Light affects everything. Without it, there would be nothing. Since the days of the ancient Greeks, many have wondered where this life-giving resource comes from and how it is created. Up until the 1900s, there were many theories regarding light, but no certain ideas. It was only during the twentieth century that light became more understood.
One of the earliest theories dates back to the fifth century B.C. Greek philosopher Empedocles proposed that light was something that the eye emanated. When objects were within the field of the eye's light flow, they interacted with the light and were transmitted to the mind of the viewer, causing sight. Plato, another Greek philosopher, had several ideas about light. One agreed with his fellow philosopher, Empedocles. Another was that light sources gave off particles. One idea regarded a change occurring between the source of light and the object struck by its rays.
It wasn't until the mid-1600s that the Greeks' theories of light were questioned. It was Robert Hooke, an English physicist, who came up with a different theory about the composition of light. He suggested that light was made up of waves. Later Christian Huygens took up the theory and expanded it. He said that light waves leaving a light source were the result of tiny wavelets, each radiating out from a point on the wave. This theory of the progression of waves is known as Huygens' Principle.
Sir Isaac Newton didn't agree with Huygens' Principal. He thought that if light was a wave, then it should be able to bend around corners. He concluded that light couldn't be a wave, since he had never observed it doing that. Instead, Newton proposed that light was made of particles, sometimes called corpuscular, which radiated out from sources of light. Each color, supposedly, corresponded with a certain type of particle, with white light composed of all of the different kinds of particles. Because Newton was so well known for his scientific work, it was generally believed that his theory was correct and that Huygens' Principle was irrelevant.
Many people had trouble believing that Huygens' Principle was correct because they could not see the reasoning behind it. Like Sir Isaac Newton, they pointed out that light couldn't bend around corners. The more common waves all had mediums. Waves in the ocean were carried by water. Waves in the air were carried by the molecules in it. Using these ideas, physicists created the idea of "ether." They defined ether as the matter that filled all of space and carried the light from the sun and the stars. However, they could not prove that ether actually existed. Another physicist, James Clerk, came up with another theory in the mid-nineteenth century. His idea was that light waves consisted of electric and magnetic forces that change very rapidly.
Albert Einstein came up with the quantum theory of light in the early twentieth century. He proposed that light was made of up of small tightly knit packs of energy, called photons or quanta (singular, quantum). A quantum's frequency is determined by the amount of energy it contains. Einstein's studies paralleled those of German theoretical physicist Max Planck. Twenty years earlier, Planck had discovered quanta, but had been very confused by it, since the idea of quanta went against all the theories of light as a wave.
Today, a combination of the wave theory and the quantum theory are accepted as correct. It still has yet to be determined which is correct, though there is evidence that either could be.