The Episode's Science
The Doppler Effect: After their first costume attempt fails (all four attempted to go as The Flash), Sheldon dresses in a black body-suit that has white lines of varying thickness on them. The lines are a visual approximation of the Doppler effect, which he describes as "It’s the apparent change in the frequency of a wave caused by relative motion between the source of the wave and the observer." This effect is commonly noticed when a train or emergency vehicle passes, and the sound of the whistle or siren changes in tone. This change in the frequency of the sound wave is due to the motion of the source. The doppler effect for light waves works in much the same way, though there are some different effects due to the theory of relativity. This causes a shift in the wavelength of the light, so it's sometimes referred to as either "redshift" or "blueshift" depending on the direction of motion of the light source.
Raj (Entering dressed as Thor): Hey. Sorry I’m late, but my hammer got stuck in the door on the bus.
Leonard: You went with Thor?
Raj: What? Just because I’m Indian I can’t be a Norse God? No, no, no, Raj has to be an Indian God. That’s racism. I mean, look at Wolowitz, he’s not English, but he’s dressed like Peter Pan. Sheldon (entering in a body suit featuring black and white vertical lines) is neither sound nor light, but he’s obviously the Doppler Effect.
Sheldon: So what time does the costume parade start?
Penny: The parade?
Sheldon: Yeah, so the judges can give out the prizes for best costume, you know, most frightening, most authentic, most accurate visual representation of a scientific principle.
Penny: Oh, Sheldon, I’m sorry but there aren’t going to be any parades or judges or prizes.
Sheldon: This party is just going to suck.
Penny: No you don’t. Oh, hey, what’s Sheldon supposed to be.
Leonard: Oh, he’s the Doppler Effect.
Sheldon: Yes. It’s the apparent change in the frequency of a wave caused by relative motion between the source of the wave and the observer.
Leonard: That’s Penny’s ex-boyfriend.
Sheldon: What do you suppose he’s doing here? Besides disrupting the local gravity field.
Leonard: If he were any bigger, he’d have moons orbiting him.
Sheldon: Oh, snap.
Leonard: Look, if this was 15,000 years ago, by virtue of his size and strength, Kurt would be entitled to his choice of female partners.
Sheldon: And male partners. Animal partners. Large primordial eggplants, pretty much whatever tickled his fancy.
Leonard: Yes, but our society has undergone a paradigm shift, in the information age, Sheldon, you and I are the alpha males. We shouldn’t have to back down.
Sheldon: True. Why don’t you text him that and see if he backs down?
Leonard: No. I’m going to assert my dominance face to face.
Sheldon: Face to face? Are you going to wait for him to sit down, or are you going to stand on a coffee table?
Leonard: Okay, I understand your impulse to try to physically intimidate me. I mean, you can’t compete with me on an intellectual level and so you’re driven to animalistic puffery.
Kurt: Are you calling me a puffy animal?
Penny: Of course not, no, he’s not, you’re not, right Leonard?
Leonard: No, I said animalistic. Of course we’re all animals, but some of us have climbed a little higher on the evolutionary tree.
Sheldon: If he understands that, you’re in trouble.
Kurt: So what, I’m unevolved?
Sheldon: You’re in trouble.
Kurt: You know, you use a lot of big words for such a little dwarf.
Penny: Okay, Kurt, please.
Leonard: No, Penny, it’s okay, I can handle this. I’m not a dwarf, I’m a Hobbit. A Hobbit. Are misfiring neurons in your hippocampus preventing the conversion from short-term to long-term memory?
Kurt: Okay, now you’re starting to make me mad.
Leonard: A homo-habilus discovering his opposable thumbs says what?
Leonard: I think I’ve made my point.