'Big Bang Theory' shows sitcom formula still works

"The somewhat unspoken collaboration between us — me, Chuck, the rest of the writers — is simply that we have to walk up to the line. We cannot cross it," Parsons said. "And we've had to go through scenes where we've had to correct on the spot going, 'We've gone too far. We must bring this back. The audience is not pleased with the way you are talking to Penny. We can be biting, and he can observe something in a situation, maybe get snarky about it, but it can't be malicious.

"And it's a fine line. It is also the words — carefully chosen words of what he can say, especially to someone like Penny that you don't want to put it in a position where people are groaning. Well, not always, at least."

"Big Bang" has grown considerably in its relatively short run — 32 episodes and counting. A big part of that is because, as Lorre promised when the show began, the character of Penny is not just a dumb blonde.

"She's not just the cute girl next door," Lorre said. "She brings a little baggage, a couple of skycaps to get her to the curb."

"Yes, she's got a lot of issues," Cuoco said. "She's definitely not perfect. She has a lot of stuff going on, too, which is cool.

"It did start out as the girl next door, but they've been writing some really great, fun stuff for me. She's a real girl. She's smart in her own way, and I think I represent the audience. Like, I'm looking at them through your eyes because they are so different than what we are all used to."

The show does not, however, mock the smart guys. Even though Sheldon is both the smartest and most misanthropic of the bunch.

"I've always been against the whole idea of just calling them 'nerds' because it doesn't define who they are," Lorre said. "They are human beings. They have parents, and they have brothers and sisters and goals and fears and …"

"And they are geniuses," Parsons interjected.

"It doesn't really give you any insight into them by giving them a name of 'nerd' or 'geek.' It doesn't begin to describe what they are," Lorre said. "In fact, they are probably the characters who will change the world.

"They may blow it up. That will be the change."

Lorre and Prady make a decided effort to make their geniuses funny without ridiculing them.

"From the beginning, we've had great respect for our characters and a desire to have their world be as real as you can make it in a comedy," Prady said. "But the things they are doing in there are real, and they are not stereotypes."

They have a consultant "for the hard science," Prady said, but they don't really need a consultant to make the, well, geeks (for lack of a better term) seem real.