The "sigma 8" parameter in cosmology is the rms fluctuation in this quantity in spheres with radius 8 megaparsecs over the dimensionless Hubble parameter.
The "sigma 8" parameter in cosmology is the rms fluctuation in this quantity in spheres with radius 8 megaparsecs over the dimensionless Hubble parameter. The Boussinesq approximation ignores its variations except in gravity terms. In elephant trunk globules and salt domes the gradient in this quantity opposes the effective gravity, resulting in the Rayleigh-Taylor instability. The Poisson equation relates it to the Laplacian of the gravitational potential, and Archimedes' principle states that the buoyant force on an object depends on the object's volume and this property of the surrounding fluid. FTP name this quantity whose average value is given by an object's mass over its volume.
The "sigma 8" parameter in cosmology is the rms fluctuation in this quantity in spheres with radius 8 megaparsecs over the dimensionless Hubble parameter.
mass-energy {density} (specifically mass {density} after “Boussinesq”)