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Chapter 12 argued that quantum statistical mechanics puts unitarily inequivalent representations to use in ways no rigid interpretation can make sense of. Two features of working QFTs which promise a quantum field theoretic realization of Chapter 12's argument are Goldstone bosons and the Higgs mechanism. This chapter explains why they're promising by presenting them as instance of broken symmetry. Then it tempers the promise by admitting that the working QFTs in which these features occur are less mathematically explicit than they need to be to persuasively realize the argument of Chapter 12. The chapter closes by extracting from this very circumstance a non-conclusive reason to lend the argument of Chapter 12 interpretive weight. The reason is that our best theories of physics are still under construction, and their successors could share with the models presented in Chapter 12 the features on which the argument of Chapter 12 hinged.

The modern theory of particle physics, called the Standard Model, describes electromagnetic, weak, and strong forces and all known forms of matter in terms a single conceptual principle. This chapter gives a short overview of the events that led to the discovery of this theory. It first explains the meaning of quantum field theory, which is the language used to describe the particle world. It then presents QED, the theory which describes the electromagnetic phenomena in the domain of particle physics. Finally, the Standard Model emerges from the synthesis of three intertwined stories: the discovery of quarks, the unification of electromagnetism with the weak force, and the understanding of the strong force in terms of QCD.

A non-abelian gauge theory is at the heart of the electroweak theory due to Weinberg and Salam and this is presented in this chapter. Symmetry breaking of the Higgs field results in the emergence of the photon, the charged W particles, and the neutral Z particle. The photon is massless, but the other three acquire mass and so the weak force becomes short-ranged.

Quantum chromodynamics the quantum gauge theory of strong interactions is presented: SU(3) being the (colour) symmetry group. The colour content of strongly interacting particles is described. Gluons, the field particles, carry colour so that they mutually interact – unlike photons. Renormalization leads to the coupling strength declining at large four momentum transfer squared q² and to binding of quarks in hadrons at small q². The cutoff in the range of the strong interaction is shown to be due to this low q² behaviour, despite the gluon being massless. In high energy interactions, say proton-proton collisions, the initial process is a hard (high q²) parton+parton to parton+parton process. After which the partons undergo softer interactions leading finally to emergent hardrons. Experiments at DESY probing proton structure with electrons are described. An account of electroweak unification completes the book. The weak interaction symmetry group is SU_L(2), L specifying handedness. This makes the electroweak symmetry U(1)⊗SUL(2). The weak force carriers, W^± and Z⁰, are massive, which is at odds with the massless carriers required by quantum gauge theories. How the BEH mechanism resolves this problem is described. It involves spontaneous symmetry breaking of the vacuum with scalar fields. The outcome are massive gauge field particles to match the W^± and Z⁰ trio, a massless photon, and a scalar field with a massive particle, the Higgs boson. The experimental programmes that discovered the vector bosons in 1983 and the Higgs in 2012 are described, including features of generic detectors. Finally puzzles revealed by our current understanding are outlined.

Verbatim descriptions are given of the use of the sep-con articulation process in creative discovery by Werner Arber on DNA restriction and modification, David Baltimore on reverse transcriptase, Baruj Benacerraf on immune responsiveness genes, Paul Berg on recombinant DNA, Allan Cormack on the CAT scan, Sheldon Glashow on the charm quark and electroweak theory, David Hubel in ocular orientation selectivity, Georges Köhler on the monoclonal antibody, Jean-Marie Lehn on supramolecular structure, Max Delbrück on genetic replication, Ivar Giaever on superconductor tunneling, Christiane Nüsslein-Volhard on segmentation pairs, Salvador Luria on the Lurian distribution, and Norman Ramsey on the separated oscillatory field method in atomic clocks.

In this chapter we develop the Glashow–Weinberg–Salam theory of electromagnetic and weak interactions based on the gauge group SU(2) × U(1). We show that the apparent difference in strength between the two interactions is due to the Brout–Englert–Higgs phenomenon which results in heavy intermediate vector bosons. The model is presented first for the leptons, and then we argue that the extension to hadrons requires the introduction of a fourth quark. We show that the GIM mechanism guarantees the natural suppression of strangeness changing neutral currents. In the same spirit, the need to introduce a natural source of CP-violation leads to a six quark model with the Cabibbo–Kobayashi–Maskawa mass matrix.

Modern physics suggests several exotic ways in which things could go terribly wrong on a very large scale. Most, but not all, are highly speculative, unlikely, or remote. Rare catastrophes might well have decisive influences on the evolution of life in the universe. So also might slow but inexorable changes in the cosmic environment in the future. Only a twisted mind will find joy in contemplating exotic ways to shower doom on the world as we know it. Putting aside that hedonistic motivation, there are several good reasons for physicists to investigate doomsday scenarios that include the following: Looking before leaping: Experimental physics often aims to produce extreme conditions that do not occur naturally on Earth (or perhaps elsewhere in the universe). Modern high-energy accelerators are one example; nuclear weapons labs are another. With new conditions come new possibilities, including – perhaps – the possibility of large-scale catstrophe. Also, new technologies enabled by advances in physics and kindred engineering disciplines might trigger social or ecological instabilities. The wisdom of ‘Look before you leap’ is one important motivation for considering worst-case scenarios. Preparing to prepare: Other drastic changes and challenges must be anticipated, even if we forego daring leaps. Such changes and challenges include exhaustion of energy supplies, possible asteroid or cometary impacts, orbital evolution and precessional instability of Earth, evolution of the Sun, and – in the very long run – some form of ‘heat death of the universe’. Many of these are long-term problems, but tough ones that, if neglected, will only loom larger. So we should prepare, or at least prepare to prepare, well in advance of crises. Wondering: Catastrophes might leave a mark on cosmic evolution, in both the physical and (exo)biological senses. Certainly, recent work has established a major role for catastrophes in sculpting terrestrial evolution (see http://www.answers.com/topic/timeline-of-evolution). So to understand the universe, we must take into account their possible occurrence. In particular, serious consideration of Fermi’s question ‘Where are they?’, or logical pursuit of anthropic reasoning, cannot be separated from thinking about how things could go drastically wrong. This will be a very unbalanced essay.