popper-logic-scientific-discovery

appendix *xi 473
left. This will (according to Bohm) overthrow the balance of forces
which keep the particle at rest; and the particle will start moving—
presumably from left to right. But although we triggered only the left
particle, the right particle will have to start simultaneously, and in the
opposite direction. It is asking much of a physicist to acquiesce in the
possibility of all these processes—all assumed ad hoc, in order to avoid
the consequences of the argument of Pauli and Einstein.
Einstein might have answered Bohm as follows, I think.
In the case considered, our physical system was a big macroscopic
ball. No reason has been given why in such a case the usual classical
view of measurement should be inapplicable. And this is a view that
conforms, after all, as well with experience as one can desire.
But leaving measurement aside, is it seriously asserted that an oscillating
ball (or two oscillating balls in a symmetric arrangement here
described) simply cannot exist while unobserved? Or, what amounts to
the same, is it seriously asserted that the assumption that it does move,
or oscillate, while unobserved, must lead to the conclusion that it does
not? And what happens if, once our observation has set the ball in
motion, it is then no longer asymmetrically interfered with so that the
system again becomes stationary? Does the particle then stop as suddenly
as it started? And is its energy transformed into field energy? Or
is the process irreversible?
Even assuming that all these questions may be answered somehow,
they illustrate, I think, the significance of Pauli’s and of Einstein’s criticism,
and of the critical use of imaginary experiments, especially the
experiment of Einstein, Podolsky, and Rosen. And I think that they also
illustrate the danger of an apologetic use of imaginary experiments.
(9) So far I have discussed the problem of pairs of particles, introduced
into the discussion by Einstein, Podolsky, and Rosen. I now turn to
some of the older imaginary experiments with single particles, such as
Heisenberg’s famous imaginary microscope through which one could
‘observe’ electrons, and ‘measure’ either their positions or their
momenta. Few imaginary experiments have exerted a greater influence
on thought about physics than this one.
With the help of his imaginary experiment, Heisenberg tried to
establish various points of which I may mention three: (a) the interpretation
of the Heisenberg indeterminacy formulae as stating the existence