murphy: You have often said that the progress of science consists in the discovery of a new mystery the moment one thinks that something fundamental has been solved. The quantum theory has opened up this big problem of causation. And I really do not think that the matter can be answered very categorically. Of course it is easy enough to see that those who take up a definite stand and say that there is no such thing as causality are illogical, in the sense that you cannot prove any such statement either by experiment or by appeal to the direct dictates of consciousness and common sense in its defence. But, all the same, it seems to me that the burden is on the determinists at least to indicate the direction in which the old formulation of causality will have to be revised in order to meet the needs of modern science.
planck: As to the first point, that about the discovery of new mysteries. This is undoubtedly true. Science cannot solve the ultimate mystery of nature. And that is because, in the last analysis, we ourselves are a part of the mystery that we are trying to solve. Music and art are, to an extent, also attempts to solve or at least to express the mystery. But to my mind the more we progress with either the more we are brought into harmony with all nature itself. And that is one of the great services of science to the individual.