Synopsis
Book by Hazen Robert M Trefil James
Extrait
CHAPTER ONE
Knowing
YOUR LIFE IS FILLED with routine—you set your alarm clock at night, take a shower in the morning, brush your teeth after breakfast, pay your bills on time, and fasten your seat belt. With each of these actions and a hundred others every day you acknowledge the power of predictability. If you don’t set the alarm you’ll probably be late for work or school. If you don’t take a shower you’ll probably smell. If you don’t fasten your seat belt and then get into a freeway accident you may die.
We all seek order to deal with life’s uncertainties. We look for patterns to help us cope. Scientists do the same thing. They constantly examine nature, guided by one overarching principle:
The universe is regular and predictable.
The universe is not random. The sun comes up every morning, the stars sweep across the sky at night. The universe moves in regular, predictable ways. Human beings can grasp the regularities of the universe and can even uncover the basic, simple laws that produce them. We call this activity “science.”
WAYS OF KNOWING
Science is one way of knowing about the world. The unspoken assumption behind the scientific endeavor is that general laws, discoverable by the human mind, exist and govern everything in the physical world. In its most advanced form, science is written in the language of mathematics, and therefore is not always easily accessible to the general public. But, like any other language, the language of science can be translated into simple English. When this is done, the beauty and simplicity of the great scientific laws can be shared by everyone.
Science is not the only way, nor always the best way, to gain an understanding of the world in which we find ourselves. Religion and philosophy help us come to grips with the meaning of life without the need for experimentation or mathematics, while art, music, and literature provide us with a kind of aesthetic, nonquantitative knowledge. You don’t need calculus to tell you whether a symphony or a poem has meaning for you. Science complements these other ways of knowing, providing us with insights about a different aspect of the universe.
The Regularity of Nature
Our ancestors perceived the universe in ways that sometimes seem very strange to us. For all but the past few hundred years of human existence the universe was viewed by most people as a place without deep order or rules, governed by the whims of the gods or even by chance. By noting the daily movements of objects in the sky, however, our ancestors got their first hints that some kind of order and regularity might exist in nature. The position of the sun, the phases of the moon, and the dominant constellations of stars cycled over the years, decades, and centuries with unerring regularity. Whatever governs its motion, the fact is that the sun does come up every morning.
Most historians of science point to the need for a reliable calendar to regulate agricultural activity as the impetus for learning about what we now call astronomy. Early astronomy provided information about when to plant crops and gave humans their first formal method of recording the passage of time. Stonehenge, the 4,000-year-old ring of stones in southern Britain, is perhaps the best-known monument to the discovery of regularity and predictability in the world we inhabit. The great markers of Stonehenge point to the spots on the horizon where the sun rises at the solstices and equinoxes—the dates we still use to mark the beginnings of the seasons. The stones may even have been used to predict eclipses. The existence of Stonehenge, built by people without writing, bears silent testimony both to the regularity of nature and to the ability of the human mind to see behind immediate appearances and discover deeper meanings in events.
The Invention of Science
Astronomy was the first science. Throughout history some of the best minds produced by the human race have pondered the meaning of the celestial display. Most of the resulting theories shared a common property—they all assumed that in some way Earth was special, and that what happened in the heavens had no relevance to phenomena on Earth. In one important version of the universe, for example, the stars and the planets turned eternally on crystal spheres, and their motion had nothing to do with mundane events like the fall of an apple in an orchard. People who believed that the universe was built this way produced a large body of accurate observations of the positions of heavenly bodies, but astronomers were divorced from craftsmen and artisans who were doing different things for the development of science.
While the astronomers were gazing into the heavens, other men and women, equally ingenious, were trying to understand the way things operated on Earth. Their motivation was practical: they studied the properties of heated metals because they wanted to develop stronger alloys, they studied the flow of fluids because they wanted to build canals, they experimented with different combinations of ingredients to make better-tasting food and more effective medicines, and so on. They never seemed to think that the prosaic tasks in which they were engaged had anything to do with the stars and planets.
The branch of science that finally broke out and forged a link between the cerebral astronomers and the practical artisans was “mechanics.” This is an old term for the study of motion. Every system, natural or man-made, contains matter in motion. Planets orbit, blood circulates, chemicals explode, people walk. Mechanics is the superbly pragmatic science of pocket billiards and car crashes, cannonballs and guided missiles. Today, the principles of mechanics point to such useful things as stronger buildings, faster cars, more exciting sports, and, as always, more sophisticated weapons. But more important from the point of view of the birth of modern science, the study of mechanics blazed the trail that subsequent scientists have followed. While studying mechanics, scientists developed and refined the scientific method, a technique that has given us so many new insights into the universe we inhabit.
THE CLOCKWORK UNIVERSE
Modern science can be said to have started with the work of Isaac Newton (1642–1727) in England. According to Newton, the universe is something like a clock. In a clock, the external appearance—the slow sweeping of the hands—is a result of the motion of internal gears. In the same way, all of the natural phenomena we see in the world around us are the result of a few natural laws working beneath the surface of things. Newton demonstrated that:
One set of laws describes all motion.
For Newton, the key fact about motion was that it occurs in response to the action of one or more forces. The “gears” that connect forces and motion are Newton’s three laws of motion, and they apply to everything that moves. Gases streaming out of an exploding star, a football thrown downfield, and blood cells in your arteries all move in compliance with these very simple, but very general, laws.
MOTION
Uniform Motion and Acceleration
If you’re going to study something like motion, the first thing you have to do is decide what sorts of motion are found in nature. Scientists recognize only two kinds: uniform and accelerated. Everything in the universe is either in uniform motion or accelerating.
Any object that stands still or moves in a straight line at constant speed is in uniform motion. A book sitting on your desk, a car driving along an interstate with the cruise control set at 65 mph, and a spaceship traveling at 1,000 miles per second in deep space are all in uniform motion.
Acceleration is any change in motion and occurs when something speeds up, slows down, or changes direction. This definition may seem a little strange, because when you drive a car “acceleration” means speeding up—not slowing down or turning a corner. Physicists use a more general meaning for acceleration—but whatever the definition, it’s something you feel in your gut. Flooring the gas pedal on your car, braking for a light, or rounding a bend all tend to move you around in your seat. And there’s nothing subtle about acceleration—people don’t ride roller coasters to experience uniform motion.
Newton’s Laws and the Idea of Force
Isaac Newton, building on results from centuries of experiments on moving objects, wrote down a compact set of laws that describes the nature of all motion. That these laws apply to such an immense assortment of situations illustrates the power behind thinking of nature as regular and predictable. Newton’s three laws of motion provide a cornerstone of physics and a model for what a science is supposed to be.
Newton’s laws tell us how to predict the motion of a system just by knowing the forces that act on it. The three laws are stated separately, but they work together like separate gears that run a clock. Like all the fundamental laws that govern science, Newton’s laws of motion may seem simple—almost simplistic. The deepest insights of the human mind often have this characteristic. Yet, as generations of physics students can testify, there is a subtlety and richness behind this apparent simplicity—how else could the laws describe everything from the orbits of Neptune’s moons to the movement of exploding gases in your car’s engine?
The First Law
Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.
Newton has hidden two important concepts in this intuitively obvious statement. The first is inertia—the tendency of objects to continue doing what they̵...
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