05 - Elementary Particles and the Forces of Nature скачать в хорошем качестве

05 - Elementary Particles and the Forces of Nature

This chapter provides a comprehensive survey of particle physics and the fundamental forces of nature. Hawking traces the historical debate over whether matter is continuous or atomic, from Aristotle through Democritus to John Dalton, culminating in Einstein's 1905 explanation of Brownian motion as definitive proof of atoms. The chapter then describes the discovery of subatomic structure: J.J. Thomson's electron, Rutherford's nucleus, and Chadwick's neutron. Hawking explains that protons and neutrons are themselves composed of quarks, named by Murray Gell-Mann, which come in six flavors (up, down, strange, charmed, bottom, top) and three colors (red, green, blue). The concept of spin is introduced, dividing particles into matter particles (spin 1/2) that obey Pauli's exclusion principle, and force-carrying particles (spin 0, 1, 2) that do not. Paul Dirac's theory predicted antimatter, confirmed by the discovery of the positron. The chapter systematically describes the four fundamental forces: gravitational (carried by gravitons), electromagnetic (photons), weak nuclear (W and Z bosons), and strong nuclear (gluons). Hawking explains confinement and asymptotic freedom in the strong force, and describes the Weinberg-Salam-Glashow electroweak unification. Grand unified theories (GUTs) are discussed, including their prediction of proton decay and their potential explanation for why the universe contains more matter than antimatter. The chapter concludes with symmetries C, P, and T, and the discoveries by Lee, Yang, Wu, Cronin, and Fitch showing that these symmetries are not always preserved, which may explain the matter-antimatter asymmetry that allowed our existence.