and origin of the Copenhagen interpretation, 54 –58
and photoelectric effect, 17
and wave mechanics, 45 –48
wave-particle duality, 6 –7
Elitzur, Avshalom, 2 , 133 –35, 138 , 144
Elitzur-Vaidman bomb puzzle, 2 –3, 135 , 135 –40, 136 , 142 , 145 , 216
entanglement, quantum
and Bell’s theorem, 103 –7, 105
and Bohmian mechanics, 150 , 164 , 177 –78, 178
and Bouwmeester’s work, 206
and EPR argument, 96 , 98
and many worlds theories, 229 , 231 , 233
Maudlin on, 107 –8
and molecular interferometry, 197
and QBism, 250
and quantum eraser, 116 –17, 121 –23, 125 –28, 131 , 139 , 144
and single-particle experiments, 91
and stochastic collapse theories, 257
and superposition mirror interferometer, 209
EPR (Einstein-Podolsky-Rosen) paper, 96 –102, 149 –50
Erhard, Werner, 255
ESSW theory, 175 , 176 –77, 181
Everett, Hugh, III, 216 , 218 –28, 233 –40, 242 , 251 , 261 –62
Faraday, Michael, 24
Feynman, Richard
and Bell’s theorem, 106
and Bohmian mechanics, 160
and first double-slit experiments, 15 –18, 22
and many worlds theories, 227 , 232
on open-mindedness, 255 –56
and origin of double-slit experiment, 3
and path integral formulation, 232 , 264
on significance of double-slit experiment, 3 –9, 108 , 266
and single-particle experiments, 62 –66, 68
Fifth Solvay International Conference on Electrons and Photons (1920), 39 , 52 –58, 155
Flack, Robert, 173 –74
Fort, Emmanuel, 158 –59
Freedman, Stuart, 104
Fresnel, Augustin-Jean, 65 –66
Fry, Edward, 104 , 106
Fuchs, Christopher, 243 –46, 248 –49, 251 , 253
general relativity, 96 –97, 187 –88, 190 , 224
Ghirardi, Giancarlo, 63 –64, 193
Gisin, Nicolas, 93
Goethe, Johann Wolfgang von, 41
Goldstein, Sheldon, 151 –55, 157 , 162 , 164 , 166 , 183 –84
Grangier, Philippe, 63 , 68 , 74 –75, 84 , 86
gravity, 23 , 96 –97
Greene, Brian, 109
GRW theory, 193 –95, 203 , 205 , 214 , 235
Hall, Michael, 259
Hardy, Lucien, 1 –2, 140 , 143 –44
Heisenberg, Werner
and atomic theory, 40 –42
and Bohmian mechanics, 151 –52
on Bohr-Schrödinger discussions, 49 –52
and Hermann’s work, 101
and matrix mechanics, 44 –46
on objectivity at quantum scales, 23
and origin of the Copenhagen interpretation, 54 –56
and QBism, 253
and quantum eraser, 129
and spontaneous collapse theories, 192
Hell, Stefan, 59 –60
Helmholtz, Hermann von, 28
Hermann, Grete, 100 –101
Hertz, Heinrich, 25 –29
hidden variables
and Bell’s theorem, 104 , 106 –7
and Bohmian mechanics, 149 –51, 154 –56, 164 , 167 , 182 , 184
dissent on Copenhagen interpretation, 217
and EPR argument, 99 –101
and future of quantum research, 257 –58, 259
and many worlds theories, 233 –35, 261 –62
and QBism, 246 , 250
and quantum eraser, 114 , 140 , 146
and single-particle experiments, 61 –62, 70 –71
Hilbert space, 237 –38, 243
Hiley, Basil, 162 , 166 –67, 173 –74, 174 –75
Høffding, Harald, 58
Holland, Peter, 162
Holt, Richard, 104
Hoyle, Fred, 53
Huygens, Christiaan, 12 –14, 16 , 23 –24
incompleteness theorem, 112
interaction-free measurements, 135 , 138 –39, 143 , 145
James, William, 217 , 244
Jordan, Pascual, 42
Jørgensen, Jørgen, 58
Kaiser, David, 255
Kuhn, Thomas, 53 –54
Lamb, Willis, 113
La Palma-Tenerife experiments, 110 , 121 –29, 122 , 126
laser interferometers, 74 –75. See also Mach-Zehnder interferometers
Lenard, Philipp, 29 , 32
locality/nonlocality, 93 –107
and Bohmian mechanics, 150 , 161 –64, 176 , 179 –81, 183
and many worlds theories, 261 –62
Maudlin on, 107 –8
and QBism, 250 –51
and quantum eraser, 112 , 128 , 139 , 144 –45
and Schrödinger’s wave mechanics, 47
and single-particle experiments, 62
and spontaneous collapse, 194
and superposition mirror interferometer, 212
and universal wavefunction, 220
and wave-particle nature of light debate, 24
Ma, Xiao-Song, 124 , 130
Mach, Ludwig, 73
Mach-Zehnder interferometers
and many worlds theories, 228 , 231 –32, 239
and molecular interferometry, 205
and QBism, 248
and quantum eraser, 123 , 127 , 134 –41
and single-particle experiments, 73 –75, 78 , 80 , 84 –88
and superposition mirror interferometer, 208 –9
many worlds theories, 2 61 –262, 215 –16, 226 –36, 235 , 250 , 260
Marshall, William, 210
matrix mechanics, 42 –45, 48
Maudlin, Tim, 93 –94, 107
Maxwell, James Clerk, 24 –26, 37 , 60 , 206
Maxwell’s equations, 32 , 35 –37, 206
Mayor, Marcel, 199
measurement problems, 218 –21, 224 , 226 , 230 –31, 261
Merli, Pier Giorgio, 67
Mermin, David, 96 , 144 , 249 , 252 –53
Miller, Warren, 86
Missiroli, GianFranco, 67
Mlynek, Jürgen, 197
molecular interferometry, 196 –205
Möllenstedt, Gottfried, 64 –67
Møller, Christian, 129
Moore, Walter, 50
Morandi, Giorgio, 3
Nelson, Edward, 153 –54
Newton, Isaac, 3 , 8 , 12 –13, 16 , 23 , 39
Newtonian physics, 10 –11, 21 , 23 –24, 39 . See also classical physics
Niels Bohr Institute, 40
Noether, Emmy, 100
Oppenheimer, Robert, 147 –48
parallel universe theories, 225 . See also many worlds theories
path integral formulation, 232
Pauli, Wolfgang, 41 , 49 , 54 –55, 129 , 151 , 155 –56
Penrose, Roger, 138 –39, 184 –85, 187 –93, 195 , 203 , 205 –7, 209 –14, 235
Philippidis, Chris, 167 , 173
photoelectric effect, 16 –17, 26 –27, 29 –32, 31 , 32 , 91
pilot-wave theory, 155 –59, 161 , 203
Pipkin, Francis, 104
Planck, Max, 29 –32, 37 –39, 66 , 191
Planck’s constant, 66
Podolsky, Boris, 96 , 225 , 226
polarized of light, 102 , 102 –6, 105 , 123 , 125 –27, 126 , 143 , 171 , 174 , 177 –81, 180 , 184
polarizing beam splitter (PBS), 123 , 126 , 126 , 177 , 178
Popper, Karl, 53 –54
positrons, 141 –44
Pozzi, Giulio, 67
Pritchard, David, 197
probability
and density matrices, 230 –31
and first double-slit experiments, 21
and many worlds theories, 230 –32, 239 –43
and matrix mechanics, 44 –45
and origin of the Copenhagen interp
retation, 57
and quantum eraser, 110 –11, 139
and Schrödinger’s wave mechanics, 47 –48
and single-particle experiments, 70 –75, 80 –81
and universal wavefunction, 219 , 221
psi-epistemic and psi-ontic theories, 245 –46, 249
quanta, 30 , 32 –34, 37
Quantum Bayesianism (QBism), 235 , 235 , 242 –43, 245 –46, 248 –54, 262
quantum eraser experiments, 113 –21, 121 –30, 130 –33, 133 –40, 140 –46, 179
quantum gravity, 188 , 224
radiation, 38 –39, 43
randomness and randomization
and Bohmian mechanics, 153
electromagnetic wave view of light, 103
and first double-slit experiments, 19
and many worlds theories, 239
and QBism, 244
and quantum eraser, 123 , 125 –28, 126 , 139 –40, 145
and Schrödinger’s wave mechanics, 48
and single-particle experiments, 68
and spontaneous collapse, 193 , 195
and superposition mirror interferometer, 211 –12
and universal wavefunction, 221
See also stochasticity
realist-anti-realist interpretations
and Bell’s theorem, 106
and Bohmian mechanics, 149 , 151 , 183
and EPR argument, 97 , 100 –101
and ESSW argument, 175
and Goldstein’s work, 153
and many worlds theories, 234 , 261 –62
and molecular interferometry, 203
and origin of the Copenhagen interpretation, 54 , 57
and pilot-wave theory, 155 –56
and QBism, 246 , 248
and quantum eraser, 110 –11, 140 , 144
and single-particle experiments, 82 , 85
relativity, 94 –97, 173 , 187 –88, 190 , 224 , 238 , 261
Renninger, Mauritius, 134
Rimini, Alberto, 193
Rosen, Nathan, 96 , 225
Rovelli, Carlo, 187
Rutherford, Ernest, 35
Salter, Robert P., 112
Schack, Rüdiger, 245 , 249
Schrödinger, Erwin, 49 –50
and Bohmian mechanics, 154 –55, 163 , 165 , 176
and Born Rule, 263
cat-in-a-box thought experiment, 83 –84, 164 –66, 189 –90, 215
development of wave mechanics, 45 –49
on entanglement, 108
and many worlds theories, 229 , 231 , 233 –35, 238
and matrix mechanics, 44 –45
and molecular interferometry, 196 –97
and quantum eraser, 111 , 114 , 116 , 133
and single-particle experiments, 59 –60, 80 , 82 , 91
and spontaneous collapse, 192 –93
and universal wavefunction, 219 , 221 –22
Scully, Marlan, 112 –16, 175 , 179
Sebens, Charles “Chip,” 240 –41
Shimizu, Fujio, 197
Shimony, Abner, 225 –26, 236
Shipley, Patricia, 101
Simon, Christoph, 210
single-particle experiments, 59 –91
Aspect’s experiment, 60 –64
beam-splitting experiments, 64 –65, 68 –75, 75 –80
Schrödinger’s skepticism of, 59 –60
single molecule interference, 202
single-photon sensitivity, 2 , 21 –22
technological advances required for, 64 –68
thought experiments on, 80 –85
and Wheeler’s delayed choice experiment, 85 –91
See also Elitzur-Vaidman bomb puzzle
single-slit experiments, 33 –35
Sinha, Urbasi, 263 , 264
Sokal, Alan, 151 –52
spacetime curvature, 190 –91
special relativity, 95 , 261
spin of particles, 98 –99, 184
spontaneous collapse theories, 190 –95
“spooky action at a distance,” 91 , 107 , 128 , 145 , 176
Squires, Euan, 140
Stein, Gertrude, 130
Steinberg, Aephraim, 132 , 167 , 170 –79, 181 –85, 232
Stern, Alexander, 223
stochasticity, 39 , 48 , 153 –54, 234 , 239 , 257 , 261
superposition, quantum
and Bohmian mechanics, 165 , 169 , 179
and Born Rule, 263
entanglement and nonlocality, 107
and many worlds theories, 229
and molecular interferometry, 196 –202, 205
Penrose’s thought experiment, 188 –90
and quantum eraser, 115 , 120 , 128 , 134 , 136 , 142 , 145
Schrödinger’s cat thought experiment, 83 –84, 215
single-particle experiments, 79 –85, 87 , 91
and spontaneous collapse, 190 –92, 194
superposition mirror interferometer, 207 –13
and universal wavefunction, 218 –21, 225 –26
surreal trajectories, 166 , 175 –77, 179 , 181 –82
Susskind, Leonard, 255 –56
Taylor, Geoffrey Ingram, 33 –35, 63
thermodynamics, 149 , 238
Thompson, Randall, 104
Thomson, J. J., 28 –29, 32 –34, 35
Tonomura, Akira, 67 –68
twistor theory, 206
uncertainty principle
and Bohmian mechanics, 150 , 164 –65, 169
and Bohr-Schrödinger discussions, 51 –52
and Copenhagen interpretation, 54 –57
and future of quantum research, 258 –59
and many worlds theories, 241
and QBism, 245 , 247
and quantum eraser, 113 –14
and single-particle experiments, 86 , 90
and spontaneous collapse, 192
universal wavefunction theory, 218 –27
Ursin, Rupert, 121 , 129 –30
Vaidman, Lev, 2 , 133 –35, 138 –40, 144 , 169 , 215 –16, 227
virtual double-slit experiment, 117 , 117 –18, 122 , 171 , 177
virtual ensembles of particles, 258 –59, 261
Von Neumann, John, 48 , 54 , 100 –102, 114 –15, 151
walking droplet experiments, 158 –62
Wallace, David, 234 , 236 –37, 239 –42, 251
wavefunctions
and Bell’s theorem, 103 –4
and Bohmian mechanics, 153 –55, 161 –68, 176
entanglement and nonlocality, 107 –8
and EPR argument, 99 –100
and future of quantum research, 257 –59, 262 –64
and many worlds theories, 215 –16, 228 –31, 233 , 237 –39, 241 –42
and molecular interferometry, 198 –202
and nonlocality–relativity conflict, 94 –98
and Penrose’s thought experiment, 189 –90
and QBism, 245 –50, 252
and quantum eraser, 114 –16, 130 –35, 139 –40, 145
and Schrödinger’s wave mechanics, 46 –48
and single-particle experiments, 80 –84
and spontaneous collapse, 192 –95
and superposition mirror interferometer, 209 , 214 –15
universal wavefunction theory, 218 –27
wave-particle duality
and Bohr-Schrödinger discussions, 50
and Feynman on double-slit experiment, 6 –7
and first double-slit experiments, 17 –22
and photoelectric effect, 31
and quantum eraser, 112 , 127 , 145
and Schrödinger’s wave mechanics, 45 –49
and significance of the double-slit experiment, 108
and virtual double-slit experiment, 117 –18
“weak measurement,” 169 –72, 171 , 174 , 179 , 182 , 240
Weber, Tullio, 193
Wheeler, John, 85 –91, 113 , 129 –30, 218 , 222 –24, 244
which-way (welcher-weg) information
and Bohmian mechanics, 179 , 181
and many
worlds theories, 233
and molecular interferometry, 197 –98
and quantum eraser, 116 , 118 –20, 123 , 125 , 127 –28, 131 –32, 136 –37, 141 –42
Wigner, Eugene, 115 , 220 , 225
Wilczek, Frank, 238
Wiseman, Howard, 170 , 240 , 242 , 257 –59, 261
World War II, 148
Yoon-Ho Kim, 116 , 120 –21
Young, Thomas, 13 –16, 17 , 22 –24, 63 , 75 , 112 , 173
Young’s experiment with sunlight, 13 –16
Zanghi, Nino, 162
Zeilinger, Anton
and Bohmian mechanics, 150 , 164
and Bouwmeester’s work, 206
and molecular interferometry, 196 –98, 203
and QBism, 253
and quantum eraser, 110 –12, 116 , 120 –21, 124 , 140
Zender, Ludwig, 73
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
ABOUT THE AUTHOR
Anil Ananthaswamy is an award-winning journalist and former staff writer and deputy news editor for the London-based New Scientist magazine. He has been a guest editor for the science writing program at the University of California, Santa Cruz, and organizes and teaches an annual science journalism workshop at the National Centre for Biological Sciences in Bengaluru, India. He is a freelance feature editor for the Proceedings of the National Academy of Science’s Front Matter . He contributes regularly to New Scientist, and has also written for Nature, National Geographic News, Discover , Nautilus, Matter, The Wall Street Journal, and the UK’s Literary Review . His first book, The Edge of Physics , was voted book of the year in 2010 by Physics World , and his second book, The Man Who Wasn’t There , won a Nautilus Book Award in 2015 and was longlisted for the 2016 PEN/E. O. Wilson Literary Science Writing Award.
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Through Two Doors at Once: The Elegant Experiment That Captures the Enigma of Our Quantum Reality Page 25