TeV, In 2011, the ALICE Collaboration measured the size of the system created in Pb-Pb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair. ALICE confirmed that the QCD matter created in Pb-Pb collisions behaves like a fluid, with strong collective motions that are well described by hydrodynamic equations. The fireball formed in nuclear collisions at the LHC is hotter, lives longer and expands to a larger size than the medium that was formed in heavy-ion collisions at RHIC. Multiplicity measurements by the ALICE experiment show that the system initially has much higher energy density and is at least 30% hotter than at RHIC, resulting in about double the particle multiplicity for each colliding nucleon pair (Aamodt et al. 2010a). Further analyses, in particular including the full dependence of these observables on centrality, will provide more insights into the properties of the system – such as initial velocities, the equation of state and the fluid viscosity – and strongly constrain the theoretical modelling of heavy-ion collisions. A perfect liquid at the LHC Off-centre nuclear collisions, with a finite impact parameter, create a strongly asymmetric "almond-shaped" fireball. However, experiments cannot measure the spatial dimensions of the interaction (except in special cases, for example in the production of pions, see). Instead, they measure the momentum distributions of the emitted particles. A correlation between the measured azimuthal momentum distribution of particles emitted from the decaying fireball and the initial spatial asymmetry can arise only from multiple interactions between the constituents of the created matter; in other words it tells us about how the matter flows, which is related to its equation of state and its thermodynamic transport properties. The measured azimuthal distribution of particles in momentum space can be decomposed into Fourier coefficients. The second Fourier coefficient (v2), called elliptic flow, is particularly sensitive to the internal friction or viscosity of the fluid, or more precisely, η/s, the ratio of the shear viscosity (η) to entropy (s) of the system. For a good fluid such as water, the η/s ratio is small. A "thick" liquid, such as honey, has large values of η/s. In heavy-ion collisions at the LHC, the ALICE collaboration found that the hot matter created in the collision behaves like a fluid with little friction, with η/s close to its lower limit (almost zero viscosity). With these measurements, ALICE has just begun to explore the temperature dependence of