By Luca Fiorani

Maxwell’s equations are, without any doubt, one of the immortal monuments of physics. You can write them on a bar bill, yet they explain all electromagnetic phenomena, from the operation of your smartphone, to the magnetic field of neutron stars. As usual in science, they are not the sudden achievement of a solitary genius, but the hard result of many decades of patient work by many physicists, in both theoretical and experimental fields.

Why are they named after James Clerk Maxwell, a Scottish mathematical physicist of the 19^th century? Because Maxwell gave them an inner coherence by adding a new term, the “displacement current”. The “displacement current” is substantially a varying electric field, without which Maxwell’s equations would yield some absurd conclusions. Moreover, it provides them with an intrinsic symmetry, harmony and beauty: a varying electric field creates a varying magnetic field that creates a varying electric field … and so on. Amazingly, the equations predict that this endless propagation of fields has the speed of light, this is why Maxwell assumed that light is an electromagnetic wave (and he was right, as experiments proved later).

This is not the end of the story though. While Newton’s laws have been swept away by Einstein’s storm – his Theory of Relativity – Maxwell’s equations still stand, unchanged.

Alexander Pope wrote: “God said: ‘Let Newton be!’, and all was light”. If he had lived later, he would probably have written “Maxwell” instead of “Newton”.