In 1915, Einstein proposed the theory of general relativity (gr), which is a regular description of the motion of matter in the gravitational field, which is one of the four basic interactions that control everything in the universe, and the existence of matter produces a gravitational field. After systematically elaborating his theory of general relativity, which holds that gravity is the distortion of space-time that occurs around massive objects, One of the questions Albert Einstein pondered was what happens when a celestial body shakes. The year after the theory of relativity was published, he pointed out the answer to the question, arguing that space-time would ripple, forming "gravitational waves", with the celestial body as the core spread outward at the speed of light.
Einstein believed that gravitational waves are space-time waves that propagate at the speed of light, which describe how objects with mass bend in space-time environments, like a tight sheet, and then place the ball in the center of the sheet, and the object with mass bends under space-time, like a folded sheet around a football.
He and other physicists immediately began arguing whether the predicted gravitational wave existed, or whether it was merely a man-made phenomenon caused by the results of new mathematical inferences. Einstein himself changed his position several times.
According to Einstein's theory of general relativity, gravitational waves occur when a giant celestial body suddenly accelerates, like when a supernova of a star explodes, or when two giant stars collide, or two dense stars merge, such as neutron stars and black holes. Due to the distance, the signal when gravitational wave energy reaches Earth is very weak. So it's hard to detect.
Scientists have been looking for the existence of gravitational waves for 100 years, and in the 1970s, American scientists discovered indirect evidence of the existence of gravitational waves in the process of observing binary star systems, and won the 1993 Nobel Prize in Physics.
For 100 years, experiments claiming to have detected gravitational waves directly and caused sensational effects, such as the Weber experiment in the 1960s and the bicep experiment in 2014, but all of which later proved to be oolong.
Since the 1990s, large laser interferometer gravitational wave detectors have been built around the world, truly opening the prelude to the golden age of gravitational wave detection.
The United States built two laser interferometer gravitational wave detectors (LIGO) in Livingston, Louisiana, and The small city of Hanford, Washington, respectively. The LIGO has a large L-shaped measuring arm, 4 km long on each side, with reflective mirrors at both ends. A beam of laser light is emitted along the opposite sides of the L-shaped vertically opposite each other and is reflected back and forth. In general, lasers cancel each other out due to interference, and the detector cannot receive a light signal, but once the gravitational wave passes, it will change the distance through which the laser passes, and thus be observed.
With ligo's help, on February 11, 2016, the United States (LIGO) officially announced the discovery of gravitational waves. The gravitational waves discovered this time stem from the merger of two black holes 1.3 billion years ago. After the merger of two black holes of different masses, the total mass is reduced, and the lost mass is released into space in the form of powerful gravitational waves, and after a long journey of 1.3 billion years, it arrived on Earth on September 14, 2015, and was captured by ligo's two twin gravitational wave detectors with a time difference of 7 milliseconds.
What is the significance of the discovery of gravitational waves? The discovery of gravitational waves will be one of the biggest breakthroughs in physics in 100 years. At this point, all of Einstein's predictions have been verified, which is the perfect end to the general relativity gr. As American scientists have said, the confirmation of gravitational waves is the last "puzzle" of gr, and several other major verifications of gr have long been proved by experiments, including: Mercury perihelion precession, light deflection in the gravitational field, gravitational redshift, radar echo time delay, black hole, spin precession. This also fully demonstrates the correctness of general relativity.
In addition, gravitational waves are a kind of material waves produced by the violent movement and change of matter and energy, and the characteristics of gravitational waves allow it to provide information that cannot be obtained by other means. It provides a new window of cosmic observation that is different from electromagnetic waves, and is a new way and new means for human beings to explore and understand the universe.
Scientists imagine that gravitational wave communication can communicate with the distant universe and reduce interference, if with the help of gravitational wave communication technology, receiving highly intelligent alien information, human beings will gain more knowledge of the universe, they will teach us how to find a new home in the depths of the universe, let us escape the dangerous environment of the earth.
At present, China is also starting gravitational wave detection programs, such as the Taiji Plan, the Lyra Program, etc., and like electromagnetic waves, gravitational waves also have different frequencies. Gravitational waves of different frequencies reflect different periods of the universe and different astrophysical processes. What the Americans caught on the ground with two 4-kilometer-long "arms" belonged to high-frequency gravitational waves. But if you want to study larger, more distant objects, you also need to detect gravitational wave signals in the middle and low frequency bands. And this requires space gravitational detection.
The core technologies involved in space gravitational wave detection include high-precision ultra-stable laser interferometer, gravitational reference sensor, ultra-high-precision no-drag control, micro-bull-class thruster, ultra-stable ultra-static satellite platform, etc. For this reason, China has overcome all technical problems and developed Taiji I, and at the end of August 2019, the Chinese Academy of Sciences successfully launched "Taiji I" at the Jiuquan Satellite Launch Center.
The "Taiji-2" will carry out on-orbit verification of most of the key technologies with higher indicators, while the "Taiji-3" will be composed of three satellites millions of kilometers apart, and really begin to detect various gravitational wave objects.
Looking forward to the day when China is going farther and farther in the "gravitational universe".