  We present the results of two-pion Bose-Einstein correlations measured in
Pb--Pb collisions at a center-of-mass energy sqrt(s_NN) = 2.76 TeV recorded by
ALICE at the Large Hadron Collider. These types of correlations allow to
extract, using the technique of femtoscopy (also known as Hanburry-Brown Twiss
interferometry, or shortly HBT), the space-time characteristics of the source
from the correlation calculated as a function of the pair momentum difference.
The femtoscopic analysis was performed using both the Spherical Harmonics
decomposition and the standard 3D Cartesian representation of the correlation
function. The source sizes in three dimensions, the HBT radii, were extracted
by fitting the experimental correlation functions. The resulting dependencies
of the radii as a function of centrality and pair transverse momentum are
shown. The results indicate the existence of a flowing medium and provide
constraints on existing dynamical models. The ALICE Pb-Pb HBT radii are also
compared to the pp analysis and other heavy-ion experiments in order to test
the multiplicity scaling between different systems.
