Big Universe, big you

You’re very small. You’re just one of eight billion living members of your species. Your species shares a planet with millions of other species. That planet orbits a star called the Sun. There are more than 100 billion stars like our Sun just in our galaxy. If you traveled at the speed of light, it would take 26,000 years to reach the center of our galaxy, the Milky Way. Now think about this: There are over two trillion galaxies like the Milky Way in the Universe.

Being human often means feeling very small in a vast Universe.

However, you’re also very big. Your body contains trillions of cells and trillions of other, microscopic creatures. There are 370 times more cells in your body than there are stars in the Milky Way galaxy. You’re also a member of an extraordinarily powerful species—Homo sapiens. Our species has reshaped the planet you call home—Earth.

Learning Big History can help you understand how you fit into this big Universe, and it can help you understand the very big impacts you have on the world around you. But first, you’ll need to know what Big History is and why you’re learning about stars and cells in a history class.

What is history?

History is a field of study that tries to improve our understanding of the past and how it affects our present. Historians are scholars who study history. They ask questions about the past and write books or articles using evidence they find. The main job of a historian is to interpret the past for people in the present. That’s one of the reasons history is valuable—it can help you understand the present and prepare for the future.

What is Big History?

There are many different types of history. Some historians study one person or one country. Some write about large regions or even the whole planet. Most historians focus on the last 10,000 years or less of human history. But historians who study Big History are interested in everything—the whole Universe from the beginning of time to the future.

There’s a lot more to history than the human story. If you think of history as the story of life on Earth, almost all of it happened before our species even existed. Homo sapiens have only been on Earth for the last 250,000 years—less than 0.01% of the history of life on Earth.

Thresholds of increasing complexity

Big History covers the history of the Universe, but it would be impossible for this course to include everything that ever existed, everywhere. Historians make choices about what to include and what to leave out in the stories they tell. Even historians who write about one person’s life can’t tell the whole story of everything that ever happened to that person. So, they organize their story into different parts, each with a focus.

Big Historians organize their story around eight turning points in the history of the Universe, which we call thresholds of increasing complexity—or just thresholds. These are moments when the Universe became significantly more complex. Complexity just means that things got more complicated—either there was more stuff, more different kinds of stuff, or something started to do new, more precise sorts of stuff. For example: The emptiness of space is very simple—just a few atoms floating around a vacuum. A modern city on Earth, however—with all the life, energy, technology, and social organization—is very complex and very complicated.

Each threshold of increasing complexity was a moment when new ingredients emerged at just the right time and with just the right conditions. We call these Goldilocks Conditions. For example, our planet is at just the right distance from the Sun, with just the right sort of atmosphere to allow liquid water. Those just-right Goldilocks Conditions are what allowed for a new type of complexity: life on Earth—Big History’s Threshold 5.

The Big History story begins with Threshold 1: The Big Bang—the beginning of our Universe—and travels through the birth and death of stars and the formation of Earth and everything that lives on it. Each threshold added new complexity to the Universe when just the right ingredients and conditions were present. Thresholds 6, 7, and 8 focus on human history, from our evolution as a species to the world-altering technologies we use in the present. Taken together, the thresholds tell the story of how our Universe started and how our modern world came to be.

What’s the next threshold?

The story of the Universe isn’t only about the past. We know that the Big History story doesn’t really end with Threshold 8. So, what’s next? What might be the next threshold of increasing complexity? When you reach the end of this course, you’ll use evidence from the past to think about the future. Big Historians look across the thresholds to understand the connections between past and present. With that understanding, developing an opinion about the future is more than a random guessing game. It’s a way of expressing your own point of view about what the future will be like, based on evidence that extends back billions of years.