Hans Salzwedel, age 12, of Winston Salem, North Carolina, for his question:
What is light made of?
This problem puzzled great brains for centuries. Some concluded that light is made from tiny particles called corpuscles. Others were sure that light is an assortment of vibrating waves. Most agreed that it is some form of energy. But for some 200 years, the experts thought that it came in either waves or corpuscles. Finally the dispute was settled in the simplest way possible. Both sides were proved right.
We now know that light is a form of energy, a special blend of electricity and magnetism called electromagnetic energy. As such it is a phenomenon, which means that it just is. Naturally we want to know more than this. And, after centuries of probing, scientists can explain a great deal about how it behaves, which is the nature of light.
For earthlings, the most familiar source of light is the blazing sun. Our neighborhood star is a fiery nuclear furnace, pouring forth radiant energies in all directions. These electromagnetic energies include radio, visible light plus invisible ranges of infrared and ultra¬violet light. All these energies fan out from a source which is the sun, and travel in straight lines at an average speed of 186,000 miles per second.
They travel in pulsing waves of longer and shorter lengths. Radio, light and other forms of electromagnetic energy travel in waves of dif¬ferent lengths, each vibrating at its own frequency of so many pulses per second. Light has a series of different frequencies ranging from the short blue rays of the spectrum to the long red rays.
The nature of light is the same, whether its source is the sun, a lamp or a camp fire. It fans out in straight lines from its source. Its assorted wavelengths vibrate at different frequencies as they go. Their angles are separated when a beam of white light passes through a glass prism. Then the separate wavelengths display the banded colors of the rainbow.
In the 1600s, the great Isaac Newton observed how the colors nor¬mally blended. in ordinary light are. separated by a glass prism. He concluded that light must be made from tiny particles, streaming forth in straight lines. Newton’s amazing theories were never quite wrong. But in this case, he was only half right. Though scientists considered his theory of light, until modern times most of them disagreed with his corpuscular, or particle theory.
Around 1900, Max Planck of Germany demonstrated that light travels in infinitesimal packages of energy called quanta. The energy in each quantum is related to its wavelength—to its length and to the number of its vibrations per second. We might say that light is made of wave¬lengths of electromagnetic energy traveling in quantum particles.
It is hard to picture the fact that light is both waves and par¬ticles. However, we can compare it roughly with the ocean. Its water is made of molecule particles and the surface of the sea heaves up and down in tossing waves. Naturally, the antics of the ocean are related only very vaguely to the antics of light.