It was likely a flowery, temperate day in June when Hugh Everett’s daughter attempted suicide. Her brother found her on the bathroom floor, limp and loose and almost lifeless. She made it to the hospital on time to survive though the event barely made an impression on her father. Everett, who would be revered for his work in physics and top secret military developments at the Pentagon, merely gave an upward glance from his newspaper and uttered something dismissive about the whole event. He didn’t know his daughter was so sad, he remarked. He died in bed just a month later, amongst the heavy heat of the 1980’s July.
But though that is the reality of what happened in our world, in another world things might have unfolded very differently. Everett would have been a warmer man, or his daughter a happier girl. The house would not have borne the signs of chain-smoking and alcoholism. It would have been a different life. And it was Everett’s work in the field of quantum mechanics that enables us to even fantasize about this — that he could have led billions and billions of different realities just as right now there are copies of us leading realities we’ve never even daydreamed about. In some of them our choices are decidedly better; in others they may be much worse.
His multiple worlds begin with the simple, beautiful mathematics of the Schrodinger equation.
The difference between classical mechanics and quantum mechanics comes down to predictability and limitation. We can see classical mechanics at work in our everyday lives. The gears of our great machines spin around and around while overhead astronomical bodies trace their path across our expansive skies. These things are real, with a clear past and a future which we can understand. But these same Newtonian laws break down once we enter a microscopic scale. There’s a strangeness infused here. The nature of the quantum world is not definite but probabilistic in nature. Setting up identical experiments won’t give you identical results. The regularity of quantum mechanics doesn’t come from individual measurements, it comes from the statistical distributions of many measurements. You cannot, for example, know where any one particle will end up even if you have the exact same experiment with the exact same particle. But statistical regularities allow you to establish where the particle is most likely going to end up. The probability of finding it in one location will be higher than finding it at another. Electrons, quarks, neutrinos, and other particles of nature all follow this behavior.
During the famous double-slit experiment, electrons fired at a barrier containing two slits will create an interference pattern, behaving as if they know there are two slits even when individual particles are fired one at a time. It’s only until a detector or observer of some kind is introduced to the experiment that the electrons choose a single slit, creating the two bands scientists originally expected from regular matter. When they are not being observed, particles will behave like waves as they travel from their source to their destination. This behavior, along with the probabilistic nature of quantum mechanics, gives us particles’ probability waves.
For larger objects, probability waves are so narrow that there’s a near 100% chance that the object will land where Newtonian laws say they will. This is why Newton’s laws work so well in day to day life. But the smaller an object becomes, the wider spread its probability wave and the more locations it’s likely to be found. The function of the Schrodinger equation — vital to quantum mechanics — is straightforward and effortless. Give it the current state of the probability wave and it’ll predict how the wave will change as time goes on. And because it has a characteristic known as linearity, a complex wave can be broken apart into smaller, easier to understand pieces and then put back together again when you’re finished. Developed in 1926, there has not been a single conflict with the equation’s quantum mechanical predictions in the near century of scientific experiments.
The Schrodinger equation is consistent and applies to all particles, whether they be individual or cumulative (as in you or me). It’s elegant math that should apply to all measurements. Its linearity, however, does give rise to one detail. If there are multiple places where a particle might be found, to find the answer you’d add the measurement of each individual possibility so that an electron with five possible outcomes will give you a probability wave that’s the result of those five individual measurements. And this extends to our brains as well. They will imagine the electron as being in five different places all at once.
Therein lies the problem — the question which leads to the unfurling of the quantum multiverse. If there are many different possible outcomes, why do we only experience one? How is the shift made from the uncertain and probabilistic quantum world to the singular experience we have in our lives?
In the Copenhagen Interpretation, the act of observation causes the probability wave to “collapse”. The collapsed wave now says there’s a 100% chance the particle will land in one location and 0% chance it’ll land anywhere else. Once you’ve stopped looking, the probability wave once again spreads out. But there’s a problem. The Schrodinger equation doesn’t allow for a wave collapse. A messy and precarious solution was introduced: use the equation if there was no observation being made and disregard it if there was.
But Everett was able to suggest a more gratifying solution: one mind doesn’t register multiple results. Instead, each possible result causes the splitting of the observer so that each possible measurement is observed by a different copy of you. The value of the probability wave determines how many parallel realities are created. Every possibility — every quantum measurement — is realized in a separate world. This leads to a huge number of worlds being constantly created with each particle interaction in the universe and each copy of you being no less genuine than any other. There is no one world that holds the real you; they’re all the real you but in different worlds you’re making different choices, making different inquiries out of life. There are scientific proposals which say that higher wave probabilities lead to more genuine copies of yourself but what exactly that means is difficult to answer.
Because each possibility does take place in its own world and because every new you is as genuine as any other, this introduces a mechanism for immortality. Quantum transitions which might give you a disease in this world will always have an alternate reality where no disease ever develops. Your death in one world would continuously have new branching universes where you live on in one way or another — through quantum possibilities masquerading as luck. But there are, of course, details of this theory that are yet to be clarified. Does consciousness only ebb into living copies so that you are truly immortal? And what of quantum situations where there is no possibility in which you survive? The related theory, quantum suicide, asks that you imagine pointing a gun at your head and pulling the trigger. With each pull of the trigger, you will both survive and die an infinite number of times as new parallel universes express each possibility. You will continue to survive and you will continue to die indefinitely but since you experience only outcomes in which you live, from your perspective you will know immortality, never death.
Despite the obvious intricacies with this thought experiment, Everett believed in the theory of quantum immortality. Though his son may have found him dead that hazy summer morning in Virginia, in his subjective experience Everett continued to live on. Perhaps he entered a more forgiving universe in which he’d placed his children before his work. Upon touching his father’s body, Everett’s son remarked on what a detached moment it was for him. He couldn’t remember ever feeling his father’s skin before, or of the family thinking of Everett as anything other than an unfeeling piece of furniture in the house. A little over a decade later Elizabeth attempted again to take her life and this time succeeded. She ingested a great deal of sleeping pills and wrote in her note about her father. She was leaving, she said, to go see him again. Not in heaven, but in a different universe where they could meet once more. Her father had asked for his ashes to be thrown out with the trash. His wife kept the remains for many years but then finally complied, setting the remains of the physicist out with the garbage.