The celebration of the triumph of light over darkness has been a part of Indian culture for a long time now. Today, as we celebrate light, let us do so by enriching our understanding of where the idea and concept of light first emerged, to where it is today. So let us take a look at a brief history of light through scientists who have made major contributions to our understanding of what light really is.
Although there have been many contributors, over many years, who have contributed to our understanding of light, for the sake of simplicity we can divide the history of light into four eras:
The first era belongs to the Greeks, with their center in Athens and later Alexandria. It extends from 800 BC till around 200 AD. The second era belongs to the Islamic civilization, with its centers in Baghdad and Cordoba. This era can be said to last till middle to late 13th century. The third era started in Europe around the 14th century and the final era began at the dawn of the 20th century.
Let us now begin our story.
“The essence of light is white light. Colors are made up of a mixture of lightness and darkness.”
It is believed that the foundation for modern optics field was laid in ancient Greece. The earliest studies concerning light had to do with understanding vision. For example, Democritus believed that the visual image did not arise directly in the eye, but the air between the object and the eye. On the other hand, Epicurus proposed that atoms ﬂow continuously from the body of the object into the eye. Another alternate theory of vision by Plato and his followers stressed that light consisted of rays emitted by the eyes. When the rays strike the object the viewer is able to perceive things such as the color, shape, and size of the object. This idea of extra-mission theory of light would be inﬂuential for almost 1000 years, until Alhazen would prove it to be wrong.
“Why does the moon appear larger near the horizon than it does when higher up in the sky ?”
–Ibn al-Haytham (Alhazen)
“Light is comprised of colored particles.”
–Sir Isaac Newton
Isaac Newton is arguably one of the most prominent and popular figures in the field of Science. Around the end of the 17th century he performed various experiments on light, the most famous of which is perhaps his experiment with sunlight and prism where he showed that white light is composed of many colors, and that each individual color cannot be used to re-create white light, nor can they be broken down further. He greatly contributed to the development of the science of optics by collecting technology on lenses, prisms, mirrors, telescopes, microscopes and optical polishing.
Alongside these ideas, many scientists, including Newton’s rival Robert Hooke, had proposed the idea that light is a wave but it wasn’t until 1800 that the experiments of Thomas Young showed that light can exhibit interference- crests and troughs of the waves can add or subtract to give bright and dark regions. He proposed that light of different colors has different wavelengths, and that we see these colors with sets of three detectors in our eyes for the three primary colors.
“Light is a photon”
German-born theoretical physicist Einstein is often called the greatest physicist of the 20th century, because of his groundbreaking research that had a great impact on physics. In March 1905 , Einstein created the quantum theory of light- the idea that light exists as tiny packets, or particles, which he called photons. Although Einstein’s quantum theory of light treated light as particles, his theory of special relativity saw light as a continuous field of waves. Einstein, at age 26, had proposed light as both wave and particle!
Einstein’s photon is a substance that is seen as the key to the origins of space and life, and there are great deal more to photons and the duality of light than what we understand today, so the journey of light and optics research is far from over.