popper-logic-scientific-discovery

484
new appendices
statistical description of an aggregate of systems, rather than a description
of one single system. But first of all, he ought to say so clearly; and
secondly, I do not believe that we shall have to be satisfied for ever with
so loose and flimsy a description of nature.
It should be noticed that some of the precise predictions which I can
obtain for the system B (according to the freely chosen way of measuring
A) may well be related to each other in the same way as are
measurements of momentum and of position. One can therefore
hardly avoid the conclusion that the system B has indeed a definite
momentum and a definite position co-ordinate. For if, upon freely
choosing to do so [that is, without interfering with it], I am able to
predict something, then this something must exist in reality.
A [method of] description which, like the one now in use, is
statistical in principle, can only be a passing phase, in my opinion.
I wish to say again* that I do not believe that you are right in your
thesis that it is impossible to derive statistical conclusions from a
deterministic theory. Only think of classical statistical mechanics (gas
theory, or the theory of Brownian movement). Example: a material
point moves with constant velocity in a closed circle; I can calculate the
probability of finding it at a given time within a given part of the
periphery. What is essential is merely this: that I do not know the initial
state, or that I do not know it precisely!
* This is an allusion to a previous letter. K. R. P.
With kind regards,
Yours,
A. Einstein.