newton versus huygens -- 12/9/20

Today's selection -- from Cosmos: Possible Worlds by Ann Druyan. Young Isaac Newton and young Christiaan Huygens were contemporaries obsessed with discovering the properties of light:

"No one is more light-obsessed than astronomers. And as soon as they began studying light, it baffled even the very best of them.

"Take Isaac Newton, for example. As a young man in the win­ter of 1665-66, he worked tirelessly in his bedroom at Wools­thorpe, his ancestral home in Lincolnshire, England, trying to figure out the physics of light and color. So desperate to under­stand their nature, he was willing to stick needles in his eyes -- ­literally. By the time Newton was in his 20s, he'd already laid the foundations of a new branch of mathematics called calculus, and he had conducted a series of experiments that led him to con­clude that color was an aspect of light. Newton wanted to find out which of the things we see are properties of light, and which are caused by our nerves. Was color hiding inside the light, or was it in our eyes?

"With a burning desire to know, Newton summoned up his cour­age, picked up a needle, called a bodkin, and with grim determina­tion, proceeded to press the needle into the lower part of his own left eye. Newton stoically wrote up 'an experiment to put pressure on the eye,' replete with illustration in his Opticks notebook. He carefully noted that if he conducted the experiment in a room filled with light, even with his eyes shut, some light would pass through his eyelids and he would see a great broad 'blewish circle.' It may not sound like much of a result considering the pain he must have experienced, but it was with simple, homemade experiments such as this one that Newton became the first person to explain rainbows, and how white light hides a whole palette of colors inside itself.

Huygens' 1659 sketches for a projection of Death taking off his head

"Most people thought of the phenomena that Newton studied as being 'just the way things are' -- the way an apple falls, the way a ray of light shines through a window. Newton's greatness stemmed from his questioning of the 'why' and 'how' of ordinary things, much as normal four-year-olds do.

"Newton asked, for instance: What was light made of? If you could break light apart into its tiniest component parts, what would you see? Newton noticed that light moved in straight lines. How else to explain the edges of shadows? Or the straightness of those inspirational rays of sunlight that poke through clouds? Or the darkness that results from a total solar eclipse? From these obser­vations, Newton reasoned that light must consist of a stream of particles -- or 'corpuscles,' as he called them -- that a ray of light was like a stream of bullets striking the retina of the eye.

"But there was one man, over in Holland, who vigorously dis­agreed with Newton's particle theory of light. And it was none other than Christiaan Huygens, the Dutch astronomer who was the first to understand the nature of Saturn's rings and to discover its largest moon, Titan. He shared Isaac Newton's insatiable curi­osity about ordinary things, and, despite his lifelong battle with severe depression, when it came to changing the world, he was no slouch himself. Huygens invented the pendulum clock. He worked out the mathematical formulas necessary to create a pendulum with an arc that would accurately and consistently measure out uniform increments of time, establishing a standard for precise timekeeping that remained unbeatable for three centuries.

"Huygens sketched a prototype for a new machine that he thought might have some promise. He called it a 'magic lantern.' A few hundred years would pass before it evolved into a working motion picture projector, but back in the 17th century, Huygens already had an idea for a movie, possibly influenced by his gloomy disposition. Huygens made a series of pen and ink sketches, car­toons for an animation of Death performing a little dance. Death takes a playful little bow before removing his own skull and tucking it under his arm as if it were a bowler hat. He struts around, headless but cocky, before replacing his skull to its rightful position, bows once again, and just stands there, grinning at us, eerily.

"Huygens, like Newton, also invented his own new branch of mathematics, a predictive theory of the outcomes of games of chance. We now call it probability theory. And, like Newton, Huy­gens had his own theory of light. But it was very different from Newton's. Huygens didn't think light consisted of particles, like bullets firing along a single path. Huygens saw light as a wave spreading out in all directions.

"It was already known in his time that sound must travel as a wave. A voice could be easily heard around a door when it was slightly ajar. Sound must travel around the door as water would. Strike a tuning fork against something metal and hold it up to watch it vibrate. As you listen to its hum you can almost see the sound waves emanating in all directions. Huygens thought that light moved the same way sound did, spreading out as waves.

"So, which genius was right? The answer to the question of whether light was a particle or a wave would prove to be complicated."



Ann Druyan


Cosmos: Possible Worlds


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Copyright 2020 Ann Druyan


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