Scientist find Quantum Mechanics a very useful way of explaining many of their experiments but it does contain some apparently odd ideas. Instead when you measure the position, for example, of a particle the act of measuring it disturbs the particle and alters what you are measuring. Because of this Quantum Mechanics can be very philosophical and Schrodinger's cat is the name given to one of the more famous philosophical problems. The problem goes like this. Imagine you had a radioactive atom.
Radioactive atoms have surplus energy and are unstable.
At any moment it will give out this surplus energy and return to being a normal atom. We say it is in two 'states' - one excited and one unexcited. One day, a guy called Edwin Schrodinger came up with an idea for an experiment. If the atom decays then a mechanism detects this and swings the hammer, breaks the bottle of poison and the cat dies. If the atom doesn't decay the mechanism doesn't move the hammer, the poison stays in the bottle and the cat lives.