The business about Schrodinger's cat (called the Schrodinger Paradox) is this:
(from
http://www.windows.ucar.edu/tour/link=/kids_space/scat.html&edu=high )
"A cat is penned up in a steel chamber, along with the following diabolical device (which must be secured against direct interference by the cat): in a Geiger counter there is a tiny bit of radioactive substance, so small that perhaps in the course of one hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer which shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The first atomic decay would have poisoned it. The Psi function for the entire system would express this by having in it the living and the dead cat (pardon the expression) mixed or smeared out in equal parts. It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation." -- Erwin Schrodinger
Translation by John D. Trimmer
Basically what Schrodinger is saying is that because of the way the experiment is set up, the cat has a 50% chance of being alive, and a 50% chance of being dead. It is just as likely that the cat is alive as that it is dead, so Schrodinger said that until the box is opened, the cat is both alive and dead. This is obviously false, the cat cannot be both alive and dead at the same time. This problem is meant to illustrate a theory of quantum mechanics called "indeterminacy." Indeterminacy says that there can be more than one correct answer to a problem which physically can only have one answer.
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(me, now) Stated another way, if you don't look into the box, the cat is in a state of indeterminacy. It is both alive and dead, at the same time. By looking into the box, you force the system into choosing one of two outcomes. Interference by the observer changes the system to a state of determinacy - one of the choices becomes concrete reality.
The whole business of paradoxes in quantum theory goes away when you realize that common sense has no place in quantum theory. Common sense is a filter with which people view the world. And, as with all filters, what gets through is either incomplete or changed. Unfortunately for Schrodinger, he didn't abandon common sense, and used his example to show that he believed there was something wrong with quantum theory.
