A colleague who is a professor and a mom recently said to me, “I eat string cheese every single day of my life. Swear to God it doesn’t taste the same if you don’t pull strings off.” She was of course referring to that perverse group of people who prefer to chomp string cheese like a carrot stick instead of delicately peeling off strings along the long dimension.
Because it’s the kind of person I am, that got me thinking about anisotropy: a fancy word for a common concept, the idea that the properties of a bulk material are different in different directions. Does string cheese really taste different when cut in the longitudinal and transverse directions? It certainly seems plausible…
Anisotropy seems to be the norm in life. For example, we design and manufacture materials so that they have maximum strength along the directions where we need maximum strength, sometimes sacrificing other directions. Often, the very nature of the manufacturing process imposes lasting anisotropies within a material. This is certainly true in the case of string cheese, which is much easier to pull than bite (you’re wasting energy, biters!) in part because of the way it’s made. Could this affect the way our taste receptors respond to compounds in the cheese? Who knows?!
In science, anisotropy makes things complicated (and interesting!) because it forces us to speak of the properties of a material “in a particular direction” rather than “of the material” per se. If we’re measuring in a situation where anisotropy is expected, we have to either work really hard to measure in a specific direction or account as best we can for averaging effects over the measured area or volume.
I’m most familiar with this idea in the context of organic semiconductors, whose electronic properties are often anisotropic because of the way they’re made. Materials scientists and engineers are continuing to study how the microstructure of a material relates to charge-carrier mobility and how we can control the former along desired directions of current flow.