Previously, astronomers believed that the universe was infinite, but Einstein’s theory of general relativity indicates that our universe actually has a boundary, which exists in a higher dimension of space.
Before discussing the boundary of the universe, we first need to understand the boundaries within the universe, starting from the Solar System to the Milky Way, then to the Large and Small Magellanic Clouds, and finally to the Andromeda Galaxy, which is 2.54 million light-years away from us. These independent and closed celestial systems have clear boundaries, with light years of distance between stars and millions of light years of emptiness between galaxies creating distinct separations.
However, from Einstein’s perspective, the very fabric of space-time in the universe belongs to three-dimensional space plus one additional dimension of time, meaning that the entire universe is part of a closed four-dimensional superstructure at the macroscopic level. This implies that if someone travels in a spaceship at the speed of light in any direction, they will eventually return to their starting point. The pilot of the spacecraft might believe they are moving straight up, but in a closed universe, the very geodesic path is a closed curve that leads back to the origin before they even realize it.
In traditional geometry, we often think of space as flat, but in reality, according to general relativity, space can indeed be curved. This is due to mass and energy altering the surrounding space, causing it to curve. We often use Einstein’s famous equation E = mc² to describe this phenomenon, indicating that the presence of mass and energy affects the properties of space-time. It can be argued that the curvature of space is fundamental to the wonders of the universe. (Image: Allthatsinteresting)
This finite model of the universe is actually similar to a human journey on Earth; both move straight forward but ultimately return to the starting point. Similarly, if you want to see the entire Earth, you must ascend vertically from the ground into space; only then can you view the Earth in its entirety and assess its limitations.
Thus, if humanity wishes to perceive the limits of the universe in the future, they must first open a new direction or dimension in three-dimensional space and then travel at the speed of light or faster-than-light speeds in that new direction, allowing them to escape the world they currently inhabit.
Apart from its immense scale, the mass in the universe is also unimaginable. Stars are the most basic building blocks of the universe, and they combine to form star clusters, nebulae, and galaxies. However, the mass of individual stars is relatively insignificant. Scientists have discovered massive stellar explosions, colossal flares from these explosions releasing energy equivalent to that of all the stars in the entire galaxy combined. (Image: Allthatsinteresting).
According to the theory of parallel universes, our current universe is just one of many parallel universes. There are countless universes in vast super-space. Each universe is the product of a big bang. Different cosmic bubbles have different laws of the universe; for example, in our universe, the speed of light is 300,000 km/s, but in other universes, it might be 30,000 or 300 km/s.
However, with humanity’s current technology, discussing the boundaries of the universe is still a distant prospect, as even the Webb Telescope—the most powerful telescope humanity has—cannot see the boundaries of the universe but can only roughly infer its existence. The universe has a diameter of 93 billion light-years, and at present, humanity can only observe 2 trillion galaxies within it, remaining quite vague about the macroscopic appearance of the universe.
The universe is a vast and mysterious existence, filled with countless wonders and riddles that continuously baffle humanity in their exploration. With advancements in technology and the development of scientific theories, we gradually realize that the universe may not only exist in the familiar three-dimensional space but also have the potential for spatial curvature and parallel universes. (Image: Allthatsinteresting).
In some science fiction films, the Milky Way, with a diameter of 100,000 light-years, is merely a string of beads around a kitten’s neck, and these beads are just marbles used by advanced alien civilizations for gaming. Perhaps in the future, we might discover that the entire universe is just a microscopic grain of a macroscopic object at a higher level.
In this case, our universe may just be a small part of a larger universe, akin to Russian matryoshka dolls, or the universe could be contained within a grain of sand, possibly resting on the beach of an unimaginably vast world. Perhaps intelligent civilizations from other dimensions are currently observing the Sun and Earth, just as we observe electrons and protons.
The universe remains the greatest mystery for human civilization, and the questions regarding its boundaries will certainly be discussed many times in the future. However, regardless of where the boundaries of the universe lie or what secrets they conceal, humanity remains a civilization that has emerged on Earth.
