The energy landscape of a glass has a hierarchy of minima: local basins within metabasins.
At low T, a particle (system) gets trapped — first in a local minimum, then in a metabasin.
τ_escape ∝ e^(ΔE/T) (Arrhenius/Kramers)
Aging: after a quench, the system keeps finding deeper minima — equilibration time grows with age t_w.
The mean-square displacement shows a two-step relaxation (β-regime = rattling in cage, α-regime = structural rearrangement).
Replica theory (Parisi 1979) explains the glass transition via replica symmetry breaking.