The idea behind quantum immortality is that there are infinite universes, and everything that can happen, happens in at least one of those universes. Thus, if you were to fall from a building, for example, then you would, in at least on of those universes, land in a bush or tree, or get blown onto a canopy, etc.
The scenarios described in quantum immortality usually only cover drastic events, though, where the “decision” between live and die is obvious. A gun fires, a bomb explodes, you fall from a building, etc.
But old age is not quite as obvious as that. It’s a lot more gradual.
Having said, that, though, maybe old age is the same?
When we say that someone died of old age, what comes to mind is that someone gradually declined until either they just stopped breathing, or their heart stopped.
Those are definitive moments that, if we’re talking about old age degeneration, and not something traumatic, has no obvious cause and is random in nature. Will the heart stop now, or in a minute? Will this be the last breath? It’s impossible to predict, making this ideal for quantum immortality.
You see, with quantum immortality, the fact that something is random means that it will happen in some universes, and won’t happen in others.
So, in many universes, the person that’s lying on the bed dies this hour. In some others, in a few hours, and in even rarer universes, the person lasts the day and is still hanging on tomorrow.
Quantum immortality relies on there being a universe for every possibility. Not just most. Every. So, if there is a random chance that the person will survive the day, even if the chance is one in billions, then it will definitely happen.
And because every death has some cause behind it, even if we don’t yet know what the cause is, the person that is dying on the bed just has to last long enough for the cause to be found and its cure applied.
Quantum immortality guarantees that the person will survive long enough, even if it’s tens (or hundreds!) of years. Luckily, though, we are living in very interesting times, and all causes of death are being discovered and cured, with new cures available almost every week.
With quantum immortality, old age is not to be feared – it just means you’ll be sick for a while until the cure for aging (*cough*senolytics*cough*) is found.