Résumé :
The observed acceleration in the expansion of the universe requires,
within the standard model of cosmology, the presence of a new form
of exotic dark energy. The current paradigm is based on
the Cosmological Principle which assumes the approximate homogeneity
and isotropy of matter and radiation, as observed in the near-isotropy
of the CMB temperature pattern and in the homogeneity on scales probed
by large-scale structures. Relaxing the assumption of radial homogeneity
on scales larger than about 1 Gpc, and observing from a preferred
vantage point close to the centre of a large-scale void, allows one to
describe within the framework of a Lemaitre-Tolman-Bondi spacetime
all cosmological observations without requiring a cosmological
constant or other form of dark energy. The special location
of the observer violates the Copernican Principle, and we present
here a comprehensive review of observational tests of this basic tenet,
including a new sensitive probe based on strong gravitational lensing.
