HOLLYWOOD - It makes absolute sense that the folks at the Apple store Genius Bar would freak out at the sight of the cast of “The Big Bang Theory.” Or that thousands of fans would fill a room to spend time with them at Comic-Con last summer. But when the paparazzi of Mexico City went so berserk over the five actors during a promotional visit in December that they required an armed bodyguard, the young cast knew their little sitcom was turning into a sensation.

Statistically, “Big Bang” is defying all kinds of odds, most notably in that it's thriving at a time when the multi-camera format has been declared dead and network television as a whole is struggling. In its sophomore season, the buddy comedy has registered 20 percent more viewers, reaching the 10 million mark, and building enough confidence at CBS that it has been renewed for two more years.

At its core, “Big Bang” is a show about brainy best friends, genius nerds and social misfits who for the first time on TV are the source of the joke, not the butt of it. But on a deeper level, it's also about love, loyalty, friendship and the frailties of the human spirit mixed in with quantum physics and superhero fanboydom. Think “Weird Science” meets “Friends.”

Behind the scenes, the show is even more like “Friends.” The “Big Bang” cast has gelled personally in a way that is rare on television and is reminiscent of Jennifer Aniston and the gang, a group that stuck together even during contract negotiations. It may be too early for the “Big Bang” actors to be landing million-dollar-per-episode deals, but their close relationships and on-camera chemistry are highly in their favor.

“You don't have to be friends with your colleagues,” said Johnny Galecki, who plays Leonard, the heart of the show, and the most recognizable actor of the group when it premiered, primarily from his work on “Roseanne.” “But it all happened very naturally. The good thing is we allow ourselves our bad moods and dark days. There's no expectation to be buddy-buddy either. We're all kind of bracing for the day when we disappoint each other, anger each other, or get under someone's skin because so far we've just had so much fun.”

How much fun? The “Big Bang” gang works Monday through Friday, has at least two dinners a week together, and has vacationed together. They meet for drinks, play Scrabble, “and we know everything about each other, and that's good and bad,” said Kaley Cuoco, who plays Penny, the actress-waitress who lives next door to the genius physicists, Leonard and Sheldon (Jim Parsons).

“It's one of the luckiest things,” said Simon Helberg, who plays Howard Wolowitz, an engineer who fancies himself a Casanova. “We have a shorthand with each other. There's no tension. There's just honesty, and it doesn't feel competitive.”

If they were a family, Galecki and Parsons would be the parents, Helberg the protective older brother, Kunal Nayyar the picked-on middle child and Cuoco would be the smart-aleck little sister who gives them hair styling tips before a photo shoot.

“It was so cute,” Cuoco said. “I love these boys more than anything. This is the best environment for me: me and a bunch of men. It doesn't get any more fun than this.”