Schrödinger's cat

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Schrödinger's cat is a thought experiment about quantum physics. It was proposed by Erwin Schrödinger.

There is a room, with a cat in it. Also a Geiger counter and a little bit of a radioactive element are in the room. Within some time, say one hour, one of the atoms may decay, or it may not. The Geiger counter can of course measure that. If it does measure the decay, it will release some poisonous gas, which will kill the cat.

The question now is, if the cat is dead, or if it is alive, at the end of this hour.

Schrödinger's interpretation is that as long as the door is closed, the cat is both dead and alive in dual superposed quantum states. When the door is opened, the quantum states are resolved and the cat is observed to be either alive or dead.