The Big Bang Theory

After Sheldon's mother (LAURIE METCALF) and Leonard's father (JUDD HIRSCH) share an evening together, everyone deals with an awkward morning after in the tenth season premiere.

Colonel Williams, an Air Force representative from the Department of Material Command, sits down for a talk with Howard.

Tensions rise when the guys struggle to complete their government project on time -- and Sheldon tries an energy drink to stay awake. And Penny & Amy go to a geologist's "party."

When Amy's apartment floods, she proposes a "cohabitation experiment" with Sheldon. And Raj learns the gender of Howard and Bernadette's baby before they do.

Sheldon threatens to break off their relationship when Amy refuses to adhere to his "bathroom schedule" putting their cohabitation experiment in jeopardy.

Penny is invited to appear in a local Comic-Con for her role in "Serial Ape-ist," where she's surprised to learn she has fans. Also Amy & Sheldon host their first brunch.

In order to remain Sheldon's roomie, Amy fibs about repairs being made to her apartment. Later, they present a episode of "Fun with Flags" in Penny's apartment.

In order to continue living with Sheldon, Amy lies to him about repairs being made to her apartment; and they host an "on location" episode of "Fun with Flags" in Penny's apartment

After a successful experiment combining their genes, Sheldon is determined to procreate with Amy. Also, Raj is embarrassed with his new date's occupation.

Sheldon struggles to contain his jealousy when CalTech geologist Bert (BRIAN POSEHN) wins the MacArthur Genius Fellowship. STEPHEN HAWKING returns.

A battle ensues when Leonard and Sheldon argue over who will get custody of their shared belongings. CHRISTOPHER LLOYD guest stars.

While Sheldon and Amy celebrate Amy's birthday, Howard and Bernadette welcome their new Baby Wolowitz.

Sheldon and Amy visit Leonard and Penny for the first time since the holidays and share details about their terrible trip to Texas. Laurie Metcalf returns as Sheldon's mother.

When Leonard and Penny fight, Sheldon plays the unlikely peacemaker. Meanwhile, Howard and Raj try to fix a squeaky floorboard in the baby's room.

While Raj gets dating advice from his ex-girlfriends, Sheldon gets help reading people's feelings when he beta tests an emotion-detection invention.

With Sheldon hindering progress on the guidance-system project, Leonard and Howard figure the only way they can get back on track is to engineer a distraction by getting him tickets to a historic railroad.

Leonard & Howard try to distract Sheldon by giving him tickets to a historic railway, while Penny & Amy take Bernadette out for the night, leaving Raj and Stuart with the baby.

Amy is furious when she learns Sheldon has shared intimate details of their relationship with people at the university, prompting their first fight since moving in together.

Without financial backing from his father, Raj finds himself in a cash crunch and turns to Sheldon to help him get his head above water. Meanwhile, Penny considers crashing the guys' annual Comic-Con getaway.

When Raj is cut off from his father's fortune, he appoints Sheldon in charge of his finances to help him get out of debt. Also, Penny considers joining Leonard at Comic-Con.

When Raj moves out of his apartment, Leonard and Penny offer him Sheldon's old room. Christine Baranski returns as Leonard's mother, Beverly.

Leonard, Penny and Raj adjust to their new living arrangement, while Sheldon takes an interest in Amy's work.

Sheldon pushes himself to the limit when he collaborates on projects with Leonard and Howard as well as Amy on the same day. And, Bernadette nears the end of her maternity leave.

Howard and Bernadette have a hard time leaving Halley in daycare when Bernadette returns to work. Also, Bert introduces the gang to his new girlfriend, Rebecca (APRIL BOWLBY).