Facts of the Matter
Richard Brill

Sunday, December 19, 2004

Apple legend reveals
just part of genius

"If I have seen further it is by standing upon the shoulders of giants."

-- Sir Isaac Newton
1642 - 1727

Sir Isaac Newton was born on Christmas eve in 1642 at his family estate at Woolsthorpe, 90 miles north of London. His birth date is now listed as Jan. 4, 1643, because of an updated calendar, but that's another story. It was Christmas eve at the time.

Just about everyone has heard the legend of Newton and the apple and how it induced the theory of gravity when it fell on his head. Like many legends, this one is only partially true. The apple did not fall on his head, and the concept of gravitation was not merely a flash of inspiration, but was developed over time.

A falling apple did play a role. Newton told a friend, "... the notion of gravitation came to my mind. It was occasion'd by the fall of an apple, as I sat in a contemplative mood."

Newton's methods and the laws of nature that he formulated form the basis for all of modern science. The analytical process that he used to solve problems by breaking them down into a sequence of smaller problems is used today in computer programming. His methods of mathematical analysis are used in every aspect of physical science and engineering, including designing bridges, launching satellites and interplanetary spacecraft, even designing complex electronic circuits. His writings also define concepts of mass, space and time, the fundamental variables used in defining the physical universe.

Newton's influence extends far beyond the physical sciences. Thomas Jefferson was a fan of Newton's physics and saw it as a model for a democratic system of laws which, like the solar system, continues to run in a self-regulating system once set in motion. Adam Smith, the father of economics, saw the equilibrium between supply and demand as a parallel to the dynamic between force and inertia.

Newton's elegant mathematical description of gravity described the motion of the moon and planets in precise terms. It also described under one system the motion of the planets with freefall. Freefall motion had been quantified by Galileo (1564-1642), but even his genius failed to make the connection between the earthly and heavenly realms in one "Universal" set of laws.

Although the idea that Earth was not the physical center of the universe was generally accepted by scientists in northern Europe by Newton's time, it was contrary to the zeitgeist of his time, which still incorporated the multiverse that Aristotle had defined 2,000 years earlier. Aristotle's system had been adopted by the Church as the "official" cosmology, and was the source of the disagreement between Galileo and the Church.

Aristotle's multiverse, divided into three concentric regions, was based on the Pythagorean model wherein the earthly realm was called Uranos and extended to the orbit of the moon. From there to the stars was Cosmos, home of the sun, moon and planets, bounded by the stars. Beyond the stars was Olympos, the realm of the gods.

Aristotle's model required different rules for the behavior of objects in the three realms, but Newton challenged the model by considering the effects of a boundary between the realms.

Newton, being the consummate critical thinker, asked questions that would lead to further questions, one step at a time until the pieces came together. He later wrote about this: "I was like a boy playing on the seashore, and diverting myself now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me."

This is where the falling apple comes into the plot. Newton imagined the apple at increasingly higher elevations and wondered if it would weigh less as it was taken farther from Earth's center.

If the apple did "lose" weight with height, then it did not seem reasonable that there would be a boundary that could change the fundamental character of the apple and the relationship between weight and distance from Earth.

Earlier philosophers did not consider that it was possible to get anything as high as that boundary, so there was no question about what might happen if one crossed it.

Newton crossed the boundary in his mind by questioning what might happen if something could be moved to the boundary from Earth. Could it be that moving the object back and forth across the boundary would cause it to undergo a fundamental change in its behavior and composition? Newton reasoned that it is possible, but not likely.

Then, he wondered if the apple could be moved continuously farther away from Earth and if it did lose weight, if the force that caused its weight extended all the way to the moon. He reasoned that it is "more reasonable to think that it might than to assume that it does not."

Newton performed a few simple calculations that showed that if the apple were as far away from Earth as the moon, the gravitational force exerted on it would just be equal to force necessary to keep it in orbit at that distance.

By this series of logic, mathematical formulation and calculation, he verified the relationship between distance and gravitational force that turned out to be the key to the puzzle of planetary motion and freefall.

Newton's law of gravitation is now the basis for calculating the trajectories for all projectiles, everything from artillery to interplanetary space flight.

It is difficult to say which of Newton's contributions are more important, the mathematics, the physics, the unification of the universe, or the mechanical paradigm that launched the industrial revolution and ultimately spurred the rapid pace of technology growth that we see today.

Regardless of which is most important, Sir Isaac Newton deserves the accolades that were awarded him in his lifetime and since. He stands as one of the most influential figures in history if not the greatest genius of all time.

Richard Brill picks up where your high school science teacher left off. He is a professor of science at Honolulu Community College, where he teaches earth and physical science and investigates life and the universe. He can be contacted by e-mail at rickb@hcc.hawaii.edu

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