  We propose a classical mechanism for the cosmic expansion during the
radiation-dominated era. This mechanism assumes that the Universe is a
two-component gas. The first component is a gas of ultra-relativistic "normal"
particles described by an equation of state of an ideal quantum gas of massless
particles. The second component consist of "unusual" charged particles (namely,
either with ultra-high charge or with ultra-high mass) that provide the
important mechanism of expansion due to their interaction with the "normal"
component of the gas. This interaction is described by the
Reissner--Nordstr\"om metric purely geometrically -- the ``unusual'' particles
are modeled as zero-dimensional naked singularities inside spheres of
gravitational repulsion. The radius of a repulsive sphere is inversely
proportional to the energy of an incoming particle or the temperature. The
expansion mechanism is based on the inflating of the "unusual" particles (of
charge $Q$) with the drop of the temperature -- this drives apart all neutral
particles and particles of specific charge $q/m$ such that ${sign}(Q) q/m \ge -
1$. The Reissner--Nordstr\"om expansion naturally ends at recombination. We
discuss the range of model parameters within which the proposed expansion
mechanism is consistent with the restrictions regarding quantum effects.
