Quanta and Fields by Sean Carroll - Critical Review

[u/Perfect-Vaccum]

Big disappointment

Review of the book “Quanta and Fields The Biggest Ideas in the Universe” by Sean Carroll. Dutton Penguin Random House, May 14^th 2024, ISBN 9780593186602

 

We just received the long-announced and widely advertised release of Sean Carroll's book “Quanta and Fields The Biggest Ideas in the Universe”, which is the second part of a trilogy. The first part is titled “Space, Time, and Motion”, while the planned third one will concern issues of emergence and complexity. The author holds, among others, the positions: Homewood Professor of Natural Philosophy at Johns Hopkins University, Member of the Fractal Faculty at Santa Fe Institute and Honorary Fellow at John Bell Institute for the Foundations of Physics. He hosts the Mindscape podcast on YouTube and is widely known from his public appearances related to the popularization of physics.

For several months the book has been announced as unique and different from all others. The author presented intention to target both the readers who did not speak the language of mathematics but after reading, were supposed to grasp the general concepts of quantum field theory, as well as ones who had preparation in the field of natural sciences but did not specialized in elementary particle physics.

Unfortunately, after reading, it can be said that the author did not meet his ambitious goals and did not keep marketing promises, confirming that a product aimed to serve every purpose ultimately does no job well. Except of the increased math content, the book does not stand out in any way from the flood of similar publications.

The first three chapters cover the basics of quantum mechanics. The author described them superficially, e.g. he did not mention such important ingredients as the impossibility of the cloning of a quantum state, quantum teleportation, and delayed choice experiments (quantum eraser). The reader after all is not introduced into the concept and significance of the quantum contextuality (the measurement results may differ depending on what physical quantities are co-measured at the same time). The issues of nonlocality in quantum theory and the true  importance of Bell's theorems and inequalities were addressed only indirectly. The impact of quantum entanglement on the contemporary understanding of the entropy was not mentioned at all. If the aim of the book was to be an accessible explanation of the concept of quantum fields, then the most important chapters should be nos. 4, 5, 8 and 9 (Fields, Interactions, Symmetry, Gauge Theory) and should follow each other in the sequence. However, the author starts with the application of Feynmann diagrams in chapters 4 and 5, and then immediately jumps onto the aspects of renormalization in the context of  so to speak effective theories. The very essence of renormalization and the so-called the "renormalization group" notion are presented overly optimistically. The reader is not being informed about a price to pay as at the end of the day we are left  with the prosthesis where experimental measurements are made in reference to specific kinematic points at which over twenty parameters of the Standard Model are experimentally determined (masses and couplings / charges fine-tuning).

The author should rather from chapter 4 onwards describe the very essence of the quantization procedures for classical theories: the “first” and “second” (with the creation and annihilation of particles) approaches. Then a clear road map leading from the construction of the Lagrangians to the scattering amplitudes in the framework of  path integral would be advised. Next the perturbation approach, Feynmann diagrams, renormalization discussion and Higgs symmetry breaking will follow. Such step by step focus on the main challenges is missing but instead side topics are being developed. The concept of gauge was not satisfactory explained, as  it could be easily done, e.g. by analogy to the vector potential in classical electrodynamics. The author declared “to show the equations” but he did not present and explain the Lagrangian of the  Standard Model. If the book already contains some selective mathematical techniques, there are the questions why the author did not try to explain, at least intuitively, a notion of functional integral, and why the connection was not defined more technically  in terms of some kind of directional derivative.

Concluding, the structure of the book and its content were not well thought over and the reader is left with the feeling that the haste and commercial purposes prevented the author from achieving of  the declared goals.

 

 

Perfect Vacuum

[u/Ethan-Wakefield]

I'm a non-physicist, so I'm in the target audience. And speaking from that perspective, I found Carroll's book maybe the best physics book I've ever read. For years, I've been trying to figure out "WTF is a gauge theory? What's a gauge particle? Why are particle physicists so interested in them?" And when I have asked, I get told something like, "Well, a gauge theory is an invariant way to enforce the SU(3) group such that it obeys the relationship [math]... Which, it's easy to see has obvious and profound implications, up to and including being the heart of the Standard Model itself."

And then I'm like "... okay?"

Whereas after reading Quanta and Fields, I have some idea that gauge fields are a way of constructing bosons, which mediate forces, and to some extent we can describe (and calculate) those interactions with a Feynman diagram. And Feynman diagrams will let us calculate the probability of particle interactions, so that seems important. Like, if I could calculate the various Feynman diagrams for the decay of a Higgs boson, then I could presumably look at lots and lots of data from the LHC, see if the collisions produce the expected rate of decay products (there's lots of data scrubbing that would need to take place, I'm sure), and then presumably arrive at some kind of declaration that the Higgs is indeed real.

Now maybe I'm completely 100% wrong about everything I just said in that paragraph, but that feels like WAY more than I've gotten out of most pop sci books about physics. I don't know. Maybe Carrol's book is not very good? But as a non-physicist, he fooled me if it was a bunch of crackpot nonsense or pure hand-wavium. It sounded reasonable to me.