Abstract
We describe similarities in the features of various glassy systems where interactions and randomness compete. For example, Coulomb glasses have a gap in their single-particle density of states centred at the Fermi energy. This gap is analogous to the hole in the distribution of local fields of spin glasses and of ordinary glasses with dipolar interactions between two-level systems. When the field or energy where these holes are centred is suddenly shifted by the application of an external field, a new hole or gap develops roughly logarithmically in time. Such slow relaxation is characteristic of glassy systems. If we assume that this logarithmic behaviour applies for small perturbations, then thermal fluctuations will lead to fluctuations in the density of states and l/f noise.