xkcd's What If?

What would happen if the Earth and all terrestrial objects suddenly stopped spinning, but the atmosphere retained its velocity?

What would happen if you tried to hit a baseball pitched at 90% the speed of light?

Stopping rain from falling on something with an umbrella is boring. What if you tried to stop rain with a laser that targeted and vaporized each incoming droplet before it could come within ten feet of the ground?

How long could a nuclear submarine last in orbit?

What if I took a swim in a typical spent nuclear fuel pool? Would I need to dive to actually experience a fatal amount of radiation? How long could I safely stay at the surface?

What would happen if everyone on earth stood as close to each other as they could, jumped, and landed on the ground all at the same instant?

If all the lightning that occurs worldwide on any given day all struck the same place at once, what would happen to that place?

If every human somehow simply disappeared from the face of the earth, how long would it be before the last artificial light source would go out?

How quickly would the oceans drain if a circular portal 20 meters in diameter appeared at the bottom of Challenger Deep, the deepest spot in the ocean? How would the Earth change as the water is being drained?

If you had a printed version of the whole of Wikipedia, how many printers would you need in order to keep up with the changes made to the live version?

Suppose you did drain earth’s oceans and dumped the water on top of the Curiosity rover, how would Mars change as the water accumulated?

What would happen if you spent a nanosecond on the surface of the sun? Would it warm you up, burn you to a cinder, or do nothing at all?

What if a glass of water was, all of a sudden, literally half empty? The pessimist is probably more right about how it would turn out than the optimist.

How long would it take for people to notice their weight gain if the mean radius of the world increased by 1 cm every second? (Assuming the average composition of rock were maintained)

If every person on Earth aimed a laser pointer at the Moon at the same time, would it change color?

What if we tried a laser array with even MORE power?

What if there were a lake on the Moon? What would it be like to swim in it? Presuming that it’s sheltered in a regular atmosphere, in some giant dome or something.