Hundreds of physicists (and a few journalists) journeyed to Helgoland, the birthplace of quantum mechanics, and grappled with what they have and haven’t learned about reality. In the summer of 1925, a young Werner Heisenberg retreated to Helgoland in the North Sea and reemerged with the first full-fledged version of quantum mechanics. A century later, the theory’s meaning remains unsettled. Señor Salme for Quanta Magazine “Happy 100th birthday, quantum mechanics!” a physicist bellowed into a mi...