Let me start off by saying (its relevance will soon be revealed) I have a bachelor of science in mathematics and a master's in computer science (and I wasn't in the bottom 50% of the class), and after the first 300 or so pages (out of 1200) the math in this book (and it's at least 40% or more straight math, not text, and often without text explaining the math) is way above my head and is left often undefined in the text. The author doesn't even do the courtesy of pointing the reader to textbooks where these concepts, such as pseudo-Riemannian geometry and anti-de Sitter spaces and Seiberg/Gromov-Witten manifolds, are defined and can be learned.
The book fails in its promise and purpose to be a self-contained guide to the current mathematical- or theoretical-physical understanding of the universe. Required prerequisites: understanding of linear algebra (Lie, Poisson, Frobenius, Ricci calculus), scalars and higher rank TENSORS (and MORE tensors), several varieties of noneuclidean geometry (Minkowski, de Sitter, Riemann), scalars, topology and n-manifolds, group theory (Lie groups), gauge theory, etc., or the willingness to learn these from expensive secondary sources, because Penrose will not teach you them here and the arguments of the book are incomprehensible without them. Without them, one would be reduced to skimming the 20% of the book that is text (especially the final chapter, which is comprehensible to any semieducated layman) and taking the author's word for the rest of it. Just about the only thing he explains in full is twistor theory (his own invention).
It is far from accessible to the layman (I have postgraduate training in math and I was a good student and its inaccessible to me), and to grasp the concepts in this book, I'd have to spend probably a year of free time and a thousand or more dollars in secondary sources (if I bought them used and cheap). I bought this book to get a $20 overview (like Collier's 'A Most Incomprehensible Thing' for the theories of relativity [I prefer the original 'invariance'], which was technical but self-contained and comprehensible; reading that is the only thing that gave me any knowledge at all of tensors, which this book is chock full of): what I got was in essence a 1200 page bibliography without the authors being noted and without the important works being starred.
This is a very ambitious book which fails utterly in execution.
The author goes from explaining what complex and irrational numbers are and why they are useful (this is freshman high school math) in the introduction to pseudo-Riemannian geometry (this is postgraduate pure math) 200 pages later. He spends about five pages defining all of classical mechanics, and then assumes that you understand classical mechanics. This same breakneck pace is kept up throughout, which is how he manages to range from logarithms and complex numbers to doctoral-level mathematics in 500 or 600 pages. Once he goes out of the pure math and back to applied math (i.e.. physics proper) it gets a little easier but I'd still not recommend trying to tackle this book with less than a bachelor's degree in math (if you're a math nerd and keep your knowledge up) or a master's in math or physics or some other strongly quantitative discipline (if you're not), or a self-taught prodigy in pure maths.
The book promises to be a self-contained guide to the best mathematical understanding of the universe we have, but it ends up more like the author just stuck the important theorems in with a minimum of explanation (he does hit almost all of them: one thing that struck me as unnecessarily erudite - showing off - and odd was the statement of Maxwell's field equations, which is mathematically simple and elegant, in terms of tensors, which are very, very difficult), so it's a complete guide if you already know all of the math (in which case you don't need the book): it's much more of a refresher and quick reference for people who already are familiar with and understand (or at one time understood) the concepts the author represents.
See attached pictures (representative pages from 250-, and these are not nearly the most difficult of the equations): No, you're not the only person going 'smh, wtf' at that math. (Not to mention yet again that many of the terms are never defined in-text! The author goes from explaining that he'll have to use logarithms in the introduction, to this stuff which is Chinese to me as a math major, within a few hundred pages. It seems Penrose let his mathematical understanding [brilliance for all I can tell, I have no idea what he's saying] run away with itself after writing the preface for a book where he's apologetic about using logs and then sticking that preface on this work.)
I still have to award two stars for the obvious intensity and depths of erudition which Penrose funneled in to this work, but only two because it doesn't even partially fulfill its stated purpose or self-description.
*I have familiarized myself additionally with pure math concepts like number theory, group theory, field and Galois theory and combinatorics, along with stochastic calculus and linear algebra to a degree. I am even partially comprehending of tensors after reading 'A Most Incomprehensible Thing', a lay mathematicians' introduction to relativity. In other words, I'm an educated lay mathematician, and the stated target audience for this book is 'educated laymen' with AP high school or gen ed college math in general.
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The Road to Reality : A Complete Guide to the Laws of the Universe Hardcover – February 22, 2005
by
Roger Penrose
(Author)
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Roger Penrose
(Author)
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From one of our greatest living scientists, a magnificent book that provides, for the serious lay reader, the most comprehensive and sophisticated account we have yet had of the physical universe and the essentials of its underlying mathematical theory.
Since the earliest efforts of the ancient Greeks to find order amid the chaos around us, there has been continual accelerated progress toward understanding the laws that govern our universe. And the particularly important advances made by means of the revolutionary theories of relativity and quantum mechanics have deeply altered our vision of the cosmos and provided us with models of unprecedented accuracy.
What Roger Penrose so brilliantly accomplishes in this book is threefold. First, he gives us an overall narrative description of our present understanding of the universe and its physical behaviors–from the unseeable, minuscule movement of the subatomic particle to the journeys of the planets and the stars in the vastness of time and space.
Second, he evokes the extraordinary beauty that lies in the mysterious and profound relationships between these physical behaviors and the subtle mathematical ideas that explain and interpret them.
Third, Penrose comes to the arresting conclusion–as he explores the compatibility of the two grand classic theories of modern physics–that Einstein’s general theory of relativity stands firm while quantum theory, as presently constituted, still needs refashioning.
Along the way, he talks about a wealth of issues, controversies, and phenomena; about the roles of various kinds of numbers in physics, ideas of calculus and modern geometry, visions of infinity, the big bang, black holes, the profound challenge of the second law of thermodynamics, string and M theory, loop quantum gravity, twistors, and educated guesses about science in the near future. In The Road to Reality he has given us a work of enormous scope, intention, and achievement–a complete and essential work of science
Since the earliest efforts of the ancient Greeks to find order amid the chaos around us, there has been continual accelerated progress toward understanding the laws that govern our universe. And the particularly important advances made by means of the revolutionary theories of relativity and quantum mechanics have deeply altered our vision of the cosmos and provided us with models of unprecedented accuracy.
What Roger Penrose so brilliantly accomplishes in this book is threefold. First, he gives us an overall narrative description of our present understanding of the universe and its physical behaviors–from the unseeable, minuscule movement of the subatomic particle to the journeys of the planets and the stars in the vastness of time and space.
Second, he evokes the extraordinary beauty that lies in the mysterious and profound relationships between these physical behaviors and the subtle mathematical ideas that explain and interpret them.
Third, Penrose comes to the arresting conclusion–as he explores the compatibility of the two grand classic theories of modern physics–that Einstein’s general theory of relativity stands firm while quantum theory, as presently constituted, still needs refashioning.
Along the way, he talks about a wealth of issues, controversies, and phenomena; about the roles of various kinds of numbers in physics, ideas of calculus and modern geometry, visions of infinity, the big bang, black holes, the profound challenge of the second law of thermodynamics, string and M theory, loop quantum gravity, twistors, and educated guesses about science in the near future. In The Road to Reality he has given us a work of enormous scope, intention, and achievement–a complete and essential work of science
-
Print length1136 pages
-
LanguageEnglish
-
PublisherKnopf
-
Publication dateFebruary 22, 2005
-
Dimensions6.63 x 2.23 x 9.44 inches
-
ISBN-100679454438
-
ISBN-13978-0679454434
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Editorial Reviews
Amazon.com Review
If Albert Einstein were alive, he would have a copy of The Road to Reality on his bookshelf. So would Isaac Newton. This may be the most complete mathematical explanation of the universe yet published, and Roger Penrose richly deserves the accolades he will receive for it. That said, let us be perfectly clear: this is not an easy book to read. The number of people in the world who can understand everything in it could probably take a taxi together to Penrose's next lecture. Still, math-friendly readers looking for a substantial and possibly even thrillingly difficult intellectual experience should pick up a copy (carefully--it's over a thousand pages long and weighs nearly 4 pounds) and start at the beginning, where Penrose sets out his purpose: to describe "the search for the underlying principles that govern the behavior of our universe." Beginning with the deceptively simple geometry of Pythagoras and the Greeks, Penrose guides readers through the fundamentals--the incontrovertible bricks that hold up the fanciful mathematical structures of later chapters. From such theoretical delights as complex-number calculus, Riemann surfaces, and Clifford bundles, the tour takes us quickly on to the nature of spacetime. The bulk of the book is then devoted to quantum physics, cosmological theories (including Penrose's favored ideas about string theory and universal inflation), and what we know about how the universe is held together. For physicists, mathematicians, and advanced students, The Road to Reality is an essential field guide to the universe. For enthusiastic amateurs, the book is a project to tackle a bit at a time, one with unimaginable intellectual rewards. --Therese Littleton
From Publishers Weekly
At first, this hefty new tome from Oxford physicist Penrose (The Emperor's NewMind) looks suspiciously like a textbook, complete with hundreds of diagrams and pages full of mathematical notation. On a closer reading, however, one discovers that the book is something entirely different and far more remarkable. Unlike a textbook, the purpose of which is purely to impart information, this volume is written to explore the beautiful and elegant connection between mathematics and the physical world. Penrose spends the first third of his book walking us through a seminar in high-level mathematics, but only so he can present modern physics on its own terms, without resorting to analogies or simplifications (as he explains in his preface, "in modern physics, one cannot avoid facing up to the subtleties of much sophisticated mathematics"). Those who work their way through these initial chapters will find themselves rewarded with a deep and sophisticated tour of the past and present of modern physics. Penrose transcends the constraints of the popular science genre with a unique combination of respect for the complexity of the material and respect for the abilities of his readers. This book sometimes begs comparison with Stephen Hawking's A Brief History of Time, and while Penrose's vibrantly challenging volume deserves similar success, it will also likely lie unfinished on as many bookshelves as Hawking's. For those hardy readers willing to invest their time and mental energies, however, there are few books more deserving of the effort. 390 illus. (Feb. 24)
Copyright © Reed Business Information, a division of Reed Elsevier Inc. All rights reserved.
Copyright © Reed Business Information, a division of Reed Elsevier Inc. All rights reserved.
Review
Praise for The Road to Reality by Roger Penrose
“A truly remarkable book...Penrose does much to reveal the beauty and subtlety that connects nature and the human imagination, demonstrating that the quest to understand the reality of our physical world, and the extent and limits of our mental capacities, is an awesome, never-ending journey rather than a one-way cul-de-sac.”
—London Sunday Times
“Penrose’s work is genuinely magnificent, and the most stimulating book I have read in a long time.”
—Scotland on Sunday
“Science needs more people like Penrose, willing and able to point out the flaws in fashionable models from a position of authority and to signpost alternative roads to follow.”
—The Independent
“What a joy it is to read a book that doesn't simplify, doesn't dodge the difficult questions, and doesn't always pretend to have answers...Penrose’s appetite is heroic, his knowledge encyclopedic, his modesty a reminder that not all physicists claim to be able to explain the world in 250 pages.”
—London Times
“For physics fans, the high point of the year will undoubtedly be The Road to Reality.”
—Guardian
“A truly remarkable book...Penrose does much to reveal the beauty and subtlety that connects nature and the human imagination, demonstrating that the quest to understand the reality of our physical world, and the extent and limits of our mental capacities, is an awesome, never-ending journey rather than a one-way cul-de-sac.”
—London Sunday Times
“Penrose’s work is genuinely magnificent, and the most stimulating book I have read in a long time.”
—Scotland on Sunday
“Science needs more people like Penrose, willing and able to point out the flaws in fashionable models from a position of authority and to signpost alternative roads to follow.”
—The Independent
“What a joy it is to read a book that doesn't simplify, doesn't dodge the difficult questions, and doesn't always pretend to have answers...Penrose’s appetite is heroic, his knowledge encyclopedic, his modesty a reminder that not all physicists claim to be able to explain the world in 250 pages.”
—London Times
“For physics fans, the high point of the year will undoubtedly be The Road to Reality.”
—Guardian
About the Author
Roger Penrose is Emeritus Rouse Ball Professor of Mathematics at Oxford University. He has received a number of prizes and awards, including the 1988 Wolf Prize for physics, which he shared with Stephen Hawking for their joint contribution to our understanding of the universe. His books include The Emperor’s New Mind, Shadows of the Mind, and The Nature of Space and Time, which he wrote with Hawking. He has lectured extensively at universities throughout America. He lives in Oxford.
Excerpt. © Reprinted by permission. All rights reserved.
Preface
The purpose of this book is to convey to the reader some feeling for what is surely one of the most important and exciting voyages of discovery that humanity has embarked upon. This is the search for the underlying principles that govern the behaviour of our universe. It is a voyage that has lasted for more than two-and-a-half millennia, so it should not surprise us that substantial progress has at last been made. But this journey has proved to be a profoundly difficult one, and real understanding has, for the most part, come but slowly. This inherent difficulty has led us in many false directions; hence we should learn caution. Yet the 20th century has delivered us extraordinary new insights–some so impressive that many scientists of today have voiced the opinion that we may be close to a basic understanding of all the underlying principles of physics. In my descriptions of the current fundamental theories, the 20th century having now drawn to its close, I shall try to take a more sober view. Not all my opinions may be welcomed by these ‘optimists’, but I expect further changes of direction greater even than those of the last century.
The reader will find that in this book I have not shied away from presenting mathematical formulae, despite dire warnings of the severe reduction in readership that this will entail. I have thought seriously about this question, and have come to the conclusion that what I have to say cannot reasonably be conveyed without a certain amount of mathematical notation and the exploration of genuine mathematical concepts. The understanding that we have of the principles that actually underlie the behaviour of our physical world indeed depends upon some appreciation of its mathematics. Some people might take this as a cause for despair, as they will have formed the belief that they have no capacity for mathematics, no matter at how elementary a level. How could it be possible, they might well argue, for them to comprehend the research going on at the cutting edge of physical theory if they cannot even master the manipulation of fractions? Well, I certainly see the difficulty.
Yet I am an optimist in matters of conveying understanding. Perhaps I am an incurable optimist. I wonder whether those readers who cannot manipulate fractions–or those who claim that they cannot manipulate fractions–are not deluding themselves at least a little, and that a good proportion of them actually have a potential in this direction that they are not aware of. No doubt there are some who, when confronted with a line of mathematical symbols, however simply presented, can see only the stern face of a parent or teacher who tried to force into them a non-comprehending parrot-like apparent competence–a duty, and a duty alone–and no hint of the magic or beauty of the subject might be allowed to come through. Perhaps for some it is too late; but, as I say, I am an optimist and I believe that there are many out there, even among those who could never master the manipulation of fractions, who have the capacity to catch some glimpse of a wonderful world that I believe must be, to a significant degree, genuinely accessible to them.
One of my mother’s closest friends, when she was a young girl, was among those who could not grasp fractions. This lady once told me so herself after she had retired from a successful career as a ballet dancer. I was still young, not yet fully launched in my activities as a mathematician, but was recognized as someone who enjoyed working in that subject. ‘It’s all that cancelling’, she said to me, ‘I could just never get the hang of cancelling.’ She was an elegant and highly intelligent woman, and there is no doubt in my mind that the mental qualities that are required in comprehending the sophisticated choreography that is central to ballet are in no way inferior to those which must be brought to bear on a mathematical problem. So, grossly overestimating my expositional abilities, I attempted, as others had done before, to explain to her the simplicity and logical nature of the procedure of ‘cancelling’.
I believe that my efforts were as unsuccessful as were those of others. (Incidentally, her father had been a prominent scientist, and a Fellow of the Royal Society, so she must have had a background adequate for the comprehension of scientific matters. Perhaps the ‘stern face’ could have been a factor here, I do not know.) But on reflection, I now wonder whether she, and many others like her, did not have a more rational hang-up–one that with all my mathematical glibness I had not noticed. There is, indeed, a profound issue that one comes up against again and again in mathematics and in mathematical physics, which one first encounters in the seemingly innocent operation of cancelling a common factor from the numerator and denominator of an ordinary numerical fraction.
Those for whom the action of cancelling has become second nature, because of repeated familiarity with such operations, may find themselves insensitive to a difficulty that actually lurks behind this seemingly simple procedure. Perhaps many of those who find cancelling mysterious are seeing a certain profound issue more deeply than those of us who press onwards in a cavalier way, seeming to ignore it. What issue is this? It concerns the very way in which mathematicians can provide an existence to their mathematical entities and how such entities may relate to physical reality.
I recall that when at school, at the age of about 11, I was somewhat taken aback when the teacher asked the class what a fraction (such as 3/8) actually is! Various suggestions came forth concerning the dividing up of pieces of pie and the like, but these were rejected by the teacher on the (valid) grounds that they merely referred to imprecise physical situations to which the precise mathematical notion of a fraction was to be applied; they did not tell us what that clear-cut mathematical notion actually is. Other suggestions came forward, such as 3/8 is ‘something with a 3 at the top and an 8 at the bottom with a horizontal line in between’ and I was distinctly surprised to find that the teacher seemed to be taking these suggestions seriously! I do not clearly recall how the matter was finally resolved, but with the hindsight gained from my much later experiences as a mathematics undergraduate, I guess my schoolteacher was making a brave attempt at telling us the definition of a fraction in terms of the ubiquitous mathematical notion of an equivalence class.
What is this notion? How can it be applied in the case of a fraction and tell us what a fraction actually is? Let us start with my classmate’s ‘something with a 3 at the top and an 8 on the bottom’. Basically, this is suggesting to us that a fraction is specified by an ordered pair of whole numbers, in this case the numbers 3 and 8. But we clearly cannot regard the fraction as being such an ordered pair because, for example, the fraction 6/16 is the same number as the fraction 3/8, whereas the pair (6, 16) is certainly not the same as the pair (3, 8). This is only an issue of cancelling; for we can write 6/16 as 3x2/8x2 and then cancel the 2 from the top and the bottom to get 3/8. Why are we allowed to do this and thereby, in some sense, ‘equate’ the pair (6, 16) with the pair (3, 8)? The mathematician’s answer–which may well sound like a cop-out–has the cancelling rule just built in to the definition of a fraction: a pair of whole numbers (a x n, b x n) is deemed to represent the same fraction as the pair (a, b) whenever n is any non-zero whole number (and where we should not allow b to be zero either).
But even this does not tell us what a fraction is; it merely tells us something about the way in which we represent fractions. What is a fraction, then? According to the mathematician’s ‘‘equivalence class’’ notion, the fraction 3/8, for example, simply is the infinite collection of all
pairs
(3, 8), ( – 3, – 8), (6, 16), ( – 6, – 16), (9, 24), ( – 9, – 24), (12, 32), . . . ,
where each pair can be obtained from each of the other pairs in the list by repeated application of the above cancellation rule.* [ * This is called an ‘equivalence class’ because it actually is a class of entities (the entities, in this particular case, being pairs of whole numbers), each member of which is deemed to be equivalent, in a specified sense, to each of the other members.] We also need definitions telling us how to add, subtract, and multiply such infinite collections of pairs of whole numbers, where the normal rules of algebra hold, and how to identify the whole numbers themselves as particular types of
fraction.
This definition covers all that we mathematically need of fractions (such as 1/2 being a number that, when added to itself, gives the number 1, etc.), and the operation of cancelling is, as we have seen, built into the definition. Yet it seems all very formal and we may indeed wonder whether it really captures the intuitive notion of what a fraction is. Although this ubiquitous equivalence class procedure, of which the above illustration is just a particular instance, is very powerful as a pure-mathematical tool for establishing consistency and mathematical existence, it can provide us with very topheavy-looking entities. It hardly conveys to us the intuitive notion of what 3/8 is, for example! No wonder my mother’s friend was confused.
In my descriptions of mathematical notions, I shall try to avoid, as far as I can, the kind of mathematical pedantry that leads us to define a fraction in terms of an ‘infinite class of pairs’ even though it certainly has its value in mathematical rigour and precision. In my descriptions here I shall be more concerned with conveying the id...
The purpose of this book is to convey to the reader some feeling for what is surely one of the most important and exciting voyages of discovery that humanity has embarked upon. This is the search for the underlying principles that govern the behaviour of our universe. It is a voyage that has lasted for more than two-and-a-half millennia, so it should not surprise us that substantial progress has at last been made. But this journey has proved to be a profoundly difficult one, and real understanding has, for the most part, come but slowly. This inherent difficulty has led us in many false directions; hence we should learn caution. Yet the 20th century has delivered us extraordinary new insights–some so impressive that many scientists of today have voiced the opinion that we may be close to a basic understanding of all the underlying principles of physics. In my descriptions of the current fundamental theories, the 20th century having now drawn to its close, I shall try to take a more sober view. Not all my opinions may be welcomed by these ‘optimists’, but I expect further changes of direction greater even than those of the last century.
The reader will find that in this book I have not shied away from presenting mathematical formulae, despite dire warnings of the severe reduction in readership that this will entail. I have thought seriously about this question, and have come to the conclusion that what I have to say cannot reasonably be conveyed without a certain amount of mathematical notation and the exploration of genuine mathematical concepts. The understanding that we have of the principles that actually underlie the behaviour of our physical world indeed depends upon some appreciation of its mathematics. Some people might take this as a cause for despair, as they will have formed the belief that they have no capacity for mathematics, no matter at how elementary a level. How could it be possible, they might well argue, for them to comprehend the research going on at the cutting edge of physical theory if they cannot even master the manipulation of fractions? Well, I certainly see the difficulty.
Yet I am an optimist in matters of conveying understanding. Perhaps I am an incurable optimist. I wonder whether those readers who cannot manipulate fractions–or those who claim that they cannot manipulate fractions–are not deluding themselves at least a little, and that a good proportion of them actually have a potential in this direction that they are not aware of. No doubt there are some who, when confronted with a line of mathematical symbols, however simply presented, can see only the stern face of a parent or teacher who tried to force into them a non-comprehending parrot-like apparent competence–a duty, and a duty alone–and no hint of the magic or beauty of the subject might be allowed to come through. Perhaps for some it is too late; but, as I say, I am an optimist and I believe that there are many out there, even among those who could never master the manipulation of fractions, who have the capacity to catch some glimpse of a wonderful world that I believe must be, to a significant degree, genuinely accessible to them.
One of my mother’s closest friends, when she was a young girl, was among those who could not grasp fractions. This lady once told me so herself after she had retired from a successful career as a ballet dancer. I was still young, not yet fully launched in my activities as a mathematician, but was recognized as someone who enjoyed working in that subject. ‘It’s all that cancelling’, she said to me, ‘I could just never get the hang of cancelling.’ She was an elegant and highly intelligent woman, and there is no doubt in my mind that the mental qualities that are required in comprehending the sophisticated choreography that is central to ballet are in no way inferior to those which must be brought to bear on a mathematical problem. So, grossly overestimating my expositional abilities, I attempted, as others had done before, to explain to her the simplicity and logical nature of the procedure of ‘cancelling’.
I believe that my efforts were as unsuccessful as were those of others. (Incidentally, her father had been a prominent scientist, and a Fellow of the Royal Society, so she must have had a background adequate for the comprehension of scientific matters. Perhaps the ‘stern face’ could have been a factor here, I do not know.) But on reflection, I now wonder whether she, and many others like her, did not have a more rational hang-up–one that with all my mathematical glibness I had not noticed. There is, indeed, a profound issue that one comes up against again and again in mathematics and in mathematical physics, which one first encounters in the seemingly innocent operation of cancelling a common factor from the numerator and denominator of an ordinary numerical fraction.
Those for whom the action of cancelling has become second nature, because of repeated familiarity with such operations, may find themselves insensitive to a difficulty that actually lurks behind this seemingly simple procedure. Perhaps many of those who find cancelling mysterious are seeing a certain profound issue more deeply than those of us who press onwards in a cavalier way, seeming to ignore it. What issue is this? It concerns the very way in which mathematicians can provide an existence to their mathematical entities and how such entities may relate to physical reality.
I recall that when at school, at the age of about 11, I was somewhat taken aback when the teacher asked the class what a fraction (such as 3/8) actually is! Various suggestions came forth concerning the dividing up of pieces of pie and the like, but these were rejected by the teacher on the (valid) grounds that they merely referred to imprecise physical situations to which the precise mathematical notion of a fraction was to be applied; they did not tell us what that clear-cut mathematical notion actually is. Other suggestions came forward, such as 3/8 is ‘something with a 3 at the top and an 8 at the bottom with a horizontal line in between’ and I was distinctly surprised to find that the teacher seemed to be taking these suggestions seriously! I do not clearly recall how the matter was finally resolved, but with the hindsight gained from my much later experiences as a mathematics undergraduate, I guess my schoolteacher was making a brave attempt at telling us the definition of a fraction in terms of the ubiquitous mathematical notion of an equivalence class.
What is this notion? How can it be applied in the case of a fraction and tell us what a fraction actually is? Let us start with my classmate’s ‘something with a 3 at the top and an 8 on the bottom’. Basically, this is suggesting to us that a fraction is specified by an ordered pair of whole numbers, in this case the numbers 3 and 8. But we clearly cannot regard the fraction as being such an ordered pair because, for example, the fraction 6/16 is the same number as the fraction 3/8, whereas the pair (6, 16) is certainly not the same as the pair (3, 8). This is only an issue of cancelling; for we can write 6/16 as 3x2/8x2 and then cancel the 2 from the top and the bottom to get 3/8. Why are we allowed to do this and thereby, in some sense, ‘equate’ the pair (6, 16) with the pair (3, 8)? The mathematician’s answer–which may well sound like a cop-out–has the cancelling rule just built in to the definition of a fraction: a pair of whole numbers (a x n, b x n) is deemed to represent the same fraction as the pair (a, b) whenever n is any non-zero whole number (and where we should not allow b to be zero either).
But even this does not tell us what a fraction is; it merely tells us something about the way in which we represent fractions. What is a fraction, then? According to the mathematician’s ‘‘equivalence class’’ notion, the fraction 3/8, for example, simply is the infinite collection of all
pairs
(3, 8), ( – 3, – 8), (6, 16), ( – 6, – 16), (9, 24), ( – 9, – 24), (12, 32), . . . ,
where each pair can be obtained from each of the other pairs in the list by repeated application of the above cancellation rule.* [ * This is called an ‘equivalence class’ because it actually is a class of entities (the entities, in this particular case, being pairs of whole numbers), each member of which is deemed to be equivalent, in a specified sense, to each of the other members.] We also need definitions telling us how to add, subtract, and multiply such infinite collections of pairs of whole numbers, where the normal rules of algebra hold, and how to identify the whole numbers themselves as particular types of
fraction.
This definition covers all that we mathematically need of fractions (such as 1/2 being a number that, when added to itself, gives the number 1, etc.), and the operation of cancelling is, as we have seen, built into the definition. Yet it seems all very formal and we may indeed wonder whether it really captures the intuitive notion of what a fraction is. Although this ubiquitous equivalence class procedure, of which the above illustration is just a particular instance, is very powerful as a pure-mathematical tool for establishing consistency and mathematical existence, it can provide us with very topheavy-looking entities. It hardly conveys to us the intuitive notion of what 3/8 is, for example! No wonder my mother’s friend was confused.
In my descriptions of mathematical notions, I shall try to avoid, as far as I can, the kind of mathematical pedantry that leads us to define a fraction in terms of an ‘infinite class of pairs’ even though it certainly has its value in mathematical rigour and precision. In my descriptions here I shall be more concerned with conveying the id...
Product details
- Publisher : Knopf (February 22, 2005)
- Language : English
- Hardcover : 1136 pages
- ISBN-10 : 0679454438
- ISBN-13 : 978-0679454434
- Item Weight : 3.4 pounds
- Dimensions : 6.63 x 2.23 x 9.44 inches
-
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4.6 out of 5 stars
4.6 out of 5
770 global ratings
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2.0 out of 5 stars
An erudite but failed effort, far from self-contained: ostensibly targeted at the 'educated layman'
Reviewed in the United States on April 24, 2018Verified Purchase
2.0 out of 5 stars
An erudite but failed effort, far from self-contained: ostensibly targeted at the 'educated layman'
By Vagabond of Letters on April 24, 2018
Let me start off by saying (its relevance will soon be revealed) I have a bachelor of science in mathematics and a master's in computer science (and I wasn't in the bottom 50% of the class), and after the first 300 or so pages (out of 1200) the math in this book (and it's at least 40% or more straight math, not text, and often without text explaining the math) is way above my head and is left often undefined in the text. The author doesn't even do the courtesy of pointing the reader to textbooks where these concepts, such as pseudo-Riemannian geometry and anti-de Sitter spaces and Seiberg/Gromov-Witten manifolds, are defined and can be learned.By Vagabond of Letters on April 24, 2018
The book fails in its promise and purpose to be a self-contained guide to the current mathematical- or theoretical-physical understanding of the universe. Required prerequisites: understanding of linear algebra (Lie, Poisson, Frobenius, Ricci calculus), scalars and higher rank TENSORS (and MORE tensors), several varieties of noneuclidean geometry (Minkowski, de Sitter, Riemann), scalars, topology and n-manifolds, group theory (Lie groups), gauge theory, etc., or the willingness to learn these from expensive secondary sources, because Penrose will not teach you them here and the arguments of the book are incomprehensible without them. Without them, one would be reduced to skimming the 20% of the book that is text (especially the final chapter, which is comprehensible to any semieducated layman) and taking the author's word for the rest of it. Just about the only thing he explains in full is twistor theory (his own invention).
It is far from accessible to the layman (I have postgraduate training in math and I was a good student and its inaccessible to me), and to grasp the concepts in this book, I'd have to spend probably a year of free time and a thousand or more dollars in secondary sources (if I bought them used and cheap). I bought this book to get a $20 overview (like Collier's 'A Most Incomprehensible Thing' for the theories of relativity [I prefer the original 'invariance'], which was technical but self-contained and comprehensible; reading that is the only thing that gave me any knowledge at all of tensors, which this book is chock full of): what I got was in essence a 1200 page bibliography without the authors being noted and without the important works being starred.
This is a very ambitious book which fails utterly in execution.
The author goes from explaining what complex and irrational numbers are and why they are useful (this is freshman high school math) in the introduction to pseudo-Riemannian geometry (this is postgraduate pure math) 200 pages later. He spends about five pages defining all of classical mechanics, and then assumes that you understand classical mechanics. This same breakneck pace is kept up throughout, which is how he manages to range from logarithms and complex numbers to doctoral-level mathematics in 500 or 600 pages. Once he goes out of the pure math and back to applied math (i.e.. physics proper) it gets a little easier but I'd still not recommend trying to tackle this book with less than a bachelor's degree in math (if you're a math nerd and keep your knowledge up) or a master's in math or physics or some other strongly quantitative discipline (if you're not), or a self-taught prodigy in pure maths.
The book promises to be a self-contained guide to the best mathematical understanding of the universe we have, but it ends up more like the author just stuck the important theorems in with a minimum of explanation (he does hit almost all of them: one thing that struck me as unnecessarily erudite - showing off - and odd was the statement of Maxwell's field equations, which is mathematically simple and elegant, in terms of tensors, which are very, very difficult), so it's a complete guide if you already know all of the math (in which case you don't need the book): it's much more of a refresher and quick reference for people who already are familiar with and understand (or at one time understood) the concepts the author represents.
See attached pictures (representative pages from 250-, and these are not nearly the most difficult of the equations): No, you're not the only person going 'smh, wtf' at that math. (Not to mention yet again that many of the terms are never defined in-text! The author goes from explaining that he'll have to use logarithms in the introduction, to this stuff which is Chinese to me as a math major, within a few hundred pages. It seems Penrose let his mathematical understanding [brilliance for all I can tell, I have no idea what he's saying] run away with itself after writing the preface for a book where he's apologetic about using logs and then sticking that preface on this work.)
I still have to award two stars for the obvious intensity and depths of erudition which Penrose funneled in to this work, but only two because it doesn't even partially fulfill its stated purpose or self-description.
*I have familiarized myself additionally with pure math concepts like number theory, group theory, field and Galois theory and combinatorics, along with stochastic calculus and linear algebra to a degree. I am even partially comprehending of tensors after reading 'A Most Incomprehensible Thing', a lay mathematicians' introduction to relativity. In other words, I'm an educated lay mathematician, and the stated target audience for this book is 'educated laymen' with AP high school or gen ed college math in general.
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Reviewed in the United States on August 9, 2018
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Oh what hopes were dashed with this book. Even reviewers with years of mathematics and physics training seem to have been disappointed. This is an extremely difficult and obscure text, at least in the opinion of an educated non-mathematician and lay citizen theoretician, and there will never be any kind of reward for all the torturous eyestrain and wasted time trying to build an edifice out of insubstantial and unclarified blocks of inadequately explained "mathematics." In fact, sometimes the supposed "mathematics" seems more like idiosyncratic opinions attempting to justify some agenda which is never explicitly revealed.
Yeah, I guess I'm an idiot, and I gave up. Reading crap that stops making sense because I really really wish I could understand it is a futile exercise. But I'm probably not going to discard the book, I'll keep it along with Whiteheads "Process and Reality" and Hermes Trismegistus's "Divine Pymander" and Gurdjieff's "Beelzebub's Tales to His Grandson" and other similarly unpenetratable writings to impress people with my book collection (without admitting I couldn't manage to get past the first quarter of many books). Perhaps in my old age I am learning to appreciate neo-Luddite perspectives, and I'm beginning to suspect that books, along with technology, and other people's ideas and philosophies in general, are overrated and distracting, from a certain worldview, to the individual's path of discovery and self-realization. I agree with Penrose about the magic and elegance of the non-Euclidian geometries and logarithms and complex numbers and "e," and it is love and wonder for just that kind of knowledge that motivated me to buy this book and attempt reading it. But I cannot justify paying for a book just because it mentions and recommends learning about fascinating concepts without explaining those concepts in terms a lay person could vaguely understand.
Yeah, I guess I'm an idiot, and I gave up. Reading crap that stops making sense because I really really wish I could understand it is a futile exercise. But I'm probably not going to discard the book, I'll keep it along with Whiteheads "Process and Reality" and Hermes Trismegistus's "Divine Pymander" and Gurdjieff's "Beelzebub's Tales to His Grandson" and other similarly unpenetratable writings to impress people with my book collection (without admitting I couldn't manage to get past the first quarter of many books). Perhaps in my old age I am learning to appreciate neo-Luddite perspectives, and I'm beginning to suspect that books, along with technology, and other people's ideas and philosophies in general, are overrated and distracting, from a certain worldview, to the individual's path of discovery and self-realization. I agree with Penrose about the magic and elegance of the non-Euclidian geometries and logarithms and complex numbers and "e," and it is love and wonder for just that kind of knowledge that motivated me to buy this book and attempt reading it. But I cannot justify paying for a book just because it mentions and recommends learning about fascinating concepts without explaining those concepts in terms a lay person could vaguely understand.
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Reviewed in the United States on July 10, 2015
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While this will not make you a mathematical wizard, it does try and explain calculus, complex numbers (and quaternoins) as well as a host of mathematical topics in laymen terms. Penrose does not stop there – he moves on to advanced topics such as Riemann Surfaces, Group theory (lie groups), fiber bundles, twistor theory (to which Penrose contributed heavily ) and other advanced topics. He offers the reader the option of skipping the math and reading the physics applications of the math. For those interested in problem solving, interesting problems accompany most chapters. His treatment of complex number calculus and his chapter on Quantum Entanglement stand out as above par. If you ever struggled to understand the value of complex numbers or how they simplify actual problem solving, Penrose provides simple and elegant explanations. There is no doubt that a book of such grandiose breadth will attract critics, but overall, the book has more ‘goodies’ than negatives. It is targeted towards a very large audience – from high school students (with some physics and calculus) to the advanced undergraduate student to the layperson with some mathematical exposure – looking to learn more.
While not an easy read, it is a great starting point for anyone looking to get back into physics - by approaching it from the mathematical side (Penrose is actually a mathematical physicist - he holds one of the most prestigious chairs in the world of mathematics). For those who are interested in the NEXT book after this one, I had compiled a list of similar 'self learning' books :
http://www.anujvarma.com/self-learning-booksfor-advanced-physics/
While not an easy read, it is a great starting point for anyone looking to get back into physics - by approaching it from the mathematical side (Penrose is actually a mathematical physicist - he holds one of the most prestigious chairs in the world of mathematics). For those who are interested in the NEXT book after this one, I had compiled a list of similar 'self learning' books :
http://www.anujvarma.com/self-learning-booksfor-advanced-physics/
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Top reviews from other countries
DGC
5.0 out of 5 stars
A good companion book for those studying Physics from text books.
Reviewed in the United Kingdom on May 16, 2016Verified Purchase
I studied Physics at university some 45 years ago, and started a PhD, hoping to go into theoretical physics, but went into electronic and software engineering instead. Since retiring I have been buying numerous text books to refresh my memory and try and get to grips with the topics in modern theoretical physics.
This book covers the various maths topics I've been grappling with, e.g manifolds, differential forms, fibre bundles etc, plus fundamentals of quantum field theory, general relativity, string theory and so on.
It treats these in a coherent way from a pure mathematics viewpoint, and which I find very interesting.
The book is certainly not an easy read, even for people with some maths background, and frequently jumps between straightforward and esoteric new topics. But I'm making progress, currently up to page 200, so only 900 pages to go!
It is a good companion for my text books on the various topics it covers, and I would heartily recommend it.
This book covers the various maths topics I've been grappling with, e.g manifolds, differential forms, fibre bundles etc, plus fundamentals of quantum field theory, general relativity, string theory and so on.
It treats these in a coherent way from a pure mathematics viewpoint, and which I find very interesting.
The book is certainly not an easy read, even for people with some maths background, and frequently jumps between straightforward and esoteric new topics. But I'm making progress, currently up to page 200, so only 900 pages to go!
It is a good companion for my text books on the various topics it covers, and I would heartily recommend it.
20 people found this helpful
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David Irvine
4.0 out of 5 stars
A very hard read.... But enlightening
Reviewed in the United Kingdom on September 9, 2021Verified Purchase
Having graduated 40+ years ago with a degree in computer science and mathematics, and having read about the first 100 pages so far I can honestly say I have understood about 1/3 of what I have read. I'm sure it's going to get harder as I progress through Roger Penrose's Road to Reality, but it is addictive and very thought provoking. The sad thing is I think Roger Penrose is trying to explain many concepts clearly and topologically, and maybe 5+ years ago I would of grasped most of the wonderful concepts. But I do get a 'flavour' of what Roger Penrose is explaining. Fascinating!
Only 4 stars because I think this book does require degree level mathematics or physics to be able to grasp many of the ideas.
Only 4 stars because I think this book does require degree level mathematics or physics to be able to grasp many of the ideas.
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Aidan B
5.0 out of 5 stars
Great, but not an easy read.
Reviewed in the United Kingdom on August 23, 2019Verified Purchase
Great, but not an easy read. I am not far through yet, but it seems to get quite tough deeper into the book. It's fairly ironic as I was reading this hoping to have some easy "popular science" physics with the amazing perspective of Sir Roger Penrose.
Having said that, it is for the better that this requires a bit of thought to go through as the insights that Sir Roger Penrose has into the relationships between maths and physics in different areas is great, and definitely gets one pondering!
From what I can tell, a lot of the book focuses on maths, before delving more deeply into the physics. In terms of the physics (and maths), I would definitely say that you might get more from the book (and it would be easier to read) if you already have some previous knowledge on the topics so that you can tell the difference between his opinion and 'generally accepted' scientific fact.
Having said that, it is for the better that this requires a bit of thought to go through as the insights that Sir Roger Penrose has into the relationships between maths and physics in different areas is great, and definitely gets one pondering!
From what I can tell, a lot of the book focuses on maths, before delving more deeply into the physics. In terms of the physics (and maths), I would definitely say that you might get more from the book (and it would be easier to read) if you already have some previous knowledge on the topics so that you can tell the difference between his opinion and 'generally accepted' scientific fact.
2 people found this helpful
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Stavros Karapanos
5.0 out of 5 stars
The quality of the received book was decent. The delay was due to Covid-19, so it was expected.
Reviewed in the United Kingdom on May 10, 2020Verified Purchase
After I heard two podcasts, by Lex Fridman - AI Podcast, who hosted Sir Roger Penrose and another with Eric Weinstein (Podcast #88), where after a question that has been made by Lex Fridman at 1:33:35 Eric Weinstein mentions this book as "a self contained invitation to understand our deepest nature". The above podcasts prioritized again this book to my purchase list.
5 people found this helpful
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Basque-refugee-13
3.0 out of 5 stars
I've only given this book three stars because I don't ...
Reviewed in the United Kingdom on November 22, 2015Verified Purchase
I've only given this book three stars because I don't believe it does what it says on the box. The blurb states, "It assumes no particular specialist knowledge on the part of the reader, so that, for example, the early chapters give us the vital mathematical background to the physical theories explored later in the book.
However, I found the mathematics in the first nine or ten chapters quite demanding ( that's as far as I had the patience to go), and anyone without a solid scientific background would be completly lost by the end of chapture 2. Each chapter has large numbers of problems so that the reader can check they are keeping up with the arguments. I very much doubt that, with the possible exception of a few wunderkind, any non-specialist has ever read the book in the way the writer obviously intended. If you can do the maths in this book, or even follow them with any confidence, then I think you would probably have little difficulty passing a first degree in mathematics. That is not my idea of a general reader.
For now, the book is parked on my bookshelf awaiting the time when I can give it the attention that I am sure it deserves, and perhaps it will provide no end of entertainment when I retire. Until then I shall stick to lighter reading.
However, I found the mathematics in the first nine or ten chapters quite demanding ( that's as far as I had the patience to go), and anyone without a solid scientific background would be completly lost by the end of chapture 2. Each chapter has large numbers of problems so that the reader can check they are keeping up with the arguments. I very much doubt that, with the possible exception of a few wunderkind, any non-specialist has ever read the book in the way the writer obviously intended. If you can do the maths in this book, or even follow them with any confidence, then I think you would probably have little difficulty passing a first degree in mathematics. That is not my idea of a general reader.
For now, the book is parked on my bookshelf awaiting the time when I can give it the attention that I am sure it deserves, and perhaps it will provide no end of entertainment when I retire. Until then I shall stick to lighter reading.
19 people found this helpful
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