TABLE OF CONTENTS The discovery of the quantum of energy in the early years of the twentieth century provided an explanation of the photoelectric effect and it enabled the success of Bohr's quantum model of the atom. This model and the other successes of that time contributed to what is known as "quantum theory."
Nevertheless, the existence of the energy quantum, whether in light or in atoms, posed a serious problem for physics, since it was incompatible with both Newton's mechanics and Maxwell's electromagnetic wave theory. In these theories energy is always continuous and infinitely divisible. But these "classical" theories were constructed on the basis of events occurring in the visible, human-scale world, ranging from planets to microscopic objects. Perhaps, then, we should not be surprised that nature might behave differently when we enter into regions far removed from everyday experience, such as the interior of atoms or the sub-microscopic structure of minute quantities of light. And when we are surprised, it only impresses upon us even more how intricate and exquisite nature really is.
By the mid-1920s scientists realized that the quantum theory was inadequate and that a new theory was needed to encompass the quantum world at the subatomic level, a new quantum mechanics in which the quantum is built into the foundations of physics from the beginning. An important clue to the new mechanics came from the further study of particles and waves.
Einstein's hypothesis of light quanta created a...
