  Alexander Friedmann and Georges Lema\^itre are undoubtedly the real fathers
of Big Bang cosmologies. In this article I study the influences their work
underwent due to some religious as well as anti-religious ideas. During his
career Lema\^itre faced criticisms coming from non-believing scientists, who
reproached him (wrongly) to have developed his primeval atom cosmology for
conciliatory reasons. In the former case of Friedmann, we know that his 1922
proposal of a "creation of the world out of nothing" was criticized by Einstein
for metaphysical reasons. The essence of such hostile reactions is the fact
that presumably "good" scientific contents should not be influenced by
religious ideas. Nevertheless, metaphysical and theological ideas can play an
important role inside the science research processes, as an epistemological
tool helping to clarify the use of some fundamental notions.
