Statements of this general kind are commonplace in physics: Theoryoften allows one to deduce from the outcome of certain measurements ona system what the outcome of some alternative possible measurementswould necessarily be

He used the ‘essentialambiguity’ that he identified, which concerned what he viewed as an overlyrestrictive view of the meaning of “without in any way disturbing a system”,to enlarge the meaning of “disturb”, not to curtail its meaning by arbitrarilylimiting the scope of logical reasoning

the faster-than-light influence that Bohr deduced from ananalysis of possible knowledge-based predictions is essentially the same as theone that I deduced from an analysis of the Hardy experiment. However, thesophistication of the Hardy experiment, in comparison to the simple EPR ex-periment, allows the nature of this influence to be exposed now more clearlythan before

This result, whichis what the analysis of the Hardy experiment shows, gives solid support toBohr’s position as opposed to EPR

But this means that one cannot pass from thefact that one can measure either q1 or p1, and hence determine either q2 orp2, to the conclusion that both results are simultaneously well defined

Mermin gets involved in questions of definitions and meanings, as didBohr. But Bohr had to involve himself with such matters because he wasconfronted by a characterization of “physical reality” that was basically aliento what arises from his own knowledge-based approach. Hence he was forced,in effect, to redefine this key term to bring it into line with his own philosophy.

A main objective of my work was to rid the argument of these “real-ity” questions that have led into a philosophical quadmire of interminabledisputes

By this argument Bohr disputes the key EPR claim that performinga measurement on one of two correlated—but currently non-interacting—systems does not “disturb” the other.So the point of Bohr’s argument is to assert that within his knowledge-based and prediction-oriented Copenhagen framework there IS an action-at-a-distance influence, and the existence of this action-at-a-distance influenceblocks the EPR (implicit) claim that there is none, thereby blocking appli-cation of the EPR criterion of reality

hus, from Bohr’s perspective, in which the meaningof “physical reality” is tied to our acquiring the knowledge needed to makepredictions about it, measuring q1 does disturb the other system because itproduces “an influence on the very conditions which define the possible typesof predictions regarding future behavior of the [other] system.” Thus if wemeasure q1 then we cannot make a prediction about p2

predictions about theoutcomes of our later possible observations, then performing one of the earlierpossible measurements may exclude the possibility of performing an alterna-tive possible one

Plotnit-sky suggests that the reason that Bell does not understand Bohr’s argumentis perhaps that he refuses to read the full argument that gives meaning tothese important phrases. I am confident that Bell, a thorough scientist, didexamine Bohr’s full argument carefully before publically criticizing it

This situation, in which there is a subtle action-at-a-distance influence,but no simple direct one, certainly brings to mind Bohr’s basic claim in hisreply to EPR:[T]here is... no question of a mechanical disturbance of the system underinvestigation...[but] there is essentially the question of an influence on thevery conditions which define the possible types of predictions regarding thefuture behavior of the system.In both cases there is a denial of any (proof of a) direct mechanical distur-bance of events in the single actually occurring situation, but an affirmationof the existence of an influence of some kind.