Megascopic Quantum Phenomena
297
quantum physics. Recognizing that the Copenhagen interpretation may not be complete, it will be valuable to remind the reader of the most important stances before
starting to make any attempts to construct a more general theory.
Schlosshauer and Camilleri [22] takes up the unresolved disagreements between
Bohr and Heisenberg: “In order to meaningfully speak of observation in quantum
mechanics, Bohr concluded, “one must therefore cut out a partial system somewhere from the world, and one must make ‘statements’ or ‘observations’ just about
this partial system” [23] … Bohr’s epistemological demand for a “cut between the
observed system on the one hand and the observer and his apparatus on the other
hand” also became a key theme of Heisenberg’s thinking. However, for Heisenberg,
the object–instrument divide was coincident with the quantum–classical divide… It
is important to realize that Heisenberg’s views on the cut were somewhat at odds
with Bohr’s own view of the problem. Indeed, in an exchange of correspondence in
1935 Heisenberg and Bohr argued the point without resolution. Some twenty years
later Heisenberg would report that “Bohr has emphasized that it is more realistic to
state that the division into the object and rest of the world is not arbitrary” and that the
object is determined by the very nature of the experiment [24]. In a letter to Heelan
in 1975, Heisenberg also explained that he and Bohr had never really resolved their
disagreement. Heisenberg remained convinced “that a cut could be moved around
to some extent while Bohr preferred to think that the position is uniquely defined in
every experiment” [25].”
Heisenberg’s argument for the arbitrary position of the cut reads as follows: “The
dividing line between the system to be observed and the measuring apparatus is
immediately defined by the nature of the problem but it obviously signifies no discontinuity of the physical process. For this reason there must, within certain limits,
exist complete freedom in choosing the position of the dividing line [26].”
Heisenberg’s quantum-classical divide is also supported by von Weizsäcker, who
tries to relate irreversibility and classicality: “Having thus accepted the falsity of
classical physics, taken literally, we must ask how it can be explained as an essentially
good approximation [when describing objects at the macrolevel]… This amounts to
asking what physical condition must be imposed on a quantum-theoretical system
in order that it should show the features which we describe as “classical.”… I am
unable to prove mathematically that the condition of irreversibility would suffice to
define a classical approximation, but I feel confident it is a necessary condition [27].”
The position of an arbitrary cut was also shared by von Neumann [28]. He suggested that the entangled state of the object and the instrument collapses to a determinate state whenever a measurement takes place. So what finally causes such a
collapse seems to be the mind of the observer. Other physicists also argued the latter
boundary, i.e. the observer’s consciousness, such as London and Bauer [29], Peierls
[30], Wigner [31], etc.
The philosopher Jan Faye discusses, in his Stanford Encyclopedia article [32],
the ambiguities, significances and implications of the Copenhagen interpretation, in
particular Howard’s and Henderson’s careful analyses: “Don Howard [33] goes as
far as concluding that “until Heisenberg coined the term in 1955, there was no unitary Copenhagen interpretation of quantum mechanics.” The term apparently occurs
297
quantum physics. Recognizing that the Copenhagen interpretation may not be complete, it will be valuable to remind the reader of the most important stances before
starting to make any attempts to construct a more general theory.
Schlosshauer and Camilleri [22] takes up the unresolved disagreements between
Bohr and Heisenberg: “In order to meaningfully speak of observation in quantum
mechanics, Bohr concluded, “one must therefore cut out a partial system somewhere from the world, and one must make ‘statements’ or ‘observations’ just about
this partial system” [23] … Bohr’s epistemological demand for a “cut between the
observed system on the one hand and the observer and his apparatus on the other
hand” also became a key theme of Heisenberg’s thinking. However, for Heisenberg,
the object–instrument divide was coincident with the quantum–classical divide… It
is important to realize that Heisenberg’s views on the cut were somewhat at odds
with Bohr’s own view of the problem. Indeed, in an exchange of correspondence in
1935 Heisenberg and Bohr argued the point without resolution. Some twenty years
later Heisenberg would report that “Bohr has emphasized that it is more realistic to
state that the division into the object and rest of the world is not arbitrary” and that the
object is determined by the very nature of the experiment [24]. In a letter to Heelan
in 1975, Heisenberg also explained that he and Bohr had never really resolved their
disagreement. Heisenberg remained convinced “that a cut could be moved around
to some extent while Bohr preferred to think that the position is uniquely defined in
every experiment” [25].”
Heisenberg’s argument for the arbitrary position of the cut reads as follows: “The
dividing line between the system to be observed and the measuring apparatus is
immediately defined by the nature of the problem but it obviously signifies no discontinuity of the physical process. For this reason there must, within certain limits,
exist complete freedom in choosing the position of the dividing line [26].”
Heisenberg’s quantum-classical divide is also supported by von Weizsäcker, who
tries to relate irreversibility and classicality: “Having thus accepted the falsity of
classical physics, taken literally, we must ask how it can be explained as an essentially
good approximation [when describing objects at the macrolevel]… This amounts to
asking what physical condition must be imposed on a quantum-theoretical system
in order that it should show the features which we describe as “classical.”… I am
unable to prove mathematically that the condition of irreversibility would suffice to
define a classical approximation, but I feel confident it is a necessary condition [27].”
The position of an arbitrary cut was also shared by von Neumann [28]. He suggested that the entangled state of the object and the instrument collapses to a determinate state whenever a measurement takes place. So what finally causes such a
collapse seems to be the mind of the observer. Other physicists also argued the latter
boundary, i.e. the observer’s consciousness, such as London and Bauer [29], Peierls
[30], Wigner [31], etc.
The philosopher Jan Faye discusses, in his Stanford Encyclopedia article [32],
the ambiguities, significances and implications of the Copenhagen interpretation, in
particular Howard’s and Henderson’s careful analyses: “Don Howard [33] goes as
far as concluding that “until Heisenberg coined the term in 1955, there was no unitary Copenhagen interpretation of quantum mechanics.” The term apparently occurs