On 30 May 2012, at 18:31, John Clark wrote:

On Wed, May 30, 2012 Bruno Marchal <marc...@ulb.ac.be> wrote: > The axiom of choice is not a physical law.That is true, but it is consistent with empirical physical evidenceabout how the universe works. In non-mathematical language the Axiomof Choice says that every event need not have an associated cause,and like all good axioms it is not intuitively obvious that itsopposite must be true. And as a bonus it appears that our Universefollows the Axiom of Choice, some things really do happen for noreason, some things are random.

`The axiom of choice just asserts that an arbitrary product of a family`

`of non empty set is non empty. It is equivalent with the statement`

`that all set can be well ordered. It is trivial on finites sets, and`

`looks rather intuitive on infinite sets.`

`There is no clue of direct relationship with physics, other than`

`assuring (another consequence) that infinite linear spaces have alway`

`a base, and things of that type.`

`It has a priori nothing to do with free will, neither with physics,`

`and the term "choice" has no serious relation with the notion of human`

`choice.`

`Interestingly ZF and ZFC which proves much more arithmetical sentences`

`than PA, are actually equivalent, i.e. proves the same arithmetical`

`sentences. The choice (C) add nothing to arithmetic from ZF pov. This`

`is not obvious and the proof relies on GĂ¶del constructible universes.`

`I refer you to a good book on axiomatic set theory.`

`This does not mean I am not using it, as you need it to prove the`

`completeness of the predicate logic, which uses the fact that each`

`consistent set of first order sentences can be extended into one`

`maximal consistent set. This needs the axiom of choice. This allows`

`the fundamental relation (consistent <=> having a model), and (proof`

`<=> true in all models).`

Bruno

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