The theory of quantum suicide bears a striking resemblance to Schrödinger's cat experiment. It relies on the Copenhagen interpretation and the many-worlds theory, but viewed from the perspective of the cat—which, in this case, has been replaced by a man with a gun pointed at his head. Every time he pulls the trigger, the universe splits in two, depending on whether the gun fires or not. Physics suggests that if he repeated the experiment indefinitely, he would become immortal. Is this possible, or is it just a delusion of physicists?
The paradox of Schrödinger's cat, designed by the famous physicist Erwin Schrödinger, exposed one of the strangest aspects of quantum mechanics. Schrödinger imagined a cat locked inside a box, along with a device capable of releasing a powerful poison if alpha particles were detected. Since the box contains only a single radioactive atom with a 50% chance of decaying and emitting an alpha particle, quantum physics tells us that until we open the box, the cat is simultaneously alive and dead. It is we who, upon opening the box to look inside, collapse the cat's wave function, forcing the unfortunate feline into a “definitive” state. The idea of “quantum suicide” is essentially the same, but with a man in place of the cat.
In effect, the thought experiment of quantum suicide assumes a man seated inside a closed room with a gun aimed at his head. The gun's operation is tied to the state of a quantum particle. Every time the man pulls the trigger, the quantum state determines whether the bullet leaves the barrel or not. This means that when the subject decides to end his life, just like Schrödinger's cat, he has a 50% chance of dying instantly or emerging completely unharmed. As with the other experiment, each time the trigger is pulled, the universe splits in two. In one of these versions of the universe, the subject is safe and sound; in the other, he dies. And it continues splitting over and over, each time the gun is fired.
This imaginary experiment was proposed by Hans Moravec in 1987 and, independently, by Bruno Marchal in 1988. A decade later, in 1998, it was further developed by Max Tegmark. At the quantum level, matter behaves in ways that defy common sense—assuming such a thing exists—and the scientific method cannot always be applied practically. That is why physicists resort to this kind of thought experiment. In the case of quantum suicide, the aim is to test the existence of many parallel worlds.
This theory was proposed in 1957 by Hugh Everett III, and postulates that for every possible outcome of any action, the universe splits into two. In one, the outcome is one thing; in the other, the opposite. For example, if you toss a coin, the universe splits into two: one where it lands heads, the other tails. The same happens trillions of times per second with every particle that changes state or every atom that decays. This process was named “decoherence” by Everett, and it suggests the existence of an unimaginable number of parallel universes, created in industrial quantities since the beginning of time.
Returning to our suicidal experimenter, each time he presses the trigger, the gun either fires or not, causing him to die or not. Each time, the universe splits to accommodate each possible outcome. At the moment he dies, the universe stops splitting because of the experiment: the only possible result is continued death. But each time the shot doesn't happen, there are two possible outcomes: he continues living or he dies.
Obviously, because the universe splits and each resulting version has no contact with the others, the version containing the living man is unaware of the version of himself that is dead in the other universe. He simply goes on living and pulling the trigger again and again, creating a new universe each time. In one of those versions, he will never die, and he will never know that he has died countless times in the parallel universes created. He reaches a state that physicists like to call “quantum immortality”.
The Copenhagen Interpretation
Of course, there is only one universe in which this situation occurs. In the others, a huge number of versions of the man die and do not access this kind of immortality. Got it? Fabulous. Now let's see how this theory differs from another called the Copenhagen interpretation. The Copenhagen interpretation was proposed by Niels Henrik David Bohr in 1920, and basically states that a particle does not exist in one state or another, but in all possible states simultaneously. Only when we observe the particle does it adopt one of those states. The possibility that a particle exists in several states at once is called coherent superposition. The sum of all these states is called the wave function of the object. There is a lot of mathematics involved, but in reality it's not essential to grasp the idea. The fact is that when we observe the object, the superposition collapses and the object is forced to take one of the states in its wave function. This is the view explained in Schrödinger's cat paradox.
Which of the two alternatives is true? We don't know. Quantum physics is a relatively new branch of science, and to anyone who doesn't have a couple of doctorates under their belt, it sounds just as ridiculous to hear that the universe is constantly splitting as to hear that a cat is both alive and dead. We can only theorize about what happens at the quantum level, a world where the “usual” rules don't apply and many of the formulas that govern physics seem to lead to nonsensical theories. Niels Henrik David Bohr, the Danish physicist who made important contributions to our understanding of the atom's structure and quantum mechanics, once said that “whoever is not shocked by quantum theory has not understood it.” What do you think?
For more on this topic, see Quantum suicide on Wikipedia.
