In some of the world’s rivers, an incoming high tide can arrive as a smooth jump decorated by undulations, or as a breaking wave. The river reverses direction and flows upstream. In this lecture Michael Berry explains tidal bores via analogies with tsunamis, rainbows, horizons in relativity, and ideas from quantum physics; the concept of a ‘minimal model’ in mathematical explanation; different ways in which different cultures describe the same thing; and the first unification in fundamental physics.   Michael Berry is Emeritus Professor of Physics, H H Wills Physics Laboratory, University of Bristol.