Your weekend was radical. Your friends loved your "Bitchin' Summer 2014" playlist, and together you drove around for hours, singing along. Later on, at the barbecue, you were nominated DJ. As the party progressed, you got a little bolder and threw on some deep cuts. A cute friend of a friend of a friend complimented your taste, and the two of you started talking about music. Before long the conversation drifted to other topics, and you two talked for hours.

Music has chemistry, both in maintaining friendships and helping us forge new ones. But science is still pretty far behind in understanding music's power to create social bonds. "To this day, it hasn’t struck people that there must have been tremendous evolutionary pressure for music," said Petr Janata, a psychologist who studies music and the brain at UC Davis. But this doesn't mean we are completely without answers. Since at least the late '80s, researchers have been studying how music affects peoples' social lives.

A number of studies have used surveys and controlled experiments to confirm what seems pretty obvious: People express their identity through music. In one study, from 2007, researchers had strangers meet in a chat room with the only instruction being to learn about one another. After analyzing the transcripts, the researchers found the most common topic, by far, was musical preferences. Another study from 2003 (paywall) used a series of experiments to establish how people link their taste in musical genres to their personality characteristics. "There's a lot of correlation between the type of music you like and your personality," said Janata.

Other studies have found people readily make assumptions about someone else's identity based solely on their musical preferences. Several studies asked people to describe personality aspects of fans of various music genres. It turns out there's a lot of agreement about the various stereotypes of music fans. One study showed that many people described top 40 fans as outgoing. In another, most subjects agreed that heavy metal fans have bad moods. Yet another showed people believe classical music listeners as more likely to enjoy a glass of wine than a doobie.

These generalities don't necessarily hold up for all places and all points in time. In a 1989 study (paywall) asking women and men to rate potential dates, heavy metal dudes rated pretty favorably among the ladies (this was the heyday of Mötley Crüe and The Scorpions, after all). The guys went for women who were into classical (no doubt a sign of classiness and intelligence). Place probably matters too: It's hard to imagine much common ground in the public perception of a mariachi fan in Mexico versus one in Connecticut.

People project their personalities through music, and make assumptions about other peoples' personalities based on their playlists. But, how does this equate to friendship and romance? Is it reasonable to assume that music is a shorthand for compatibility?

In 2011, a group of researchers set out to see exactly whether music actually had the power to draw people with the same values together. The researchers used pairs of college kids who had been randomly assigned as dorm room mates for around 1-2 months. They had each kid describe their musical tastes and fill out a survey to determine their values. Also, each subject was asked how much they liked their room mate, and to rate how similar their own values were with what they perceived were their room mate's values. After controlling for factors like difference in age and study subject, the researchers found with compatible tastes in rock, hip hop, and other western musical genres tended to share similar values, and be more socially drawn to one another. (The study also included genres like K-pop, Chinese Opera, and movie soundtracks, none of which showed strong correlations with values or likability.)

Studies like these show strong indications that people use compatible musical tastes to help them choose their friends, but a lot more research is needed before we know for sure. But there's no doubt that music is a powerful force in many people's lives. Whether you turn it up loudly and sing along, wearing the music's emotion like garlands of your own inner feelings, or just use it as nonintrusive background noise while you work, your choice of music may be telling the people around you more than you realize about your personality and values. Scientists still have a lot to learn about the role music plays in our social lives, Janata says. "It is something that engages the brain so strongly that the brain wants it and is willing to put energy into it, therefore it’s a significant phenomena to be understood."