| Chapter 1 - What is Time? | 1 |
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| The Nature of Time | 2 |
| Direction of Time | 2 |
| Time Never Stops | 2 |
| Speed of Time | 3 |
| Time Appears to be Continuous | 3 |
| Quantum Time: Time May be Discrete | 3 |
| Does Time Simply Exist, or is it Caused by Something? | 4 |
| Time Seems Infinite | 5 |
| Does Time Have a Beginning or End? | 5 |
| Chapter 2 – How do we measure time? | 7 |
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| The History of Measuring Time | 7 |
| Why 60 Seconds? Why 60 Minutes? Why 24 Hours? | 9 |
| How Scientists Define Time | 10 |
| Calendars | 11 |
| Leap Seconds | 12 |
| Time of Day | 13 |
| Before Mechanical Clocks Were Invented | 13 |
| Mechanical Clocks | 20 |
| Pendulum Clocks: A Giant Leap | 20 |
| Spring-Driven Clocks: Time Becomes Portable | 21 |
| Electric Clocks: Powering Time | 21 |
| Quartz Clocks: a Crystal Revolution | 21 |
| Atomic Clocks: the Master Timekeepers | 21 |
| Chapter 3 – Time Gets Weirder | 22 |
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| Time is Relative | 22 |
| The Hafele–Keating Experiment (1971) | 23 |
| Gravity and Time: Clocks on Mountains | 23 |
| Watching Muons | 24 |
| Because Time is Relative | 24 |
| How GPS works | 26 |
| Time Can Bend and Stretch | 29 |
| Time Bends When You Move Very Fast | 30 |
| What Does It Mean for Time to Stretch? | 30 |
| Why Does Time Stretch at High Speeds? | 31 |
| Time Bends When Gravity is Strong | 32 |
| Conclusion | 33 |
| Is Time Just Part of a Simulation? | 33 |
| Time Can Not be Undone | 34 |
| Entropy and the Arrow of Time | 35 |
| New Scientific Theories About Reversing Time | 35 |
| Cause and Effect are Linked to Time | 36 |
| What Is Cause and Effect? | 37 |
| Why Time Matters for Cause and Effect | 37 |
| What Happens in the Strange World of Quantum Physics? | 37 |
| Conclusion | 38 |
| Cyclical time | 38 |
| Ancient Beliefs About Cyclical Time | 38 |
| Natural Examples of Cyclical Time | 39 |
| Modern Scientific Ideas About Cyclical Time | 39 |
| Conclusion | 40 |
| Block Time: Is the Universe Frozen? | 40 |
| How Precise Clocks May Warp Time | 41 |
| Imaginary Time | 42 |
| How Is Imaginary Time Different? | 43 |
| Why Do Scientists Use Imaginary Time? | 43 |
| Is Imaginary Time Real? | 43 |
| Conclusion | 44 |
| Is Time Real? | 44 |
| Chapter 4 – Perception of Time | 45 |
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| How Does the Brain Measure Time? | 45 |
| Why Does Time Feel Different Sometimes? | 46 |
| How Scientists Study Time Perception | 47 |
| Special Tricks of the Mind | 47 |
| Conclusion | 48 |
| Chapter 5 – Time travel | 48 |
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| cientific Thought on Time Travel | 48 |
| Cosmic Strings: Threads of the Early Universe | 50 |
| Movies That Illustrate Time Travel | 51 |
| Back to the Future (1985): | 51 |
| Interstellar (2014): | 52 |
| The Adam Project (2022): | 53 |
| The Time Travel Paradox | 53 |
| Time Travel by Telescope | 54 |
| Conclusion | 54 |
| Chapter 6 – Weird Thoughts About Time | 55 |
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| Does the Future Already Exist? | 55 |
| Living in Space-Time. | 55 |
| What if We Lived in Space Without Time? | 56 |
| What if We Lived in Time Without Space? | 56 |
| What if We Lived With Neither Space nor Time? | 57 |
| Learning Activities | 58 |
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| Thought Experiments | 58 |
| Twin Time Activity | 58 |
| Block Time Activity | 60 |
| No Space, No Time Activity | 61 |
| Backward Time Activity | 62 |
| Paused Time Activity | 64 |
| Discrete Time Activity | 67 |
| Simple Experiments | 68 |
| Stick Clock Activity | 68 |
| Sundial Activity | 70 |
| Hour Glass Activity | 71 |
| Candle Clock Activity | 73 |
| Water Clock Activity | 75 |
| Explore Your Perception of Time | 77 |
| Creative Activities | 78 |
| Draw Time | 78 |
| Invent a New Clock | 78 |
| Time Capsule | 78 |
| Simulated Day | 78 |
| Appendix | 79 |
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| Measurement of Time | 79 |
| Quotes About Time | 82 |
| Riddles About Time | 84 |
| Jokes About Time | 85 |
| Glossary | 87 |
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