Our human observation of the universe is limited by two major factors, one of which is that the speed of light is limited, which causes those very distant rays of light that have not yet spread to the earth, and the other factor is that the universe has been accelerating and expanding, which causes the celestial bodies to be far away from each other, and the farther away they are, the faster they can move away from each other, so that those objects that are very far away from us are moving away from us faster than the speed of light, and we cannot observe them.
So we can only observe the universe on a limited scale, and as it stands, our farthest observation distance in the universe is about 46.5 billion light-years, that is, the universe we know is a spherical space with a radius of 46.5 billion light-years. So we have the question, since the universe is known to have a radius of 46.5 billion light-years, what would we see if we flew out of that range?
According to the observations of the universe by scientists over the years, from a large scale point of view, the distribution of matter and energy in the universe is isotropic, in short, we look in all directions of the universe, the macroscopic structure of the universe is the same, it is as if we take a small boat drifting in the depths of the ocean, no matter which direction you look, the sea surface is the same, but the sea surface is two-dimensional, the universe is three-dimensional.
So it can be said that if we fly to the edge of the known universe, then we can see a lot of celestial objects that we have never seen before, but in general, the macroscopic universe we see will not be significantly different.
This speculation is a bit boring, but we are talking about what we will see if we fly out of the known universe, and we do not say that we can only fly 46.5 billion light years, so if we fly farther, what will we see?
Einstein told us that objects with mass can bend the originally straight three-dimensional space, and because the universe is isotropic, the universe will have a whole curvature, which can be divided into the following three cases.
It can be seen that if the curvature of the universe is negative or zero, the universe is open. And when the curvature of the universe is positive, the shape of the universe is a closed three-dimensional sphere, in this case, if we fly towards the same aspect, as long as we fly faster than the speed of the expansion of the universe, then after flying for a long enough time, we can return to the starting point, as if we have been walking on the surface of the earth to the same aspect, except that the surface of the earth is a two-dimensional sphere, and the universe is a three-dimensional sphere with one more dimension.
It can be seen that if we consider it purely from the perspective of three-dimensional space, then no matter what shape the universe is, in our eyes, the universe is borderless, in this case, no matter how far we fly in the universe, we cannot fly to the edge of the universe, and because of the isotropy of the universe, so although we can see different celestial bodies in different positions, in our eyes, the macroscopic structure of the universe is always the same.
As shown in the figure above, points A, B and C are all above the two-dimensional sphere, while point D is outside the two-dimensional sphere, and it is obvious that only point D can see the full picture of this two-dimensional sphere, and this is the reason why D point has an additional dimension.
This means that if we want to expand our field of vision, we need to fly out of the three-dimensional space and observe from a higher dimension. And if we do, then we will look directly at the shape of the universe, which may be a closed spherical surface, or a curved saddle surface, or like a flat piece of paper, but these shapes have a three-dimensional structure.
So the question is, on a larger scale, what is outside the universe? Although no one knows the definitive answer to this question, many hypotheses have been put forward, such as the idea that the outside of the universe is a void, with neither time nor space, and certainly without any matter or energy.
It is also believed that there are other universes outside our universe, whose number may be infinite, and whose internal physical laws may also be different, and these universes together with our universe form an infinite structure. It is worth mentioning that there is an interesting view that the universe we live in may be a super black hole, why do you say that? Let's move on.
A black hole is a kind of enclosed space in the universe that is completely isolated from the outside world, its shape is a three-dimensional sphere, and its radius is called the Schwarzschild radius, and the specific calculation formula is as follows.
We can simply understand that when the natural radius of an object with mass is smaller than its Schwarzschild radius, it becomes a black hole. As can be seen from the figure above, the Schwarzschild radius of an object is proportional to its mass, and we all know that the volume of the sphere is proportional to the cubic root of its natural radius, which means that for a uniformly dense sphere, when its mass exceeds a critical value, its Schwarzschild radius will exceed the natural radius of the object.
Since the known universe is isotropic, we can think of it as an object with uniform density, according to the estimation of observational data, the mass of the known universe is 10^54 kg, and it can be substituted into the above formula to conclude that the Schwarzschild radius of the known universe is about 1566.71 light years.
Obviously, this is far beyond the natural radius of the known universe of 46.5 billion light-years, which is why it has been proposed that our universe is a super black hole, and beyond this black hole, a much larger universe is wrapped in it, just as there are many black holes in our universe.
It should be noted that the above views are reasonable speculations based on the cognition of the known universe, and are not the conclusions of the scientific community, so it is enough for everyone to understand, and there is no need to take it too seriously.
Well, today we will talk about this first, welcome to pay attention to us, we will see you next time.
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