Until recently, it was thought that matter is immortal, but this is no longer assumed by the technique of physics. An atom is now merely a convenient way of grouping certain occurrences ; it is convenient, up to a point, to think of the atom as a nucleus with attendant electrons, but the electrons at one time cannot be identified with those at another, and in any case no modern physicist thinks of them as "real." While there was still material substance which was supposed to be eternal, it was easy to argue that minds must be equally eternal ; but this argument, which was never a very strong one, can now no longer be used.
Source: Religion and Science, 1935, chapt. 5:
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