The season is notable for bringing together icons of science and science fiction:
: The milestone episode, "The Recombination Hypothesis," sees Leonard and Penny attempt a "beta test" of their relationship after their initial breakup, marking a central narrative shift for the series. The Big Bang Theory Season 5 Complete Pack
: Leonard Nimoy provides the voice for a Sheldon-sized Spock action figure, and Brent Spiner appears alongside series regular Wil Wheaton . The season is notable for bringing together icons
: Amy Farrah Fowler (Mayim Bialik) and Bernadette Rostenkowski (Melissa Rauch) are promoted to main characters, providing a female social circle for Penny that mirrors the guys' group. "The Recombination Hypothesis