This book is foremost a piece of scientific popularization. Cassé leads us on an historical stroll through physics. First we meet the ideas of Galileo and Newton. Then Einstein modifies the classical notions of time and space. Finally quantum mechanics revolutionize our sense of matter. On a deeper level, Cassé sees physics as an arena for debate on the nature of reality. This is why scientific discourse often tends toward reverie and poetic meditation, particularly when concerning itself with the void, a central notion for modern physics and the complex protagonist of Cassé's scientific journey.