Quantum mechanics - Wikipedia duced by Arnold Sommerfeld .[11] This phase is known as old quantum theory . According to Planck, each energy element (E) is proportional to its frequency (ν): E = h ν {\displaystyle E=h\nu \ } <span>, [imagelink] [emptylink] Max Planck is considered the father of the quantum theory. where h is Planck's constant . Planck cautiously insisted that this was simply an aspect of the proces