I have been searching for an explanation of how a change in pressure propagates thru a fluid to become isotropic. My question is that if the time scale measured is small enough ( much less than the distance divided speed of sound ) will we see the pressure change have an initial direction and most importantly does that direction require a hard surface (the container) to refract/reflect as suggested below ? If it think of the average molecular kinetic action of the pressure increase as this pressure increase represents an increase in average energy and this will flow away from high to low( will have an initial direction) and the average increase in molecular energy will be transferred through the fluid until a hard surface is encountered at which point the kinetic energy will be dispersed (Reflected) in another direction of increasing randomness. I have found the following blurb from https://www.princeton.edu/~asmits/Bicycle_web/pressure.html Pressure: transmission through a fluid An important property of pressure is that it is transmitted through the fluid. When an inflated bicycle tube is pressed at one point, for example, the pressure increases at every other point in the tube. Measurements show that the increase is the same at every point and equal to the applied pressure. For example, if an extra pressure of 5 psi were suddenly applied at the tube valve, the pressure would increase at every point of the tube by exactly this amount. This property of transmitting pressure undiminished is a well established experimental fact, and it is a property possessed by all fluids. The transmission does not occur instantaneously, but at a rate that depends on the speed of sound in the medium and the shape of the container. The speed of sound is important because it measures the rate at which pressure disturbances propagate (sound is just a pressure disturbance travelling through a medium). The shape of the container is important because pressure waves refract and reflect of the walls of the container and this increases the distance and time the pressure waves need to travel.