Quantum
Early History | Planck's Contribution | Einstein's Contribution | Bohr Atom | Wave Mechanics | Matrix Mechanics | Quantum Meaning | Uncertainty | Quantum Results | Developments | The Future | Two Holes | Quantum Time Waits for No Cosmos

In 1911 Rutherford established the existence of the atomic nucleus. He assumed, on the basis of experimental evidence obtained from the scattering of alpha particles by the nuclei of gold atoms, that every atom consists of a dense, positively charged nucleus, surrounded by negatively charged electrons revolving around the nucleus as planets revolve around the sun. The classical electromagnetic theory developed by the British physicist James Clerk Maxwell unequivocally predicted that an electron revolving around a nucleus will continuously radiate electromagnetic energy until it has lost all its energy, and eventually will fall into the nucleus. Thus, according to classical theory, an atom, as described by Rutherford, is unstable. This difficulty led the Danish physicist Niels Bohr, in 1913, to postulate that in an atom the classical theory does not hold, and that electrons move in fixed orbits. Every change in orbit by the electron corresponds to the absorption or emission of a quantum of radiation.

The application of Bohr's theory to atoms with more than one electron proved difficult. The mathematical equations for the next simplest atom, the helium atom, were solved during the 1910s and 1920s, but the results were not entirely in accordance with experiment. For more complex atoms, only approximate solutions of the equations are possible, and these are only partly concordant with observations.

Quantum
Early History | Planck's Contribution | Einstein's Contribution | Bohr Atom | Wave Mechanics | Matrix Mechanics | Quantum Meaning | Uncertainty | Quantum Results | Developments | The Future | Two Holes | Quantum Time Waits for No Cosmos