Introduction 1
I The Subatomic World
1. What is a quantum, anyway? 3
2. Where do the laws of quantum physics hold sway? 5
3. What is the correspondence principle? 7
4. How big is an atom? 9
5. What is inside an atom? 9
6. Why is solid matter solid if it is mostly empty space? 13
7. How big is an electron? Is there anything inside it? 14
II Digging Deeper
8. How big is a nucleus? What is inside it? 18
9. How big are protons and neutrons? What is inside them? 22
10. What is Planck's constant and what is its significance? 24
11. What is a photon? 27
12. What is the photoelectric effect? 29
13. What particles are believed to be fundamental? What particles are composite? 30
14. What is the standard model? 33
III The Small and the Swift
15. What are some quantum scales of distance? 34
16. How far can one particle "reach out" to influence another one? 35
17. How fast do particles move? 38
18. What are some quantum scales of time? 40
19. What is the meaning of E = mc²? 41
20. What is electric charge? 44
21. What is spin? 46
IV Quantum Lumps and Quantum Jumps
22. What are some things that are lumpy (and some that are not)? 50
23. What is a "state of motion"? 52
24. Is a hydrogen atom in an excited state of motion the same atom in a different state or is it a different atom? 54
25. What are quantum numbers? What are the rules for combining them? 56
26. What is a quantum jump? 61
27. What is the role of probability in quantum physics? 64
28. Is there any certainty in the quantum world? 68
V Atoms and Nuclei
29. What is a line spectrum? What does it reveal about atoms? 70
30. Why is the chart of the elements periodic? 75
31. Why are heavy atoms nearly the same size as lightweight atoms? 78
32. How do protons and neutrons move within a nucleus? 79
33. What are atomic number and atomic mass? 83
VI And More about Nuclei
34. Why does the periodic table end? 85
35. What is radioactivity? What are its forms? 87
36. Why is the neutron stable within a nucleus but unstable when alone? 92
37. What is nuclear fission? Why does it release energy? 94
38. What about nuclear fusion? 98
VII Particles
39. What is a lepton? What are its flavors? 101
40. How many distinct neutrinos are there? How do we know? 105
41. Do neutrinos have mass? Why do they "oscillate"? 108
42. Are there really only three generations of particles? 114
43. How do we know that all electrons are identical? 116
VIII And More Particles
44. Names, names, names. What do they all mean? 118
45. What are the properties of quarks? How do they combine? 119
46. What are the composite particles? How many are there? 123
47. Does every particle have to be a fermion or a boson? What sets these two classes apart? 126
48. What is a Bose-Einstein condensate? 130
49. How did bosons and fermions get their names? 133
IX Interactions
50. What is a Feynman diagram? 137
51. What are the essential features of Feynman diagrams? 141
52. How do Feynman diagrams illustrate the strong, weak, and electromagnetic interactions? 144
53. Which particles are stable? Which are unstable? What does it mean to say that a particle decays? 148
54. What is scattering? 149
55. What is the same before and after a scattering or a decay? 151
56. What changes during a scattering or decay? 152
X Constancy during Change
57. What are the "big four" absolute conservation laws? 154
58. What additional absolute conservation laws operate in the quantum world? 156
59. What is the TCP theorem? 157
60. What conservation laws are only "partial"? 160
61. What symmetry principles are only "partial"? 163
62. What are laws of compulsion and of prohibition? 167
63. . How are the concepts of symmetry, invariance, and conservation related? 169
XI Waves and Particles
64. What do waves and particles have in common? How do they differ? 173
65. What is the de Broglie equation? What is its significance? 174
66. How are waves related to quantum lumps? 177
67. How do waves relate to the size of atoms? 180
68. What is diffraction? What is interference? 182
69. What is the two-slit experiment? Why is it important? 183
70. What is tunneling? 186
XII Waves and Probability
71. What is a wave function? What is Schrödinger's equation? 189
72. How do waves determine probabilities? 192
73. How do waves prevent particles from having fixed positions? 195
74. What is the uncertainty principle? 197
75. How does the uncertainty principle relate to the wave nature of matter? 199
76. What is superposition? 202
77. Are waves necessary? 204
XIII Quantum Physics and Technology
78. How are particles pushed close to the speed of light? 207
79. How are high-energy particles detected? 211
80. How does a laser work? 215
81. How do electrons behave in a metal? 218
82. What is a semiconductor? 220
83. What is a p-n junction? Why is it a diode? 222
84. What are some uses of diodes? 224
85. What is a transistor? 226
XIV Quantum Physics at Every Scale
86. Why do black holes evaporate? 228
87. How does quantum physics operate in the center of the Sun? 231
88. What is superconductivity? 233
89. What is superfluidity? 236
90. What is a Josephson junction? 237
91. What is a quantum dot? 239
92. What is a quark-gluon plasma? 240
93. What is the Planck length? What is quantum foam? 242
XV Frontiers and Puzzles
94. Why are physicists in love with the number 137? 244
95. What is entanglement? 247
96. What is Bell's inequality? 250
97. What is a qubit? What is quantum computing? 253
98. What is the Higgs particle? Why is it important? 255
99. What is string theory? 257
100. What is the "measurement problem"? 259
101. How come the quantum? 263
Appendix A 265
Appendix B 271
Acknowledgments 275
Index 277