[red75prime]

Branching of multiverse on every measurement event is an approximation. The branches aren't fully isolated. I suspect that extremely low amplitude branches undergo merger events, which makes it impossible to have coherent timeline in them. But I'm completely out of my depth here.

[jerf]

I don't think that's an official part of the theory. It may be true, but I don't think anyone's proposed it.

Defining "low amplitude" branch meaningfully would be a real challenge. As I like to say sometimes, the probability of anything happening is indistinguishable from zero. 15-16 billion years after the Big Bang, we've already got a pretty low amplitude, one that would require something like arrow notation (as I reference in another comment) to describe where we are now relative to where the universe started. Heck, it takes arrow notation just to describe how much probability mass we're shedding every second.

(It actually occurs to me after a discussion of this that I can tweak an argument I've been growing over the years to prove that you can't have all three of "a universe that never ends", "the quantum multiverse", and "a coherent conscious experience".)

[red75prime]

A world where each and every person still lives would be pretty bizarre. That's around 107 billion people.

[jerf]

Such a world is utterly dominated by the worlds in which you are kept conscious, but nobody else is. If QI keeps you conscious for a billion years, you'll be alone.

(I keep typing "you are kept alive", but that's not the promise. Only conscious. Being "alive" will be extraneous to that.)