A theory that contains three fundamental constants from which one can
build length, time, and mass (or force) etalons satisfies with that a
necessary criterion of a ''universal unified field theory.'' In order
to interpret such a theory physically, one has to translate it into th
e Galilei-Newtonian language. This leads to classical ''pictures'' who
se compatibility is ensured by introducing appropriate measurement-the
oretical principles which imply corresponding uncertainty relations. I
n this paper we compare different (mainly gravitational) theories from
the paint of view of the fundamental constants underlying each case,
and of the respective uncertainty relations. Assuming Eddington's hypo
thesis of large cosmic numbers, it is argued in particular that in qua
ntized general relativity one arrives at less stringent limitations on
cosmology than in other conceivable approaches satisfying the princip
le of minimal coupling. These limitations, however, are in all cases s
trong enough to bar the way to quantum cosmology. Instead one is led t
o a Diophantean concept.