OPEN PROBLEMS IN  COSMOLOGY  (II)

About one century before Christ, Posidonius was already declaring: {\it The material world is conserved through an immense force, and alternately contracts and expands in the vacuum following its physical transmutations: now consumed by fire, and now giving origin again to the creation of the cosmos}.  The idea of a cyclic evolution of our Cosmos, with a series of Big-Bangs, may be therefore regarded as an integral part of our cultural heritage; and perhaps for that reason the Big-Bang Theory is popular and well-accepted.    We too shall show how from it, and by very simple calculations, it is possible to evaluate at once,  e.g.,  the mass of our Cosmos, in agreement with the astrophysical predictions.

But alternative theories, equally serious, exist: which, moreover, can yield more precise or simpler explications of various aspects.... e.g. the Stationary State theory  illustrated in this meeting by Prof. H. Arp.

We shall first recall the theory by Eddington, Regener, Nernst, Finlay-Freundlich, which received contributions also from Guillaume, Born,  de Broglie and others (among whom Hubble himself).  Such a theory predicted before all, since 1933, on purely thermodynamical bases, that the Background Radiation (discovered in 1996) had to correspond to  an absolute temperature T of 2.8 Kelvin (the present-time experimental value being T = 2.7 K). Moreover, it explained the Red Shift phenomenon as due not to a Doppler effect, but to the fact that light looses energy proportionally to the path travelled in the intergalactic spaces.

We shall then recall the theory of the mathematician Arcidiacono (a scholar of Fantappi\'e), who in a sense reconciled the "stationary" with the "expansive" models by showing that, if our Cosmos were a de Sitter space-time (a hypersphere in 5 dimensions), it would appear to us, observers, as an oscillating universe, with a temporal origin, and therefore endowed with the Red-Shift phenomenon.