On 8/27/2025 5:07 PM, Bruce Kellett wrote:
On Thu, Aug 28, 2025 at 5:16 AM Brent Meeker <[email protected]> wrote:

    I think some specificity would help this debate.  Suppose N=6, so
    there are 64 different sequences in 64 different worlds.  The
    number of observers is irrelevants; we can suppose the results are
    recorded mechanically in each world.  Further suppose that a=b so
    there is no question of whether amplitudes are being respected. 
    Then in one of the worlds we have 011000.  Per the Born rule its
    probability is 0.2344.  In MWI it is 1/64=0.0156.  The difference
    arises because the observers applying the Born rule looks at it as
    an instance of 2 out of 6 successes.


The trouble with this is that you are treating this as an instance of Bernoulli trials with probability p= 0.5. When every outcome occurs with every trial we no longer have a Binomial distribution The Binomial distribution assumes that you have x successes out of N trials. In the Everettian case you have one success on every trial.

So your probability above for 2 successes applies to Bernoulli trials with one as the 'success'. The thing is that the probability of getting a zero is also 1/2, so we also have four successes out of six trials in your example. The Binomial probability for this result is also 0.2344. Actually, if we regard this experiment as a test of the Born rule, we have four zeros in 6 trials, which gives an estimate of the probability as 4/6 = 0.667, or as two ones in 6 trials which gives an estimate of the probability as 2/6 = 0.333, neither estimate is equivalent to |a|^2 = 0.5. The difference becomes more pronounced as N increases. The problem with your analysis is that you are assuming a binomial distribution. and we do not have any such distribution.
That's how an experimenter will compute the probability of 2 successes in 6 trials given p=0.5.   Yes, the probability estimate is 0.33 given 2 in 6.  The probability of the result given p is not generally the same as the estimate of p given the result.  The former is binomial distributed.  The estimates of p aren't part of a distribution since they don't add up to 1.

Brent


Bruce

    So why can't the MWI observer do the same calculation?  He
    certainly can. /He can apply the Born rule./  But when he does so,
    it can't be interpreted as a probability of his branch since such
    probabilities would add up to much more than 1.0 when summed over
    the 64 different worlds.  From the standpoint of statistics 011000
    is the same as 001010 and their probabilities sum.  Their
    difference is just incidental, but they are different worlds in
    MWI and summing them makes no sense.

    Brent

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