One dimension is linear, and there is a primitive creature that can only move linearly, that is, there is only the concept of front and back. Two-dimensional is plane and can only be operated in one plane. Three-dimensional is the concept of space, that is, in a space, four-dimensional is the concept of crossing space, which can cross from one space to another. There is a story in a science fiction film that a man is locked in a prison, but he can escape. In fact, this is because he crossed the space, from a space.
Parallel universe, or multiverse, refers to a theory that has not been proved by physics. According to this theory, there are probably other universes besides our universe, and these universes are a reaction to the possible state of the universe. These universes may have the same or different basic physical constants from those we know.
Parallel universes are often used to explain that different processes of an event or the subsequent development of different decisions exist in different parallel universes; This theory is often used to explain other paradoxes, such as some paradoxes about time travel, such as "a ball fell into just visiting and hit itself in the past, making it impossible to enter just visiting". To solve this paradox, besides assuming that time travel is impossible, it can also be explained by parallel universe. According to the parallel universe theory, the ball hitting itself and not hitting itself are two different parallel universes, and so on.
At first, scientists put forward a series of "natural possibilities" instead of the hypothesis of modern physics: the size of the universe is infinite (or at least large enough), and as astronomical observations have pointed out, matter is evenly distributed. In this case, according to the statistical law, it can be concluded that all events (no matter how similar or identical) will happen countless times: there will be countless planets that will give birth to human beings, among which there will be people exactly like you-with the same looks, names, memories and even the same actions and choices as you-and there will be more than one such person, to be exact, infinite.
The latest cosmological observation shows that the concept of parallel universe is not a metaphor. Space seems to be infinite. If so, all possible things will happen, no matter how absurd. Beyond our astronomical observations, there is a universe exactly like ours. Astronomers even calculated their average distance from the earth.
You may never see your shadow. The farthest distance that you can observe is the farthest distance that light has traveled since BIGBANG: about 654.38+0.4 billion light years, which is 4x10.26 meters-which defines the size of our observable horizon, or simply, the size of the universe, also called Hubble volume. Similarly, the other universe you live in is also a sphere of the same size. The above is the most intuitive explanation of "parallel universe". Every universe is a small part of a larger "multiverse".