Elisabeth Ramsey, age 13, of Walnut, N. C., for her question:
What exactly is light?
The nature of light has puzzled men for centuries and even now we are able only to suggest theories concerning it. We know that it is radiant energy pouring forth from a lamp, a star or some other luminous body. It is electromagnetic energy, which means that it is used by the motion of atomic particles called electrons.
Isaac Newton thought that light was a stream of tiny bodies which he called corpuscles. His theory went out of date when James Clark Maxwell put forth his theory of light as an electromagnetic wave motion. Each of these theories explained some, but not ail, of the ways in which light behaves.
Modern physicists explain light by the Quantum Theory. It is built on the knowledge that an atom is a nucleus in the center of one or more orbiting electrons. The electrons orbit in shells, one shell outside another, and each electron has a definite amount of energy, so much and no more. An electron in an inner shell has proportionately less energy than an electron in an outer shell.
Under certain conditions, electrons gain extra energy. When this happens, they hop from an inner shell to an outer shell ‑ from a small orbit to a larger one. It may get enough energy to hop into an orbit several sizes larger. Then it drops back, and this is when it gives off energy in the form of light.
Remember, the electrons have a very definite amount of energy, depending upon the shells in which they orbit. As they drop back into their smaller orbits they also give forth light energy in very definite amounts. The amount of energy given forth when an electron drops one step from a shell to the next inner shell is called a quantum and this modern theory of the nature of light is called the Quantum Theory.
Max Planck, Albert Einstein and Nils Bohr were the scientists who showed how this theory accounts for the nature of light?
We see, then, that light does come forth in a series of tiny bursts, though not in a stream of small. bodies as the great Newton suggested. We know too, that Maxwell's wave theory was correct, though it told only part of the story. Light travels in waves, depending upon the energy levels from which the electrons dump and back to which they fall.
All light, whether it be from a lamp, from the sun or, from, a distant star, behaves in the same manner. It is started by excited electrons and it fans out in all directions, It is the fastest traveler in the universe, whipping along at about 186,000 a second ‑ or roughly six million, million miles in a year.