The Nerdvana Annihilation
Sheldon: Why’d you set it for the day before yesterday?
Leonard: Because I want to go back and keep myself from getting a time machine.
Sheldon: You can’t. If you were to prevent yourself from buying it in the past, you would not have it available in the present to travel back and stop yourself from buying it, ergo, you would still have it. This is a classic rookie time travel mistake.
Leonard: Can I go back and prevent you from explaining that to me?
Sheldon: Same paradox. If you were to travel back in time and say, knock me unconscious, you would not then have the conversation that irritated you, motivating you to go back and knock me unconscious.
Leonard: What if I knocked you unconscious right now?
Sheldon: [PAUSE] It won’t change the past.
Leonard: But it’d make the present so much nicer...
Nov 2nd