Sports fans of a certain age will recall marveling at the versatility of Bo Jackson. Not only was he a star baseball player for the Kansas City Royals, he was also a celebrated football player for the Los Angeles Raiders. While many youngsters dream of greatness in one sport, Mr. Jackson managed to be great at two.
Sir Isaac Newton was the Bo Jackson of his time. Not only did he invent the laws of motion, he laid the foundation for geometric optics. If you have ever drawn a bunch of straight lines to predict the image from a lens or mirror, you have applied the concepts laid out in his second blockbuster, the Opticks.
Newton believed that light was composed of miniscule particles that traveled in straight lines called rays. These little corpuscles, as he named them, bounced off of mirrors just like billiard balls bounce from the bumpers of a pool table. When encountering a lens they bend ever so slightly upon entry and exit, but travel in straight lines each step along the way.
During the course of Newton’s lifetime, an alternative theory of light began to emerge. Rather than little particles traveling in straight lines through space, this new theory proposed that light was composed of tiny vibrations in some underlying medium, like the water waves that travel from the wake of a passing boat to the shore.
QUANTUM LEAP
Newton is also famous for having stood in a dark room studying the rainbow created when a narrow beam of sunlight passed through a triangular prism. He rightly concluded that white light is made up of many different colors, which the prism decomposes. However, he not-so-rightly reasoned that red light bends less than violet light because it has a greater internal “strength.” Here Newton made an uncharacteristic error that, ironically, foreshadowed the demise of his particle theory in favor of the competing wave theory.
Newton rejected this wave concept on the grounds that it seemed inconsistent with his successful geometric approach to lenses and mirrors. And, given Newton’s high regard among physicists of his day, his rejection of the wave theory of light prevented it from gaining any real traction for many decades. But even Newton couldn’t trump experimental evidence, and eventually—a mere two centuries later—his classical particle theory of light was effectively dead.
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