Schrodinger's cat. Composite illustration of a mirror image of a cat in a box. A quantum event (such as the decay of a radioactive particle) will trigger an event that will kill the cat, but if the box is sealed it is not known whether the quantum event has taken place or not. In this hypothetical situation, the cat is thought to be both alive and dead until observed. This is because according to quantum physics, a quantum event exists in a state of 'superposition' where both outcomes simultaneously exist until it is observed. This thought experiment was devised in 1935 by the Austrian physicist Erwin Schrodinger (1887-1961).