First order phase transitions in cosmology

We review the observable effects produced by phase transitions occurring al ong with inflation. Firstly, we present a model which is able to generate a locally open universe as the result of a very early phase transition peake d at a precise epoch. Then, we show how the same model can produce primordi al voids on the large scale structure, able to imprint in an observable way the microwave background. Finally, we speculate on the possibility of merg ing the two mechanisms in the same process. (C) 1999 Elsevier Science B.V. All rights reserved.