What exactly is a shared universe on television? It’s basically when two or more independent television programs exist within the same world. For example, the character Ursula Buffay appeared in the sitcom Friends as Phoebe’s estranged sister. But before she was on Friends, she also made several appearances as a rather rude waitress at Riff’s on Mad About You. Therefore, we can surmise that Friends and Mad About You exist within the same universe. Since both shows take place in New York City, it’s not really hard to imagine a scenario where Chandler and Joey bump into Paul and Jamie Buchman while taking a stroll down Fifth Avenue. But these sitcoms aren't the only shows that fit this bill - this list is full of TV Shows in the same universe.

There is a same universe TV conspiracy theory called “The Tommy Westphall Universe” that contends every popular American television show exists in the same universe. The theory is based on the finale of the 1980s hospital drama St. Elsewhere, which revealed at the end of the show’s finale that the entire six season series had actually taken place within the child Tommy Westphall's dream. Because St. Elsewhere had crossover episodes with several other shows like Cheers, M*A*S*H, and The Bob Newhart Show, and those shows have crossed over with other shows, a connection can be made that links every one of those programs together.

That same universe television theory may or may not hold water. However, due to television’s fondness for crossover episodes that are produced to boost ratings and bring in a demo audience from one program over to another program, combined with spin-off series, there are several really interesting shows that exist in the same universe. Some are rather obvious like the CSI franchise, while others, like Magnum P.I. and Murder, She Wrote, are more unexpected.

Make your voice heard. Vote up the shared universe theories you think are most likely to be true.