Are Cats Liquid? The Deborah Number and the Rheology of Cats
Marc-Antoine Fardin won the 2017 Ig Nobel Prize in Physics for proving, rigorously, that cats are liquid. The argument rests on the Deborah number De = τ/T: if the material’s relaxation time τ is shorter than the observation time T, the material behaves as a fluid. A cat filling a sink (De ≈ 0.008) is a liquid. A cat bouncing off a table (De ≫ 1) is a solid. The classification is not a joke — it is standard rheology, applied to an unusual substrate.