# How long does it take to know when the sun goes out? Is it eight minutes? It could take tens of thousands of years

For life on earth, water, oxygen and sufficient sunlight are three essential requirements. Without any of them, life can not survive and continue. The life of the earth mainly lives on the surface of the earth, with 71% of the ocean on the surface and abundant oxygen. Among the three essential factors needed for life, the earth itself takes up two, and the other abundant sunlight is what the earth itself does not have. We need other sources, and this source is the sun of the star at the center of the solar system.

The sun plays an important role in the birth of life on earth. Without it, the earth will not have liquid water, thick atmosphere, warm climate, natural life and human beings. It can be said that the sun can also be regarded as the mother of life on earth. Maybe for people in ancient times, they never thought about what they would do when the sun no longer glows and heats?

Because in the eyes of the ancients, the sun is an eternal fireball, it will not go out, will always shine on the earth. However, when human beings enter the era of science and technology, with the help of science and technology, they have more knowledge of the sun, and then we understand that the sun is just a star, and its life span will vary greatly according to its mass.

The life span of massive stars may be only tens of millions of years, while the life span of yellow dwarfs such as the sun is relatively longer, reaching about 10 billion years. Today’s sun has been burning for 5 billion years, and it has completed half of its life. In another 5 billion years, the sun will be completely extinguished, and then the earth will no longer have sunlight.

So someone once raised such an interesting topic: how long does it take for human beings to know after the sun goes out? Maybe someone will say, isn’t this a very simple math problem? The distance between the earth and the sun is about 149.6 million kilometers, and the speed of light is 300000 kilometers per second. The final calculation time is about 8 minutes and 18 seconds. In other words, after the sun goes out, there will be no more photons reaching the earth after 8 minutes and 18 seconds, and the earth will fall into permanent darkness.

So is the time accurate? After the sun goes out, can we really see the arrival of permanent darkness in eight minutes? If you think so, it’s a big mistake. After the sun goes out, the time to leave the earth with permanent darkness is much longer than we think. It may take tens of thousands of years. What’s the matter?

It’s not difficult to solve this mystery. First of all, we need to understand that the combustion of the sun is completely different from ordinary combustion. It’s a combustion mode of nuclear fusion. We can see the sun as a huge nuclear fusion reactor, its interior is full of hydrogen and helium, and nuclear fusion is going on all the time in the center. It’s also the source of the sun’s energy.

In the process of nuclear fusion, the energy released by the sun every second is equivalent to the total energy produced by the simultaneous explosion of 1.8 billion nuclear weapons. The burning state on the surface of the sun is actually caused by photons running out of the sun. How long does it take for the light released from the center of the sun to reach the surface of the sun?

Some people may think that the speed of light is so fast, even from the center of the sun to the surface of the sun is a very short time, is that really the case? The real answer may make many people feel unthinkable. It’s not easy for the photons in the center of the sun to come to the surface of the sun. They need to go through many obstacles. It’s a long process.

The internal structure of the sun is much more complex than the nuclear fusion reactor we imagined. Because the sun is a huge and highly dense plasma sphere, the photons produced by deep nuclear fusion can not reach the surface of the sun. Because there are numerous electrons, ions and atoms inside, photons must compete with these “obstacles” if they want to reach the surface.

When photons are generated by nuclear fusion, they need to interact with various substances in the process of constantly moving outward, and in this process, they will continue to consume the energy of photons. The photons generated in the center of the sun, at the beginning, are powerful gamma rays. After reaching the surface, due to the weakening of energy, they finally become X-rays.

The process of photons moving from the inside to the surface is not a straight-line process. The reason is that it may collide with protons and other particles in the process of walking, thus changing its direction. Therefore, this process is a curved and tortuous process. It will take at least ten thousand years to complete this series of twists and turns. If you are not lucky, it may take tens of thousands of years.

Only after photons reach the surface from the inside can they become runaway Mustangs, galloping freely in space, and reaching the earth in 8 minutes. So when the fusion inside the sun stops, that is, the sun goes out and no longer produces any photon energy.

Although the interior of the sun is out and no longer produces photons, there will still be a steady stream of photons on the surface of the sun reporting from the interior, which will last for tens of thousands of years. And living on the earth, we naturally don’t know that the sun has gone out. What we can see is that the sun is still burning and the earth is still shining.

It is not until tens of thousands of years later that there are no photons inside the sun reaching the surface, and the last photons reach the earth that we can truly usher in permanent darkness. Of course, this is a very ideal state for us. In fact, the earth can’t resist the moment when the sun’s surface really goes out.

With the end of hydrogen fuel inside the sun, the whole sun will continue to expand, forming a red giant. And the expanding sun will slowly approach the earth, so that the earth’s temperature will continue to rise, the atmosphere will continue to be stripped, liquid water evaporation, life can not survive. The whole earth becomes a desolate purgatory planet, and then the expanding sun will completely engulf the whole earth. If you are lucky, maybe the earth will still have a dense metal core.

And this time may happen in 3 billion years. When the sun’s surface goes out, the outer layer of the sun’s material will continue to peel off, the inner core will collapse, and finally evolve into a white dwarf. Therefore, the earth can’t wait until 5 billion years later, and human beings need to withdraw the earth in the process of the sun’s transformation to a red giant.

If at that time, humans still exist and have become a powerful interstellar civilization, then we can leave the solar system and go to other galaxies to survive. If we miss the earth, maybe we can transform it into a wandering planet and leave the solar system with the earth. Go to a new galaxy and start a new time. It can be seen that the fate of mankind in the future can only be changed by relying on science and technology.