  Pauli blocking of spontaneous emission is responsible for the stability of
atoms. Higher electronic orbitals cannot decay to lower-lying states if they
are already occupied -- this is Pauli blocking due to occupation of internal
states. Pauli blocking also occurs when free atoms scatter light elastically
(Rayleigh scattering) and the final external momentum states are already
occupied. A suppression of the total rate of light scattering requires a
quantum-degenerate Fermi gas with a Fermi energy larger than the photon recoil
energy. This has been predicted more than 30 years ago, but never realized.
Here we report the creation of a dense Fermi gas of ultracold lithium atoms and
show that at low temperatures light scattering is suppressed. We also explore
the suppression of inelastic light scattering when two colliding atoms emit
light shifted in frequency.
