# How long does it take for us to walk a light-year distance?

This paper takes part in the series essay competition of “great science” of Recordunkown.

From the day of human birth, we have seen the vast world of the earth. In the eyes of the ancients, the earth was vast and could never be completed. The ancients basically walked on their feet, and the most advanced means of transportation were just carriages.

Most of the ancients believed that the earth was a boundless world, which could not be completed by manpower. However, with the continuous development of human civilization, when we enter the era of science and technology, we realize that the world of the earth is not boundless, but a sphere on which human beings live.

Standing outside the earth, we can easily see that the earth has its own size. The circumference of the earth is about 40076km from the equator. Although the distance is relatively large, it can still be completed at the speed of human walking. If there are no obstacles along the way, at a walking speed of 5 kilometers per hour, it will take about 8015 hours to walk around the equator, which is about a year.

Of course, the above situation is only in our ideal state. In fact, the earth’s surface is full of various risks, and there are also obstacles from the ocean and other terrain. We can’t walk along the equator on foot. When we look at this data, we will understand that the earth is not big, and we can travel all over the world with the pace of human beings. Otherwise, Homo sapiens, the ancestor of modern human beings tens of thousands of years ago, could not have come to Asia from Africa.

On the earth, in order to better measure the distance, we have meters, kilometers and other distance units. These distance units play an important role in the development of human beings on the earth. However, the limitations of these distance units come into being when human beings walk out of the earth and see the vast universe.

We can measure the distance on the earth in meters or kilometers, but in the face of the vast universe, these distance units are too small. If we measure and record the distance between celestial bodies in the universe in meters, such as the distance between stars, then a distance is a huge number. A thick stack of paper may only be able to record the distance between two stars, and the distance between galaxies is even more distant, so that we can not record it in the distance unit of the earth.

At this time, scientists proposed a new unit of distance: light years. Light year refers to the distance that light travels in a year. It is used to measure the distance between distant celestial bodies in the universe. It is a distance unit belonging to the space of the universe. So what’s the distance in a light year?

As we all know, the speed of light is about 300000 kilometers per second, and the time of a year is about 31556925.9747 seconds, so the distance that light travels in a year is 9.46 trillion kilometers. So it won’t take long for human beings to walk through the earth. How long does it take for human beings to walk through a light year?

We can make a simple calculation. As we said earlier, the speed of human walking is about 5 kilometers per hour, while an hour is 3600 seconds. We can walk 120 kilometers a day, 3600 kilometers a month and 43200 kilometers a year without stopping. It takes 219 million years for a person to walk a light year.

The figure of 219 million years makes many people feel incredible. In the era of earth life, dinosaurs were just born 219 million years ago. At that time, the earth was not divided into six plates, and it was still a whole Pangea. At the walking speed of human beings, it will take us more than 200 million years to walk a light year. Obviously, we can’t walk at all. The life span of human beings is only about 100 years, but it is only millions of years since the birth of human beings.

The light year is only the most basic unit of distance in the universe, equivalent to the meter of the earth’s time. One light year seems very far away to us, but in the universe, one light year is nothing at all. The nearest star system to the solar system is also 4.2 light years away from us. And the entire solar system, including the diameter of the Oort cloud, can reach more than one light year.

It is when we see the vastness of the universe that many people worry about the future of mankind. You know, at present, the fastest detector of mankind is the Parker solar detector, with a speed of 95 kilometers per second. This speed is incredible on earth, but it is still a pediatrician in front of the speed of light, not even the speed of tortoise.

So is the speed of light fast in the universe? Of course not. In fact, the speed of light can only be regarded as a tortoise speed in the universe. If you want to know that the diameter of the Milky way is more than 100000 light-years, it will take at least 100000 light-years to travel through the Milky way at the speed of light. And the Milky way is just a grain of dust in the universe. On top of it, there is the even more vast Virgo supercluster, which reaches hundreds of millions of light-years.

At present, the observable cosmic range is 93 billion light-years, which is not the whole universe. It may be just the tip of the iceberg of the whole universe. If we can fly at the speed of light in the vast space, we can only move within the limited range of the Milky way and can not reach other large galaxies, such as Andromeda, the neighbor of the Milky way, which is millions of light-years away from the Milky way.

It can be seen that the speed of light is nothing in the universe, and human beings are too small in front of the universe. If we want to really explore the mysteries of the universe and become the overlord of the universe, we need to have the ability to travel all over the universe. And this kind of ability needs a speed pattern beyond our cognition, which can also be called spatial jump.

It is impossible for the traditional speed model to explore the whole universe. Whether it is the speed of light or ordinary superluminal flight, the scope of the universe we can explore is also very limited. Only with the ability to break the space and realize the legendary space jump, can we hope to quickly travel to every corner of the universe.

Of course, to achieve this goal, human beings need to face a lot of problems and take a very long time. The first impression of the universe we have observed is that it is very lonely. According to the age of 13.8 billion years, there should be a lot of intelligent civilization. If some of these civilizations had developed early, they would have had the ability to leap in space. However, up to now, we have not found any advanced civilizations coming to the earth.

This result makes many scientists feel afraid. The lonely universe indicates that the big filtering rule may be real. In the process of the development of cosmic civilization, it will go through one filter after another, and the higher the civilization level, the greater the danger it will face. Many ancient wisdom civilizations may disappear in the universe because of the existence of the big filter.

If so, then human beings may not be able to reach the end of science and have the ability to travel all over the universe. Even so, human beings can not be pessimistic. Only by making great efforts to develop science and technology step by step can we be strong enough to discover the truth behind the universe.

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