Abstract: The traditional order parameters used to distinguish solid from fluid phases are related to microscopic structure, notably crystalline symmetry. However it has been too difficult to prove that any models, even highly simplified ones such as hard spheres, have an ordered phase in such a sense. I will discuss two possible alternative (macroscopic) order parameters, one related to shear and the other to surface tension. If time permits I will discuss the parallel problems in constrained networks and in static granular materials.
Short bio of Charles Radin. He obtained his PhD in physics in 1970 under Gerard Emch at the Univ of Rochester. He then had postdocs in physics at the Univ of Nijmegen under Edward Verboven and Princeton Univ under Arthur Wightman, then in math at Rockefeller Univ under Mark Kac and the Univ of Pennsylvania under Richard Kadison. In 1976 he moved to the Univ of Texas at Austin as assistant professor, where he rose to his current rank of Professor of Mathematics. He has worked on energy ground states, quasicrystals, granular matter and constrained networks, mostly to try to understand the solid/fluid phase transition.