Bruno Marchal wrote:
> Hi Brent,
>
> On 14 Nov 2008, at 07:02, Brent Meeker wrote:
>
>   
>> I think there is a misunderstanding of the MWI.  Although the  
>> details haven't
>> been worked out (and maybe they won't be, c.f. Dowker and Kent) it  
>> is generally
>> thought that you, as a big hot macroscopic body, do not split into  
>> significantly
>> different Korys because your interaction with the environment keeps  
>> the Kory
>> part of the wave function continuously decohered.  So in a Feynman  
>> path-integral
>> picture, you are a very tight bundle of paths centered around the  
>> classical
>> path.  Only if some microscopic split gets amplified and affects you  
>> do you "split".
>>     
>
>
>
> You cannot use decoherence to introduce a collapse of the wave  
> function. The MW is just the SWE.
> If Kory looks at a spin of particle in the superposition state (up +  
> down), the swe gives
> Kory seeing up + Kory seeing down. 

Which is an example of amplifying (since otherwise Kory couldn't see it) 
a microscopic event.

> Decoherence explains only why none  
> Korys can be aware of their superposition.
> The many-world is just literal QM without collapse, that is, it is the  
> SWE.
> The tightness of the Feynman bundle explains the normality (shortness)  
> of the most probable paths. It explains why in most universe quantum  
> white rabbit are rare.
>   

That was my point.  The SWE indicates that every microscopic event that 
happens or doesn't happen stochastically splits the wave function.  But 
these events don't generally cause a split of Kory or other classical 
objects.  Those "objects" are not in some pure state anyway.  They are 
already "fuzzy" and their interaction with the environment keeps the 
fuzzy bundle along the classical path.  There are microscopic splittings 
that are 'within' the fuzz, but I think these are far below the 
substitution level envisioned for your teleporter thought experiment.

Brent

> I will not insist because it is out of the MGA topic on which, as I  
> said to Tholerus, I will (try to) concentrate
> May be you could search more detalied
> explanations on this that I have already given, and others have given,  
> on the FOR-list.
>
>
>   
>> I doubt that it will ever be possible to build a teleporter.  
>> Lawrence Krauss
>> wrote about the problem in "The Physics of Star Trek".  I'm not sure  
>> what it
>> would mean for Bruno's argument if a teleporter were shown to be  
>> strictly
>> impossible; after all it's just a thought experiment.
>>     
>
>
> You are right. reasoning with thought experiments asks for  
> possibilities in principle, not for possibilities in practice. This is  
> important to understand for the MGA  (as it is for UDA).
>
> best,
>
> Bruno
>
> http://iridia.ulb.ac.be/~marchal/
>
>
>
>
> >
>
>   


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