An important question to ask about light behaving as a wave is what does it wave in? The idea that there was some type of invisible fluid or element that was part of the universe can be dated all the way back to Aristotle. Remember the four Greek elements: earth, air, fire, and water? It was thought that there was a fifth one that helped to explain the movement of the celestial bodies in the heavens, because it was believed that something was needed to support and guide them in their perfect circles.
The belief in the existence of a substance called ether (not the anesthetic) dates back to the ancient Greeks. It was originally believed to be some sort of material that permeated all of creation. Many scientists believed it existed up until the end of the nineteenth century. Today it is often associated with the energy or life force found in traditional Chinese medicine and the Ayurvedic medical practices of India. In China it's called Chi and in India it's called Prana. In esoteric philosophy it is thought to make up the etheric body or energy body that is the life force that animates our physical bodies.
In a speech delivered in 1889, Heinrich Hertz said:
That statement really reflected how many prominent scientists felt. Isaac Newton along with Michael Faraday and James Clerk Maxwell all believed that there had to be some substance that acted as a medium to transmit the forces of gravity, electricity, and electromagnetic waves through space. However, they had different views on exactly what this substance was. Newton himself had no idea what it was, as seen in this letter to a friend.
Michael Faraday only had a formal education through the eighth grade and had no interest in mathematics. His brilliance laid in his innate ability to put his ideas into experiments. Over the years, he invented the first electric motor, showed that magnetism could be converted into electricity, designed and built the first dynamo, and made the first electrical transformer. He became the Grand Old Man of English science, but his contemporaries read his papers more for the results he found rather than what they meant. He was a strong believer in the unity of all types of physical interaction, a belief that was also fundamental to Einstein and which lies at the core of the search for a unified theory today.
Remember Michael Faraday? As an experimenter Faraday was extraordinary. His ideas were unlike anybody else's and he had little to do with the experts at the universities. He was an intuitive thinker and many of the ideas that he expressed were difficult for the typically rational approach of many of the other scientists. He was not that good at the higher mathematics of algebra and calculus, so he worked out his theories strictly through experimentation rather than mathematical equations.
According to Faraday, matter is atomic, which was something that most scientists agreed upon. Each atom had an “atmosphere of force” around it, an idea that had never been clearly defined and had no better name. He later developed this idea into the term “field,” a form of ether that had lines of force running through it. As mentioned before, the best way to see this is to put iron filings on a piece of paper and place a magnet under the paper. You will see a pattern in the filings created by the magnetic field. Here again was the idea that this field had to exist in something; it couldn't just float about in empty space.
After years of experimentation, Faraday's discoveries suggested that electric and magnetic fields were more than just forces; they also had a dynamic interaction. This capacity to use one to create the other led to the term “electromagnetic field.” And perhaps his greatest insight was that an electromagnetic field could affect a ray of polarized light. He realized that there had to be some connection between electromagnetism and light waves.
Polarized light is a form of light in which the electromagnetic waves of light move only in one plane. Normally they move at right angles to each other. If you don't quite under-stand this, think of a normal light wave as a rotating barbershop pole. The spiraling coloring lines are moving around and around in three dimensions. Now if you flatten the pole out, you just have lines moving zig-zag up and down on a flat piece of paper. A polaroid filter does the same thing. It only allows waves of light to move up and down, or left and right, rather than around and around. (This has nothing to do with the Polaroid camera; they just liked the name.)
The man who would bring electromagnetism and light together was James Clerk Maxwell. He developed mathematical formulas that connect electric fields with electric charges, magnetic fields with electric currents, and those that connect electric and magnetic fields together. These are the formulas that express the mathematical unification of electricity and magnetism. There is not a word about the properties of ether in all of this; he was only concerned with fields and their sources. However, he was still an ardent believer in it as can be seen in this article he wrote for the Encyclopedia Britannica:
The existence of ether is no longer one of the hot topics in science today. It was disproved by some experiments done in the nineteenth century, but these were set up to measure the existence of ether in just a certain way. Albert Einstein didn't believe that there was any problem with his theory on general relativity and the co-existence of ether. Whether it really exists or not has never really been proven. When I discuss general relativity in a few chapters, we'll come back and look at ether again to see how it may relate to properties of space.
Maxwell, like Newton and Faraday, believed that the existence of ether was necessary, but like them, he had no clue as to what it really was. He kept his views about ether out of his mathematical formulas, not just because he didn't know what it was, but because it wasn't necessary in developing his mathematical formulas. However, his belief in ether did lie behind his theories of how electromagnetic waves moved through space.
Maxwell's theories explain so many different facts of electricity and magnetism that there is no serious doubt that they are accurate. His mathematical formulas are the cornerstone of classical physics in electromagnetic radiation. From the work that he did, he was able to calculate the speed of electromagnetic waves, and because the speed of light (which had been discovered by Léon Foucoult) was essentially the same, he deduced that light was electromagnetic, although he gave no experimental evidence to support this.
Excerpted from The Complete Idiot's Guide to Theories of the Universe © 2001 by Gary F. Moring. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.