Cover of InterWorld

I recently read InterWorld by Neil Gaiman and Michael Reaves; a book about an inter-dimensional traveller who joins a corps consisting only of alternate versions of himself preventing the forces of magic and technology from taking over the altiverse – yes, really! The book is kind of childish and I suspect I wasn’t the target audience but it did keep me thoroughly entertained from beginning to end. What I especially enjoyed about it was the setting; it was detailed and very well thought out. The technobabble, while certainly intended to be over one’s head, actually made a little bit of sense and while the setting was clearly intended only as a canvas on which to paint a cool story, the underlying world-mechanics were nevertheless sophisticated and well thought out. I’ll gladly recommend the book.

However, enough about that since this isn’t a book review. What really struck me wasn’t even in the book proper but inconspicuously hidden away at the back in an author’s note:

This is a work of fiction. Still, given an infinite number of possible worlds, it must be true on one of them. And if a story is set in infinite number of possible universes is true in one of them, then it must be true in all of them. So maybe it’s not as fictional as we think.

Quite possibly this is the best and most intuitive explanation of the counter-intuitive S5 Modal System statement that if something is possibly necessary then it is also actual.

◊□P→P

Maybe this is beyond the pale geekery on my part but it amuses me that either Gaiman or Reaves or both are so philosophically savvy – if only by accident – that they would include sound modal logic in a science fiction novel for youngsters.

Well done, those men!