Since the Big Bang, matter in the universe has been distributed throughout space and time. However, as galaxies formed at different times and had different initial masses, the gravitational forces of these galaxies also vary.
If we conduct an investigation into the distribution of galaxies in the universe, we will find that in certain areas, the number of galaxies is concentrated significantly, and these regions often shine brightly, whereas others are scattered in groups of galaxies, resembling homes in the suburbs of a city.
In the observable universe with a diameter of 93 billion light-years, there are indeed some regions that are not black holes, but within this spacetime, there are no stars or planets, and dark matter and dark energy do not exist. This is often likened to voids or gaps in the universe.
The Boötes Void is a spacetime region with a diameter of nearly 250 million light-years, containing very few galaxies. It is the largest void we have ever known in the universe. (Image: ZME)
This spacetime region is called a cosmic void
The closest void to Earth is the Boötes Void, which is 700 million light-years away from us. Inside it, there are no stars and everything is completely shrouded in darkness, its operational range is astonishingly vast at 250 million light-years – while the diameter of the Milky Way is only 180,000 light-years; and the diameter of the Solar System is just 2 light-years. In other words, if the Solar System were at the center of the Boötes Void, astronomers might feel that there is only one galaxy in the universe: The Solar System Galaxy.
Matter is too scarce in the Boötes Void. (Illustration: Zhihu).
Because matter is too scarce in the Boötes Void with a diameter of 250 million light-years, many science fiction enthusiasts feel that the Boötes Void seems to have been formed unnaturally, as if some force had forcibly cleared out that 250 million light-years. Meanwhile, conspiracy theorists suggest that this strange void is the result of extraterrestrial wars, perhaps a conflict between two ancient supercivilizations, which ultimately created this space devoid of any matter.
Of course, the scientific community would certainly not endorse these baseless speculations, so research into the Boötes Void must rely on scientific detection methods.
The center of the Boötes Void is approximately 700 million light-years from Earth. (Image: Zhihu).
In the cosmic microwave background radiation map reflecting the entire universe, the Boötes Void has almost no matter within it, resulting in its temperature being significantly lower than the surrounding spacetime, leaving a blue cold spot on the microwave background radiation map. In the future, if a spacecraft from human civilization accidentally enters this area, it would be like an ant falling into the Pacific Ocean; the people on the spacecraft would lose all sources of light and would be unable to access stars that could replenish thermonuclear fuel.
The endless night with a diameter of 250 million light-years resembles a colossal wall that cannot be crossed in the universe, which for any civilization that has not mastered ultra-light spacecraft technology or deep-space travel technology, this spacetime is insurmountable and could hinder the expansion of most civilizations.
The seed of the Boötes Void likely formed at the beginning of the Big Bang. (Illustration: Science Alert).
How did the Boötes Void form?
Astronomers believe that the seed of the Boötes Void likely formed at the time of the Big Bang. Subsequently, as the universe accelerated its expansion, the Boötes Void grew larger, eventually forming the diameter we observe today.
The Big Bang theory posits that our universe originated from an explosion caused by quantum fluctuations, and before the Big Bang, quantum disturbances in the field indicated that there must have been some relatively empty spaces within the particles of the Big Bang. With the explosion in the early stages of the Big Bang, these spaces developed into cosmic voids, and the Boötes Void is just one of them.
Of course, there is also a hypothesis that the Boötes Void with a diameter of 250 million light-years did not form naturally, but rather consists of many smaller voids merging during the expansion of the universe, similar to how black holes devour one another to form larger black holes.
The Boötes Void may have formed from the merging of smaller voids, like many soap bubbles coming together to form a larger bubble. (Image: Zhihu).
Currently, we are even within a void, but this void is too large for us to notice – the Milky Way belongs to the Laniakea Supercluster, which contains about 100,000 galaxies. It may seem large enough, but when scaled to a more macroscopic state, the Laniakea Supercluster is merely a point surrounded by voids.
What is certain now is that for a long time into the future, the voids in the universe will be walls preventing human civilization from observing the universe. Humanity may never know what lies beyond those voids and will have no chance to cross these gaps – a region with a diameter of hundreds of millions of light-years, a dark region devoid of internal energy supply.
