Author(s): Roger Penrose
What can fashionable ideas, blind faith, or pure fantasy possibly have to do with the scientific quest to understand the universe? Surely, theoretical physicists are immune to mere trends, dogmatic beliefs, or flights of fancy? In fact, acclaimed physicist and bestselling author Roger Penrose argues that researchers working at the extreme frontiers of physics are just as susceptible to these forces as anyone else. In this provocative book, he argues that fashion, faith, and fantasy, while sometimes productive and even essential in physics, may be leading today's researchers astray in three of the field's most important areas--string theory, quantum mechanics, and cosmology. Arguing that string theory has veered away from physical reality by positing six extra hidden dimensions, Penrose cautions that the fashionable nature of a theory can cloud our judgment of its plausibility. In the case of quantum mechanics, its stunning success in explaining the atomic universe has led to an uncritical faith that it must also apply to reasonably massive objects, and Penrose responds by suggesting possible changes in quantum theory. Turning to cosmology, he argues that most of the current fantastical ideas about the origins of the universe cannot be true, but that an even wilder reality may lie behind them. Finally, Penrose describes how fashion, faith, and fantasy have ironically also shaped his own work, from twistor theory, a possible alternative to string theory that is beginning to acquire a fashionable status, to "conformal cyclic cosmology," an idea so fantastic that it could be called "conformal crazy cosmology." The result is an important critique of some of the most significant developments in physics today from one of its most eminent figures.
Roger Penrose, one the world's foremost theoretical physicists, has won numerous prizes, including the Albert Einstein Medal, for his fundamental contributions to general relativity and cosmology. He is the bestselling author, with Stephen Hawking, of The Nature of Space and Time (Princeton). Penrose's other books include Cycles of Time: An Extraordinary New View of the Universe and The Road to Reality: A Complete Guide to the Laws of the Universe (both Vintage). He is the Rouse Ball Professor of Mathematics Emeritus at the University of Oxford and lives in Oxford, England.
Acknowledgements ix Preface xi Are fashion, faith, or fantasy relevant to fundamental science? xi 1 Fashion 1 1.1 Mathematical elegance as a driving force 1 1.2 Some fashionable physics of the past 10 1.3 Particle-physics background to string theory 17 1.4 The superposition principle in QFT 20 1.5 The power of Feynman diagrams 25 1.6 The original key ideas of string theory 32 1.7 Time in Einstein's general relativity 42 1.8 Weyl's gauge theory of electromagnetism 52 1.9 Functional freedom in Kaluza-Klein and string models 59 1.10 Quantum obstructions to functional freedom? 69 1.11 Classical instability of higher-dimensional string theory 77 1.12 The fashionable status of string theory 82 1.13 M-theory 90 1.14 Supersymmetry 95 1.15 AdS/CFT 104 1.16 Brane-worlds and the landscape 117 2 Faith 121 2.1 The quantum revelation 121 2.2 Max Planck's E = hnu 126 2.3 The wave-particle paradox 133 2.4 Quantum and classical levels: C, U, and R 138 2.5 Wave function of a point-like particle 145 2.6 Wave function of a photon 153 2.7 Quantum linearity 158 2.8 Quantum measurement 164 2.9 The geometry of quantum spin 174 2.10 Quantum entanglement and EPR effects 182 2.11 Quantum functional freedom 188 2.12 Quantum reality 198 2.13 Objective quantum state reduction: a limit to the quantum faith? 204 3 Fantasy 216 3.1 The Big Bang and FLRW cosmologies 216 3.2 Black holes and local irregularities 230 3.3 The second law of thermodynamics 241 3.4 The Big Bang paradox 250 3.5 Horizons, comoving volumes, and conformal diagrams 258 3.6 The phenomenal precision in the Big Bang 270 3.7 Cosmological entropy? 275 3.8 Vacuum energy 285 3.9 Inflationary cosmology 294 3.10 The anthropic principle 310 3.11 Some more fantastical cosmologies 323 4 A New Physics for the Universe? 334 4.1 Twistor theory: an alternative to strings? 334 4.2 Whither quantum foundations? 353 4.3 Conformal crazy cosmology? 371 4.4 A personal coda 391 Appendix A Mathematical Appendix 397 A.1 Iterated exponents 397 A.2 Functional freedom of fields 401 A.3 Vector spaces 407 A.4 Vector bases, coordinates, and duals 413 A.5 Mathematics of manifolds 417 A.6 Manifolds in physics 425 A.7 Bundles 431 A.8 Functional freedom via bundles 439 A.9 Complex numbers 445 A.10 Complex geometry 448 A.11 Harmonic analysis 458 References 469 Index 491