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QED: The Strange Theory of Light and Matter
 
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QED: The Strange Theory of Light and Matter [Format Kindle]

Richard P. Feynman , A. Zee
4.0 étoiles sur 5  Voir tous les commentaires (1 commentaire client)

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Celebrated for his brilliantly quirky insights into the physical world, Nobel laureate Richard Feynman also possessed an extraordinary talent for explaining difficult concepts to the general public. Here Feynman provides a classic and definitive introduction to QED (namely, quantum electrodynamics), that part of quantum field theory describing the interactions of light with charged particles. Using everyday language, spatial concepts, visualizations, and his renowned “Feynman diagrams” instead of advanced mathematics, Feynman clearly and humorously communicates both the substance and spirit of QED to the layperson. A. Zee’s introduction places Feynman’s book and his seminal contribution to QED in historical context and further highlights Feynman’s uniquely appealing and illuminating style.


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4.0 étoiles sur 5 Nice book 7 septembre 2014
Par jaime
Format:Broché|Achat vérifié
It's not a book with a formal theory of QED but with a transcription of four conferences he gave in Australia. As all his books, has a different approach really insightful which opens your mind and takes you to rethink all you think you knew.
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Amazon.com: 4.7 étoiles sur 5  108 commentaires
286 internautes sur 292 ont trouvé ce commentaire utile 
5.0 étoiles sur 5 One of Feynman's best 17 octobre 2007
Par Metallurgist - Publié sur Amazon.com
Format:Broché|Achat vérifié
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 150-page 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 hocus-pocus (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 Dirac-Feynman 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.
58 internautes sur 59 ont trouvé ce commentaire utile 
5.0 étoiles sur 5 Highly comprehensible 20 juillet 2008
Par Ian J. Miller - Publié sur Amazon.com
Format:Broché|Achat vérifié
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 time-of-flight 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 tour-de 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 electron-photon 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 non-specialist 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.
141 internautes sur 152 ont trouvé ce commentaire utile 
5.0 étoiles sur 5 Finally understood refraction 16 avril 2007
Par M. Greene - Publié sur Amazon.com
Format:Broché
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 wave-like 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 internautes sur 19 ont trouvé ce commentaire utile 
5.0 étoiles sur 5 Quantum field theory for pedestrians 1 février 2009
Par J. Koelman - Publié sur Amazon.com
Format:Broché
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 internautes sur 13 ont trouvé ce commentaire utile 
4.0 étoiles sur 5 adding arrows 21 octobre 2010
Par arpard fazakas - Publié sur Amazon.com
Format:Broché
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 loop-de-loops 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 multi-colored 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.
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