As 'Big Bang Theory' ends, will Sheldon get his Nobel Prize?

Will Sheldon and Amy win a Nobel Prize? Who will make a surprise cameo? And will the elevator finally be fixed?

"The Big Bang Theory," the show about four brilliant but socially inept scientists that made geeks and comic book nerds pop culture cool, airs its final two episodes on Thursday, bringing to a conclusion the most-watched comedy on U.S. television.

"It’s really a very sweet finale. It pulls at your heartstrings," Kaley Cuoco, who plays Penny, told reporters after the final episode was taped last month.

In the run-up to the finale, fans have seen theoretical physicist Sheldon Cooper (Jim Parsons) and his neurobiologist wife Amy (Mayim Bialik) hoping to win a Nobel Prize; experimental physicist Leonard (Johnny Galecki) have a reconciliation of sorts with his cold-hearted mother Beverly (Christine Baranski); hopeless romantic astrophysicist Raj (Kunal Nayyar) decide against moving to London to marry; and comic book store owner Stuart (Kevin Sussman) and girlfriend Denise (Lauren Lapkus) agree to move in together.

Broadcaster CBS says the first of Thursday's double episodes sees Sheldon and Amy awaiting big news, while the second has Raj making a new friend, Penny and Leonard trying to keep a secret, and mechanical engineer Howard (Simon Helberg) and his microbiologist wife Bernadette (Melissa Rauch) leaving their kids for the first time.

It remains to be seen whether the broken elevator in Sheldon's apartment building, which has been a running gag since 2007, will be repaired.

The finale will be followed by a retrospective looking at some of the most memorable moments over the last 12 years.

"The Big Bang Theory" began in 2007 and went on to win 10 Emmy awards, four of them for Parsons. Five years later, it was the No. 1 comedy on U.S. television with an audience of some 20 million people, and as far afield as Russia and France.

"We’re a show about 'the other people.' And I think everyone has a little bit of 'not belonging' in them," said Bialik, explaining the show's popularity.

Over the years, the show's "Bazinga!" catchphrase, used by Sheldon when playing a prank or telling a joke, entered pop culture and inspired the name of a species of bee found in Brazil and a jellyfish found in Australia.

The series also saw cameos by the likes of British theoretical physicist Stephen Hawking, Tesla Inc Chief Executive Elon Musk, Apple Inc co-founder Steve Wozniak, astronaut Buzz Aldrin, "Star Trek" actors William Shatner and George Takei, and Marvel comics legend Stan Lee.