“Fundamental” Physics: Molecular Dynamics vs. Hydrodynamics

Condensed matter physics concerns the “study of matter at everyday length and energy scales.” [12] The physics of such systems is by and large decoupled from the more “fundamental” physics at small lengths and higher energies. The nature of this decoupling is of great interest and brings with it the possibility of understanding aspects of how certain phenomena can be emergent. I believe there are important problems (many problems, in fact) for which “fundamental theory” will be completely inadequate for explanation. How a drop breaks as it drips from a faucet is one such problem. I will examine this problem from two perspectives. First, from the perspective of a (perhaps) less “fundamental” theory, continuum hydrodynamics. Second, from the perspective of state-of-the-art simulations in the (perhaps) more “fundamental” theory of molecular dynamics. Let me begin the discussion by quoting at some length a statement concerning the concept of “fundamental physics” with which I have some sympathy. This comes from the introduction to David R. Nelson’s recent book Defects and Geometry in Condensed Matter Physics.