For much of human history, it was considered that the Sun and Earth were all that was there in the universe along with several pointy, twinkling stars in the night sky. It was only in the 16th century that astronomers were able to discover that there was so much more to the universe than we thought. Using their giant telescopes, astronomers discovered that the Sun was just one star among the 100 billion other stars circling around in the Milky Way galaxy. And the Milky Way galaxy was just one galaxy among the 10 billion galaxies fleeting away from each other like cosmic shrapnel from one single point of colossal explosion – the Big Bang.
Since the dawn of humanity, people have wandered everywhere in search of life, driven, and possessed by the one question that haunts astronomers and physicists to this very day – “Are we alone in this universe?” We have conquered the Earth and now plan to be an extra-terrestrial species in our ardent desire to find intelligent life among the stars. However, just when we presumed to understand the fundamental laws of our universe, we are bogged down with a new question, “Are we the only versions of ourselves in this universe?”
An increasing number of physicists are getting convinced that our universe is not alone, but is just one among a multitude of others like drops on an infinite ocean of time. Among them is Max Tegmark, from the University of Pennsylvania, who imagines a multiverse where each of the universes follows its own laws of physics. This would mean that the so-called theory of everything would have nothing special about it since it could only explain the phenomenon of our own universe.
Machine Gun Experiment: We can understand the existence of a multiverse using the bizarre machine gun experiment proposed by Max Tegmark. There is a spotless laboratory, which is empty, except for a woman in a white lab coat, an elderly gentleman, and a machine gun set up at the center of the floor. The woman stands at a control panel, with her index finger on a red button. The elderly gentleman stands on the other side of the room, with the machine gun in between. The machine gun is set up such that each time it fires or does not fire, it makes a dull click. Whether it fires or not, is completely random. The experiment begins, four clicks are heard. The man is still alive. From the woman’s perspective, the shot is fired during the fifth click and the man dies. However, from the man’s perspective, the shot was not fired and he is still alive after the fifth click. How is this possible?
Each time the machine gun must fire a bullet, it both does and does not. At that moment, the Universe splits into two realities: the shot was fired and the man died (the woman’s perspective), and the other in which the shot was not fired, so the identical version of the man was the man survives (the man’s perspective). The next time the gun clicks, it both fires and does not fire, creating two more new realities, two more new versions of the man and woman. And this keeps going on.
Tegmark remarked that in most cases, the man will eventually die, but he will not be aware of these realities since he would already be dead. The only realities that he would be aware of are the ones in which he would have survived.
Theory of atoms and their strange nature: Now that you have an idea about the multiverse, the next question is why are an increasing number of physicists convinced that the multiverse is real and not pure science fiction? The reason may explain one of the greatest mysteries in modern-day science – the strange behavior of atoms compared to the everyday macroscopic things.
The theory that describes the atom and its constituents, the quantum theory is the most scientific theory ever devised, with predictions accurate to several decimal places in thousands of experiments. However, despite its spectacular predictions, the quantum theory tells us a bizarre property of atoms and they’re like, to exist in several places at the same time.
“The quantum theory of parallel universes is not some troublesome, optional interpretation, emerging from arcane theoretical considerations. It is the explanation – the only one that is tenable – of a remarkable and counter-intuitive reality” – David Deutsch, The Fabric of Reality
This should be impossible for matter to exist in two separate places, however, this rule seems to be broken at the microscopic level. The quantum nature of the atoms can be verified in the double-slit experiment which directs a beam of light or electrons or fully-fledged atoms at a wall through two vertical slits. Each particle is expected to pass through one of the two slits. However, the interference pattern formed on the wall depicts that each particle passes through both the slits simultaneously! This puzzled many physicists who were concerned as to why the tables, furniture despite being made up of atoms cannot exist in several places at a given time.
Copenhagen interpretation: According to the Copenhagen interpretation, the act of ‘observing’ a microscopic particle like an atom is vital. The event of observation triggers the atom, forcing it to decide one place out of all the possible places, to exist. This crazy behavior of atoms is tolerated till the instant of observation. Therefore, the particle behaves like a well-defined localized object. In the case of the double-slit experiment, the Copenhagen interpretation suggests that the particles would pass through both the slits simultaneously in the case of no observation. On being observed, the particle is forced to choose one slit over the other and move through it only.
Many Worlds interpretation: A much easier interpretation to understanding the difference in the behavior of the microscopic and macroscopic world was the Many Worlds interpretation by Princeton graduate student, Hugh Everett III in 1957. The Many Worlds interpretation concluded that the quantum theory applied to both the macroscopic and microscopic world. In short, the world of atoms is not so different from our world. However, this meant that the same chair could simultaneously exist in two separate places. But then why have not humans ever encountered a schizophrenic chair? This is because, when we perceive the chair in two separate places, our mind exists in two different states, one which perceives the chair in one place, the other in the other place. Thus, there will be two versions of us, each perceiving a different version of the chair unaware of the other.
When Everett proposed this interpretation in 1957, he was asked a question, “Why does the pencil fall only downwards? Why can we not see it fall in all directions at once?” This question had to wait till the 1980s to be answered by Heinz Deiter Zeh (University of Heidelberg, Germany) and Wojciech Zurek (Los Alamos National Laboratory, New Mexico) who investigated a phenomenon known as environmentally induced decoherence. The crucial idea was that the superpositions in which the atoms and their like existed in several states at once were extremely fragile. They could exist in only one condition – when the object that was in a schizophrenic state was totally isolated from its surroundings. The smallest interaction, even a single photon could shatter its superposition making it fall in one direction, a process known as decoherence. Thus, the key idea of decoherence was that the collision of an object with a single photon could destroy its quantum nature, having a collateral effect on its fragile nature.
Human Consequences of the Many Worlds idea: Tegmark’s machine gun experiment proposes a remarkably interesting consequence: if you die in one reality, you still live on in the others. And since you will only perceive the realities in which you are still alive, you will find yourself to be immune to all life-threatening situations. This is because, in every situation where you will die in one universe, there will be another universe where an identical version of you would live through that situation. Thus, you would not die at 60 or 70 years, instead, you will live many more years than that in separate realities. In some realities, you might even be able to download your consciousness onto the digital platform. Thus, if Many Worlds idea is correct, then the only certainty in life would be immortality and not death.
The Many Worlds also resolves the famous Grandfather paradox. According to David Deutsch, the man goes back in time and kills his grandfather. However, the grandfather that he killed was not his grandfather but another version of his grandfather in a universe where the murderer was never born.
The reason physicists disliked and will continue to dislike the Many Worlds idea is because of the horrors of such accumulation of a multitude of universes. The physicists were happy with a 4-dimensional universe, 3 dimensions of space, and one of time, which was beyond our control. However, the idea of several universes just like your own or with different fundamental laws is bone-chilling.
Conclusion: If there is anything we have learned from science in the 20th Century, the underlying reality is that the Universe with its warped space-time and singularities is nothing like the everyday reality of our senses. Tegmark has accurately stated,
“Nature is under no obligation to make things easier for human brains or human senses. And that means it is under no obligation to provide us with a single reality rather than a bewildering infinity.”