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281 of 287 people found the following review helpful
5.0 out of 5 stars
One of Feynman's best,
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This review is from: QED: The Strange Theory of Light and Matter (Princeton Science Library) (Paperback)
Caveat  Be sure to read Professor Zee's introduction as well as Feynman's introduction before you read the rest of the book. More about this at the end of this review.
In my opinion this is one of the best of Feynman's introductory physics books. He does close to the impossible by explaining the rudimentary ideas of Quantum Electro Dynamics (QED) in a manner that is reasonably accessible to those with some physics background. He explains Feynman diagrams and shows why light is partially reflected from a glass, how it is transmitted through the glass, how it interacts with the electrons in the glass and many more things. This is done via his arrows and the rules for their rotation, addition and multiplication. One reviewer has criticized this book because Feynman does not actually show how to determine the length of the arrows (the square of which is the probability of the action being considered occurring) and the how you determine their proper rotation. True, but as is stated in Feynman's introduction, this was never the intention of the book. If you want to learn how to create the arrows used in a Feynman diagram and use them to solve even the most rudimentary problem, you have to major in physics as an undergraduate, do well enough to get into a theoretical physics graduate program and then stick with the program until the second year, when you will take elementary QED. You will then have to take even more classes before you can solve harder problems. Clearly, it is not possible to do all this in a 150page book aimed at a general audience. He does, however, give the reader a clear indication of what these calculations are like, even if you are not actually given enough information to perform one on your own. Feynman is fair enough not to hide the difficulties involved in actually computing things. He briefly discusses the process of renormalization (that he admits is not mathematically legitimate), which is required to get answers that agreed with experimental data and the difficulties in determining the coupling constants that are also required. In the end, he admits that there is no mathematically rigorous support for QED. Its virtue lies in the fact that it provides the correct answers, even if the approach to getting them involve a bit of hocuspocus (again his words). The last 20 pages of the book show how the approaches used in QED, as strange as they are, were used to create an analogous approach for determining what goes on in the nucleus of an atom. This short section shows complexity of nuclear physics and the role that QED has played in trying to unify a baffling plethora of experimental data. Unfortunately, this last section is largely out of date and is hopelessly complicated. Fortunately, it is only 20 pages long. As mentioned in the beginning of this review, you should read Zee's introduction as well as Feynman's, before you get into the rest of the book. Zee puts QED into proper perspective. Along with wave and matrix mechanics, the DiracFeynman path integral method that is described in this book is another approach to quantum mechanics. Zee also points out that while it is a very powerful approach for many problems, it is unworkable for others that are easily solved by wave or matrix mechanics. Feynman's introduction is very important because he emphatically states that photons and electrons are particles and that the idea of their also being waves stems from the idea that many features of their behavior could be explained by assuming that they were waves. He shows that you can explain these effects using QED, without having to assume that they are waves. This eliminates the many paradoxes that are created when one assumes that photons and electrons exhibit dual, wave/particle behavior. QED is not, however, without its own complications. Some of this behavior depends upon the frequency of the photon or electron. Frequency is generally thought of as a wave property, but it can also be thought of a just a parameter that defined the energy of the photon or electron. This is a fundamental idea separating QED from wave based quantum theories. Feynman does not try to speculate why photons and electrons obey the rules of QED because he does not know why, nor does anyone else and we probably are incapable of knowing why. He is completely satisfied that his calculations agree with experimental data to a degree that is unsurpassed by any other theoretical physics calculation. I would recommend this book to anyone who is interested in getting an idea of what QED is all about and to those who seek a deeper understanding of physical phenomena. You will learn how QED explains many things, some of which from the basis for the paradoxes discussed at length in books such as "In search of Schrodinger's cat". Reading this book is a good antidote for the head spinning paradoxes described in that book. Feynman believes that they stem from using a poor analogy (that of waves) to explain the behavior of particles. As far as the deeper questions of why photons and electrons obey the ruled of QED, he does not care, so long as he can get the right answer. This may therefore not be the book for you if you are interested in this deepest WHY, but it definitely is if you want to know more about Feynman's powerful approach to quantum mechanics.
57 of 58 people found the following review helpful
5.0 out of 5 stars
Highly comprehensible,
By Ian J. Miller (Lower Hutt, New Zealand)  See all my reviews
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This review is from: QED: The Strange Theory of Light and Matter (Princeton Science Library) (Paperback)
This book covers four lectures that explains QED in terms of the path integral method, which was developed by the author. Needless to say, this is authoritative on this approach, but it also remarkably clear and comprehensible. Notwithstanding that, I would recommend slow and careful reading, as you may find a small sequence of statements that seem perhaps a little unjustified. Later, Feynman fronts up to some of these, and explains why he oversimplified to get things going. If you see them first, and this is not unreasonable, I believe you will get more from the text. The first lecture is a general introduction that shows how the path of the photon as a particle can be followed in terms of timeofflight from all possible paths. The assertion is, the photon is a particle, not a wave, however there is no explanation for why there is a term that I would call the phase. The second lecture is a tourde force and explains in terms of this particle treatment, why light reflects and diffracts, and is particularly interesting in why light behaves as if it is reflected only from the front and back of glass, whereas it is actually scattered by electrons throughout the glass. The third lecture covers electronphoton interactions, and covers Feynman diagrams and shows why QED is the most accurate theory ever proposed. The fourth lecture may seem a bit of a disappointment. The author tries to cover a very wide range of phenomena, which he terms "loose ends", and in some ways this chapter has been overtaken somewhat, nevertheless it also gives a look into Feynman's mind, and that also is well worth the price of the book. It is also here that the issue of renormalization is discussed  if you could call Feynman admitting it is "a dippy procedure" a discussion.
Why buy the book? I suspect this is probably the best chance a nonspecialist has of understanding the basis of QED. The biggest disappointment? Feynman dismisses wave theory, which everybody else uses, and replaces it with a monumental raft of integrals. My initial thoughts were that waves are effectively an analogue way of solving those integrals, perhaps a gift from nature, and it is a pity I can't ask Feynman why that option was dismissed.
139 of 150 people found the following review helpful
5.0 out of 5 stars
Finally understood refraction,
By M. Greene (Salinas, Ca United States)  See all my reviews
This review is from: QED: The Strange Theory of Light and Matter (Princeton Science Library) (Paperback)
When I was a senior in high school, I asked my physics teacher why light bent when it entered a lens. He responded with an analogy about soldiers marching on a field and entering a marsh. The first soldiers entering the marsh would slow down and "bend" the column until all the soldiers were in the marsh.
The analogy made no sense to me because we were talking about light, not soldiers. He responded that light travels in waves and if I viewed the soldiers as a wave front, I could understand his analogy. I left the conversation feeling very stupid for not "getting it." and thinking the analogy had so many holes in it. For example, it didn't explain why the lens was a marsh as far as light goes. It wasn't until I read QED that I realized I didn't get the soldier analogy because my teacher was wrong  light doesn't travel in waves, it travels in discrete little packets called photons. In QED, Feynman opens his first chapter by saying a couple of things. First he tells you that the theory he's going to describe to you has been experimentally verified out to 10 decimal places so it's probably right. He then gives you a quick review of what matter is and then tells you "light comes in particles. Not waves, particles." No wavicles, just little bits of light. He tells you that photons go from place to place, an electron goes from place to place and the electron will sometimes either absorb or emit a photon. From that basis, the rest of the book shows how that model explains why light bends when it enters a lens, why mirrors reflect, why oil slicks show different colors, why peacock feathers iridesce along a with host of other phenomena. He also explains why light has wavelike properties despite the fact that light comes in packets. The first reviewer is right  there are questions left unanswered but that doesn't diminish the book. The framework Feynman develops in four chapters gives you a clear mental image of what's going on. Bohr and Pauli disliked Feynman's approach because it violated the Copenhagen approach of eschewing all models. In their view, only mathematics would suffice to understand quantum mechanics. I for one, am very glad Feynman ignored them, developed his approach and eventually gave the 4 lectures that are the basis of the book. If you think light travels in waves, read this book. It's truly wonderful. If you're as dumb as I am, you'll have to read it multiple times but it's definitely worth it.
19 of 19 people found the following review helpful
5.0 out of 5 stars
Quantum field theory for pedestrians,
By
This review is from: QED: The Strange Theory of Light and Matter (Princeton Science Library) (Paperback)
Quantum Electro Dynamics (QED) is the fundamental theory that explains all the physics you'll ever experience (assuming you're not a nuclear physicist and neither have plans to plunge into a black hole). QED is the result of unifying Einstein's special relativity with quantum mechanics, and forms the leading example for virtually all fundamental physics developed in the second half of the twentieth century.
Can the key ideas and principles of such a deep theory be explained to 'the average interested Joe'? With this book Feynman demonstrates it is possible. So is this the book for YOU? It depends. I think the best way to see whether this book matches your expectations is to read Zee's superb introduction. Unfortunately, the 'Look Inside' preview functionality is missing for this book. However, Zee's introduction to QED is available via his website: [...] Have a look, and you'll know whether this book fits your expectations.
13 of 13 people found the following review helpful
4.0 out of 5 stars
adding arrows,
This review is from: QED: The Strange Theory of Light and Matter (Princeton Science Library) (Paperback)
I highly recommend this book to anyone without a formal background in quantum physics or higher math who is interested in learning about the modern explanation for how the world works at the atomic level. Richard Feynman is one of the originators of this worldview, and in this book manages to present an explanation which is at once true to the actual math while avoiding actually delving too deeply into the math. It's all about the math because as someone once said, "mathematics is the language of physics". That Feynman was able to carry off this seemingly impossible feat is evidence of his exceptional teaching ability. As he once said, if you can't explain something to a freshman, you don't really understand it.
In a nutshell, he explains that everything that happens in the world of atoms and light particles is governed by probability and chance. Every event has a certain numerical factor associated with it called an "amplitude", and the probability of the event occuring is the square of the amplitude. He doesn't get into the very complicated math of actually calculating the amplitude, but he explains two fundamental rules about amplitudes: first, if a single event can happen in more than one way, such as a light particle going from point A to point B by more than one path, then you add the amplitudes for each way the event can happen and then square the sum to determine the probability of the event happening. On the other hand, if there is a sequence of events, first event 1 then event 2, for example first a light particle goes from point A to point B, then from point B to point C,you multiply the amplitude for event 1 times the amplitude for event 2 and then square the product to get the amplitude for the sequence of events to occur. Then he explains that an amplitude can be thought of as an arrow, with both a length and a direction, and that to add amplitudes you line up all the individual arrows tip to tail, draw one big arrow from the first tail to the last tip, and that arrow is the amplitude which is the sum of the individual amplitudes. (I forget how you multiply the arrows.) Then he gives an example using partial reflection of light from glass, a mystery known since Newton's time which was not solved until the advent of quantum theory. Here light particles are emitted from a source, travel to a glass surface, and a certain percentage bounce off the front side of the glass and go back to a detector, the percentage varying from 0 to 4% based on the thickness of the glass. The mystery has been how the light bouncing off the front surface knows how thick the glass is. He shows that in order to solve the mystery, you have to include an amplitude for every path that a light particle can take from the light source to both the front surface and back surface of the glass and back to the detector, including loopdeloops that go around Jupiter 15 times, and paths that go to the far end of the universe and back. Since these are all different ways the same event can occur, the rule for amplitudes says you have to add all these amplitudes to get the final amplitude. I.e., you have to add up all the amplitudes for every possible path the particle can take to either surface, no matter how crazy. And then if you do, you find that you end up with an amplitude which is basically the same as if you had the light particle going in the shortest possible path (i.e., a straight line) directly from the source to the front surface of the glass and then back again back by the shortest possible path (i.e., a straight line) to the detector, just like we "know" light does, and varying with the thickness of the glass just as observed. But if you don't include all possible paths in your summing up of the amplitudes, you won't get the right answer for partial reflection! This is all so cool and fascinating. You end up actually seeing how the mathematical apparatus of quantum electrodynamics explains this phenomenon, without having to know that the arrows are actually complex numbers, and that adding, multiplying, and squaring arrows is just the arithmetic of complex numbers. As the Guinness man says, "brilliant"! For those who enjoyed the book, or want to learn more, or are confused, or learn better by listening and watching than by reading, I highly recommend watching a series of four lectures Feynman gave at the University of New Zealand in Auckland in the sixties, which goes over the same material. You get the inimitable Feynman persona, with interesting asides on the Mayans, and astronomy, and all sorts of other tangentially related topics, delivered in a quintessential New York accent, accompanied by diagrams in multicolored chalk on the blackboard. It's available on the world's most well known Internet video site, which I'm not sure I can mention by name in this review, so I won't. Each lecture is an hour and a half, but in my opinion worth every minute.
10 of 10 people found the following review helpful
5.0 out of 5 stars
One of my favorites,
By Tyler Forge "realist" (Sunnydale, CA)  See all my reviews
This review is from: QED: The Strange Theory of Light and Matter (Princeton Science Library) (Paperback)
I bought an earlier printing of QED well over a decade ago. It is one of those books that continues to intrude on your thinking for many years. My physics education stopped just after statistical field theory  in other words I was already comfortable with the material covered by QED and this book is on my shelf next to a QED book with far more nuts and bolts type details. The Feynman book is far more worn from use.
I know it's geeky, but I I've even referred to it to help clarify philosophical arguments. After all, it's just the nature of our perceived reality. I enjoy Feynman's writing because I find him to be a very deep and insightful thinker in general. As a philosopher, he uses physics as the lens to focus and discipline his thoughts. He then presents his conclusions with astounding clarity.
9 of 9 people found the following review helpful
5.0 out of 5 stars
A Fantastic Theory,
By
This review is from: QED: The Strange Theory of Light and Matter (Princeton Science Library) (Paperback)
Even though these lectures are more than 20 years old, Feynman did an incredible job of explaining a fundamental concept in Physics. I can see now why he received the Nobel prize for his work in this area. I would call him the Carl Sagan of Physics, except that Mr. Sagan's popularity came later in time. QED is so bizarre and incredible, yet so accurate and powerful a theory that it boggles the mind! Mr. Feynman's explanation is so complete and articulate that anyone can understand it. This theory explains the physical underpinnings of most of our daily experience, the interactions of photons with matter, yet it is a complete surprise!
9 of 9 people found the following review helpful
5.0 out of 5 stars
Awed by the actual complexity of nature (unlearned years of oversimplification that was inaccurate),
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This review is from: QED: The Strange Theory of Light and Matter (Princeton Science Library) (Paperback)
This is one of my favorite books of all time. This book changed the way I view the world and was inspiring.
Throughout high school and college, we are taught statements that light moves in a straight line as facts. The reality is that this is not a fact but rather a simplification. The real mechanisms which this book explains are not that much harder to understand but a lot more beautiful, interesting and amazing. I unlearned years of Physics I was taught and am now even more interested in learning more. Feynman not only makes reading this book rewarding but also very easy. One of the things I greatly appreciate is that Feynman does not simplify without letting you know what he is doing and why. I wish that someone when I was in high school had told me that light appearing to move in a straight line is a simplification of a complex process of interactions of photons with each other. At that age I may not have bother to learn the reality but at least would have kept my mind open. I recommend this book to everyone curious and interested in how nature works. I am reading my copy for the third time now and it still continues to awe me.
10 of 11 people found the following review helpful
4.0 out of 5 stars
College Physics came racing back to me fullspeed. Fascinating read!,
By
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This review is from: QED: The Strange Theory of Light and Matter (Princeton Science Library) (Paperback)
I didn't know exactly what to expect, but bought this based on suggestions from a blog. It is actually a transcript of a series of lectures from Feynman and not specifically a book, per se.
That may be a good thing though, as a lecture is probably a little lighter reading and this is heady stuff. Quite a bit of the beginning of the book is introductions and anecdotal stories about the various popphysicists. Once you get into the actual lectures, you jump right into light as a wave vs a particle and it goes straight into the building blocks of the universe and what understand (and don't understand) about them. The nice thing is that this is intended for the educated reader, but not for the PhDinAtomicPhysics reader. So if you have a basic grasp of physics, you will likely be able to follow this book. If you hated science, this won't magically open the world of particle physics to you. My only real complaint about the book is the location of the diagrams. Often the text will be talking about something that is two pages away in the diagrams and I found myself looking at the wrong diagram and being confused, or having to flip back and forth between a couple of pages to find the correct diagram once I figured out what was going on. This is distracting and unnecessary. Overall, highly recommended as a challenging read for anyone who has an interest in physics and the building blocks of our universe and a desire to stretch their brainmuscles a little bit once again.
6 of 6 people found the following review helpful
5.0 out of 5 stars
A bridge for nonexpert into properties of quantum phenomenon,
By A. Menon (Hong Kong)  See all my reviews
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This review is from: QED: The Strange Theory of Light and Matter (Princeton Science Library) (Paperback)
I personally feel a bit silly writing a review about the merit's of Feynman's QED... The book is a masterpiece and a prime example of a world class physicist bringing to the non expert the basic tools that are used to describe the universe we live in. The writing is lively and perfectly paced. Rather than most quantum mechanics for lay people literature, this really does describe a methodology for understanding the real results of experiments that are discussed. Feynman developes an ingenious method of arrows with clocks and how these particles with clocks explain waviness if one imagines the clocks as measuring the wave properties of the experiment.
The book describes using the framework developed within the book, the path integral description of quantum mechanics. That sounds more complicated than it actually is... The author describes how when summing over all the trajectories of the vectors he has constructed one naturally can predict/explain the outcome that seems so unintuitive. The glass experiment, reflection properties and oscillation properties set as a lucid example of path integral formalism at work. Feynmen develops the framework to the furthest extent he can and stops before spin which would complicate the formalism. I am not a physicist and do not have the training and this book really cleared up a lot (it probably introduced more questions than answers, but thats a good thing). The dscription of particles running a clock as a representation of a wave (implicitly that is how its used to measure the probability amplitude) is genius and it actually gives me a proper mental picture of how to think about quantum phenomenon. Again, i feel a bit silly reviewing this book, i dont feel like my words of praise really do any justice to it, but if at least my positivity encourages others to read this book, then that is good enough. 
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QED: The Strange Theory of Light and Matter (Princeton Science Library) by Richard P. Feynman (Paperback  April 24, 2006)
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