Location: Valeria Ferrari Fest, University of Rome “La Sapienza”
In this talk, with subtitle “a fable of a travel in space and time with Valeria”, I give my recollection of my work and personal interaction with Valeria Ferrari during the preparation of my undergraduate Laurea thesis in the University of Rome “La Sapienza”. Starting from this and our work with Jesus Ibanez on exact solutions of Einstein equations describing the collision of plane gravitational waves, I summarise what I learned from Valeria and how I used this knowledge later in my work, studying other exactly solutions in cosmology as well as in cases where approximate methods are used, meanwhile also sometime collaborating with other Valeria students, i.e. Donato Bini, Leonardo Gualtieri and Emanuele Berti. As a sort of present for Valeria, I end the talk presenting a recent work on Bianchi IX cosmologies, showing new solutions that arise from assuming a nonlinear equation of state and a negative anisotropic pressure; these results in an eternal Universe with no singularities and an infinite sequence of bounces that, starting from generic initial conditions, become more and more isotropic. Thus, in this context the observed isotropy of the Universe on the largest scales is the result of the dynamics, rather than an a-priory assumption.