Bruno Marchal wrote:
> 
> On 08 Jul 2008, at 01:08, Brent Meeker wrote:
> 
>> Ronald Held wrote:
>>> I am giving a talk on the Multiverse to Star Trek fans in several
>>> weeks. I would appreciate any advice and suggestions, since as of  
>>> now,
>>> I have an outline based on Tegmark's four levels.
>>>
>> One thing I would avoid is presenting the multiverse (of any level)  
>> as the
>> latest "gee-whiz, science has discovered that..."  It is interesting
>> speculative metaphysics.  Good fodder for SciFi fans but not yet  
>> science.
> 
> 
> I disagree. It is the collapse axiom which has been a speculation all  
> along: to avoid
> macroscopic superpositions. I totally agree with David Deutsch that QM  
> is the science
> of parallel universes, except that I have abandoned eventually the  
> very notion of
> "primary physical universe",  and I prefer the many histories or many  
> dreams wording
> which fit better with respect to the mind-body problem in the  
> mechanist frame.
> I am not saying that the MW solves all conceptual problems of QM  
> 'course. But the belief
> in the existence and unicity of the Physical Universe is equivalent to  
> saying that
> QM is false, and up to now, *that* is the speculation.
> Then with just the digital mechanist thesis, the existence of the many  
> dreams is even
> more obvious. That physics has to emerge from those many dreams is  
> (apparently)
> a bit less obvious, but I am not even sure given that I have not yet  
> heard
> any  objection but wishful thinking.
> 
> If I look to a particle in the state "(UP + DOWN)",  the state "I  
> cross (UP + DOWN)"
> evolves (by SWE) to:
> 
> "I-seeing-UP cross UP + I-seeing-DOWN cross DOWN",
> 
> I don't see how to avoid this without abandoning QM. 

If we can't show that a quasi-classical world emerges from QM we will 
abandon it - at least as fundamental.  Perhaps the long sought quantum 
theory of gravity will come to the rescue.

>The collapse can  
> be explained
> *phenomenologically* (first person plural)  through MW + decoherence.
> And if I make a decision based on what state I measure on the  
> particle, the divergence will
> propagate.
> 
> And Weinberg has given a convincing argument that once SWE is made  
> slightly non
> linear, then, not only we keep the Many Worlds/Dreams, but interaction  
> is made
> possible between them (falsifying then thermodynamics though: that is  
> why I don't
> take that the delinearisation of the SWE idea very seriously). That's  
> speculation.

Do you have a reference for Weinberg?  I'd like to read his paper.  I 
wonder how it would apply to the idea that there is a smallest unit of 
probability amplitude.

Do you agree that the other forms of multiverse, besides Everett's, are 
speculative?

Brent

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


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