Physicist Max Born described the theory behind molecular orbitals in 1926. Today, it is known as Born's rule and is part of the Copenhagen interpretation of quantum mechanics. When initially proposed, this theory did not agree with the atom model of Niels Bohr. Bohr's model described electrons as "orbiting" the nucleus, as they moved around in circles. However, the Born model eventually gained popular support because it was able to describe the locations of electrons within molecules and explained a number of previously inexplicable chemical reactions.