How long can 'The Big Bang Theory' go on?

The Big Bang Theory has done what few shows on television have done before: It has actually grown in viewership since its first season by more than 10 million viewers — and it keeps getting bigger.

The CBS comedy closed out last season with 18.6 million viewers and a 6.2 rating in the adults 18-to-49 demographic, making it the No. 1 comedy in both measures, a feat unheard of for a show heading into its seventh season these days. The ratings are only topped by the show's eight Emmy nominations, including Comedy Series, Lead Actor in a Comedy Series for Jim Parsons and Supporting Actress in a Comedy Series for Mayim Bialik.

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But how long can this roller coaster last?

"Not to make any predictions whatsoever, but in as far as the lifeline of most shows — at the seventh year, obviously, we're over the halfway mark — I personally don't feel like we've told half the stories that these characters have to tell," star Johnny Galecki said at Thursday's Warner Bros.-hosted Emmy panel on the Bangset, moderated by TV Guide Magazine's Rob Moynihan. "I'm certainly not halfway through personally working with all of these people, so I hope [to continue]."

"The answer changes after every season," executive producer Bill Prady told TVGuide.com after the panel. "If you'd ask the question after Season 4, you'd say, 'Boy, it would be great to get to Season 8.' But then you have a season like last year and you say, 'Well, maybe there's more to it than that.' It's possible to keep going because everybody likes each other and no one has gone crazy and no one is mean."

Prady attributes Bang's ratings and popularity surge to a number of changes, including Steve Molaro taking over as showrunner, the addition female cast members — Bialik's Amy Farrah Fowler and Melissa Rauch's Bernadette Rostenkowski — and the show running in syndication. "One of the great things about a Chuck Lorre-style show is that every episode is welcoming," Prady said. "While we do tell serialized stories, at any point you come in, you'll get all the information you need in the episode to catch up."

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"The relationship with the audience today on television is so fragile," Lorre said during the panel. "There are so many things to watch — people could conceivably read — so for us to have a relationship with an audience that has some kind of a sustained relationship over time, we have to make a great show every week. If you go into a restaurant and you get a bad meal, you don't go back. That's how we feel about The Big Bang Theory. Every week has to be a show that we're proud of and we did everything we possibly [could] to be a great show."

While quick pacing became a trend last season, Bang has always prided itself on taking things slow, especially when it comes to Raj (Kunal Nayyar) finally speaking to a woman for the first time without alcohol in the Season 6 finale. And like the slow burn of Amy and Sheldon's relationship, Molaro said the writers tend not to think too far ahead, but rather plan things episode to episode. "This season, we're realizing that there are pairings of these characters that we've barely scratched the surface on," he said. "Wolowitz [Simon Helberg] and Amy spend time together for the first time ever. So I feel like we've got a long way to go. As far as how many years, I can't put a number on it, but I cautiously and optimistically believe it'll be a long time."

Lorre added: "As long as everybody is having a good time and the audience still cares ... you don't want to overstay your welcome, but you don't want to miss out on an opportunity like this. I just know we're having a blast now and it's a lot of fun. It doesn't feel like Year 7 at all."

What's great about being so far down the line now, Galecki said, is that the characters are more comfortable with each other, lending to greater comedy. "It's less about the guys' relationship with science and more about their relationships," he said. "There's an intimacy there just in how long they've known each other, whether that's been all of the guys or Leonard and Penny's [Kaley Cuoco] relationship now. For example, their insecurities aren't so on the surface any longer. They can poke fun of each other and push each other's buttons in a very loving manner."

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It should also come as no surprise that the No. 1 comedy on TV also attracts high-caliber guest stars, whether it's Christine Baranski and Laurie Metcalf as Leonard Hofstadter and Sheldon Cooper's mothers, respectively, geek gods Wil Wheton and Stan Lee, or the brightest minds in the field, including Stephen Hawking and real-life astronaut Mike Massimino. But it was Bob Newhart, nominated for Guest Actor in a Comedy Series, over whom the cast fawned Thursday night — to the point where he joked, "Can we do this every week?" Without missing a beat, Cuoco replied, "Well, you paid me $20 to say that." Newhart will reprise his role as Sheldon's childhood TV idol for at least two more episodes in Season 7. "It belongs to the young people," he said of a regular TV gig. "I had two great series. I'm not looking for work."

Maybe when the show does come to an end, we'll finally learn Penny's last name, which has yet to be revealed, a la Mr. Big's first name in Sex and the City — two shows you'd never think would be compared. "Maybe it'll be Hofstadter one day," Cuoco said to aww's from the crowd.

The Big Bang Theory returns with a one-hour premiere on Thursday, Sept. 26 at 8/7c on CBS.

(Full disclosure: TVGuide.com is owned by CBS.)