  The Casimir effect in quantum electrodynamics (QED) is perhaps the best-known
example of fluctuation-induced long-ranged force acting on objects (conducting
plates) immersed in a fluctuating medium (quantum electromagnetic field in
vacuum). A similar effect emerges in statistical physics, where the force
acting, e.g., on colloidal particles immersed in a binary liquid mixture is
affected by the classical thermal fluctuations occurring in the surrounding
medium. The resulting Casimir-like force acquires universal features upon
approaching a critical point of the medium and becomes long-ranged at
criticality. In turn, this universality allows one to investigate theoretically
the temperature dependence of the force via representative models and to
stringently test the corresponding predictions in experiments. In contrast to
QED, the Casimir force resulting from critical fluctuations can be easily tuned
with respect to strength and sign by surface treatments and temperature
control. We present some recent advances in the theoretical study of the
universal properties of the critical Casimir force arising in thin films. The
corresponding predictions compare very well with the experimental results
obtained for wetting layers of various fluids. We discuss how the Casimir force
between a colloidal particle and a planar wall immersed in a binary liquid
mixture has been measured with femto-Newton accuracy, comparing these
experimental results with the corresponding theoretical predictions.
