The analogy of the cave.[footnote]This is what I understand to be the analogy of the cave, I have yet to read The Republic so please bare with me and feel free to correct me. I swear, as soon as 1984 is finished I'll be all up in Plato's business.[/footnote]
If prisoners have been strung up on a wall for their entire lives, seeing only shadows projected onto the cave wall, then that is what they know to exist. If they were to stay in the cave forever, then they would only know of that one experience and would define that as existence. They would never know of the world outside the cave or that life is more than shadows until they were freed and could go out and experience the cave.
Similarly, we will only ever know of this existence and won't be able to say that one another doesn't exist without experiencing some other form of existence.
Until someone experiences other existence, then what we know as existence now is all we will ever know. We cannot say that this is not existence because there is no other existence to know of.
If I scale it down a little and swap things around, until you observe[footnote]Observe as in know of them,. You have seen light bounce from them and have experienced them as a physical entity.[/footnote] someone else, you cannot know of their existence and therefore do not exist.
For all you know, I am merely an advanced AI because you have not observed me, because you know nothing of my existence as a physical entity.
