popper-logic-scientific-discovery

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some structural components of a theory of experience
that the segment of the sequence has this very great length—or in
other words, that the ‘world’ lasts long enough—then our assumption
of randomness entitles us to expect the occurrence of a cosmic period
in which the law of gravity will seem to hold good, although ‘in
reality’ nothing ever occurs but random scattering. This type of
‘explanation’ by means of an assumption of randomness is applicable
to any regularity we choose. In fact we can in this way ‘explain’ our
whole world, with all its observed regularities, as a phase in a random
chaos—as an accumulation of purely accidental coincidences.
It seems clear to me that speculations of this kind are ‘metaphysical’,
and that they are without any significance for science. And it seems
equally clear that this fact is connected with their nonfalsifiability—
with the fact that we can always and in all circumstances indulge in
them. My criterion of demarcation thus seems to agree here quite well
with the general use of the word ‘metaphysical’.
Theories involving probability, therefore, if they are applied without
special precautions, are not to be regarded as scientific. We must rule
out their metaphysical use if they are to have any use in the practice of
empirical science.* 1
68 PROBABILITY IN PHYSICS
The problem of decidability troubles only the methodologist, not the
physicist.* 1 If asked to produce a practically applicable concept of
* 1 When writing this, I thought that speculations of the kind described would be easily
recognizable as useless, just because of their unlimited applicability. But they seem to be
more tempting than I imagined. For it has been argued, for example by J. B. S. Haldane
(in Nature 122, 1928, p. 808; cf. also his Inequality of Man, pp. 163 f.) that if we accept the
probability theory of entropy, we must regard it as certain, or as almost certain, that the
world will wind itself up again accidentally if only we wait long enough. This argument
has of course been frequently repeated since by others. Yet it is, I think, a perfect example
of the kind of argument here criticized, and one which would allow us to expect, with
near certainty, anything we liked. Which all goes to show the dangers inherent in the
existential form shared by probability statements with most of the statements of metaphysics.
(Cf. section 15.)
* 1 The problem here discussed has been treated in a clear and thorough way long ago by
the physicists P. and T. Ehrenfest, Encycl. d. Math, Wiss. 4th Teilband, Heft 6 (12.12.1911)
section 30. They treated it as a conceptual and epistemological problem. They introduced the