Any Way You Stack It, \$14.3 Trillion Is A Mind-Bender The U.S. government is \$14.3 trillion in debt. Stacked in dollar bills, that amount would stretch to the moon and back — twice. Still, it's pretty hard to wrap your head around a number that big, so the human brain has come up with ways to deal with gargantuan numbers.

## Any Way You Stack It, \$14.3 Trillion Is A Mind-Bender

• <iframe src="https://www.npr.org/player/embed/136930966/136949101" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
• Transcript
Any Way You Stack It, \$14.3 Trillion Is A Mind-Bender

# < Any Way You Stack It, \$14.3 Trillion Is A Mind-Bender

## Any Way You Stack It, \$14.3 Trillion Is A Mind-Bender

• <iframe src="https://www.npr.org/player/embed/136930966/136949101" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
• Transcript

SCOTT SIMON, host:

The U.S. government is \$14.3 trillion in debt. And when we first neared that twelve-zero trillion dollar mark in 1981, President Ronald Reagan said that the height of our debt amounted to a stack of \$1,000 bills about 67 miles high. That's somewhere in the thermosphere. Today, that pile of \$1,000 bills would be floating in space, more than 900 miles above the Earth. There aren't any \$1,000 bills in circulation anymore, so here's an astronomical analogy about today's debt: If you stack up 14.3 trillion one dollar bills, that pile would stretch to the Moon and back twice. Unless you're Buzz Aldrin, that's hard for most of us to visualize. How big of a number can our brains process?

For help with this gargantuan problem, we turn to our Math Guy, Keith Devlin of Stanford University. He joins us from the campus there in Palo Alto.

Keith, thanks so much for being with us.

Professor KEITH DEVLIN (Stanford University): Hi, Scott. Good morning.

SIMON: So what is the biggest number that human beings can really comprehend?

PROF. DEVLIN: Seven, actually, Scott. That means that...

(Soundbite of laughter)

PROF. DEVLIN: Thats quite a bit short of the national debt. Now if you show someone, an adult person, up to seven objects, they will instantly be able to recognize how many there are. If the collection is bigger than seven we have to visualize them as in groups or we have to count them.

SIMON: But I mean does that even apply to Stephen Hawking or you for that matter?

DAVIES: Thats just a basic feature of the human brain. And, in fact, we were only able to sort of develop all of our signs, technology, architecture and so forth because we invented numbers around 10,000 years ago.

SIMON: Is there some kind of innate ability in human beings that helps us recognize number groups or do we have to be taught, to quote the old song from South Pacific?

(Soundbite of laughter)

PROF. DEVLIN: Young children within a couple of days of birth certainly exhibit an understanding of the numbers one, two and three. If you show a very small child a collection of three things and then distract them when you take one thing away, they will know instantly that one thing has been removed. But it really does come down to having numbers. Without numbers we would be essentially enumerate in all senses of the word.

SIMON: So when we say 14.3 though, I mean is that such a fantastic number, it's meaningless to most of us?

(Soundbite of laughter)

PROF. DEVLIN: Its essentially meaningless. When people often say this is an astronomical number, well, it's actually way beyond astronomical. The best estimates the astronomers have is that there are about 200 billion stars in the Milky Way and about 150 billion galaxies. But the human body has about a hundred trillion cells in it. So the human body has seven times more cells than the national debt. So the national debt is like, you know, equivalent to one leg or something like that.

SIMON: I think we probably ought to avoid all anatomical analogies.

(Soundbite of laughter)

SIMON: But what kind of analogy would you use to help us understand?

PROF. DEVLIN: Dollar bills is good.

SIMON: Mm-hmm.

Prof. DEVLIN: A dollar bills is slightly more than 16 square inches. And I like to think of it as carpeting an area. For example, if you take one million one dollar bills, that'll cover roughly two football fields. Take a billion dollar bills, thats about four square miles. A small town. My guess is the Stanford campus is probably about four square miles. So I can imagine carpeting the Stanford campus with a billion one-dollar bills. If you...

SIMON: I believe it is.

(Soundbite of laughter)

SIMON: Just ask the parents paying for tuition.

Prof. DEVLIN: But if you go all the way to the national debt of 14.3 trillion, appropriately enough I think, that would exactly cover President Obama's home state of Illinois.

SIMON: But Keith, if they're actually to do that they'd never get that money out of Chicago.

(Soundbite of laughter)

Prof. DEVLIN: I'm glad you said that. But I was thinking it, Scott.

SIMON: WEEKEND EDITIONs Math Guy Keith Devlin, joining us from the campus of Stanford, where one way or another the campus is paved with gold.

Prof. DEVLIN: Thanks, Scott. I can see you've got my number.

(Soundbite of theme song, Magnificent Seven)

SIMON: I believe that's the theme from the Magnificent Seven, right?

Youre listening to WEEKEND EDITION from NPR News.