  Energy correlators characterize the asymptotic energy flow in scattering
events produced at colliders, from which the microscopic physics of the
scattering can be deduced. This view of collisions is akin to analyses of the
Cosmic Microwave Background, and a range of promising phenomenological
applications of energy correlators have been identified, including the study of
hadronization, the deadcone effect, measuring $\alpha_s$ and the top quark
mass. While $N$-point energy correlators are interesting to study for larger
values of $N$, their evaluation is computationally intensive, scaling like
$M^N/N!$, where $M$ is the number of particles. In this letter we develop a
fast method for their evaluation, exploiting that correlations at a given
angular scale are insensitive to effects at other (widely-separated) scales.
For concreteness we focus on the projected energy correlator, which projects
onto the largest separation between the $N$ directions. E.g.~for $N=7$ we find
a speed up of up to four orders of magnitude, depending on the desired
accuracy. We also consider the possibility of raising the energy to a power
higher than one in the energy correlator, which has been proposed to reduce
soft sensitivity, and further cuts back the required computation time. These
higher-power correlators are not collinear safe, but as a byproduct our
approach suggests a natural method to regularize them, such that they can be
described using perturbation theory. This letter is accompanied by a public
code that implements our method.
