Modern physics is the branch of physics that emerged in the late 19th and early 20th centuries, revolutionizing our understanding of the fundamental laws governing the universe at both the smallest and largest scales. It encompasses quantum mechanics, relativity, nuclear physics, particle physics, astrophysics, and cosmology. This book is aimed at undergraduate and graduate students, introducing them to the mysteries of modern physics. Throughout this book, we minimize the derivation of equations, allowing readers to develop intuitive understandings of these concepts. By shedding light on the unsolved mysteries of modern physics, we aim to reveal how the progress of experimental technology not only solves existing puzzles but also uncovers new ones.