  By studying perturbations about the vacuum, we show that Horava gravity
suffers from two different strong coupling problems, extending all the way into
the deep infra-red. The first of these is associated with the principle of
detailed balance and explains why solutions to General Relativity are typically
not recovered in models that preserve this structure. The second of these
occurs even without detailed balance and is associated with the breaking of
diffeomorphism invariance, required for anisotropic scaling in the UV. Since
there is a reduced symmetry group there are additional degrees of freedom,
which need not decouple in the infra-red. Indeed, we use the Stuckelberg trick
to show that one of these extra modes become strongly coupled as the parameters
approach their desired infra-red fixed point. Whilst we can evade the first
strong coupling problem by breaking detailed balance, we cannot avoid the
second, whatever the form of the potential. Therefore the original Horava
model, and its "phenomenologically viable" extensions do not have a
perturbative General Relativity limit at any scale. Experiments which confirm
the perturbative gravitational wave prediction of General Relativity, such as
the cumulative shift of the periastron time of binary pulsars, will presumably
rule out the theory.
