[ExI] John A. Wheeler

scerir scerir at libero.it
Thu Apr 17 14:31:07 UTC 2008

I have always thought that a large problem 
in quantum measurement is the 'shutter speed'. [etc.]

# While position measurements are not performed
using cameras and shutters [1], it is true there is an 
impossibility of any sharp distinction between the
behaviour of atomic objects and the interaction
with the measuring instruments which serve to define
the conditions under which the phenomena appear.
This conspiracy has different names and faces, like
Bohr's complementarity [2], WAY theorem, KS contextuality.

[1]  The theoretical treatment of a very fast shutter requires (imo)
a time-dependent Schroedinger equation, and it is (imo) a difficult
subject. See,ie, Marcos Moshinshy 'Diffraction in Time', Physical Review, 
vol. 88, n. 3, (1952), pages 625-631.

[2] 'However, since the discovery of the quantum of action, 
we know that the classical ideal cannot be attained 
in the description of atomic phenomena. In particular, 
any attempt at an ordering in space-time leads to 
a break in the causal chain, since such an attempt
is bound up with an essential exchange of momentum 
and energy between the individuals and the measuring
rods and clocks used for observation; and just this 
exchange cannot be taken into account if the measuring 
instruments are to fulfil their purpose. Conversely, 
any conclusion, based in an unambiguous manner upon the
strict conservation of energy and momentum, with
regard to the dynamical behaviour of the individual 
units obviously necessitates a complete renunciation 
of following their course in space and time'.
-N.Bohr, 'Atomic Theory and the Description of Nature', 
pp. 97-8, Cambridge University Press, 1934

More information about the extropy-chat mailing list