Sheldon is considering dark matter as his next field of study. He already did some research on the topic in The Pirate Solution (2009) when he hired Raj to help him with it, although this was mostly done to prevent Raj from being fired and possibly deported.
Sheldon asks Penny if she ever paid for a meal. In the pilot, she bought the guys food since her ex boyfriend stole their clothes.
Title Reference: The revival of "Anything Can Happen Thursday", which was first established in The Hofstadter Isotope (2009).