Gravitational waves propagate in the form of waves and at a limited speed. According to the general theory of relativity, an accelerating object will produce gravitational waves. The main properties of gravitational waves are: shear waves and plane waves at the far source; There are two independent polarization states; Carrying energy; Propagation at the speed of light in a vacuum, etc. Gravitational waves carry energy and should be detectable. However, the intensity of gravitational waves is very weak, and the absorption efficiency of matter to gravitational waves is extremely low, so it is extremely difficult to directly detect gravitational waves. Some people claim that gravitational waves have been detected in the laboratory, but they have not been recognized. Astronomers indirectly verify the existence of gravitational waves by observing the changes of orbital parameters of binary stars. For example, the revolution of binary star system, the rotation of neutron star, the explosion of supernova, and the formation, collision and capture of black hole matter predicted by theory can all radiate strong gravitational waves. We predict that the strongest gravitational waves that can be observed on the earth will come from distant and ancient events, in which a lot of energy moves violently (examples include the collision of two neutron stars or two extremely heavy black holes). Such fluctuations will cause changes in the relative distances of various parts of the earth, but the maximum range of these changes should be only 10-2 1. For the arm of LIGO gravitational wave detector, this change is less than one thousandth of the diameter of a proton. This is very abstract. The first is inflation, which will produce gravitational waves when it suddenly stops. Gravitational waves will have an impact on photons generated during the skyrocketing process (that is, the current cosmic background radiation). How do you say this? At that time, photons will also be polarized when they travel through the universe because they are scattered by electrons. Gravitational waves will slightly change this polarization mode. When these ripples propagate in time and space, they will replace electrons in a unique way, thus leaving their footprints in the cosmic microwave background. Simply put, it is the background radiation of the universe that magnifies everything before, making it possible to peek at the moment when the universe was born.