NPR.

This is the indicator from Planet Money. I'm Daryan Woods.

Recently, I got a postcard from Alex Mayassi, contributed to Planet Money.

Dear Daryan. It was from the Mayassi, contributed to Planet Money. Dear Darien.

It was from the cesium fountain, atomic clocks in Colorado.

These are the clocks that set time for wristwatches, wall clocks, and phones all across the country.

These atomic clocks are examples of public goods.

A public good is some service or benefit that you can't exclude people from. So the whole world benefits from atomic clocks. They help us set the time better. Also, more people benefiting from the public good doesn't take away from others. So you can talk about things like streetlights or national security as being

public goods.

These atomic clocks measure the length of a second by the resonant frequencies of atoms.

They are the world's most accurate type of clocks. The ones here are some of several hundred

around the world, used to coordinate time for everyone.

Where are we? Without such accurate shared time, GPS locations would be off,

internet errors would proliferate, and power grids could fail.

Clocking out for now, Alex.

Alex Mayassi is also the author of the new Planet Money book.

That book has a gorgeously illustrated collection of postcards of more public goods

from around the world.

So I thought, I've got to go.

Today on the show, Alex Marasi and I are going to take you on a virtual world tour of

spectacular public goods,

one whimsical postcard at a time.

...