It's all arrows, man. All about arrows. Physics is not a subject I have a terribly good grasp on mainly because my eyes glaze over at the sight of advanced mathematical equations, however Feynman is a pretty great at making the complex subjects of particle physics and quantum mechanics intelligible to the layest of laypersons. Fortunately I also read this with able-minded people who translated the math into clearer ideas which of course opened things up to broader philosophical speculation--something I am pretty good with. The introduction to the book is also worth reading by itself at the very least.

"I think I can safely say that nobody understands quantum mechanics."

-Richard Feynman

He was also a very funny and clever man who left behind a whole host of aphoristic gems, for instance:

"A poet once said, 'The whole universe is in a glass of wine.' We will probably never know in what sense he meant it, for poets do not write to be understood. But it is true that if we look at a glass of wine closely enough we see the entire universe. There are the things of physics: the twisting liquid which evaporates depending on the wind and weather, the reflection in the glass; and our imagination adds atoms. The glass is a distillation of the earth's rocks, and in its composition we see the secrets of the universe's age, and the evolution of stars. What strange array of chemicals are in the wine? How did they come to be? There are the ferments, the enzymes, the substrates, and the products. There in wine is found the great generalization; all life is fermentation. Nobody can discover the chemistry of wine without discovering, as did Louis Pasteur, the cause of much disease. How vivid is the claret, pressing its existence into the consciousness that watches it! If our small minds, for some convenience, divide this glass of wine, this universe, into parts -- physics, biology, geology, astronomy, psychology, and so on -- remember that nature does not know it! So let us put it all back together, not forgetting ultimately what it is for. Let it give us one more final pleasure; drink it and forget it all!"

Its a subject that got glazed over when I was in Engineering and after that, a wiki entry that I frequented whenever I had questions. Feynman targets this book to, well, everyone. He holds your hand and shows how things work. Its a slow step by step process and if you invest some time, its highly rewarding and quite refreshing to be taught physics by a man who is long dead but doesn't really feel so when you read his words. You get transposed to his classroom as he explains basic concepts and the paradox surrounding the most natural thing in this world: light.

Its a re-read which I enjoyed and will get on to re-reading some of his other famous lectures.

Che l’enorme varietà della Natura sia il risultato di una monotona ripetizione di tre eventi base in varie combinazioni non è un’idea facile da accettare.
Ma è proprio così.

I understand a little more than zero about quantum electrodynamics now. Honestly, this book made me appreciate the simplifying power of math. Since Feynman was trying to explain all of these concepts without math, he would go on for paragraphs sometimes explaining something that could have been written as a simple formula. Because of that, the lack of math in this book ended up being a hindrance to my personal understanding. That said, physics is wacky and counterintuitive, and I'm glad I increased my knowledge in this area

My reaction upon finishing this book:



(Any excuse for a Breaking Bad reference.)

Seriously, though, this is one of the best pop science books I’ve yet encountered. I read Surely You're Joking, Mr. Feynman!: Adventures of a Curious Character last year, and was thoroughly impressed by Feynman’s animated personality and his passion for physics. Now I find myself even more impressed by his exceptional teaching ability. QED: The Strange Theory of Light and Matter is a collection of 4 lectures he gave to the general public on the subject of quantum electrodynamics. The book is intended for laypeople, is written in very accessible language, and provides “Feynman diagrams” instead of advanced mathematical formulae. A rather lengthy summary of these fascinating lectures follows. If you don’t want any spoilers, or whatever you want to call them, then skip ahead to the final paragraph.

The first lecture deals with photons, and how light behaves like particles. This is discussed in detail w.r.t. the partial reflection of monochrome light by glass. There’s already some fascinating shit right here, let me tell you! See, physicists can’t predict which photons will get reflected and which will pass through the glass. All they can tell you is the overall probability that it will happen. In other words, “identical photons are always coming down in the same direction to the same piece of glass,” and this somehow winds up “producing different results” each time. Who knew that “partial reflection by a single surface” was a “deep mystery and a difficult problem”?! Bizarre.

Feynman then teaches us how to calculate the probability of photons bouncing off either the front or the back surface of sheets of glass of varying thickness. The lecture concludes with a discussion of iridescence (the colors produced by the reflection of white light by two surfaces). Neat-o.

In the second lecture, Feynman uses QED to explain why, when light reflects off a mirror, the angle of incidence is equal to the angle of reflection. This is weirder than you might assume. (Actually, “weirder than you’d assume” sums up the entire book remarkably well!) The phenomenon discussed here is also the basis for diffraction gratings. Then he covers how light travels from air into water, and what causes mirages.

Feynman goes on to explain why light appears to travel in straight lines. Incredibly, it behaves as such only when you give it enough wiggle room, so to speak. For “when you try to squeeze light [or restrict its path] too much to make sure it’s going in only a straight line, it refuses to cooperate and begins to spread out.” This is not altogether dissimilar to the behavior of surly teenagers. Perhaps we can reasonably refer to them as “little rays of sunshine” in an unironic fashion from now on! :D Bad joke, sorry. Anyway, the manner in which focusing lenses work is next revealed, and the lecture concludes with how quantum theory calculates the probability of compound events.

The third lecture introduces electrons, which behave similarly to photons: somewhat like waves, somewhat like particles. (Feynman jokes about “wavicles,” a term I actually love to death, and will enthusiastically champion from now on!) We learn of the three basic actions from which all the phenomena of light and electrons arise: 1) photons rollicking about, 2) electrons rollicking about, and 3) electrons emitting or absorbing photons. As per the first item, we learn that “light doesn’t go only at the speed of light.” So yeah, that happens. It’s anarchy, I tell you! Madness! And the third action is even stranger. Hint: time travel may or may not be involved. Oh, you beautiful, depraved little positrons, you.

Next, Feynman covers how electrons behave in atoms. He re-examines the partial reflection of light from glass in far greater detail than he did earlier, and we can now see why the former simplification was in fact warranted. (We previously treated light as reflecting from the “front” and ”back” surfaces of a sheet of glass, as opposed to what light actually does, which is to be scattered by the electrons inside the glass.) This scattering is also the reason light appears to move more slowly in glass or water than it does in a vacuum or in air. Also of interest is how lasers work: photons tend to go to the same point in space-time. (These lunatics are predisposed to travel in packs!) It turns out the reverse is true for electrons. Their aversion to one another is known as the “Exclusion Principle,” and helps explain chemical properties of atoms.

Before finishing the lecture by discussing polarization, Feynman examines the complexity of the magnetic moments of electrons. This is fairly bananas, even considering the fact that the entire book is pretty much out to lunch. Here is what can happen: an “electron goes along for a while and suddenly emits a photon; then (horrors!) it absorbs its own photon. Perhaps there’s something ‘immoral’ about that, but the electron does it!” (You really have to love his sense of humor.) I’ve included some Feynman diagrams which depict this wanton immorality:



The fourth and final lecture deals with some problems associated with quantum theory. It also looks at the relation of QED to the rest of physics, and includes a discussion of fundamental particles such as quarks and gluons, to name but a couple.

Overall, this short book is packed full of mind-blowing information. I really appreciated all of the helpful diagrams that illustrate the very peculiar concepts under discussion. Also, Feynman is an excellent teacher. I just loved his occasional bursts of exuberance and humor. His enthusiasm for his subject is irresistible, his subject itself truly extraordinary.

Throughout the years of reading both popular and less-popular science, I’ve kind of steered clear of Richard Feynman. The main reason is that what others describe as a “larger than life persona” I tend to describe as really bloody annoying, what with his bongos and womanizing and oh-so-clever quips where he always gets the upper hand with the old and rusty physics establishment. Having now fought my way through QED, I can see that this may have been a mistake. My annoyance with his autobiographical works has kept me away from some truly gorgeous scientific writing.

The thing is, I’m not sure if it is even possible to explain quantum mechanics properly without all the higher math, but if it is possible, this is likely the only proper way – with a lot of “this is how it is, and don’t ask why, because even we, physicists, do not know”, and a lot of weird and unexpected analogies, such as his substitution of “little clock hands” for the harmonic oscillator that pops up every which way in QM. The only problem I had was that knowing the “proper” theory it took me a while to fully intuitively accept and adopt his “tiny clocks running” description and match it with the complex numbers/oscillators he is describing in this roundabout fashion. However, once that clicked into place, his descriptions of simple everyday phenomena, such as reflection and diffraction, the two-slit experiment, and later on the interaction of electrons and photons, really popped off of the page and sort of “broadened the groove” wherein all the counter-intuitiveness of QM is trying to get a foothold in my brain.

The name Richard Feynman is probably known to just about everyone who's had a college course in physics - as well as to many others. College students of physics may well have learned the subject from The Feynman Lectures on Physics. But Feynman also wrote a number of books for general readers, not just physics students. For instance: What Do You Care What Other People Think?. Many others know Feynman for having demonstrated the cause of the 1986 Challenger space shuttle disaster a few months after it happened.

The book under review here was published 1n 1985. The date is significant for various reasons. One is that the theories under discussion had already been partly sketched out in that decade, but with many loose ends. And, sadly, Feynman died in 1988 at the young age of 69. Yet he had much earlier shared a Nobel Prize in 1965 - together with Julian Schwinger and Sin-Itiro Tomonaga - for developing in the late 1940s the theory of Quantum Electrodynamics (QED), the subject of the book under review.

The book is basically a transcript of four lectures Feynman delivered in 1983, with a few updates based on new findings over the next two years. It's short (152 pages) but dense with ideas. Since the lectures were intended for college students and interested members of the general public, Feynman did his best to make them as intelligible as he could, by using mostly "ordinary" language, with as few technical terms as possible. Nevertheless, readers should understand that the basic concepts themselves are inherently complicated and mostly far outside of everyday experience. The book really isn't for anyone who has little idea what things like electrons, atoms, and atomic nuclei actually are. But for anyone who's already somewhat at ease with the basic concepts, the book is unsurpassable as an introduction to its subject.

There's really almost nothing to criticize about the presentation. If you want to go beyond the most rudimentary ideas of atomic and nuclear physics, there's probably no better place to start than this book. You'll already know that electrons are fundamental particles that are present in all atoms and are also (by themselves) the basic units of electricity. You probably also know that light can be understood both as "waves" and also particles called "photons". In these lectures, Feynman focuses entirely on the particle nature of light, because QED is the theory that fully describes how electrons and photons interact with each other. QED is still the best theoretical description of interactions between electrons and photons. But besides that, it's also a model for more advanced theories of interactions among all other known fundamental particles, such as protons, neutrons, muons (heavier cousins of electrons), quarks, etc. Some of what was known about the latter particles when the book was published is discussed in the 4th lecture, but it's outside the scope of QED per se.

The first lecture consists of basic details of the behavior of light, especially how it interacts with semi-transparent media such as glass. The second lecture goes into detail about how light is either reflected by or transmitted through different types of media. The third lecture describes how the behavior of light can be explained in terms of the interactions between photons and electrons. The fourth lecture reveals how the behavior of all other known fundamental particles is similar in many respects to the behavior of photons and electrons - as far as was known around 1985.

One interesting point Feynman makes is that light does not travel only in a straight line, and it can actually take any imaginable path. However, he doesn't explain that light (photons) actually has wave properties, and that the photon field in fact extends across the universe. So it's necessary to take into account an infinite number of paths when computing photon behavior. Elsewhere, the technicque QED uses is sometimes called "summation over paths" or "path integration".

It's the third lecture that gets into the details of how QED explains the interactions of photons and electrons with themselves and each other. The basic mechanism is based on "Feynman diagrams", which are abstract graphic representations of the interaction. Probabilities are associated with each step of an interaction. This makes it possible to compute a probability for the outcome of the whole interaction. Additionally, there are two numerical constants that are involved in the calculation. The first constant is "spin", an abstract characteristic of any fundamental particle. It has the value 1/2 for an electron and 1 for a photon. The other constant is mass. The mass of a photon is exactly 0. Although there's no known theoretical explanation for the mass of an electron, it can be measured to high precision by experiments.

Interactions can be arbitrarily complex, with any number of individual steps. To calculate the probability of a final outcome it's necessary to take the sum of probabilities of all possible combinations of steps that can occur. The values of spin and (electron) mass are also involved at each step. Probabilities are just numbers between 0 and 1, but since probabilities for each step are multiplied together, complex interactions will have very low probabilities. Since there are an infinite number of possible interaction diagrams, the probability of any particular total interaction will be an infinite sum of (mostly very small) numbers.

Mathematically, it's entirely possible for an infinite sum of small numbers to be either infinite or a finite number. For example, the infinite sum of reciprocals of positive integers is infinite. But the infinite sum of reciprocals of squares of positive integers is finite. In fact, the value, intriguingly, happens to be π²/6.

Since there are infinitely many possible steps in an interaction, it's necessary to sum an infinite series of small numbers. But if QED is to make any sense the result must be finite and less than or equal to 1. It turns out that everything depends on the values of particle masses and spins, and on the electron's mass in particular. In practice, of course, infinite sums can't be calculated on a computer. Any calculation must have only a finite number of terms, and any additional terms have to be left out. Also, the exact value of an electron's mass isn't known precisely, since there's no theoretical explanation for it. So only the best-known approximate value can be used.

So when physicists consider a particular interaction they are able to measure experimentally to some high degree of accuracy, it turns out that the approximate measured values from experiment and computer calculation agree to within the same (very small) level of uncertainty. Feynman, however, found this result to be unsatisfying because although the theory of QED is "confirmed" by all experimental results, there was no mathematical proof of its validity. So he called the theory - his own theory - a sort of unsatisfactory "dippy process" and "hocus-pocus".

Although QED is a theory of the force known as electromagnetism, analogs of the theory have been developed to describe two other physical forces: the "weak" nuclear force and the "strong" nuclear force. For any type of massive particle, not just electrons, the particle's mass-energy can be related to the mass of an electron. The theories of these other forces have turned out to be fairly similar to QED, so it has provided a good pattern to follow. Consequently, the mass of an electron also figures in these theories. So calculations in these other theories involve that mass, even though it's known only approximately from experiments. Physicists call this process "renormalization", and so it's an important question whether the other theories can correctly be renormalized.

Although the theories of the weak and strong nuclear forces are considerably more complex than QED, and are still being refined and compared against experimental results, gaining the best understanding of QED is necessary for any physicist (or anyone else) who wants to deal with the other forces. So Feynman's little book is one of the best places to start from.

This book contains four lectures given by Nobel Prize winning physicist Richard Feynman at UCLA in 1983. Feynman was a leader in the path integral formulation of quantum electrodynamics (QED) for which he won a Nobel prize. These lectures are intended for the non-scientist, but are best suited to those with a deep interest in the subject and the patience to wrestle with some complex ideas. The introduction to the 2006 edition puts this book of lectures halfway between a popular science book and a textbook. QED is a quantum field theory that describes the interaction of light and matter. To explain this, Feynman begins with the partial reflection of light by glass. Feynman shows us how to determine the probability of each photon being reflected. Rather than take us through complex numbers and integral calculus, he uses a system of arrows. The arrows’ length and direction are summed to provide an answer. While this seems straightforward at first, each ensuing example is more complicated requiring more steps. Along the way we learn about the strange world of photons and electrons and how QED is able to describe their interaction. At the end Feynman gives his takes on related subjects such as quantum chromodynamics. His well noted irreverent manner comes through in all the lectures. Feynman uses plain language that can be entertaining, at times flippant and self-deprecating. Feynman’s arrows accompanied by many illustrations and his famous diagrams make a difficult subject more accessible, but I did not find this to be a light read. Without prior familiarity with the topic, I would have been lost. But I was fascinated by his approach that uniquely complimented other books I have read about quantum field theory.

I’m bumped done.
Feynman landed the plane exactly where I wanted.

I have absolutely no idea how we got here. I had no business reading this book. But it was two dollars. And on a topic that I was interested in. And hoped it would lead me to more understanding on the index of refraction. But 100 pages in I just Figured
finishthe book.


Turns out we are now on the path that I want to be.

So let's see where this goes.

n  I love this area of physics and I think it’s wonderful: it is called quantum electrodynamics, or QED for short.n

I love this book and I think it’s wonderful: it is called QED: The Strange Theory of Light and Matter, or QED for short.
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I feel as though I’ve been searching for this book for a long time, and now I’ve finally found it. In scarcely 150 pages, Feynman takes you inside the logic of this famously obscure subject. What was before unintelligible is breezy in Feynman’s hands. What had before seemed impossible and bizarre of the physical world—particles behaving like waves, going back in time, eluding measurement—is, in Feynman’s presentation, just Nature being goofy.
tt
So here’s the mystery. Newton proposed, in his Opticks, that light is corpuscular, or comes in little packets like raindrops. But it was later observed that light can interfere with itself, so it must be a wave. (For a while, English physicists were loath to admit that Newton could be wrong.) Then experimenters ran into trouble again when they discovered that if you take an extremely dim light and aim it at a detector, you don’t get one continuous signal, but a series of beeps and pauses like Morse code. So it appears that light comes in packets after all. But wait! In certain circumstances, if you shoot these particles one-by-one, you get an interference pattern like a wave. So light was both a particle and a wave? How was that possible?
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Feynman begins by saying that this question—How is this possible?—isn’t the right one to ask. Physics is an experimental science, so its task is to come up with a theory that will make predictions that agree with experiments, not to resolve philosophical paradoxes. In this book, that’s just what he does: he explains what physicists are doing when they are making these predictions. To do this, he must delve into the math. But he does not wish to explain how his graduate students do it (which wouldn’t be feasible in a book of this size, anyway), but to explain what is going on behind the scenes when they do these calculations. It’s like teaching children to add with pebbles rather than on paper.
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Feynman begins by telling us that, in quantum physics, we calculate probabilities, not certainties. That’s a bit disappointing, but that’s the way nature is. So when a physicist is calculating the probability that a photon will pass through or reflect off a pane of glass, they use “probability amplitudes,” which can sometimes reinforce and sometimes cancel one another. With this method, we can predict how many photons out of 100 will reflect, and how many will pass through. Not only that, but we can also deduce the wavelike properties of photons interacting with electrons to astounding levels of accuracy—so accurate that if you were measuring the distance from New York to Los Angeles, the uncertainty would be equivalent to the width of a hair. So as far as scientific theories go, QED is pretty dang good.
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But what are “probability amplitudes” in reality? It seems a bit cheap at first, like Feynman merely found a clever way to talk about particles as waves without having to use the word “wave.” Feynman describes how to calculate the answer by picturing the particle as having a little clock hand that spins extremely fast, giving you an angle. In the end, two arrows (the amplitudes) are added up, the result is squared, and there’s your answer—a percentage. But what is really going on down there when the photon is traveling from the light source to the detector? What is happening before our measurements? Surely, there are no clock-hands attached to the particles. What's the mechanism behind all this?

Of course, this is the kind of questioning that Feynman discourages. In his words:

So this framework of amplitudes has no experimental doubt about it: you can have all the philosophical worries you want as to what the amplitudes mean (if, indeed, they mean anything at all), but because physics is an experimental science and the framework agrees with experiment, it’s good enough for us so far.

So, really, there’s no way of knowing what’s going on before the particle is detected, since it is, in principle, undetectable. And in science, only things that can be measured are real. All of the stuff used to obtain the answer is just an intellectual apparatus, a tool for calculation.
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Yet it’s hard to be as content with this as Feynman. If you wanted to learn how a car works, you’d want to know what’s going on in the engine, the transmission, the steering and braking. If somebody told you, “It works by turning the key and stepping on the gas,” you’d feel like you were cheated. But this is what we must do in QED. Nature doesn’t allow us to look under the hood. We can step on the gas and the thing moves; we can come up with an equation that helps us predict how fast the car will go depending on how much we press on the pedal. But what makes it go? Who knows? As Feynman said:

It is my task to convince you not to turn away because you don’t understand it. You see, my physics students don’t understand it either. That is because I don’t understand it. Nobody does.

My biggest mistake here was reading this in small bursts. It was helpful to have things framed in layman's terms, but I still found myself not "getting it" at times, and I think that was probably because I was only reading it in short bursts and then not taking time to make sure I went back and really understood before forging onward. I did gain new insights and understanding into many details that were unknown to me about quantum electrodynamics, including some exposure to things like gluons, mesons, quarks, and such which I've heard of, but never really had much understanding of before. I think the reviews are high for this because the people likely to read this are physics majors and technical types--I think a broader sampling of non-technical readers would likely result in lower reviews because many people would still find it incomprehensible, despite Feynman's talent for making complex stuff understandable. If you are on the fence about reading this, consider browsing the Wikipedia entry on quantum electrodynamics which has a short section on "Feynman's view of quantum electrodynamics." It gives a short idea of what one will find in the book.

You could call me a science groupie. I put on Cosmos while I clean the house, snatch up Michio Kaku's books like they won't be there tomorrow, know all the words to every Symphony of Science song ever, and follow Neil deGrasse Tyson on Twitter--but that doesn't mean I know the first thing about real science. I couldn't solve a linear algebraic equation even if the world depended on it (sorry, world). Instead, I revere famous physicists from afar while most women my age drool over movie stars like What's-His-Face. You know the one. That really hott one.

Anyway. Richard Feynman is definitely in the top five on my list of favorite physicists. (Yep, I have a list. Expect nothing less from a girl who named her cat Sagan.) I love Feynman's sense of humor and his whimsical world-view. He may be gone, but he's not forgotten. So when I had a stupid question about light, I figured it was high time I read his book on the subject. My stupid question goes like this: Why is it that, when you turn off a light, the room immediately goes dark? Where does the light go? Why doesn't it bounce around the room for a bit before dispersing? If light is everywhere, why is the universe so dark?

Well, this book didn't really help me answer those questions. If Feynman taught me anything here, it's that light is the honey badger of particles: it does what it wants, and leaves tiny arrows in its wake. Or something. I'm not sure.