An introductory overview about Cosmological Inflation

Institut d Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France riazuelo iap.fr 

In the late seventies, the history of the early Universe was described with the help of the hot Big-Bang scenario the universe originated from an initial singularity and had then expanded, being filled by radiation and subsequently by non relativistic matter (baryon and Dark Matter). 

In a sense, all these problems had to do with some choice of initial conditions for the Universe. In particular, the Universe had to be supposed initially homogeneous and isotropic. These features had to be put by hand in order the cosmological scenario to work properly, a situation which was of course very uncomfortable. 

In its original formulation, inflation provided an explanation for the homogeneity and isotropy of the Universe (Guth 1981). It also explained why no heavy relics were observed in the Universe. Moreover, it was soon realized that for some unexpected reason, it could seed the density perturbations which gave birth to all the structures we observe in the Universe (Vilenkin 1982 Linde 

1982 Starobinsky 1982). Therefore, even though there is no explicit proof for such scenario, inflation has rapidly become a very popular scenario1 

---