It's often entertained on LessWrong that if we live in some sort of a big world, then conscious observers will necessarily be immortal in a subjective sense. The most familiar form of this idea is quantum immortality in the context of MWI, but arguably a similar sort of what I would call 'big world immortality' is also implied if, for example, we live in another sort of multiverse or in a simulation.

It seems to me that big world scenarios are well accepted here, but that a lot of people don't take big world immortality very seriously. This confuses me, and I wonder if I'm missing something. I suppose that there are good counterarguments that I haven't come across or that haven't actually been presented yet because people haven't spent that much time thinking about stuff like this. The ones I have read are from Max Tegmark, who's stated that he doesn't believe quantum immortality to be true because death is a gradual, not a binary process, and (in Our Mathematical Universe) because he doesn't expect the necessary infinities to actually occur in nature. I'm not sure how credible I find these.

So, should we take big world immortality seriously? I'd appreciate any input, as this has been bothering me quite a bit as of late and had a rather detrimental effect on my life. Note that I'm not exactly very thrilled about this; to me, this kind of involuntary immortality, that nevertheless doesn't guarantee that anyone else will survive from an observers point of view, sounds pretty horrible. David Lewis presented a very pessimistic scenario in 'How Many Lives Has Schrödinger's Cat' as well.