Two-point microrheology and the electrostatic analogy

The recent experiments of Crocker et al. [Phys. Rev. Lett. 85, 888 (2000)] suggest that microrheological measurements obtained from the correlated fluctuations of widely-separated probe particles determine the theological properties of soft, complex materials more accurately than do the more traditional particle autocorrelations. This presents an interesting problem in viscoelastic dynamics. We develop an important, simplifing analogy between the present viscoelastic problem and classical electrostatics, Using this analogy and direct calculation we analyze both the one- and two-particle correlations in a viscoelastic medium in order to explain this observation.