One of the most interesting stories in the history of science is ether and the nature of light. Scientists devised the theory of ether to explain the actions of light.
For many years, scientists thought of light as a wave. The reason was that light did wave-like things. It could experience interference when two out-of-phase light waves canceled each other. Light could refract and diffract, which are things waves can do.
The problem was that light also did things that only particles could do. For example, light could knock electrons out of certain materials causing what is known as the photoelectric effect. That means that light has mass. Waves don’t have mass. The problem became more complex when considering how light from the Sun reaches the Earth. Waves can’t go through a vacuum, and yet light gets here from the Sun.
To resolve this issue, scientists proposed that space was not a vacuum but was full of something called ether. They thought ether must be the substance that was being waved so light could travel through it. In 1887, two scientists, Albert Michelson and Edward Morely, built a device that could measure the speed of light. Their actual purpose was to measure the movement of the ether by measuring the speed of light as Earth moved relative to the Sun. Their result showed that the speed of light was the same regardless of Earth’s position or motion. This created more questions about ether and the nature of light.
It was up to Albert Einstein to answer those questions. In simple terms, he explained that light is a substance that moves independently of the observer. The speed of light is a universal constant. Today we know that light has both wave and particle properties and always travels at a constant speed. High school students can duplicate the measuring techniques and see the dual nature of light in the laboratory. Welcome to the wonderful world of relativity.
Ether and the nature of light were no longer so mysterious. Ether did not exist, and it was not necessary. The speed of light is part of virtually every physics equation. It allows us to understand the atomic bomb, measure distances in space, and understand time and the age of the creation. It provides the foundation of quantum theory and even shows up in equations describing thermodynamics and chemistry interactions. Light is two-dimensional, having no thickness in the direction it moves. When light is stopped by a barrier, its energy turns into heat, so the object stopping the light does not gain mass.
Discovering the nature of light is a story of how science works. We can propose a theory and test it with experiments. In that way, we can come to understand things we observe in nature. What science once considered to be factual (like ether) may turn out to be incorrect. The speed of light is a constant in a world that is in continuous change. God’s creation is more strange and wonderful than any of us realize or can imagine.
— John N. Clayton © 2021