  Sound waves are observed and studied in an optically trapped degenerate Fermi
gas of spin-up and spin-down atoms with magnetically tunable interactions.
Measurements are made throughout the crossover region, from a
weakly-interacting Fermi gas through the resonant Fermi superfluid regime to a
Bose condensate of dimer molecules. The measured sound velocities test the
equation of state and confirm the universal hypothesis.
