Applying knowledge of the fundamental interactions to the universe
At the beginning of the XX century, we were not aware of the existence of great number of galaxies yet, so the universe was identified with our galaxy, called the Milky Way, and other galaxies were thought to be obscure nebulae. Studying the pulsating stars in the Andromeda Nebula, Edwin Hubble concluded that they are located far beyond the stars of the Milky Way, and the red shift of the spectrum of their light has led astronomers to the discovery of expansion of the universe. By that time, spectroscopy was already based on the knowledge of particles — electrons and atoms — that later made it possible also to realize the origin of the Cosmic Microwave Background. The subsequent rapid development of elementary particle physics led to an understanding of nuclear reactions in stars, the origin of chemical elements, and provided a picture of the processes in the early hot universe.