= Jeans swindle
{c}
{title2=$\nabla^2\delta\phi=4\pi G\delta\rho$}
The <Jeans swindle> is the removal of the unperturbed uniform density's gravitational field when treating an infinite homogeneous Newtonian medium as static. Without such subtraction or an external supporting prescription, a nonzero constant density and zero background gravitational <acceleration> cannot satisfy Poisson's equation. Linear perturbations then obey $\nabla^2\delta\phi=4\pi G\delta\rho$. This is a specified idealization, not an exact isolated infinite equilibrium.
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