Passages from “Popper Selections,” edited by David Miller
“In the development of science observations and experiments play only the role of critical arguments. And they play this role alongside other, non-observational arguments. It is an important role; but the significance of observations and experiments depends entirely upon the question whether or not they may be used to criticize theories.” 29
“For science does not develop by encyclopaedic accumulation of essential information, as Aristotle thought, but by a much more revolutionary method; it progresses by bold ideas, by the advancement of new and very strange theories, and the overthrow of the old ones. But this view of scientific method means that in science there is no ‘knowledge’, in the sense in which Plato and Aristotle understood the word, in the sense which implies finality; in science, we never have sufficient reason for the belief that we have attained the truth. What we usually call ‘scientific knowledge’ is, as a rule, not knowledge in this sense, but rather information regarding the various competing hypotheses and the way in which they have stood up to various tests… This view means, furthermore, that we have no proofs in science (excepting, of course, pure mathematics and logic). In the empirical sciences, which alone can furnish us with information about the world we live in, proofs do not occur, if we mean by ‘proof’ an argument which established once and for ever the truth of a theory. (What may occur, however, are refutations of scientific theories.) On the other hand, pure mathematics and logic, which permit of proofs, give us no information about the world, but only develop the means of describing it. Thus we could say…: In so far as a scientific statement speaks about reality, it must be falsifiable; and in so far as it is not falsifiable, it does not speak about reality.” 91
“Thus our logical analysis leads us direct to a theory of method, and especially to the following methodological rule: try out, and aim at, bold theories, with great informative content; and then let these bold theories compete, by discussing them critically and by testing them severely.” 112
“On the contrary, even if our physical theories should be true, it is perfectly possible that the world as we know it, with all its pragmatically relevant regularities, may completely disintegrate in the next second. This should be obvious to anybody today; but I said so before Hiroshima: there are infinitely many possible causes of local, partial, or total disaster… All this would hold even if we could be certain that our physical and biological theories were true. But we do not know it. On the contrary, we have very good reason to suspect even the best of the them; and this adds, of course, further infinities to the infinite possibilities of catastrophe… Even if we assume that we have been successful – that our physical theories are true – we can learn from our cosmology how infinitely improbable this success is: our theories tell us that the world is almost completely empty, and that empty space is filled with chaotic radiation. And almost all places which are not empty are occupied either by chaotic dust, or by gases, or be very hot stars – all in conditions which seem to make the application of any physical method of acquiring knowledge impossible. There are many worlds, possible and actual worlds, in which the search for knowledge and for regularities would fail. And even in the world as we actually know it from the sciences, the occurrence of conditions under which life, and the search for knowledge, could arise – and succeed – seems to be almost infinitely improbable. Moreover, it seems that if ever such conditions should appear, they would be bound to disappear again, after a time which, cosmologically speaking, is very short.” 115