Spotify today unveiled Serendipity, an online map that displays a stream of coordinates when two users played the same song at the same time. Serendipity isn't live, but is reflective of real-time data recorded recently over a one hour period. As each pair of listeners flashes onto the screen, the song they chose starts playing for a few fleeting moments before another song comes on. Serendipity only displays users who clicked Play within one tenth of a second of each other, Spotify says. The site isn't particularly useful, but is a fantastic visualization of how music spreads — and of the reach of Spotify's user base. It's also just a fun way to hear what the world is listening to.

Serendipity was built by Kyle McDonald, a Brooklyn-based digital artist who recently became Spotify's first "artist in residence." The company, which is well known for its frequent hackathons, hack days, and jam sessions, largely gave McDonald the key to its data castle. "25-50 million people are listening to music [on Spotify] at any moment," says McDonald, "and 10-20,000 songs are started every second!" This data formed the basis for Serendipity.

Serendipity is accurate to one tenth of a second

While at Spotify, McDonald also built a live feed of music shared on social networks by all Spotify users, as well as a globe of glowing white pixels representing users around the world. He also explored hypotheses about why users might all click the Thumbs Up button at the same time during a song — in hopes of finding "the biggest beat drop" of all time. Inside the new data Spotify inherited when it acquired The Echo Nest, McDonald even tracked down "mainstreamness," a secret attribute the company assigned to every song based on how hip it was.

Most of these explorations, including a version of Serendipity that shows live updates, were only distributed internally — meant to spur interesting ideas for future features. "Imagine if we could have 'tangled sessions,'" says McDonald, "or an app that would pair you up with someone so you could listen to the same song at the same time." Turntable.fm once filled a similar need, notably, but was used for groups instead of individual listening sessions. Hellman wouldn't name any specific upcoming features, but said that serendipity — the concept, not the website — would likely play an important role in future offerings from the company.

Correction: An earlier version of this article stated that Serendipity was a live stream of global coordinates. Serendipity was recorded over one hour of one day, Spotify says, but is reflective of real-time data.