The Big Bang Theory is celebrating the four-year mark since it began airing in 2009 appearing in Paleyfest this week. The series has clearly grown since the first airing.

The popular television series depicts the story of two roommates, physicists Leonard Hofstadter (played by Johnny Galecki) and Sheldon Cooper (Jim Parson), as well as their friends and colleagues, engineer Howard Wolowitz (Simon Helberg) and astrophysicist Raj Koothrappali (Kunal Nayyar).

Sources reported The Big Bang Theory is the second most watched-show on television, with more than 20 million viewers per episode. They come behind NCIS.

"You're kind of forced to watch the show now," star Simon Helberg said Wednesday night at Paleyfest, according to The Examiner. "We're shoving it down people's throats, and then they're learning that they love that."

Actor Jim Parsons, who plays Sheldon Cooper in the television hit, is unable to comprehend the amount of popularity the show has received, according to the report.

"There's something impossible to fathom about viewers and numbers and things like that," Parsons explained. "I can barely picture 20 people in one room. If you want to say 17 or 18 million, well you've lost me."

The Big Bang Theory co-creators Chuck Lorre and Bill Prady attended the event, allowing actors to give away small details as to the direction of the show, but trying not to spoil upcoming episodes.

"Well I think (Howard's) pants will probably be as skinny and probably a bit tighter," said Helberg. "Howard and Bernadette probably will ... God, God help them if they have children. We know she hates them and we know that Howard, essentially, is a child. So I wish them luck."