Turns out it wasn't just an active set... but a radioactive one.
The Big Bang Theory was known for its inclusion of science, often incorporating real math and scientific principles into the episodes. Many scientists even say the series helped make subjects like physics and astronomy cool.
It became so famous in the scientific community that many notable figures stopped by the sitcom's set. Bill Nye, Stephen Hawking, George Smoot, and Steve Wozniak are just a few who wound up having cameo appearances on the show.
"Steve (Wozniak) actually came back and visited like five more times after he filmed his episode," co-creator Chuck Lorre said while chatting with EW for the show's 15th anniversary. "He'd just come by and hang out."
Michael Yarish/CBS Simon Helberg, Melissa Rauch, Kunal Nayyar, Mayim Bialik, Jim Parsons, Johnny Galecki, and Kaley Cuoco on 'The Big Bang Theory'
In addition to those who made their way on-camera, many others paid a visit to the studio just to check it out. During one shoot, a famed physicist stopped by... and noticed something a little peculiar. "One day this super famous physicist was visiting," co-creator Bill Prady says. "We're doing the set tour we always give after taping because everyone wants to get their picture taken in Sheldon's spot."
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During the tour, the physicist noticed one of the props in Leonard and Sheldon's apartment. Prady says, "People always ask what that thing on the wall post was, it was this wooden box that was actually an antique Geiger counter. The physicist looks at it and goes, 'That's an old Geiger counter.'" (A Geiger counter is a device used to detect radiation).
It turns out the Geiger counter was more than just a unique prop. "'You know,'" Prady remembers the scientist saying, "'those old Geiger counters often had a piece of uranium in them which was used to calibrate them, before people realized that's a stupid idea. I wonder if there's uranium in that.'"
As if it were a scene taken straight from a Big Bang episode, the scientist just so happened to have a working Geiger counter in the trunk of his car. "He went out and grabbed it," Prady says, "and came back in with it, and brought it over to the set and, of course, the thing starts going off and making noises. He opened [the prop] up and said, 'I'm going to put this in a lead box and take it away now,' and then he removed a piece of uranium from the Geiger counter and left!"
"It's sorta like a class-action suit waiting to happen," Lorre says with a laugh. "I can see some law firm with a commercial on CNN saying 'Were you or a loved one ever on the set of The Big Bang Theory?'"
Fortunately, according to the CDC, uranium is much less toxic than other radioactive materials, with much of the danger coming from inhaling it in large quantities, so it's doubtful that it affected any of the cast or crew.