New State of Matter Found in Chicken's Eye

Posted on February 25, 2014

Scientists have discovered a new state of matter, called disordered hyperuniformity, in the eye of a chicken. The discovery was made by scientists from Princeton University and Washington University in St. Louis and reported here in the journal, Physical Review E. The diagram above depicts the spatial distribution of the five types of light-sensitive cells, called cones, in the chicken retina.

The researchers say the unusual arrangement of cells in a chicken's eye constitutes the first known biological occurrence of a potentially new state of matter known as disordered hyperuniformity. The scientists say these systems have a "hidden order" that allows them to behave like both crystal and liquid states of matter. Like crystals these states of matter greatly suppress variations in the density of particles across large spatial distances and like liquids disordered hyperuniform systems have the same physical properties in all directions. The systems exhibit order over large distances and disorder over small distances.

Salvatore Torquato, a Princeton professor of chemistry, says in the announcement, "Disordered hyperuniform materials possess a hidden order. We've since discovered that such physical systems are endowed with exotic physical properties and therefore have novel capabilities. The more we learn about these special disordered systems, the more we find that they really should be considered a new distinguishable state of matter."

Visual cells are evenly distributed in an obvious pattern in the eyes of many creatures. The researchers developed a computer-simulation model to determine what is going on with cones (light-sensitive cells) in chicken retinas. This enabled them to determine that each chicken cone has an "exclusion region" that other cones cannot enter. Cones of the same type shut out each other more than they do unlike cones. This variant exclusion leads to distinctive cone patterns. Each type of cone's pattern overlays the pattern of another cone so that the formations are intertwined in an organized but disordered way. While it appeared the chicken cones were irregularly placed, their distribution was actually uniform over large distances. Torquato says this is disordered hyperuniformity.

He says, "Because the cones are of different sizes it's not easy for the system to go into a crystal or ordered state. The system is frustrated from finding what might be the optimal solution, which would be the typical ordered arrangement. While the pattern must be disordered, it must also be as uniform as possible. Thus, disordered hyperuniformity is an excellent solution."

Joseph Corbo, a co-author of the paper and associate professor of pathology and immunology, and genetics at Washington University in St. Louis, explains that nature found a unique workaround to cramming so many cones into the compact chicken eye. He says, "These findings are significant because they suggest that the arrangement of photoreceptors in the bird, although not perfectly regular, are, in fact, as regular as they can be given the packing constraints in the epithelium."

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