The Un(solv)able Problem: After a years-long intellectual journey, three mathematicians have discovered that a problem of central importance in physics is impossible to solve-and that means other big questions may be undecidable, too

The there of us were sitting together in a cafe in seefeld, A small town deep in the austrian Alps. It was the summer of 2012, and we were stuck. Not stuck in the café-the sun was shining, the snow on the Alps was glistening, and the beautiful surroundings were sorely tempting us to abandon the mathematical problem we were stuck on and head outdoors. We were trying to explore the connections between 20th-century mathematical results by Kurt Gödel and Alan Turing and quantum physics. That, at least, was the dream. A dream that had begun back in 2010, during a semester-long program on quantum information at the Mittag-Leer Institute near Stockholm.