  We study the kinematics of dark matter using the massive cluster of galaxies
1E0657-56. The velocity of the "bullet" subcluster has been measured by X-ray
emission from the shock front, and the masses and separation of the main and
sub-clusters have been measured by gravitational lensing. The velocity with
gravity alone is calculated in a variety of models of the initial conditions,
mass distribution and accretion history; it is much higher than expected, by at
least 2.4 sigma. The probability of so large a subcluster velocity in
cosmological simulations is <~ 10^{-7}. A long range force with strength ~ 0.4
- 1.2 times that of gravity would provide the needed additional acceleration.
