Schedule Apr 21, 2004
Evidence from Type Ia Supernovae for a Decelerating, then Accelerating Universe and Dark Energy
Dr. Alex Filippenko, Berkeley

The measured distances of type Ia (hydrogen-deficient) supernovae as a function of redshift (z) have shown that the expansion of the Universe is currently accelerating, probably due to the presence of repulsive dark energy (X) such as Einstein's cosmological constant (Lambda). Combining all of the data with existing results from large-scale surveys, we find a best fit for Omega_M and Omega_X of 0.28 and 0.72 (respectively), in excellent agreement with the values (0.27 and 0.73) recently derived from WMAP measurements of the cosmic microwave background radiation. A number of possible systematic effects (dust, supernova evolution) thus far don't seem to eliminate the need for Omega_X > 0. Most recently, analyses of supernovae at z = 1.0-1.7 reveal an early epoch of deceleration, followed by acceleration. Several groups are now in the process of measuring hundreds of supernovae with z = 0.2-0.8, to determine the equation of state of the dark energy, w_X = P/(rho c^2); thus far, the best-fit value is w_X = -1, and the data are consistent with dw/dz = 0, suggesting that the dark energy may indeed be the cosmological constant or something quite similar.

Other video options
To begin viewing slides, click on the first slide below.
[01] [02] [03] [04] [05] [06] [07] [08] [09] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62]

Author entry (protected)