Friedmann-Lemaitre Models, continued:
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Friedmann-Lemaitre Eqs. describe the evolution of the 
scale factor R(t):


and


where        is the density,       the pressure,        is the 
cosmological constant, and       is the curvature constant 
of the universe:

			+1     (closed, will recollapse)
			 0     (critical, always expanding)
			-1     (open, always expanding)

Introduce the following parameters:

				expansion rate, Hubble constant

				deceleration parameter

				critical density

				density parameter, 

Quantitites subscripted with a "0" refer to z=0 (here and now).  
In terms of the scaling factor R: