The gas station at the end of the Universe

From where you’re sitting, the farthest edge of the observable Universe is about 273,356,081,100,000,000,000,000 miles away. That’s 273 sextillion, 356 quintillion, 81 quadrillion, 100 trillion miles—give or take.

That’s a silly number—and it’s useless to you. That’s because I’m not using the right scale.

If a friend asked how far it is from school to the nearest gas station, you wouldn’t say it’s 0.000000000000000000000183% of 546,712,162,200,000,000,000,000 miles, would you? Of course not. You’d say: “It’s like, a mile down the street.”

If we’re measuring the Universe, though—or measuring the distance between galaxies—it doesn’t make sense to use miles. Instead, when we’re talking about cosmic scales, we use something called light-years. A light-year is the distance that light can travel in one year. One light-year is about 5.88 trillion miles. So, another way to say that the Universe is 546,712,162,200,000,000,000,000 miles wide is to say that it’s 93 billion light-years wide. It’s still a big number, but changing the scale makes it a lot easier to understand.

What is scale?

In Big History, scale means the perspective—big picture or little picture—we’re choosing to look at things. It can refer to both geography and to time. For geography (or space), we use scales measured in nanometers, cities, continents, planets, and light-years. For time, we have scales that use nanoseconds, seconds, hours, centuries, and epochs. It’s a little like zooming in and out with your phone’s camera. In Big History, we might want to zoom in to examine tiny details, such as a single atom or the life of one person. Other times, we might want to zoom out to see a much bigger picture, like how the Universe has changed over billions of years, or how humans have changed the Earth over thousands of years.

Different scales are useful for different topics. Studying a cell in your body? You might measure things in nanometers. Trying to understand the migration of your family? You’ll think in terms of miles, countries, and continents. If you’re thinking about the history of life on Earth, you’ll measure time in eons and epochs. But if you’re trying to remember where you left your phone this morning, it’s probably best to think back in hours and minutes.

In Big History, our scales change with each threshold. That’s because as the Universe got more complex, change happened faster. So, the scales we use get smaller and smaller. For example, the first five thresholds happened over billions of years, but Threshold 6 started just 250,000 years ago, with the rise of our species. Then, Threshold 7: Agriculture began only about 12,000 years ago. And Threshold 8: The Modern Revolution kicked off just 300 years ago.

We will also be zooming in on scales of space, from the whole Universe down to individual human beings.

Scale-switching

All historians make choices about what scale they’ll use to tell their stories. Do they tell the story of a single country, like the United States? Or do they zoom in to a single city, or zoom out to the whole world? In Big History, you’ll need to shift scales constantly, from whole galaxies to the life of a single bacterium. To do that, you’ll need to learn a new skill: scale-switching.

Scale-switching is the act of changing how “zoomed in” or “zoomed out” we are when we study something. We might start by looking closely at one thing—such as the invention of a new technology—and then zooming out to see how it fits into a larger story—like how that invention sparked the Industrial Revolution. As you move through the thresholds of this course, you’ll see how your life—and all life on this planet—fits into the grand story of increasing complexity, a story that’s been unfolding for the last 13.8 billion years.

Using scale-switching

Here’s an example of solving a question about the present using different scales of time. Today, scientists are asking whether our climate is changing and why. Some scientists are studying the last 200 years of historical data to see if weather patterns are changing and if human activity is the cause. Other researchers are using written records from explorers and scholars from the past 2,000 years of history to see whether there were other periods in human history when the climate changed a lot. Finally, some scientists are using natural evidence like tree rings, soil analysis, and ice cores to find out how Earth’s climate has changed over hundreds of thousands or even millions of years. Only by combining evidence from all these scales can scientists really begin to understand if our climate is changing in unnatural ways and if recent human activity is to blame.

In Big History, we use scale-switching similarly to those climate-change scientists. Take for example, how you fit into the Big History story. We can begin with a question: Why you are studying Big History today? You, your teachers, and others in your life made recent decisions that brought you here. But you’re also here thanks to the actions of many generations of ancestors who probably moved across large regions of the world over centuries. Their movement was shaped by even longer and bigger processes such as the evolution of humans and the formation of the Earth. Then, going back even further, you begin to see how the death (and birth) of stars and even the Big Bang contributed to the big story of how you ended up studying the history of the Universe. So, while we began with a question about you, in the process, we’ve switched scales of both time and space to figure out the answer to that simple question.

Scale-switching helps us see connections and allows us to ask big questions, like Where did everything come from? Or, How did humans become so different from other animals? By switching scales, we can gather pieces of evidence from across time and space to answer these questions and to understand the world we live in today.