Schrödinger's cat, often described as a paradox, is a thought experiment devised by Erwin Schrödinger. It attempts to illustrate what he saw as the problems of the Copenhagen interpretation of quantum mechanics when it is applied beyond just atomic or subatomic systems.
The concept of superposition, one of the strangest in quantum mechanics, helped provoke Schrödinger's conjecture. Broadly stated, the superposition is the combination of all the possible positions of a subatomic particle. The Copenhagen interpretation implies that the superposition only undergoes collapse into a definite state at the exact moment of quantum measurement.
Schrödinger's mind-game was meant to criticize the strangeness of this. Influenced by a suggestion of Albert Einstein, Schrödinger extrapolated the concept to a larger scale. He proposed a scenario with a cat in a sealed box, where the cat's life or death was dependent on the state of a subatomic particle. According to Schrödinger, the Copenhagen interpretation implies that the cat remains both alive and dead until the box is opened.
Schrödinger did not wish to promote the idea of dead-and-alive cats as a serious possibility; quite the reverse: the thought experiment serves to illustrate the bizarreness of quantum mechanics and the mathematics necessary to describe quantum states. Several interpretations of quantum mechanics have been put forward in an attempt to resolve the paradox. How they treat it is often used as a way of illustrating and comparing their particular features, strengths and weaknesses.