RESOLVING THE LEDGER
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The mathematical reality behind a $40-trillion national debt
An investigation into the incomprehensibly, unfathomably large amount of money the U.S. owes
The U.S. national debt surpassed $40 trillion for the first time on Wednesday. That's a mind-blowing number .
The number 40 trillion is 4 with 13 zeroes after it. If you laid all those dollar bills out end to end, you'd make it from Earth to the sun and back 20 times.
Spread out over the approximately 343 million people in the U.S. , the figure amounts to $116,618 of debt per resident. A single person trying to spend $40 trillion would need 1.27 million years to do it if they spent a dollar every second.
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Forty trillion is more than the number of cells in the human body (about 35 trillion), the distance in miles to Alpha Centauri (25 trillion) or trees on Earth (three trillion). It's about 40 times more money than the most any human has ever been valued ( Elon Musk's net worth hit $1 trillion in June ).
The national debt has been growing prodigiously for some time. It hit what was then a record of $39 trillion in March and had reached $38 trillion last October.
These relative trillions, of course, are hard for the human brain to comprehend. The difference between 38 trillion or 39 trillion and 40 trillion isn't something we can picture, just as the difference between a billion and a trillion is hard to fathom.
Can you picture the differences between a pile of sand with a million grains, another with a billion and a third with a trillion? I can't either.
Most people estimate the jump from a million to a billion to be about the same as between a billion and a trillion. But it's not. Each number is expressed with three additional zeroes, yet going from a million to a billion requires adding 999 million. Going from a billion to a trillion takes the addition of 999 billion —or, expressed another way, 999,000 million.
It's not our fault that our brains aren't wired to contemplate such huge numbers. There's some evidence from studying Indigenous cultures that human minds intuitively value the relationship between numbers more than the absolute difference between them. For instance, our brains are primed to perceive 1 and 2 as farther apart than 8 and 9 because, relatively, 2 is twice the size of 1, whereas 9 is only 1 ⁄ 8 larger than 8. Yet objectively, they are both the same distance apart on the number line.
Clara Moskowitz is chief of reporters at Scientific American, where she covers astronomy, space, physics and mathematics. She has been at Scientific American for more than a decade; previously she worked at Space.com. Moskowitz has reported live from rocket launches, space shuttle liftoffs and landings, suborbital spaceflight training, mountaintop observatories, and more. She has a bachelor's degree in astronomy and physics from Wesleyan University and a graduate degree in science communication from the University of California, Santa Cruz.
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