[Fis] A curious tale and QBism

[Bruno Marchal]

Hello Hans,

On 02 Feb 2017, at 16:32, Hans von Baeyer wrote:

> Thank you Pedro for mentioning my new book.
>
> Actually, there is a connection between my book and the curious  
> tale.  QBists look at the future as a web of interlaced personal,  
> numerical probability estimates, with no certainties anchored in  
> REAL mechanisms.  The probability that CERN will blow up the world  
> is small enough to be negligible for most people, but not for all.   
> The thing QBists reject as in principle unattainable is ABSOLUTE  
> certainty, which many lay people and some physicists (Einstein was  
> among them) continue to long for.
>

I am not absolutely certain about this. (grin).

Nor am I sure that Einstein defended absolute certainty (an  
epistemological notion). He defended determinism (a metaphysical or  
theological notion), which is neutral on what human or other creature  
can know, believe, know-for-sure or predict, ....

If we discard, like Feynman, the reduction of the wave postulate in  
quantum mechanics, we come back to a purely deterministic physics, but  
this does not enforce *any* certainty for any human, at least  
concerning physical prediction.

I tend to think that in the tiny "constructive" part of arithmetic  
(known as sigma_1 arithmetic: it allows only existential quantifiers),  
we can have something akin to certainty. It is hard to doubt that 3+4  
= 7, for example, or that it exists some number n such that n + 4 = 7.

Bruno





> Hans Christian von Baeyer
>
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http://iridia.ulb.ac.be/~marchal/



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