of the theorem. This could have been done many years earlier, but, without Superstring Theory underlying the Supergravity theory other problems such as anomalies may never have been solved.

The unification scheme proposed by M theory is very attractive and could satisfy all our desires for unification: all particles and interactions may be explained in a unified way. Further, we no longer have different Superstring Theories to choose from. All the arbitrariness we had have disappeared, but only to be replaced by the arbitrariness in the choice of vacuum. Now there is only one theory and everything depends on that. But the theory seems to have nothing to tell us yet about how it chooses the vacuum and why our Universe is as we see it.

It has to be mentioned that, nowadays, we ask much more from a good candidate to *the* vacuum of our theory: it is not enough (but it is, certainly, a good starting point) that it gives the Standard Model of Particle Physics, but it should also explain the evolution of our Universe, that is, according to the most extended prejudices, it should give rise to an inflationary era and explain, in a fundamental way, 