It's funny, but I made a similar argument to some people over on the Subgenius mailing list about three weeks ago. (If you can afford to read another hundred emails a day, it often makes for highly entertaining reading, but even more, the synchronicities with this list are often mind-blowing.) But I digress.
>From: Dan Fabulich <firstname.lastname@example.org>
>The reason your question is harder to think about after the split is
>because when a split version of you thinks about the other split version
>of you, the other split version necessarily seems a little less real.
>This is not a fact about physics; this is a fact about psychology and the
>way we use language.
I don't have a problem with two realities existing simultaneously. In fact, my point is that because an infinite number of potential realities exist all the time (because the infinite possibilities for universal bi-, tri-, multi-furcation have mostly *not* collapsed), the study of how a universe bi-, tri-, or multi-furcates lacks usefulness until it starts predicting how it will collapse -- i.e., which of the many options will be favoured for us to perceive. And since quantum physics seems not to do that, I question its utility.
>Now we return to your question, "why do I perceive A and not B?" I'd
>argue that this is because it's very natural for one to think of a person
>on one side of the branch as different from the person on the other side
>of the branch. The other version of you is perceiving B, but since that
>version isn't "you," "you" aren't perceiving B. That is why "you"
>perceive A and not B. If you were to call both splits in both branches
>"you," which comes quite naturally BEFORE the split, since before the
>split both versions DO seem more like yourself, the question would seem
As and when we have a split where we identify the A-outcome and/or the B-outcome as having occured, I agree that perceiving the other possibility will be more difficult. Because at that point, the universe has already collapsed. Schrodinger's cat is ultimately either alive or dead, however many potential universes exist prior to our determining its aliveness or deadness. But what of the events that don't reach the threshold of our perception? They necessarily require multiple universes to exist simultaneously.
Certainly, every time we perceive something, we collapse myriads of universes down -- not to one, necessarily, but to a smaller number than existed previously. But here it is. We always exist in multiple universes, since even if we could pinpoint everything in space and time, no single vector can explain the space-time coordinates of everything to the exclusion of all other possible vectors.
What I'm suggesting is that all this gets us is a fancy way of saying we can't ever predict anything with absolute certainty. It's more than sensitive dependence on initial conditions that prevents this, since initial conditions are themselves a multiplicity of possibilities. And therefore, until we come up with a physics that either resolves this or builds a new set of laws that incorporates it, all we've got is glorified taoism. And that's fine, so far as it goes: we can sit on a mountaintop or in front of a computer and spout hifalutin wise-sounding stuff, but it moves us nary a whisper closer to the ultimate truth.
Um, or something like that.