The world we know is not infinite. Many wonder, if the universe is finite, then it must be part of something larger.
Such questions may never cease, even though one day we might discover what lies beyond the boundaries of the universe.
The Universe is Just a Grain of Sand in the Galaxy
Our universe was born from a big bang. This explosion originated from a singularity with an undefined and potentially infinite density. After this explosion, space and time were created, initially manifesting as light radiation, which gradually formed heavier elementary particles that combined to create atoms, molecules, and the smallest particles of dust and gas, culminating in galaxies, stars, planets… and ultimately, the life we know today.
According to current estimates, we can accurately predict that the aforementioned big bang occurred about 14 billion years ago. Our Earth came into existence about 10 billion years later, and human intelligence emerged approximately 15,000 to 20,000 years ago (during the late Ice Age).
For a long time, humans have been seeking to understand our origins in the universe. After thousands of years of mistakenly believing we were the center of the universe, revolutions in understanding from the time of Copernicus and Galileo (16th and 17th centuries) up to this point, as we delve deeper into the 21st century, have revealed much about our true position.
We are not just microorganisms on a planet orbiting the Sun; the Sun is not the only star; it is just one of the 200 billion stars in the Milky Way galaxy.
This galaxy, in turn, is just one of over 50 members of the Local Group, a collection of galaxies within the Virgo Supercluster—one of thousands, millions, or even billions of superclusters in this universe.
Yet, at this point in time, the farthest humans have ever ventured is the Moon, our satellite. The distance of 384,000 km from Earth to the Moon seems vast when compared to our everyday measures. But let’s try to put it into perspective.
At a speed of approximately 300,000 kilometers per second, light takes just over 1 second to send an image from Earth to the Moon, yet it would take over 50 billion years to reach the edge of the universe. It seems unlikely that our civilization will allow us to escape from this tiny galaxy even in the next few hundred years.
It seems unlikely that in a few hundred years we will escape from this galaxy.
Nevertheless, even if we cannot venture into the distant cosmos, humanity continues to observe it. To date, we have been able to receive signals from places billions of light-years away (even if that information pertains to billions of years ago and the distances at that time may not have been billions of light-years).
The universe is a multidimensional space (more than 4 dimensions) and it also has its limits, which are continually expanding. Research in recent years suggests that our universe may not end with a collapse and retraction of matter; it continues to expand, resulting in an increasingly diluted density until all interactions cease.
Despite this, no matter how much the universe expands, it is still like a balloon being gradually inflated; it may keep getting larger, but ultimately, it must have a limit.
What Lies Beyond the Universe?
As of now, there is no concrete evidence for the existence of anything outside the universe, but a model known as the multiverse is of great interest to many because it explains the possibilities of other universes and life beyond our limits.
Essentially, the multiverse is merely a proposed model based on the hypothesis of historical multiplicity and probabilities in quantum mechanics.
It is sometimes referred to as parallel universes, with the main concept being that our universe is not unique, and there may be other universes existing parallel to ours. This multiverse theory has 4 levels, each differing from our universe in various ways.
Level 1: The existence of other universes independent of our own. They have the same physical properties as ours, differing only in probabilities and conditions, leading to different outcomes.
In this level, there could be life like ours, with civilizations similar to ours, though their characteristics might vary slightly. Currently, a rather vague piece of evidence for this is the anisotropy observed in certain points of the cosmic microwave background radiation.
As we know, this radiation was emitted not long after the Big Bang and spread throughout the universe; what we observe today is its residue, serving as witnesses to the early universe.
The anisotropy in this radiation raises questions about whether our universe has collided with other universes, as the multiverse theory suggests, although these remain mere questions for now.
Level 2: At this level, we perceive the multiverse as “bubbles” formed in an empty space. These bubbles may be moving away from each other, much like galaxies are moving apart in our universe.
This hypothesis introduces more differences. The physical and mathematical equations remain unchanged across universes, but not only the initial conditions differ; there may also be different physical constants such as the speed of light and the gravitational constant, resulting in different material structures.
Level 3: This is the hypothesis of historical/multiversal worlds that we often encounter in science fiction films. There may be parallel worlds to ours, but with differing constants leading to different consequences. Just like the robotic cat
Doraemon, when he returns to the past to help Nobita, it represents a different world and history, while the original history continues in another parallel world.
Level 4: In this model, the differences are most pronounced. The parallel universes are nearly identical to ours. Not only are the conditions in physical constants different, but the physical laws are also entirely different.
The geometry of the universes at this level varies completely. While our current universe is open, there may be many closed universes, flat universes, and universes with complex spacetime structures, continuously fluctuating… and there may even be open universes with different physical laws, with fundamental particles that are completely alien, where we would have no chance of surviving if hypothetically transported there.
Currently, efforts are underway to search for additional signs similar to the anisotropies in the radiation to provide evidence for the existence of the multiverse (at any level). However, with today’s technology, any measurements of this background radiation are not yet absolutely accurate. Even if evidence of other universes exists, the chances of observing them are virtually impossible.
