The Recombination Hypothesis

The Recombination Hypothesis is the thirteenth episode of the fifth season of the CBS sitcom The Big Bang Theory. Coincidentally, it is also the show's 100th episode. It is set to air on January 19th, 2012.

Summary
Leonard, who broke up with Priya, asks Penny out to a spur-of the-moment romantic dinner for two, and the duo contemplates on their relationship.

Title Reference
The title refers to the hypothesis of Leonard and Penny getting back together again, thus the recombination of the pair.

Trivia

 * This episode marks the 100th episode for the show, which began airing on September 24, 2007 with the Pilot episode.
 * This episode is also the second episode to air for the year 2012.

Reference

 * Based on the summary from fanforum.com, posted by the user ennaxor.
 * Press release on spoilertv.com