Sheldon: Look at Planck's Constant. People say it's arbitrary. It could not be less arbitrary. If it varied even slightly, life as we know it would not exist. Bam! Now, let's reconsider the entire argument, but with entropy reversed and effect preceding cause, so you are thinking of a universe that's not expanding from the center. No, it is retreating from a, from a possibility space. Bam! This is a space where we are all essentially Alice through the Looking Glass, standing in front the Red Queen, and we're being offered a cracker to quench our thirst. Bam! Of course, in another universe, let's call it universe prime, there's another Sheldon. Let's call him Sheldon prime...
Penny: We should have let him go to bed.
Leonard: Bam.

Leonard: Penny, as a scientist, my job is to figure out why things happen. But I don't think I'll ever understand how someone like me could get to be with someone like you. You know maybe I don't need to understand it, I just need to be grateful. I love you, Penny.

Leonard: What would you be if you were attached to another object by an inclined plane, wrapped helically around an axis?
Sheldon: Screwed?
Leonard: There you go.

Leonard: My point is, while you're spending all this time on your own, building computers or practicing your cello, what you're really doing is becoming interesting. When people finally do notice you, they're gonna find someone a lot cooler than they thought. And for those of you that were popular in high school, it's over, sorry. Thank you. Congratulations.

Sheldon: I'm sorry, coffee's out of the question. When I moved to California I promised my mother that I wouldn't start doing drugs.

Sheldon: You are effectively paying yourself five dollars and nineteen cents a day.
Penny: A day?
Sheldon: There are children working in sneaker factories in Indonesia who out-earn you.

Sheldon: Camouflaging bald spots. That's primarily a male concern. Perhaps we could expand our market.
Penny: How are flower barrettes going to appeal to men?
Wolowitz: We add Bluetooth.