Take "Three-body" as an example, in which the endless stream of ideas is amazing. Especially the spacecraft that can fly faster than light, many people are eager to try and expect this kind of spacecraft to really appear in the future. The future may be too far away, so imagine it now. If we fly a spaceship flying one light-year per second, how long will it take us to reach the edge of the universe, and what can we see on the journey?
First of all, before flying, we need to make it clear that light years are units of length. Literally, light travels in a straight line in a cosmic vacuum environment for one year. The speed of light is 299792458 m/s, so the specific value of a light-year is 9460730472580800 m, which is 9.4607 10 12 km.
Knowing the specific value, we can start flying. If we can fly a light-year in one second, we will reach the edge of the solar system in one second. It should be noted that there are two definitions of the edge of the solar system. The first one is outside the heliosphere, which is the edge of the Voyager probe. The second is outside the gravitational range of the sun, that is, outside the Oort cloud. It took us a second to fly near the Oort cloud, and then we will really rush out of the solar system.
After flying out of the solar system, it takes about 3.22 seconds to reach proxima centauri in Centauri A, which is the closest star to the solar system. Eight seconds later, we can see the brightest star in the sky, namely Sirius. At this time, it is close at hand, which is quite different from when we look up at the earth.
After flying for dozens of seconds, we will meet many planets that have been observed on the earth. For example, the brightest "diamond planet", Cancer 55e, looks like a shining ball of light in the universe.
After about 15 minutes, a light will appear before our eyes. This is made by Betelgeuse, the brightest blue Supergiant star in the universe discovered by human beings at present. It is about 863 light years away from the earth, and its luminosity is1.2000 times that of the sun.
If our naked eyes look directly at this strong light, we may be blind, so we may have to wear special glasses during interstellar travel. Six hours later, we will fulfill a dream of mankind, that is, to fly out of the Milky Way, because at this time, everyone has reached the edge of the Milky Way. Here, we may be able to take pictures of the Milky Way in the spaceship. After all, we have never taken a panoramic view of this beautiful galaxy from the perspective of God before.
Next, we will go to the nearby Andromeda galaxy, which is extremely huge, about 1.6 times the diameter of the Milky Way, and 2.54 million light years away from the Earth. Even if you can fly a light-year in a second, it will take a long time to cross, at least a month.
Then the scope of the universe will make us feel how small we are. For example, it will take at least two years to fly over virgo supercluster with a radius of 654.38 billion light years. It will be hundreds of years before we reach the largest black hole ton6 18. At this time, the passengers on the spacecraft may have changed for several generations. After all, our life is so short.
So, after hundreds of years, have we reached the edge of the universe? It turns out that we think too much, but it's still far away. According to the size of Hubble, its radius is about 46 billion light years. This means that even if we fly a spaceship at the speed of one light-year per second, it will take us about 1450 years to reach the edge of the known universe.
It can be seen that the speed of light, which is already very fast in our view, is also very slow in front of the vast universe. Needless to say, people's life span is only a few decades, and it is generally difficult to live to a hundred years old. Therefore, even if we start now, it is impossible to reach the edge of the universe in our lifetime.
In addition, if the universe inflation model really shows, the universe is actually expanding, and the expansion speed far exceeds the speed of light. This means that we are driving a spaceship close to the edge of the universe, but the edge of the universe has been accelerating away from us.
And our spacecraft can only reach one light-year per second, which means that our flight speed will never keep up with the expansion of the universe. If our technology is not enough to speed up the spacecraft, the descendants on the spacecraft will not reach the edge of the universe even if they can continue forever.
What's more, the known edge of the universe actually belongs to the Hubble volume, and we can only determine this edge when we see the light from a distant place. It's hard to say whether there are other celestial bodies behind this light. We thought it was the edge of the universe, but it was only a small part of the universe.
In that case, does the universe have boundaries? This problem is actually difficult to explain, because even with the help of tools, we can't "see" that far, so the boundary of the universe is still an unknown thing for human beings. The boundary we are talking about now is actually the observable edge of the universe.
Professor of physics department of California Institute of Technology put it this way:
So the boundary of the universe we are talking about now is not the boundary that everyone can see and touch. It is the result of tracing back after the light reaches the earth. In fact, the universe is not as simple as most people think. It can extend in all directions or be self-enclosed. But it is like a sphere we see in our daily life. There is no such thing as an advantage. You won't return to the starting point until you walk around.
Since the speed of light is too slow in front of the universe, can we try to fly faster than light? In this case, if we compress the time again, maybe we can compress 1000 to 100, or even 10, so that human beings may catch up with the expansion of the universe and really reach the edge of the universe.
However, according to Einstein's theory in special relativity, the speed of light cannot be surpassed, so from the perspective of modern science and technology, it is impossible to fly faster than light. But countries all over the world are still carrying out research on superluminal. After all, our journey destination is not only the edge of the solar system, but the farther and wider universe.
Professor Lin Jin, a scientist from China Academy of Launch Vehicles, pointed out in his academic report at the Third Forum on the Development of Modern Basic Science:
It can be seen that superluminal flight is actually possible in theory. However, at present, humans can't even build a light-speed spaceship, so it's too early to consider a superluminal spaceship from now on. But this is not too ambitious. After all, we have to face and solve this problem sooner or later.
Many people should have heard of mirror universe, or multiverse. This means that there is a larger space than our universe, full of many bubble universes, which are similar, but not exactly the same.
If humans really find the edge of the universe, when they get there and continue to explore outward, they may have crossed the edge of the current "bubble universe" and entered another nearby universe.
Therefore, even at the edge of the universe, there is no particularly clear boundary. After all, the transparent film of "bubble" may have crossed as early as it was formed, and the universe is like a "Russian doll" nested in a ring.