to a usual boosted slice of Schwarzschild are higher order in perturbation theory than the ones one obtains in a collision. Because of this fact, they grow fast with the perturbative parameter and perturbation theory breaks down early for the estimation of the involved energy in the calculations of the current paper. The breakdown occurs earlier for a single hole than for a collision of holes (at least computed in the center-of-momentum frame).

Connected with the latter point is another interesting insight gained from the analysis of this paper. It has to do with the choice of frame used to describe collisions of black holes in perturbation theory. The situation is illustrated in figure \[fig3\]. One would expect these two collisions to be physically equivalent. However, if one considers conformal black holes and expands in perturbation theory, the collision at the bottom will contain terms that behave exactly like those we discuss in the current paper, whereas the top collision does not. If we power count, for the bottom collision, the extrinsic curvature has leading terms that behave like $P$ and are $\ell=1$ and the conformal factor has terms that behave like $L^2$ plus terms that behave like $P^2$ at 