This is a strange idea that requires a weird interpretation or view of Many World theory. First, quantum level effects must exist on the macro scale of our everyday lives. Second, every event that occurs must somehow have a ton of other ways it could have turned out, even if no decision-making was involved on our part. I think both of those claims are a bit odd even for Many Worlds, but hey let’s go with it.
The idea of quantum immortality is that every time you die, a parallel reality splits off in which you didn’t die. This happens because whatever killed you in this reality ends up taking a different causal path in the split reality, this is supposed to refer back to the cat in the box being both dead and alive at the same time… again, not sure if that is really a macro-scale phenomenon but hey. Maybe it is and we just don’t know it.
And that’s the cool idea about quantum immortality: even when we die, an identical version of ourselves splits off into another parallel reality a la Many Worlds theory, and ‘we’ go on living. ‘We’ never experience dying because when we die in this reality, our subjective self-consciousness no longer exists here, therefore we cannot be experiencing anything. But we still exist in the split reality. Let’s say you step out into the road for some reason and a car hits you, bam, you die. But in the split reality the car just barely misses you because of any number of countless possible things that happened just slightly differently to delay your stepping into the road by a second or two. All that needs to occur is one small difference based on a quantum fluctuation, and now you are alive. The car missed you.
So according to Many Worlds theory, both realities exist. But you are only aware of the one in which you are alive.
In this way, every time we die, we split off and keep existing. AND we are only ever aware of the realities in which we exist. Cool huh?
An interesting consequence of this idea is that we might never be able to die. Ever. Unless there were literally NO possible changes AT ALL, ANYWHERE in our reality that could have happened and caused our death to have been avoided. But that seems impossible, because there should always be some alternate reality in which something was different that caused us to keep living. Even if we get very very old and die of old age, at that moment there should be another reality in which life-extension technology already exists and you didn’t die. Or an alternate reality in which they had better medicine to keep you alive for longer. Or an alternate reality like Metamorphosis of Prime Intellect, in that story the AI becomes so powerful it merges with reality and keeps every human alive forever, if they somehow die it just recreates them again. Etc and etc, if you think about it there are almost endless possibilities for alternate realities that could split off leading to you still being alive, no matter how you ended up dying.
So how far does all that go into the future? Well, theoretically it should go forever. There should be parallel realities in which life extension or transhuman technologies already exist and people do not die anymore. Maybe that isn’t even that far off in our real world, or maybe it already exists for the very exclusively rich and powerful, who knows. In any case, the weirdest consequence of this idea is that you might never die. Ever. Or maybe at least until the literal universe itself dissolves in countless thousands of millions of billions of trillions of years from now or whenever that might actually occur… but even then, there are probably parallel universes where time travel exists so the ‘you’ facing universal annihilation can just go back in time and keep looping in time forever, therefore still achieving immortality.
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