A cat can be alive and dead at the same time, is actually explained by the quantum theory.

This refers to Schrödinger's cat, a famous thought experiment in quantum mechanics proposed by Erwin Schrödinger in 1935. It illustrates the concept of quantum superposition, where a quantum system exists in multiple states simultaneously until observed. The thought experiment places a cat in a box with a radioactive source that may or may trigger poison - until observed, the cat is theoretically both alive and dead. This paradox highlights the bizarre nature of quantum mechanics.