100 years ago, a quantum experiment explained why we don't fall through our chairs

Physicists still argue about how to interpret the experiment. A century ago, Otto Stern and Walther Gerlach made one of the most iconic observations in the history of physics: the discovery that electron spin can only take one of two values. Davide Castelvecchi explores how the groundbreaking basic concept of quantum spin provides an understanding of a vast range of physical phenomena.