The Physicist's World
Tom Grissom
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O Nature, and O soul of man! how far beyond all utterance are your linked analogies! not the smallest atom stirs or lives in matter, but has its cunning duplicate in mind.
Herman Melville, Moby-Dick
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Table of Contents
Introduction
Motion
To Be or Not-To-Be
Atoms and the Void
Motion Constrained
How vs Why
Enter Newton
The Laws of Motion
Action at a Distance
Matter and Light
Heat and the Arrow of Time
Who's Really Moving, and What's the Correct Time?
Curved Space: The New Gravity
What You See Is What You Get
A Footnote: Quantum Gravity
Equations That Go Berserk
The Physicist's World
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A Note to the Reader
Our story contains a modicum of mathematics. I have used it sparingly, and judiciously; but to eliminate it altogether would have been dishonest, a form of intellectual deception and condescension, and an insult to your curiosity and intelligence. Telling the story of the physicist's world without the use of at least some mathematics is akin to trying to describe the experience of poetry to someone who has never seen or heard a poem. Physics, after all, is a mathematical description of the world. We want our story by its form as well as by its content to convey something of what we are talking about. We cannot properly comprehend how physics works without understanding something about the crucial role that mathematics plays in it, and the only way to accomplish that is through experiencing at least a small part of it for yourself. I have tried to accomplish that by taking some of the most important ideas and presenting them in a semi-quantitative way.
An important aspect of our story concerns the kind of limitations that physics in the twentieth century has imposed on our ultimate knowledge of the world. These are limitations arising from efforts to describe the world quantitatively, and can only be properly understood and appreciated in terms of those same quantitative ideas. To try to talk about them in any other way would unnecessarily obscure and mystify their significance.
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I have not included mathematics where I thought I could do as well without it, or where I thought that its difficulty might confuse rather than clarify. I have included it in all those instances where I regarded it essential to properly understand the most fundamental ideas. And in every case I have tried to say in words the same things that the equations express symbolically, in order that one may reinforce and help explain the other, sometimes perhaps at the expense of repeating myself and becoming unduly redundant. Hopefully I have erred on the side of being too pedantic rather than risk being unclear or misunderstood.
I would discourage you from omitting the mathematical equations, even on a first reading. They constitute an essential component of the story and should be included even when you are not sure that you understand everything. Often what you find confusing will clear up as you continue, if you have first invested a little time in trying to think your way through the mathematical expressions. The key is not to omit anything, but at the same time not to become bogged down and stop just because some point is not absolutely clear. The struggle to understand is also an essential element of the physicist's world, just as much as the exhilarating sense of elation and satisfaction that comes from finally succeeding. Only a modest struggle on your part will let you truly experience the drive and passion for understanding that from the very beginning has been the impetus behind the creation of our story.
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Introduction
With consciousness comes awareness, and with awareness comes storytelling. Of the different kinds of stories that we devise in order to explain things to ourselves and make sense out of the world, none is more fascinating or more central to who we are than that told by the physicist about the nature of the material world around us. The story of the physicist's world has its roots in the very origins of western philosophy and has continuously evolved to reflect our changing understanding of the reality behind things. It began to take on its current form with the beginnings of modern science in the seventeenth century, and in our own time it has embraced the strange epistemology of twentieth century physics. Epistemology: a word that takes us back to our Greek beginnings in western thought: the inquiry into what we can know and how we can know it. What we can know limits the field of inquiry; how we can know it determines the nature of the inquiry itself. I was still quite young when I first became aware of wanting to understand the nature of things, the De Rerum Natura of Lucretius, of wanting to understand everything - and to understand it completely - the way I imagined as a child that I would be able to understand my immediate surroundings and the day to day events of my life. Of course, later, we come to realize that this impulse arises out of an unconscious awareness that the world is mysterious, that even in the smallest and least significant of phenomena - like the burning of a candle or the splashing of raindrops on a parched earth - there is something unfathomable, something that drives us to seek refuge in the quest for understanding, even, if need be, in the illusion of understanding.
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It is an impulse that led me to pursue physics when I might have done something else. My earliest interest was biology. I grew up out of doors and by inclination I was a naturalist, living out of field guides and identifying the birds, mammals, trees, and plants of my native soil - the Delta country of the Yazoo River basin in northwest Mississippi. Yet even then it seemed to me that the natural philosophers - the physicists - were onto a more fruitful approach. Out of a few simple principles came the impressive ordering of a vast array of phenomena, an ordering and an understanding that went far beyond the mere naming of things; things that seemed to my unschooled mind to share more differences than similarities. The diversity of biological phenomena appeared staggering and overwhelming. Newton's three laws of motion and the law of universal gravitation sufficed to order the entire universe. I found the illusion of this latter approach more appealing, and more satisfying, to my youthful desire for understanding.
With maturity and age, however, comes a sobering wisdom. During our lives we accumulate knowledge and a store of memories. But everything in our minds, and all our memories, are to some extent made up. We are the ones who remember. And either in the process of recording our impressions, or in recalling them later, we make subtle changes, molding and shaping what we know to agree with our cumulative experience of the world as we have lived it, each to some extent differently in our individual lives. There are matters of fact, to be sure: the sun rises and sets; we are born, live, and die. Beyond that, most of what we know is less distinct and is constantly being modified by each new thing that we learn and remember. It is as true of the physicist's world as it is the world of the poet or the philosopher, since all are creations of the mind, depictions of a reality that can never be absolute no matter how earnestly we seek it.
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The absolute stops whenever we attempt to go beyond simple matters of fact, and facts by themselves are seldom of lasting interest. More important to us are the judgements we make about the plain facts of our existence, the world that we create in our minds to organize and explain our experiences - the stories that we tell ourselves about the world. The story of the physicist's world is but one more way of understanding the phenomena around us, and we shall see that it like all the others is very much a mental construct, distinct from the separate reality that lies behind things. The real world always is out there, beyond my window; and it remains forever illusive and unknowable, in ways that no depiction created by the mind can ever hope to overcome, no matter how strictly we may adhere to the rigid facts of our existence. We will find that in our mental creations even the facts take on a certain flexibility and irrelevance unsuspected before the twentieth century, though in retrospect perhaps it should not have been. We will examine the physicist's world for its limitations and shortcomings as well as for its triumphs and truths. Both, we will discover, are equally interesting, and equally revealing; and both are essential to any complete understanding of what we can know about the material universe.
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Our impulse to ultimately understand the nature of things has found scant encouragement in the twentieth century. On the one hand it has been a century filled with remarkable scientific achievement, a time of true intellectual revolution, comparable to the beginnings of science itself in the seventeenth century. Yet each singular advance has been built upon the discovery of insurmountable limitations in what we can know about the world. Limitations that derive not from any practical considerations having to do with measurement precision or the like, but resulting from the nature of the world itself. Nature it seems has built in limits to what we are permitted to know, what it is even possible to know. Our instinctual suspicion that the world at its core is mysterious and unfathomable finds vindication in the epistemology of twentieth century physics.
Our century began with the theory of relativity, and the discovery that the speed of light in free space represents an upper limit to how rapidly any form of matter or energy - and hence information - can be transmitted. When we look up at the night sky we see it not as it appears now, but the way it looked when the light first began its long journey to our eyes, a journey that even for the nearest star began something like three years earlier, and for stars outside our own galaxy began millions of years ago. Any prospect of finding out what is happening now is limited by how far light can travel in one lifetime or in the relatively short span of human affairs. Our knowledge of everything beyond a tiny region of nearby space is confined to what occurred in the past. Most of the universe can be seen only in the remote past, and for us has no conceivably knowable future. We may view the macroscopic world it seems only by looking through a one way mirror that gives us glimpses of how it used to be. The farther we peer, the more remote in time the images that we see.
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The quantum theory developed during the early part of the century has shown that we are likewise limited in trying to extend our knowledge in the other direction - into the remotely small and inaccessible regions of the universe. Here the restrictions are equally fundamental and are even more baffling and bizarre. Concepts of space and time derived from our direct sensory perceptions break down and give way to a loss of certainty in the meaning of position and speed, energy and time. Strict determinism in predicting the outcome of an event is replaced by a set of vague probabilities designating the likelihood of each possible outcome, with the final result determined only by the act of measurement itself. The uncertainty principle restricts the precision with which the position and speed of a particle can be known simultaneously. The properties of matter become increasingly more numerous and complex and further removed from our direct sense perceptions as the nature and location of matter become more diffuse. We are permitted to know the position of a particle exactly only if we surrender all information about how fast and in what direction it is moving; or to measure its progress exactly only if we give up all knowledge of where it is located. The concrete realm of our senses devolves into a miasma of phantoms which steadfastly refuse to be pinned down. The best we can achieve is the uneasy compromise offered to us by the uncertainty principle, which can be taken as the fundamental axiom of microscopic nature.
Likely we should not be surprised by such limitations. We are creatures of the intermediate, trapped somewhere between the twin remotenesses of the very small and the very large. Expressed in powers of ten we are situated roughly midway between the size of the atomic nucleus and the distance light travels in a year, intermediate between the size of an atom and the size of a star, excluded from either extreme - by our infinitude in the one case and by our overwhelming bulk in the other. Nothing in our direct experience can be expected to have prepared us for the nature of phenomena in either of these excluded regions. We cannot know what we have never experienced. Or at the very least our experiences in one realm cannot be expected to carry over into these other realms without surprises. Viewed this way, if we had been much larger we would have discovered relativity physics at the outset; or much smaller and we would have found quantum physics to be the correct depiction of events; and in either case Newtonian physics would seem like only a clumsy and crude approximation.
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For a while it was possible to take solace in such a view. The physics of the microcosm and the macrocosm might seem strange to us but everything was still all right in the world of our immediate sensory experiences. If I have never directly experienced an atom or moved at the speed of light, I can nevertheless feel secure in my knowledge of the world that I can actually see and touch. Yet even this solace has been short lived. The discovery of deterministic chaos at the end of the century has identified physical phenomena directly accessible to our senses whose outcomes, though completely deterministic, are inherently unpredictable - and hence unknowable - even if all of the initial conditions are specified. We find ourselves banished from at least a portion of the last remaining stronghold of our most secure knowledge of the world. The irony of all these limitations is that the physicist's world gains, by its ability to examine the limits to our knowledge, what it loses in being unable to completely describe the real world.
We live in a time when it has become common to replace reality with some abstract creation of the human mind. In place of the real world we substitute a depiction of reality derived from a limited portion of our total experience. We "model" the world in some fashion. It is better - and more convincing - if the model is mathematical, and best of all if it is implemented on a computer. Even to those who should know better a computer model somehow suggests that we have transcended the limitations of the human mind. We then use the model to tell us about the real world, which of course it cannot do or can do in only a very limited way. "Virtual reality" is just the most recent example of this process, describing as it does the latest fad of representing reality by computer generated images, to which can be added other sensory experiences such as sound and smell and touch.
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But virtual reality is only a new name for what has been happening since the rise of modern science in the seventeenth century. We have replaced history with theories of history - from Hegel to Marx to Toynbee to Postmodernism. We have created political sciences, social sciences, political economies, and theories of psychology to model politics, society, economics, and the mind. All of these efforts stem in one way or another from well-intentioned but misguided attempts to mimic the startling success of Newtonian physics in understanding the workings of the material universe. The physicist's world is the prototypical virtual reality.
Yet understanding the simple motions of material bodies in the natural world is a far cry from understanding the infinitely more complex interactions of humans. Beyond the hope that springs eternal in the human makeup the two have nothing in common. There is nothing in the success of physics to suggest that the same methods of inquiry (the how we can know of epistemology) will lead to any productive understanding in the vastly different and more complex arena of human affairs. Only a species more interested in ideas themselves than in what the ideas are about would be seduced into thinking it possible. For the success of physics is not due to the nature of the inquiry alone but to the field of inquiry as well.
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The physicist's world is built on a very specific - and very limited - response to the twin questions of epistemology about what we can know and how we can know it. Its accomplishments are derived more from the restricted nature of the inquiry than from the methods employed. The success of physics is a very limited kind of success, one that can never be total or complete. The physicist's world is an impoverished and skeletal representation of the real world, in just the same way that those misguided disciplines built upon the shifting sands of imitation are an impoverished and skeletal mis-representation of the real world of human affairs. This was true even before the startling discoveries of the twentieth century and to some extent in anticipation of those discoveries. With them, these limitations have become a permanent part of the very foundations of physical science, just as they are an observable part of the real world. There are important lessons that we can learn from better understanding the mental world created by the physicist, from understanding what it can and cannot, or does and does not, tell us about the real world outside our window.