First Post-Minkowskian approach to turbulent gravity

Abstract

We compute the metric fluctuations induced by a turbulent energy-matter tensor within the first order Post-Minkowskian approximation. It is found that the turbulent energy cascade can in principle interfere with the process of black hole formation, leading to a potentially strong coupling between these two highly nonlinear phenomena. It is further found that a power-law turbulent energy spectrum $E(k) \sim k^{-n}$ generates metric fluctuations scaling like $x^{n-2}$, where $x$ is a four-dimensional distance from an arbitrary origin in spacetime. This highlights the onset of metric singularities whenever $n <2$, meaning that $2d$ fluid turbulence ($n=3$) yields smooth %(differentiable) metric fluctuations, scaling like $x$, while $3d$ turbulence ($n=5/3$) yields a weakly singular metric $x^{-1/3}$and purely random fluctuations, $n=1$, generate a stronger $1/x$ singularity. Finally, the effect of metric fluctuations on the geodesic motion of test particles is also discussed as a potential technique to extract information on the spectral characteristics of fluctuating spacetime.