Schrödinger's cat
In simple terms, Schrödinger stated that if you place a cat and something that could kill the cat (a radioactive atom) in a box and sealed it, you would not know if the cat was dead or alive until you opened the box, so that until the box was opened, the cat was (in a sense) both "dead and alive". This is used to represent how scientific theory works. No one knows if any scientific theory is right or wrong until said theory can be tested and proved.