Transcript: The big bang model is described by a small number of cosmological parameters. Astronomers talk about a world model, but in fact they’re talking about a description of the entire universe. If these parameters are measured, the entire history of the universe, past, present, and future, can be described although the detailed behavior of objects within the universe is too complex to be described in this way. Cosmological parameters require difficult observations, work at the limit of ground-based and space-based telescopes. Scientists need independent measurements using different techniques, and even then there are limitations imposed by the fact that we only have one universe to study. The basic cosmological parameters are the current expansion rate or the Hubble constant, the baryon content of the universe, that is normal matter, the dark matter content of the universe, the cosmological constant, and the age of the universe. Different types of observations are required to measure each of these quantities.