6. Philosophical Implications of the Uncertainty
Relations. In their original interpretation, as we have
seen, the Heisenberg uncertainty relations express first
of all a principle of limited measurability of dynamical
variables (position, momentum, energy, etc.) of indi-
vidual microsystems (particles, photons), though ac-
cording to the complementarity interpretation their
significance is not restricted merely to such a principle
(Grünbaum, 1957). But even qua such a principle their
epistemological implications were soon recognized and
the relations became an issue of extensive discussions.
Heisenberg himself saw their philosophical import in
the fact that they imply a renunciation of the causality
principle in its “strong formulation,” viz., “If we know
exactly the present, we can predict the future.” Since,
now, in view of these relations the present can never
be known exactly, Heisenberg argued, the causality
principle as formulated, though logically and not re-
futed, must necessarily remain an “empty” statement;
for it is not the conclusion, but rather the premiss
which is false.
In view of the intimate connection between the statistical
character of the quantum theory and the imprecision of
all perception, it may be suggested that behind the statis-
tical universe of perception there lies hidden a “real” world
ruled by causality. Such speculation seems to us—and this
we stress with emphasis—useless and meaningless. For
physics has to confine itself to the formal description of
the relations among perceptions
(Heisenberg [1927], p. 197).
Using the terminology of the introductory section
of this article, we may say that Heisenberg interpreted
the uncertainties appearing in the relations carrying
his name not only as i-indeterminacies, but also as
a-indeterminacies, provided the causality principle is
understood in its strong formulation, and a fortiori also
as u-indeterminacies. His idea that the unascertainabil-
ity of exact initial values obstructs predictability and
hence deprives causality of any operational meaning
was soon hailed, particularly by M. Schlick, as a “sur-
prising” solution of the age-old problem of causality,
a solution which had never been anticipated in spite
of the many discussions on this issue (Schlick, 1931).
Heisenberg's uncertainty relations were also re-
garded as a possible resolution of the long-standing
conflict between determinism and the doctrine of free
will. “If the atom has indeterminacy, surely the human
mind will have an equal indeterminacy; for we can
scarcely accept a theory which makes out the mind
to be more mechanistic than the atom” (Eddington,
1932). The Epicurean-Lucretian theory of the “minute
swerving of the elements” enjoyed an unexpected re-
vival in the twentieth century.
The philosophical impact of the uncertainty rela-
tions on the development of the subject-object prob-
lem, one of the crucial stages of the interaction be-
tween problems of physics and of epistemology,
problems which still persist, was discussed in great
detail by Ernst Cassirer (Cassirer, 1936, 1937).
Heisenberg's interpretation of the uncertainty rela-
tions, however, became soon the target also of other
serious criticisms. In a lecture delivered in 1932
Schrödinger, who only two years earlier gave a general,
and compared with Heisenberg's formula still more
restrictive, derivation of the relations for any pair of
noncommuting operators, challenged Heisenberg's
view as inconsistent; Schrödinger claimed that a denial
of sharp values for position and momentum amounts
to renouncing the very concept of a particle (mass-
point) (Schrödinger, 1930; 1932). Max von Laue
charged Heisenberg's conclusions as unwarranted and
hasty (von Laue, 1932). Karl Popper challenged
Heisenberg with having given “a causal explanation
why causal explanations are impossible” (Popper,
1935). The main attack, however, was launched within
physics itself—by Albert Einstein in his debate with
Niels Bohr.
