What If? Serious Scientific Answers to Absurd Hypothetical Questions

They say there are no stupid questions, but that's obviously wrong. Still, trying to thoroughly answer a stupid question can take you to some pretty interesting places. It starts with a simple curiosity, a playful "what if," and then the math takes over, leading down paths of delightful and often catastrophic speculation. It's a journey that begins not with grand theories, but with the kind of questions a five-year-old might ask about whether there are more hard things or soft things in the world.

What if the Earth and everything on it suddenly stopped spinning, but the atmosphere kept its thousand-mile-per-hour velocity? The answer is that nearly everyone would die, and then things would get interesting. A supersonic wind would scour the surface of the planet, reducing virtually all human structures to ruins. In Boston, the winds would be twice as strong as a tornado, tearing skyscrapers from their foundations. Anyone caught on the surface would be pulverized by flying debris. The only survivors would be those deep underground - in subway tunnels or scientific bunkers - and the researchers at the South Pole, who would first notice the trouble when the outside world went completely, unnervingly silent.

The aftermath would be even stranger. The friction of the wind would generate a global heat blast, igniting thunderstorms and churning the oceans into a chaotic mix of spray and frigid, upwelled water. The day-night cycle would end, leaving one half of the planet to bake for six months while the other froze. And yet, our faithful companion, the Moon, would begin to gently tug on the silent Earth, its gravity slowly, patiently, starting our world's spin once more.

Consider another scenario: a baseball pitched at 90 percent the speed of light. The air molecules in its path wouldn't have time to get out of the way. The ball would slam into them so hard that their atoms would fuse, releasing a burst of gamma rays. An expanding bubble of incandescent plasma would race toward the batter, only slightly ahead of the ball itself. By the time it reached home plate - a mere 70 nanoseconds later - the ball would be a cloud of disintegrating particles. It would hit the bat, the batter, and the catcher, carrying them all backward as they vaporized. From a hilltop outside the city, you would see a blinding light, followed by a mushroom cloud. Everything within a mile of the park would be leveled. Major League Baseball Rule 6.08(b) suggests that the batter would be considered “hit by pitch” and would be eligible to advance to first base.

Some questions are less about explosive destruction and more about invisible, creeping dread. What if you went for a swim in a spent nuclear fuel pool? Assuming you're a good swimmer, you could tread water for hours. The water is an excellent radiation shield. As long as you stay near the surface, you might actually receive a lower dose of radiation than you would walking around on the street. The danger comes from diving. Swim down to the bottom, touch one of the fresh fuel canisters, and you'd receive a fatal dose. But as long as you don't dive deep or pick up any strange metal tubes you find lying around, you'd probably be fine. When I asked a friend who works at a research reactor what would happen, he thought for a moment. “In our reactor?” he said. “You'd die pretty quickly, before reaching the water, from gunshot wounds.”

The questions can also pull you across the vastness of time. Step into a time machine in Times Square and go back 1,000 years, and you would find yourself in a forest of chestnut and oak, stalked by wolves and mountain lions. Go back 100,000 years, and you might meet the terrifying short-faced bear or the saber-toothed cat. A billion years, and you'd arrive on the supercontinent of Rodinia, a world without plants or animals, where mats of blue-green algae were pumping toxic oxygen into the atmosphere, triggering the greatest extinction in history. And a million years in the future? The glaciers will have advanced again, grinding our cities to dust. Our most lasting relic will likely be a thin, out-of-place layer of processed hydrocarbons - the fossilized fragments of our shampoo bottles and shopping bags.

Sometimes, a simple pun can lead to planetary-scale horror. What if you gathered a mole (the unit of measurement) of moles (the furry critter)? That's 6.022 x 10²³ animals. Their combined mass would be more than half that of the Moon. Pulled together by gravity in deep space, they would form a sphere of meat, a new planet with a surface gravity like Pluto's. The pressure in the interior would be high enough to kill all bacteria, sterilizing the mole remains. Near the surface, anaerobic decomposition would generate heat and methane, which would erupt in geysers of death, blasting mole bodies into space. Eventually, the planet would cool and freeze solid, a silent, furry monument to a terrible idea.

From building a jetpack out of downward-firing machine guns to calculating the lethal dose of neutrinos from a nearby supernova, the universe is full of fascinating possibilities. Exploring them reveals the beautiful, strange, and often terrifying consistency of the laws of physics. They show us that if you drop a steak from orbit, it will be charred on the outside but raw on the inside, and that if everyone on Earth jumped at once, the planet wouldn't budge, but our civilization would collapse as seven billion people found themselves stranded in Rhode Island. The world is a wondrous place, and it's even more wondrous when you apply a little math.