Chasing the dragon: tidal bores in the UK and elsewhere; quantum and relativistic analogies

In some of the world’s rivers, an incoming high tide can arrive as a breaking wave, or as a smooth jump decorated by waves. An approximate theory is inspired by hamiltonians in quantum mechanics, and there is an analogy with white hole horizons in relativity. This dramatic phenomenon, in which the river flows backwards, illustrates the first unification in physics: the same force - gravity - keeps us on the ground, holds the moon in its orbit, and pulls the tides.