Joseph Zenisek, age 13, of Cleveland, Ohio, for his question:

Does light travel sometimes in waves and then in particles?

Dust can blow up or down or swirl around in a playful whirlwind. These dusty antics involve both motion and particles of matter. But the energy of motion exits from the picture when the dust settles. Light is energy that never pauses but it also moves along in infinitesimal particles.

The nature of light baffled the best minds for many centuries. Young Isaac New¬ton began to crack the impossible problem in the 1600s but the jigsaw puzzle was not organized into a complete picture until the beginning of the 20th century. Physicists now explain the nature of light as a complex, interwoven phenomenon involving both waves and particles. Both waves and particles are involved every step of the way. Every strand of light is composed of an astronomical number of units traveling to¬gether in pulsing waves.

Physicists of the 17th and 18th centuries had a choice. Those on one side argued that light travels along in infinitesimal particles called corpuscules. Those on the opposing side argued that light travels in pulsing waves. Both theories could explain the bouncy reflection of light and its bending refraction. But the wave theory could not explain how light fans out in straight lines. The corpuscular theory was popular until 1801 when a new experiment revealed an overlapping of light rays called interference. Later, researchers found that straight lines of light can, under certain conditions, bend around corners.

The nature of light was still a puzzlement in 1860, when still another concept was added to the confusion. This theory saw light as a form of electromagnetic energy, traveling at the same speed though on wave lengths different from radio and other forms of electromagnetic energy, The corpuscular theory of light particles was more or less dropped for the next 40 years.

Then a whole new concept was added. It was the quantum theory and it showed that light is indeed made of particles. These infinitesimal, energetic packages travel on assorted wave lengths at a speed of 186,000 miles per second. The particles are quanta units of light. The waves are rhythmical pulses of energy. Light cannot travel sometimes in waves and sometimes in particles. Both quanta units and electro¬magnetic energy waves are involved every step of the way. This modern theory explains the bewildering details in the complex behavior of light. It also shows that the scientists of the past had no cause for dispute. The wave theorists and the corpus¬cular theories each had half of the total jigsaw puzzle.

The nature of light is an immense astonishingly complex problem. We still have more to learn about it, though the major pattern is in place. The solution of such a cosmic mystery is bound to reward mankind with suitable advantages. Our knowledge of light and how it behaves has led the way to new microscopes, TVs and improved cameras and dozens of other astounding gadgets. It was needed to create the laser beam and countless other miracles of the future.