Is it possible for humans to travel across the Earth?

Today I want to talk to you about a question that will open your mind. If you keep digging into the ground with a shovel, after digging through the earth, will your head or your feet come out of the ground? You can use your imagination.

If we go beyond our current knowledge and dig through the earth, we are actually upside down. This problem was solved in the Age of Exploration. At that time, many people did not understand the theory of the spherical earth. They thought, if the earth is round, then those people across from us, are they upside down? ? ? But the great Sir Newton told us that there is universal gravitation!

So, they are also facing upwards. When you dig to the core of the Earth, the direction of your gravity has already made a 180-degree turn . Next, you must turn 180 degrees and continue digging upwards.

If you don't turn, just imagine the feeling of hanging upside down.

01, Mission Impossible

Actually, I was wondering, if we really use a shovel to dig, what is the shovel made of? The following is the composition of the earth.

The radius of the earth is 6371 kilometers. Let’s start our journey through time.

02. Crossing the Earth's crust - the lithosphere

The lithosphere we feel is the crust, which has an average thickness of 17 kilometers, and a ratio of about 1:374 to the radius of the Earth. To use a figurative metaphor, if you are a 187cm tall man, then the thickness of the crust is about 0.5cm of hair. If you dig through the crust, it is equivalent to the length of a hair increasing by one week.

03. Through the mantle – 2865 km

Well, let's assume you are really good and you are not afraid of the 17-kilometer crust and you dig through it (the deepest depth humans have drilled so far is only 12 kilometers). After you have dug through such a thin layer of crust, you will encounter the mantle, which is about 2,865 kilometers thick. This layer is already very, very difficult to dig.

The upper mantle is still composed of partially molten material, while the lower mantle has a large amount of molten material. In other words, the mantle is similar to porridge. At this time, how to dig it? ? ?

Not only that, the temperature of the mantle is already very high. Near the mantle and the core, the temperature is basically 3500℃.

You know, real gold is not afraid of fire. In fact, the melting point of gold is 1063 degrees Celsius, which is 427 degrees lower than the melting point of iron. At 3500℃, well, steel and the like will melt.

However, I heard that there is a magical element on earth called hafnium, which increases the melting point when combined with many things.

It is said that the current record for the melting point in the world is an alloy of hafnium, nitrogen and carbon, which has a melting point of 4120°C. This is two-thirds of the temperature of the sun. The previous record was hafnium tantalum carbide, which had a melting point of 3942°C.

Well, at this point, you are still a bunker, crossing the mantle

04. Through the Earth's Core - 3470 km

Welcome to the real hell - the core of the earth

The Earth's core can be roughly divided into a liquid outer core and a solid inner core.

Liquid outer core : temperature 2900-5100℃ (including transition layer)

Solid core : temperature 5100-6371℃

What does this mean? Even if you have the legendary hafnium wire to protect your body, sorry, you still can't pass the core of the earth because it has been melted.

You should know that the surface temperature of the sun is 5500℃, which means that the temperature of the earth's core exceeds the surface temperature of the sun.

I remember when Kim Jong-un said that North Korea would land on the sun within two years, an American reporter asked, "How can you go to the sun when the temperature is so high?" The audience fell silent. Kim Jong-un thought for a moment and said, "We'll go at night." Thunderous applause broke out. Obama, who was watching the live broadcast, said, "This is ridiculous. There is no sun at night." His colleagues around him also applauded. However, at this time, Char's thunderous applause could not help you cross the earth's core.

This reminds me of those stories.

The Bible records that hell is "a dark bottomless pit, with undying worms and unquenchable fire burning, causing people to suffer forever day and night." The Ksitigarbha Sutra also mentions the Avici Hell: There is only one hell, named Avici. The circumference of the hell is 18,000 miles, and the walls are 1,000 miles high, all made of iron, with fire from above penetrating the bottom and fire from below penetrating the top. Iron snakes and iron dogs, spitting fire and chasing, run east and west on the walls.

The core of the earth is hell for human beings!

Further down, there is the solid inner core. The core is solid, also known as the iron-nickel core, and its material composition is mainly iron and nickel. According to simulations by Japanese scientists, in this core with a pressure of 3 million atmospheres, there are actually crystals everywhere.

05. Supplement

1. Regarding the question of gravity , I don't want to explain too much, so I'll move on to this answer - What is the universal gravitation at the center of the earth? - Physics. Except for a certain theoretical point, there is gravity at other locations.

This figure shows that from the center of the earth to the surface, the gravitational force per unit mass increases in a linear manner, from 0 at the center of the earth to 9.8N/kg at the surface. From this, it can be seen that the gravitational force near the center of the earth is almost non-existent, very very small, so there will be no expansion or bursting.

2. Regarding how the Earth's structure was derived, you can refer to - How do humans know the composition of the mantle and core? - Earth. The general explanation is: it is inferred based on seismic waves.

Scientists have discovered that the velocity of seismic waves changes suddenly at a certain depth inside the Earth, and this change is global . In 1909, Croatian scientist Mohorovic discovered that the velocity of waves jumps discontinuously at 33 kilometers underground, and thus determined the boundary between the crust and the mantle, the " Moho discontinuity." - The boundary between the crust and the mantle In 1914, German-American scientist Gutenberg discovered that the velocity of waves changes dramatically at about 2,885 kilometers underground, and thus defined the boundary between the mantle and the core, the "Gutenberg discontinuity." - The boundary between the mantle and the core

Then the radius of the earth is the total length, so there are three component sizes. How is the radius of the earth derived? ? ?

Method 1: Arc Measurement in Ancient Greece

In the third century BC, the Greek astronomer Eratosthenes (276-194 BC) first measured the radius of the earth. He found that on the summer solstice, when the sun shines directly on the well S in the city of Sai (now Aswan, Egypt), the angle between the zenith of point A in Alexandria and the sun is 7.2° (the zenith is the point where the plumb line extends infinitely upward and intersects the sky "celestial sphere"). He believed that the two places were on the same meridian, so the central angle SOA of the arc between the two places was 7.2°. It is also known that the distance between A and S measured during the caravan travel was about 5,000 ancient Greek miles. According to the relationship between the arc length and the central angle of the circle, he calculated that the radius of the earth was about 40,000 ancient Greek miles. It is generally believed that 1 ancient Greek mile is about 158.5 meters, so he measured the radius of the earth to be about 6,340 kilometers.

Method 2: Modern arc measurement. In modern times, the radius of the earth is still measured by arc measurement, but it is only used to calculate the radius of two points that are far apart.

When calculating the distance between points, the method of laying out triangulation is adopted. For example, when calculating the distance between points M and N, the triangulation points can be laid out as shown in Figure 2, and the degrees of each internal angle of △AMB, △ABC, △BCD, △CDE, and △EDN can be measured with a theodolite, and then the length of the baseline MA near point M can be measured, and finally the length of MN can be calculated.

Method 3: Back-calculation. After Cavendish measured the gravitational constant, he could use the law of universal gravitation to observe the periods of other planets through astronomy, and use the universal gravitation to calculate the mass of the earth. He could also use the volume formula of a sphere to approximate the equatorial radius.