Actor Jim Parsons accepts the Best Actor in a Comedy Series award for "The Big Bang Theory" at the 4th Annual Critics' Choice Television Awards at the Beverly Hilton in Beverly Hills, California June 19, 2014. REUTERS/Mario Anzuoni
Actor Jim Parsons accepts the Best Actor in a Comedy Series award for "The Big Bang Theory" at the 4th Annual Critics' Choice Television Awards at the Beverly Hilton in Beverly Hills, California June 19, 2014. REUTERS/Mario Anzuoni Reuters/Mario Anzuoni

The last season of "The Big Bang Theory" saw Sheldon wanting to change his topic of research from string theory to something else. He was unable to do that. The episode 6 of "The Big Bang Theory" Season 8, "The Expedition Approximation, reveals that Sheldon's new topic is dark matter. He believes that it is the most exciting time in the history of the field, as he has started doing it.

Raj tells that the government funded the biggest experiment to detect dark matter. Research teams are being sent to the abandoned salt mines for the experiment. Raj suggests that if they apply to be one of the teams, they could be on the ground floor of something big. This can benefit both theoretical physics and astrophysics. The rest of the group make fun of them. Sheldon misses the days when he could not tell when someone is making fun of him.

Raj comes up with the idea of simulated environment, creating the conditions of the mine to see if they can handle being in an actual mine. The duo zero-in on the University's underground steam tunnels to check that out. Iniside the steamy tunnel, Sheldon reveals to Raj that he is "plagued by an internal struggle," which is of the emotional kind. Sheldon says that with the dark matter, he is back to square one and he feels frightened. Raj tells him that he thinks about Voyager, the space probe, when he feels frightened. Sheldon sees a family of rats and without telling Raj he exits the tunnel. He has managed to spend 11 minutes in the tunnel.

Also in the episode, Penny gives Leonard an envelope. Leonard opens it to find that there is money in it. Penny tells him that now that she has got the company's car, she sold the other car, the one that Leonard gave her. She is returning him his money and says that now they are even. Leonard is not happy about that. He tries to return the money but Penny stops him from doing so. Penny has taken a picture of them in the car and "put it in a pink frame, with puffy paint around it that says best fiancé ever." Later, she tells Leonard that he is hung up on the money because he feels that she is now less dependent on him and that can be scary. Leonard tells Penny she may have a problem because of control issues. She retorts that he might be insecure.

Penny and Leonard go to Howard and Bernadette's place to ask how they handle money as a couple. Bernadette admits that they sometimes fight over money. She says that it can be awkward since she makes so much more money than Howard. This triggers a fight between Howard and Bernadette. Bernadette later tells Leonard and Penny that money is a sensitive topic for Howard because of the difference in their incomes. Leonard does not think that Penny earning more than him will be a problem in their relationship, as he saw his mother emasculate his father financially and in every aspect of life. Bernadette and Howard's fight has given Penny and Leonard a lesson on what not to do.