What lies beyond the boundaries of the universe?

The world we know is not infinite. Many people wonder, if the universe is finite, then it must be part of something.

Such questions will never end even though one day we may know what lies beyond the borders of the universe.

The universe is just a grain of sand in the galaxy

Our universe was born from a big bang. This explosion must have originated from a singularity with an indefinite, and perhaps unlimited, density. After this explosion, space and time were created, first as light radiation, then gradually forming heavier elementary particles, which combined together into atoms, molecules, the smallest dust and gas particles, and the final result was galaxies, stars, planets. and our life today.

According to today's data, we can estimate quite accurately that the above big bang happened about 14 billion years ago, 10 billion years later our Earth was born, and intelligent humans appeared about 15,000 - 20,000 years ago (mid and late ice age).

For a long time, humans have been constantly searching for their origin in the universe. After thousands of years of mistakenly believing that we are the center of the universe, the revolutions in perception from the time of Copernicus, Galileo (16th, 17th century) until now when we have gone more than 10 years into the 21st century, have given us a better understanding of our true position.

We are not just microorganisms on a planet orbiting the Sun, but the Sun itself is not the only star, it is just one of 200 billion stars in the Milky Way galaxy.

Meanwhile, this galaxy is just one of more than 50 members of the Local Group, a galaxy population located in the Virgo galaxy supercluster - one of thousands, millions or billions of galaxy superclusters in the universe.

Yet, to date, the furthest humans have ever set foot on is our satellite, the Moon. The 384,000km from Earth to the Moon may seem like a lot when you consider the everyday scale. But let's put it into perspective.

At a speed of approximately 300,000 kilometers per second, it takes light just over 1 second to send an image from Earth to the Moon, but it would take it more than 50 billion years to reach the edge of the universe . Perhaps our civilization in the next few hundred years will hardly allow us to travel even beyond this small galaxy.

Maybe we won't be out of this galaxy for a few hundred years.

However, even though we cannot go out into space ourselves, humans have not stopped observing it. Until now, we have been able to receive signals from places billions of light years away (even though it is only information about them billions of years ago, and maybe their distance was not even a few billion light years back then).

The universe is a high-dimensional space (more than 4) and it also has its limits , which are increasing due to the constant expansion. Research in recent years has shown that our universe will probably not end with a collapse and collapse of matter, it will continue to expand, making the density more and more diluted until all interactions disappear.

Even so, no matter how much the universe expands, it is still just a balloon that is being blown up, it can keep getting bigger and bigger, but ultimately it must have a limit.

What is outside the universe?

To date, there is no solid evidence for the existence of anything outside the universe , but a model called the multiverse is still of interest to many people because it explains the chances of universes and life beyond our own limits.

Essentially, the multiverse is just a proposed model based on the multiple histories hypothesis and probability in quantum mechanics.

Sometimes it is also called parallel universes with the main content that our universe is not the only one but there may be other universes existing parallel to ours. This multiverse theory has 4 forms divided into 4 levels with different differences compared to our universe.

Level 1: There exists other universes independent of ours. They have the same physical properties as ours, no difference, except that the probabilities and conditions are different, so they will produce different results.

There could be life like us, and civilizations just like us, with perhaps slightly different properties. At present, a rather faint evidence for this is the irregularity at some points in the detected background radiation.

As we know, this background radiation was emitted not long after the Big Bang and spread throughout the universe, what we obtain today is its remnant, so it is the witness to the early period of the universe.

The unevenness in this radiation background raises the question of whether the universe collides with other universes as proposed by the multiverse theory, of course, until now these are still just doubts.

Level 2: At this level, we see the multiverse as 'bubbles' born in empty space. These bubbles may be pushing apart from each other just like galaxies are moving apart in our universe.

In this hypothesis there is more difference. The physical and mathematical equations are still the same between the universes but not only the initial conditions are different but also the physical constants such as the speed of light, the gravitational constant. may be different due to the different structures of matter.

Level 3 : This is the multiple history/multiple world hypothesis that we often see in science fiction movies. There may be worlds parallel to ours but with different constants leading to different consequences. Like the robot cat.

Doraemon, in fact when the robot cat Doraemon returns to the past to help Nobita, it is a different world and history, while the original history still happens in another parallel world.

Level 4: This model is the most blatant. The parallel universes have almost nothing in common with ours. Not only the conditions in the physical constants, but also the physical laws are completely different.

The geometry of universes at this level is completely different, while our universe today is an open universe, there are many closed universes, flat universes, universes with complex spacetime structures, constantly fluctuating. and there are even open universes but with different physical laws, completely strange elementary particles, where we have no chance of survival if we were pushed there.

Nowadays, people try to find other signs similar to irregularities in radiation as evidence for the existence of the multiverse (at any level), but with today's technology, any measurement of this background radiation is not absolutely accurate. Assuming there is evidence of other universes, the possibility of being able to observe them is impossible.