  Contemporary observational and theoretical studies on the temporal nature of
microscopic measurements renewed the discussion about the fundamental
constants, leading to the possibility of light speed variation and superluminal
pulse propagation. Gain assisted experiments using anomalous dispersion near an
absorption line in atomic gas, a "fast - light" medium, seem to lead to a wave
group velocity vG exceeding c, the vacuum speed of light; moreover, definition
of the information velocity vi sets the question of interpretation of the three
speeds: one view is that vi = vG, but this violates Causality; another view is
that vi = c in all situations, but this limits, a priori, the transport of
information. Another view is that vi, vG and c are distinct. This contribution
follows the last possibility. A draft discussion on space-time is given.
