As we well know, in classical physics every particle has a well-defined position and velocity: if we know them, we can predict its entire future. For centuries that was the certainty of Newton's mechanics. Then Werner Karl Heisenberg arrived and that certainty, however solid, was no longer enough. In its place he proposed an idea with truly unique characteristics: at the atomic level there are no trajectories, there are only probabilities. Measuring changes. The intuition dates back to 1925. Heisenberg, at just 24 years old on the island of Helgoland, gave up describing electron orbits and stated only what is actually observed - the spectral lines, the intensities, the frequencies. Matrix mechanics was born: position times momentum is not equal to momentum times position. Order matters. Seen from the outside, that non-commutativity is the heart of the quantum. It is called the uncertainty principle, formalized in 1927. The more precisely you try to know where a particle is, the less you can know how fast it is moving, and vice versa. It is not a limitation of the instruments, it is nature itself that does not allow both things together. The theory explains phenomena that classical physics alone left unresolved. An atom does not collapse, its energies are in steps, particles cross barriers: it is one of the most beautiful results of 20th-century physics. It has a constant and it raises a still open problem, the boundary between possibility and reality: if everything is probability, when does it become a fact? Heisenberg himself changed his mind more than once. The question is alive. It is not a laboratory accessory and it is not worn. It is a map of the infinitely small: it is for those who study matter, for those who seek to unite chemistry and physics, for those who want to understand whether even "knowing everything" has a limit. It is almost a hundred years old and it continues to be debated. Few human "theories" can say the same. The discussion is not yet closed. If you are interested in publishing one of your own (and wish to protect it in the best way first) contact us at the telephone numbers indicated at the end of the page or write to us using the appropriate ELECTRONIC FORM. We remind surfers that the texts present in this section are protected by copyright, which prohibits total or partial reproduction. The scientific theories disclosed here belong to the heritage of knowledge; their exposition in these pages is protected as an original elaboration.