The sun is the absolute ruler of the solar system, and its mass occupies more than 99.86% of the total mass of the solar system. The nuclear fusion reaction of the sun makes the temperature of the sun extremely high, the surface temperature of the sun is as high as 6000 degrees, and the core temperature is as high as 15 million degrees.

The main source of Earth's energy is solar radiation, which is produced by nuclear fusion reactions that rely on the sun. But the question is, why can the earth be heated by the sun, but why is the temperature in space close to absolute zero?

solar fusion

Know that the greater the mass, the greater the gravitational force. Due to the huge mass of the sun, the gravity of the sun is huge, which causes the core of the sun to be severely squeezed and the temperature soars.

The core material of the sun is in a plasma state at a high temperature, which is different from the three states we see every day. Plasma states are characterized by the absence of a complete atomic structure, because the electrons gain enough energy to escape the nuclei of atoms. Therefore, the inner core of the sun is a state where particles such as nuclei, electrons, photons, etc. are mixed.

It should be known that the main substances that make up the sun are hydrogen and helium nuclei. Therefore, the nuclei of the core of the sun are mainly hydrogen and helium nuclei. It stands to reason that the hydrogen nucleus is positively charged and repels the same charge. Therefore, there is electrostatic repulsion between hydrogen nuclei, and nuclear fusion reaction is not easy to occur.

If you want to force the hydrogen nuclei to react, you need to input enough energy. But the sun's core isn't hot enough to provide enough energy. Specifically: the temperature of the core of the sun is only 15 million degrees, and the minimum threshold for the nuclear fusion reaction of the hydrogen nucleus has reached 100 million degrees . Therefore, from a macroscopic point of view, the nuclear fusion reaction of hydrogen nuclei should not occur in the core of the sun. However, there is an effect in the microscopic world, which is called the quantum tunneling effect .

The so-called quantum tunneling effect means that the reaction that originally required input energy to trigger, also has a certain probability to occur in the microscopic world, but the probability is extremely low. As mentioned above, the sun is the master of the solar system, and the number of particles inside is extremely large. Therefore, no matter how small the probability is, it may happen.

Therefore , with the cooperation of weak force, the nuclear fusion reaction can occur in the core of the sun, but the reaction rate will be relatively slow and last for a long time, instead of exploding all at once like a hydrogen bomb that is also a hydrogen atomic nuclear reaction.

In the process of solar nuclear fusion reaction, 4 hydrogen nuclei undergo three stages of reaction, and under the action of weak force, a helium-4 nucleus is finally generated, which is accompanied by the production of 3 photons and 2 neutrinos.

Since the core of the sun is in a plasma state, photons are involved in electromagnetic interactions. As a result, photons do not rush directly from the core of the sun to the surface of the sun, but instead stumble outwards. According to scientists' statistics, it takes an average of 140,000 years for photons to travel from the core of the sun to the surface of the sun .

After reaching the surface of the sun, the photons will rush to the sea of ​​stars, and only a very small part of them will rush to the earth. This part of the photons is the main energy source of the earth. If we compare the matter of solar radiation with money, it is equivalent to the sun throwing 70 trillion into space every second, while the radiation to the earth is less than 30,000 . Even so, the side of the Earth that faces the sun will get warmer due to the sun's radiation. That is to say, a considerable part of this part of solar radiation is converted into heat, which increases the temperature of the earth.

But the question is, the earth can be heated by the sun, why is the cosmic space around the sun still at absolute zero?

The nature of temperature

This actually requires a deep understanding of "hot". First of all, heat and temperature are two different things, and temperature is a physical quantity that measures how hot or cold a substance is . Secondly, if we look at temperature from a microscopic perspective, we find that the essence of temperature is actually the intensity of thermal motion of particles. How should this be understood?

We know that everything is made of particles. But in fact, the particles are not arranged neatly together, they actually "move" and move randomly.

The problem is that we have no way to describe particles one by one, and the number of particles that make up matter is huge. Therefore, scientists use statistical methods to describe the whole of particles. Scientists have found that when the particles are moving as a whole, the temperature is higher; otherwise, the temperature is lower.

The problem with this description is that it is based on large-scale statistics. It means that for this conclusion to be established, there needs to be a sufficient number of particles.

The earth is a celestial body with a high density of matter, and the number of particles is sufficient. Therefore, when the solar radiation is received, the thermal motion of the particles becomes violent and the temperature rises. However, space is really empty. According to scientists' observations combined with theoretical calculations, they found that the average density of the earth is about one cubic meter less than one hydrogen atom , and the number can be said to be extremely small. Therefore, space is difficult to reflect temperature . Even when solar radiation passes through, it does not add temperature to space.