  Given the considerable theoretical challenges in understanding strongly
coupled metals and non-Fermi liquids, it is valuable to have a framework to
understand properties of metals that are universal, in the sense that they must
hold in any metal. It has previously been argued that an infinite-dimensional
emergent symmetry group is such a property, at least for clean, compressible
metals. In this paper, we will show that such an emergent symmetry group has
very strong implications for the dynamics of the metal. Specifically, we show
that consideration of the hydrodynamics of the associated infinitely many
emergent conserved quantities automatically recovers the collisionless
Boltzmann equation that governs the dynamics of a Fermi liquid. Therefore, the
hydrodynamic prediction is that in the low-temperature, collisionless regime
where the emergent conservation laws hold, the dynamics and response to
external fields of a general spinless metal will be identical to a Fermi
liquid. We discuss some potential limitations to this general statement,
including the possibility of non-hydrodynamic modes. We also report some
interesting differences in the case of spinful metals.
