We haven’t been setting any records, but all the same, it’s been pretty darn cold recently. Not that there’s anything new about that. Saskatchewan is a wonderful province and I’m very fond of it, but (I trust I’m not revealing any state secrets here) it’s cold.

In winter in Canada, the cold can begin to seem like an active, implacable enemy, seeking out every chink in your armor and attacking your skin with something that you can’t see but that is obviously very sharp, since it seems to be flaying the flesh from your bones.

But the truth is, cold isn’t really anything at all. In fact, it’s the absence of something: energy.

Heat is the vibration of molecules. As those molecules lose energy, they don’t vibrate as much–and we say their temperature drops. All of the energy that warms the Earth’s air comes from the sun, and this time of the year, the sun isn’t shining in the far north. As a result, the air up there radiates its heat out into space, and becomes very, very cold. When shifting air masses bring that air down on top of us, it becomes very cold here, too. That low-energy air saps the energy out of the molecules of our skin, because energy always flows from places where there’s lots of it to places where there isn’t much. That loss of energy to the outside air is what our body registers as “cold.”

The colder it gets, the faster that energy is drained away. Fast-moving air drains that energy very fast–hence, “wind chill.” (Wind chill doesn’t, however, affect the actual air temperature, a point that’s often misunderstood. If the temperature is +1, for instance, a howling wind mightl make you feel as cold as if it were, say, -15–but water still won’t freeze.)

The faster that energy is drained away from our skin, the harder it is for our body to adjust. It’s hard anyway, because the human body really has only three ways to try to keep warm.

The first, “piloerection,” is your body’s attempt to fluff your fur. Since few folks have fur to fluff, it just makes you look like a plucked waterfowl–which is why it’s also called “goose bumps.”

Next the body closes off blood vessels close to the surface, routing warm blood to the vital inner core. If that doesn’t work, you’ll experience the body’s final line of defense: shivering, involuntary muscle contractions that can boost your body’s heat production fivefold. Eventually, however, your muscles burn up all the available fuel or get too cold to contract. After that your temperature drops like a rock, and pretty soon you’re as solid as one.

Because your head contains the most surface blood vessels of any part of your body, it radiates the most heat into the surrounding cold air. That’s why the best way to stay warm is to cover your head.

Of course, objects as well as people get cold, and they react even worse to it than we do. Cars begin to creak and rattle and plastic and rubber objects can become so brittle they crack as though made out of clay.

That’s because rapidly vibrating molecules form looser connections with their fellow molecules than do slowly vibrating molecules. The long, complex molecules making up rubber are plastic are fairly loosely bound together at room temperature. At -40, however, those molecules grip each other tightly and refuse to bend. Instead, put under enough pressure, they simply break apart.

For the same reasons, objects shrink as they cool. A crowd of people roller-skating takes up more space than a crowd of people sitting quietly, and the same is true of molecules.

This shrinking and hardening of materials is what makes your car rattle. If two materials that shrink at different rates when cooled fit together snugly at room temperature, they won’t when cooled to -40, because they’re no longer the same size relative to each other. And, of course, various shock-absorbing pieces, from rubber washers to vinyl seats, become as hard as rocks.

Cold as it has been recently, you may take some comfort in knowing that there is an absolute limit to how cold it can get. Since temperature is the vibration of molecules, when that vibration entirely ceases, it’s no longer possible for the temperature to drop any further. That point, absolute zero, is reached at -273 C.

Even in Saskatchewan, that’s not a temperature we’re liable to see any time soon…at least, not until January.

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