Schrödinger’s Cat.
Dear Dr. Boli: My physics professor was trying to explain quantum mechanics by means of a paradox he called “Schrödinger’s Cat,” but I fell asleep like halfway through. And now there’s going to be a test. So can you explain this “cat” thing to me? —Sincerely, a Student at the Community College of Yohogania County.
Dear Sir or Madam: It will be a pleasure. The “Schrödinger’s Cat” paradox is used to illustrate the strange fact that, according to quantum theory, a system may have no definite state until it is observed.
The famous paradox goes like this. Imagine that Erwin Schrödinger is trapped in a box with a large cat, such as a tiger or jaguar. The box also contains a Geiger counter and a radioactive thingamabob that has a 50% chance of emitting one Geiger, thus causing the Geiger counter to count it and make a weird noise that the cat hates. Thus there is a 50% chance that a weird noise will enrage the cat, causing it to eat Erwin Schrödinger. According to the mathematical analysis of quantum physicists, the “system”—the box full of cat, radioactive thingy, Geiger counter, and Erwin Schrödinger—is in an indefinite state, with Schrödinger neither alive nor dead, until some observer opens the box, at which point the “wave function” “collapses,” and the observer sees either Schrödinger and the cat or a somewhat fatter cat than the one that went into the box.
But the quantum weirdness gets weirder. The box and the observer also form a system, which does not have a definite state until someone else comes in the room to see what all the fuss is about: until that moment, it is undetermined whether the observer has observed Schrödinger alive or Schrödinger as a lump in a large cat. Furthermore, that new observer forms a new system with the ingredients of the previous system, and the state of the new system is not determined until it is observed by someone else, and so on. This continual regression is known as the Von Neumann Catastrophe, because the notoriously absent-minded Von Neumann, who was always late for meetings, would be the last person in the lab to come into the room to see what had happened to everybody else, probably weeks later, and the cat would be very hungry by then.
Good luck on your upcoming test.