The fate of the Universe – closed, flat or open

The fate of the Universe depends on how much matter there is. Using the Hubble constant H = 70 kms^-1 Mpc^-1 we have found that the critical density for the Universe is 9.2x10^-27 kgm^-3.

Now actual measurements suggest a density if some 4x10^-28kgm^-3. This is too low to prevent a run-away expansion but astronomers believe that a large amount of the mass of the Universe exists as "dark matter", much of which has so far been undetected. We define a quantity called Ω where: The quantity Ω = Actual average density of matter in the Universe/Critical density of the Universe.

The critical density will decide whether the Universe is:
(a) open – a run-away expansion (Ω<1)
(b) flat – an expansion but slowing (Ω = 1)
(c) closed – a final contraction, the Big Crunch (Ω>1)