If the second law of thermodynamics is assumed to be valid for the universe as a whole, it follows that the world must have had a beginning in time. This so-called entropic creation argument was introduced in the late 1860s, although versions of it, that built on decay in a general sense, can be found earlier. During the subsequent decades it and its implications were much discussed by scientists, philosophers, theologians, and social critics. The main reason for the controversial nature of the argument was that it could be, and in fact was, used apologetically, as an argument in favour of divine creation. As a consequence, some authors of a materialistic or positivistic orientation denied the general validity of the second law. From about 1920 the debate concerning the entropic argument declined, but traces of it can still be found in the modern literature on cosmology and religion.
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