’15 billion is the incredible number of years since the big bang, the great explosion from which the universe originated. Billions of galaxies, each with billions of stars like the sun… Everybody must have felt this great disproportion at least once. Still this disproportion has never meant incommensurability. Men and the sky: the two protagonists of a dialogue which started 15 billion years ago, with the formation of the protons and electrons which today are incorporated in our bodies. No civilisation has ever interrupted this dialogue, which carries on throughout time and beyond time. It is necessary for man to be a man and for the universe to be the universe. At the beginning of the century Einstein worked out a new universe, that of relativity. Other physicists were ‘crunching’ matter in order to understand its tiniest elements. The huge entities of relativity theory (space, time, energy) mix with the infinitely small (atoms, particles, weak forces) to build our image of the universe. Armed with this ingenious mental equipment and with unprecedented techniques for observation and measurement, men have been interrogating the universe for a very long time. The exhibition on astrophysics aims at drawing attention to the concepts which are used to interpret what happens in the universe and its destiny. Space, time, energy, old and poetic words which go beyond our mathematical expressions, but which nevertheless have their precise meanings in physics and maths. Another section of the exhibition deals with the great achievements of modern astrophysics and with the reconstruction of stellar evolution; some of the questions which are still open, such as the history of galaxies (including the Milky Way) are also tackled. Displaying such objects and concepts may seem incredible, but we invite all visitors to exercise their imagination.’