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some structural components of a theory of experience
meaningfully any such thing as “haziness” or “inaccuracy”. It is only to
our own thoughts that anything of this sort can apply (more especially,
if we do not know which statements . . . are true)’: a remark which is
obviously directed against that very same objective interpretation which
assumes that it is not our knowledge, but the momentum of the particle,
which gets ‘blurred’ or ‘smeared’, as it were, by having its position
precisely measured.* 1 Similar vacillations are shown by many
other authors. But whether one decides in favour of the objective or the
subjective view, the fact remains that Heisenberg’s programme has not
been carried out and that he has not succeeded in his self-imposed task
of expelling all metaphysical elements from atomic theory. Nothing
whatever is therefore to be gained by attempting, with Heisenberg, to
fuse the two opposing interpretations by a remark such as ‘. . . an
“objective” physics in this sense, i.e. a sharp division of the world into
object and subject has indeed ceased to be possible’. 9 Heisenberg has
not so far accomplished his self-imposed task: he has not yet purged
quantum theory of its metaphysical elements.
74 A BRIEF OUTLINE OF THE STATISTICAL
INTERPRETATION OF QUANTUM THEORY
In his derivation of the uncertainty relations, Heisenberg follows Bohr
in making use of the idea that atomic processes can be just as well
represented by the ‘quantum-theoretical image of a particle’ as by the
‘quantum-theoretical image of a wave’.
This idea is connected with the fact that modern quantum theory
has advanced along two different roads. Heisenberg started from the
classical particle theory of the electron which he re-interpreted according
to quantum theory; whilst Schrödinger started from the (likewise
‘classical’) wave-theory of de Broglie: he co-ordinated with each electron
a ‘wave-packet’, i.e. a group of oscillations which by interference
strengthen each other within a small region and extinguish each other
* 1 The expression ‘smeared’ is due to Schrödinger. The problem of the objective existence
or non-existence of a ‘path’—whether the path is ‘smeared’, or whether it is merely
not fully known—is, I believe, fundamental. Its importance has been enhanced by the
experiment of Einstein, Podolsky and Rosen, discussed in appendices *xi and *xii.
9 Heisenberg, Physikalische Prinzipien, p. 49.