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6 of 7 people found the following review helpful
5.0 out of 5 stars Quantum Electrodynamics (QED) made easy, 11 Dec. 2008
This review is from: QED: The Strange Theory of Light and Matter (Princeton Science Library) (Paperback)
The author is one of the greatest physicists of 20th century, and highly regarded as one of the best instructors of physics, but the reader must have some knowledge of science and strong interest in physics, and appreciate optical phenomenon; reflection of light, refraction, etc. Reading this book at first may be boring, but reading for second or third time gives you a good idea about the theory and help you understand the elegance with which the author has conveyed the material. Quantum Electrodynamics (QED) is a fundamental theory of light (photon) - matter (particle) interaction or electric field and charge interaction. The author explains how we can calculate this interaction. There are only three basic actions associated with light and electron interaction. First, a photon goes from place to place; second, an electron goes from place to place; and third, an electron emits or absorbs a photon. Each of this has amplitude - an arrow (vector) that can be calculated according to certain rules. There is no mathematics in the book but the logic, and assumptions are explained which may be difficult to assimilate unless you like to understand QED.

When an electron travels from one point to another in spacetime, it uses multiple paths before arriving at its destination according to quantum physics. It can also absorb or emit light multiple times during its path. Therefore one needs to calculate the probability of its most likely path and also the number of times it absorbs or emits radiation. Emission of light could occur when an electron interacts with positrons (antiparticle) that results in their annihilation. QED incorporates corrections to one or more photons being emitted and absorbed in its path and also all other possible paths the electron may take. All these are considered to calculate the mist likely path for its travel.

The second factor to be included in the calculation is that light has amplitude to go faster or slower than the conventional speed of light. Therefore the emission and absorption of light between two electrons could occur with three possibilities. One, the emission occurs before absorption, second, emission occurs at the same time as absorption, and third, emission occurs after absorption. The last possibility looks puzzling since light is required to go backwards in time. This is possible in mathematical calculations, and photons are said to be exchanged and the locations are used in spacetime in the formula. Additional possibilities to consider are; two and more photon exchange could occur. If we consider the effect polarization, the coupling factor j for backward moving electron is positive, hence the charge is positive and the electron is referred to as positron.

The formula calculates two numbers known as n (mass for a fake electron) and j (coupling parameter; charge of a fake electron). For a real electron, n = mass experimentally determined, and j = charge experimentally determined. The author explains the complexities in the calculation of these two numbers which are used in the formula that calculates the amplitude of electron - photon interactions.

For an atom which contains a nucleus at the center and electron in the orbit; nucleus is heavy and hence considered stationary and the electron moves in spacetime with respect to nucleus in the QED analysis. The dynamics include; electrons and nucleus exchange photons, and the photons from outside is scattered by the electron of the atom. The total amplitude of all electron scattering depends on the arrangement of electrons in the atom and they are variously called s, p, d and f orbitals that accounts for the entire chemistry and chemical reactions of elements.

1. Quantum Electrodynamics (Advanced Book Program)
2. Molecular Quantum Electrodynamics
3. Introductory quantum electrodynamics (Mathematical physics series;no.4)
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Initial post: 3 May 2010 10:12:02 BDT
Last edited by the author on 3 May 2010 10:12:59 BDT
A. Deacon says:
"Rama" is doing okay in his first paragraph except for the bit about the first read of QED being "boring". My first read, far from being "boring", left me reeling with the simplicity and elegance and power and implications of Feyman's explanation. Your first read, I speculate, will be more like mine than Rama's.

In the rest of Rama's review he (or she) tries to explain (why?) QED. Don't worry if you don't follow Rama's explanation, Feynman's is far more lucid.

I can't comment on Rama's "further reading" recommendations, I haven't read them. But in reviews it's always useful (well, nearly always) to have suggestions for further, or alternative reading.
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