popper-logic-scientific-discovery

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some structural components of a theory of experience
lines could not be identified with the frequencies of the electron’s
revolutions). Heisenberg hoped that by eliminating these unobservable
magnitudes, he might manage to cure Bohr’s theory of its
shortcomings.
There is a certain similarity between this situation and the one with
which Einstein was confronted when trying to re-interpret the
Lorentz-Fitzgerald hypothesis of contraction. This hypothesis tried to
explain the negative result of the experiments of Michelson and Morley
by making use of unobservable magnitudes such as the movements
relative to Lorentz’s immobile ether; i.e. of magnitudes inaccessible to
experimental testing. Both in this case and in that of Bohr’s theory, the
theories needing reform explained certain observable natural processes;
but both made use of the unsatisfactory assumption that
physical events and physically defined magnitudes exist which nature
succeeds in hiding from us by making them for ever inaccessible to
observational tests.
Einstein showed how the unobservable events involved in Lorentz’s
theory could be eliminated. One might be inclined to say the same of
Heisenberg’s theory, or at least of its mathematical content. However
there still seems to be room for improvement. Even from the point of
view of Heisenberg’s own interpretation of his theory, it does not seem
that his programme has been fully carried out. Nature still succeeds in
hiding from us most cunningly some of the magnitudes embodied
in the theory.
This state of affairs is connected with the so-called uncertainty principle
enunciated by Heisenberg. It may, perhaps, be explained as follows.
Every physical measurement involves an exchange of energy between
the object measured and the measuring apparatus (which might be the
observer himself). A ray of light, for example, might be directed upon
the object, and part of the dispersed light reflected by the object might
be absorbed by the measuring apparatus. Any such exchange of energy
will alter the state of the object which, after being measured, will be in
a state different from before. Thus the measurement yields, as it were,
knowledge of a state which has just been destroyed by the measuring
process itself. This interference by the measuring process with the
object measured can be neglected in the case of macroscopic objects,
but not in the case of atomic objects; for these may be very strongly