Does "Who's to know" mean the same as "Who knows"? While practicing my English listening, I heard "who's to know". It's from the following context, though I'm not sure if I correctly wrote down words from audio. Does "who's to know" mean the same as "who knows"? If so, are they used interchangeably? "What sort of form will these life forms take? I mean this planet has evolved: plants, humans, fungi, even dinosaurs. So who's to know what sort of beings there are, why out there? I mean on the sci-fi program, they always look basically humanoid, and roughly outside, but in reality who knows?"