Scientists usually write the dimension of spacetime as "3+1" instead of "4". Space has three dimensions. But space and space-time are two different concepts, and the latter is much more complicated. Due to the addition of time, when we describe an event, in addition to the original three space coordinates, there are also time coordinates. Events that occur in the same space at different times are different.
Two points moving toward each other along the line connecting them will always meet somewhere. Two points are in the same spatial position at the same time. The theory of relativity calls such events "synchronic events". Such an event occurs only when all the spatial and temporal factors of two different physical objects coincide.
Movements that take place in space also move in time; you, who are here now, cannot be anywhere else at the same time, you can only go somewhere else later. Einstein's special theory of relativity believes that the speed of light in a vacuum is a universal speed limit. If the speed of the object is close to the speed of light, strange time expansion and length contraction will occur. But the greatness of relativity also lies in the fact that it made another major discovery: Mathematically, time and space behave the same way.
If we remain completely still at a certain position in space, then the speed of the passage of time is the fastest. The faster we move through space, the slower time passes and the shorter the spatial distance between us and our destination. If we can achieve zero mass, then we can fly at the speed of light, and we can reach our destination in an instant, and time will not pass on us.
From a physical point of view, these conclusions are very shocking. Because this means that massless particles can be completely and completely stable, and in them, time does not pass. At the same time, this also means that a mass, unstable particle can travel far less than the actual distance. For example, the muon only needs to travel 660 meters to reach the ground from the top of the atmosphere, where it was born. One of the twins stays on Earth and the other enters space in a spacecraft at near-light speed. The latter will also be much younger than the former after returning to Earth, because time passes much slower on him.
Time is a dimension in which we travel all the time. The theory of relativity has developed to today, and also contains more abundant content. Space itself can have curvature. But whether space is flat or curved, as long as we travel in space, we must travel in time.
And no matter who travels through time and space, they must obey the same laws, produce the same effects, and get the same results. Without the time dimension, not only would the theory of relativity fail, but our universe would also be completely unrecognizable.
