In the years between 1924 and 1927 some of the deepest riddles that nature posed to us were solved: how to understand and describe the structure of atoms and, therefore, the structure and behavior of matter, since all matter is made of atoms. It was a truly revolutionary step, because it required the abandonment of many old concepts and pre­ judices and the creation of new concepts and a new language called quantum mechanics, in order to understand and describe what happens within and between the atoms. A new subtle reality was discovered to exist in this realm, on which the ordinary reality of our daily life is based. The new insights were achieved not by any single individual, but by a small group from different nations, with Niels Bohr in Copenhagen as the most powerful leader . Most of these people were very young, in their twenties, whereas Bohr was in his forties at that time. It was a little group of enthu­ siastic young spirits, well aware of being at the front line of knowledge, of shedding light on a previously murky and contradictory situation. Never before have so few con­ tributed so much insight into the workings of nature in such a short time. One of the young men in this group was Werner Heisenberg. He was perhaps the most active and creative among them, the one who provided the most important ideas and formulations.