"If a tree falls in the forest and no one's there to hear it, does it make a sound?"

That is the gist of this experiment once you strip it of all its contrivances. Erwin Schrödinger's original intention in creating this puzzle was to point out the absurdity of quantum physics, namely that the state of a particle is dependent on whether anyone is watching it or not. I should point out before we begin that this is a thought experiment--no cats have ever been put throught the indignity of being sealed in a room specifically to be not seen. But I'm getting ahead of myself.

To begin at the begining: you take a cat and put it in a large steel box (or chamber) where it can't be observed by any means, be they human or electronic. Also in this room is a metal box with an electron bouncing around freely inside it. According to the Copenhagen Interpretation of quantum physics¹   you cannot know exactly where a particle is at any exact moment in time and must therefore describe its location as a probability. That means that there is an equal probability that the electron is occupying any point within the box at any moment in time. The box is built so that, by some remote command, a partition can drop and divide the box exactly in half. Once that happens the location of the electron becomes easier to understand--it's either in one half of the box or another with a 50/50 shot of it being in either side.²   One side of the box can be opened to expose its contents to the rest of the room while the other side cannot. So, once the partition is in place and half the box is opened to the room, there is a 50/50 shot the electron is inside the box or bouncing around the room.

In the room (along with the cat--mustn't forget her) is an amazingly sensitive device that will detect if the the electron has been released into the room or not. If it detects the particle the device will flood the room with a poisonous gas and kill the cat, basically meaning that the cat has an even chance of living or dying once the experiment begins.

Here's where it gets interesting. According to the Copenhagen Interpretation the electron can't be in one half of the box or another until it is observed. Once someone takes a blowtorch to the box and looks at the cat, the electron 'decides' which half of the box it was in, the probability waveform collapses and the cat becomes dead or alive according to where the electron ended up.

The experiment poses some interesting questions which, even to this day, are still being debated by scientists and philosophers alike. The most pressing question is this----what are the qualifications of an observer? Must it be human? That's a little egocentric--doesn't the cat count as an observer? How large does a system have to be before it collapses the electron's probability waveform and kills (or spares) the cat?

The most irritating thing about the Copenhagen Interpretation is that, despite the philosophical quagmire it creates, it is still a working model for describing how our universe behaves. It isn't wrong, experiments have proven that. It just defies common sense.

But then again, there's nothing wrong with shaking up our preconceptions of how the universe works every once in awhile.