Peculiar-velocity equation
= Peculiar-velocity equation
For a fluid in an expanding universe, the peculiar-velocity equation is the <Euler equations for an inviscid fluid> after decomposing physical velocity into <Hubble flow> and <peculiar velocity>. It contains the Hubble-drag term $H\mathbf v$ and force $-\nabla\Phi/a$ from the <peculiar gravitational potential>.