> a recent post by john baez
> discussed a recent talk by jeffrey bub
> where jeff gave arguments against mechanism in science
>
> this was surprising to me
> as jeff has done research in bohmian mechanics over the years
> and so i was curious as to the nature of his arguments
> and asked jeff some questions
>
> he gave me a forward copy of a preprint he is completing
> and i was intrigued by his arguments
> and immediately decided usenet was the best place to turn
>
> all misrepresentations are my fault and likely on purpose
>
> ..
>
> i will not post any extended parts of the piece
> as is proper
> but i will try to give an outline of the idea
>
> the paper is called "quantum probabilities as degrees of belief"
>
> a recent paper by pitowski called "quantum mechanics as a theory of probability" is jeff's starting point
>
> you may be thinking:
> this sounds like what everyone thinks about quantum probabilities
> it's stale news
> old hat
> i must insist that they have a much more seasoned view of these issues
>
> you see
> jeffrey bub has been a leading contributor to the modal logic school of quantum interpretation in recent times
> and is quite familiar with much of the history of probabilistic interpretations of quantum mechanics
>
> because he sees the field widely
> his arguments are a bit more nuanced
>
> pitowski's article mention two dogmas often debated in foundational studies
> a) fundamental mechanics should have a dynamic mechanism for explanations; measurement should not be primitive
> (j s bell)
> b) quantum mechanics is a representation of reality
>
> jeff asserts that these dogmas are called into question by information-theoretic results
> known as "no-cloning" theorems
>
> no cloning theorems proceed by showing
> noncorrupting unitary transformations cannot clone all states
> because any two states of the system would then be identical or orthogonal
>
> http://en.wikipedia.org/wiki/No_cloning_theorem
> http://arxiv.org/pdf/quant-ph/0012121
>
> jeff argues that:
> assume there is a device that can distinguish all states - ie. a universal measurer
> it does this by itself transitioning to a distinguishable state upon measurement
> then if we assume any known state can be prepared from a reference state
> we have violated the no cloning theorem
>
> if it is fundamentally impossible to copy a dynamic state
> he argues
> then information sources exist that have no knowable model
> even if they have possible models
> and so dynamical explanations are not useful to our information
>
> what the bohmian models are really doing with their dynamical descriptions
> are providing dynamics to explain why dynamical information cannot be extracted
> they are explaining absences and lacks of information
>
> ..
>
> instead
> what is useful he argues
> is the information received in the revision of beliefs due to observing an event
>
> he interprets the projections P(H) as bayesian measures of partial belief
> where the projection postulate for state change of a system (the von neumann projection collapse)
> is just a noncommutative bayesian belief update
>
> the projections are simply conditional probabilities
> that bayesian update on information extraction
>
> this has become a common interpretation that seems to be popping up from a number of directions and subfields
> but i think this misses one of the most important points of bohmian models
> they solve the observation problem and need no classical cut
>
> the reason many bohmians are averse to taking measurements as fundamental
> is because information exchange becomes relative
> and information is local to an observer
>
> but there is no clear quantum mechanical notion of observer
> because of issues with wigner's friend and a need for classical correspondence as a fundamental principle
>
> in my opinion
> bub's objection mixes observables with beables
> and then mistakes obstructions to duplicating observable information sources
> as obstructions to meanings of existents in scientific models
>
> he mentions this information-theoretic approach might be seen as a principled instrumentalism
> which is important because bob coecke's quantum operationalism seems to make some of the same points
> but without a position against mechanism
>
> whereas the obstruction for observables is no-cloning theorems
> obstructions for beables exist in kochen-specker
>
> ..
>
> the kochen-specker theorem states that all observables cannot be given consistent values at all times
> in a theory where the observables have values independent of the context of their measurement
>
> http://plato.stanford.edu/entries/kochen-specker/
>
> this result is foundational to categorial quantisation
>
> isham and butterfield have shown
>
> http://arxiv.org/pdf/quant-ph/9803055
>
> given a collection W of boolean subalgebras
> of the lattice P(H) of projection operators
> on the hilbert space H of the system
> it forms a poset under subalgebra inclusion and can be considered a category
>
> a dual presheaf on W is the contravariant functor D:W -> Set suchThat
> O e objects(W) <-> D(O) is the set Hom(O, {0,1})
> i e morphisms(W) <-> D(i)(chi) := chi | range(i), the restriction of chi to the inclusion's range subalgebra