Forever and Again: Necessary Conditions for “Quantum Immortality” and its Practical Implications

So-called “quantum immortality” should be better called “multiverse immortality,” as it mostly depends on the existence of many copies of the observer in other worlds. We identify two necessary premises when this theory becomes true: the very large size of the Universe (not necessary because of quantum effects), and the copy-friendly theory of the personal identity. We apply decisions under uncertainty to explore the situations in which multiverse immortality could be practically used. We show that, given large uncertainty, the only practical use of the multiverse immortality is as an additive to other life extension and survival projects, because in some cases it could considerably increase their chances of success. In the case of signing for cryonics, multiverse immortality significantly increases the subjective chances of its success, and also prevents a bad form of quantum immortality (s-risk of eternal suffering). Another application of quantum immortality is the survival of a global catastrophe. We also debunk several misconceptions, such as multiverse immortality is not applicable to slow dying, or quantum immortality is similar to respawning or NDE experiences. We show that the popular objection of lowering the measure of the observer in the case of quantum immortality doesn’t work, as it compensated by merging timelines. We consider multiverse immortality as plan D of reaching immortality, where plan A is to survive until the creation of the beneficial AI via fighting aging, plan B is cryonics, and plan C is digital immortality.