Are transient positional and orientational order important approaching the glass transition?

Over the last decade light scattering experiments have demonstrated that there are long-lived clusters of substantial spatial extent (up to similar to 10(3) Angstrom) in glass forming systems well above the glass transition. Very recently-using piezo rheometry-it has been shown that there are very long lived clusters of even larger spatial extent (similar to 10mu). Here we argue that these experimental results are compatible with transient positional and transient orientational orders with long, but finite lifetimes in these systems that are not in complete thermodynamic equilibrium. We also suggest further experiments to test our picture. (C) 2003 Elsevier Science B.V. All rights reserved.