How could you come into contact with them again if you were in different universes? If your universe constantly communicates with theirs in order to know when to combine (when you begin to occupy adjacent corresponding space), in what sense do you occupy 'different universes'? How do you know there isn't just a wall that appears whenever you can't measure it - and how do you know it's there if you can't by definition measure it? (Note: only ask him these questions if you want to get back at him for confusing you.)
Also The Simple Truth, that one's good too.
Edit: I'm pretty sure the relevant bit is
Inspector Darwin looks at the two arguers, both apparently unwilling to give up their positions. “Listen,” Darwin says, more kindly now, “I have a simple notion for resolving your dispute. You say,” says Darwin, pointing to Mark, “that people’s beliefs alter their personal realities. And you fervently believe,” his finger swivels to point at Autrey, “that Mark’s beliefs can’t alter reality. So let Mark believe really hard that he can fly, and then step off a cliff. Mark shall see himself fly away like a bird, and Autrey shall see him plummet down and go splat, and you shall both be happy.”
We all pause, considering this.
“It sounds reasonable…” Mark says finally.
“There’s a cliff right there,” observes Inspector Darwin.
Autrey is wearing a look of intense concentration. Finally he shouts: “Wait! If that were true, we would all have long since departed into our own private universes, in which case the other people here are only figments of your imagination – there’s no point in trying to prove anything to us -”
A long dwindling scream comes from the nearby cliff, followed by a dull and lonely splat. Inspector Darwin flips his clipboard to the page that shows the current gene pool and pencils in a slightly lower frequency for Mark’s alleles.
(Emphasis mine.)
So I have a friend who I sit next to in class, and we talk about philosophy. Well today, he brought up that when people leave your presense, and you can't observe them any longer, you no longer have proof they exist.
Well I pointed out that it would violate the conservation of mass law, right?
So then, with a bit more prodding, I figured out that by "no longer exist", he means they exist in their world, but they no longer exist in mine. So basically you can't prove that anyone exists unless they're directly in front of you.
I'm really not certain how to go about answering this question. I mean, he challenged me to prove that my mother existed, without seeing her. Obviously I couldn't.
Is he right? Or is there some flaw in his argument, some fallacy that I'm missing?
I went through a few of the Sequences, and the closest article I could find was about not believing in the invisible. But in this case, he doesn't literally (I think) believe they just vanish, he believes they enter alternate universes that are selected when I come in contact them again.
My mind is boggled. I also apologize if this is dumb question, and it's common knowledge or has already been answered, and to my credit, I did make an attempt to figure out the answer before bothering you all. Thanks.