Maxwell’s Demon: 1820–1890

“Radiation [is] a kind of species of vibration in the lines of force which are known to connect particles and also masses of matter together,” said Michael Faraday in an unusually speculative mode in 1846. Faraday’s concept of lines of force turned into James Clerk Maxwell’s concept of electromagnetic fields, unifying magnetism, electricity, and light. Faraday had wondered if gravity might also be represented by lines of force. However, his concept of unifying all four phenomena was regarded by his peers as speculative, if not downright embarrassing. (It still has yet to be achieved!) Faraday, a superb experimentalist, and Maxwell, a genius of a theoretician, together created a description of electromagnetism that bridged the gap between Newtonian physics and quantum physics. Newtonian physics describes phenomena as they seem to exist in the real world, but quantum physics delves into the uncertainties of the smallest possible scale. Maxwell also contributed to a revolution in thermodynamics with his kinetic theory of gases, the first application of statistics to explain macroscopic phenomena by microscopic effects. The revolution in electromagnetism belongs equally to Faraday and Maxwell, as much for anticipating the yin and yang of theory and experiments that was to dominate the 20th century, as for the sweeping change in understanding the phenomena. The big dilemma with thermodynamics was the difficulty of reconciling the irreversibility of the laws of thermodynamics with the reversible equations of classical physics.