This setting in "Guardians of the Galaxy 3" has sparked heated discussion. Is there really an "anti-Earth" behind the sun?

In the recently released "Guardians of the Galaxy Vol. 3", the super villain "The High Evolutionary" created a new planet. Its size, mass, and basic environment are the same as the Earth. But in the plan of "The High Evolutionary", this new planet is used to achieve the great mission of purifying the universe. The inhabitants of the new planet are creatures with animal faces and human bodies, such as people with rabbit faces, people with rhinoceros faces, and people with lion faces. This new planet is called "Counter Earth".

The setting of Counter-Earth is not new at all, it can even be said to be very old.

The Anti-Earth Hiding on the Other Side

Pythagoras of ancient Greece was the first to propose that the earth is spherical, discovered the Pythagorean theorem, and founded the Pythagorean school that believed in numbers. This school did not believe in the geocentric theory that was popular at the time. They believed that the earth was moving, the sun was also moving, and all celestial bodies in the universe were rotating around a "central fire". However, according to human cognition and understanding at the time, only the earth contained heavy matter and had real "weight", while the sun and the stars were all made of the sacred element "ether", which was light and clean. Therefore, the entire weight of the entire universe was concentrated on the earth, and the earth was not at the position of the central fire. The center of weight, that is, the center of gravity, does not coincide with the center of rotation, that is, the central fire, which will cause the embarrassment of eccentric rotation. The ancient Greeks who pursued harmony and unity did not like this structure very much.

What should I do then?

After Pythagoras, the most important successor of the school was Philolaus in the 4th century BC. Philolaus proposed the concept of "counter-earth" and solved the problem of asymmetric weight. He believed that on the opposite side of the central fire, on the opposite side of the earth, there was an anti-earth that was exactly the same as the earth. The earth and the anti-earth revolve around the central fire at the same time, and it takes 24 hours to make one circle. Moreover, the ancient Greeks did not have the concept of the earth's gravity, and could not understand that there could be people "upside down" on the other side of the earth. Therefore, in the minds of the ancient Greeks, although the earth is a sphere, only one side can be lived. In other words, the anti-earth is always hiding on the opposite side of the central fire, and the human beings on earth cannot directly discover the central fire and the anti-earth. (See Figures 1 and 2.)

Figure 1: At night on Earth, the view is facing away from the Sun, and the central fire and the counter-Earth are not visible.

Figure 2: During the day on Earth, humans only live on one side of the Earth, and their sight lines are facing the Sun, so they cannot see the Central Fire and the Counter-Earth.

Since the Counter-Earth always maintains an angular distance of 180 degrees from the Earth, the weight of the entire universe is dispersed between the two Earths, and their center of gravity falls exactly on the central fire.

The “counterpoint” waiting for you

When the time came to the Roman era, Ptolemy perfected the theoretical system of geocentrism, and concepts full of ancient mysticism such as central fire and anti-earth were abandoned. Ptolemy was a pragmatist. In order to conform to the results of astronomical observations, in the complete version of the geocentric theory, he set the earth not precisely at the center of the universe, but a little distance away from the center. On the other side of the center of the universe, there is a "symmetry point" or "equilibrium point" (equant) at a position symmetrical to the earth. The earth and the symmetry point remain stationary in the universe. So strictly speaking, Ptolemy's "geocentrism" should be called "geostatic theory". The stars move around the core composed of the earth, the center of the universe and the symmetry point. If someone can observe the starry sky at the position of the symmetry point, they will see that the stars move around themselves at a uniform speed. Therefore, the movement of the stars observed by people on earth is no longer uniform. (See Figure 3)

In order to explain the problem of the inconstant speed of the planets and the sun, Ptolemy did not hesitate to borrow the concept of the anti-Earth. However, in Ptolemy's geocentric theory, the anti-Earth is just an observation point in the void, and there is no real planet.

Figure 3: The Earth and symmetry points in Ptolemy's geocentric theory

Later astronomers generally disliked the idea of ​​symmetry points. Not only did it destroy the simple and elegant mathematical tradition since ancient Greece, it also increased the risk of theories that required additional explanations. The movement of stars is uniform relative to the symmetry point, so why should the symmetry point have a nobler status than the earth? Later, Kepler discovered that the true orbit of planetary motion is an ellipse, not a circle. Only after considering the elliptical orbit can these strange settings in the geocentric theory be completely eliminated and a truly elegant heliocentric theory be established.

The science fiction world of heliocentrism

After the heliocentric theory was established, people generally accepted the fact that the sun was at the center and the earth and the planets revolved around the sun. However, the anti-earth idea did not disappear, but instead became a modern version of science fiction. This theme recurs in science fiction novels: on the other side of the sun, in the opposite position to the earth, there is another earth that is symmetrical with the earth. (See Figure 4)

Figure 4: A modern version of Counter-Earth

Written in 1896, From World to World is the earliest modern science fiction work about the Anti-Earth. In it, the Anti-Earth society has developed into an advanced utopian world. Since the 20th century, works such as The Other Side of the Sun and Sister Earth have similar Anti-Earth settings.

The anti-Earth setting will give rise to the imagination of the Earth's twin planets and twin social civilizations. If the same intelligent race lives in the same ecological environment as the Earth, is it possible to develop a completely different social form from the current society? In other words, is our real world today a kind of accident or the inevitable result of evolution?

Is Counter-Earth really invisible?

From an astronomical point of view, even if the Anti-Earth really exists, it cannot hide itself. Humans have already sent probes to the vicinity of Venus and Mercury, and there is a great chance to observe the symmetrical position behind the sun. Moreover, during the flight, the probe is likely to be affected by the gravity of the Anti-Earth and deviate from the preset orbit. According to calculations, as long as the diameter of the Anti-Earth exceeds 160 kilometers, the gravity it generates can be easily discovered.

Even without relying on a probe, we can still expose the Anti-Earth. The Earth's orbit around the Sun is an ellipse. When the Earth is closer to the Sun, it moves faster. On the contrary, when the Earth is farther from the Sun, it moves slower. It is difficult for the Anti-Earth to remain symmetrical with the Earth relative to the Sun and to run at exactly the same speed. In addition, there are other planets in the solar system. Under the influence of the gravity of Jupiter and Saturn, the Anti-Earth will sooner or later lose its original stable orbit and suddenly appear in front of us.

How does the villain "Supreme Evolution" in "Guardians of the Galaxy 3" solve this problem?

Although he did not place the Anti-Earth in the solar system, he still set the Anti-Earth's dimensional parameters in time and space to make it always 1 millisecond different from the real Earth, and set up a shielding field to prevent the Anti-Earth from being discovered by the Earth and to prevent the Anti-Earth from affecting the power system of the solar system. Even in the Marvel universe, the instability caused by gravitational disturbances is a major event that must be prevented.

Author: Gao Shuang, a popular science writer

Reviewer: Han Wenbiao, Researcher at Shanghai Astronomical Observatory, Chinese Academy of Sciences