Thought experiment (h/t Santiago en facebook) :
Schrödinger's President: A Venezuelan president, a flask of poison and a radioactive source are placed in a sealed box. If an internal monitor detects radioactivity (i.e. a single atom decaying), the flask is shattered, releasing the poison that kills the president. There is a supposed 50% chance of this happening. The Copenhagen interpretation of quantum mechanics implies that after a while, the president is simultaneously alive and dead. Yet, when one looks in the box, one sees the president either alive or dead, not both alive and dead. This poses the question of when exactly superposition ends and reality collapses into one possibility or the other.