This is a difficult one to answer. It’s kind of like asking “is God real?” – there is no compelling evidence either way.
Quantum Immortality (QI) is the idea that if the Many Worlds Interpretation (MWI) of Quantum Mechanics is true, then every possible universe exists and is just as real as this one, including every universe where you survive cancer, you fall from a building and land in a passing truck carrying hay, your plane doesn’t crash, cures for aging are discovered before you get old (hmm- sounds like this one, right?).
Because the MWI is just an interpretation of the math of Quantum Mechanics, and gives exactly the same results as all other interpretations (such as the popular Copenhagen Interpretation), there is no way to prove that it is correct or incorrect.
It boils down to faith, in the end – which one are you more comfortable believing?
1. that a quantum mechanical wave calculation is performed every instant of time, and a random result is magically chosen to become reality; the whole thing to be repeated ad infinitum (Copenhagen Interpretation)
2. that the quantum mechanical wave equation represents all versions of reality that exist, and that we are merely one of the results.
In one of these, a magical step is taken which has never been explained, and our universe pops out as the only result. In the other, the wave equation is simply a description of all realities and our universe is no more special than any other.
In a way, the puzzle is like the old physics/philosophy question – “Why is there something rather than nothing?”
Given that “in the beginning there was nothing” (let’s agree), it does not make sense that suddenly there is one single universe, and that is all that there can be. Exactly 1. No more. No less.
Even having 1 as the number of possible universes is not sensible. How did we get from 0 to 1?
Physics shows that it is certainly possible for a universe to appear from nothing. In fact, the Heisenberg Uncertainty Principle demands that a universe exist, because an empty universe is one in which the velocities and positions of all particles (all zero of them) are known, and that is forbidden.
But there is nothing in physics that says “there can be only one reality”. The math always takes place against hypothetical states of the universe, and there really is no difference between a fully calculated hypothetical simulation of a real universe (this one, for example), and the actual “real” thing. Especially from the point of view of a person living within that universe.
My own opinion is this: Quantum Mechanics describes the universe exactly. There are no known differences between QM and “reality”, that I am aware. So the only question is which interpretation is correct. Well, I believe that the simpler of any two explanations is usually the correct one. Because MWI does not require any magical “quantum collapse” step in its equations, I believe it is simpler and therefore probably correct.
The next part of this is to decide whether that means that the immortality part is real. That part is philosophical in nature.
Are you the exact same person that you were yesterday? Did you even exist yesterday?
The only evidence that you existed yesterday is what your memory and your senses tell you. But, your senses can be fooled, and your memory can be fooled as well. How do you know that your memories of yesterday were not planted in you while you slept?
If you were to die today, and an exact clone of you were to be created and given your memories, that clone would think it was you, and so would everyone else that knows you.
When you save your state in a computer game, make a mistake, then reload that state to carry on, to the characters in the game, it’s as if the mistake never happened in the first place.
If you die in this universe, and survive in another, it’s as if you never died in the first place.
In fact, coming back to the beginning of the article, for all you know, in another universe only a few minutes ago, you died of a heart attack. But do you remember that here? Of course not.
The only memories you can possibly have are those of a person that has survived everything thrown at them. The thoughts of a dead you might as well not exist at all.
While there is no way to “prove” that quantum immortality is real, I think it’s much more comforting to assume it is, than to presume it is not.
You gain nothing by disbelieving, other than a sense of finality and doom. At least by believing, you can be a bit happier in your day and nicer to your fellow humans, because you’re going to be around them for a very long time.