Depending on who you talk to, Paul McCartney is either alive and well or he was brutally decapitated in a car accident decades ago. In 1966, McCartney’s decision to retreat from the public eye—coupled with a series of cryptic messages in The Beatles’ music that fans claimed to decode—resulted in the theory that Paul was dead and the rest of the band was covering it up. Should you be wondering who has stood in for McCartney all these years, it’s an orphaned Scottish look-alike named Billy Shears who was trained to impersonate him.

When a monumental event happens, there’s usually a conspiracy theory to explain it. The mass shooting at Sandy Hook Elementary School was staged so that the US government could clamp down on guns; global warming is a hoax hatched by scientists; repti...