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Unravel the secrets of the universe and untangle cutting-edge physics
Yes, you actually can understand quantum physics! String Theory For Dummies is a beginner’s guide, and we make it fun to find out about the all the recent trends and theories in physics, including the basics of string theory, with friendly explanations. Build a foundation of physics knowledge, understand the various string theories and the math behind them, and hear what the opponents to string theory have to say. It’s an exciting time to be alive in advanced physics, and this updated edition covers what’s new in the string world—the Large Hadron Collider, the Higgs Boson, gravitational waves, and lots of other big headlines. Unleash your inner armchair physicist with String Theory For Dummies.
Aspiring scientists or life-long learners will both be able to gain valuable information from this book. This accessible intro into string theory is for the theorists inside anyone.
Andrew Zimmerman Jones, PhD, is the physics guide at About.com, where he writes lessons and explanations for common physics problems and questions. Andrew earned his degree in physics from Wabash College and his PhD in mathematics from Purdue University. He is the author of the previous edition of String Theory For Dummies.
Alessandro Sfondrini is a theoretical physicist. He obtained his bachelor’s and master’s degrees in physics from the University of Padova. He is currently a Rita Levi-Montalcini Fellow and assistant professor in theoretical physics and mathematical methods and models at the University of Padova, as well as a member and IBM Einstein Fellow at the Institute for Advanced Study in Princeton, New Jersey.
Introduction 1
About This Book 1
Foolish Assumptions 2
Icons Used in This Book 3
Beyond the Book 4
Where to Go from Here 4
Part 1: Introducing String Theory 5
Chapter 1: So What Is String Theory Anyway? 7
String Theory: Seeing What Vibrating Strings Can Tell Us about the Universe 8
Using tiny and huge concepts to create a theory of everything 8
A quick look at where string theory has been 10
Introducing the Key Elements of String Theory 11
Strings and branes 11
Quantum gravity 13
Unification of forces 13
Supersymmetry 13
Extra dimensions 14
Understanding the Aim of String Theory 15
Quantizing gravity 15
Unifying forces 15
Explaining matter and mass 16
Defining space and time 17
Appreciating the Theory’s Amazing (and Controversial) Implications 18
Landscape of possible theories 18
The universe as a hologram 19
Why Is String Theory So Important? 19
Chapter 2: The Physics Road Dead-Ends at Quantum Gravity 21
Understanding Two Schools of Thought on Gravity 22
Newton’s law of gravity: Gravity as force 22
Einstein’s law of gravity: Gravity as geometry 24
Describing Matter: Physical and Energy-Filled 25
Viewing matter classically: Chunks of stuff 25
Viewing matter at a quantum scale: Chunks of energy 26
Grasping for the Fundamental Forces of Physics 26
Electromagnetism: Super-speedy energy waves 27
Nuclear forces: What the strong force joins, the weak force tears apart 28
Infinities: Why Einstein and the Quanta Don’t Get Along 28
Singularities: Bending gravity to the breaking point 29
Quantum jitters: Space-time under a quantum microscope 30
Unifying the Forces 31
Einstein’s failed quest to explain everything 32
A particle of gravity: The graviton 32
Supersymmetry’s role in quantum gravity 33
Chapter 3: Accomplishments and Failures of String Theory 35
Celebrating String Theory’s Successes 36
Predicting gravity out of strings 36
Explaining what happens to a black hole (sort of) 36
Explaining quantum field theory using string theory 37
String theory keeps making a comeback 38
Being the most popular theory in town 38
Considering String Theory’s Setbacks 39
The universe doesn’t have enough particles 40
Dark energy: The discovery string theory should have predicted 40
Where did all these “fundamental” theories come from? 41
Looking into String Theory’s Future 42
Theoretical complications: Can we figure out string theory? 43
Experimental complications: Can we prove string theory? 43
Part 2: The Physics Upon Which String Theory Is Built 45
Chapter 4: Putting String Theory in Context: Understanding the Method of Science 47
Exploring the Practice of Science 48
The myth of the scientific method 48
The need for experimental falsifiability 50
The foundation of theory is mathematics 52
The rule of simplicity 53
The role of objectivity in science 53
Understanding How Scientific Change Is Viewed 54
Precision and accuracy: Science as measurement 54
Old becomes new again: Science as revolution 55
Combining forces: Science as unification 56
What happens when you break it? Science as symmetry 57
Chapter 5: What You Must Know about Classical Physics 61
This Crazy Little Thing Called Physics 62
No laughing matter: What we’re made of 62
Add a little energy: Why stuff happens 64
Symmetry: Why some laws were made to be broken 65
All Shook Up: Waves and Vibrations 67
Catching the wave 67
Getting some good vibrations 69
Newton’s Revolution: How Physics Was Born 71
Force, mass, and acceleration: Putting objects into motion 72
Gravity: A great discovery 73
Optics: Shedding light on light’s properties 74
Calculus and mathematics: Enhancing scientific understanding 74
The Forces of Light: Electricity and Magnetism 75
Light as a wave: The ether theory 75
Invisible lines of force: Electric and magnetic fields 76
Maxwell’s equations bring it all together: Electromagnetic waves 78
Two dark clouds and the birth of modern physics 79
Chapter 6: Revolutionizing Space and Time: Einstein’s Relativity 81
What Waves Light Waves? Searching for the Ether 82
No Ether? No Problem: Introducing Special Relativity 84
Unifying space and time 86
Unifying mass and energy 88
Changing Course: Introducing General Relativity 89
Gravity as acceleration 89
Gravity as geometry 91
Testing general relativity 93
Surfing the gravitational waves 96
Applying Einstein’s Work to the Mysteries of the Universe 97
Kaluza-Klein Theory — String Theory’s Predecessor 98
Chapter 7: Brushing Up on Quantum Theory Basics 101
Unlocking the First Quanta: The Birth of Quantum Physics 102
Fun with Photons: Einstein’s Nobel Idea of Light 104
Waves and Particles Living Together 107
Light as a wave: The double slit experiment 107
Particles as a wave: The de Broglie hypothesis 108
Quantum physics to the rescue: The quantum wavefunction 110
Why We Can’t Measure It All: The Uncertainty Principle 111
Dead Cats, Live Cats, and Probability in Quantum Physics 112
Does Anyone Know What Quantum Theory Means? 114
Quantum Units of Nature: Planck Units 115
Chapter 8: The Standard Model of Particle Physics 119
Atoms, Atoms, Everywhere Atoms: Introducing Atomic Theory 120
Popping Open the Atomic Hood and Seeing What’s Inside 122
Discovering the electron 122
The nucleus is the thing in the middle 123
Watching the dance inside an atom 124
The Quantum Picture of the Photon: Quantum Electrodynamics 125
Dr Feynman’s doodles explain how particles exchange information 125
Discovering that other kind of matter: Antimatter 128
Sometimes a particle is only virtual 129
Digging into the Nucleus: Quantum Chromodynamics 130
The pieces that make up the nucleus: Nucleons 130
The pieces that make up the nucleon’s parts: Quarks 131
Looking into the Types of Particles 132
Particles of force: Bosons 132
Particles of matter: Fermions 133
Gauge Bosons: Particles Holding Other Particles Together 134
Exploring the Theory of Where Mass Comes From 135
What is the Higgs field? 136
Discovering the Higgs boson at the LHC 137
From Big to Small: The Hierarchy Problem in Physics 137
Chapter 9: Physics in Space: Considering Cosmology and Astrophysics 141
The Enlightened Universe and the Birth of Modern Astrophysics 143
Everything doesn’t revolve around Earth 143
Beholding the movements of heavenly bodies 144
Introducing the Idea of an Expanding Universe 145
Discovering that energy and pressure have gravity 145
Hubble drives it home 147
Finding a Beginning: The Big Bang Theory 148
Going to bat for the big bang: Cosmic microwave background radiation 149
Understanding where the chemical elements came from 151
Using Inflation to Solve the Universe’s Problems of Flatness and Horizon 152
The universe’s issues: Too far and too flat 153
Rapid expansion early on holds the solutions 154
Dark Matter: The Source of Extra Gravity 155
Dark Energy: Pushing the Universe Apart 155
Stretching the Fabric of Space-Time into a Black Hole 158
What goes on inside a black hole? 158
What goes on at the edge of a black hole? 159
Part 3: Building String Theory: A Theory of Everything 161
Chapter 10: Early Strings and Superstrings: Unearthing the Theory’s Beginnings 163
Bosonic String Theory: The First String Theory 164
Explaining the scattering of particles with early dual resonance models 164
Exploring the first physical model: Particles as strings 166
Bosonic string theory loses out to the Standard Model 167
Why Bosonic String Theory Doesn’t Describe Our Universe 168
Massless particles 169
Tachyons 169
No electrons allowed 170
25 space dimensions, plus 1 of time 171
Supersymmetry Saves the Day: Superstring Theory 173
Fermions and bosons coexist sort of 173
Double your particle fun: Supersymmetry hypothesizes superpartners 174
Some problems get fixed, but the dimension problem remains 176
Supersymmetry and Quantum Gravity in the Disco Era 177
The graviton is found hiding in string theory 177
The other supersymmetric gravity theory: Supergravity 179
String theorists don’t get no respect 179
A Theory of Everything: The First Superstring Revolution 180
But We’ve Got Five Theories! 181
Type I string theory 182
Type IIA string theory 182
Type IIB string theory 182
Two strings in one: Heterotic strings 182
How to Fold Space: Introducing Calabi-Yau Manifolds 183
String Theory Loses Steam 185
Chapter 11: M-Theory and Beyond: Bringing String Theory Together 187
Introducing the Unifying Theory: M-Theory 187
Translating one string theory into another: Duality 188
Using two dualities to unite five superstring theories 192
The second superstring revolution begins: Connecting to the 11-dimensional theory 193
Branes: Stretching Out a String 194
The discovery of D-branes: Giving open strings something to hold on to 195
Creating particles from p-branes 196
Deducing that branes are required by M-theory 197
Uniting D-branes and p-branes into one type of brane 198
Using branes to explain black holes 199
Getting stuck on a brane: Brane worlds 200
Matrix Theory as a Potential M-Theory 200
Chapter 12: Exploring Strings and Their Landscape 203
Strings and Fields: String Field Theory 203
Splitting and joining of strings and how to avoid infinities 204
Trying to visualize how strings create loops 206
String Theory Gets Surprised by Dark Energy 208
Considering Proposals for Why Dimensions Sometimes Uncurl 209
Measurable dimensions 209
Infinite dimensions: Randall-Sundrum models 210
Understanding the Current Landscape: A Multitude of Theories 211
The anthropic principle requires observers 212
Disagreeing about the principle’s value 214
Chapter 13: Gaining Insights from the Holographic Principle 217
What’s a Hologram? 217
Creating optical holograms 218
More bang for your buck: Encoding information in fewer dimensions 219
Using Holograms to Understand Black Holes 222
Going down a black hole 222
Black holes and entropy 223
If it works for black holes, it works for me 224
Considering AdS/CFT Correspondence 226
Checking the predictions 227
AdS space, or living in an M C Escher painting 227
CFTs: conformal, but nonconformist 231
Understanding quantum gravity through AdS/CFT correspondence 232
Turning the Tables: Using Holography to Study Strongly Interacting Matter 233
The force is strong when using AdS/CFT 233
Cooking up a soup of quarks and gluons 235
Chapter 14: Putting String Theory to the Test 237
Understanding the Obstacles 238
Testing an incomplete theory with indistinct predictions 238
Testing versus proof 239
Analyzing Supersymmetry 240
Finding the missing sparticles 240
Testing implications of supersymmetry 241
Testing Gravity from Extra Dimensions 242
Checking the inverse-square law 242
Searching for gravity waves to understand inflation 243
Disproving String Theory Sounds Easier Than It Is 244
Violating relativity 244
Could proton decay spell disaster? 245
Seeking mathematical inconsistencies 246
Bootstrapping Our Way into String Theory 247
Looking for Evidence in the Cosmic Laboratory: Exploring the Universe 248
Using outer space rays to amplify small events 249
Analyzing dark matter and dark energy 252
Detecting cosmic superstrings 253
Looking for Evidence Closer to Home: Using Particle Accelerators 254
Accelerating heavy ions at the RHIC 254
Colliders of the future 255
LHC finds a boson, but no superpartners yet 256
Discovering the Higgs boson 257
Looking for superpartners 258
Part 4: The Unseen Cosmos: String Theory on the Boundaries of Knowledge 261
Chapter 15: Making Space for Extra Dimensions 263
What Are Dimensions? 264
2-Dimensional Space: Exploring the Geometry of Flatland 265
Euclidean geometry: Think back to high school geometry 265
Cartesian geometry: Merging algebra and Euclidean geometry 266
Three Dimensions of Space 267
A straight line in space: Vectors 267
Twisting 2-dimensional space in three dimensions: The Mobius strip 268
More twists in three dimensions: Non-Euclidean geometry 270
Four Dimensions of Space-Time 272
Adding More Dimensions to Make a Theory Work 273
Sending Space and Time on a Bender 274
Are Extra Dimensions Really Necessary? 275
Offering an alternative to multiple dimensions 276
Weighing fewer dimensions against simpler equations 277
Chapter 16: Our Universe — String Theory, Cosmology, and Astrophysics 279
The Start of the Universe with String Theory 280
What was before the bang? 280
What banged? 282
Explaining Black Holes with String Theory 286
String theory and the thermodynamics of a black hole 286
String theory and the black hole information paradox 288
The Evolution of the Universe 289
The swelling continues: Eternal inflation 289
The hidden matter and energy 291
The Undiscovered Country: The Future of the Cosmos 293
A universe of ice: The big freeze 293
From point to point: The big crunch 294
A new beginning: The big bounce 294
Exploring a Finely Tuned Universe 294
Chapter 17: Have Time, Will Travel 297
Temporal Mechanics 101: How Time Flies 298
The arrow of time: A one-way ticket 298
Relativity, worldlines, and worldsheets: Moving through space-time 299
Hawking’s chronology protection conjecture: You’re not going anywhere 302
Slowing Time to a Standstill with Relativity 303
Time dilation: Sometimes even the best watches run slow 303
Black hole event horizons: An extra-slow version of slow motion 304
General Relativity and Wormholes: Doorways in Space and Time 305
Taking a shortcut through space and time with a wormhole 306
Overcoming a wormhole’s instability with negative energy 308
Crossing Cosmic Strings to Allow Time Travel 310
A Two-Timing Science: String Theory Makes More Time Dimensions Possible 310
Adding a new time dimension 311
Reflecting two-time physics onto a one-time universe 311
Does two-time physics have any real applications? 312
Sending Messages through Time 313
Part 5: What the Other Guys Say: Criticisms and Alternatives 317
Chapter 18: Taking a Closer Look at the String Theory Controversy 319
The String Wars: Outlining the Arguments 320
50 years and counting: Framing the debate from the skeptic’s point of view 321
A rise of criticisms 323
Is String Theory Scientific? 324
Argument No 1: String theory explains nothing 324
Argument No 2: String theory explains too much 325
Turning a Critical Eye on String Theorists 329
Hundreds of physicists just can’t be wrong 329
Holding the keys to the academic kingdom 331
Does String Theory Describe Our Universe? 332
Making sense of extra dimensions 333
Space-time should be fluid 333
The ever-elusive superpartners 334
How finite is string theory? 335
A String Theory Rebuttal 335
What about the extra dimensions? 336
Space-time fluidity? 337
Does string theory need to be finite? 337
Trying to Make Sense of the Controversy 337
Chapter 19: Loop Quantum Gravity: String Theory’s Biggest Competitor 339
Taking the Loop: Introducing Another Road to Quantum Gravity 340
The great background debate 340
What is looping anyway? 341
Making Predictions with Loop Quantum Gravity 343
Gravity exists (Duh!) 343
Black holes contain only so much space 343
Gamma ray burst radiation travels at different speeds 344
Finding Favor and Flaw with Loop Quantum Gravity 344
The benefit of a finite theorem 344
Spending some time focusing on the flaws 345
So Are These Two Theories the Same with Different Names? 346
Chapter 20: Considering Other Ways to Explain the Universe 349
Taking Other Roads to Quantum Gravity 350
CDT: If you’ve got the time, I’ve got the space 351
Quantum Einstein gravity: Too small to tug 352
Quantum graphity: Disconnecting nodes 352
Tensor models: gluing the space-time together 353
Newton and Einstein Don’t Make All the Rules: Modifying the Law of Gravity 354
DSR: Twice as many limits as ordinary relativity 355
MOND: Disregarding dark matter 355
VSL: Light used to travel even faster 356
MOG: The bigger the distance, the greater the gravity 358
Massive gravity and bimetric theory: making the graviton heavy 359
Rewriting the Math Books and Physics Books at the Same Time 360
Compute this: Quantum information theory 360
Looking at relationships: Twistor theory 361
Uniting mathematical systems: Noncommutative geometry 362
Mathematics All the Way Down: Are We Living in a Simulation? 363
Part 6: The Part of Tens 365
Chapter 21: Ten Tests for a Theory of Quantum Gravity 367
Reproduce Gravity 368
Compute Quantum Corrections 368
Describe How Gravity and Matter Interact 368
Explain Inflation 369
Explain What Happens When Someone Enters a Black Hole 369
Explain Whether Singularities Are Allowed 369
Explain the Birth and Death of Black Holes 370
Explain the Holographic Principle 370
Provide Testable Predictions 371
Describe Its Own Limitations 371
Index 373
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