Le 06-nov.-08, à 21:45, rmiller a écrit :

>
> At 10:54 AM 11/6/2008, Bruno Marchal wrote:
>
>
>> On 06 Nov 2008, at 02:37, Thomas Laursen wrote:
>>
>>>
>>> Hi everyone, I am a complete layman but still got the illusion that
>>> maybe one day I would be able to understand the probability part of 
>>> MW
>>> if explained in a simple way. I know it's the most controversal part
>>> of MW and that there are several competing understandings of
>>> probability in MW, but still: none of them make sense to me! If every
>>> line of history is realized then how can any line of history be more
>>> probable than any other?
>>
>> Wolf's answer is probably correct, but certainly incomplete. If you
>> take QM (without collapse) norma distribution and measure can be
>> extracted from Gleason theorem. Born rule can be deduce from first
>> person indeterminacy or more politically correct variant through
>> decison theory (like Deutsch and Wallace). It is a whole field. My
>> point in this list consists to show that if you assume the mechanist
>> thesis (like Everett) then even if Deutsch proposal works it is not
>> enough to justify the probabilities. There is a big work which remains
>> to be done, but it has the advantage of taking into account the non
>> communicable part of the experiments (usually known as "the
>> experience"). But there are more abherant histories to evacuate (like
>> infinities in field theories).
>>
>> Anna Wolf's answer can be wrong in case physics is eventually purely
>> discrete, in which case probabilties should arise from pure relative
>> proportion based on dircrete relative partitioning of the multiverse.
>> I think the comp hyp excludes this though, like I think M theory, as
>> far as I grasp something there, too. Loop gravity, if literally true,
>> could lead to such ultimate discretization or provide models.
>>
>> For each position of an electron in your brain there is a (quantum)
>> computational history going through that state, and probabilities are
>> eventually all related self-indiscernibility relations (if it is
>> english).
>>
>> Bruno Marchal
>>
>> http://iridia.ulb.ac.be/~marchal/
>>
>>
>> First of all, Bruno, that answer seemed Palenesque in the extreme,
>> even for someone whose job it is to know this stuff.  The
>> correspondent indicated his was a layman's perspective.

I agree I was a bit quick.



>> How about
>> another go at it without shortcut references to Born, David Deutsch,
>> Wallace (who?) et al.
>>  As a firm believer in the adage that one who
>> really knows the subject should be able to explain it in such a way
>> that a bright ten-year-old can understand the concept.



I love and use this adage very much. I have developed UDA and AGF to 
make the comp mind-body problem comprehensible by 10 years old.
And it works! Later I have discovered that UDA + AGF are more difficult 
for older people because they have take more time to really strengthen 
their (aristotelian) prejudices.
But Thomas Laursen question was interestingly singling out points  we 
have already discussed a lot in this forum, and (I am sorry for not 
having been clear on that) my answer was a mean one for everybody.
Another problem rised by Laursen question is that it is very different 
to answer it in the context where we assume QM (where Many World are 
the Everett quantum Many Worlds), or if we assume comp (discussed a lot 
in the list) wherethe Many World are of a very different nature a 
priori.

Yet, in both case, probabilities arise from self-multiplication.

And in both case the question of how to compute them or to justify them 
is very difficult, nor even solved.

Hope I am a bit more clear.

Bruno

http://iridia.ulb.ac.be/~marchal/


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