universe? Maybe this can no longer be explained completely by science, and some of these ideas need to be used.
People have been thinking about this issue since ancient times. For example, the ancients tried to describe the "outside" and boundaries of the universe like this: Suppose a person keeps walking in one direction, where will he end up? Will it reach the so-called "boundary of the universe"? If we cross the border, where will we end up?
Not only the ancients, but people today also think like this. This is a bit like walking in one direction on the ground. Where will you end up?
The ancients believed that if you keep walking along the ground, you will eventually "fall". But now we know that the earth is round and it is impossible for it to "fall". If you keep walking, it is very likely to return to the starting point. Columbus's voyage around the world hundreds of years ago also confirmed this.
So, what about our universe? Does the universe have a certain shape like the Earth? What is outside the universe?
For humans, the universe is too big. The diameter of the observable universe reaches 93 billion light years. This value is basically equivalent to infinity for us. We cannot go around the world like Columbus "Travel around the universe".
Although humans cannot "jump out of the universe" in a direct way, wisdom can help us understand the universe in an indirect way.
For example, general relativity tells us that the space and time we are in is not static, but is very elastic, like elastic cloth, which can stretch or even tear.
What does this mean? The so-called straight-line motion we usually see with the naked eye is actually just a straight line in three-dimensional space. In four-dimensional space-time , objects have been moving in curves along the curved space-time. The so-called " geodesic " motion (the shortest in space and time) distance).
Any matter and energy can affect the surrounding space-time structure, causing space-time to be distorted. This means that if you keep walking in one direction, you will eventually return to the starting point, which is the origin, and will never arrive. The so-called "universe boundary" does not even cross the universe to reach another place.
This is the so-called "finite and boundless". The universe is limited, but the finite universe has no boundaries.
In addition, the basic meaning of our existence is space-time. You and I are part of the structure of space-time, and space-time is also a kind of material. Therefore, once we are separated from time and space, it is impossible for you and me to exist anymore. From another perspective, the place you can reach is always the universe, so you cannot transcend the universe and reach the "outside of the universe".
Of course, there is also a view that the universe is infinite. If this is true, it will be even more impossible to reach the boundary of the universe, because the infinite universe has no so-called boundary at all.
However, the infinite universe also means infinite possibilities. Somewhere far away, there must be exactly the same you and me, the exact same earth, sun and even the Milky Way!
