One of the troubles encountered by physicists in the 1900s was that the colour of light from red-hot objects differed from their expectations. Max Planck, a German physicist, found a way to predict the colour accurately. He assumed that energy radiated only as multiples of a fixed amount called quantum. This also clarified why the energy of electrons ejected from metals by light depended on the colour of the light rather than brightness.
In the next three decades, Erwin Schrodinger, Werner Heisenberg and others utilized the quantum theory to develop a new world view in which matter and energy could be both waves and particles.
These developments transformed physics. The theoretical basis of modern physics is built on two theories: the theory of relativity and quantum theory. The first one is relevant when high speeds are involved and quantum theory is required when quantities on the scale of atoms, molecules, etc. are involved.
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