Many regard Albert Einstein as the greatest physicist since Newton. What exactly did he do that is so important in physics? We provide an introduction to his physics at a level accessible to an undergraduate physics student. All equations are worked out in detail from the beginning. Einstein's doctoral thesis and his Brownian motion paper were decisive contributions to our understanding of matter as composed of molecules and atoms. Einstein was one of the founding fathers of quantum theory: his photon proposal through the investigation of blackbody radiation, his quantum theory of photoelectric effect and specific heat, his calculation of radiation fluctuation giving the first statement of wave-particle duality, his introduction of probability in the description of quantum radiative transitions, and finally the quantum statistics and Bose-Einstein condensation. Einstein's special theory of relativity gave us the famous E=mc^2 relation and the new kinematics leading to the idea of the 4-dimensi
Ta-Pei Cheng is a particle physics theorist. He received a PhD from Rockefeller University with the noted physicist and Einstein biographer Abraham Pais. He is now Professor Emeritus at the University of Missouri - St. Louis, and an Adjunct Professor at Portland State University in Oregon. He is an elected Fellow of the American Physical Society. Among many concurrent appointments, he was at the Institute for Advanced study (Princeton), the University of Minnesota, and the Lawrence Berkeley Lab. Professor Cheng is the co-author (with Ling-Fong Li) of the book Gauge Theory of Elementary Particle Physics (Oxford, 1984) that has introduced the subject to several generations of particle physics students. Its companion book GTEPP: Problems and Solutions was published in 2000. He is also the author of Relativity, Gravitation, and Cosmology: A basic introduction, (Oxford 2005, 2nd ed. 2010). It is among the first books adopting a 'physics-first approach' to the pedagogy of general relativity.