Following the season 5 finale, Howard is on the International Space Station. Unfortunately, he still has to deal with conflicts with his mother, when it's revealed that he never told her that he and Bernadette were moving out of the house. Communicating via video chat, he promises Bernadette that he will tell her, but continues to dodge the issue.
Meanwhile, Sheldon and Amy's second anniversary is marked by an obligatory date, but Sheldon discovers a loophole in the Relationship Agreement which allows him to outsource his dating duties by inviting Raj along on the date. He eventually leaves, though (more on that in a minute), leaving Sheldon on his own to declare his affection for Amy ... which he does by quoting the first Spider-Man film. Fortunately, Amy accepts this affection in stride.
Back at the apartment, Leonard and Penny's date goes quickly off the rails as Leonard is unable to keep asking about the status of their relationship, while Penny just wants to watch football. Raj shows up there to spend time with them, but when he discovers that Penny has never told Leonard she loves him, he's shocked. His attempts to browbeat her into confessing her love fail, however, and he's thrown out of the apartment.
Finally, Raj shows up at the comic book store. He shares a sad-tini (coffee liqueur in a Chewbacca mug) with Stuart, the owner of the store. After discussing a shared love of latin salsa music, Raj invites him to hang out the next night, offering to pay when Stuart says he's short on funds. It's unclear if Raj intended this as a romantic overture, but Stuart appears to have taken it as such ... opening up an intriguing new direction in the show's interpersonal dynamics.
This Episode's Science
Sheldon: Leonard, where do you stand on the anthropic principle?
Leonard: Interesting question. On the one hand, I always thought…
Sheldon: You don’t even know what it is, do you? The anthropic principle states that if we wish to explain why our universe exists the way it does, the answer is that it must have qualities that allow intelligent creatures to arise who are capable of asking the question. As I am doing so eloquently right now.
Leonard: I know what the anthropic principle is.
Sheldon: Of course. I just explained it to you. Now, where do you stand on it?
Leonard: Where do you stand on it?
Sheldon: Strongly pro.
Leonard: Then I believe that God created the world in six days, and on the seventh he made you to annoy me.
Raj: Hey, guys.
Sheldon: Yeah, wait, Raj, where do you stand on the anthropic principle?
Raj: I’m all for it.
Leonard: Well, hang on. Why do you believe that he knows what it is and I don’t?
Sheldon: Oh, Leonard. Let’s not take a saw to the branch we’re sitting on, shall we?