Gravity and large-scale structure: Observational evidence

In our present understanding, cosmological structure on large scales is formed by the action of gravity amplifying small initial fluctuations. On large scales, where fluctuations are weak and perturbation theory applies, that presumption can be tested against observations. In particular, the anisotropic shapes of structures formed by gravity predicts a characteristic behavior of the bispectrum, or third moment of density in Fourier space, that can be used as a signature to separate effects of gravity from more local, nongravitational forces that may play a role in galaxy formation.