# How far is a light year? On the cosmic scale, it is so small

Since the birth of mankind millions of years ago, with the gradual evolution and evolution of human civilization. The birth of human civilization also corresponds to the birth of various scales, such as the unit used to measure distance, the unit used to calculate time and so on. But the unit of measurement of the ancients is different from that of us now.

We now measure the distance in meters and kilometers, and the basic distance unit is meters. With the calculation standard of distance, the measurement standard of speed will naturally come into being. We stand on the earth, and the distance is measured in meters or kilometers. This is because the size of the earth is limited, and there is not much distance from the south pole to the North Pole. With the developed means of transportation, the distance of the earth has become very short.

However, when people came out of the earth to see the vast universe, we found that the earth is too small, I’m afraid even the dust is not. In the process of exploring the universe, nature can not do without the measurement of distance, and it is not appropriate to measure the distance between celestial bodies with the basic unit meter or kilometer on the earth.

If you are in the solar system, it is OK to calculate the distance in the basic unit of the earth, km. But if you look at the Milky way and the whole universe, you need a larger distance unit. At this time, light-years appear. A light-year distance is a 365 day run of photons at the speed of light, which is about 300000 kilometers per second. So how far is a light year away?

If you want to calculate the distance of one light year, others are very simple. According to our common speed formula, you can easily calculate it by computer. As long as we convert the time of one year into seconds, and then multiply it by the second speed of light, you can get the distance of one light year. Based on 365 days a year and 299800 kilometers per second of light speed, the length of a light year is about 9454492.8 million kilometers, which is about 9.46 trillion kilometers.

I believe many friends are scared by this number. If you still can’t feel how long the distance is, we can understand it by comparing it with some reference objects in reality. For example, the circumference of the earth is about 40000 kilometers, which is not only one 200 million times of a light year. A light-year distance can emit 740 million earths. The distance between the sun and the earth is about 149 million kilometers, which is 63500 times that in a light year.

It takes nearly 30 million years for an athlete to run at the speed of a 100 meter champion for a light year. It takes more than 8 million years for a 350 km / h high-speed railway to run for one light year, and it also takes about 1.2 million years for a civil aircraft to fly for one light year. After reading the comparison of these real reference objects, do you understand how long a light year is, and that the length of a light year is a number that we can’t imagine.

The distance of one light year is a huge and unimaginable number in human eyes, but it is also a very small distance unit on the scale of the universe. From the cosmic scale and the earth scale, a light year is equivalent to one meter on the earth. In the vast universe, light year is only a basic distance unit, which is no different from the basic distance unit on the earth. It is only applied in different scenarios. One is applied in small areas such as the earth or the solar system, and the other is applied in the vast universe.

With the basic cosmic distance unit of light years, it is easier for us to calculate and count the distances between galaxies and celestial bodies in the process of exploring the universe, which is more conducive to the study and exploration of the mysteries of the universe. The diameter of the solar system, including the Oort nebula, has reached one light year. Therefore, with the current scientific and technological strength of human beings, it will take more than ten thousand years to fly out of the solar system wrapped by the Oort nebula. Therefore, although Voyager 1 and Voyager 2 have entered interstellar space, they are still far away from actually flying out of the solar system.

The nearest billing Galaxy in the solar system is about 4.2 light-years away from the earth. The earth is about 26000 light-years away from the center of the Milky way. The diameter of the Milky way is more than 100000 light-years. The Andromeda galaxy, the neighbor of the Milky way, is about 2.56 million light-years away from us. From these data, we can see that one light year is really nothing in the universe. The distance between two galaxies can be as little as a few light years, but as much as several million light years.

The diameter of our galaxy, Virgo, is more than 200 million light-years, and the observable universe is 93 billion light-years. The more we know about the universe, the more we will feel the insignificance of the earth and human beings. Some people once thought that the earth’s position in the universe is equivalent to a grain of dust, but the real situation may be that it can’t even count as dust, and the dust can still be seen. However, in the universe, if you want to see the earth, you can only get close to it. Thus, the earth may be equivalent to the size of a particle in the low light level world.

After understanding the vastness of the universe, many people will feel hopeless. With the development speed of human science and technology, can we really hope to explore the whole universe? If you want to explore the universe, you must have a basic speed corresponding to light years. This basic speed is the speed of light, which is equivalent to the basic speed of the earth in meters per second.

Only when the speed of the spacecraft is based on the speed of light, far beyond the speed of light, can the dream of exploring the universe be realized. For example, the speed of a civil aircraft is about 250 meters per second. If the speed is based on the speed of light years, the speed of the spacecraft should reach 250 times the speed of light, which is a good speed. But at this speed, we may be free to explore the galaxy, even some galaxies near the galaxy, but we need to explore the whole universe faster.

On the scale of the earth, the fastest rocket can reach the first cosmic speed, that is 7900 meters per second, which allows human beings to walk out of the earth. Then, on the scale of the universe, the flying speed must reach 7900 times the speed of light, so that it is possible to explore further and even go to the edge of the universe. So how long will it take us to achieve this speed?

I believe it will be a very long time. We can’t break away from the shackles of Einstein’s theory of relativity, because according to Einstein’s theory of relativity, the speed of an object can only be infinitely close to the speed of light, but can’t reach it. Under such circumstances, even the most basic speed of light can not be achieved, let alone fly faster than light.

Therefore, every time the quality of speed is improved and changed, we need to break the shackles of the original scientific system. For example, to achieve the speed of light, we need to break the shackles of the theory of relativity. To achieve the speed of light, we also need to break the shackles of the original scientific system. It’s not so easy to do this. We need to know that the breaking of a scientific system needs to be done It may take thousands of years, tens of thousands of years, hundreds of millions of years or even more.

Although the road of human civilization will be full of all kinds of dangers, as long as human civilization can continue, we believe that one day we can realize our dream of exploring the universe freely. At that time, we will no longer be confined to the universe. It is possible that we can break through the shackles of the universe and go beyond the universe to explore more mysterious and unknown space.