Yes, you read that right. There’s a theory out there, that can neither be proven nor disproven reliably, that states that I am immortal. It was published by Hans Moravec in 1987 and Bruno Marchal in 1988 and independently developed further by Max Tegmark in 1998, and it is based on the Many Worlds Interpretation of quantum mechanics, which you can read more about here.
“Immortality” here is actually referring to the inability to die when committing what’s called “quantum suicide”; a perfectly random occurrence that may or may not cause your death. In most thought experiments, it’s in the form of a nuclear bomb that explodes if a certain radioactive isotope decays. The chance of this occurring is exactly 50%, so you have a 50/50 chance of living or dying. This concept is called the uncertainty principle, which has some… interesting… mathematics involved (more about that here). According to the Many Worlds Interpretation, every time a random event like this occurs, the universe splits into diverging realities – one for each possibility.
So there is now a universe in which the bomb triggers, and one where it doesn’t. Let’s call them universe 1 and universe 2, respectively. In only one of those branching paths do I live, so naturally my consciousness only exists in universe 2 after the event. Repeat this experiment a thousand more times, and each time the universe splits in two, and you will have created 2^1000 universes. In only one of those, you will be alive. Repeat it a billion more times, and there will still always be one universe where you are not dead. Your consciousness ceases to exist in every other possibility, so the only one that you can observe is the one you are in. Basically, you are guaranteed to be in the universe where you won a billion consecutive coin flips, because that’s the only one in which your consciousness still exists. You would probably be convinced that you are immortal, or at least very, very lucky.
This theory only holds true for the person doing the experiment, however, which is the peculiar part. I can observe my friend doing the experiment, and whether he lives or not, I will be there to observe it. Therefore, there is a true 50/50 chance that he lives according to me – he is not “immortal” in my eyes, although in his own universe he never dies.
So I guess the moral of the story is: don’t fear death, because it will never arrive.