# Re: MWI and Born's rule / Bruce

`On Fri, Feb 14, 2020 at 9:48 PM Alan Grayson <agrayson2...@gmail.com> wrote:`
```
> On Friday, February 14, 2020 at 2:49:44 AM UTC-7, Bruce wrote:
>>
>> On Fri, Feb 14, 2020 at 8:45 PM Alan Grayson <agrays...@gmail.com> wrote:
>>
>>> On Friday, February 14, 2020 at 2:34:59 AM UTC-7, Bruce wrote:
>>>>
>>>> On Fri, Feb 14, 2020 at 7:56 PM Alan Grayson <agrays...@gmail.com>
>>>> wrote:
>>>>
>>>>> On Thursday, February 13, 2020 at 4:33:52 PM UTC-7, Brent wrote:
>>>>>>
>>>>>> On 2/13/2020 1:17 PM, Alan Grayson wrote:
>>>>>>
>>>>>> Bruce argues that the MWI and Born's rule are incompatible. I don't
>>>>>> understand his argument, no doubt my failing.
>>>>>>
>>>>>>
>>>>>> 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
>>>>>
>>>>
>>>> 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.
>>>>
>>>> Bruce
>>>>
>>>
>>> But won't the hypothetical observers in OTHER worlds get the same
>>> ensembles and thus the same distributions? AG
>>>
>>
>> No, The point of MWI is that other worlds get different data.
>>
>> Bruce
>>
>
> On each individual trial of course, with the exception that some outcomes
> have the identical probability.  But since the ensembles are generated by
> the same wf, I think they're identical.  AG
>

Think again. If there are N repetitions of the measurement with two
possible outcomes, there are 2^N different sets of results. some sets have
the same or similar frequencies, but others have very different
frequencies. So many different ideas about the probabilities are obtained
in different branches. The wave function does not affect this result.

Bruce

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