How do we measure the universe's lumpiness in 3D maps?

Computing how galaxies cluster in three dimensions (the bispectrum) is crucial for extracting cosmology from large surveys, but it's computationally brutal. These researchers show the bispectrum can be broken into simpler pieces—products of two-point statistics—letting them use a clever flat-sky approximation that keeps the important physics while ditching wasteful calculations. Their method runs sub-percent accurate across cosmic distances, and they're releasing open-source code.