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≥−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.Comment: 9 pages, LaTe