xkcd's What If?

his question came from Keira, who at age four and a half wanted to build a billion-story building. Actually, it came from Keira’s dad, who wanted to help Keira appreciate how big and difficult such a project would be.

This question comes from N. Murdoch, who was thinking about how the three wise men in the Christmas story followed a star to Bethlehem where they found the baby Jesus. The question is: what if you did walk towards a known star at a fixed speed? What path would you trace on the Earth?

What would the world be like if the land masses were spread out the same way as now, but rotated by 90 degrees?

What would happen to the Earth if the Sun suddenly switched off? is probably the single most popular question submitted to What If.

his question comes from Daniel, who notes that people sometimes say “If I had all the money in the world …” in order to discuss what they would do if they had no financial constraints. Of course, it’s natural to then ask: what would happen if you literally had all of the world's money?

This question comes from Matt, who asks: I've long thought about putting a flamethrower on the front of a car to melt snow and ice before you drive across it. Now I've realized that a flamethrower is impractical, but what about a high-powered microwave emitter?

his question comes from David, who asks: what would happen if one tried to funnel Niagara Falls through a straw?

This question comes from Matt, who asks: what would happen if the Moon were replaced with an equivalently-massed black hole? And what would a lunar ("holar"?) eclipse look like?