Festival of Lights 2014

Light exerts physical pressure on objects in its path, a phenomenon which can be deduced by Maxwell’s equations, but can be more easily explained by the particle nature of light: photons strike and transfer their momentum. Light pressure is equal to the power of the light beam divided by c, the speed of light.

In the fifth century BC, Empedocles postulated that everything was composed of four elements; fire, air, earth and water. He believed that Aphrodite made the human eye out of the four elements and that she lit the fire in the eye which shone out from the eye making sight possible.

In ancient India, the Hindu schools of Samkhya and Vaisheshika, from around the early centuries CE developed theories on light. According to the Samkhya school, light is one of the five fundamental “subtle” elements (tanmatra) out of which emerge the gross elements.

If this were true, then one could see during the night just as well as during the day, so Empedocles postulated an interaction between rays from the eyes and rays from a source such as the sun.

The wave theory predicted that light waves could interfere with each other like sound waves (as noted around 1800 by Thomas Young). Young showed by means of a diffraction experiment that light behaved as waves.

Newton’s corpuscular theory implied that light would travel faster in a denser medium, while the wave theory of Huygens and others implied the opposite. At that time, the speed of light could not be measured accurately enough to decide which theory was correct.

Source: Wikipedia

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