16.0 M. Mugur-Schächter - What is at Stake in the experiments on Bell's Inequality?

The physical content of Bell's inequality expressed directly in terms of isolation and se-add parability, instead of locality, and the specific tw questions raised by this segregation are briefly investigated. This is realized via a comment on a co recent similar attempt by B. d'Espagnat.

I. d'Espagnat's treatment

Concepts and assertions. - As regards the con- cepts it is merely assumed that the words "system", "isolated system" and "proposition" can be used in the usual way. In particular, a system is conside- red "isolated" if it lies arbitrarily far from or outside the light cones of all other systems.

By means of two definitions and four assumptions (D+A) * a description is built up in conditional and operational terms - for the conception accor- ding to which an isolated system possesses intrin- sic and persistent properties. The definition 2 concerns an isolated system and the assumption 2 (2, pg. 1426) is a conditional proposition, asser- ted to be true for a system if this system is iso- lated.

Consequences and inequalities. The particular experiment envisaged by Bell' is then considered: a spin-zero particle decays into two particles U and V of equal spin, by a spin-conserving interac- tion. We denote by Eu+v an ensemble of N composite systems U+V all of the same type and identically prepared. It is shown that the strict spin-corre- lation together with the assumption that (D+A) is applicable to the U and the V of any composite system U+V EU+V, entail for EU+V the well known inequality of Bell' as well as other similar in- equalities.

*) D for Definition, A for Assumption, see appendix