  The Pauli exclusion principle forbids indistinguishable fermions to occupy
the same quantum mechanical state. Its implications are profound and it for
example accounts for the electronic shell structure of atoms. Here we perform
measurements on the scattering of off-resonant light from ultracold gasses of
fermionic atoms. For Fermi gases in the quantum degenerate regime, we observe a
marked suppression in light scattering as compared to a similarly prepared
thermal Bose gas. We attribute the observed increased transmission of light
through the quantum degenerate Fermi gas to Pauli blocking, where Fermi-Dirac
statistics causes atoms to occupy a large region of the momentum space limiting
the number of accessible states for the scattered atom. Our work confirms a
longstanding fundamental result in the theory of the optical response of
quantum gases and is an important step towards novel cooling and thermometry
mechanisms for degenerate Fermi gases.
