Why did Max Planck think that energy ought to be radiated in quantas? What were the shortcomings of the earlier theories that made the Quantum Theory a necessity. For example, the shortcomings in Galileo's model of planetary motion was that it could not explain why did the planets revolve around the sun. Newton took care of that with his theory of gravity. My question rests on the same lines, what were the disadvantages of the theories before the quantum theory?