Albert Einstein Relates That Maxwell’s Work Laid the Foundation for His Special Theory of Relativity

Classical mechanics is a model of the physics of forces acting upon bodies. It is often referred to as "Newtonian mechanics" after Isaac Newton and his laws of motion. Within this model, there was kinetic energy (which was possessed by a body by virtue of its motion and velocity) and potenital energy (which was possessed by a body by virtue of its position and was waiting to be released, such as a rock on top of a hill or water behind a dam). In Newtonian mechanics, kinetic and potential energies could readily be treated as separate phenomena and even had different formulas to determine them. Thus to physicists from the time of Newton until the 1860s, forms of energy were distinct. Then, James Clerk Maxwell (who died the year Einstein was born) made some revolutionary determinations relating to electricity, light and magnetism. He found that fields rather than forces were at work, and that electricity, magnetism and light could all be understood as aspects of a single object: the electromagnetic field.

There was another implication of Maxwell’s work, as well, one not thoroughly understood until Einstein came onto the scene: in electromagnetism, it’s hard to maintain a distinction between types of energy, because the definition of a magnetic field (and hence the magnetic potential) depends on the velocity of the observer. Thus, different observers would perceive differing amounts of kinetic and potential energies. So the potential energy would relate to a factor other than its position, contrary to Newtonian mechanics. Einstein pondered this issue and also considered the relationship of energy (the ability to do work) to matter (what all things are made of). He finally found the solution; referred to as the “Special Theory of Relativity,” it replaced Newtonian energy theory altogether. In it, Einstein established that all energy is the same (at velocities about light speed or in high gravitation fields we cannot even separate kinetic and potential energy), and that the energy of an object is in fact equivalent to and interchangable with its mass; he stated this in the most famous formula in science: E=MC2 (energy equals mass times the speed of light squared).

Albert Einstein autograph on a Typed Letter Signed on his personal letterhead, Berlin, May 8, 1928 to Ernst Eckhardt, who had written Einstein postulating that there might be two types of energy. Eckhardt is likely the German-born author, statistician and theologian of that name who made his career in the United States. In the letter, Einstein reveals the crucial part Maxwell’s work played in leading him to appreciate the fact that types of energy were aspects of the same phenomenon, an appreciation that led to the Special Theory of Relativity. “Your division of energies into Types I and II seems to me to be similar to the separation between potential and kinetic energy, as is conventional in classical mechanics. However, one has gotten away from attributing a fundamental significance to such a separation, ever since the Maxwell Theory of electro-magnetic fields demonstrated to us an energy form in an electro-magnetic field, in which this separation cannot be carried out in any natural way. It behaves in a similar way in the theory of gravitation. The modern view of Physics is therefore not particularly favorable to your interpretation; something concrete is not likely to result from such a general line of questioning.” It is interesting to note that, implicit in this letter, is Einstein’s belief that his theories have rendered classical, Newtonian mechanics archaic.