Let There Be Light: The Story of Light from Atoms to Galaxies 9781848167582, 9781848167599, 184816758X
This book is the first of its kind devoted to the key role played by light and electromagnetic radiation in the universe
805 203 32MB
English Pages 531 [552] Year 2012
Table of contents :
Contents......Page 16
Preface to the First Edition......Page 8
Preface to the Second Edition......Page 10
Acknowledgements......Page 14
Chapter 1 Introducing Light......Page 22
The middle ages......Page 23
The visible spectrum......Page 25
The astronomical method......Page 26
Terrestrial measurement......Page 27
The speed of light in context......Page 29
The journey of a photon......Page 30
The eye is like a digital camera......Page 32
Two computers — the back of the eye and the brain......Page 33
Why is the grass green?......Page 34
Seeing in the dark......Page 35
Contradictory evidence......Page 36
Light as a wave......Page 37
James Clerk Maxwell......Page 38
Light as a particle......Page 39
An illustration of duality?......Page 40
Particles have wave properties......Page 41
The Copenhagen interpretation......Page 42
The universal messenger......Page 43
The quickest route......Page 44
Light takes the quickest route......Page 45
The quickest path via a reflection......Page 46
The law of reflection......Page 47
A plane mirror......Page 48
Reversal from left to right......Page 49
A spherical concave mirror......Page 50
Applications of concave mirrors......Page 53
The ‘death rays’ of Archimedes......Page 54
A historical interlude: Pierre de Fermat (1601–1665)......Page 56
Making visible things we cannot see......Page 60
The refractive index......Page 61
The lifeguard problem......Page 62
Snell’s law......Page 63
The reverse journey......Page 64
Apparent depth......Page 65
Practical applications of total internal reflection......Page 66
Light pipes and optical fibres......Page 67
Freedom of choice when a ray meets a boundary......Page 68
The mystery......Page 69
A practical puzzle — two-way mirrors......Page 70
Converging lenses......Page 71
Fermat’s principle applied to lenses......Page 72
Ray tracing through a thin lens......Page 73
Principal rays (thin lenses)......Page 74
Breaking the symmetry......Page 75
Masking a lens......Page 77
3.4 Objects and images: diverging lenses......Page 78
Lenses in contact......Page 79
The power of a lens......Page 80
Accommodation......Page 81
Hypermetropia (long-sightedness)......Page 83
Distant objects......Page 84
Nearer but not clearer......Page 86
The simple magnifier......Page 87
Compound microscopes......Page 90
Telescopes......Page 91
3.9 A final note on Fermat’s principle......Page 92
The pioneers of generalized classical mechanics......Page 93
When light reaches us after a long, long journey......Page 94
Philosophical reasons why the earth should be round......Page 95
Experimental evidence that the earth is round......Page 96
The phases of the moon......Page 97
A lunar eclipse......Page 98
A solar eclipse......Page 100
Relative sizes of the sun and the moon......Page 102
Shrinking shadows......Page 103
The distance to the sun......Page 106
A practical problem......Page 107
Astronomical distances......Page 109
Ptolemy’s geocentric model......Page 110
Frames of reference......Page 112
Copernicus and the heliocentric model......Page 113
Where did the epicycles come from?......Page 116
4.6 After Copernicus......Page 117
Looking back with hindsight: why Brahe did not see any parallax......Page 118
Kepler’s discovery......Page 119
Galileo Galilei (1564–1642)......Page 120
4.7 The solar system in perspective......Page 123
A historical interlude: Galileo Galilei (1564–1642)......Page 125
5.1 The birth of astrophysics......Page 132
Isaac Newton and gravitation......Page 133
Falling without getting nearer......Page 134
The mystery of gravitation......Page 136
Newton’s law of gravitation......Page 137
Testing the law......Page 138
Acceleration of the moon towards the earth......Page 140
Explanation of Kepler’s laws......Page 141
Predicting the existence of new planets......Page 142
Neptune is there!......Page 143
Planets of other suns......Page 144
Other galaxies......Page 147
5.4 Reconstructing the past......Page 149
The Big Bang theory......Page 150
A blast from the past......Page 151
White dwarfs......Page 153
Supernovae......Page 154
Supernovae in other galaxies......Page 155
Pulsars......Page 157
Black holes......Page 159
Escape velocities......Page 161
How to ‘see’ the invisible......Page 162
Time stands still......Page 163
A historical interlude: Isaac Newton (1642–1727)......Page 164
6.1 Waves — the basic means of communication......Page 170
Mechanical waves in a medium......Page 172
Transverse waves......Page 173
Longitudinal waves......Page 174
Generating the sine function......Page 177
An expression for a sine wave in motion......Page 178
The superposition principle......Page 179
Path difference and phase difference......Page 180
When two waves travelling in opposite directions meet......Page 181
A string fixed at both ends......Page 183
Standing waves......Page 184
6.4 Forced oscillations and resonance......Page 185
6.5 Natural frequencies of vibration and resonance......Page 186
The Tacoma Narrows Bridge disaster......Page 187
The Mexico City earthquake......Page 188
6.6 Diffraction — waves can bend around corners......Page 189
6.7 The magic of sine and the simplicity of nature......Page 190
The sum of a number of sine waves......Page 191
A historical interlude: Jean Baptiste Joseph Fourier (1768–1830)......Page 192
Sound as a pressure wave......Page 196
The speed of sound......Page 197
Ultrasound and infrasound......Page 198
Sound navigation and ranging (SONAR)......Page 199
Ultrasound in nature......Page 201
Ultrasound in medicine......Page 202
7.3 The superposition of sound waves......Page 208
Standing waves......Page 209
7.4 Sound intensity......Page 212
Real and perceived differences in the intensity of sound......Page 213
Quantifying perception......Page 214
Intensity level (loudness)......Page 216
The ‘annoyance factor’......Page 218
7.5 Other sensations......Page 219
Tone quality......Page 221
Propagation of sound in open and confined spaces......Page 222
String instruments......Page 224
Wind instruments......Page 225
A moving observer......Page 226
A moving source......Page 227
Shock waves......Page 228
Shock waves and light......Page 230
A historical interlude: The sound barrier......Page 231
Chapter 8 Light as a Wave......Page 236
The mystery of waves in nothing......Page 237
Superposition......Page 238
Huygens’ principle......Page 239
Huygens’ principle and refraction......Page 240
Diffraction......Page 242
Huygens’ principle and diffraction......Page 243
Diffraction of light......Page 244
Other apertures......Page 246
The curious case of the opaque disc......Page 247
Images may overlap......Page 248
The Rayleigh criterion......Page 249
8.5 Other electromagnetic waves......Page 250
Message from the stars......Page 251
Other windows on the universe......Page 252
Young’s experiment......Page 253
Thin film interference......Page 256
Non-reflective coatings......Page 257
8.8 Diffraction gratings......Page 259
Practical diffraction gratings......Page 261
8.9 Other ‘lights’......Page 262
X-ray diffraction......Page 263
8.10 Coherence......Page 267
The question of phase......Page 268
Polarization of electromagnetic waves......Page 269
What happens to light as it passes through a polaroid?......Page 270
Polarization by reflection......Page 272
A historical interlude: Thomas Young (1773–1829)......Page 273
Photography......Page 276
History of the photograph......Page 278
Colour photography......Page 281
Digital photography......Page 282
Interpretation of photographic images......Page 283
The inventor......Page 284
The principle......Page 285
Making a hologram......Page 286
Why does a holographic image look so real?......Page 288
Applications of holography......Page 289
The gravitational force......Page 292
The electrostatic force......Page 293
Coulomb’s law......Page 295
Vector fields......Page 296
A picture to represent a physical law......Page 297
Gauss’s theorem......Page 299
The energy in an electric field......Page 303
Magnetic materials......Page 304
Electric currents......Page 306
Oersted’s discovery......Page 307
Ampère’s law......Page 309
Summary......Page 311
The effect of a magnetic field on an electric charge......Page 312
Definition of electrical units......Page 313
Electromagnetism......Page 314
The interaction between moving charges......Page 315
Faraday’s discovery......Page 316
Faraday’s law of electromagnetic induction......Page 318
Putting facts together......Page 319
An important extension to Ampère’s law......Page 320
The four laws......Page 322
Making an electromagnetic pulse......Page 324
The speed of the magnetic tidal wave......Page 325
Cause and effect — a summary......Page 328
Putting theory into practice......Page 330
A historical interlude: James Clerk Maxwell (1831–1879)......Page 332
The light from hot soot......Page 338
How does matter emit electromagnetic energy?......Page 339
Experimental results — the blackbody radiation spectrum......Page 340
The Stefan–Boltzmann law......Page 341
Wien’s displacement law......Page 342
Cavity radiation......Page 343
Wien’s spectral distribution law......Page 345
A cavity model based on the wave nature of light......Page 347
How can the theoretical models be ‘half right’?......Page 348
The formula — but not the explanation......Page 349
Nature’s secret......Page 350
The quantum hypothesis......Page 351
Quantum discrimination......Page 352
The distribution of energy among the oscillators......Page 353
The average energy......Page 354
What does the quantum do after it is emitted?......Page 355
A new philosophy......Page 356
A historical interlude: Max Planck (1858–1947)......Page 357
Chapter 12 The Development of Quantum Mechanics......Page 362
From oscillators to photons to other things......Page 363
The quantum enters the picture......Page 364
Quantum jumps — light comes out of the atom......Page 366
The demise of determinism......Page 367
A new way of thinking......Page 368
Light from the hydrogen atom......Page 369
A matrix for everything......Page 370
The laws of nature......Page 371
Matrices do not commute!......Page 372
Laws of nature must be built into the matrices......Page 373
One measurement disturbs the other......Page 374
A ‘table top’ experiment with polaroids......Page 375
What we have learned from the experiment......Page 376
Experimenting with a series of polaroids......Page 377
The uncertainty principle......Page 379
The Schrödinger approach......Page 381
De Broglie’s original idea......Page 382
Adapting de Broglie waves......Page 384
Uncertainty from another aspect......Page 385
A wider view......Page 386
Relativity and quantum mechanics......Page 387
Triumph out of difficulty......Page 388
Positron emission tomography......Page 389
Antiprotons and antihydrogen......Page 391
Critics of the Copenhagen interpretation......Page 392
Bell’s theorem......Page 393
A precursor of quantum reality......Page 394
A historical interlude: Niels Bohr (1885–1962)......Page 395
Chapter 13 Atoms of Light Acting as Particles......Page 402
Short sharp shocks......Page 403
There are ‘grains’ in the light beam......Page 404
How long would we expect to wait? An order-of-magnitude calculation......Page 405
The ‘lucky’ electron......Page 406
Einstein’s photoelectric equation......Page 407
Millikan’s experiment......Page 409
Current flowing uphill......Page 410
Practical applications......Page 412
Energy transfer......Page 415
Collision of X-ray photons......Page 416
The photon loses energy but does not slow down......Page 417
A historical interlude: Robert A. Millikan (1868–1953)......Page 419
Chapter 14 Atoms of Light Behaving as Waves......Page 426
Detecting a single photon......Page 427
The long thin line......Page 428
Single slit diffraction......Page 429
Measuring ‘clicks’ as photons arrive one by one......Page 430
Separating the possible paths......Page 433
Partial reflection......Page 435
The strange theory of the photon......Page 438
The rotating amplitude vector......Page 439
Why light appears to travel in straight lines......Page 441
How can we believe all this?......Page 442
What then is new?......Page 443
Quantum electrodynamics......Page 444
A historical interlude: Richard Feynman (1918–1988)......Page 446
Empty space is the same everywhere and for everyone......Page 452
Space and the ancient philosophers......Page 453
Space and time — according to Isaac Newton......Page 455
Starting with a clean slate......Page 456
Frames of reference — defining a point of view......Page 457
Specifying the prejudices......Page 459
The Michelson–Morley experiment......Page 461
Timing the ferry......Page 462
Details of the experiment......Page 464
The new model......Page 466
Nature does not discriminate......Page 467
Galileo had the right idea!......Page 469
The Galilean transformation......Page 470
Galileo’s first step......Page 471
Einstein’s second postulate......Page 472
A paradox* — how can they possibly get the same result?......Page 473
Einstein puts the facts together......Page 474
The impossible’ in mathematical form......Page 475
The gamma factor......Page 476
15.6 Pythagoras re-visited......Page 478
Moving on to three dimensions......Page 479
15.7 The fourth dimension......Page 480
Invariant interval in space–time......Page 481
The smoking astronaut......Page 483
What is the meaning of ‘simultaneous’?......Page 485
A historical interlude: Hendrik A. Lorentz (1853–1928)......Page 486
Chapter 16 Relativity Part 2: Verifiable Predictions......Page 492
Time dilation in action......Page 493
Living on borrowed time?......Page 494
16.2 Bringing energy into the picture......Page 495
Conservation of momentum — a thought experiment with snooker balls......Page 496
Interacting with another time frame......Page 497
Relativistic definition of momentum......Page 499
Energy content’......Page 500
Putting things into perspective......Page 504
High-energy particle accelerators......Page 505
Nuclear structure......Page 507
Nuclear fission......Page 509
A synopsis......Page 510
A historical interlude: Albert Einstein (1879–1955)......Page 511
Then there was light......Page 516
Collisions make particles......Page 517
Prediction and discovery of the π meson......Page 518
The forces between the particles......Page 520
The laws of the world of elementary particles......Page 522
Quarks......Page 524
The return of photographic emulsion......Page 528
More quarks......Page 531
The role of light as the carrier of the electromagnetic force......Page 532
Unification — the long hard road......Page 533
The heavy photon......Page 534
The Higgs boson......Page 537
The full circle......Page 539
Index......Page 540
About the Authors......Page 552
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