If you haven’t heard of the term, you almost certainly have heard of its application to the ubiquitous star of stage and screen, Kevin Bacon. The proposition is attractive in its simplicity: due to advances in transportation and communication technologies that allow social networks (the offline kind) to span countries and continents, any two people on Earth now can be connected by just a handful of intermediaries — friends of friends of friends. First proposed by academics in the 1920s, it was popularized in the academic circles by renowned psychologist Stanley Milgram, and given the hard value of six by nonacademic playwright John Guare.

On this day, November 8, in 1990, John Guare’s Six Degrees of Separation opened at the Beaumont Theater on Broadway, bringing to popular consciousness what scientists had been debating for decades.

Guare credited the radio pioneer Guglielmo Marconi with the quantity of six — Marconi, in his Nobel Prize acceptance speech suggested an average of six transmitter “hops” would be needed for radio signals to reach everyone in the world. The concept also influenced the work of J.J. Abrams, whose shows – most notably Lost – often feature characters unknowingly linked to one another. In this way, Abrams, a 21st century film producer is linked to Marconi, a turn-of-the-century electrical engineer, with just two connections.