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This article comes from the official account of Wechat: SF Chinese (ID:kexuejiaodian), author: SF

By analyzing the motion of long-period binaries, scientists have discovered phenomena that cannot be explained by Newton and Einstein's theory of gravity. This discovery means that we need a new theory of gravity to describe the mysteries of the universe. This will be a revolution in physics and will have a great impact on cosmology as a whole.

(by Chen Qiang / tr. by Robert Taylor)

Gravity is one of the most basic and common forces in nature. it is a kind of attraction between objects. In the history of science, there are two scientists who have made great contributions to the study of gravity. They are Newton and Einstein.

Newton put forward the law of universal gravitation in the 17th century, which holds that there is an attraction between any two objects that is proportional to their mass and inversely proportional to the square of the distance between them. Einstein put forward the general theory of relativity in the 20th century, which holds that gravity is not a real force, but a geometric effect caused by the bending of matter and energy to space-time.

The law of universal gravitation and general relativity are the two most widely accepted theories of gravity, which can explain most of the gravitational phenomena. However, in some cases, such as the study of galaxy rotation, mass distribution of galaxy clusters, cosmic expansion and so on, their results are often inconsistent with the observed data. To explain these phenomena, scientists have to assume that there is dark matter and dark energy in the universe, two mysterious components that account for about 95% of the universe's total mass and energy, but are not directly detected.

Gravity is not inversely proportional to the square of distance? However, some scientists have also proposed some modified theories of gravity in an attempt to explain gravity with a simpler and self-consistent framework without the introduction of additional assumptions such as dark matter and dark energy.

One of the most famous theories is the modified Newtonian Dynamics (MOND) theory, which was proposed by the Israeli physicist Mordehai Milgrom in 1983. According to MOND theory, Newton and Einstein's theory of gravity is only applicable to high acceleration, but at low acceleration, gravity will change, resulting in a different effect than expected. Specifically, when the gravitational acceleration of an object is less than 0.1 nm per square second, the gravitational force between objects is inversely proportional to the distance between them, not to the square of the distance.

Although MOND can explain the unusually high rotation speed at the edges of some galaxies, it does not explain the rotation of all galaxies, which scientists still need to use dark matter to explain. Nor can it explain some phenomena that can be explained by dark matter theory, such as temperature fluctuations in cosmic microwave background radiation and the formation of large-scale structures. In addition, it does not coordinate well with general relativity.

Although long-period binaries reveal the mystery of gravity, Kyu-Hyun Chae, an astronomer at Sejong University in South Korea, recently found that some observations are consistent with MOND theory.

Using data from the European Space Agency's Gaia Space Telescope, he analyzed 26500 pairs of long-period binaries within a range of 650 light-years from Earth. Long-period binaries are made up of two stars that are far apart but orbiting each other, and their orbital periods are usually more than thousands of years. The gravitational acceleration of these binaries is very low, and they are very little affected by dark matter, which makes them an ideal object to test the effectiveness of the current gravitational theory at low acceleration.

Although scientists have tried to use long-period binaries to detect gravity before, they have not achieved decisive results. However, in Cai Guixian's research, he wrote a Python program that can accurately calculate the gravitational acceleration of binary stars, thus obtaining reliable results.

He found that when two stars revolve around each other at an acceleration of less than 1 nm per square second, they begin to deviate from the law of gravitation and general relativity. When the gravitational acceleration of these stars drops to less than 0.1 nanometers per square second, they receive about 30 to 40 percent more acceleration than Newton or Einstein theory predicted. The significance of this difference is so high that it reaches the standard required by what a study can be called "discovery", that is, the standard deviation is 5 Sigma (equivalent to an error rate, about 0.00006%).

Cai Guixian believes that this is because in this case, gravity begins to follow the MOND theory rather than Newton or Einstein's theory. He also found that the observed data are more consistent with AQUAL theory. AQUAL theory is an improvement of MOND theory, which was jointly proposed by Milgrom and Israeli-American physicist Jacob Beckenstein (Jacob Bekenstein).

Trigger a new revolution in physics? This is by far the most direct and powerful evidence that Newton and Einstein's theory of gravity will "collapse" at low acceleration and need to be replaced by an improved theory of gravity.

This is of great significance to physics and astronomy, and it may trigger a new revolution in physics. If MOND is proved to be correct, then our understanding of the universe will change fundamentally. We may no longer need to assume the existence of dark matter and dark energy, but can use a simpler and more beautiful theory to describe all gravitational phenomena.

Of course, Cai Guixian's research also has some limitations. For example, he only considered binary systems, not other types of celestial systems, such as star clusters or galaxies. Therefore, this study is only a preliminary exploration of the theory of gravity, which needs more data and analysis to verify and improve. Moreover, as we said before, there are still many problems in MOND theory itself, which need to be further developed and improved. In any case, this discovery has shown us a more wonderful and mysterious universe.

References:

Https://dx.doi.org/10.3847/1538-4357/ace101

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