Stages in the Conceptul Development of Wave Mechancis

I will review conceptual advances which paved the way for the emergence of the mature form of quantum theory (quantum mechanics) in 1925-27, focusing on the contributions of Albert Einstein. I argue that Einstein’s 1905 paper on light quanta was motivated by his firm belief that equipartition of energy was inescapable within classical statistical mechanics. Moreover, his rejection of the ether in his work on Special Relativity freed physicists to accept the possibility of wavelike phenomena not supported by a substrate or medium, which is now our view of all fundamental quantum waves. Einstein’s 1907 paper on the specific heat of solids was the first application of quantization to molecular mechanics, and hence the first clear embrace of quantization of energy, strengthening his conclusion that a radical revolution in all of physics (not just electromagnetism) was upon us. In 1909 Einstein was able to derive the first rigorous result in quantum statistical mechanics, his energy/momentum fluctuation formula, which strongly supported the necessity of wave/particle duality in the new physics. Bohr in 1913 was able to explain the hydrogen spectrum in terms of quantization of electron orbits, but at the expense of accepting the possibility of accelerating charges which do not radiate, something Einstein found astonishing and puzzling. Einstein himself introduced a generalization of Bohr-Sommerfeld quantization based on topological quantization in 1917, but noted its failure for chaotic systems. In 1916-7 Einstein introduced fundamental randomness into quantum theory via the hypothesis of spontaneous emission. While much of the field focused on applying and improving Bohr’s theory (leading eventually to matrix mechanics), De Broglie and Bose inspired Einstein to move forward with a novel quantum statistical mechanics of gases which seemed to require a spatial function to be associated with each atom. This work directly motivated Schrodinger to investigate waves describing electrons and eventually to discover his equation for the complex wave function of the electron at the beginning of 1926. It is significant that the Schrodinger equation removes the puzzle of non-radiating electrons in hydrogen, due to the static nature of the charge density in an eigenstate of energy.