The Alhambra is a place of constant surprises. The pentagonal tiles in the Nasrid palace have now become the perfect example to explain a Nobel-prize winning chemistry theory.
On the morning of 8 April 1982, Israeli scientist Daniel Shechtman saw a new kind of crystal though his microscope, one formed by structures with a pattern that was ordered but not periodic (with a five-fold order of symmetry).
These are quasicrystals, completely different from more common forms of crystals such as sugar, salt, rubies and diamonds, with a structure that should be “impossible” under the theory of crystallography. Shechtman received the Nobel Prize in Chemistry in 2011 for the discovery of quasicrystals, which change the way we understand solid materials.
Juan Manuel García Ruiz, CSIC researcher at the University of Granada (UGR), maintains that the Alhambra is a “reference for crystallographers, as all possible shapes are there”.
So what have the tiles in the Alhambra got to do with quasicrystals? García Ruiz offers a very clear example: “You can tile a wall in tiles of many different shapes - squares, triangles, hexagons, etc., but not with pentagons, because these will always leave gaps. You cannot tile a wall with pentagonal tiles only. Another possibility is to use more than one shape, pentagons and diamonds, for example”. Although most tiles in the Alhambra are “symmetrical, with two, three, four and six-fold orders of symmetry, in some parts they possess five-fold rotational symmetry.” Just like quasicrystals.
Rafael Pérez Gómez, lecturer with the Department of Applied Mathematics at UGR, explains that the structure of the quasicrystals should not be confused with that of most tiles used in the palace, which follow repetitive patterns. Those most similar to Shechtman’s model are those which have “false five-fold orders of symmetry and which do not follow a periodic structure”. These are found, he explains, in the Lindaraja Mirador.
Although scientists were initially baffled at how atoms could fail to follow regular rules, these mediaeval tiles helped them to understand.
At the time, the discovery was so controversial that Shechtman was asked to leave his work group. However, he continued to battle against the laws of chemistry until science and scientists accepted the new structure.
According to García Ruiz, the Nobel prize is an acknowledgement of the determination and perseverance of a scientist who was marginalised and whose discovery was pooh-poohed. “He kept on with his experiments, swimming against the tide”.
Manuela de la Corte, Granada Hoy and Patronato de la Alhambra y Generalife