appendix b
t h e u n c e r t a i n t y p r i n c i p l e i s n o t
t h e b a s i s o f c o m p l e m e n t a r i t y
Einstein was tenacious in his e√orts to find a way to defeat the uncertai
principle, and his arguments inevitably focus on the question of disturban
But one should not depend on Einstein’s framing of the question to fra
Bohr’s response, since Bohr is continually calling into question the premi
of Einstein’s challenges. Physicists are well acquainted with arguments co
cerning disturbances in the form of momentum exchanges; their ba
grounds in classical physics make this mode of thinking quite natural.
the other hand, it is certainly not part of our training to question the intuit
ontological assumption that individual objects possess inherently determ
nate properties and that the role of measurement is to reveal such properti
So it is surely the case that Heisenberg’s account of uncertainty seems mu
more intuitive than Bohr’s account of indeterminacy, and the fact that E
stein frames the issues in terms of questions of disturbance seems to sta
the deck in favor of misunderstanding Bohr’s account. But, admittedly, Bo
does not help matters, either: he is sometimes inconsistent in his use
terminology, and his terminological choices sometimes have connotatio
that conflict with what he otherwise says he is claiming. Despite these oc
sional rhetorical lapses (which occur even after his philosophy-physics h
reached a more mature stage), he is explicit in his disavowal of disturban
as an issue, not only in his 1936 paper, as has been pointed out by ma
scholars, but also as early as 1927, as I have argued.∞ So one has to proce
with caution in trying to discern the meaning of particular passages: one h
to take into account the larger ‘‘context,’’ as it were.
There are two articles where Bohr gives considerable attention to
discussions with Einstein concerning the recoiling-slit experiment. One
Bohr’s 1949 paper entitled ‘‘Discussion with Einstein on Epistemologi
Problems in Atomic Physics,’’ which was written in honor of Einstein and
primarily an account of their famous debates; the other is Bohr’s 19
response to Einstein, Podolsky, and Rosen. In the 1949 account, Bohr
plains that since
the momentum transfer to the first diaphragm [i.e., the recoiling slit] oug
to be di√erent if the electron was assumed to pass through the upper or t
lower slit in the second diaphragm [i.e., the two-slit di√raction gratin
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