Let us look to the future or, at the very least, a ridiculous sci-fi version thereof. Baseball players, pumped full of astronomical quantities of steroids or equipped with bionic baseball-throwing robot arms, are somehow managing to launch fastballs at 90 percent of the speed of light—roughly 270 million meters per second (or 604 million miles per hour). What would it be like to be the batter? The pitch would be pretty hard to hit, right?
Unfortunately it wouldn’t be so simple, or so mundane.
The ball is going so fast that everything else is practically stationary. Even the molecules in the air are stationary. Air molecules vibrate back and forth at a few hundred miles per hour, but the ball is moving through them at 600 million miles per hour. This means that as far as the ball is concerned, they’re just hanging there, frozen.
After about 70 nanoseconds the ball arrives at home plate. The batter hasn’t even seen the pitcher let go of the ball, since the light carrying that information arrives at about the same time the ball does. Collisions with the air have eaten the ball away almost completely, and it is now a bullet-shaped cloud of expanding plasma (mainly carbon, oxygen, hydrogen, and nitrogen) ramming into the air and triggering more fusion as it goes. The shell of x-rays hits the batter first, and a handful of nanoseconds later the debris cloud hits.
Suppose you’re watching from a hilltop outside the city. The first thing you see is a blinding light, far outshining the sun. This gradually fades over the course of a few seconds, and a growing fireball rises into a mushroom cloud. Then, with a great roar, the blast wave arrives, tearing up trees and shredding houses.
This unexpectedly terrifying revelation was put together as the first of a new series by xkcd comic Randall Munroe, where the physicist-turned-cartoonist set out to answer user-submitted questions. Munroe’s second entry calculates the odds of guessing a perfect score on the SAT. (Hint: it doesn’t end well.)
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