Pagina 210 di 212

However, already in the 'twenties, the Russian mathematician

Friedman showed that a different hypothesis was natural from a

purely theoretical point of view. He realized that it was

possible to preserve hypothesis (1) without introducing the less

natural cosmological term into the field equations of

gravitation, if one was ready to drop hypothesis (2). Namely, the

original field equations admit a solution in which the "world

radius" depends on time (expanding space). In that sense one can

say, according to Friedman, that the theory demands an expansion

of space.