What if you kept squishing an object—like the rabbit on this page—into a smaller and smaller space? You'd want to pull your hand away fast, because soon the rabbit would create a kind of sinkhole, and nothing, including light, could get out once it entered. Everything—including the rabbit—would fall in and never come out again!

These bottomless dimples in space are called black holes. Before Einstein there were predictions that there might be something like black holes, but his General Theory of Relativity helped people to understand years later how they exist.

Image Credits:

Kid photos: courtesy of Denis Finnin, AMNH; It's All Relative: Jim Paillot Rabbit, elephant, and ant: Francesco Santalacia; You Light Up My Life!: Cathy Sanchez Duvivier