Multiple Universes

In 1972, Hugh Everett formulated the many-worlds interpretation of quantum mechanics. In layman's terms, this means that there is a very large, perhaps infinite, number of universes since everything that could possibly have happened in our past (but didn't) has occurred in the past of some other universe(s). Parallel universes might provide a way out of paradoxes because all possible quantum events can occur in mutually exclusive histories. These alternate, or parallel, histories would form a branching tree symbolizing all possible outcomes of any interaction. If all possibilities exist, any paradoxes could be explained by having the paradoxical events happening in a different universe. Thus time travel then involves not moving forward and backwards through a single universe, but moving horizontally between similar universes.

A curious consequence of many-worlds is an experiment known as the quantum suicide machine has been proposed by cosmologist Max Tegmark. It examines the Schrödinger's Cat experiment from the point of view of the cat.

For example, a man sits down before a gun, which is pointed at his head. This is no ordinary gun; i­t's rigged to a machine that measures the spin of a quantum particle. Each time the trigger is pulled, the spin of the quantum particle is measured. Depending on the measurement, the gun will either fire, or it won't. If the quantum particle is measured as spinning in a clockwise motion, the gun will fire. If the particle is spinning counterclockwise, the gun won't go off. There'll only be a click.

Nervously, the man takes a breath and pulls the trigger. The gun clicks. He pulls the trigger again. Click. And again: click. The man will continue to pull the trigger again and again with the same result: The gun won't fire. Although it's functioning properly and loaded with bullets, no matter how many times he pulls the trigger, the gun will never fire. He'll continue this process for eternity, becoming immortal.

Go back in time to the beginning of the experiment. The man pulls the trigger for the very first time, and the particle is now measured as spinning clockwise. The gun fires. The man is dead.

But, wait. The man already pulled the trigger the first time -- and an infinite amount of times following that -- and we already know the gun didn't fire. How can the man be dead? The man is unaware, but he's both alive and dead. Each time he pulls the trigger, the universe is split in two. It will continue to split, again and again, each time the trigger is pulled, and become quantum immortal.

The idea behind quantum immortality is that the experimenter will remain alive in, and thus remain able to experience, at least one of the universes in this set, even though these universes form a tiny subset of all possible universes. Over time, the experimenter would therefore never perceive his or her own death.