Max Planck, German theoretical physicist, c 1920.
© Science Museum / Science & Society Picture Library
Following his abandonment of clasical physical principles, Max Planck (1858-1947) introduced the hypothesis that oscillating atoms absorb and emit energy only in discrete bundles (called quanta) and not continuously, as had previously been asumed. The succes of his work and subsequent developments by other physicists, Albert Einstein (1879-1955) among them, established the quantum theory of modern physics, of which Planck is justly regarded as the father. In 1918, his work in the field was rewarded with the Nobel Prize.