# Re: The Nature of Contingency: Quantum Physics as Modal Realism

On Sat, Apr 23, 2022 at 11:18 AM George Kahrimanis <gekah...@gmail.com>
wrote:

> On Friday, April 22, 2022 at 1:54:36 AM UTC+3 Bruce wrote:
>
> we now know that MWI is inconsistent with any sensible interpretation of
>> probability; strict MWI is inconsistent with the Born rule.
>
>
> Dittos!!! At least, mostly.
>
> What do you mean "we now know"? Any citations, pretty please?
>

This has been argued by people like Adrian Kent and David Albert. See
Albert's "Mindscape" discussion with Sean Carroll, for example. Or Kent's
contribution to the volume "Many Worlds? Everett, Quantum Theory, and
Reality" (Oxford, 2010).

In claiming that MWI is inconsistent with the Born rule, I point to the
fact that MWI insists that every outcome occurs (in different branches) on
every trial. This means that for the state

a|0> + b|1>

there is a branch with result |0> and another branch with result |1> for
every trial, independent of the coefficients a and b. The Born rule, on the
other hand, says that the probability of obtaining |0> is |a|^2, and the
probability of obtaining |1> is |b|^2. (Note that there is no branching
with the application of the Born rule -- there is just one result, obtained
with the specified probability.) Over N trials, strict MWI (one example of
each result, on different branches) implies that the relative frequency of
|0> and |1> results tends to 0.5 for the majority of branches, regardless
of the coefficients a and b. Whereas the Born rule says the the proportion
of |0> results, for example, will tend to |a|^2  for large N. (Recall that
|a|^2 + |b|^2 = 1). For general and and b, these predictions are
incompatible. So MWI is inconsistent with the Born rule.

Bruce

>

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