Tom Kirk, age 12, of Girard, Ohio, for his question:
How can light be waves and particles?
This conundrum pops up every year, when students in school are introduced to the phenomenon of light. It seems that ordinary words fall flat on their faces when we try to use them to explain the wondrous mysteries of something we cannot see. Certainly the words "wave" and "particle" fail to give a true picture of the nature of light. However, people continue to use these terms because they grew up gradually, as the mysteries of light were revealed.
Light is a complex form of energy and only energy. ,It knows nothing of ocean waves or wavy hair dos. In every other realm of science, a particle is a small unit of matter. Since light is energy, it must be totally unrelated to particles of this sort. When studying light, perhaps we should stand waves and particles in a corner, facing the wall.
In the light department, the word wave would be useful, if somebody hadn't sliced it in half. Actually it is an abbreviation of wavelength, which rightfully belongs in the realm of energy. Wavelengths are the pulsing vibrations of speeding energy. They are unrelated to wavy seas and wavy hair, and to any other form of matter. Perhaps the term wavelength arose because varying intensities of pulsing vibrations reminded somebody of the up and down motions of the ocean waves. The length of a wavelength can be measured from one maximum intensity to the next somewhat like measuring ocean waves from crest to crest. The vibrations of light energy are measured in cycles or frequencies, which are so many pulses per second.
Isaac Newton was the first person to suspect that light may be composed of miniature bundles. He called them corpuscles and did not refer to them as particles. That term arose during the century in which scientists disputed whether light is composed of wavelengths or miniscule bundles of some sort. The wavelength theory was settled in the 1860s, when James Clark Maxwell suggested that light is a form of electromagnetic energy, with a rightful band on his electromagnetic spectrum.
The so called particle theory was settled in 1900, when Max Planck demonstrated that light travels in infinistesimal packages of energy. He called them quanta and the energy of a quantum is related to wavelength. This settled the 100 year dispute as to whether light is wavelengths or corpuscles. It is both.
Light, as we know, travels in straight lines at 186,000 miles per second. Its quanta vibrate in transverse wavelengths at right angles to these straight lines. The quanta are units of energy. The wavelengths are their vibrations.
The band of visible light on Maxwell's electromagnetic spectrum includes a vast variety of wavelengths. Actually it is a blend of longer and shorter wavelengths, traveling together at the same speed. The infinitesimal quanta vibrate back and forth across the lines in which the light is traveling.