By Erwin Schrödinger, an Austrian quantum physicist proposed a theory or more of a paradox about a cat in a box.
This experiment (Which he actually never did), Involved putting a cat in a cardboard box and placing a poison in a flask connected to a radioactive source which had a 50% chance of going off and releasing the poison.
When the cat was in the box, it was considered both dead and alive at the same time, until you open the box. (Which is considered as an act of measurement)
Watch the video below to learn more: