The original concept of quantum immortality was first published in 1987 by Hans Moravec. It is directly implied by the Many Worlds interpretation of quantum theory of Hugh Everett (1957). He noticed that it was an implication of quantum theory, and although he did not write about quantum immortality it is clear he expected to live on after death.
It is increasingly accepted that the universe includes all possible worlds, as described by Everett. This means that for every event that actually happens in the world, the other possible versions of that event happen too, in a parallel version of the world. The basic idea of quantum immortality arises in this context. Whenever you might die at the next moment, there is always an alternative moment, a different variation of reality, in which you survive. The idea is that since there is nothing to experience in the version of reality where you die, you only ever experience the one where you survive. As Marcus Chown states:
If the Many Worlds is correct, it seems the only certainty in life is not death but immortality. We’re all gonna live forever. (2002, 40)
Russian Roulette with a revolver is often used as an example. There are six possible positions of the bullet, so mechanically there are six possible outcomes. In five of them you just hears the gun just go click. There is a lot more noise in the other outcome, but you are not going to hear it because in this version of reality you no longer exist. But as there is nothing to experience in that version of reality, you inevitably experience one of the other five. That is the theory. It is examined in colourful detail in the article Does Quantum Theory Imply You Are Immortal?.
A Long Life
So if the standard idea of quantum immortality is correct we do not need to worry about Schrödinger’s cat. This is a famous thought experiment described in Schrödinger’s cat. In one version of the world he dies, but in another he survives. Quantum immortality would mean that for the cat the outcome is always survival.
Max Tegmark has examined this idea in some depth, as he describes it in his New Scientist interview with Marcus Chown Dying to Know. (That article is behind a paywall, but Tegmark reproduces it on his site – it is about a third of the way down his page The Universes of Max Tegmark.)
This kind of idea is seldom taken seriously for a number of reasons. Primarily it is unimaginable if it is taken literally. If we just go on and on and on, the body must fail more and more. So the improbability of survival must reach a hard limit at some point. But as Tegmark points out, if the idea is correct we should expect to personally survive much longer than ordinary probability would suggest. As he describes, this would not be something we would notice in the world because the increasingly unreasonable probabilities would only operate for the individual in their personal world.
The Moravec Jump
There is, however, a different kind of quantum immortality which is a good deal more interesting. As Hans Moravec states, a proper immortality is inevitable. When we die:
We lose our ties to physical reality, but, in the space of all possible worlds, that cannot be the end. Our consciousness continues to exist in some of those, and we will always find ourselves in worlds where we exist and never in ones where we don’t. (1998)
In other words, somewhere, somehow, in the universe of all possible worlds your consciousness goes on. In the infinity of possible worlds, there is inevitably a version of the world in which there is a logical continuation of your experience of reality. You live on. So the experience of death in this world leads straight on to the experience of life in the next world.
The weak point in this idea is continuity. Why should experience carry on to a different world? This is where the nature of consciousness is of crucial importance. As described in Relativity, the experiencing consciousness, ‘phenomenal consciousness’, has to be a property of the universe itself. This is spirit. This means that consciousness is to the space of all possible worlds as a computer system is to all of its memory. The computer can access any place in the memory, and it can jump from one point to another. It can play Part 1 of a movie from one block of memory then continue straight on and play Part 2 of the movie from a different block of memory. Consciousness does exactly the same thing except that each part of the ‘movie’ is a lifetime in the space of all possible worlds. When there is an end to one lifetime, consciousness simply experiences the lifetime that makes the most natural continuation, wherever that happens to exist in the universe. So death is not the end. It is just a jump from this lifetime to the next. I call it the Moravec jump.
What will it be like? As David Deutsch explains, with advanced technology it will soon be possible to make complete, functional human bodies:
Illness and old age are going to be cured soon – certainly within the next few lifetimes … by creating backups of the states of brains, which could be uploaded into new, blank brains in identical bodies if a person should die. (2011, 455)
Somewhere in the space of all possible worlds, some society in the future will take this to the next step. They will be using this technology to make new people, complete with adult characters and capabilities. They give each body a character by uploading an adult world hologram into the brain, a record of a lifetime of experiences. Let’s say they want a broad spectrum of characters, so they make sure that this initialisation is random.
Because the initialisation of the character is random, in the universe of all possible worlds every possible version of this process will actually happen. So in one of these worlds it is your world hologram, exactly as it is at the moment of your death, that gets used to initialise this brand new body. So you are the one that wakes up in this new body, next moment after death. Of course, this is fantastically improbable but that makes no odds. In the infinite space of all possible worlds it has to exist. You die. You wake up.
This must be one of the greatest revelations in the meaning of the new physics we have discovered. In the light of an eternity of lifetimes everything is different. We are infants compared to what we will become in due course. So this world is a kindergarten world! As we are just now finding out, the conscious mind is the soul. We are immortal, empowered, and we have free will. And we are constantly evolving. What we will become in time we can barely begin to imagine.