You’ve been too polite to mention it, but I’ve been looking particularly old these days. I can’t say for sure if it’s how my gray hair frames my face or if it’s the leathered wrinkles around my eyes. It could just be the tired sag of my skin. In any case, things look rough on the other side of my mirror. Fortunately, I can’t see as well as I used to, so I don’t really notice.

I take some solace in the fact that this is natural. One of the most fundamental but seemingly boring rules of the universe is summarized as “the second law of thermodynamics.” In my past, my distant, foolish youth, I brushed aside this statement as just mundane and depressing. In an introductory physics class, you could learn that it assures that inefficiencies are inevitable, or that some measure called “entropy” will always increase. For myself, I appreciate that this statement tells us that time has a direction, and you can always get a sense of time streaming forward as natural processes erode: desks get messy, mountains crumble, stars die. If you find some video of an event over the long haul of time, you can figure out which direction the movie should be played based on this premise. A star never un-explodes and a desk never cleans itself — and if I clean the desk, it’s at the expense of having to eat some breakfast, digest some food and, well, get a little bit older.

There are also plenty of things that cycle regularly, natural beats of a drum to keep the rhythm of our universe. I was visiting some fourth graders a couple of weeks ago and we investigated properties of waves. They wiggle back and forth, carrying energy from one place to another as they keep up a predictable, constant oscillation. Timing devices might be calibrated to the inner workings of an atom, and even a very basic watch is tuned to the resonant vibration of a quartz crystal. My favorite timing device, a pendulum, could be made by something as simple as a yo-yo hanging from its string. The sway back and forth is always dependent on the length of that string and the gravity pulling it to and fro. (You can determine what planet you’re on by timing this for a given length.)

On a grander level, there are the rhythms of astronomical bodies. Our moon’s orbit is roughly a month, and each planet has a known timing to its path around the sun. Astronomers time the travels of stars, perhaps the wobbles they make that tell us something about planets orbiting in these other systems. Earth, the planet we stand upon (as I can verify with my pendulum), goes through its own cycle that I’m reminded of this time of year.

It’s been getting darker with each passing date, shorter amounts of daylight and the sun lower in the sky. And yet, that cycles too. It eventually gets better, sunnier again. As of this date, our days start to get longer. Sure, we think of it as the first day of winter, but it’s maybe more accurately thought of as a turnaround point in a cycle. We’re bouncing back. We celebrate this through so many holidays around winter solstice.

On the scale of deep time, even this will wear out. But compared with human history, these annual events are an immutable regularity. We get hurled around on this very solid rock in a very stable orbit and with a very well-oriented tilt, and all these together provide a cycle where there must be a darkest day of each year.

But that means that there are lighter days as well. It’s a beginning. Unlike my progressively more wrinkled and worn self, the year renews. From the shortest day, things can only get more light and more warm, gradually and unnoticeably until one evening you’re watching a sunset long after dinner. Trees leaf out, blossoms bloom, snow melts, eventually. Looking forward, I see a chance at redemption, opportunity to try again. Our darkest, coldest days remind us there can also be brighter days ahead.

Adam Johnston is a professor of physics and director of the Center for Science and Mathematics Education at Weber State University, where he helps prepare future teachers and supports educators throughout Utah.

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