A clear, plain-English guide to this complex scientific theory String theory is the hottest topic in physics right now, with books on the subject (pro and con) flying out of the stores. String Theory For Dummies offers an accessible introduction to this highly mathematical "theory of everything," which posits ten or more dimensions in an attempt to explain the basic nature of matter and energy. Written for both students and people interested in science, this guide explains concepts, discusses the string theory's hypotheses and predictions, and presents the math in an approachable manner. It features in-depth examples and an easy-to-understand style so that readers can understand this controversial, cutting-edge theory.

Table of Contents:
Introduction 1 About This Book 1 Conventions Used in This Book 2 What You’re Not to Read 3 Foolish Assumptions 3 How This Book Is Organized 4 Part I: Introducing String Theory 4 Part II: The Physics Upon Which String Theory Is Built 4 Part III: Building String Theory: A Theory of Everything 5 Part IV: The Unseen Cosmos: String Theory on the Boundaries of Knowledge 5 Part V: What the Other Guys Say: Criticism and Alternatives 5 Part VI: The Part of Tens 5 Icons Used in this Book 6 Where to Go from Here 6 Part I: Introducing String Theory 7 Chapter 1: So What Is String Theory Anyway? 9 String Theory: Seeing What Vibrating Strings Can Tell Us about the Universe 9 Using tiny and huge concepts to create a theory of everything 10 A quick look at where string theory has been 11 Introducing the Key Elements of String Theory 12 Strings and branes 12 Quantum gravity 14 Unification of forces 14 Supersymmetry 15 Extra dimensions 15 Understanding the Aim of String Theory 16 Explaining matter and mass 16 Defining space and time 17 Quantizing gravity 18 Unifying forces 18 Appreciating the Theory’s Amazing (and Controversial) Implications 19 Landscape of possible theories 19 Parallel universes 20 Wormholes 20 The universe as a hologram 21 Time travel 21 The big bang 21 The end of the universe 22 Why Is String Theory So Important? 22 Chapter 2: The Physics Road Dead Ends at Quantum Gravity 25 Understanding Two Schools of Thought on Gravity 26 Newton’s law of gravity: Gravity as force 26 Einstein’s law of gravity: Gravity as geometry 28 Describing Matter: Physical and Energy-Filled 28 Viewing matter classically: Chunks of stuff 29 Viewing matter at a quantum scale: Chunks of energy 29 Grasping for the Fundamental Forces of Physics 30 Electromagnetism: Super-speedy energy waves 30 Nuclear forces: What the strong force joins, the weak force tears apart 31 Infinities: Why Einstein and the Quanta Don’t Get Along 32 Singularities: Bending gravity to the breaking point 33 Quantum jitters: Space-time under a quantum microscope 33 Unifying the Forces 35 Einstein’s failed quest to explain everything 35 A particle of gravity: The graviton 36 Supersymmetry’s role in quantum gravity 37 Chapter 3: Accomplishments and Failures of String Theory 39 Celebrating String Theory’s Successes 39 Predicting gravity out of strings 40 Explaining what happens to a black hole (sort of) 40 Explaining quantum fi eld theory using string theory 41 Like John Travolta, string theory keeps making a comeback 41 Being the most popular theory in town 42 Considering String Theory’s Setbacks 43 The universe doesn’t have enough particles 43 Dark energy: The discovery string theory should have predicted 44 Where did all of these “fundamental” theories come from? 45 Looking into String Theory’s Future 45 Theoretical complications: Can we figure out string theory? 46 Experimental complications: Can we prove string theory? 46 Part II: The Physics upon Which String Theory is Built 49 Chapter 4: Putting String Theory in Context: Understanding the Method of Science 51 Exploring the Practice of Science 52 The myth of the scientific method 52 The need for experimental falsifiability 53 The foundation of theory is mathematics 55 The rule of simplicity 56 The role of objectivity in science 57 Understanding How Scientific Change Is Viewed 57 Old becomes new again: Science as revolution 58 Combining forces: Science as unification 59 What happens when you break it? Science as symmetry 60 Chapter 5: What You Must Know about Classical Physics 63 This Crazy Little Thing Called Physics 63 No laughing matter: What we’re made of 64 Add a little energy: Why stuff happens 66 Symmetry: Why some laws were made to be broken 67 All Shook Up: Waves and Vibrations 68 Catching the wave 69 Getting some good vibrations 70 Newton’s Revolution: How Physics Was Born 72 Force, mass, and acceleration: Putting objects into motion 73 Gravity: A great discovery 74 Optics: Shedding light on light’s properties 75 Calculus and mathematics: Enhancing scientific understanding 75 The Forces of Light: Electricity and Magnetism 75 Light as a wave: The ether theory 76 Invisible lines of force: Electric and magnetic fields 76 Maxwell’s equations bring it all together: Electromagnetic waves 79 Two dark clouds and the birth of modern physics 80 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 85 Unifying mass and energy 87 Changing Course: Introducing General Relativity 89 Gravity as acceleration 89 Gravity as geometry 91 Testing general relativity 92 Applying Einstein’s Work to the Mysteries of the Universe 95 Kaluza-Klein Theory — String Theory’s Predecessor 96 Chapter 7: Brushing Up on Quantum Theory Basics 99 Unlocking the First Quanta: The Birth of Quantum Physics 100 Fun with Photons: Einstein’s Nobel Idea of Light 102 Waves and Particles Living Together 105 Light as a wave: The double slit experiment 105 Particles as a wave: The de Broglie hypothesis 106 Quantum physics to the rescue: The quantum wavefunction 108 Why We Can’t Measure It All: The Uncertainty Principle 109 Dead Cats, Live Cats, and Probability in Quantum Physics 111 Does Anyone Know What Quantum Theory Means? 112 Interactions transform quantum systems: The Copenhagen interpretation 113 If no one’s there to see it, does the universe exist? The participatory anthropic principle 113 All possibilities take place: The many worlds interpretation 114 What are the odds? Consistent histories 115 Searching for more fundamental data: The hidden variables interpretation 115 Quantum Units of Nature — Planck Units 116 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 121 Discovering the electron 122 The nucleus is the thing in the middle 123 Watching the dance inside an atom 123 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 127 Sometimes a particle is only virtual 128 Digging into the Nucleus: Quantum Chromodynamics 129 The pieces that make up the nucleus: Nucleons 129 The pieces that make up the nucleon’s pieces: Quarks 130 Looking into the Types of Particles 131 Particles of force: Bosons 131 Particles of matter: Fermions 132 Gauge Bosons: Particles Holding Other Particles Together 133 Exploring the Theory of Where Mass Comes From 134 From Big to Small: The Hierarchy Problem in Physics 135 Chapter 9: Physics in Space: Considering Cosmology and Astrophysics 137 Creating an Incorrect Model of the Universe 138 Aristotle assigns realms to the universe 138 Ptolemy puts Earth at the center of the universe (and the Catholic Church agrees) 139 The Enlightened Universe: Some Changes Allowed 141 Copernicus corrects what’s where in the universe 141 Beholding the movements of heavenly bodies 142 Introducing the Idea of an Expanding Universe 143 Discovering that energy and pressure have gravity 143 Hubble drives it home 145 Finding a Beginning: The Big Bang Theory 146 Bucking the big bang: The steady state theory 147 Going to bat for the big bang: Cosmic microwave background radiation 148 Understanding where the chemical elements came from 150 Using Inflation to Solve the Universe’s Problems of Flatness and Horizon 150 The universe’s issues: Too far and too flat 151 Rapid expansion early on holds the solutions 152 Dark Matter: The Source of Extra Gravity 153 Dark Energy: Pushing the Universe Apart 153 Stretching the Fabric of Space-Time into a Black Hole 156 What goes on inside a black hole? 156 What goes on at the edge of a black hole? 157 Part III: Building String Theory: A Theory of Everything 159 Chapter 10: Early Strings and Superstrings: Unearthing the Theory’s Beginnings 161 Bosonic String Theory: The First String Theory 161 Explaining the scattering of particles with early dual resonance models 162 Exploring the first physical model: Particles as strings 164 Bosonic string theory loses out to the Standard Model 165 Why Bosonic String Theory Doesn’t Describe Our Universe 166 Massless particles 166 Tachyons 167 No electrons allowed 168 25 space dimensions, plus 1 of time 168 Supersymmetry Saves the Day: Superstring Theory 170 Fermions and bosons coexist sort of 171 Double your particle fun: Supersymmetry hypothesizes superpartners 172 Some problems get fixed, but the dimension problem remains 173 Supersymmetry and Quantum Gravity in the Disco Era 174 The graviton is found hiding in string theory 174 The other supersymmetric gravity theory: Supergravity 176 String theorists don’t get no respect 176 A Theory of Everything: The First Superstring Revolution 177 But We’ve Got Five Theories! 178 Type I string theory 179 Type IIA string theory 179 Type IIB string theory 179 Two strings in one: Heterotic strings 179 How to Fold Space: Introducing Calabi-Yau Manifolds 180 String Theory Loses Steam 182 Chapter 11: M-Theory and Beyond: Bringing String Theory Together 183 Introducing the Unifying Theory: M-Theory 183 Translating one string theory into another: Duality 184 Using two dualities to unite five superstring theories 188 The second superstring revolution begins: Connecting to the 11-dimensional theory 188 Branes: Stretching Out a String 190 The discovery of D-branes: Giving open strings something to hold on to 190 Creating particles from p-branes 192 Deducing that branes are required by M-theory 192 Uniting D-branes and p-branes into one type of brane 193 Using branes to explain black holes 194 Getting stuck on a brane: Brane worlds 195 Matrix Theory as a Potential M-Theory 196 Gaining Insight from the Holographic Principle 197 Capturing multidimensional information on a flat surface 197 Connecting the holographic principle to our reality 198 Considering AdS/CFT correspondence 199 String Theory Gets Surprised by Dark Energy 200 Considering Proposals for Why Dimensions Sometimes Uncurl 201 Measurable dimensions 202 Infinite dimensions: Randall-Sundrum models 202 Understanding the Current Landscape: A Multitude of Theories 204 The anthropic principle requires observers 204 Disagreeing about the principle’s value 207 Chapter 12: Putting String Theory to the Test 209 Understanding the Obstacles 210 Testing an incomplete theory with indistinct predictions 210 Test versus proof 211 Testing Supersymmetry 211 Finding the missing sparticles 212 Testing implications of supersymmetry 212 Testing Gravity from Extra Dimensions 213 Testing the inverse square law 214 Searching for gravity waves in the CMBR 214 Disproving String Theory Sounds Easier Than It Is 215 Violating relativity 215 Mathematical inconsistencies 216 Could Proton Decay Spell Disaster? 217 Looking for Evidence in the Cosmic Laboratory: Exploring the Universe 218 Using outer space rays to amplify small events 218 Analyzing dark matter and dark energy 222 Detecting cosmic superstrings 222 Looking for Evidence Closer to Home: Using Particle Accelerators 223 Relativistic Heavy Ion Collider (RHIC) 224 Large Hadron Collider (LHC) 224 Colliders of the future 226 Part IV: The Unseen Cosmos: String Theory on the Boundaries of Knowledge 227 Chapter 13: Making Space for Extra Dimensions 229 What Are Dimensions? 229 2-Dimensional Space: Exploring the Geometry of Flatland 230 Euclidean geometry: Think back to high school geometry 231 Cartesian geometry: Merging algebra and Euclidean geometry 231 Three Dimensions of Space 233 A straight line in space: Vectors 233 Twisting 2-dimensional space in three dimensions: The Mobius strip 234 More twists in three dimensions: Non-Euclidean geometry 236 Four Dimensions of Space-Time 237 Adding More Dimensions to Make a Theory Work 238 Sending Space and Time on a Bender 239 Are Extra Dimensions Really Necessary? 240 Offering an alternative to multiple dimensions 241 Weighing fewer dimensions against simpler equations 242 Chapter 14: Our Universe — String Theory, Cosmology, and Astrophysics 245 The Start of the Universe with String Theory 245 What was before the bang? 246 What banged? 247 Explaining Black Holes with String Theory 250 String theory and the thermodynamics of a black hole 250 String theory and the black hole information paradox 252 The Evolution of the Universe 253 The swelling continues: Eternal inflation 253 The hidden matter and energy 255 The Undiscovered Country: The Future of the Cosmos 257 A universe of ice: The big freeze 257 From point to point: The big crunch 257 A new beginning: The big bounce 258 Exploring a Finely Tuned Universe 258 Chapter 15: Parallel Universes: Maybe You Can Be Two Places at Once 261 Exploring the Multiverse: A Theory of Parallel Universes 261 Level 1: If you go far enough, you’ll get back home 264 Level 2: If you go far enough, you’ll fall into wonderland 265 Level 3: If you stay where you are, you’ll run into yourself 267 Level 4: Somewhere over the rainbow, there’s a magical land 269 Accessing Other Universes 270 A history of hyperspace 270 How quantum mechanics can get us from here to there 272 Chapter 16: Have Time, Will Travel 275 Temporal Mechanics 101: How Time Flies 276 The arrow of time: A one-way ticket 276 Relativity, worldlines, and worldsheets: Moving through space-time 278 Hawking’s chronology protection conjecture: You’re not going anywhere 279 Slowing Time to a Standstill with Relativity 280 Time dilation: Sometimes even the best watches run slow 281 Black hole event horizons: An extra-slow version of slow motion 282 General Relativity and Wormholes: Doorways in Space and Time 282 Taking a shortcut through space and time with a wormhole 284 Overcoming a wormhole’s instability with negative energy 286 Crossing Cosmic Strings to Allow Time Travel 286 A Two-Timing Science: String Theory Makes More Time Dimensions Possible 287 Adding a new time dimension 287 Reflecting two-time onto a one-time universe 288 Does two-time physics have any real applications? 289 Sending Messages through Time 290 Time Travel Paradoxes 290 The twin paradox 291 The grandfather paradox 292 Where are the time travelers? 292 Part V: What the Other Guys Say: Criticisms and Alternatives 295 Chapter 17: Taking a Closer Look at the String Theory Controversy 297 The String Wars: Outlining the Arguments 298 Thirty years and counting: Framing the debate from the skeptic’s point of view 299 A rise of criticisms 300 Is String Theory Scientific? 301 Argument No. 1: String theory explains nothing 301 Argument No. 2: String theory explains too much 302 Turning a Critical Eye to String Theorists 305 Hundreds of physicists just can’t be wrong 305 Holding the keys to the academic kingdom 306 Does String Theory Describe Our Universe? 308 Making sense of extra dimensions 309 Space-time should be fluid 309 How finite is string theory? 310 A String Theory Rebuttal 311 Chapter 18: Loop Quantum Gravity: String Theory’s Biggest Competitor 313 Taking the Loop: Introducing Another Road to Quantum Gravity 313 The great background debate 314 What is looping anyway? 314 Making Predictions with Loop Quantum Gravity 317 Gravity exists (Duh!) 317 Black holes contain only so much space 317 Gamma ray burst radiation travels at different speeds 318 Finding Favor and Flaw with Loop Quantum Gravity 318 The benefit of a finite theorem 318 Spending some time focusing on the flaws 319 So Are These Two Theories the Same with Different Names? 320 Chapter 19: Considering Other Ways to Explain the Universe 323 Taking Other Roads to Quantum Gravity 324 Causal dynamical triangulations (CDT): If you’ve got the time, I’ve got the space 324 Quantum Einstein gravity: Too small to tug 325 Quantum graphity: Disconnecting nodes 326 Internal relativity: Spinning the universe into existence 327 Newton and Einstein Don’t Make All the Rules: Modifying the Law of Gravity 328 Doubly special relativity (DSR): Twice as many limits as ordinary relativity 328 Modified Newtonian dynamics (MOND): Disregarding dark matter 328 Variable speed of light (VSL): Light used to travel even faster 329 Modified gravity (MOG): The bigger the distance, the greater the gravity 331 Rewriting the Math Books and Physics Books at the Same Time 332 Compute this: Quantum information theory 333 Looking at relationships: Twistor theory 334 Uniting mathematical systems: Noncommutative geometry 334 Part VI: The Part of Tens 337 Chapter 20: Ten Questions a Theory of Everything Should (Ideally) Answer 339 The Big Bang: What Banged (and Inflated)? 340 Baryon Asymmetry: Why Does Matter Exist? 340 Hierarchy Issues: Why Are There Gaps in Forces, Particles, and Energy Levels? 341 Fine-Tuning: Why Do Fundamental Constants Have the Values They Do? 341 Black Hole Information Paradox: What Happens to Missing Black Hole Matter? 341 Quantum Interpretation: What Does Quantum Mechanics Mean? 342 Dark Mystery No. 1: What Is Dark Matter (and Why Is There So Much)? 343 Dark Mystery No. 2: What Is Dark Energy (and Why Is It So Weak)? 343 Time Symmetry: Why Does Time Seem to Move Forward? 344 The End of the Universe: What Comes Next? 344 Chapter 21: Ten Notable String Theorists 345 Edward Witten 345 John Henry Schwarz 346 Yoichiro Nambu 347 Leonard Susskind 347 David Gross 348 Joe Polchinski 348 Juan Maldacena 348 Lisa Randall 349 Michio Kaku 349 Brian Greene 350 Index 351