The original version of this story appeared in Quanta Magazine.
The reason we can gracefully glide on an ice-skating rink or clumsily slip on an icy sidewalk is that the surface of ice is coated by a thin watery layer. Scientists generally agree that this lubricating, liquidlike layer is what makes ice slippery. They disagree, though, about why the layer forms.
Three main theories about the phenomenon have been debated over the past two centuries. Last year, researchers in Germany put forward a fourth hypothesis that they say solves the puzzle.
But does it? A consensus feels nearer but has yet to be reached. For now,