Letter | Published:

Causality or Indeterminism?



MR. BARKAS in his letter in Nature of November 25 says, "My difficulty is that if the final result of, say, one million, or billion, photons is regular (that is, determined), then how can the choice of any... be individually indeterminate". I should like to point out that the final result is not strictly regular or determined. With increasing numbers of photons, the fluctuations about the mean become less and less proportionally significant, until, for many purposes, they can be left out of account. The same is true of the pressure of a gas. If we calculate the pressure from observations on a surface sufficiently large, then the fluctuations may be altogether inconsiderable and the pressure can be regarded as constant; but if we take a surface sufficiently small—say, for example, a smoke particle—then the fluctuations will be large and will be the origin of the characteristic Brownian movement.

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  1. 1

    Pelzer, Proc. Phys. Soc., 56, 195 (1944).

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