On July 19, 1982, a 19-year-old man named Mark Oliver found his 51-year-old father, Hugh Everett III, dead in bed. Heart failure had taken from this world a physicist who loved to eat, smoke and drink, and who was suspicious of conventional medicine. He had arranged that, after his death, his ashes be thrown in the trash, something that his wife took several years to fulfill. Her daughter, Elizabeth, committed suicide in 1996. In her farewell note, she asked that “please put my ashes in the water… or in the trash; maybe that way I end up in the right parallel universe with dad.”

Because **Everett was the inventor of the parallel universes or multiverses** .

Everett disliked the commonly accepted solution to what is called the measurement problem in quantum mechanics, and so he developed a theory known as the **Many Worlds Interpretation** (also called the Many Histories Interpretation).

The matter is as follows. One of the consequences of quantum mechanics – the theory that describes how the subatomic world behaves – which has been inconceivable to many physicists since it appeared in the 1920s, is that a system does not have its properties well defined until the you measure In other words: our daily experience tells us that if someone disappears from our sight when walking through a door, they do not cease to exist, we have simply stopped seeing them. But in the subatomic world this is not true: **reality, understood as something objective that is out there, does not exist** , it is only an illusion; we do not see things in themselves, but aspects of what they are. This is the so-called *Copenhagen interpretation* , proposed by Niels Bohr in 1927 and which comes to say that we must accept that there is no deep reality, that we live in a ghost world where nothing is defined until it is measured. To put it more or less poetically, **the Moon does not exist until someone looks at it** .

This is where Everett’s radical proposal from 1957, later taken up by Neil Graham and Bryce De Witt in 1970, is linked. does not have a defined weight but rather a probabilistic distribution of possible weights (35% that it weighs 70 kg, 15% that it is 75 kg, etc.), and that it is not until it stands on a scale that it ‘acquires’ a specific weight. So he decided to find a way to avoid it. And he found it, although the price to pay was quite high: his theory forces the entire universe to split into two, three, four… depending on the number of values that the measurement can take. For example, we know that the spin of a proton can only take on two values, 1/2 and -1/2. Well, at the moment of measurement, the entire universe would split into two and in one the spin would be 1/2 and in the other -1/2. That is, **we will have two absolutely identical universes except for that insignificant difference** in the properties of a single proton out of the millions of millions of millions of protons that exist. And this happens every time some quantum measurement is made somewhere.

As we can see, solving the measurement problem leads us to two extremes: either we accept that we live in a phantom universe where nothing is defined, or we live in a world where everything is real and there are **an infinity of parallel universes** . Which one are we left with? There is no way of knowing, but it may help us make up our minds that if the Many Worlds interpretation is correct, then we are all immortal. To understand this we must take a look at a peculiar paradox, **quantum suicide** .

Let us imagine that a physics professor, tired of thinking about the problem of measurement, decides to commit suicide by designing a peculiar device to which he fixes a revolver that, in turn, points at his head. Attached to the trigger is a device that measures the spin of a proton every ten seconds. If the value of 1/2 is obtained when making the measurement, the revolver is fired and kills the physicist. If -1/2 is output, only a ‘click’ is heard. In this case, the apparatus provides a new proton and starts over, up to ten times.

According to the Copenhagen interpretation, the physicist has a 50% chance of surviving the first 10 seconds, a 25% chance of surviving after 20 seconds, and only a 0.1% chance of surviving after 100 seconds.

But the Many Worlds interpretation solves the problem differently. As every 10 seconds the universe divides in two, in one branch the physicist dies but in the other he lives. Thus, after 100 seconds our physical is dead in all universes… except one. ” **The experimenter will discover that he is immortal** ” says the physicist Max Tegmark. However, this argument only works for the physics teacher. For his assistant, who is watching the experiment in terror, the end result is the same regardless of the correct interpretation: if it is Copenhagen, his boss had a 0.1% chance of surviving; if it is the Many Worlds, it only had a 0.1% chance of being in the universe in which its boss survives.

But, let’s insist, your boss doesn’t care. If Conpehague’s is good, he only has a 0.1% chance of surviving, but if Everett’s is correct, he knows with absolute certainty that he will come out of the experiment alive, because **there will be a universe in which he will not die** . And he will not be a different person, but an exact copy of himself: the only difference with the rest of his other *selves* is that he will not have a bullet in his head.

Obviously, no one is aware of this multiplication of universes and no one, except in the Marvel Multiverse, can travel from one to another. The idea that our body and our consciousness could have billions of copies living side by side but unable to see or touch each other is shocking, but **the underlying theory is absolutely consistent** . “Each quantum transition -explained De Witt- that takes place in every star, every galaxy, in every remote corner of the universe is dividing our local world into myriads of copies of itself. It’s schizophrenia with a vengeance!”