Science: Quantum Immortality

First, let us consider the many-worlds interpretation of quantum mechanics because this is essential to understanding the concept of quantum immortality.

In what follows I will presume that you have a basic acquaintance to the concepts of quantum mechanics.

In the many-worlds interpretation of quantum mechanics, the wave function collapse mechanism is substituted by a splitting of the observed system - each new branch corresponding to one possibility. Suppose the wave function of a system S is the superposition of two measurable states A and B. According to the Copenhagen interpretation, on measurement the wave function collapses and the system evolves from being in a mixed state to the measured state. In the many-worlds interpretation, the system splits into two: one yielding the value A and the other B. If we apply this interpretation to all the systems i.e., to our world itself then the this universe is continuously splitting and branching so that all quantum-theoretically possible combinations of measurements are realized. Thus the splitting leads to a tree structure in which following one line of branches from the root yields one possible world. One may also state that mixed quantum mechanical states result from superposition of more than one world.

Secondly, let us come to the idea of Quantum Immortality.

The many-worlds interpretation implies that any likely event, however improbable, does get realized in some world. Now imagine the process by which a man X is led to his death dependent upon factors each of which may or may not happen. Note that even if one of the contributing factors to death is such that the quantum theory predicts it with a 100% probability then the death is a must no matter how and how many time the observer's world splits and branches. Otherwise, of course, there will be worlds in which none of the factors contributing to death may happen. Consequently, these will be the worlds in which X will not die. All the worlds being considered together, X will continue to live in some worlds and thus X will be immortal.

But is this really the sense in which a living being can be said to be immortal? This leads us to the third part of our argument.

Assuming that we understand the meaning of consciousness, it is not as if when the man dies in one world his consciousness is transferred to another. Like all other attributes, consciousness too should split along with X as should his identity. On death, few worlds will inherit consciousness while others won't.

If the above assumptions hold (including absence of a 100% probable factor leading to death) then I (the first person) should also continue to live forever. But the "I" is also splitting. And the likelihood that the "I" that is writing all this is the same "I" that is immortal (or say, the "I" which will live for 1000 years) is just as much as the fraction of worlds in which this "I" is immortal (or, has a life span of 1000 years). To get an idea of this likelihood we can do our maths in this very world if we could calculate the probability of this "I" surviving forever (or for 1000 years). I have included this '1000 years' alternative so that you wouldn't at once assert impossibility of the referred event.

Maybe, one could argue, the probability of observing a 1000 year old man can be increased if we include in our survey all the men on the earth. Yes, the likelihood will increase roughly six billion times but how significant that increase will be depends upon the result that we arrive at (which, for all you know, could be too low to expect to yield a positive outcome in an experiment. Thus it must be extremely unlikely for any of the experiments to witness a 1000-year old man.

We have so far assumed that the identities across the various worlds do not interact. Suppose, in some way, they did. In other words, suppose the various worlds interfere with each other. Then, for any given man, in the long run, we should expect a certain concoction of many of his dead versions and a very small fraction (relative to the number of the dead versions) of his immortal or near-immortal versions. Although I have not given due thought to this aspect I think the identity as we assert it in terms of "I" cannot be a superposition of the dead and immortal "I".

I will try to explain why I think so. Call it the splitting of the world into more than one or the collapse of the wave function, the end result is that you, as the observer capable of asserting an identity, finally record only one possible state of a system even though others were likely. This record becomes a part of your history. The other possibilities which were potential until the measurement had occured do not become history. At least, not in your world. If these possibilities are part of the records in other worlds, then those other worlds also have a different copy of "you" than the one in this world. Since you are unable to see those other possibilities as interfering with your records; and also the same quantum theory that leads you to hypothesize the other worlds gives you no clue as to their existence, I believe that the various worlds, if they exist, do not interfere. Thus there cannot be a trans-world identity of an individual. As a result, few of your copies (formed as a result of splitting of the world) would be immortal, but the majority will not be. Whether you are immortal or not depends upon which particular copy you are.

Let us remember that the idea of quantum immortality makes sense only if all your copies can somehow interact or interfere or superpose etc. (choose your verb) and the resultant "you" carries a single consciousness (whatever that means) that spans across the many worlds.

I hope the above is useful in clarifying the ideas and issues related to quantum immortality.