(bright music) - One, two, three, go!

- Don't rush me.

- Philip, I'm gonna catch you.

- I know, but how do I know?

- Because I'm your wife?

Don't you trust me?

- Of course!

- Then do it!

- Okay, here we go.

I can't.

- Forget it.

- No, no, no.

I can do this.

Alright, one, two, three.

Ahh!

(crash) (bright music) Trust is hard.

Counting on something you can't see or touch to be there for you when you need it can be scary, but whether we like it or not, you and everyone you know plays a global game of trust every day.

It's called money.

- Money is imaginary.

This bill can't be used as food, or clothing, or shelter, and yet it has value because we've all agreed to pretend that it does.

The employee who accepts a paycheck for their hours of work, the shopper who puts a new pair of shoes on their credit card, and even the bank robber, risking his life for a bag full of Benjamins.

They're all putting their faith in a collective fantasy that only works because everyone else believes in it too.

- [Philip] The earliest types of currencies were things that had practical value, like food, or livestock, or furs.

These commodity monies didn't require much trust.

- A toolmaker is willing to accept a bag of barley as payment because even if he has more than he needs, he can be pretty sure that someone else will want it because, you know, you can eat it.

- But commodity money isn't very convenient.

Try schlepping 40 bags of barley across town just to pay your rent, and if your landlord doesn't spend it right away, it could mold or get eaten by rats, and if he wants to buy a tool from you, he has to carry the sacks all the way back to your house.

- At some point, someone realized that life would be so much easier if instead of actually carrying sacks of barley back and forth, we could just agree to pretend to carry sacks of barley back and forth.

We'd just need some way to keep track of it all.

- This 5,000 year old Sumerian clay tablet is one of the earliest examples of writing ever found.

It says, 29,086 measures of barley, 37 months.

Writing wasn't invented for royal decrees or epic poems.

It was invented to keep track of imaginary sacks of barley.

In other words, credits and debits.

So when Saint Paul wrote that love of money is the root of all evil, he may have had a point, but he couldn't have written it down if it weren't for money.

- Once humans were willing to think about value symbolically, it wasn't long before we started using other materials as currency, but of all the elements on the periodic table, which one should we use?

- Well, first, it should be a solid.

As much fun as a wallet full of helium would be, you wouldn't want it floating away.

- And it can't be toxic to humans, obviously.

- It shouldn't be reactive or radioactive.

- It should be easy to extract and smelt.

Rare enough to be valuable, but common enough to be practical.

- It shouldn't corrode, rust, or degrade, but it should be soft enough to cut and shape.

- And it should be pretty.

- That really only leaves a few good options, and the best fit is gold.

We're used to thinking of gold as inherently precious, but the main reason we use it as a currency is because it's great at being a currency.

Physically, it's not much more useful than a paper bill.

- [Julia] Maybe less.

At least you can burn paper for warmth.

- So that paranoid survivalist burying bullion in his backyard is still playing the trust game.

He's trusting that even after the apocalypse, everyone will agree to pretend that his gold is valuable.

- The next big financial innovation came around 640 B.C.E., in what is now Turkey, when someone had the bright idea to pre-weigh lumps of gold and stamp them with the royal seal, and ca-ching, the first coins were born.

- That stamp is the king's personal guarantee of the coin's worth.

No need to weigh it or test its purity.

If you can trust the king, you can trust this coin.

Counterfeiting is essentially royal impersonation, a serious offense, and still known today as a lese-majeste crime.

- Coins were so convenient that they quickly spread all over the world, and almost every incarnation had some sort of symbol of trusted authority on it, and if you were lucky enough to have a lot of these coins, you'd need somewhere safe to store them, so banks were founded, where you could exchange your gold coins for a slip of paper called a promissory note, a promise the bearer could come back for their coins whenever they wanted, but a funny thing happened.

These notes were so light and convenient that people actually preferred them as currency, and voila, paper money.

(bright music) - Governments eventually took over the role of printing bank notes and covered them will all types of assurances that this is more than just a flat rectangle of cotton and linen.

We especially love to put images of famous people on our bills, not just to honor the people, but to use their stature and respect to reinforce trust in the currency.

I mean, look at old George there.

Doesn't he seem so trustworthy?

- This money is real.

I cannot tell a lie.

- So when you deposit your paycheck in the bank, you're taking it on faith that you'll be able to withdraw it later as cash, which is a promise that can be redeemed for gold, which you're hoping other people will exchange for food, and shelter, and all the other stuff we need to live.

Wow, that's some inception-levels of trust going on there.

Kinda scary when you think about it.

- Sure, but the fact that money is imaginary does give you a lot more power in your relationship with it.

How you think about money affects its very nature.

- And in a future episode, we'll look at how this global trust experiment has moved beyond the physical realm into the invisible world of cyberspace.

How can trust possibly survive when the majority of the world's wealth exists only in the minds of computers?

- We trust you'll keep watching.