Bruce Johnson, age 11, of Pleasure Ridge Park, Kentucky, for his question:
What are photons?
For centuries the best brains of science wrestled with the nature of light. Some stressed its wave like behavior. Others suspected that it acted like tiny corpuscle units. Then the photon was tracked to its lair. It showed that the explanation of how light be¬haves includes both the wave and the corpuscle theories.
A phenomenon is a:fact or event that can be sensed as real and the real world teems with phenomena that can be seen or smelled, heard or touched, felt or sensed. Light, we are told, is a phenomenon. But this grandish statement says only that it is an observable fact. Naturally, this is not enough to satisfy our curiosity. After ages of probing the mysterious phenomenon, we now can explain most of its highly complex nature and behavior. The final picture fell into place in the modern age, when the photon was pinpointed.
The invisible, infinitesimal photon is a basic bundle of electromagnetic energy, the radiant energy of radio and X rays, ultraviolet and infrared and also the rainbow spectrum of ordinary visible light. It is the basic unit in which this energy travels. The photon particles of sunlight are emitted by agitated atoms vibrating in the sun. They fan out in waves, zooming through space at 186,000 miles per second. Swarms of them strike the countless vari¬ety of substances on the surface of the earth.
These earthy substances are made of matter, of atoms and particles with shells of orbiting electrons. A photon has no matter. But it can transfer its invisible quota of energy to a moving charged particle of matter. An electron is a negatively charged particle of matter in zooming orbital motion. It is just the right size to absorb the energy of one photon. The electron uses this peppy photon energy to hop into an outer orbit of more energetic electrons. After a moment it emits its photon and drops back to its former level. This absorbing and emitting of photon energy can be calculated and used.
The electromagnetic energies involved vibrate in cycles of so many frequencies per second. The rainbow spectrum of visible light ranges all the way from the short wave blue rays of high frequency down to the longer wave lengths of lower frequency red rays.
The photon energy emitted by a burning element reveals a pattern of colored bands on the spectrum. Each element reveals its own color frequency and its spectrum pattern is its very own signature. Photon units of light energy reveal the gases in a distant stare They also run our radios, our photoelectric cells and perform countless other mechanical chores. In radio and TV, swarming photons are born in the broadcasting antenna. They zoom out and some strike our home antennas. There they are absorbed by electrons and relayed down for processing in our receiving sets.
We think of a particle as a tiny unit of matter. This is true of the electron and other atomic particles. These busy particles are units of material and therefore they have mass or weight. The photon, however, is not a particle of matter. It has no mass or weight. It is a unit of raw electromagnetic energy and no more. However, physicists classify the photon as an elementary particle along with electrons, mesons, and other orderly units of matter.