We review the Random First Order Transition Theory of the glass transition, emphasizing the experimental tests of the theory. Many distinct phenomena are quantitatively predicted or explained by the theory, both above and below the glass transition temperature Tg. These include: the viscosity catastrophe and heat capacity jump at Tg, and their connection; the non-exponentiality of relaxations and their correlation with the fragility; dynamic heterogeneity in supercooled liquids owing to the mosaic structure; deviations from the Vogel-Fulcher law, connected with strings or fractral cooperative rearrangements; deviations from the Stokes-Einstein relation close to Tg; aging, and its correlation with fragility; the excess density of states at cryogenic temperatures due to two level tunneling systems and the Boson Peak. Contents

The random first-order transition theory of the dynamics of supercooled liquids is extended to treat aging phenomena in nonequilibrium structural glasses. A reformulation of the idea of "entropic droplets" in terms of libraries of local energy landscapes is introduced which treats in a uniform way the supercooled liquid (reproducing earlier results) and glassy regimes. The resulting microscopic theory of aging makes contact with the Nayaranaswamy-Moynihan-Tool nonlinear relaxation formalism and the Hodge-Scherer extrapolation of the Adam-Gibbs formula, but deviations from both approaches are predicted and shown to be consistent with experiment. The nonlinearity of glassy relaxation is shown to quantitatively correlate with liquid fragility. The residual non-Arrhenius temperature dependence of relaxation observed in quenched glasses is explained. The broadening of relaxation spectra in the nonequilibrium glass with decreasing temperature is quantitatively predicted. The theory leads to the prediction of spatially fluctuating fictive temperatures in the long-aged glassy state, which have non-Gaussian statistics. This can give rise to "ultraslow" relaxations in systems after deep quenches.

Long-living mesoscopic clusters of a dense protein liquid are a necessary kinetic intermediate for the formation of solid aggregates of native and misfolded protein molecules; in turn, these aggregates underlie physiological and pathological processes and laboratory and industrial procedures. We argue that the clusters consist of a nonequilibrium mixture of single protein molecules and long-lived complexes of proteins. The puzzling mesoscopic size of the clusters is determined by the lifetime and diffusivity of these complexes. We predict and observe a crossover of cluster dynamics to critical-like density fluctuations at high protein concentrations. We predict and experimentally confirm that cluster dynamics obey a universal, diffusion-like scaling with time and wave vector, including in the critical-like regime. Nontrivial dependencies of the cluster size and volume fraction on the protein concentration are established. Possible mechanisms of complex formation include domain swapping, hydration forces, dispersive interactions, and other, system-specific, interactions. We highlight the significance of the hydration interaction and domain swapping with regard to the ubiquity of the clusters and their sensitivity to the chemical composition of the solvent. Our findings suggest novel ways to control protein aggregation.

According to the Random First Order Transition (RFOT) theory of glasses, the barriers for activated dynamics in supercooled liquids vanish as the temperature of a viscous liquid approaches the dynamical transition temperature from below. This occurs due to a decrease of the surface tension between local meta-stable molecular arrangements much like at a spinodal.The dynamical transition thus represents a crossover from the low T activated bevavior to a collisional transport regime at high T . This barrier softening explains the deviation of the relaxation times, as a function of temperature, from the simple log τ ∝ 1/s c dependence at the high viscosity to a mode-mode coupling dominated result at lower viscosity. By calculating the barrier softening effects, the RFOT theory provides a unified microscopic way to interpret structural relaxation data for many distinct classes of structural glass formers over the measured temperature range. The theory also provides an unambiguous procedure to determine the size of dynamically cooperative regions in the presence of barrier renormalization effects using the experimental temperature dependence of the relaxation times and the configurational entropy data. We use the RFOT theory framework to discuss data for tri-naphthyl benzene, salol, propanol and silica as representative systems.A unified picture of the dynamics of supercooled liquids has emerged based on a theory of random first order transitions [1,2,3]. The mean field approaches to structural glasses exhibit two transi-

Several puzzling regularities concerning the low temperature excitations of glasses are quantitatively explained by quantizing domain wall motions of the random first order glass transition theory. The density of excitations agrees with experiment and scales with the size of a dynamically coherent region at Tg, being about 200 molecules. The phonon coupling depends on the Lindemann ratio for vitrification yielding the observed universal relation l/λ ≃ 150 between phonon wavelength λ and mean free path l. Multilevel behavior is predicted to occur in the temperature range of the thermal conductivity plateau.PACS Numbers: 66.35.+a, 64.70.Pf, 66.60.+f Decades ago, measurements of the heat capacity and thermal conductivity of glasses at cryogenic temperatures revealed the presence of excitable degrees of freedom not present in perfect crystals [1]. These could be described as two level tunneling systems whose energies and tunneling matrix elements were randomly distributed [2,3]. Coupling the tunneling systems to phonons explained the thermal measurements and also predicted novel physical effects, such as the nonlinear absorption of sound and a phonon echo, which were later observed [4,5].The nature of the tunneling entities has remained obscure. Thoughtful experimentalists and theorists have noticed puzzles when the model quantitatively confronts experimental data [6][7][8]. For example, the entropy contained in these excitations is much less than the residual entropy frozen in at the glass transition. Yet, the density of two level systems varies only modestly from material to material. There is also a mysterious nearly universal relation between the density of the two level systems and their coupling to phonons which can be deduced from the observation that the mean free path of phonons is about 150 times their wave length at low temperature [7]. If the two level systems arise from the motions of highly localized specific configurations of atoms, as in impurity doped crystals, instead of such a universal relation we would expect significant variation with the glass's chemical composition. These facts lead Yu and Leggett [8], as well as others [9,10], to investigate the possibility that the experimentally observed excitations are really highly renormalized collective excitations of a system of microscopic tunneling entities that interact strongly through the exchange of phonons. While such a coupling seems to be present, manifesting itself in spectral diffusion of the two level entities [11], quantitative calculations based on the interacting model suggest that thermodynamic manifestations of the interaction should be confined to ultra low temperatures [10,12]. This scenario then has not yet explained the observations which called it forth.Here we explore an alternative view of the quantum excitations of a glass. Rather than regarding the tunneling entities as extrinsic we quantize the excitations that are responsible for the activated dynamical events in a liquid which slow as the glass transition is approached....