The presence of memories in your mind is evidence about things you can no longer see. When someone leaves your presence, you are left with a memory of them having existed. This should be very convincing evidence to you; it is quite rare to have clear memories of people that don’t exist. On the other hand, if you try to communicate this evidence to other people, it’s less convincing to them, because you might miscommunicate, or lie, and these are much more common than false memories.
Of course, it is possible that the person you remember having existed, stepped into an incinerator or otherwise stopped existing while you weren’t looking. But focusing on sufficiently-rare exceptions is a mistake; you can’t ever have 100-point-0 certainty about anything (that would require a literally-infinite amount of evidence), but 99-and-some-more-nines percent certainty really is sufficient. Emphasizing the difference between these two levels of certainty is usually an instance of the fallacy of gray.
As for the “personal worlds” stuff—we do in fact all occupy the same world, and talking about peoples’ individual worlds is just a confused way of talking about the contents of different peoples’ heads.
The presence of memories in your mind is evidence about things you can no longer see. When someone leaves your presence, you are left with a memory of them having existed. This should be very convincing evidence to you; it is quite rare to have clear memories of people that don’t exist. On the other hand, if you try to communicate this evidence to other people, it’s less convincing to them, because you might miscommunicate, or lie, and these are much more common than false memories.
Of course, it is possible that the person you remember having existed, stepped into an incinerator or otherwise stopped existing while you weren’t looking. But focusing on sufficiently-rare exceptions is a mistake; you can’t ever have 100-point-0 certainty about anything (that would require a literally-infinite amount of evidence), but 99-and-some-more-nines percent certainty really is sufficient. Emphasizing the difference between these two levels of certainty is usually an instance of the fallacy of gray.
As for the “personal worlds” stuff—we do in fact all occupy the same world, and talking about peoples’ individual worlds is just a confused way of talking about the contents of different peoples’ heads.