The beginning of the 20th century brought the start of a revolution in physics such as in the beginning of 1900, Max Planck, Albert Einstein, Niels Bohr and others developed quantum theories to explain various anomalous experimental results, In 1925, Werner Heisenberg and Erwin Schrödinger formulated quantum mechanics. The observation by Edwin Hubble in 1929 that the speed at which galaxies recede positively correlates with their distance, led to the understanding that the universe is expanding, and the formulation of the Big Bang theory by Georges Lemaître.