A simple, non-technical introduction to the pre-big bang scenario is given,
emphasizing physical motivations, considerations, and consequences over
formalism.Comment: 15 pages, macros included, 4 figures, lecture presented at the Erice
School of Subnuclear Physics, 35th Course "Highlights: 50 Years Later",
Erice, Italy, August 26-September 4, 1997 revised version, references
updated, fig. 3 more precisely describe
