if there's only one person in the entire world, and that person picks up a rock off the ground and examines it, is that evidence that rocks exist? or does it require another person to be present, and see the rock, for the rock to exist? i would venture to say that the rock itself was plenty evidence to the person who picked it up and examined it, that rocks do indeed exist. what if there were no people?! would rocks exist? no one would know right?