German physicist Max Planck was one of the pioneers of quantum mechanics in the early 20th century, earning the 1918 Nobel Prize in Physics for his discovery of quanta. There has never been a whisper of scandal about the man's integrity or his scientific work. So a pair of science historians were puzzled when they discovered that a scientific journal had inexplicably retracted two of Planck's papers from the 1940s.

The journal in question is Naturwissenschaften, now known as The Science of Nature. The journal typically adds a large RETRACTED notice across digital papers that have been retracted, leaving them available for download. But it has removed the two Planck papers entirely, leaving just a blank page (and empty PDFs) with a brief note saying the articles had been "withdrawn due to article violation.”

Physics historian Yves Gingras of the University of Quebec in Montreal was browsing the blog Retraction Watch's list of Nobel Prize winners who have had scientific papers retracted, just out of curiosity. Gingras was shocked to see Planck's name on the list and enlisted fellow historian Mahdi Khelfaoui, of the University of Quebec at Trois-Rivieres, to investigate why the two papers had been retracted. They outlined their findings in a preprint posted to the physics arXiv.