More snow. More icy cold. But here’s an encouraging scientific thought. Scientifically speaking, there is no such thing as cold. “Cold” doesn’t exist. It is simply the relative absence of thermal energy, just as “darkness” is the relative absence of light.

What is thermal energy? It is a form of molecular motion. Heat molecules up, and they move faster. They get “hotter.” Take their thermal energy away, and they move slower (until at some point, they come to a virtual standstill). They get “colder.” Our human measuring stick of cold — temperature — measures this molecular motion.

This episode of the award-winning PBS television series Nova shows how scientists used imagination and experimentation to finally figure out, less than 200 years ago, what “cold” truly is. When you have the time, it is well worth your time to watch. Take the laptop over by the fire, because baby, it’s relatively lacking in thermal energy outside!