Our Universe is not accelerating or decelerating as currently portrayed using new supernova studies. - This is illusionary ! The fragment products of any violent burn or explosion shall move out at great variety of speeds based on the uneven composition of explosive substances or fuel so converted or consumed.
We see by analogy an onion-like layering of galaxies speeding away from us at varying speeds. If each galaxy were to be plotted as to speed and distance, we would get a scatter plot roughly following some "s" curve, when each galaxy's contribution was averaged out. This curve would indicate a faster or slower than average distribution that a na´ve observation would identify some sections of the curve as accelerating or decelerating periods.
Similar distributions are reflected in the light curve signatures collected from Gamma Ray Bursts (GRB's). Each of the many recorded GRB light signatures show unique graphs of explosions. No two alike ! See:
No explosions have a uniform spherical burn. If one could examine each stage of an explosion at leisure it should be like watching a flame consuming its fuel - in layers, expelling ash, some faster than average, some slower and all speeds in between following some declining power curve. Further each explosion must start at some point - a point that does not encompass or surround the fuel supply creating a bias or skew that affects the exploding, violent burn.
This is the state of affairs, the understanding of which, is a major tool necessary for analyzing the state of our Universe as well as each galaxy's velocity, direction, shape, orientation, etc. - The result of a Big Bang explosion In Space.
For a more detailed discussion of the Sven/Einstein model see: http://www.AllNewUniverse.com/article13.html