Howard begins to get on everyone's nerves by continually mentioning that he's been to outer space. Meanwhile, Stuart is once again hosting a Halloween costume party as his only chance to meet women, but when Raj volunteers to help him plan it, it taxes his party planning skills to their limits.
Continuing the all-too-long-running existential crisis surrounding Leonard and Penny's relationship, the girls convince Penny that she should take an interest in his work. When she shows up at his laboratory, she's impressed by seeing him at his element, which helps to rekindle the flame in their relationship.
This Episode's Science
Scientific Method - When Leonard observes that Howard is able to turn anything around to remind people that he's been to the International Space Station, Sheldon suggests that they test the hypothesis through an experiment. When Leonard get results that confirm the hypothesis, Sheldon attempts to replicate the results with a follow-up experiment. When he is successful in replicating the results, Leonard attempts to exchange a fist bump with Sheldon (which is not part of the scientific method, explaining why Sheldon appears to be unfamiliar with it).
Holographic Principle - While they're in Leonard's laboratory, he shows off some holograms to Penny and then begins to explain the holographic principle to her, using poetic language well worthy of Carl Sagan. This scene is the source of the episode's title. However, so far as I know, the actual physical display that he was using was special effects, and science can't actually create a 3-dimensional holographic display of that type.
Leonard: [Quietly, to Sheldon in the comic book store.] Ever notice that Howard can take any topic and use it to remind us that he went to outer space.
Sheldon: Interesting hypothesis. Let's apply the scientific method. Perform an experiment.
Leonard: Okay. [Louder] Hey, Howard, any thoughts on where we should get dinner?
Howard: Anywhere but the space station. You know, on a good day, dinner was a bag full of meatloaf. But, hey, you don't go there for the food, you go there for the view.
Sheldon: [Quietly, to Leonard] Fascinating. Let me see if I can duplicate the result. [Louder] Howard, I've always thought the lemon is an under-rated fruit. Care to weigh in?
Howard: Not really. [Howard turns away from them to go back to looking through comics.]
Sheldon: Oh, well.
Howard: [Turning abruptly back toward the pair.] You know, people say the Soyuz capsule was a lemon, but that baby got me to space and back.
[Leonard extends his hand to fist-bump Sheldon, who shakes the fist, apparently unaware of this particular cultural activity.]
Penny: I guess I could probably try a little harder. [In reference to her relationship with Leonard.]
Bernadette: You could start by taking an interest in his work.
Penny: Yeah, that's kind of a problem.
Penny: I'm not really clear on what he does.
Bernadette: He's an experimental physicist.
Penny: Yeah, I'm not really clear what that means.
Amy: He takes hypotheses and design protocols to determine their accuracy.
Penny: Yeah, you're really just making it worse.
Leonard: [Narrating a 3-dimensional holographic display that he's showing off to Penny in his lab.] The holographic principle suggests that what we all experience very day in three dimensions may really just be information on a surface located at the farthest reaches of our cosmos. So it's possible that our lives are really just acting out a painting on the largest canvas of the universe.