Feb 28, 2024 17:00:00

Is the universe finite? What strange things would happen if it were infinite?

The universe is extremely vast, and even with modern science and technology, only a small amount is known about it. Humanity does not even have an answer to the age-old question, 'Is the universe finite or infinite?'

Kurzgesagt , a science YouTube channel, explains when the universe is finite and when it is infinite.

The Paradox of an Infinite Universe - YouTube


The universe is 'the area that includes all celestial bodies and space.' However, we can only observe the ' observable universe '. It is said that the universe was born about 13.7 billion years ago, but because the universe is constantly expanding, the size of the observable universe is much larger than 13.7 billion light years. The galaxy at the source of the light emitted 13.7 billion years ago would be approximately 45 billion light years away, taking into account the expansion of the universe.

In other words, 'observing' means capturing the light and energy that reaches below us. When considering the end of the observable universe, this is a wall created by time, so it doesn't have much meaning from a larger perspective.

The real universe is much larger than the observable universe. Whether the entire universe is finite or infinite is an age-old debate that is still being researched.

We tend to think that the fact that the universe is finite means that there must be an end, but that is not the case. For example, if a small ant continues to walk on a round orange, it will circle around once and return to its original location. The surface of an orange is finite, but for ants there is no boundary.

The same thing as this orange may be happening in 3D space. We exist on a finite earth, but what we see is the side that is closer to the horizon than the horizon. For example, you cannot observe Brazil even if you are in Japan. The observable universe is about 45 billion light years, which means that the distance to this horizon is about 45 billion light years, and from this calculation, the entire hyperspherical universe is at least 1000 times larger than the observable universe. must be large. However, in the case of the universe, it is a multidimensionally closed hypersphere , so it is impossible for us who live in three-dimensional space to visualize and recognize it.

A sphere is by no means the only shape that is ``finite but endless.'' For example, not only a sphere but also a donut-like shape (

torus ) is a ``finite but endless'' shape. However, unlike a ball, which travels the same distance when it circles from the same place in different directions, a torus travels different distances depending on the direction even if it starts from the same place.

This property greatly changes the distance of light emitted from a single star. Therefore, it is quite possible to observe the moment a star is born and the moment it dies at the same time. Unlike a hyperspherical universe, a supertorus-shaped universe with such strange properties would be several times the size of the observable universe at its smallest.

The story up to this point is based on the assumption that the universe is finite. Of course, there is also the possibility that there is an infinite world outside the observable universe.

At the time of writing the article, the ``

inflation theory '' was the established theory, and it is believed that the universe was born as a mass of ultra-high temperature, high density energy through a rapid expansion called the ``Big Bang'', and is still expanding today. Masu. The assumption that the universe is infinite and the fact that the universe continues to expand seem contradictory. However, expanding and being infinite are not contradictory. Because even if infinity expands, it is still infinite.

If the universe is infinite, it is possible that ``an entity that is exactly the same as you, down to the single atom that makes up the universe, exists separately from you within the same universe.'' Considering the probability of this actually happening, it's almost impossible, but if the universe is infinite, something like this could happen.

If a star like Earth were to exist, the probability is that it would be at least 10 to the power of ²⁹ light years away. This is well beyond the observable universe. In other words, even if there were an infinite number of beings exactly like us in an infinite universe, they would never be able to interact with each other because they are further apart than the observable region.

At this point, it seems more like science fiction than science, but if the universe is infinite, there are possibilities, and infinity is a concept that is so huge that it transcends human consciousness. We do not know whether the universe is finite or infinite, but what we do know is that we can only observe a universe with a radius of about 45 billion light years, but even that is too vast for humans.