XIII.

Hertz to the Rescue

The true hero of the unification of electromagnetism and light is Heinrich Hertz, who, in a series of experiments from 1873 to 1888, confirmed all the predictions of Maxwell's theory.

Waves have a wavelength, which is the distance between crests. The crests of water waves in the ocean typically may be 6 to 9 m apart, while sound wavelengths range in centimeters. Electromagnetism also comes in waves. The difference between various electromagnetic waves—infrared, microwaves, X rays, radio waves—is simply a matter of their wavelengths. Visible light—blue, green, orange, red—is in the middle of the electromagnetic spectrum. Radio waves and microwaves have longer wavelengths. Ultraviolet, X rays, and gamma rays have shorter wavelengths.

Using a high-voltage coil and a detection device, Hertz found a way to generate electromagnetic waves and measure their speed. He showed that these waves had the same reflection, refraction, and polarization properties as visible light waves and that these waves could be focused. It turned out that Maxwell was right. Hertz, in subjecting Maxwell's theory to rigorous experiment, clarified and simplified it into a system of four equations.

After Hertz, Maxwell's ideas became generally accepted, and the old problem of action-at-a-distance was put to rest. Forces in the form of fields propagated through space with a finite velocity, the speed of light. Maxwell believed that he needed a medium to support his electric and magnetic fields, so he adapted the popular notion of an all-pervading ether, in which the electric and magnetic fields vibrated. This part of Maxwell’s theory would be discarded when the existence of the ether was disproved by experimentation in the late 1800s.

The Faraday-Maxwell-Hertz triumph spelled another success for reductionism (the idea that complex forces can be explained as aspects of a single force). No longer did universities have to hire a professor of electricity, a professor of magnetism, and a professor of light or optics. Since these subjects are all unified, only one staff position is now needed (more money for the football team). A vast set of phenomena was thus encompassed, including things created by science and technology and things belonging to the natural world—things like motors and generators, transformers, and an entire electrical power industry, and things like sunlight and starlight; radio, radar and microwaves; and infrared and ultraviolet light and X rays and gamma rays.

Maxwell’s four simple equations are famous in the world of physics, and physics and engineering students the world over wear T-shirts sporting them. For our purposes, it is not important to list them or explain their workings. The point is that they symbolize the scientific summons, “Let there be light!”

Maxwell's original equations were very long and bulky. Hertz rewrote them into much simpler versions that were easier to work with and understand. Hertz was a rare example of a scientist who was more than the usual experimenter with only a working grasp of theory. He was exceptional in both areas. Like Faraday, he was aware of, but uninterested in, the immense practical importance of his work. Hertz's theoretical work consisted largely of reducing and popularizing Maxwell’s theory, an effort that made great strides in physicists’ continuing quest to unify all the forces of nature.

As the 19th century drew to a close, the powerful combination of Newton’s laws of motion, Newton’s law of gravity, and Maxwell’s equations provided the tools needed to explain seemingly all scientific phenomenon. Gravitational force explained the solar system and the motion of objects, matter was somehow made of electrically charged objects, and Newton’s law of motion enabled calculations that showed how these charged objects could attract to make atoms. The chemists had already proven the existence of atoms; only their detailed structure remained to be discovered. In 1897 British physicist Sir Joseph J. Thomson discovered the electron, further clarifying the basic structure of matter. The laws of thermodynamics, generated in part by Faraday’s discoveries, also helped round out the scientific picture by giving direction to chemical reactions and physical processes, and ushered in the beginning of the Industrial Revolution.

Optimism about the so-called end of science, the belief that all scientific mysteries could be understood, began to fade around 1900. With the end of the millennium, it became increasingly clear that some of the puzzles of physics could not be solved by the Newton/Maxwell set of intellectual armaments, however powerful they might be. The challenge inherent in this realization heralded a revolution, one that would prove to make the 20th century the most scientifically productive era in the history of humankind.

About the author: Physicist, professor, and author Leon M. Lederman is director emeritus of the Fermi National Accelerator Laboratory in Batavia, Illinois. Lederman won the Nobel Prize in physics in 1988 for his work with elementary particles. He has taught at Columbia University in New York City, the University of Chicago, and the Illinois Institute of Technology in Chicago.