
Mensa-fied best friends and roommates Leonard and Sheldon, physicists who work at the California Institute of Technology, may be able to tell everybody more than they want to know about quantum physics, but getting through most basic social situations, especially ones involving women, totally baffles them. How lucky, then, that babe-alicious waitress/aspiring actress Penny moves in next door. Frequently seen hanging out with Leonard and Sheldon are friends and fellow Caltech scientists Wolowitz and Koothrappali. Will worlds collide? Does Einstein theorize in the woods?

Leonard is horrified when his mother (Christine Baranski) visits.

After her apartment floods, Amy suggests that she and Sheldon move in together; Koothrappali finds out the gender of Howard and Bernadette's baby before they do.

Leonard is happy to meet new neighbor Penny, but his roommate thinks he is chasing an impossible dream.

Leonard and Penny offer Sheldon's old room to Raj after he moves out of his apartment.