According to the many-worlds theory, every possible outcome of every possible action exists simultaneously in parallel realities. Schrödinger's cat is the most famous example of this. A cat is placed in a box with a canister of cyanide. There's a 50% chance that the canister will be broken within the hour and once that hour is up, the cat exists in a quantum state of being simultaneously alive and dead. Without opening the box, we can't tell which is true and so both states are possible realities.
[ And if you talk to Kitty at the costume party a few days from now, you'll see it in costume form. ]