The Cosmic Calendar

Trying to imagine 13.8 billion years of the universe isn’t something that comes naturally for human beings. Our hearts beat once a second, give or take, and we sleep for a few hours at a time each day.

Years gradually drag by for us, and then decades. We might even live a century, but trying to wrap your head around the scale of billions of years certainly doesn’t come easily to anyone. Our bodies are attuned to the scale of our habitat, and it’s fair to say that our minds are also wired to think within the time scale of a human lifespan.

As a kid, I loved learning about how things worked, but like my fellow human beings, thinking along these time scales wasn’t natural for me.

Carl Sagan came to my young brain’s rescue with his iteration of the Cosmic Calendar. Instead of trying to think directly about this insurmountable time-mountain, try using an analogy to something much more familiar to us: one calendar year.

Here’s Sagan, explaining things as only he could:

For me, thinking about larger spans of time always starts with what I understand: me. My own lifespan goes back almost half a century now, and I like to think I can imagine—understand, grasp—how much time will go by over the next fifty years. I have a sense of one Goatfury unit, in other words.

Let’s call this length of time a century. I get what a century is, because it’s within the scope of what I’ve lived through. I wrote about this a bit in Personalizing the Passage of Time; you might enjoy reading that if you haven’t already seen it.

Armed with my yardstick—my understanding of what a century “feels like”—I aim to venture further back in history. Going back two centuries might seem like an intimidating thought experiment, but I remind myself that I already sort of understand one century, or one Goatfury.

Unfortunately, the above approach only goes so far. I might be able to get a sense of a few hundred years this way, but even that starts to become a stretch.

That’s when the analogy really comes in handy. Take a look at this updated version of Sagan’s conception:

image: brendantheraven

All of human history takes place in the last 12 or 13 seconds, right as Dick Clark is about to start the countdown. Prehistory comes just before that, but even anatomically modern humans only go back about ten minutes.

“Venus” figurines and other sculptures start showing up during the last commercial break before the ball drops, around one minute until midnight.

Göbekli Tepe is built with 30 seconds to go. With perhaps 20 seconds left, beer makes its debut.

Writing gradually comes into being as the countdown begins.

The Roman monarchy, republic, and empire all appear and disappear during the last five seconds.

With two seconds left, coffee is invented.

Europe and the Americas were connected with about a second to go. Digital computers, video games, and the internet have all been within the last fragment of a second, and our lives are almost the blink of an eye.