Everything is connected. My mother provided my existence in the first place. When she walks out of the room, she still breathes in oxygen and breathes out carbon dioxide, she still consumes food and water, releases methane, sheds skin as dust, absorbs sunlight, and consumes products. This book I hold in my hand, it required the existence of a bookbinder, of a writer, of an editor, an accountant, a tax man, a delivery man, a construction worker, a copyright official, and on and on. These people poured their existence into that object, just as all of my ancestors going back a billion years poured their existence into me. Right now, me typing this on a screen, requires all of them, everything, all connected, all pouring into this moment. Without those people, without those worlds and physical laws, without even you, without your questions and thoughts, I wouldn't be here, doing this; I would be someone else, or nothing at all.
I am, therefore you are.
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.