A century ago, Einstein's insight into time and space completely changed our understanding of the universe. His predictions about gravitational waves, curvature of spacetime, time expansion and black holes are inspiring.

Einstein believed that mass had an influence in four-dimensional space-time. Space-time will bend under the influence of massive objects (such as the sun or black holes). The famous gravitational field equation is expressed in mathematical language. The left part of the equal sign reveals the curvature of time and space, and the right part describes the distribution of matter. Physicist john archibald wheeler explained:? Matter tells spacetime how to bend, and spacetime tells matter how to move. . Gravitational waves are the transfer phenomenon of space-time bending.

1. How is the gravitational wave proposed?

Einstein imagined that gravity came from the bending of space. When an object affected by gravity changes its shape, it will cause ripples in space. When these ripples pass through the earth, will our local space fluctuate with them? Jitter? Be stretched or squeezed. But this effect is very weak, because gravity is a weak force.

The degree of gravitational stretching in daily life is very small. If we see two cars passing by, we will also emit gravitational waves, but the energy is infinitely small. Even if the earth revolves around the sun, or two stars revolve around each other, the gravitational waves they emit are not detectable.

19 16 In June, Einstein submitted a landmark paper "Approximate Integral of Gravitational Field Equation" to the Prussian Academy of Sciences in Berlin, which was the first work in the history of science to predict gravitational waves.

Einstein's theory holds that different gravitational wave sources will have different frequencies and amplitudes. For example, two black holes with very close orbits complete 100 cycles per second, and the frequency of gravitational waves they emit is 200Hz. For observers far away from black holes, there are 200 peaks passing by every second. Because gravitational waves travel at the speed of light, the corresponding wavelength is 1500 km.

The amplitude of gravitational waves is a measure of their intensity, and it is the degree to which space-time is stretched and compressed. The amplitude is inversely proportional to the distance from the observer to the double black hole, and directly proportional to the mass of the black hole and the acceleration around each other. If two black holes spiral close, the amplitude and frequency of gravitational waves will increase at the same time.

At that time, many scientists did not pay attention to it, thinking that gravitational waves were too weak to be detected even if they existed. Astronomer Arthur Eddington believes that gravitational waves are only a mathematical singular solution of general relativity and have no physical significance.

1955 Shortly after Einstein's death, academic views began to change, especially after theoretical physicist Pirani and others proved that gravitational waves carried energy. Gravitational waves have since entered the category of real physical phenomena, and the remaining question is? Capture? they ...

It should be explained that gravitational waves are? Spatial density? The three-dimensional propagation of ripples, that is, in all directions of space, may be stronger in one direction than in other directions. The transmission of gravitational waves by any celestial body is transparent and unimpeded.

The intuitive way to visualize gravitational waves is that the spatial density ripple of gravitational waves is very similar to passing through a gently shaking jelly, which represents a blank space.

2. How are gravitational waves detected and confirmed?

On February, 2065438 1 1, the American gravitational wave observatory announced at the press conference in Washington, D.C. that LIGO (Laser Interferometer Gravitational Wave Observatory) detector? Capture? Gravitational waves. Gravitational waves come from the collision of two black holes, which are1300 million light years away from us, and are named GW 1509 14. LIGO was conceived by Kip Thorne, a professor of theoretical physics at California Institute of Technology, and his colleagues, physicists Rainer Weiss and Ronald Drever.

LIGO has two similar detectors, about 3000 kilometers apart, one in hanford, Washington, and the other in Livingston, Louisiana. They have extremely high sensitivity, and the time measurement accuracy is 10- 18 seconds.

The first gravitational wave signal detected by LIGO comes from a distant double black hole event. This wave travels at the speed of light in space and broke into our galaxy about 654.38 million years ago. When it approaches the Earth in the Milky Way, it sends tiny signals to stars and planets.

September 20 14 15, 09:50:45 universal time, the first gravitational wave reached the earth. In less than 1 sec, the earth is stretched and compressed by this series of ripples in time and space 10 2 1, which is only one tenth of the diameter of a proton. Everything on the earth expands and contracts with it. LIGO detector recorded this tiny vibration. Soon, everything was calm again. Gravitational waves continue to spread forward. 1.3 seconds later, they crossed the lunar orbit, and within a few hours, they left the solar system and continued to distort everything on their way.

This chart named GW 1509 14 shows that the real measured value of gravitational wave signal is based on the theory of merging two black holes with 36 and 29 solar masses respectively. Forecast? These values match almost exactly. It sounds amazing, but it is a rigorous science.

The LlGO organization explained that with the approach of double black holes, the mutual rotation speeds up, and the strong acceleration increases the amplitude of gravitational waves. The shorter the orbital period means the higher the frequency. In the end, the two black holes merged at a very high speed to form a larger black hole, the mass of which is about 62 times that of the sun. Another three times the mass of the sun is converted into curvature of spacetime energy (e = MC 2), which is emitted in the form of a huge gravitational storm.

Black holes bend the surrounding space-time, and the curvature of space-time represents a certain amount of energy. According to general relativity, energy is equivalent to mass, so energy produces extra bending.

Since then, several gravitational waves have been recorded. For example, the waveform of the second gravitational wave signal GW 15 1226 is consistent with the expected theoretical waveform of the merger of two black holes with solar masses of 14.2 times and 7.5 times, respectively, which originated from the merger of two black holes with a distance of1400 million light years from the earth.

Today, a new generation of more powerful gravitational wave detector aLIGO has been put into trial operation. With what? Virgo galaxy cluster? The named Italian Virgo detector has joined the LIGO- Virgo joint system.

LISA Pathfinder of the European Space Agency has been launched and plans to detect gravitational waves in space, which is more like the space version of LIGO. KAGRA Kamoka gravitational wave detector of Japan National Astronomical Observatory cooperated with Virgo this year, and GEO600 of European Gravitational Observatory also joined the cooperation. Indians? LIGO- India? The detector is scheduled to be put into operation in 2024.

China Academy of Sciences has also formulated a project called? Space Tai Chi? The space-based exploration plan will launch a gravitational wave satellite group around 2030, and it is planned to directly detect space gravitational waves. This marks that the astronomical research in China has reached a new height.