Physicists have wondered for decades whether infinitely dense points known as singularities can ever exist outside black holes, which would expose the mysteries of quantum gravity for all to see. Singularities--snags in the otherwise smooth fabric of space and time where Albert Einstein's classical gravity theory breaks down and the unknown quantum theory of gravity is needed--seem to always come cloaked in darkness, hiding from view behind the event horizons of black holes. The British physicist and mathematician Sir Roger Penrose conjectured in 1969 that visible or "naked" singularities are actually forbidden from forming in nature, in a kind of cosmic censorship. But why should quantum gravity censor itself? Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.

Black holes are indisputably weird. These objects, formed when the center of massive stars collapse in upon itself, are so dense that nothing, not even light, can escape their gravitational pull. Let's, for argument's sake, suppose you have the bad luck to venture too close to a black hole and get pulled past its event horizon but you are lucky enough to make it past the event horizon alive (without being spaghettified). Believe it or not, things get much, much weirder once you cross the event horizon. You are now headed toward the center of the black hole -- the singularity, which is an infinitely small region of infinite density.