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 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 multicamera 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.”

The “Big Bang” cast has gelled personally in a way that is rare on television.

“You don’t have to be friends with your colleagues,” said Johnny Galecki, who plays Leonard, the heart of the show, and who previously appeared 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.”

The “Big Bang” gang 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.”

Many of the show’s laughs center on obsessive-compulsive disorder, which is where Parsons comes in, playing Sheldon. Sheldon’s obsessive-compulsive personal routine, his penchant for condescending soliloquies and meticulous takeout food ordering, combined with his hypochondria and lack of social filters, exasperates his friends daily.

Fans adore the theoretical physicist/child prodigy who is clueless about how high-maintenance he is. That paired with Parsons’ impressive comedic delivery and ability to memorize polysyllabic jargon is the reason the character was the first to break out.

“These guys work hard,” show co-creator Bill Prady said. “From time to time, they’ll get together to prep for the table read. I’ve never heard of a cast doing that. And they always find stuff that winds up being a guide for us as we rewrite. It’s an unbelievably constructive collaboration.”