The existence of a preferred, dynamical time vector breaks the Lorentz symmetry of the theory, more precisely it breaks the invariance under boosts. This symmetry breaking may lead to a Higgs mechanism for the graviton which would alter long distance physics, perhaps yielding an explanation for recent supernova data which would otherwise be explained by a cosmological constant. The effect of breaking Lorentz invariance on quantum field theory has a long history leading back at least to the work of Markus Fierz and Wolfgang Pauli in 1939. Recently it has regained popularity with, for example, the paper "Effective Field Theory for Massive Gravitons and Gravity in Theory Space" by Nima Arkani-Hamed, Howard Georgi and Matthew Schwartz. Einstein-aether theories provide a concrete example of a theory with broken Lorentz invariance and so have proven to be a natural setting for such investigations. In 2004, Eling, Jacobson and Mattingly wrote a review of the status Einstein aether theory as of 2004.