On April 8, 1982, Dan Shechtman, on sabbatical at the US National Bureau of Standards, observes under an electron microscope the diffraction pattern of a rapidly cooled aluminum-manganese alloy, and records in his lab notebook an annotation that would become famous: "10 fold ???". The pattern showed a ten-pointed symmetry — mathematically equivalent to a five- or eleven-fold rotational symmetry — that crystallography considered absolutely impossible: since the 19th century it had been known that periodic crystal structures could only exhibit two-, three-, four-, or six-fold symmetries, because no other symmetry allows space to be filled repeatedly with no gaps. Shechtman had found a new state of matter: solids with long-range order but no translational periodicity, later named quasicrystals. The scientific community reacted with skepticism bordering on hostility; Linus Pauling, a two-time Nobel laureate, went so far as to publicly declare that "there is no such thing as quasicrystals, only quasi-scientists", and Shechtman's own research group leader asked him to leave the team, considering the finding an embarrassment. Shechtman persisted, verifying the result for nearly two years before publishing it in 1984 together with Ilan Blech, Denis Gratias, and John Cahn. The connection to Penrose tilings, geometrically capable of generating exactly that kind of non-periodic symmetry, helped convince the community that the phenomenon was real and not an experimental artifact. The finding forced a formal redefinition of what a crystal is.