 Cosmologists actually observe the universe's density parameter to be consistent with unity and its curvature to be consistent with flatness.The Milne universe is a special case of a more general Friedmann–Lemaître–Robertson–Walker model (FLRW).The Milne solution can be obtained from the more generic FLRW model by demanding that the energy density, pressure and cosmological constant all equal zero and the spatial curvature is negative.