The universe is constantly expanding. In what kind of space is it expanding? Inseparable from the universe is not fast enough

On the earth, most people may not care how big the universe is, because the size of the universe seems to have nothing to do with them, because for them, the earth is already big enough, and it is too big to walk in a lifetime. Finish. Even so, human beings still look up at the deep space under the guidance of their dreams, and this look is really surprising. The universe is too big. The earth where humans live is located in the solar system, and this star system with a radius of one light year is definitely an insurmountable space for today's human beings, although we can launch some spacecraft like "travelers", Let them fly aimlessly out of the solar system, but it definitely can't be regarded as leaving the solar system in the true sense.

The solar system is everything to human beings, but it is insignificant to the universe. The solar system belongs to the Milky Way. In the Milky Way, stars like the sun are calculated in hundreds of billions, and the Milky Way belongs to the local group of galaxies, the local galaxy. The group is also a component of the Super Virgo galaxy cluster, and how many such galaxy clusters are there in the universe? No one can tell.

So how big is this universe that can hold massive galaxy clusters? The radius of the observable universe reaches 46.5 billion light-years, and what we usually call the universe refers to this observable universe.

So beyond the observable universe, is there an unobservable universe? Of course there is. Living on Earth, everything is so close to us and the speed of light itself is so fast that we mistakenly think that "seeing" is an instantaneous thing. In fact, the fact that we can see things is due to the reflection of the light on this thing into our eyes, and the light cannot be teleported. Although it is fast, it also takes time. Its speed is 299792458 meters per second. . So, the sun we see is the sun 8 minutes ago, and the Sirius we see is Sirius 8.6 years ago.

The farther it is from the earth, the longer it takes for light to reach the earth, and beyond a certain distance, the light does not have enough time to reach the earth, so we naturally cannot see it. This is the observable universe. outside world.

So is the observable universe larger, or is the area outside the observable universe larger? Since we cannot make observations, we don't know exactly how large the region beyond the observable universe is, but we know it must be much larger than the observable universe. The universe was not so huge from the beginning. The original universe was just a singularity with an infinitely small volume. After that, the singularity exploded and the universe continued to expand. After 13.8 billion years, it has its current size, and The 13.8 billion years were calculated based on data sent back by the Planck satellite. Similarly, we can use existing data for calculations and inferences to estimate the size of the entire universe. At present, scientists believe that the radius of the entire universe should be no less than 12 trillion light-years, which is much larger than the 46.5 billion light-years of the observable universe. Unfortunately, we will never be able to verify it.

Since the universe has been expanding since its birth, what kind of space did it expand in? In fact, there is no so-called space that carries the universe. Before the birth of the universe, space did not exist at all. It was the expansion of the universe that created space.

Since there is no space before the birth of the universe, then there is no space outside the universe, at least there is no "space" in our usual sense. So what is beyond the universe? It could be a higher dimensional world. And our ability to enter that better dimensional world depends on the shape of our universe. According to the general theory of relativity, space-time is curved, and it is the mass in space that causes the curvature of space-time. The greater the mass of an object, the greater the degree of curvature of the surrounding space-time.

There is an enormous amount of mass and energy in the universe that causes space to warp, and we can't calculate whether the mass and energy are enough to make the universe a closed shape.

We can give an example, such as we are two-dimensional creatures living on paper, for us, this paper is the whole universe, if this paper is flat and open, then as long as we are fast enough, we can walk To the edge of the paper, and finally out of the paper, to the three-dimensional world. But if this piece of paper is extremely curved, so that the curvature closes and becomes a paper ball, then no matter how fast we go, we cannot leave this piece of paper. The reason is that as two-dimensional creatures, we cannot jump out of the paper and enter the three-dimensional world, we can only Moving on a piece of paper, no matter how much the paper expands, it is a ball, finite and unbounded, and it can never go out.

In the same way, if our universe is closed and there are higher dimensional worlds outside the universe, then we will never be able to see its true content. Of course, these are only theoretical inferences. In fact, with our existing capabilities, we not only do not know what the world outside the universe is like, but also cannot calculate the shape of the universe with known information.