
Fig13_11 Accelerating universe
Fig. 13.11 . The Hubble diagram plot of the apparent magnitude of Type Ia supernovae plotted as a function of their redshift (top). At a redshift below about z = 0.1, there is a linear fit to the data, but at larger redshifts the observations begin to diverge from a straight line. The curved departures for distant supernovae at high redshift indicate an accelerating universe in which the speed of expansion is increasing. The observed data can be compared to cosmological models with different values of the omega parameter, W. It is the ratio of the inferred density to the critical mass density needed to stop the expansion of the universe in the future. The subscript L denotes the cosmological constant, a possible form of dark energy, while the subscript m denotes matter. (Adapted from Saul Perlmutter, Physics Today April 2003.)
Copyright 2010, Professor Kenneth R. Lang, Tufts University

