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On Albert Einstein's seventy-sixth and final birthday, a friend gave him a simple toy made from a broomstick, a brass ball attached to a length of string, and a weak spring. Einstein was delighted: the toy worked on a principle he had conceived fifty years earlier when he was working on his revolutionary theory of gravity—a principle whose implications are still confounding physicists today.
Starting with this winning anecdote, Anthony Zee begins his animated discussion of phenomena ranging from the emergence of galaxies to the curvature of space-time, evidence for the existence of gravity waves, and the shape of the universe in the first nanoseconds of creation and today. Making complex ideas accessible without oversimplifying, Zee leads the reader through the implications of Einstein's theory and its influence on modern physics. His playful and lucid style conveys the excitement of some of the latest developments in physics, and his new Afterword brings things even further up-to-date.
Starting with this winning anecdote, Anthony Zee begins his animated discussion of phenomena ranging from the emergence of galaxies to the curvature of space-time, evidence for the existence of gravity waves, and the shape of the universe in the first nanoseconds of creation and today. Making complex ideas accessible without oversimplifying, Zee leads the reader through the implications of Einstein's theory and its influence on modern physics.
-NEWTON in his memoirs
Who will ever know if the story is true? It sounds as if it were fabricated by some scriptwriter. Actually, it was first told by Newton himself in his old age. In any case, it's a pretty good story, tinged with the Judeo-Christian imagery of the apple as the fruit of knowledge.
This great genius was the first person on his father's side able to write his name. His father's brother saw no need to educate his sons, and they died illiterate. His mother was barely able to write and not particularly enthusiastic about sending Isaac to school. Newton was educated only at the urging of his mother's brother; that maternal uncle was in fact the only educated person in the entire clan.
Newton's paternal ancestors had risen within a century from obscure peasanthood to land ownership, a rise suggesting that they were above average in intelligence. Newton's father, said to be "a wild, extravagant, and weak man," died six months after his marriage. Newton was born fatherless some months later, on Christmas morning 1642. He was premature and so tiny that no one expected him to live.
When the fatherless boy turned three, his mother remarried, to a sixty-three-year-old clergyman. Bombastic and rather obnoxious, the reverend refused to let Newton live with his mother. Psychoanalysts have not hesitated to seize upon this traumatic loss of mother as an explanation for Newton's later behavior. As befitting the religious upbringing of the time, Newton kept note of his sins, and one of them was threatening to burn his stepfather and mother and their house.
When Newton was ten, his stepfather died. He was reunited with his mother but apparently felt intense jealousy, as his stepfather had in the meantime produced three children with Newton's mother. The reunion was brief as he was soon sent off to school in town. He lodged with an apothecary and apparently grew quite attached to the apothecary's stepdaughter. It was to be the first and last romantic attachment to a woman in his life.
When Newton turned seventeen, his mother decided that it was time for him to come home and help on the farm. Told to herd sheep, Newton would simply wander off and read. Court records showed that on several occasions he was fined for allowing his sheep to stray into the neighbor's fields. Newton's own list of sins for this period included "Punching my sister," "Peevishness with my mother," "Falling out with the servants," and "Striking many." The servants hated him and described him as a surly and lazy good-for-nothing.
Meanwhile, Newton's maternal uncle and the schoolmaster lobbied with his mother to let Newton go back to school. She relented only when the schoolmaster offered to waive the fee and to take Newton in at his own home. Newton's mother appeared to be quite a miser, as she was actually rather wealthy from the combined estates of her two husbands. When Newton went to Cambridge, he had to enroll as a subsizar, a poverty student who earned his way by performing menial tasks for the wealthier students. He fetched beer and emptied chamber pots, among other duties. The experience was mortifying for someone who grew up being surly to servants.
Richard S. Westfall, a leading Newton biographer, describes Newton as "a tortured man, an extremely neurotic personality who teetered always, at least through middle age, on the verge of breakdown." Small wonder, after that kind of boyhood. It doesn't take much psychoanalysis to see Newton's numerous bitter and nasty disputes with his scientific contemporaries as an expression of his infantile rage at his stepfather.
Newton was particularly ruthless in crushing his major scientific rival, Robert Hooke, seven years his senior and considered England's greatest scientist until Newton appeared on the scene. It is interesting to note in this connection that the often quoted line "If I have seen farther it is by standing upon the shoulders of Giants" is usually misinterpreted as evidence of Newton's modesty. In fact, the line was a sarcastic dig at Hooke, who was rather short and crooked in his posture. Some present-day physicists have been known to use the variant "If I have seen farther it is by looking over the shoulders of midgets" to put down their colleagues.
On the whole, Newton's years at Cambridge were the happiest of his life up till the plague years. Compared to the centers of learning on the Continent, Cambridge was an intellectual backwater at the time. The university had a prescribed curriculum based in part on Aristotelian studies, but fortunately by the 1660s the strict Aristotelian curriculum was not taken seriously, even at Cambridge. Newton, fortunately, was by and large left alone. He had time to reflect and to read what he wanted. By the time the plague came, he had already discovered the writings of Galileo and Descartes and invented the beginnings of calculus.
By thinking on it continually.
-NEWTON (reply given when asked how he discovered the law of gravity)
Newton discovered that any two objects attract each other. The more massive the objects, the stronger is this universal force of gravitation. As the two objects move farther apart, the attraction between them weakens, but it never quite decreases to zero.
As is well known by now, the apple falls because the earth is pulling it down. In fact, since not only apples but also all objects fall, the force apparently does not depend on the precise nature of the object, only on its mass-that is, the amount of "substance" contained in the object. How does this force depend on the mass?
I should emphasize that Newton's law of motion F = ma is about the effect of forces in general. The force may be electric, magnetic, gravitational, or whatever. Until Newton, people were blinded by everpresent friction into believing that a force is necessary to keep an object moving at a constant velocity. Perhaps by watching a skater gliding gracefully across a pond of ice, Newton realized that if friction were minimal, an object. would maintain its velocity for a long time even without any force being exerted on the object. His law states that in the absence of friction a force exerted on an object changes the object's velocity-that is, it produces an acceleration.
Indeed, the gravitational force causes objects to accelerate as they fall. Already, Galileo had determined that falling objects accelerate at about thirty-two feet per second per second. That means that after falling for a second, a falling object is moving at a speed of thirty-two feet per second; after two seconds, sixty-four feet per second; and so on. Of course, air resistance would slow it down some.
Given all this, Newton deduced that the earth's gravitational pull on an object is proportional to its mass n in other words, F is equal to m times some constant. Call the constant g for gravity. Thus, F = mg. The proof is to show that this accords with Galileo's observations. That's easy. The acceleration is a = F /m= mg/m = g. The mass m cancels out! The acceleration does not depend on the mass of the object!
But that's exactly right! Galileo said that the acceleration of a falling object is thirty-two feet per second per second. Period. He didn't have to specify what the object's mass is. To underline this key point, let us suppose erroneously that the gravitational force is proportional to the mass squared, for example. Then the acceleration of a falling object would be a = F/m = constant xm z/m = constant xm. Thus an object twice as massive as another would accelerate twice as much as the other. That would contradict Galileo's observations.
Supposedly, Galileo demonstrated that all objects fall at the same rate by climbing up on the Leaning Tower of Pisa and dropping off two cannonballs of different sizes, showing that they hit the ground at the same time. Most people refused to believe Galileo, asking him how a rock and a feather could be said to fall at the same rate. These people didn't appreciate that air resistance on the feather far exceeds that on the rock. It is a dramatic and true fact that in a vacuum a rock and a feather would fall side by side.
As we will see, that falling objects fall at the same rate provides the clue to the true, nature of gravity and the cornerstone on which Einstein will construct his theory of gravity. From this fact flow the profound secrets of space and time...
|Preface to the Oxford Edition|
|Prologue: The Apple and the Moon|
|Pt. I||The Rise of Gravity||1|
|1||An Old Man's Toy||3|
|2||Hastening Through Space and Time||18|
|3||The Mighty Shall Be Weak||32|
|Pt. II||The Expanding Universe||47|
|5||Darkness at Night||70|
|6||From the Big Chill to the Big Bang||85|
|Pt. III||Structures out of the Void||103|
|7||The Universe Begets Matter||105|
|8||The Rich Get Richer||123|
|9||From Hair Whorls to the Edge of Creation||134|
|10||Ghost Riders in the Sky||155|
|11||Crowned with a Halo||175|
|Pt. IV||The Mystery of Gravity||189|
|12||The Fall and Rise of Gravity||191|
|13||The Music of Strings||211|
|14||The Thinking Man and the Laughing God||231|
Physics began with gravity. Two great theorists, Newton and Einstein, one building upon the other, strove to reveal the secrets of this universal force. Since Einstein, physicists have pondered, argued, and fought about the underlying character of gravity. The force we are most intimate with is a mysterious interloper from a realm of energy far beyond our experience. We know gravity by happenstance.
The titanic clash between gravity and the quantum has rocked the physics world for half a century. In recent years, a strangely beautiful theory of strings has captivated many physicists and promised to explain all. Yet a major paradox in our understanding of gravity continues to taunt us.
We will explore gravity-its inner character and its outward manifestations. In the Prologue, we review Newtonian gravity. In Part 1, we trace our understanding of gravity from the old man's toy to the quantum age. From this discussion of gravity, we move naturally on to a glimpse of gravity at play and at work in the universe. In Part 2, we follow the universe from the big chill to the big bang. In Part 3, we consider how matter and structure emerged out of the void. In the evolution of the universe, the hand of gravity is sometimes direct and evident; at other times it is hidden behind the scenes but is just as indispensable. From this tour of the universe, we return in Part 4 to gaze at the innermost secrets of gravity. Thus, a book in four movements: gravity, universe, universe, and gravity.
This book is about gravity and about the universe. My ambition here is to explain the physics of gravity as well as the physics of phenomena involving gravity, as represented most dramatically by the dynamic universe. Cosmology is certainly of deep interest and shares equal billing with the physics of gravity. Cosmology is also considerably more accessible to the lay reader. Ultimately, however, the passion of the fundamental physicist lies more with the mystery of why we fall than with the life of the universe.
I would also like to say a few words in tribute to George Gamow, the late Russian-American physicist who fashioned modern physical cosmology out of the general notion of the big bang, as I describe in chapter 6. An ebullient and irreverent jokester, Gamow was notorious for the fun he managed to have while doing physics. Quite a few physicists now feel that the Nobel Prize committee passed him over unjustly. Perhaps they didn't like the way he treated physics as an amusing hobby rather than as a serious profession. Oh well, in any case, his style appeals to me. Gamow also wrote a delightful series of popular physics books. I went into physics partly because of a chance encounter with one of his books during high school. I recommend those books.
I did not want to write the kind of popular physics book that merely serves up headlines. As a physicist and a professor, I want to explain as much as possible. But in discussing quantum gravity and the superstring theory in Part 4, when the full subtleties of the quantum field theory come into play, I can, alas, do no more than give you the flavor of the physics involved. For those who want more, I can only suggest that you embrace a career in theoretical physics, as I did when I read George Gamow's confession in one of his popular physics books that he just couldn't explain quantum statistics.
On the other hand, I also want to report on the excitement of the latest developments. The trick is to avoid the kind of developments that are here today and gone tomorrow. Over the four years or so from the first writing to the publication of this book, the popular press has reported breathlessly on quite a few exciting "discoveries." By and large, I discuss in this book only what I believe will endure, at least in broad outline. When I do talk about speculative suggestions, I try to make clear that they are just that.
I have never liked how popular science books distort history and perpetuate the myth that a handful of individuals is responsible for all discoveries. Regretfully, I can't avoid doing the same: The name Einstein appears on virtually every page. I would have loved to recount the historical currents and influences leading up to Newton's great discovery, for instance, but I can do no more than hint at them. What little I can introduce can be regarded only as a sketch, if not a caricature, of history.
Posted February 12, 2004
It would take a better writer than I to express how much enjoyment I have found in this book and its predecessor, 'Fearful Symmetry'. All the kudos, awards, and notoriety that have come to Dr. Zee from his work are, in my humble opinion, richly deserved. Years ago, I picked up 'An Old Man's Toy' without any particular expectations. Reading it, I was reminded of essays by Asimov, Heinlein and the like, in that the style was light, but hides a powerful message. He takes difficult subjects and allows us - the less formally trained ¿ to catch a glimmer of the secrets that have been uncovered during a lifetime in physics. I sought out 'Fearful Symmetry' and saw how the concepts of beauty and symmetry drive theoretical research, and what must have drove him to write that book. It became another treasured part of my library. Both have been of great interest to both my son as well. Having been exposed to those two works placed him in a marvelous position with his Chemistry and Physics instructors. I very much look forward to getting around to both of his other books, 'Quantum Field Theory in a Nutshell' and 'Swallowing Clouds'.Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.