Why your brain struggles with big numbers : Short Wave In celebration of our 1000th episode, we're wrapping our heads around big numbers. Educational neuroscientist Elizabeth Toomarian talks about why humans' evolutionarily-old brains are so bad at comprehending large quantities–like the national debt and the size of the universe–and how to better equip ourselves to understand important issues like our finances and the impacts of climate change.

Interested in other ways our brains make sense of the world? Email us at shortwave@npr.org.

Why big numbers break our brains

Why big numbers break our brains

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Human brains aren't built to comprehend large numbers, like the national debt or how much to save for retirement. But with a few tools — analogies, metaphors and visualizations — we can get better at it. erhui1979/Getty Images hide caption

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Human brains aren't built to comprehend large numbers, like the national debt or how much to save for retirement. But with a few tools — analogies, metaphors and visualizations — we can get better at it.

erhui1979/Getty Images

Imagine a horizontal line. The very left is marked one thousand and the very right is marked one billion. On this line, where would you add a marker to represent one million?

If you said somewhere in the middle, you answered the same as the roughly 50 percent of people who have done this exercise in a number line study. But the answer is actually much closer to one thousand since there are one thousand millions in one billion.

This error makes sense because "our human brains are pretty bad at comprehending large numbers," says Elizabeth Toomarian, an educational neuroscientist at Stanford University.

She studies how the brain makes sense of numbers. Or doesn't.

Ancient brains

"Our brains are evolutionarily very old and we are pushing them to do things that we've only just recently conceptualized," says Toomarian.

Instead, the human brain is built to understand how much of something is in its environment. For example, which bush has more berries or how many predators are in that clearing?

But comprehending the national debt or imagining the size of our universe? "We certainly can use our brains in that way, but we're recycling these sort of evolutionarily old brain architectures to do something really new," she says. In other words, it's not our fault that we have trouble wrapping our heads around big numbers.

Built to compare, not count

Our brains are fairly good at determining how many of something is in our environment–as long as that number is low, at a maximum of about four or maybe five objects. Beyond that, people make more mistakes. "We're really processing [numbers past four or even five] in a totally different way. We actually might even be using a different brain system altogether," says Toomarian.

This way of processing relies on estimation, a way to compare rather than count. One modern day example: assessing which grocery line is shortest at check out. To determine which checkout line to go to, we're not necessarily counting how many people are in each line; rather, we're generally comparing line lengths.

The brain can handle these kinds of comparisons, but conceptualizing scenarios with large numbers is harder, like assessing how much data storage we need in our phones or saving for retirement.

Making it in a big number world

So what can we do about the struggle to understand big numbers? Toomarian suggests using metaphors, analogies and visualizations. These techniques bring big numbers down to a more comprehensible scale and ideally make it relevant to something in our daily lives.

For example, it may be difficult for most people to accurately place the extinction of the dinosaurs on a timeline between the Big Bang and human existence because the first two both seem relegated to the distant path. But when reconceptualizing these events using a "cosmic calendar," it becomes easier.

The Big Bang occurred at 12 a.m. on January 1st on the cosmic calendar. Dinosaurs were only present for roughly the last week of the year. And humans only showed up in the last eight seconds: December 31st, at 12:59:52 p.m. It's clear now that dinosaurs are much closer to humans than the Big Bang on a timeline.

These metaphors and analogies are important if people are to really weigh the costs and benefits of events in their lives. The concept not only applies to long-term fiscal decisions, but public policies. Toomarian recently co-authored an article with graduate student Lindsey Hasak in The Conversation on the scale of COVID-19 deaths. In it, they write that "If the brain were built to understand these kinds of numbers, perhaps we would have made different individual decisions or taken different collective action. Instead, we now mourn for the million people behind the number."

Interested in other ways our ancient brains operate in a modern world? Email us at shortwave@npr.org.

Listen to Short Wave on Spotify, Apple Podcasts and Google Podcasts.

This episode was produced by Berly McCoy, edited by Rebecca Ramirez and fact checked by Susie Cummings. The audio engineer was Maggie Luthar.