Chapter 2-3 Time and Space
All existence in the physical world is inseparable from time and space.
Time is the continuity and sequence of material motion. Continuity refers to the fact that the motion of any object must go through a process, whether long or short. Sequence means that time has only one direction and is irreversible. In our understanding, the passage of time always moves along the axis of "past→present→future". Once the present moment has passed, it can never return. Ancient wisdom, expressed in sayings like "Time does not come back once it is gone" and "An inch of time is worth an inch of gold, but an inch of gold cannot buy an inch of time," emphasizes the irreversibility of time, urging people to cherish it.
Space is the extension or expansion of moving matter, referring to the position, scale, and volume of objects. Space is characterized by its three-dimensionality (or even higher). The space we live in is three-dimensional. The term "dimension" comes from Latin, meaning "to measure completely". The number of dimensions is determined by the number of measurements required. In three-dimensional space, every object has a certain length, width, and height, and it always has a relationship of front-back, left-right, and up-down with surrounding objects.
Theoretically, in our three-dimensional space, nothing exists without length, width, and height. Therefore, in three-dimensional space, the human eye cannot see anything that does not belong to this space. This implies that beings in one dimension, two dimensions, or higher than three dimensions are beyond human visual perception. Whether such beings exist remains scientifically undetermined.
In ancient China, time and space were referred to as the cosmos. The saying "Four directions and up and down are called 'space', and the past and present are called 'time'" captures this concept. The four directions and up and down refer to the various directions in space, while the past, present, and future refer to the continuum of time. Our ancestors believed that the cosmos is a unified entity composed of space, time, matter, and energy, encompassing all things.
This brings us to the possibility that time might not exist in the universe at all; the concept of "time" could be entirely an invention of humans in the three-dimensional space on Earth. We have defined a "year" as Earth's revolution around the Sun and a "day" as Earth's rotation over 24 hours, naming this concept "time". In the universal perspective, time is merely another dimension within space, which can be beyond three dimensions and extend to four, five, six or even N dimensions. Buddhist teachings mention the existence of the 33 Heavens, such as Brahma Heaven, Trayastrimsa Heaven, and Tusita Heaven, suggesting unknown dimensions beyond human comprehension.
If time is considered a dimension, in a higher-dimensional space like four dimensions, time becomes another vector (a concept from mathematics), where each point on this vector can be accessed easily. For instance, as Prof. Shi Yigong once said, "When I speak here today, do you think the information disappears after my speech? No, because if you track faster than light, you can surely see my speech from ten years ago."
If time is a variable that can be freely accessed, then what we cannot see or touch in three-dimensional space might be "visualized" in four-dimensional space and beyond, just as we can clearly see length, width, and height in three dimensions. Thus, even though we might not record or remember everything ourselves, from a higher-dimensional perspective, everything that has happened in the universe throughout the river of time is recorded, allowing simultaneous observation of the past, present, and future.
Figure 2.5 is an imaginative illustration: zero-dimensional space is a point; one-dimensional space is a line, which is a variable composed of countless points and can be represented by the X-axis in mathematics, allowing basic arithmetic operations. Two-dimensional space is a plane, formed by the variables X and Y, composed of countless lines, like the images or photos we see. In three-dimensional space, there are the variables X, Y, and Z, which constitute the three-dimensional space we are familiar with. In higher dimensions, it might feel like an infinite "matryoshka doll", and no one can "depict" the appearance of higher-dimensional space within the three-dimensional world.
Figure 2.5: From one dimension to five dimensions
(fourth and fifth dimensions are purely imaginary)
Why can people in the three-dimensional world not perceive the four-dimensional space? We speculate that higher dimensions can achieve absolute "invisibility" to lower dimensions. Humans living in a three-dimensional space possess (or can only exhibit) three-dimensional cognitive and sensory abilities.
A typical analogy often used is that of crawling creatures like ants, which can only "cognize" two-dimensional space. For example, a child places an ant on a piece of paper and puts a piece of food not far from it. The ant smells the food and crawls towards it. However, just as it is about to reach the food, the child removes it. The ant has no idea what has happened, no matter how much it circles around; it doesn't realize that the child in the three-dimensional space has played a trick on it.
Similarly, if higher-dimensional spaces do indeed exist, humans might be like that ant: all our actions and thoughts could be perceived by higher dimensions, yet we, being constantly "observed", remain completely unaware. Even our every move might have been "designed" in advance by the higher-dimensional space, with our ability to achieve our goals already "predetermined". Yet, the vast majority of people feel nothing of these "gods" towering above them, as if they exist in complete "invisibility".
The book "The Earth" has a passage that describes our planet, which is like a "magnetic bubble":
"We live in a series of bubbles, nested within each other like Russian dolls. Beyond Earth's sphere of influence lies a larger bubble dominated by the Sun. Beyond that large bubble are multiple overlapping bubbles, formed by the ever-expanding remnants of stars or supernova explosions from long ago. All these bubbles exist within our Milky Way galaxy. The Milky Way is part of a supercluster of galaxies within the known universe, and this supercluster itself may just be a single bubble in the quantum foam of many worlds."
