How does Light Travel?

One of the great mysteries of the world in which we live is light. We still do not know exactly what it is. It can only be describe in terms of what it does. We know light is a from of energy. Like some other forms of energy (heat, radio waves and X-rays) the speed, frequency and length of it waves can be measured.

Its behavior in other ways make it similar  to these other forms of energy, too. We know the speed of light. It travels at about 186,000 miles per second. this means that in a year, a beam of light travels 5,880,000,000,000 miles. That is the distance which astronomers call a "light year", and it is the unit used to measure distances in outer space.

In trying to understand what light is and  how it travels, many theories have been developed. In the seventeenth century, Sir Isaac Newton said that light must be made up of "corpuscles". Somewhat like tiny bullets shot from the light source. But this "corpuscular" theory of light could not explain many of the ways in which light behaves.


At about the same time, a man named Christian Huygens developed a "wave theory" of light. His idea was that a luminous of lighted particle started pulses, or waves much as a pebble dropped into a pool makes waves. Whether light is waves or corpuscles was argued for nearly 150 years.

Gradually, as certain effects of light corpuscles died out. Scientists now believe that light behaves both as particles and as waves. Experiments can show either idea to be true. So wee simply cannot give a complete answer to "whats is light?".

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