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3.2. Model-Dependent Determinations

The following derivations of the mass density parameter are based on the hierarchical clustering model of cosmic structure formation assuming the cold dark matter dominance. The extraction of Omega is, therefore, indirect, but on the other hand, it is reasonable to appeal to such models since Omega is the parameter that predominantly controls structure formation. Note that CDM model is the only model known today that successfully predicts widely different observations, yet there are no observations strong enough to refute its validity. We do not discuss results from cosmological models where physical processes other than gravity play a major role.