Below is a classic thought experiment, pillaged from my book The Geeks' Guide to World Domination (Be Afraid, Beautiful People). I'll post a new thought experiment each day this week.
But, imagine you had a box filled with molecules, vibrating away at various speeds and creating by their interaction a constant temperature inside the box. Now, stick a divider down the middle of the box, splitting it into two chambers. In this divider is a tiny door operated by a demon (potentially Dick Cheney). The demon opens and closes the door, allowing faster (hotter) particles to bounce naturally into the right chamber and slower (cooler) particles to bounce into the left chamber. Over time, the order of the system is increased—the right chamber gets hotter and the left chamber gets cooler. Remember, the demon has added or subtracted nothing from the system, only opened and closed a door, thus allowing particles to pass through on their natural paths.
Does this violate the Second Law of Thermodynamics? What d'you think?