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Theory in a nutshell

Quantum Field Theory, as Simply as Possible; By A. Zee; Published by Princeton University Press; 392 pages; $39.95

A primer that lets readers gain an appreciation for the dynamic, exciting field of quantum field theory.

Every now and then, we see particle physics-related news in the papers: "Higgs boson detected!", "Large Hadron Collider makes new discovery". Or else we hear of terms we definitely didn't learn in school: "Up and down quarks", "Lagrangian". But for some reason, we never connect these dots. There also never seems to be a map of the whole territory.

Quantum Field Theory, as Simply as Possible, by Anthony Zee, attempts to fill this gap. The book is a summation of the concepts and history of Quantum Field Theory (QFT) in 350 pages. As is necessary for such a primer, Zee skips lightly over the surface, alighting here and there to give us a taste of the theory and let us feel its implications. We do not complete this book and become masters of the field, of course, but we do gain an appreciation for a dynamic, involved and exciting field of study.

But let's start at the beginning. What exactly is QFT? The Chinese-American physicist-writer calls it a combination of quantum mechanics and special relativity. Quantum mechanics, Zee writes cheekily, addresses very small particles moving slowly, and special relativity explains large objects moving fast. Thus: QFT is just the study of very small particles, moving very fast. This may sound simplistic, but, explained this way, it's a concept we don't forget.

Zee takes readers along the scenic route to get to this understanding. The first few chapters explain the basics of quantum mechanics, then we go through special relativity and, with this preparation, jump into the various aspects of QFT.


Perhaps the first thing we understand is that a huge mindset change is required to grasp QFT. We've been taught in school, for example, that light sometimes behaves as a wave and something as a particle. We've also heard enough about Einstein's famous equation about matter and energy being interchangeable. What happens when we put these together? Basically, that all particles are packets of energy/waves, and, also, that a fundamental particle can be created and destroyed. "Fundamental" particles, in fact, aren't permanent; they are temporary manifestations in their respective fields (which is why it's called field theory).

In fact, according to QFT, this is happening continuously around us, and the interaction of energy, particles and waves through the various fundamental forces of the universe is what gives the universe its shape and form. The various particles we hear about — Higgs boson, positrons, the various quarks — only exist for minuscule amounts of time before disappearing back into their field.

We soon realise that most of QFT is only about a century old since the first postulates. Newton and even Einstein belong to another era, but Richard Feynman? And Peter Higgs? Feynman was on the committee investigating the space shuttle Challenger disaster! Higgs won the Nobel Prize in 2013! The famous quirky-looking Feynman diagrams are a recent novelty to most readers. But so critical are they that Zee uses them throughout to explain fundamental particle interactions. None of this makes it into school textbooks in India. This is a field that is still evolving. We still see occasional articles and tweets arguing over some of the tenets of the field and whether it's worth digging deeper into proving the theories. Zee is critical of the so-called string theory, preferring to reserve judgement on whether it solves the open issues.


The reader will inevitably want to go deeper into some of the ideas (a triumph for the book, in my opinion). Several of the popular equations and theories, such as the Dirac equation, or Schrödinger's work, are not expanded upon due to length constraints. Zee often points to his other books for more details. There are also good videos on YouTube for supplementary exploration. Some take different opinions of the same material, and we are forced to think critically about Zee's points of view.

QFT is evolving in the new age of communication, and this gives us a chance at a ringside seat. While it takes some study and involvement, Zee's book provides us with an entry ticket and a summary of what has happened so far. Worth the price of admission.

Sudarshan Purohit is a writer, a translator – and a software engineer.


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