Somewhere in China, 2,400 meters underground, humans are waiting for a moment to happen, and the result may subvert cognition

"Our day is the other half's night, our starry sky is completely different from what they see, we have different time, but we live on the same planet." The above paragraph describes the different worldviews of people living in the northern and southern hemispheres. (For example, in the picture below, the left side is the North Pole starry sky, and the right side is the South Pole starry sky.)

The sky we see at the poles is completely different

Today we are going to talk about dark matter. Let’s make a hypothesis first: Do you think dark matter constitutes another world that is completely different from ours? (Welcome to discuss)

Kapteyn

Kapteyn's Star is a red subdwarf star; it is the closest halo star to the Solar System. It has an apparent magnitude of approximately 9 and can be seen with binoculars or a telescope.

Kapteyn's Star has a diameter of only 30% of the Sun's, but is 1.2% as bright as the Sun. Kapteyn's Star may have been part of the Omega Centauri globular cluster in the past, itself a dwarf galaxy that was likely swallowed by the Milky Way in the distant past.

This star is named after the Dutch astronomer Jacobus Kapteyn. This star is quite special. It moves at a high speed in the Milky Way halo against the direction of the Milky Way's rotation, with a very high movement of more than 8 arc seconds per year. It has been calculated that Kapteyn's star may have a movement speed of 490 kilometers per second. This was the fastest moving star at the time. (Our solar system, in the Milky Way, moves about 19.2 million kilometers per day.)

It was because of Kapteyn's research on moving stars that he proposed in 1922 that the movement of stellar systems could be used to indirectly infer the possible existence of invisible matter around stars. This was the first time the term invisible matter (dark matter) appeared in the astronomical community.

Jacobs Kapteyn

How to prove the existence of dark matter?

In 1932, astronomer Jan Oort conducted a study on the motion of stars near the solar system to investigate the existence of dark matter, but failed to draw a firm conclusion on the existence of dark matter.

In 1933, astrophysicist Fritz Zwicky used spectral redshift to measure the speed of each galaxy in the Coma Cluster relative to the cluster. Then, using the virial theorem, he found that the velocity dispersion of galaxies in the cluster was too high. The gravitational force generated by the mass of the visible galaxies in the cluster alone could not bind them to the cluster. Therefore, there should be a large amount of dark matter in the cluster, whose mass is at least a hundred times that of the visible galaxies.

Galaxy Clusters

A galaxy cluster is a collection of many galaxies like the Milky Way in a self-ordered manner in the same space. They have gravitational influences on each other, but there is an invisible substance that binds them together.

Virgo Cluster

In 1959, FD Kahn and L. Woltjer studied the relative motion between the Andromeda Galaxy and the Milky Way, which attract each other. Based on their speed of approach and distance, they deduced that the dark matter in the Milky Way cluster where we humans live should be about ten times more massive than visible matter. Our Milky Way and the Andromeda Galaxy attract each other, and it is estimated that they will collide in 3.8 billion years.

Another important evidence for the existence of dark matter comes from the study of the rotation speed of stars in the Andromeda Galaxy by Vera Rubin and Kent Ford in 1970. Using high-precision spectral measurement technology, they can detect the relationship between the rotation speed of peripheral stars far away from the galactic core region and the distance around the galaxy.

According to Newton's law of universal gravitation, if the mass of a galaxy is mainly concentrated in the visible stars in the core of the galaxy, the speed of the stars in the outer part of the galaxy will decrease with distance. However, observation results show that the speed of the stars in the outer part of the galaxy is constant within a fairly large range. This means that there may be a large amount of invisible matter in the galaxy, which is not only distributed in the core of the galaxy, and its mass is much greater than the sum of the masses of the luminous stars.

rId17

The speed of the outer stars is constant

The galaxy rotation curve describes the relationship between the orbital speed of visible celestial bodies in a spiral galaxy and their distance from the center of the galaxy. Based on the observation of the mass distribution of visible celestial bodies in spiral galaxies and the calculation of the law of universal gravitation, the speed of celestial bodies near the periphery orbiting the center of the galaxy should be slower than that of celestial bodies near the center. However, the measurement of the rotation curves of a large number of spiral galaxies shows that the speed of celestial bodies in the periphery is almost the same as that of celestial bodies in the interior, which is much higher than expected. This suggests that there is a huge amount of invisible matter in these galaxies.

What is dark matter?

In the famous science fiction novel "The Three-Body Problem", the Trisolarans rely on their sophons to interfere with human particle colliders, completely blocking the development of human quantum physics and thus "locking" human technology. Dark matter is also a reality that scares particle physicists.

The existence of dark matter has been widely recognized, but humans have little understanding of its properties. Currently known properties of dark matter include only a few limited aspects:

(1) Dark matter participates in gravitational interactions, so it should have mass, but the mass of a single dark matter particle cannot be determined.

(2) Dark matter should be highly stable. Since there is evidence of dark matter at different stages of the formation of cosmic structure, dark matter should be stable on a time scale of the age of the universe (tens of billions of years).

(3) Dark matter basically does not participate in electromagnetic interactions. The interaction between dark matter and photons must be very weak, so that dark matter basically does not emit light. Dark matter also basically does not participate in strong interactions, otherwise the process of primordial nucleosynthesis will be disturbed, the abundance of light elements will change, and it will lead to inconsistency with current observations.

(4) Computer simulations of the formation of large-scale structures in the universe show that the speed of dark matter should be much lower than the speed of light, that is, "cold dark matter". Otherwise, our universe would not be able to form the observed large-scale structures under the influence of gravity.

Combining these basic properties, we can conclude that the elementary particles (or elementary matter) that make up dark matter do not belong to any of the elementary particles we know. This poses a subversive challenge to the standard model of particle physics in the current mainstream field of basic physics.

Although people have made many astronomical observations of dark matter, its composition is still not fully understood. Early theories of dark matter focused on some hidden conventional matter celestial bodies, such as black holes, neutron stars, aged white dwarfs, brown dwarfs, etc. These celestial bodies are generally classified as massive and compact celestial bodies.

However, astronomical observations over the years have not been able to find enough of these massive, compact objects. It is generally believed that difficult-to-detect baryonic matter (such as massive, compact objects and some gases) does contribute to some of the dark matter effect, but evidence indicates that this type of matter only accounts for a small part of it. The rest is called "non-baryonic dark matter."

In addition, observational data such as galaxy speed curves, gravitational lenses, cosmic microwave background radiation, and light-to-mass ratio also indicate that 85%-90% of the mass in the universe does not participate in electromagnetic interactions. This type of "non-baryonic dark matter" is generally speculated to be composed of one or more elementary particles that are different from conventional matter (electrons, protons, neutrons, neutrinos, etc.). Research estimates that detectable matter only accounts for about 4.6% of the total mass-energy of the universe, undetectable dark matter accounts for 23%, and the remaining dark energy accounts for 72%.

Dark matter detection

Because dark matter is a particle with a "special personality" in the universe. It has a large mass, but its force is very small. It hardly interacts with the atoms or electrons of the matter we know. "Trillions of dark matter may pass through your body every day, but you can't feel it, because the scattering cross section of dark matter is very small." To put it in an analogy, it's like a football can be blocked by a net, but a small iron ball can pass through the net, because its cross section is smaller than the mesh of the net.

In order to study the invisible and intangible dark matter, China has established its first ultra-deep underground laboratory, the "China Jinping Underground Laboratory". The second phase of the "China Jinping Underground Laboratory" project is now steadily advancing under the Jinping Hydropower Station in the Jinping Dahewan of the Yalong River in Liangshan Yi Autonomous Prefecture, Sichuan Province. It is located 2,400 meters underground under the rock cover and is the world's deepest and largest ultra-deep underground laboratory.

The laboratory uses an underground tunnel built when a hydroelectric power station was built locally. A space 40 meters long, 6 meters wide and 6 meters high was excavated on its side. Therefore, compared with some foreign underground laboratories that were "born" from mines, it is more convenient to use. The tunnel is buried 2,500 meters deep, because the deeper it is buried, the less interference from cosmic rays. The cosmic ray flux in Jinping Underground Laboratory can be reduced to one ten-millionth to one hundred-millionth of the ground level, making it the underground laboratory with the lowest cosmic ray flux in the world.

It takes about 20 minutes to drive from the ground to the underground laboratory. Once the instrument is running stably, he only needs to monitor the operation of the detector in the office on the ground, and all the data from the underground laboratory will be transmitted to the ground, so researchers do not need to "guard" the detector 24 hours a day.

The core device for detecting dark matter is a high-purity germanium detector. The purity must reach 12~13 (99.99999999999999%)

The principle is to wait for dark matter particles to collide with germanium atoms and emit noise signals that are captured by the detector.

There are dozens of similar dark matter underground laboratories around the world, but so far no trace of dark matter has been found.

Soul torture

Actually, I feel quite sad when writing this. There is a thought in my mind: why is the "real world" that we can see and touch every day only a minority in the universe? (Less than 5%) Is it possible that our world is the invisible existence in the real universe?

Combining the ancients' views on the concept of yin and yang, do you think we are on the yang side or the yin side?

This reminds me of Lao Tzu, who wrote in the Tao Te Ching 2,500 years ago:

Chapter 14 of Tao Te Ching: "If you look at it and cannot see it, it is called Yi. If you listen to it and cannot hear it, it is called Xi. If you grasp it and cannot touch it, it is called Wei. These three cannot be questioned, so they are mixed into one. It is not bright above, and it is not dark below. It cannot be named. It returns to nothingness. This is called the shape of no shape and the image of no object. This is called Huohuang. If you meet it, you cannot see its head. If you follow it, you cannot see its tail. Holding on to the ancient Tao to control the present, being able to know the ancient beginning is called the Tao Ji.

Translation: It cannot be seen, so it is called "Yi"; it cannot be heard, so it is called "Xi"; it cannot be touched, so it is called "Wei". The shapes of these three cannot be traced, as they are originally one. The top of it does not appear bright and clear; nor does the bottom of it appear dark and obscure. It has no beginning or end, stretches endlessly but cannot be named, and all movements return to a state of formlessness and imagelessness. This is the shape without a shape, and the image of an object is not seen. This is "Huohuang". Facing it, you cannot see its front; following it, you cannot see its back. Grasp the "Tao" that has already existed to control the concrete things that exist in reality. Being able to recognize and understand the beginning of the universe is called knowing the law of "Tao".

Doesn’t this so-called Tao look very similar to the “dark matter and dark energy” we have been searching for?

Is this world of ours the “world of the living” as we understand it, or the “world of the dead” in another world?

Opening question: Do you think there is another world in dark matter that is completely different from ours?

My answer: Yin and Yang cannot sense each other, but they are integrated in one universe. Perhaps the creatures in the "dark matter" world are also struggling to explore our 5% existence.