Water, at exactly zero degrees, doesn’t know what it wants to be. Add the tiniest nudge of energy and it stays liquid; subtract the same and it snaps into ice, molecules locking into a perfect repeating lattice. The tipping point itself, that knife-edge moment of indecision, is its own strange kind of object. For decades, physicists suspected something similar could happen to spacetime. Not water molecules, but the very fabric of the universe, organising itself into a crystal-like structure right on the threshold of becoming a black hole. Now, for the first time, a team from Vienna and Frankfurt has written down an exact mathematical description of what that object looks like, using nothing more than paper and pencil.
Miguel Silva Rodrigues