This is a popular book on relativity written by physicist Li Miao for children. Einstein's revolution in science and technology has brought great changes to our world in the 20th century. It has changed our cognition of time, space, matter and motion. A series of fantastic predictions have come true one by one, including gravitational waves detected in recent years. In this book, starting from this world-famous event, uncle Miao tells his children about the incomprehensible concepts of gravity, space-time, speed of light, etc. There are a lot of wonderful illustrations in the book, together with a variety of interesting thought experiments, to help children understand this field which has a great impact on modern physics.