Since the constant is known and the expansion rate can be measured by observing the speed at which distant galaxies are receding from us, can be determined. Its value is currently around 10 −26 kg m −3 . The ratio of the actual density to this critical value is called Ω, and its difference from 1 determines the geometry of the universe: Ω > 1 corresponds to a greater than critical density, , and hence a closed universe . Ω < 1 gives a low density open universe , and Ω equal to exactly 1 gives a flat universe .