# Re: MWI and Born's rule / Bruce

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On 2/14/2020 1:34 AM, Bruce Kellett wrote:
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On Fri, Feb 14, 2020 at 7:56 PM Alan Grayson <agrayson2...@gmail.com <mailto:agrayson2...@gmail.com>> wrote:
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On Thursday, February 13, 2020 at 4:33:52 PM UTC-7, Brent wrote:

On 2/13/2020 1:17 PM, Alan Grayson wrote:
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Bruce argues that the MWI and Born's rule are
incompatible. I don't understand his argument, no doubt
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my failing.
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I don't think they are incompatible; it's just that the Born
rule has to stuck in somehow.  It's not implicit in the SWE
and can't be derived from the linear evolution.  Somehow a
probability has to be introduced.  Once there is a probability
measure, then it can be argued via Gleason's theorem that the
only consistent measure is the Born rule.

Brent

I think what Bruce is trying to show, is that using the MWI, one
CANNOT derive Born's rule as claimed by its advocates. But whether
one affirms MWI or not, the only thing one has to work with is an
ensemble generated by measurements in THIS world. So if you cannot
derive Born's rule using a one-world theory, it would seem
impossible to do so with many-worlds, since in operational terms
-- what is observed -- the two interpretations are
indistinguishable.  AG

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That's quite an astute observation, Alan. The thing is, we can move on from there. If Many-worlds is true, all possible sets of measurements are generated, and most will give different values for the probabilities. For the observers getting the alternative data, there is nothing to tell them that they are getting the wrong answer. MWI is incoherent.
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Since it's an interpretation, not a theory, then there's nothing to tell us we're getting the wrong answer either.  We only think "answers" are wrong if they aren't replicated.
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Brent

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Bruce

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```            ISTM that whether we affirm one world or many worlds, all
we can ever measure is what observe in this world, and it
is from this world that we generate an ensemble after
many trials from which to observe and affirm Born's rule.
What am I missing, if anything? TIA, AG

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