Close your eyes and let your imagination guide you beyond the boundaries of the world you know. Imagine yourself floating not in a single universe, but in a multitude of parallel realities, each with its infinite variations, each with a version of yourself that has made different choices, lived alternative lives. A multiverse, like those in the movies. Yet it is not a film: this extraordinary and unsettling vision emerges spontaneously from the most advanced theories of modern physics, From 'many-worlds interpretation of quantum mechanics tocosmic inflation.
The concept of the multiverse both fascinates and dismays us, leading us to question everything we thought we knew about the nature of reality. Let's talk about it together, because, whether we accept it or not, this idea is redesigning the way we perceive the cosmos and our place within it, and will be part of the future of science.
The quantum multiverse: many worlds, many possibilities
Imagine observing a subatomic particle, such as an electron. According to quantum mechanics, this particle behaves strangely: instead of being in a single well-defined state, it seems to exist in a superposition of possible states, as if it were in multiple places at the same time or had multiple energies at the same time. It's a bit as if the electron were in a sort of "quantum limbo", in which all possibilities coexist.
However, the moment we make a measurement to know where the electron is or how much energy it has, something surprising happens: this multiplicity of possibilities is instantly reduced to a single defined state. It is as if our observation forced the electron to "choose" one of the many possibilities in which it found itself.
But what about the other possibilities? Do they vanish into thin air or materialize in some way?
The many-worlds interpretation of quantum mechanics, proposed by the physicist Hugh Everett III in 1957, suggests a fascinating answer. Which? Every possible measurement outcome occurs in a parallel universe. In other words, the moment we observe the electron, the universe “splits” into multiple versions. Each corresponding to one of the possible states in which the electron could be found. In each of these parallel universes, there is a version of ourselves that observed the electron in a different state. It's an idea that may seem bizarre and counterintuitive, but it emerges naturally from the equations of quantum mechanics. It offers us a new and surprising perspective on the nature of reality, suggesting that what we perceive as “real” may be just one of many possibilities in a vast multiverse of parallel realities.
Cosmic inflation and the “bubbles” of universes
The idea of the multiverse, as mentioned, is not limited only to the microscopic world of subatomic particles. Even on enormously larger scales, at the cosmic level, there are theories that suggest the existence of multiple universes. One of these is the theory of cosmic inflation.
According to this theory, in the very first moments after the Big Bang our universe went through a phase of extremely rapid and tumultuous expansion. During this period of inflation, the universe expanded exponentially, becoming billions of times larger in a fraction of a second.
The most interesting aspect of this theory? Quantum fluctuations, that is, tiny variations in the energy and density of space-time, may have occurred during inflation. These fluctuations may have given rise to multiple “bubbles” of space-time, each of which may have developed into a universe of its own, with its own physical laws and fundamental constants.
In other words, inflation could have generated a multitude of parallel universes, of which ours would be just one among many. These universes could be completely different from ours, with different physical laws and properties. And they could host forms of matter and energy unknown to us. It's a fascinating and disconcerting image at the same time, which forces us to rethink our place in the universe. If the inflation theory is correct, our universe may be just a small island in a vast archipelago of universes, a fragment of reality in a cosmic multiverse infinitely larger and more complex than we can imagine.
The problem of “fine-tuning” and the need for the multiverse
Many scientists find the idea of the multiverse attractive for several reasons, but one of the most fascinating concerns what it is called the problem of “fine-tuning”.
When we observe our universe, we notice that the physical laws and fundamental constants that govern it seem to be perfectly calibrated to allow the existence of complex structures such as galaxies, stars, planets. Especially life.
Even small variations in these laws and constants would make the universe very different and probably uninhabitable. For example, if the force of gravity were slightly weaker, stars would not form; if it were slightly stronger, stars would burn too quickly and burn out before life had a chance to evolve. Likewise, if the nuclear force were just a little weaker, atoms would not bond to form complex molecules; if it were any stronger, all the hydrogen in the universe would have fused into helium in the first minutes after the Big Bang, making the formation of stars and planets impossible.
It almost seems that someone has precisely "adjusted" the knobs of physical laws to make our existence possible. But why is our universe so perfectly “tuned”?
The idea of the multiverse offers a possible explanation: if there are countless universes, each with its own laws and physical constants, it is not surprising that at least one of them, by pure chance, has the right characteristics to host life. We could imagine the multiverse as a huge collection of universes, most of which are barren and inhospitable deserts. But in the midst of this vastness, there is a universe – ours – that has won the cosmic lottery, with the perfect settings for the existence of galaxies, stars, planets and living beings.
Naturally, we find ourselves in this "lucky" universe: if it were otherwise, we wouldn't be here asking ourselves the question!
This reasoning, while fascinating, does not convince all physicists. Some find this too speculative or unparsimonious of an explanation. However, it offers an intriguing perspective on one of science's greatest mysteries: why does our universe seem tailor-made for us? Don't look to me for the answer, of course.
The limits of science and the fascination of the unknown
Of course, the idea of the multiverse raises profound questions about the nature of science. Since, at least for now, we have no way of directly observing these parallel universes, we are in the realm of speculation, however fascinating and mathematically founded.
Some scientists believe that a theory that cannot be tested experimentally is not real science, but others point out that many of our most advanced theories, from general relativity to quantum mechanics, have aspects that elude direct verification. Perhaps, they suggest, we need to accept that there will always be mysteries that science cannot fully reveal, and that the task of theoretical physics is to go as far as mathematics and imagination can take us, even at the cost of losing contact with reality. empirical.
Towards new frontiers of the possible
In any case, the idea of the multiverse fascinates us because it touches deep chords in our psyche: the desire to explore the unknown, to imagine alternative possibilities, to question what we take for granted. Whether it is a bold theoretical speculation or a faithful description of reality, the multiverse reminds us that the cosmos is much larger, stranger and more surprising than we can conceive.
Perhaps, in some remote corner of this infinite web of universes, there is a version of me who is writing completely different things to you. Maybe clearer to read, why not?
After all, as the great physicist Richard Feynman loved to say, “our imagination is stretched to the max. Not as in fiction, to imagine things that don't really exist, but precisely to understand those that do exist."
