This article (and news story) is great for many reasons. Mostly, it shows why the melding of physics and biology is so fruitful. Without physics, it is hard to explain why we should get so excited (a “new phase of matter”!) but without biology, we probably would not have guessed that something so weird would (or could) evolve in the first place. In other words, physics helps us describe the world, but it is a little too unbounded… life comes and reminds us where the limits really are, and sometimes, they are beyond what we thought was possible. It is also pretty neat that there are still many mysteries to explore, even in familiar farm animals.
Phases of matter depend on the interactions between particles. Gasses are basically collections or atoms or molecules that bounce off each other randomly. Interparticle attraction is required for solids to form a crystal lattice.
Magnets can also be thought of as having phases. The interaction between dipoles allows for the possibility of long range ordering. In the chicken eye, cones of the same type “repel” each other, solving an evolutionary problem of efficient packing. The end result is somewhere between a solid and a liquid:
“At one level, it’s like a crystal that greatly suppresses differences in the density of particles across large spatial distances. But at another scale, it’s liquid-like in that it exhibits similar physical properties in all directions.”