INTRODUCTION TO THE BASIC METHODS OF UNDERSTANGING AND PROBING THE UNIVERSE

The earliest understanding and observation of the universe began with visible light. Subsequently, due to Maxwell's prediction of electromagnetic waves in 1865, Hertz's confirmation in 1887, and Jansky's discovery of radio radiation in the Milky Way in 1933, visible light observation has been expanded to multi-band electromagnetic wave observation, leading to the emergence of multi-band astronomy. In 1912, Hess discovered cosmic rays, providing an additional means in addition to electromagnetic wave observation, and opened the prelude to multi-messenger astronomy. In 1987, Davis and Koshiba discovered neutrino signals from supernova explosions, which was the first time that humans detected neutrinos from the universe, and since then there has been another kind of messenger to understand and observe the universe. Later, in 2016, the Laser Interferometric Gravitational-wave Observatory in the United States detected gravitational waves, which completed the last piece of the puzzle for verifying Einstein's general theory of relativity and made gravitational waves the last messenger known to multi-messenger astronomy. This paper introduces the discovery history, basic concepts, and basic principles of detecting the universe of the four messengers of electromagnetic waves, cosmic rays, neutrinos and gravitational waves. The representative experiments are collected and organized. A brief introduction is given to one of the typical experiments. It is expected to give a relatively complete description of the development of multi-band multi-messenger astronomy.