comparison
with MWI is made. I merely point out that this comparison is not
valid.
You did not. You take the MWI before Graham refuted it. Deutsch is
more right on this than most, even in physics. But, we don't postulate
a physical reality, and with UDA-step 7, Deustch view is proved, in
comp. That his solution remains valid for QM is what the math should
show or refute.
As I said in a recent post, I think John Clark's trouble with the
use of personal pronouns stems from a hasty glossing of questions of
personal identity in brain substitution/duplication scenarios. I
find Nozick's closest continuer notion a useful starting point. He
takes personal identity to follow the closest continuer of the
initial state, provided there is no closer or tied continuation. If
there is a tie (as in step 3), the rule is that two new persons are
created. I think this solves John's personal pronoun issue. However,
this does need to be discussed more fully.
OK, but as you seem to have seen, Nozick theory is refuted by
computationalism, through steps 2, 3 and 4.
Bruno
Bruce
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