Did we see the sunshine eight minutes ago or tens of thousands of years ago?

Many people have a misconception that sunlight is directly produced by nuclear reaction, and it needs to reach the surface from the nuclear reaction zone (core) of the sun before it can be launched into space and accepted by us. They believe that when light reaches the core from the inside of the sun, it will undergo many times of electron absorption and emission, eventually making the distance only 2 seconds, but the light needs tens of thousands of years.

In fact, the above explanation is completely wrong, or that's not how the sun comes!

First of all, to be clear, the sunshine we saw was indeed eight minutes ago. Because the average distance from the sun to the earth is1.500 million kilometers, it takes 8 minutes and 20 seconds for light to travel so far. So the light we received from the surface of the sun was generated on the surface of the sun eight days ago. Therefore, if the sun suddenly stops nuclear fusion and does not release heat and sunlight, then we must wait for 8 minutes to know. But, as the title says, it is wrong to say that it was just the sun tens of thousands of years ago!

Why is everyone's explanation wrong? First of all, all the energy of the sun does come from nuclear reactions. Nuclear reaction will release huge energy, but this huge energy does not mean light energy, but heat energy. Heat energy is related to the movement of molecules. The stronger the molecular motion, the hotter the object. The nuclear reaction inside the sun is to make my whole sun hot and dry through the transfer of heat. Heat can be dissipated by radiation transition, and the light emitted by the sun is actually the radiation transition of heat on the surface of the sun, not from the inside.

Of course, the sunshine was eight minutes ago. The average distance between the sun and the earth is 654.38+49.6 million kilometers. It takes about 500 seconds for light to reach the earth from the surface of the earth, and one minute is 60 seconds, which means it takes about 8 minutes and 20 seconds for sunlight to reach the earth. So all the sunshine we saw came out about 8 minutes ago.

You may have seen the principle of sunlight in some popular science books or articles. The sun's gravity causes the pressure and temperature of the core to increase. When the core pressure and temperature reach high enough (about 300 billion atmospheres, 15 million kelvin), the core hydrogen will be ignited for nuclear fusion, and a lot of energy will be released, including neutrinos and high-energy photons.

Before we go on, we can have a look at the structure of the sun:

According to the current theoretical model, the interior of the sun is divided into different regions. From inside to outside, they are: the core area where hydrogen fusion is located (the central radius is about 1/4), the radiation area where photons radiate outward (the radius is about 1/4 to 0.86 times the radius), the troposphere for heat exchange (the radius to the surface is about 0.86 times), and the photosphere emitting blackbody radiation (the surface thickness here is about 500 kilometers)

As mentioned above, a large number of neutrinos and high-energy gamma photons are released after the hydrogen nuclear reaction in the core area, among which neutrinos are extremely small because they do not participate in electromagnetic interaction, and their radiation in the solar plasma ocean is almost unimpeded. Because neutrinos are extremely small in mass and close to the speed of light, they will actually reach the earth in about 8 minutes after being radiated by the hydrogen nuclear reaction, but for the same reason, most of them will penetrate the earth without hindrance and will not bring any energy to the earth from the sun. Only a tiny part will interact with the earth's matter and release energy, including the part intercepted by the earth neutrino detector.

But high-energy photons are not so lucky. After they are radiated by the hydrogen fusion reaction, they are quickly absorbed by the plasma ocean near the core because the photons themselves participate in the electromagnetic interaction. However, due to the extremely high energy, the absorbed radiation is quickly released, and the radiation pressure generated by the extremely high energy and the inward contraction pressure of defying gravity reach a delicate balance, so that the nuclear fusion of nuclear hydrogen can be carried out relatively slowly, so that all nuclear hydrogen will not be ignited and consumed as quickly as a hydrogen bomb. It is precisely because of this delicate balance that our sun can continue to shine10 billion years.

The energy of this radiation gradually decreases in the process of outward propagation. With the increase of the distance from the core, the temperature gradually decreases, and at the same time, the frequency of emitted photons also decreases accordingly. From gamma rays in the core area to X rays in the radiation area, to far ultraviolet rays, and then to ultraviolet rays, when it reaches the photosphere on the surface, the peak of its thermal radiation spectrum is already in the visible range.

So a lot of sunlight we see is visible light, which is actually the result of natural selection.

From gamma rays to visible light, this process of absorption and release is a bit tortuous and bizarre. Similar to the process of scattering, there is no definite path. Therefore, when these gamma photons arrive at the surface of the sun from the core nuclear fusion, the time they pass is different and the final frequency is different.

The spectrum of sunlight is a blackbody spectrum closely related to temperature. Blackbody spectrum is a continuous spectrum of photons with various frequencies, and the surface temperature of the sun is about 5770K, and the corresponding peak of blackbody radiation spectrum is near yellow-green light, so solar radiation is mainly concentrated near visible light.

Although the time and frequency of core radiation reaching the surface of the sun are different, just as its radiation frequency has a peak value, its time reaching the surface also has an average value, about tens of thousands of years. But obviously, the last photon is not the photon produced by the core. Because the sun is blackbody radiation, blackbody radiation is the thermal radiation generated by its surface temperature. Therefore, although the sun shines due to core nuclear fusion, the sunlight actually comes from the surface of the earth, so it reaches the earth after about 80 minutes.

This question is simple. Little friends who know a little about astronomy will come with their mouths open. The sunlight we saw came to the earth from the surface of the sun 8 minutes and 20 seconds ago. The calculation process is also very simple. The earth's orbit around the sun is elliptical. Perihelion is 1.45438+0 billion kilometers away from the sun, and apohelion is 1.52 billion kilometers away from the sun. The average distance is1.500 million kilometers, and the speed of light in vacuum is 300,000 kilometers per second. The result of simple division is 8 minutes and 20 seconds.

The sun is an ordinary star in the universe, with a medium-mass red dwarf, and its life span is about 65.438+0 billion years. In about 5 billion years, it will become a dense star-a white dwarf. Sunlight is produced because the inner core of the sun carries out nuclear fusion under the conditions provided by its own gravitational collapse, releasing light and heat. This means that photons are generated from the core of the sun and come out from the sun to the earth. Then some people may say that the radius of the sun is 690 thousand kilometers, so adding 2 seconds on the basis of 8 minutes and 20 seconds is enough. Is it true?/You don't say.

Actually, it's not. Simply put, photons do not travel in a straight line inside the sun. Like headless flies, they need to change direction every time they touch other particles, so they arrive at the surface of the sun in less than 2 seconds. This problem is in George? The relevant calculations in the popular science book From One to Infinity written by Gamov are as follows:

This means that the sunshine we see every day can be traced back to more than 100 thousand years ago. What were our ancestors doing at that time?

Text/science black hole, graph/source network invasion and deletion

To borrow a fashionable phrase, the sunshine we see exists.

Yes, not eight minutes, nor tens of thousands of years. No matter how long or short, any time difference is meaningless, because in the face of the fastest information transmission speed in the universe, any expression of light is simultaneous, and light bridges the distance between different spatial positions, making different positions become the same time. Any photon at this time is not only the sender of atomic motion information, but also the equal sign of time formula, connecting the two ends of the photon being sent and received!

I believe many people have heard the saying that the sun we saw was the sun eight minutes ago (in fact, it was eight minutes and twenty seconds, usually eight minutes). This is easy to understand. After all, the earth is 65.438+0.5 billion kilometers away from the sun, and the time to fly 65.438+0.5 billion kilometers is about eight minutes, so there is nothing wrong with the sun we saw eight minutes ago!

However, if you deeply understand the luminous principle and the whole process of the sun, you will understand that although the sunlight we see is emitted from the surface of the sun, strictly speaking, the surface of the sun cannot produce any light, and the root of light is the core of the sun, that is, the nuclear fusion of the core of the sun!

The radius of the sun is about 700,000 kilometers, and it only takes a little more than 2 seconds to fly at the speed of light! So does it really take only 2 seconds for the light generated by the core of the sun to fly to the surface of the sun?

In fact, it is far from it! The light produced by nuclear fusion needs hardships to reach the surface of the sun! Because the sun is full of hydrogen and helium, the light generated will be absorbed by electrons and then released. The huge pressure inside the sun makes the density of electrons very high, and the process of absorption and release is repeated, so the process of absorption and release of light is also very long, and it takes about100000 years to reach the surface from the core of the sun!

So the sun we saw was 10 million years ago? This statement is not rigorous and smacks of "stealing concepts". After all, no matter what happens inside the sun, we will only notice how long it takes for the light on the surface of the sun to reach the earth!

Therefore, it doesn't matter how long we saw the sun. It is important that we understand the mechanism of light generation inside the sun and how light reaches the surface of the sun. Knowing this, the problem becomes very simple, depending on which angle you understand it!

The distance between the sun and the earth is1.500 million km, the speed of light is 300,000 km/s, and it takes 8 minutes for sunlight to reach the ground from the sun. However, the latest research shows that it takes about 20 thousand years for photons inside the sun to reach the surface of the sun.

Solar energy has such huge energy, that is, in the environment of 15 million℃ and 300 billion atmospheres, the hydrogen-helium fusion reaction is going on all the time, and the photons generated by high temperature will reach the surface of the sun during the reaction, which is not as fast as expected.

The generated photons will be blocked by the absorption of countless electrons and elements in the sun. Even the fastest photon in the universe has to hit a wall anywhere in the sun. It turned out that it took only 2 seconds to "defeat" countless "checkpoints", which was even worse than "Guan Yunchang passed five customs and cut six generals"