What If?

What If? Plot Summary

Introduction

We humans have always been fascinated by the "what if" questions. What if the Earth stopped spinning? What if everyone jumped at once? These seemingly absurd hypothetical scenarios might appear trivial at first glance, but they actually serve as perfect gateways into understanding profound scientific principles. This book takes us on a journey through the realm of the impossible, using rigorous scientific analysis to explore questions that range from amusing thought experiments to potentially catastrophic scenarios. The beauty of these absurd questions lies in their ability to illuminate scientific concepts in ways that conventional approaches cannot. By pushing our understanding to extreme limits, we gain insights into physics, biology, astronomy, and mathematics that might otherwise remain obscure. Throughout these pages, you'll discover how the laws of thermodynamics apply to hair dryers turned to maximum power, how orbital mechanics would affect a submarine in space, and why a raindrop the size of a city would be catastrophic. These explorations not only satisfy our curiosity but also sharpen our critical thinking skills and deepen our appreciation for how science helps us understand the boundaries of our reality.

Chapter 1: The Physics of Extreme Events

When we push physical systems to their limits, the results can be both fascinating and terrifying. Consider what would happen if all the world's lightning strikes occurred in the same place simultaneously. This isn't just a matter of bright lights and loud noises – the energy released would be equivalent to about two atomic bombs, creating a plasma channel six meters in diameter and leaving a crater the size of a basketball court. The resulting shockwave would flatten trees and buildings for miles around. Scale plays a crucial role in extreme physics. A relativistic baseball – one traveling at 90% the speed of light – demonstrates this perfectly. Upon release, the ball would immediately begin colliding with air molecules so violently that they would fuse with atoms on the ball's surface, creating a continuous fusion reaction. The resulting expanding bubble of plasma and radiation would vaporize everything within miles, leaving a sizable crater where a city once stood. This isn't just a baseball game gone wrong – it's a demonstration of how relativistic effects transform ordinary objects into weapons of mass destruction. Temperature extremes reveal equally surprising physics. If a standard hair dryer were placed in an airtight box and turned on indefinitely, the temperature would rise until equilibrium was reached – about 60°C with a standard 1875-watt dryer. But what if we kept increasing the power? At 18,750 watts, the box would reach 200°C. At 187 megawatts, the box would glow white-hot at 2400°C, melting through most materials and creating a pool of lava beneath it. This isn't just about heat – it's about energy transfer, thermodynamics, and material science pushed to breaking points. The most extreme events often involve astronomical scales. A magnitude 15 earthquake would release approximately 10^32 joules of energy – roughly equivalent to the gravitational binding energy of Earth itself. In other words, such an earthquake wouldn't just damage buildings; it would literally tear the planet apart. This helps us understand why the Richter scale has no practical upper limit – beyond certain magnitudes, we're no longer talking about earthquakes but planetary destruction. What makes these extreme scenarios so valuable is how they strip away our everyday assumptions. When we consider a steak dropped from the edge of space, we must account for atmospheric compression, heat dissipation, and terminal velocity – concepts that apply to everything from space shuttle reentry to meteorite impacts. These absurd questions thus become powerful tools for understanding the fundamental forces that shape our universe.

Chapter 2: Cosmic Catastrophes and Planetary Phenomena

What would happen if the Sun suddenly switched off? This seemingly simple question opens a window into our complex relationship with our star. Without the Sun, Earth would immediately begin cooling, though not as quickly as you might think. The oceans, with their enormous heat capacity, would release warmth gradually. Within weeks, however, photosynthesis would cease, and within months, global temperatures would plummet below freezing worldwide. Within a year, the oceans would begin to freeze over, starting from the poles. The atmosphere would eventually condense and freeze onto the surface, leaving a cold, dark world orbiting a dead star. Planetary rotation creates phenomena we take for granted. If Earth suddenly stopped spinning while the atmosphere retained its velocity, the results would be catastrophic. At the equator, where the surface moves at about 1,000 mph relative to Earth's axis, everyone would experience supersonic winds. These winds would destroy virtually all human structures, strip the surface bare, and create a roiling mix of wind, spray, fog, and rapid temperature changes as the atmosphere interacted with the suddenly stationary surface. The physics behind this scenario helps explain why planetary rotation is so crucial to climate stability. The movement of celestial bodies creates other fascinating possibilities. If you were placed on the opposite side of an uninhabited Earth-like planet from another person, how long would it take to find each other? The physicist's simple answer – about 3,000 years of random walking – ignores human psychology and strategy. A better approach would be to leave trails and markers, similar to how ants find food and return to their colonies. This scenario demonstrates how search algorithms and probability theory apply to real-world problems of exploration and discovery. Scale changes everything in planetary science. If we expanded Earth's radius by just one centimeter per second, the effects would be barely noticeable at first. After a day, you'd weigh only 0.01% more. After a month, cracks would begin appearing in concrete structures as the surface expanded. After five years, gravity would be 25% stronger, and most infrastructure would have collapsed. After 40 years, with gravity tripled, even the strongest humans could barely walk, trees would collapse under their own weight, and crops couldn't stand upright. This thought experiment reveals how finely tuned our bodies and ecosystems are to Earth's specific gravitational conditions. Our cosmic neighborhood presents its own absurdities. If you attempted to fly a Cessna aircraft on different planets, the results would vary dramatically. On Mars, the thin atmosphere would require near-supersonic speeds just to achieve lift. On Venus, the plane would fly well briefly before melting in the extreme heat. On Titan, Saturn's largest moon, the dense atmosphere and low gravity would make human-powered flight possible – you could fly by flapping artificial wings, though the -290°F temperature would quickly freeze any unprotected equipment or person. These scenarios help us understand how atmospheric density, gravity, and temperature interact to create the conditions for flight.

Chapter 3: Human Survival in Impossible Scenarios

How long could a human survive in various extreme environments? If you suddenly began rising steadily at one foot per second, your journey would start benignly enough. After 30 seconds, you'd be 30 feet off the ground. After two hours and two kilometers, the temperature would drop below freezing. By the seven-hour mark, you'd reach the "Death Zone" above 8,000 meters, where oxygen content is too low to support human life. Your blood oxygen would plummet, and you would quickly lose consciousness and die. This scenario illustrates how our survival depends on the specific atmospheric conditions that exist near Earth's surface. Water presents its own survival challenges. If you were to swim in a spent nuclear fuel pool, you'd face surprisingly few immediate dangers. The water provides excellent radiation shielding, and as long as you stayed away from the fuel rods at the bottom, you'd receive less radiation than walking around on the street. The real danger would come if you dove to the bottom or picked up something highly radioactive. This counterintuitive scenario demonstrates how radiation exposure follows the inverse square law and how water effectively blocks many types of radiation. Space presents perhaps the most hostile environment for human survival. If a nuclear submarine were somehow placed in orbit, the crew would face immediate problems. While the hull would easily withstand the pressure differential, the submarine's oxygen generation system requires water to function. Without it, the crew would have only a few days of reserve oxygen. Temperature regulation would also become critical – without the ocean's cooling effect, the submarine would need to carefully manage its reactor output to avoid overheating. This scenario highlights the challenges of life support systems in space and why spacecraft design differs so dramatically from submarine design. Extreme acceleration forces pose another survival challenge. If you tried to touch a bullet with the density of a neutron star, you'd experience increasingly strong gravitational forces as you approached. Within 20 centimeters, the pull would become too strong to resist. If your fingertip actually made contact, the pressure would be so intense that blood would break through your skin, creating what one fictional character described as "an adequate vacuuming system." This thought experiment illustrates how extreme density creates gravitational fields that can overcome molecular bonds in ordinary matter. These survival scenarios aren't merely entertaining thought experiments – they help us understand the precise environmental conditions humans require to survive. By examining these edge cases, we gain appreciation for the narrow range of temperatures, pressures, and radiation levels that make human life possible, and the engineering challenges involved in creating artificial environments that can sustain us beyond those natural boundaries.

Chapter 4: Mathematical Curiosities and Probability Puzzles

How many unique English tweets are possible? This seemingly simple question opens a fascinating window into information theory. While Twitter's 140-character limit technically allows for 27^140 possible strings using the English alphabet plus spaces (approximately 10^200), most would be meaningless gibberish. Information theorist Claude Shannon determined that written English contains about 1.1 bits of information per character, suggesting there are roughly 2^(140×1.1) ≈ 2×10^46 meaningfully different English tweets. This number is so vast that if you spent your entire life reading tweets, you wouldn't make a dent in the possibilities. This demonstrates how combinatorial explosion creates practical infinities even within seemingly limited systems. Probability creates counterintuitive results in many scenarios. If everyone who took the SAT guessed on every multiple-choice question, how many perfect scores would there be? With 158 multiple-choice questions and 5 options each, the probability of getting all correct by guessing is 1 in 5^158, or approximately 1 in 10^110. Even if all four million 17-year-olds took the test, and each used a computer to take it a million times daily for five billion years, the chance of anyone getting a perfect score on just the math section would be about 0.0001%. This illustrates how quickly probability diminishes with multiple independent events. Random encounters create another probability puzzle. If you call a random phone number and say "God bless you," what are the chances the person who answers just sneezed? Based on average sneeze frequency (about 200-400 sneezes per person per year) and assuming a sneeze lasts about 1-2 seconds, the probability is roughly 1 in 40,000. Interestingly, this is far more likely than calling someone who just committed murder (about 1 in 1,000,000,000), but still extremely improbable. This calculation demonstrates how we can quantify the likelihood of coincidences using basic probability theory. The mathematics of scale reveals surprising relationships. If you were to build a bridge of LEGO bricks from London to New York, how many bricks would you need? The Atlantic Ocean is about 5,500 kilometers wide, requiring about 350 million standard bricks laid end to end. While this seems enormous, it's actually feasible – over 400 billion LEGO pieces have been produced. However, building a bridge capable of supporting traffic would require vastly more bricks and would face insurmountable engineering challenges from ocean currents and waves. This scenario illustrates how engineering feasibility often depends on exponential rather than linear scaling factors. These mathematical curiosities do more than entertain – they help us develop intuition about large numbers, probability, and scale. By exploring these edge cases, we gain tools for evaluating claims, understanding risks, and appreciating the mathematical structures that underlie our world. They remind us that mathematics isn't just about calculation but about developing frameworks for understanding complex systems.

Chapter 5: Biological Oddities and Thought Experiments

What would happen if everyone on Earth stayed away from each other for a couple of weeks? Could we eradicate the common cold? This thought experiment reveals fascinating aspects of disease transmission. Rhinoviruses, which cause most colds, are completely eliminated from the body by the immune system after infection. With no animal reservoirs, if humans isolated perfectly, these viruses would theoretically die out. However, the plan would fail because immunocompromised people can harbor viruses for months or years, serving as reservoirs. Additionally, the logistical challenges would be insurmountable – distributing food, maintaining essential services, and finding space for 7 billion people to isolate would likely cause societal collapse. This scenario illustrates both viral epidemiology and the complex interdependencies of modern civilization. Human genetics creates equally fascinating thought experiments. If a woman had sperm cells made from her own stem cells and used them to impregnate herself, what would be her relationship to her daughter? The child would have an inbreeding coefficient of 0.50 – equivalent to three generations of sibling marriages – likely causing severe genetic damage. This occurs because half the child's chromosomes would have their "partner" chromosomes replaced by copies of themselves, increasing the chances of harmful recessive traits manifesting. This scenario illustrates why sexual reproduction evolved – it increases genetic diversity and reduces the expression of harmful mutations. The limits of human capability create another category of biological curiosities. How high can a human throw something? Humans excel at throwing compared to other animals, with professional baseball pitchers achieving speeds of 100 mph. If throwing straight upward, an average person could launch a baseball about three "giraffes" high (15 meters), while professional pitcher Aroldis Chapman could achieve fourteen "giraffes" (70 meters). This seemingly simple question reveals the remarkable neural timing capabilities humans have evolved – a pitcher must release the ball within half a millisecond of the optimal point, despite nerve impulses taking five milliseconds to travel the length of the arm. Collective human behavior presents its own absurdities. If everyone on Earth stood as close together as possible and jumped simultaneously, what would happen? The Earth, outweighing humanity by a factor of ten trillion, would be pushed down by less than an atom's width. The real consequences would come after landing – the sudden concentration of humanity would create catastrophic logistical problems. With all people gathered in an area the size of Rhode Island, transportation networks would collapse, food and water would quickly run out, and disease would spread rapidly. This scenario demonstrates both the insignificance of human physical force on a planetary scale and the fragility of our distribution networks. These biological thought experiments help us understand fundamental principles of evolution, genetics, physiology, and ecology. By examining edge cases and impossible scenarios, we gain insight into why our bodies and societies function as they do, and the constraints that shape biological systems at every level from cells to ecosystems.

Chapter 6: Energy, Technology and Their Limits

How much computing power could we achieve if the entire world population stopped what they were doing and started performing calculations? This question reveals fascinating aspects of human vs. computer capabilities. Using benchmark tests, a human performing calculations by hand can execute about one instruction every 90 seconds. By comparison, a modern smartphone processor works about 70 times faster than the entire world population combined. The year when a single desktop computer first surpassed humanity's combined computing power? 1994. However, when measuring neural complexity rather than raw calculation speed, computers didn't surpass a single human brain until around 2004. This comparison illustrates both how specialized our brains are for certain tasks and how rapidly computing technology has advanced. The physics of transportation creates hard limits on what's possible. Getting to orbit isn't difficult because space is high up – it's difficult because you need to go incredibly fast sideways. While space begins about 100 kilometers above Earth, reaching orbital velocity requires speeds of about 8 kilometers per second. This is why rockets expend most of their energy accelerating horizontally rather than vertically. To visualize this speed: if you were moving at orbital velocity on Earth's surface, you'd cross the length of a football field before a rifle bullet traveled 10 yards. This principle explains why spacecraft need massive rockets despite space being relatively close. Energy transfer between systems reveals other technological limits. When comparing internet bandwidth to physical transportation of data, FedEx still wins. Cisco estimates total internet traffic at 167 terabits per second, but a fleet of FedEx aircraft loaded with high-density storage devices could theoretically transfer 14 petabits per second – almost 100 times more. Even with fiber optic advances, physical transportation will likely maintain this advantage for decades, though at the cost of high latency. This demonstrates how different metrics (bandwidth vs. latency) create different optimal solutions for information transfer. Power generation faces similar physical constraints. Could you boil a cup of tea just by stirring it vigorously? The math says no – heating water from room temperature to near boiling in two minutes requires about 700 watts of power, equivalent to what a microwave provides. Stirring by hand adds only about a ten-millionth of a watt. Even if you could somehow stir fast enough to add significant energy, the tea would cavitate (form vacuum bubbles) and cool through increased surface area rather than heat up. This example illustrates how energy transformations follow strict physical laws that limit what's possible regardless of effort. These technological thought experiments help us understand the fundamental physical principles that constrain our engineering capabilities. By exploring these limits, we gain appreciation for both the remarkable achievements of modern technology and the immutable physical laws that define what's ultimately possible, regardless of our ingenuity or resources.

Chapter 7: Earth Science Through Absurd Hypotheticals

What if a rainstorm dropped all its water in a single giant drop? This scenario transforms a common natural phenomenon into a catastrophic event. A typical thunderstorm contains about 600 million tons of water – enough to form a sphere over a kilometer in diameter. When this massive drop hits the ground at over 200 meters per second, it creates a supersonic omnidirectional jet that scours everything within kilometers. The wall of water expands outward, demolishing structures up to 30 kilometers away. This thought experiment illustrates how the distributed nature of rainfall is crucial for life on Earth – concentrated energy release, even from something as benign as rain, can be devastating. Draining the oceans presents another Earth-altering scenario. If a 10-meter radius portal to space opened at the bottom of the Mariana Trench, the oceans would drain surprisingly slowly – less than a centimeter per day initially. There wouldn't even be a visible whirlpool at the surface. Over centuries, as the water level dropped, new islands would appear, continents would expand, and inland seas would form as basins disconnected from the main oceans. Eventually, the mid-ocean ridges would emerge as vast mountain ranges, creating a dramatically different Earth with shallow seas covering only a fraction of today's ocean basins. This scenario helps us visualize the true scale and topography of Earth's ocean floor. Earth's rotation creates another category of hypotheticals. What is the longest possible sunset you can experience while driving on paved roads? At the equator, sunset lasts just over two minutes, while in London it can take 200-300 seconds. The absolute longest would be at the South Pole in March, where sunset takes 38-40 hours as the Sun circles just above the horizon. However, there are no paved roads near the poles. The optimal strategy for maximizing sunset duration on paved roads would be to drive in northern Scandinavia during summer, using specific routes to stay ahead of the terminator line, achieving a sunset about 95 minutes long. This scenario demonstrates how latitude affects day length and the complex geometry of Earth's rotation. Geological time scales reveal Earth's dynamic nature. If Earth's radius expanded by one centimeter per second while maintaining its average composition, the effects would initially be subtle. After a day, gravity would increase by only 0.01%. After a month, with a 0.4% gravity increase, cracks would begin appearing in long structures. After five years, gravity would be 25% stronger, and most infrastructure would have collapsed. After 100 years, with gravity six times stronger, humans couldn't move and would die from oxygen toxicity as the atmosphere became too dense to breathe. After 300 years, the Moon would pass within Earth's Roche limit and break apart, temporarily giving Earth rings. This thought experiment illustrates how Earth's specific size and gravity are precisely balanced to support life as we know it. These Earth science hypotheticals do more than entertain – they help us visualize geological processes that normally occur too slowly or on too large a scale for human perception. By compressing time or altering physical parameters, we gain intuition about the dynamic systems that shape our planet and the delicate balance that makes it habitable.

Summary

At its core, this exploration of absurd hypotheticals reveals a profound truth: the laws of physics, chemistry, and biology that govern our universe are consistent even in the most extreme scenarios. By pushing these principles to their limits through seemingly ridiculous questions, we gain deeper insights into how our world actually works. Whether calculating the energy released by a relativistic baseball or determining how long a human could survive rising steadily into the atmosphere, these thought experiments strip away our everyday assumptions and force us to confront fundamental scientific principles in their purest form. The next time you find yourself wondering about some impossible scenario – what would happen if everyone on Earth pointed a laser at the Moon, or how many LEGO bricks it would take to build a bridge across the Atlantic – remember that such questions aren't merely idle curiosities. They're opportunities to explore the boundaries of scientific understanding and develop intuition about complex systems. For those intrigued by this approach to learning, consider exploring computational modeling or thought experiments in your own field of interest. The absurd questions you ask today might lead to the scientific breakthroughs of tomorrow, or at the very least, provide a fascinating new lens through which to view the remarkable universe we inhabit.

About Author

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Randall Munroe

Randall Munroe, a former NASA roboticist, is the creator of the webcomic xkcd and the author of xkcd: volume 0. The International Astronomical Union recently named an asteroid after him; asteroid 4942 Munroe is big enough to cause a mass extinction if it ever hits a planet like Earth. He lives in Cambridge, Massachusetts.

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