This book concludes the series Physics for Everyone by the world-renowned scientist, winner of the Nobel and Lenin prizes, academician Lev Landau and the distinguished physicist Alexander Kitaigorodosky, This book discusses in a simple easy-to-understand manner the phenomenon of electromagnetic waves, thermal radiation, and current treatment of spectroscopic analysis. Provides an introduction to the field of nuclear physics and explains the most common types of lasers. Outlines principal aspects theory of relativity and quantum theory.