[roywiggins]

Hold on, assumption 2 does not seem right. There should be lots of versions of you cheerfully experiencing timelines that involve an imminent lightning strike, gamma ray burst, etc. Those things haven't happened yet, so those worlds still have a conscious you in them. Retroactively declaring those selves unconscious seems to be a much stronger idea than quantum immortality.

Also, there is a way to test quantum immortality for everyone, not just yourself. Build a world-spanning doomsday machine. Give it to highly unstable, paranoid people, and distribute the ability to trigger it widely. Perhaps add in some geopolitical tensions, technical failures, ego, and military-industrial collusion. Make it really unlikely that it will remain untriggered. The longer we experience a world with such a device armed and ready, the more likely quantum immortality is true. There would be all sorts of bizarre close calls, and the world history would get more deranged by the year as timelines trigger the device and drop out, leaving progressively weirder timelines to survive.

But that would be crazy, nobody would ever build such a thing.

[roywiggins]

Part of the reason 2) can't be right is that there are lots of versions of you that are similar, but not quite the same. Suppose you're born with a severe life-limiting genetic disease caused by a single de novo mutation that will kill you by age 20. But in another timeline, there's a person who was born exactly the same as you were, but without the mutation, who will definitely live longer than you. Are you and them the same person, so you're not conscious? Is your consciousness proof that you're not the same person, after all? Should we consider everyone with a life-limiting disease p-zombies?